As filed with the Securities and Exchange Commission on August 14, 2020March 28, 2024

Registration No. 333-

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM S-3

REGISTRATION STATEMENT

UNDER

THE SECURITIES ACT OF 1933

SELLAS Life Sciences Group, Inc.

(Exact name of registrant as specified in its charter)

7 Times Square, Suite 2503

New York, New York 10036

(917) 438-4353

(Address, including zip code, and telephone number, including area code, of registrant’s principal executive offices)

Angelos M. Stergiou, M.D., ScD h.c.

President and Chief Executive Officer

7 Times Square, Suite 2503

New York, New YorkNY 10036

(917) 438-4353(646) 200-5278

(Name, address, including zip code, and telephone number, including area code, of agent for service)

Copies to:

Joel I. Papernik, Esq.

Daniel A. Bagliebter, Esq.

Mintz, Levin, Cohn, Ferris, Glovsky and Popeo, P.C.

666919 Third Avenue

New York, New York 1001710022

(212) 935-3000

Approximate date of commencement of proposed sale to the public: From time to time after the effective date of this registration statement.

If the only securities being registered on this form are being offered pursuant to dividend or interest reinvestment plans, please check the following box.box: ¨

If any of the securities being registered on this form are to be offered on a delayed or continuous basis pursuant to Rule 415 under the Securities Act of 1933, other than securities offered only in connection with dividend or interest reinvestment plans, check the following box.box: x

If this form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, please check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. ¨

If this form is a post-effective amendment filed pursuant to Rule 462(c) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering. ¨

If this form is a registration statement pursuant to General Instruction I.D. or a post-effective amendment thereto that shall become effective upon filing with the Commission pursuant to Rule 462(e) under the Securities Act, check the following box. ¨

If this form is a post-effective amendment to a registration statement filed pursuant to General Instruction I.D. filed to register additional securities or additional classes of securities pursuant to Rule 413(b) under the Securities Act, check the following box. ¨

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, a smaller reporting company, or an emerging growth company. See the definitions of "large“large accelerated filer," "accelerated filer" "smaller” “accelerated filer,” “smaller reporting company"company” and "emerging“emerging growth company"company” in Rule 12b-2 of the Exchange Act.

Emerging growth company ¨

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 7(a)(2)(B) of the Securities Act. ¨

CALCULATION OF REGISTRATION FEE

The Registrant hereby amends this Registration Statementregistration statement on such date or dates as may be necessary to delay its effective date until the Registrant shall file a further amendment whichthat specifically states that this Registration Statementregistration statement shall thereafter become effective in accordance with Section 8(a) of the Securities Act of 1933, as amended, or until this Registration Statementthe registration statement shall become effective on such date as the Securities and Exchange Commission, acting pursuant to said Section 8(a), may determine.

The information in this prospectus is not complete and may be changed.  A registration statement relating to these securities has been filed with the Securities and Exchange Commission.  The selling stockholders may not sell these securities until the Securities and Exchange Commission declares the registration statement effective.  This prospectus is not an offer to sell these securities and is not soliciting an offer to buy these securities in any state where the offer or sale is not permitted.

SUBJECT TO COMPLETION, DATED AUGUST 14, 2020MARCH 28, 2024

PROSPECTUS

5,488,156 Shares of Common Stock 

The selling stockholders of SELLAS Life Sciences Group, Inc.  (“SELLAS,” “we,” “us” or the “Company”) listed beginning on page 8 of this prospectus$200,000,000

Common Stock

Preferred Stock

Debt Securities

Warrants

Rights

Units

From time to time, we may offer and resell undersell up to an aggregate amount of $200,000,000 of any combination of the securities described in this prospectus (i) up to 2,744,078 shares of our Common Stock and (ii) up to 2,744,078 shares of our Common Stockin one or more offerings. We may also offer such securities as may be issuable upon conversion, redemption, repurchase, exchange or exercise of warrants acquired by certain of the selling stockholders under the Purchase Agreement (defined below) (the “Warrants”).  The selling stockholders acquired the shares of Common Stock and the Warrants from us pursuant to a Securities Purchase Agreement (the “Purchase Agreement”, dated July 31, 2020, by and among the Company and the investors listed therein (the “Investors”).any securities registered hereunder, including any applicable anti-dilution provisions.

We are registering the resaleThis prospectus provides a general description of the shares of Common Stock covered bysecurities we may offer. Each time we sell securities pursuant to this prospectus, we will provide the specific terms of these offerings in one or more supplements to this prospectus. We may also authorize one or more free writing prospectuses to be provided to you in connection with these offerings. The prospectus supplement and any related free writing prospectus may also add, update or change information contained in this prospectus. You should carefully read this prospectus, the applicable prospectus supplement and any related free writing prospectus, as requiredwell as any documents incorporated by the Registration Rights Agreement we entered into with the Investors on July 31, 2020.  The selling stockholders will receive all of the proceeds from any sales of the shares offered hereby.  We will not receivereference, before buying any of the proceeds, but we will incur expenses in connection with the offering.  To the extent the Warrants are exercised for cash, if at all, we will receive the exercise price of the Warrants.securities being offered.

The selling stockholdersThis prospectus may sell these shares through public or private transactions at market prices prevailing atnot be used to consummate a sale of securities unless it is accompanied by the time of sale or at negotiated prices.  The timing and amount of any sale are within the sole discretion of the selling stockholders.  Our registration of the shares of Common Stock covered by thisapplicable prospectus does not mean that the selling stockholders will offer or sell any of the shares.  For further information regarding the possible methods by which the shares may be distributed, see “Plan of Distribution” beginning on page 11 of this prospectus.supplement.

Our Common Stockcommon stock is listedtraded on The Nasdaq Capital Market under the symbol “SLS.“SLS.” The last reported saleOn March 27, 2024, the closing price of our Common Stockcommon stock, as reported on August 10, 2020The Nasdaq Capital Market, was $3.49$1.03 per share. The applicable prospectus supplement will contain information, where applicable, as to any other listings on The Nasdaq Capital Market or any securities market or other exchange of the securities, if any, covered by the prospectus supplement.

Investing in our Common Stock is highly speculative andsecurities involves a significanthigh degree of risk. Please considerYou should review carefully the specific factors set forthrisks and uncertainties described under "Risk Factors"the heading “Risk Factors” contained in this prospectus beginning on page 59 and any applicable prospectus supplement and in any free writing prospectuses we have authorized for use in connection with a specific offering, and under similar headings in the other documents that are incorporated by reference into this prospectus.

The securities may be sold directly by us to investors, through agents designated from time to time or to or through underwriters or dealers, on a continuous or delayed basis. For additional information on the methods of sale, you should refer to the section titled “Plan of Distribution” in this prospectus. If any agents or underwriters are involved in the sale of any securities with respect to which this prospectus is being delivered, the names of such agents or underwriters and any applicable fees, commissions, discounts and over-allotment options will be set forth in our filings witha prospectus supplement. The price to the Securitiespublic of such securities and Exchange Commission.the net proceeds we expect to receive from such sale will also be set forth in a prospectus supplement.

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of these securities or passed upon the accuracydetermined if this prospectus is truthful or adequacy of the disclosures in this prospectus.complete. Any representation to the contrary is a criminal offense.

The date of this prospectus is              August _____________, 2020, 2024.

TABLE OF CONTENTS

PAGE

ABOUT THIS PROSPECTUS

This prospectus is part of a registration statement that we have filed with the Securities and Exchange Commission, (the “SEC”) pursuant to whichor the selling stockholders named hereinSEC, using a “shelf” registration process. Under this shelf registration process, we may, from time to time, offer and sell, either individually or otherwise disposein combination, in one or more offerings, up to a total dollar amount of $200,000,000 of any combination of the shares of our Common Stock covered bysecurities described in this prospectus. You should not assumeThis prospectus provides you with a general description of the securities we may offer.

Each time we offer securities under this prospectus, we will provide a prospectus supplement that will contain more specific information about the terms of that offering. We may also authorize one or more free writing prospectuses to be provided to you that may contain material information relating to these offerings. The prospectus supplement and any related free writing prospectus that we may authorize to be provided to you may also add, update or change any of the information contained in this prospectus is accurate on any date subsequent toor in the date set forth on the front cover of this prospectus ordocuments that any information we have incorporated by reference into this prospectus. We urge you to carefully read this prospectus, any applicable prospectus supplement and any related free writing prospectuses we have authorized for use in connection with a specific offering, together with the information incorporated herein by reference as described under the heading “Incorporation by Reference,” before buying any of the securities being offered.

This prospectus may not be used to consummate a sale of securities unless it is correctaccompanied by a prospectus supplement.

You should rely only on the information contained in, or incorporated by reference into, this prospectus and any applicable prospectus supplement, along with the information contained in any free writing prospectuses we have authorized for use in connection with a specific offering. We have not authorized anyone to provide you with information in addition to or different from that contained in this prospectus, any applicable prospectus supplement and any related free writing prospectus. We take no responsibility for, and can provide no assurances as to the reliability of, any information not contained in this prospectus, any applicable prospectus supplement or any related free writing prospectus that we may authorize to be provided to you. This prospectus is an offer to sell only the securities offered hereby, but only under circumstances and in jurisdictions where it is lawful to do so.

You should assume that the information in this prospectus, any applicable prospectus supplement or any related free writing prospectus, is accurate only as of the date subsequent toon the front of the document and that any information incorporated by reference is accurate only as of the date of the document incorporated by reference, even thoughregardless of the time of delivery of this prospectus, any applicable prospectus supplement or any related free writing prospectus, or any sale of a security. Our business, financial condition, results of operations and prospects may have changed since those dates.

To the extent there is delivered or shares of Common Stock are sold or otherwise disposed of on a later date.  It is important for you to read and consider allconflict between the information contained in this prospectus, includingon the documentsone hand, and the information contained in any document incorporated by reference therein, in making your investment decision.  Youfiled with the SEC before the date of this prospectus, on the other hand, you should also read and considerrely on the information in this prospectus. If any statement in a document incorporated by reference is inconsistent with a statement in another document incorporated by reference having a later date, the statement in the document having the later date modifies or supersedes the earlier statement.

This prospectus contains summaries of certain provisions contained in some of the documents described herein, but reference is made to the actual documents for complete information. All of the summaries are qualified in their entirety by the actual documents. Copies of some of the documents referred to herein have been filed, will be filed or will be incorporated by reference as exhibits to the registration statement of which we have referredthis prospectus is a part, and you undermay obtain copies of those documents as described below in the section titled “Where You Can Find Additional Information” and “Information Incorporated by Reference” in this prospectus.More Information.”

We have not authorized anyone to give any information or to make any representation to you other than those contained or incorporated by reference in this prospectus.  You must not rely upon any information or representation not contained or incorporated by reference in this prospectus.  This prospectus does not constitute an offer to sell or the solicitation of an offer to buy any of our shares of Common Stock other than the shares of our Common Stock covered hereby, nor does this prospectus constitute an offer to sell or the solicitation of an offer to buy any securities in any jurisdiction to any person to whom it is unlawful to make such offer or solicitation in such jurisdiction.  Persons who come into possession of this prospectus in jurisdictions outside the United States are required to inform themselves about, and to observe, any restrictions as to the offering and the distribution of this prospectus applicable to those jurisdictions.

Unless we have indicated otherwise, or the context otherwise requires, references in this prospectus to “SELLAS,The names “SELLAS Life Sciences Group, Inc.,” “SELLAS,” the “Company,” “we,” “us”SELLAS logo, and “our” refer toother trademarks or service marks of SELLAS Life Sciences Group, Inc. appearing in this prospectus are the property of SELLAS Life Sciences Group, Inc. Other trademarks, service marks or trade names appearing in this prospectus are the property of their respective owners. We do not intend the use or display of other companies’ trade names, trademarks or service marks to imply a relationship with, or endorsement or sponsorship of or by either, of these other companies.

RISK FACTORS

RISK FACTORS

Investing in our securities involves a high degree of risk. YouBefore deciding whether to invest in our securities, you should carefully consider and evaluate all of the information containedrisks described in the documents incorporated by reference in this prospectus the accompanyingand any applicable prospectus and in the documentssupplement, as well as other information we include or incorporate by reference into this prospectus and accompanyingany applicable prospectus supplement, before you decide to purchase our securities.  In particular, you should carefully consider and evaluate the risks and uncertainties described under the heading "Risk Factors" in our Annual Report on Form 10-K for the fiscal year ended December 31, 2019.  Any of the risks and uncertainties set forth in that report, as updated by annual, quarterly and other reports and documents that we file with the SEC and incorporate by reference into this prospectusmaking an investment decision. Our business, financial condition or any prospectus, could materially and adversely affect our business, results of operations and financial condition, which in turn could be materially and adversely affectaffected by any of these risks. The trading price of our securities could decline due to the valueoccurrence of any securities offered by this prospectus.  As a result,of these risks, and you couldmay lose all or part of your investment.

THE OFFERING

On July 31, 2020, we entered into the "Purchase Agreement" with certain investors (each an “Investor” and, collectively, the “Investors”), pursuant to which we issued and sold, in a private placement (the “Offering”), 2,744,078 shares of the Company's common stock, par value $0.0001 per share (the “Common Stock”), at a purchase price of $3.335 per share (the “Shares”) and warrants to purchase up to 2,744,078 shares of Common Stock at an exercise price of $3.30 per share (the “Warrants”). The Warrants were immediately exercisable upon issuance and expire five years from the date of issuance.

In connection with the Offering, we entered into a Registration Rights Agreement (the “Registration Rights Agreement”) with the Investors, pursuant to which we are obligated, among other things, to (i) file a registration statement with the U.S. Securities and Exchange Commission (the “SEC”) within 20 days following the entrance into the Registration Rights Agreement for purposes of registering the Shares and the shares of Common Stock issuable upon exercise of the Warrants for resale by the Investors, (ii) use our reasonable best efforts to have the registration statement declared effective as soon as practicable after filing, and in any event no later than sixty (60) days after the entrance into the Registration Rights Agreement (or ninety (90) days after the entrance into the Registration Rights Agreement if the registration statement is reviewed by the SEC), and (iii) maintain the registration until all registrable securities may be sold pursuant to Rule 144 under the Securities Act, without restriction as to volume.  The Registration Rights Agreement contains customary terms and conditions for a transaction of this type, including certain customary cash penalties on the Registrant for its failure to satisfy specified filing and effectiveness time periods.

The foregoing descriptions of the Purchase Agreement, the Registration Rights Agreement and the form of Warrant are not complete and are subject to and qualified in their entirety by reference to the Purchase Agreement, the Registration Rights Agreement and the form of Warrant, respectively, copies of which are attached as Exhibits 10.1, 10.2 and 4.1, respectively, to the Current Report on Form 8-K dated August 4, 2020, and are incorporated herein by reference.

CAUTIONARY NOTE REGARDING FORWARD-LOOKING STATEMENTS

This prospectus and the documents incorporated herein by reference also contain forward-looking statements that involve risks and uncertainties. Actual results could differ materially from those anticipated in these forward-looking statements as a result of certain factors, including the risks described in the documents incorporated herein by reference, including in (1) our most recent Annual Report on Form 10-K on file with the SEC, (2) our most recent Quarterly Reports on Form 10-Q on file with the SEC and (3) any amendments thereto reflected in subsequent filings with the SEC, all of which are incorporated by reference into this prospectus includein their entirety, together with other information in this prospectus, the applicable prospectus supplement and the documents incorporated by reference that we may authorize for use in connection with a specific offering. Please also read carefully the section below entitled “Special Note Regarding Forward-Looking Statements.”

SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS

This prospectus, the applicable prospectus supplement, and the documents incorporated by reference contain forward-looking statements withinabout us and our industry that involve substantial risks and uncertainties. All statements other than statements of historical facts contained in this prospectus, the meaning of Section 27A ofapplicable prospectus supplement, and the Securities Act of 1933 and Section 21E of the Securities Exchange Act of 1934, as amended, that relate to future events ordocumented incorporated by reference, including statements regarding our future financial performancecondition, business strategy and involve knownplans, and unknown risks, uncertainties and other factors that may cause our actual results, levelsobjectives of activity, performance or achievements to differ materially from anymanagement for future results, levels of activity, performance or achievements expressed or implied by theseoperations, are forward-looking statements. WordsIn some cases, you can identify forward-looking statements by terminology such as but not limited to,“aim,” “anticipate,” “aim,“assume,” “believe,” “contemplate,” “continue,” “could,” “design,” “due,” “estimate,” “expect,” “goal,” “intend,” “may,” “might,“objective,” “plan,” “predict,” “poise,” “project,“positioned,” “potential,” “suggest,“seek,” “should,” “strategy,” “target,” “will,” “would,”“would” and other similar expressions that are predictions of or phrases,indicate future events and future trends, or the negative of those expressionsthese terms or phrases, are intended to identifyother comparable terminology.

We have based these forward-looking statements although not alllargely on our current expectations and projections about future events and financial trends that we believe may affect our financial condition, results of operations, business strategy and financial needs. These forward-looking statements contain these identifying words. Although we believe that we haveare subject to a reasonable basis for each forward-looking statementnumber of known and unknown risks, uncertainties and assumptions, including risks described in the section titled “Risk Factors” contained in our most recent Annual Report on Form 10-K and Quarterly Reports on Form 10-Q and incorporated by reference in this prospectus, as the same may be amended, supplemented or superseded by the risks and uncertainties described under similar headings in the other documents that are filed after the date hereof and incorporated by reference into this prospectus, we caution you that these statements are based on our projections of the future that are subject to known and unknown risks and uncertainties and other factors that may cause our actual results, level of activity, performance or achievements expressed or implied by these forward-looking statements, to differ. The section in this prospectus entitled “Risk Factors” and the sections in our periodic reports, including the 2019 Form 10-K entitled “Business,” and in the 2019 Form 10-K and our most recent quarterly report on Form 10-Q entitled “Management’s Discussion and Analysis of Financial Condition and Results of Operations,” as well as other sections in this prospectus and the documents or reports incorporated by reference into this prospectus, discuss some of the factors that could contribute to these differences. These forward-looking statements include,regarding, among other things, statements about:things:

Our current product candidatesThese risks are undergoing clinical development and have not been approved by the FDA or the European Commission. These product candidates have not been, nor may they ever be, approved by any regulatory agency or competent authorities nor marketed anywhere in the world.

We may not actually achieve the plans, intentions or expectations disclosed in our forward-looking statements, and you should not place undue reliance on our forward-looking statements. Forward-looking statements should be regarded solely as our current plans, estimates and beliefs. We have included important factors in the cautionary statements included in this document, particularly in the section entitled “Risk Factors” beginning on page 5exhaustive. Other sections of this prospectus, the applicable prospectus supplement, or the documents incorporated herein by reference may include additional factors that we believe could cause actual results or events to differ materially from the forward-looking statements that we make.harm our business and financial performance. Moreover, we operate in a very competitive and rapidly changing environment. New risksrisk factors emerge from time to time. Ittime, and it is not possible for our management to predict all risks,risk factors, nor can we assess the impact of all factors on our business or the extent to which any factor, or combination of factors, may cause actual results to differ materially from those contained in, or implied by, any forward-looking statements we may make. Given these risks and uncertainties, readers are cautionedstatements.

You should not to place undue reliance on such forward-looking statements. Allrely upon forward-looking statements are qualified in their entirety by this cautionary statement. Our forward-looking statements do not reflectas predictions of future events. We cannot assure you that the potential impact of any future acquisitions, mergers, dispositions, joint ventures or investments we may make. You should read this prospectusevents and the documents that we have filed as exhibits to this prospectus and incorporated by reference herein completely and with the understanding that our actual future results may be materially different from the plans, intentions and expectations disclosedcircumstances reflected in the forward-looking statements we make.will be achieved or occur. Although we believe that the expectations reflected in the forward-looking statements are reasonable, we cannot guarantee future results, levels of activity, performance or performance. The forward-looking statements contained in this prospectus are madeachievements. Except as of the date of this prospectus andrequired by law, we do not assume anyundertake no obligation to update publicly any forward-looking statements whether as a result of new information, future events or otherwise, except as required by applicable law.

You should also consider carefully the statements set forth in the sections titled "Risk Factors" or elsewhere in this prospectus, in the accompanying prospectus and in the documents incorporated or deemed incorporated herein or therein by reference, which address various factors that could cause results or events to differ from those described in the forward-looking statements.  All subsequent written and oral forward-looking statements attributable to us or to persons acting on our behalf are expressly qualified in their entirety by the applicable cautionary statements.  We have no plans to update these forward-looking statements.

USE OF PROCEEDS

We will not receivefor any of the proceeds from the sale of Common Stock by the selling stockholders named in this prospectus, and the selling stockholders will receive all of the proceeds from this offering.

We may receive up to approximately $9.1 million in aggregate gross proceeds from cash exercises of the Warrants, based on the per share exercise price of the Warrants. Any proceeds we receive from the exercise of the Warrants will be used to advance our clinical programs and for general corporate purposes. The holders of the Warrants are not obligated to exercise their Warrants, and we cannot predict whether holders of the Warrants will choose to exercise all or any of their Warrants.

SELLING STOCKHOLDERS

This prospectus relates to the sale or other disposition of up to 5,488,156 shares of our Common Stock and shares of Common Stock issuable to the selling stockholders upon exercise of the Warrants by the selling stockholders named below, and their donees, pledgees, transferees or other successors-in-interest selling shares of Common Stock or interests in shares of Common Stock receivedreason after the date of this prospectus from a selling stockholder as a gift, pledge, partnership distribution or other transfer.  The shares of Common Stock covered hereby were issued by usto conform these statements to actual results or to changes in the Offering.  See “The Offering” beginning on page 5 of this prospectus.our expectations.

The table below sets forth information as of August 13, 2020, to our knowledge, for the selling stockholders and other information regarding the beneficial ownership (as determined under Section 13(d) of the Exchange ActYou should carefully read this prospectus, and the rules and regulations thereunder) ofapplicable prospectus supplement, together with the shares of Common Stock heldinformation incorporated herein by the selling stockholders.  The second column lists the number of shares of Common Stock and percentage beneficially owned by the selling stockholders as of July 31, 2020.  The third column lists the maximum number of shares of Common Stock that may be sold or otherwise disposed of by the selling stockholders pursuant to the registration statement of which this prospectus forms a part.  The selling stockholders may sell or otherwise dispose of some, all or none of their shares.  Pursuant to Rules 13d-3 and 13d-5 of the Exchange Act, beneficial ownership includes any shares of our Common Stock as to which a stockholder has sole or shared voting power or investment power, and also any shares of our Common Stock which the stockholder has the right to acquire within 60 days of August 13, 2020.  The percentage of beneficial ownership for the selling stockholders is based on 9,461,978 shares of our Common Stock outstanding as of August 13, 2020 and the number of shares of our Common Stock issuable upon exercise or conversion of convertible securities that are currently exercisable or convertible or are exercisable or convertible within 60 days of August 13, 2020 beneficially owned by the applicable selling stockholder.  Exceptreference as described below, to our knowledge, none ofunder the selling stockholders has been an officer or director of ours or of our affiliates within the past three years or has any material relationship with us or our affiliates within the past three years.  Our knowledge is based on information providedheading “Incorporation by the selling stockholders in connection with the filing of this prospectus,Reference,” as well as information obtained from relevant Schedule 13D and 13G filings.

The shares of Common Stock being covered hereby may be sold or otherwise disposed of from timethe documents filed as exhibits to time during the period the registration statement of which this prospectus is a part remains effective,with the understanding that our actual future results, levels of activity, performance and achievements may be materially different from what we expect. We qualify all of our forward-looking statements by these cautionary statements.

Except as required by law, we assume no obligation to update these forward-looking statements publicly, or to update the reasons actual results could differ materially from those anticipated in these forward-looking statements, even if new information becomes available in the future.

USE OF PROCEEDS

Except as described in any applicable prospectus supplement or in any related free writing prospectuses we may authorize for use in connection with a specific offering, we currently intend to use the net proceeds from the sale of the securities offered by us hereunder, if any, for working capital, capital expenditures and other general corporate purposes including research and development of our product candidates (including clinical trial activities), and general and administrative expenses. In addition, we may use a portion of the proceeds for the accountacquisition of, the selling stockholders.  Afteror investment in, technologies, solutions or businesses that complement our business, although we have no present commitments or agreements to enter into any such acquisitions or investments. As of the date of effectivenessthis prospectus, we cannot specify with certainty all of the particular uses for the net proceeds to us from the sale of the securities offered by us hereunder. We will set forth in the applicable prospectus supplement or free writing prospectus our intended use for the net proceeds received from the sale of any securities sold pursuant to the prospectus supplement or free writing prospectus.

DILUTION

We will set forth in a prospectus supplement the following information regarding any material dilution of the equity interests of investors purchasing securities in an offering under this prospectus:

DESCRIPTION OF CAPITAL STOCK

The following description of our capital stock summarizes the material terms and provisions of our common stock and our preferred stock. For the complete terms of our common stock, please refer to our amended and restated certificate of incorporation and our amended and restated bylaws, each as amended to date, that are incorporated by reference into the registration statement of which this prospectus is a part or may be incorporated by reference into this prospectus. The terms of these securities may also be affected by the sellingDelaware General Corporation Law. The summary below is qualified in its entirety by reference to our amended and restated certificate of incorporation and amended and restated bylaws, which are filed as exhibits to the registration statement of which this prospectus is a part.

General

Our amended and restated certificate of incorporation authorizes us to issue up to 350,000,000 shares of common stock, $0.0001 par value per share, and 5,000,000 shares of preferred stock, $0.0001 par value per share.

As of December 31, 2023, there were:

Common stock

Voting

Each holder of our common stock is entitled to one vote for each share on all matters submitted to a vote of the stockholders, including the election of directors. Our amended and restated certificate of incorporation and amended and restated bylaws do not provide for cumulative voting rights. Because of this absence of cumulative voting, the holders of a majority of the shares of common stock entitled to vote in any election of directors can elect all the directors standing for election, if they should so choose.

Dividends

Subject to preferences that may sellbe applicable to any then outstanding shares of preferred stock, holders of common stock are entitled to receive ratably those dividends, if any, as may be declared from time to time by our board of directors out of legally available funds.

Liquidation

In the event of our dissolution or transfer,liquidation, holders of common stock will be entitled to share ratably in transactions coveredthe net assets legally available for distribution to stockholders after the payment of all our debts and other liabilities and the satisfaction of any preferential rights that may be granted to the holders of any then outstanding shares of preferred stock.

Rights and Preferences

Holders of common stock have no preemptive, conversion or subscription rights, and there are no redemption or sinking fund provisions applicable to the common stock. The rights, preferences, and privileges of the holders of common stock are subject to, and may be adversely affected by, the rights of the holders of shares of any series of preferred stock.

Fully-paid

All of the outstanding shares of our common stock are, and the shares of common stock issued upon the conversion of any securities convertible into our common stock will be, fully paid and non-assessable. The shares of common stock offered by this prospectus or upon the conversion of any preferred stock or debt securities or exercise of any warrants offered pursuant to this prospectus, when issued and paid for, will also be, fully paid and non-assessable.

Preferred stock

Under our amended and restated certificate of incorporation, our board of directors has the authority, without further action by our stockholders, to issue up to 5,000,000 shares of preferred stock in transactions exempt fromone or more series and to fix the registration requirementsrights, preferences, privileges and restrictions thereof. These rights, preferences and privileges could include dividend rights, conversion rights, voting rights, terms of redemption, liquidation preferences, sinking fund terms and the Securities Act, somenumber of shares constituting any series or the designation of such series, any or all of their Common Stock.which may be greater than the rights of common stock. The issuance of our preferred stock could adversely affect the voting power of holders of common stock and the likelihood that such holders will receive dividend payments and payments upon liquidation. In addition, the issuance of preferred stock could have the effect of delaying, deferring or preventing a change of control of our company or other corporate action.

Information aboutThe following summary of terms of our preferred stock is not complete. You should refer to the selling stockholdersprovisions of our amended and restated certificate of incorporation and amended and restated bylaws and the resolutions containing the terms of each class or series of the preferred stock which have been or will be filed with the SEC at or prior to the time of issuance of such class or series of preferred stock and described in the applicable prospectus supplement. The applicable prospectus supplement may change over time.  Any changedalso state that any of the terms set forth herein are inapplicable to such series of preferred stock, provided that the information will be set forth in such prospectus supplement does not constitute material changes to the information herein such that it alters the nature of the offering or the securities offered.

Our board of directors will fix the designations, voting powers, preferences and rights of the preferred stock of each series we issue under this prospectus, as well as the qualifications, limitations or restrictions thereof, in the certificate of designation relating to that series. We will file as an amendmentexhibit to the registration statement or supplement toof which this prospectus is a part, or will incorporate by reference from reports that we file with the SEC, the form of any certificate of designation that describes the terms of the series of preferred stock we are offering. We will describe in the applicable prospectus supplement the terms of the series of preferred stock being offered, including, to the extent required by law.applicable:

If we issue shares of preferred stock under this prospectus, they will be validly issued, fully paid and non-assessable.

The DGCL provides that the holders of preferred stock will have the right to vote separately as a class on any proposal involving fundamental changes in the rights of holders of such preferred stock. This right is in addition to any voting rights that may be provided for in the applicable certificate of designation.

The issuance of our preferred stock could adversely affect the voting power, conversion or other rights of holders of common stock and reduce the likelihood that such holders will receive dividend payments and payments upon liquidation. In addition, the issuance of preferred stock could have the effect of delaying, deferring or preventing a change in control of our company or other corporate action. Additionally, the issuance of preferred stock may have the effect of decreasing the market price of our common stock.

Possible Anti-Takeover Effects of Delaware Law and Our Certificate of Incorporation and Bylaws

Provisions of the DGCL and our amended and restated certificate of incorporation and amended and restated bylaws could make it more difficult to acquire our company by means of a tender offer, a proxy contest or otherwise, or to remove incumbent officers and directors. These provisions, summarized below, are expected to discourage certain types of coercive takeover practices and takeover bids that our board of directors may consider inadequate and to encourage persons seeking to acquire control of our company to first negotiate with our board of directors. We believe that the benefits of increased protection of our ability to negotiate with the proponent of an unfriendly or unsolicited proposal to acquire or restructure our company outweigh the disadvantages of discouraging takeover or acquisition proposals because, among other things, negotiation of these proposals could result in an improvement of their terms.

Classified Board

Our amended and restated certificate of incorporation and our amended and restated bylaws provide that our board of directors is divided into three classes. The directors designated as Class I directors have terms expiring at the annual meeting of stockholders in 2026. The directors designated as Class II directors will have terms expiring at the annual meeting of stockholders in 2024, and the directors designated as Class III directors will have terms expiring at the annual meeting of stockholders in 2025. Directors for each class will be elected at the annual meeting of stockholders held in the year in which the term for that class expires and thereafter will serve for a term of three years. At any meeting of stockholders for the election of directors at which a quorum is present, the election will be determined by a plurality of the votes cast by the stockholders entitled to vote at the election. Under the classified board provisions, it would take at least two elections of directors for any individual or group to gain control of our board. Accordingly, these provisions could discourage a third party from initiating a proxy contest, making a tender offer or otherwise attempting to gain control of our company.

Removal of Directors

Our amended and restated bylaws provide that our stockholders may only remove our directors with cause.

Amendment

Our amended and restated certificate of incorporation and our amended and restated bylaws provide that the affirmative vote of the holders of at least 75% of our voting stock then outstanding is required to amend certain provisions relating to the number, term, election and removal of our directors, the filling of our board vacancies, stockholder notice procedures, the calling of special meetings of stockholders and the indemnification of directors. Further, any amendments of our bylaws must be approved by our stockholders as our amended and restated certificate of incorporation does not authorize our board of directors to amend our bylaws.

PLAN OF DISTRIBUTIONSize of Board and Vacancies

Each selling stockholderOur amended and restated bylaws provide that the number of directors on our board of directors is fixed exclusively by our board of directors. Newly created directorships resulting from any increase in our authorized number of directors will be filled by a majority of our board of directors then in office, provided that a majority of the securitiesentire board of directors, or a quorum, is present and any vacancies in our board of their pledgees, assigneesdirectors resulting from death, resignation, retirement, disqualification, removal from office or other cause will be filled generally by the majority vote of our remaining directors in office, even if less than a quorum is present.

Special Stockholder Meetings

Our amended and successors-in-interestrestated certificate of incorporation provides that only the Chairman of our board of directors, our Chief Executive Officer or our board of directors pursuant to a resolution adopted by a majority of the total number of directors we would have if there were no vacancies may from timecall special meetings of our stockholders.

Stockholder Action by Unanimous Written Consent

Our amended and restated certificate of incorporation expressly eliminates the right of our stockholders to time, sellact by written consent.

Requirements for Advance Notification of Stockholder Nominations and Proposals

Our amended and restated bylaws provide advance notice procedures with respect to stockholder proposals and nomination of candidates for election as directors other than nominations made by or at the direction of board of directors or a committee of our board of directors.

No Cumulative Voting

The DGCL provides that stockholders are denied the right to cumulate votes in the election of directors unless our certificate of incorporation provides otherwise. Our amended and restated certificate of incorporation does not provide for cumulative voting.

Undesignated Preferred Stock

The authority that is possessed by our board of directors to issue preferred stock could potentially be used to discourage attempts by third parties to obtain control of our company through a merger, tender offer, proxy contest, or otherwise by making it more difficult or costlier to obtain control of our company. Our board of directors may issue preferred stock with voting rights or conversion rights that, if exercised, could adversely affect the voting power of the holders of common stock.

Authorized but Unissued Shares

Our authorized but unissued shares of common stock and preferred stock will be available for future issuance without stockholder approval. We may use additional shares for a variety of purposes, including future public offerings to raise additional capital, to fund acquisitions and as employee compensation. The existence of authorized but unissued shares of common stock and preferred stock could render more difficult or discourage an attempt to obtain control of our company by means of a proxy contest, tender offer, merger or otherwise.

The above provisions may deter a hostile takeover or delay a change in control or management of our company.

Listing on The Nasdaq Capital Market

Our common stock is listed on The Nasdaq Capital Market under the symbol “SLS”. On March 27, 2024, the closing price of our common stock was $1.03 per share. As of March 27, 2024, we had approximately 35 stockholders of record.

The applicable prospectus supplement will contain information, where applicable, as to other listing, if any, or all of their securities covered hereby on The Nasdaq Capital Market or other securities exchange of the preferred stock covered by such prospectus supplement.

Transfer Agent and Registrar

The transfer agent and registrar for our capital stock is Computershare Trust Company, N.A. Its address is 250 Royall Street, Canton, MA 02021. Its telephone number is (201) 680-4503.

DESCRIPTION OF DEBT SECURITIES

We may issue debt securities from time to time, in one or more series, as either senior or subordinated debt or as senior or subordinated convertible debt. While the terms we have summarized below will apply generally to any debt securities that we may offer under this prospectus, we will describe the particular terms of any debt securities that we may offer in more detail in the applicable prospectus supplement. The terms of any debt securities offered under a prospectus supplement may differ from the terms described below. Unless the context requires otherwise, whenever we refer to the indenture, we also are referring to any supplemental indentures that specify the terms of a particular series of debt securities.

We will issue the debt securities under the indenture that we will enter into with the trustee named in the indenture. The indenture will be qualified under the Trust Indenture Act of 1939, as amended, or the Trust Indenture Act. We have filed forms of senior and subordinated indentures as exhibits to the registration statement of which this prospectus is a part, and supplemental indentures and forms of debt securities containing the terms of the debt securities being offered will be filed as exhibits to the registration statement of which this prospectus is a part or will be incorporated by reference from reports that we file with the SEC.

The following summary of material provisions of the debt securities and the indenture is subject to, and qualified in its entirety by reference to, all of the provisions of the indenture applicable to a particular series of debt securities. We urge you to read the applicable prospectus supplements and any related free writing prospectuses related to the debt securities that we may offer under this prospectus, as well as the complete indenture that contains the terms of the debt securities.

General

The indenture does not limit the amount of debt securities that we may issue. It provides that we may issue debt securities up to the principal amount that we may authorize and may be in any currency or currency unit that we may designate. Except for the limitations on consolidation, merger and sale of all or substantially all of our assets contained in the indenture, the terms of the indenture do not contain any covenants or other provisions designed to give holders of any debt securities protection against changes in our operations, financial condition or transactions involving us.

We may issue the debt securities issued under the indenture as “discount securities,” which means they may be sold at a discount below their stated principal amount. These debt securities, as well as other debt securities that are not issued at a discount, may be issued with “original issue discount,” or OID, for U.S. federal income tax purposes because of interest payment and other characteristics or terms of the debt securities. Material U.S. federal income tax considerations applicable to debt securities issued with OID will be described in more detail in any applicable prospectus supplement.

We will describe in the applicable prospectus supplement the terms of the series of debt securities being offered, including:

Conversion or Exchange Rights

We will set forth in the applicable prospectus supplement the terms on which a series of debt securities may be convertible into or exchangeable for our common stock or our other securities. We will include provisions as to settlement upon conversion or exchange and whether conversion or exchange is mandatory, at the option of the holder or at our option. We may include provisions pursuant to which the number of shares of our common stock or our other securities that the holders of the series of debt securities receive would be subject to adjustment.

Consolidation, Merger or Sale

Unless we provide otherwise in the prospectus supplement applicable to a particular series of debt securities, the indenture will not contain any covenant that restricts our ability to merge or consolidate, or sell, convey, transfer or otherwise dispose of our assets as an entirety or substantially as an entirety. However, any successor to or acquirer of such assets (other than a subsidiary of ours) must assume all of our obligations under the indenture or the debt securities, as appropriate.

Events of Default under the Indenture

Unless we provide otherwise in the prospectus supplement applicable to a particular series of debt securities, the following are events of default under the indenture with respect to any series of debt securities that we may issue:

If an event of default with respect to debt securities of any series occurs and is continuing, other than an event of default specified in the last bullet point above, the trustee or the holders of at least 25% in aggregate principal amount of the outstanding debt securities of that series, by notice to us in writing, and to the trustee if notice is given by such holders, may declare the unpaid principal of, premium, if any, and accrued interest, if any, due and payable immediately. If an event of default specified in the last bullet point above occurs with respect to us, the principal amount of and accrued interest, if any, of each issue of debt securities then outstanding shall be due and payable without any notice or other action on the part of the trustee or any holder.

The holders of a majority in principal amount of the outstanding debt securities of an affected series may waive any default or event of default with respect to the series and its consequences, except defaults or events of default regarding payment of principal, premium, if any, or interest, unless we have cured the default or event of default in accordance with the indenture. Any waiver shall cure the default or event of default.

Subject to the terms of the indenture, if an event of default under an indenture shall occur and be continuing, the trustee will be under no obligation to exercise any of its rights or powers under such indenture at the request or direction of any of the holders of the applicable series of debt securities, unless such holders have offered the trustee reasonable indemnity. The holders of a majority in principal amount of the outstanding debt securities of any series will have the right to direct the time, method and place of conducting any proceeding for any remedy available to the trustee, or exercising any trust or power conferred on the trustee, with respect to the debt securities of that series, provided that:

These limitations do not apply to a suit instituted by a holder of debt securities if we default in the payment of the principal, premium, if any, or interest on, the debt securities.

We will periodically file statements with the trustee regarding our compliance with specified covenants in the indenture.

Modification of Indenture; Waiver

We and the trustee may change an indenture without the consent of any holders with respect to specific matters:

In addition, under the indenture, the rights of holders of a series of debt securities may be changed by us and the trustee with the written consent of the holders of at least a majority in aggregate principal amount of the outstanding debt securities of each series that is affected. However, unless we provide otherwise in the prospectus supplement applicable to a particular series of debt securities, we and the trustee may make the following changes only with the consent of each holder of any outstanding debt securities affected:

Discharge

Each indenture provides that we can elect to be discharged from our obligations with respect to one or more series of debt securities, except for specified obligations, including obligations to:

In order to exercise our rights to be discharged, we must deposit with the trustee money or government obligations sufficient to pay all the principal of, any premium, if any, and interest on, the debt securities of the series on the dates payments are due.

Form, Exchange and Transfer

We will issue the debt securities of each series only in fully registered form without coupons and, unless we provide otherwise in the applicable prospectus supplement, in denominations of $1,000 and any integral multiple thereof. The indenture provides that we may issue debt securities of a series in temporary or permanent global form and as book-entry securities that will be deposited with, or on behalf of, The Depository Trust Company, or DTC, or another depositary named by us and identified in the applicable prospectus supplement with respect to that series. To the extent the debt securities of a series are issued in global form and as book-entry, a description of terms relating to any book-entry securities will be set forth in the applicable prospectus supplement.

At the option of the holder, subject to the terms of the indenture and the limitations applicable to global securities described in the applicable prospectus supplement, the holder of the debt securities of any series can exchange the debt securities for other debt securities of the same series, in any authorized denomination and of like tenor and aggregate principal amount.

Subject to the terms of the indenture and the limitations applicable to global securities set forth in the applicable prospectus supplement, holders of the debt securities may present the debt securities for exchange or for registration of transfer, duly endorsed or with the form of transfer endorsed thereon duly executed if so required by us or the security registrar, at the office of the security registrar or at the office of any transfer agent designated by us for this purpose. Unless otherwise provided in the debt securities that the holder presents for transfer or exchange, we will impose no service charge for any registration of transfer or exchange, but we may require payment of any taxes or other governmental charges.

We will name in the applicable prospectus supplement the security registrar, and any transfer agent in addition to the security registrar, that we initially designate for any debt securities. We may at any time designate additional transfer agents or rescind the designation of any transfer agent or approve a change in the office through which any transfer agent acts, except that we will be required to maintain a transfer agent in each place of payment for the debt securities of each series.

If we elect to redeem the debt securities of any series, we will not be required to:

Information Concerning the Trustee

The trustee, other than during the occurrence and continuance of an event of default under an indenture, undertakes to perform only those duties as are specifically set forth in the applicable indenture. Upon an event of default under an indenture, the trustee must use the same degree of care as a prudent person would exercise or use in the conduct of his or her own affairs. Subject to this provision, the trustee is under no obligation to exercise any of the powers given it by the indenture at the request of any holder of debt securities unless it is offered reasonable security and indemnity against the costs, expenses and liabilities that it might incur.

Payment and Paying Agents

Unless we otherwise indicate in the applicable prospectus supplement, we will make payment of the interest on any debt securities on any interest payment date to the person in whose name the debt securities, or one or more predecessor securities, are registered at the close of business on the regular record date for the interest.

We will pay principal of and any premium and interest on the debt securities of a particular series at the office of the paying agents designated by us, except that unless we otherwise indicate in the applicable prospectus supplement, we will make interest payments by check that we will mail to the holder or by wire transfer to certain holders. Unless we otherwise indicate in the applicable prospectus supplement, we will designate the corporate trust office of the trustee as our sole paying agent for payments with respect to debt securities of each series. We will name in the applicable prospectus supplement any other paying agents that we initially designate for the debt securities of a particular series. We will maintain a paying agent in each place of payment for the debt securities of a particular series.

All money we pay to a paying agent or the trustee for the payment of the principal of or any premium or interest on any debt securities that remains unclaimed at the end of two years after such principal, premium or interest has become due and payable will be repaid to us, and the holder of the debt security thereafter may look only to us for payment thereof.

Governing Law

The indenture and the debt securities will be governed by and construed in accordance with the internal laws of the State of New York, except to the extent that the Trust Indenture Act of 1939 is applicable.

DESCRIPTION OF WARRANTS

The following description, together with the additional information we may include in any applicable prospectus supplement and in any related free writing prospectus that we may authorize to be distributed to you, summarizes the material terms and provisions of the warrants that we may offer under this prospectus, which may consist of warrants to purchase common stock, exchange, market preferred stock and/or trading facilitydebt securities and may be issued in one or more series. Warrants may be offered independently or in combination with common stock, preferred stock or debt securities offered by any prospectus supplement, and may be attached to or separate from those securities. While the terms we have summarized below will apply generally to any warrants that we may offer under this prospectus, we will describe the particular terms of any series of warrants that we may offer in more detail in the applicable prospectus supplement. The following description of warrants will apply to the warrants offered by this prospectus unless we provide otherwise in the applicable prospectus supplement. The applicable prospectus supplement for a particular series of warrants may specify different or additional terms.

We have filed forms of the warrant agreements and forms of warrant certificates containing the terms of the warrants that may be offered as exhibits to the registration statement of which this prospectus is a part. We will file as exhibits to the registration statement of which this prospectus is a part, or will incorporate by reference from reports that we file with the SEC, the form of warrant and/or the warrant agreement and warrant certificate, as applicable, that contain the terms of the particular series of warrants we are offering, and any supplemental agreements, before the issuance of such warrants. The following summaries of material terms and provisions of the warrants are subject to, and qualified in their entirety by reference to, all the provisions of the form of warrant and/or the warrant agreement and warrant certificate, as applicable, and any supplemental agreements applicable to a particular series of warrants that we may offer under this prospectus. We urge you to read the applicable prospectus supplement related to the particular series of warrants that we may offer under this prospectus, as well as any related free writing prospectus, and the complete form of warrant and/or the warrant agreement and warrant certificate, as applicable, and any supplemental agreements, that contain the terms of the warrants.

General

We will describe in the applicable prospectus supplement the terms of the series of warrants being offered, including, to the extent applicable:

Before exercising their warrants, holders of warrants will not have any of the rights of holders of the securities purchasable upon such exercise, including:

Exercise of Warrants

Each warrant will entitle the holder to purchase the securities that we specify in the applicable prospectus supplement at the exercise price that we describe in the applicable prospectus supplement. The warrants may be exercised as set forth in the prospectus supplement relating to the warrants offered. Unless we otherwise specify in the applicable prospectus supplement, warrants may be exercised at any time up to the specified time on the expiration date that we set forth in the applicable prospectus supplement. After the close of business on the expiration date, unexercised warrants will become void.

Unless we otherwise specify in the applicable prospectus supplement, holders of the warrants may exercise the warrants by delivering the warrant or warrant certificate, as applicable, representing the warrants to be exercised together with specified information, and paying the required amount to the warrant agent in immediately available funds, as provided in the applicable prospectus supplement. We will set forth in the applicable warrant or warrant certificate and in the applicable prospectus supplement the information that the holder of the warrant will be required to deliver to the warrant agent in connection with the exercise of the warrant.

Upon receipt of the required payment and the warrant or warrant certificate, as applicable, properly completed and duly executed at the corporate trust office of the warrant agent, if any, or any other office, including ours, indicated in the prospectus supplement, we will, as soon as practicable, issue and deliver the securities purchasable upon such exercise. If less than all of the warrants (or the warrants represented by such warrant certificate) are exercised, a new warrant or a new warrant certificate, as applicable, will be issued for the remaining warrants. If we so indicate in the applicable prospectus supplement, holders of the warrants may surrender securities as all or part of the exercise price for warrants.

Governing Law

Unless we provide otherwise in the applicable prospectus supplement, the warrants, warrant agreements, and any claim, controversy or dispute arising under or related to the warrants or warrant agreements will be governed by and construed in accordance with the laws of the State of New York.

Enforceability of Rights by Holders of Warrants

Each warrant agent, if any, will act solely as our agent under the applicable warrant agreement and will not assume any obligation or relationship of agency or trust with any holder of any warrant. A single bank or trust company may act as warrant agent for more than one issue of warrants. A warrant agent will have no duty or responsibility in case of any default by us under the applicable warrant agreement or warrant, including any duty or responsibility to initiate any proceedings at law or otherwise, or to make any demand upon us. Any holder of a warrant may, without the consent of the related warrant agent or the holder of any other warrant, enforce by appropriate legal action its right to exercise, and receive the securities purchasable upon exercise of, its warrants.

Outstanding Warrants

Certain of our outstanding warrants contain customary net exercise provisions and provisions for the adjustment of the exercise price and the number of shares issuable upon the exercise of the warrant in the event of certain stock dividends, stock splits, recapitalizations, reclassifications, consolidations and other fundamental transactions, as well as, in certain circumstances, price-based anti-dilution adjustments.

DESCRIPTION OF RIGHTS

General

We may issue rights to our stockholders to purchase shares of our common stock, preferred stock or the other securities described in this prospectus. We may offer rights separately or together with one or more additional rights, debt securities, preferred stock, common stock, warrants or any combination of those securities in the form of units, as described in the applicable prospectus supplement. Each series of rights will be issued under a separate rights agreement to be entered into between us and a bank or trust company, as rights agent. The rights agent will act solely as our agent in connection with the certificates relating to the rights of the series of certificates and will not assume any obligation or relationship of agency or trust for or with any holders of rights certificates or beneficial owners of rights. The following description sets forth certain general terms and provisions of the rights to which any prospectus supplement may relate. The particular terms of the rights to which any prospectus supplement may relate and the extent, if any, to which the general provisions may apply to the rights so offered will be described in the applicable prospectus supplement. To the extent that any particular terms of the rights, rights agreement or rights certificates described in a prospectus supplement differ from any of the terms described below, then the terms described below will be deemed to have been superseded by that prospectus supplement. We encourage you to read the applicable rights agreement and rights certificate for additional information before you decide whether to purchase any of our rights. We will provide in a prospectus supplement the following terms of the rights being issued:

Each right will entitle the holder of rights to purchase for cash the principal amount of shares of common stock, preferred stock or other securities at the exercise price provided in the applicable prospectus supplement. Rights may be exercised at any time up to the close of business on the expiration date for the rights provided in the applicable prospectus supplement.

Holders may exercise rights as described in the applicable prospectus supplement. Upon receipt of payment and the rights certificate properly completed and duly executed at the corporate trust office of the rights agent or any other office indicated in the prospectus supplement, we will, as soon as practicable, forward the shares of common stock, preferred stock or other securities, as applicable, purchasable upon exercise of the rights. If less than all of the rights issued in any rights offering are exercised, we may offer any unsubscribed securities directly to persons other than stockholders, to or through agents, underwriters or dealers or through a combination of such methods, including pursuant to standby arrangements, as described in the applicable prospectus supplement.

Rights Agent

The rights agent for any rights we offer will be set forth in the applicable prospectus supplement.

DESCRIPTION OF UNITS

The following description, together with the additional information that we include in any applicable prospectus supplement and in any free writing prospectus that we may authorize to be distributed to you, summarizes the material terms and provisions of the units that we may offer under this prospectus. While the terms we have summarized below will apply generally to any units that we may offer under this prospectus, we will describe the particular terms of any series of units in more detail in the applicable prospectus supplement. The terms of any units offered under a prospectus supplement may differ from the terms described below.

We will incorporate by reference from reports that we file with the SEC, the form of unit agreement that describes the terms of the series of units we are offering, and any supplemental agreements, before the issuance of the related series of units. The following summaries of material terms and provisions of the units are subject to, and qualified in their entirety by reference to, all the provisions of the unit agreement and any supplemental agreements applicable to a particular series of units. We urge you to read the applicable prospectus supplements related to the particular series of units that we may offer under this prospectus, as well as any related free writing prospectuses and the complete unit agreement and any supplemental agreements that contain the terms of the units.

General

We may issue units consisting of common stock, preferred stock, one or more debt securities, warrants or rights for the purchase of common stock, preferred stock and/or debt securities in one or more series in any combination. Each unit will be issued so that the holder of the unit is also the holder of each security included in the unit. Thus, the holder of a unit will have the rights and obligations of a holder of each security included in the unit. The unit agreement under which a unit is issued may provide that the securities included in the unit may not be held or transferred separately, at any time or at any time before a specified date.

We will describe in the applicable prospectus supplement the terms of the series of units being offered, including:

The provisions described in this section, as well as those set forth in any prospectus supplement or as described under “Description of Common Stock,” “Description of Preferred Stock,” “Description of Debt Securities,” “Description of Warrants” and “Description of Rights” will apply to each unit, as applicable, and to any common stock, preferred stock, debt security, warrant or right included in each unit, as applicable.

Unit Agent

The name and address of the unit agent, if any, for any units we offer will be set forth in the applicable prospectus supplement.

Issuance in Series

We may issue units in such amounts and in such numerous distinct series as we determine.

Enforceability of Rights by Holders of Units

Each unit agent will act solely as our agent under the applicable unit agreement and will not assume any obligation or relationship of agency or trust with any holder of any unit. A single bank or trust company may act as unit agent for more than one series of units. A unit agent will have no duty or responsibility in case of any default by us under the applicable unit agreement or unit, including any duty or responsibility to initiate any proceedings at law or otherwise, or to make any demand upon us. Any holder of a unit may, without the consent of the related unit agent or the holder of any other unit, enforce by appropriate legal action its rights as holder under any security included in the unit.

LEGAL OWNERSHIP OF SECURITIES

We can issue securities in registered form or in the form of one or more global securities. We describe global securities in greater detail below. We refer to those persons who have securities registered in their own names on the books that we or any applicable trustee, depositary or warrant agent maintain for this purpose as the “holders” of those securities. These persons are the legal holders of the securities. We refer to those persons who, indirectly through others, own beneficial interests in securities that are not registered in their own names, as “indirect holders” of those securities. As we discuss below, indirect holders are not legal holders, and investors in securities issued in book-entry form or in street name will be indirect holders.

Book-Entry Holders

We may issue securities in book-entry form only, as we will specify in the applicable prospectus supplement. This means securities may be represented by one or more global securities registered in the name of a financial institution that holds them as depositary on behalf of other financial institutions that participate in the depositary’s book-entry system. These participating institutions, which are referred to as participants, in turn, hold beneficial interests in the securities on behalf of themselves or their customers.

Only the person in whose name a security is registered is recognized as the holder of that security. Securities issued in global form will be registered in the name of the depositary or its participants. Consequently, for securities issued in global form, we will recognize only the depositary as the holder of the securities, and we will make all payments on the securities to the depositary. The depositary passes along the payments it receives to its participants, which in turn pass the payments along to their customers who are the beneficial owners. The depositary and its participants do so under agreements they have made with one another or with their customers; they are not obligated to do so under the terms of the securities.

As a result, investors in a global security will not own securities directly. Instead, they will own beneficial interests in a global security, through a bank, broker or other financial institution that participates in the depositary’s book-entry system or holds an interest through a participant. As long as the securities are tradedissued in global form, investors will be indirect holders, and not legal holders, of the securities.

Street Name Holders

We may terminate a global security or issue securities in non-global form. In these cases, investors may choose to hold their securities in their own names or in private transactions.“street name.” Securities held by an investor in street name would be registered in the name of a bank, broker or other financial institution that the investor chooses, and the investor would hold only a beneficial interest in those securities through an account he or she maintains at that institution.

For securities held in street name, we or any applicable trustee or depositary will recognize only the intermediary banks, brokers and other financial institutions in whose names the securities are registered as the holders of those securities, and we or any applicable trustee or depositary will make all payments on those securities to them. These salesinstitutions pass along the payments they receive to their customers who are the beneficial owners, but only because they agree to do so in their customer agreements or because they are legally required to do so. Investors who hold securities in street name will be indirect holders, not holders, of those securities.

Legal Holders

Our obligations, as well as the obligations of any applicable trustee and of any third parties employed by us or a trustee, run only to the legal holders of the securities. We do not have obligations to investors who hold beneficial interests in global securities, in street name or by any other indirect means. This will be the case whether an investor chooses to be an indirect holder of a security or has no choice because we are issuing the securities only in global form.

For example, once we make a payment or give a notice to the legal holder, we have no further responsibility for the payment or notice even if that legal holder is required, under agreements with its participants or customers or by law, to pass it along to the indirect holders but does not do so. Similarly, we may be at fixedwant to obtain the approval of the legal holders to amend an indenture, to relieve us of the consequences of a default or negotiated prices. of our obligation to comply with a particular provision of the indenture or for other purposes. In such an event, we would seek approval only from the legal holders, and not the indirect holders, of the securities. Whether and how the legal holders contact the indirect holders is up to the legal holders.

Special Considerations for Indirect Holders

If you hold securities through a bank, broker or other financial institution, either in book-entry form or in street name, you should check with your own institution to find out:

Global Securities

A selling stockholder may use anyglobal security is a security that represents one or moreany other number of individual securities held by a depositary. Generally, all securities represented by the same global securities will have the same terms.

Each security issued in book-entry form will be represented by a global security that we issue to, deposit with and register in the name of a financial institution or its nominee that we select. The financial institution that we select for this purpose is called the depositary. Unless we specify otherwise in the applicable prospectus supplement, DTC will be the depositary for all securities issued in book-entry form.

A global security may not be transferred to or registered in the name of anyone other than the depositary, its nominee or a successor depositary, unless special termination situations arise. We describe those situations below under “Special Situations When a Global Security Will Be Terminated.” As a result of these arrangements, the depositary, or its nominee, will be the sole registered owner and legal holder of all securities represented by a global security, and investors will be permitted to own only beneficial interests in a global security. Beneficial interests must be held by means of an account with a broker, bank or other financial institution that in turn has an account with the depositary or with another institution that does. Thus, an investor whose security is represented by a global security will not be a legal holder of the security, but only an indirect holder of a beneficial interest in the global security.

If the prospectus supplement for a particular security indicates that the security will be issued in global form only, then the security will be represented by a global security at all times unless and until the global security is terminated. If termination occurs, we may issue the securities through another book-entry clearing system or decide that the securities may no longer be held through any book-entry clearing system.

Special Considerations for Global Securities

The rights of an indirect holder relating to a global security will be governed by the account rules of the investor’s financial institution and of the depositary, as well as general laws relating to securities transfers. We do not recognize an indirect holder as a holder of securities and instead deal only with the depositary that holds the global security.

If securities are issued only in the form of a global security, an investor should be aware of the following:

Special Situations When a Global Security Will Be Terminated

In a few special situations described below, the global security will terminate and interests in it will be exchanged for physical certificates representing those interests. After that exchange, the choice of whether to hold securities directly or in street name will be up to the investor. Investors must consult their own banks, brokers or other financial institutions to find out how to have their interests in securities transferred to their own name, so that they will be direct holders. We have described the rights of holders and street name investors above.

Unless we provide otherwise in the applicable prospectus supplement, the global security will terminate when the following methods when selling securities:special situations occur:

The applicable prospectus supplement may also list additional situations for terminating a global security that would apply only to the particular series of securities covered by the applicable prospectus supplement. When a global security terminates, the depositary, and not we or any applicable trustee, is responsible for deciding the names of the institutions that will be the initial direct holders.

PLAN OF DISTRIBUTION

We may sell our securities from time to time:

We may directly solicit offers to purchase securities, or agents may be designated to solicit such offers. In any applicable prospectus supplement relating to such offering, we will name any agent that could be viewed as an underwriter under the Securities Act and describe any commissions that we must pay to any such agent. Any such agent will be acting on a best efforts basis for the period of its appointment or, if indicated in the applicable prospectus supplement, on a firm commitment basis. This prospectus may be used in connection with any offering of our securities through any of these methods or other methods described in the applicable prospectus supplement.

The distribution of our securities may be effected from time to time in one or more transactions:

The selling stockholders may also sellEach prospectus supplement will describe the method of distribution of the securities under Rule 144 orand any other exemption from registration under the Securities Act of 1933, as amended (the “Securities Act”), if available, rather than under this prospectus.applicable restrictions.

Broker-dealers engaged by the selling stockholdersA prospectus supplement or supplements (and any related free writing prospectus that we may arrange for other brokers-dealers to participate in sales. Broker-dealers may receive commissions or discounts from the selling stockholders (or, if any broker-dealer acts as agent for the purchaser of securities, from the purchaser) in amountsauthorize to be negotiated, but, except asprovided to you with respect to a particular offering) will describe the terms of the offering of our securities, including the following:

If any underwriters or agents are used in the sale of our securities in respect of which this prospectus is delivered, we will enter into an underwriting agreement, sales agreement or other agreement with them at the time of sale to them, and we will set forth in athe applicable prospectus supplement relating to this Prospectus, insuch offering the casenames of an agency transaction not in excessthe underwriters or agents and the terms of a customary brokerage commission in compliancethe related agreement with FINRA Rule 2121; and in the case of a principal transaction a markup or markdown in compliance with FINRA Rule 2121.them.

In connection with the offering of securities, we may grant to the underwriters an option to purchase additional securities with an additional underwriting commission, as may be set forth in the applicable prospectus supplement.

If a dealer is used in the sale of the securities or interests therein,in respect of which the selling stockholders may enter into hedging transactions with broker-dealers or other financial institutions, which may in turn engage in short sales of the securities in the course of hedging the positions they assume. The selling stockholders may alsoprospectus is delivered, we will sell securities short and deliver thesesuch securities to close out their short positions, or loan or pledge the securities to broker-dealers that in turn may sell these securities.dealer, as principal. The selling stockholders may also enter into option or other transactions with broker-dealers or other financial institutions or create one or more derivative securities which require the delivery to such broker-dealer or other financial institution of securities offered by this prospectus, which securities such broker-dealer or other financial institution may resell pursuant to this prospectus (as supplemented or amended to reflect such transaction).

The selling stockholders and any broker-dealers or agents that are involved in selling the securitiesdealer, who may be deemed to be “underwriters” within the meaning ofan “underwriter” as that term is defined in the Securities Act, in connection withmay then resell such sales. In such event, any commissions receivedsecurities to the public at varying prices to be determined by such broker-dealers ordealer at the time of resale.

We may provide agents and any profit on the resale of the securities purchased by them may be deemed to be underwriting commissions or discounts under the Securities Act. Each selling stockholder has informed the Company that it does not have any written or oral agreement or understanding, directly or indirectly,underwriters with any person to distribute the securities.

The Company is required to pay certain fees and expenses incurred by the Company incident to the registration of the securities. The Company has agreed to indemnify the selling stockholdersindemnification against certain losses, claims, damages andcivil liabilities, including liabilities under the Securities Act.Act, or contribution with respect to payments that the agents or underwriters may make with respect to those liabilities.

If so indicated in the applicable prospectus supplement, we will authorize underwriters or other persons acting as agents to solicit offers by certain institutions to purchase securities from us pursuant to delayed delivery contracts providing for payment and delivery on the date stated in the applicable prospectus supplement. Each contract will be for an amount not less than, and the aggregate amount of securities sold pursuant to such contracts shall not be less nor more than, the respective amounts stated in the applicable prospectus supplement. Institutions with whom the contracts, when authorized, may be made include commercial and savings banks, insurance companies, pension funds, investment companies, educational and charitable institutions and other institutions. Delayed delivery contracts will not be subject to any conditions except that:

Offered securities may also be offered and sold, if so indicated in the applicable prospectus supplement, in connection with a remarketing upon their purchase, in accordance with a redemption or repayment pursuant to their terms, or otherwise, by one or more remarketing firms, acting as principals for their own accounts or as agents for us. Any remarketing firm will be identified and the terms of its agreement, if any, with us and its compensation will be described in the applicable prospectus supplement. Remarketing firms may be deemed to be underwriters in connection with their remarketing of offered securities.

Certain agents, underwriters and dealers, and their associates and affiliates, may be customers of, have borrowing relationships with, engage in other transactions with, or perform services, including investment banking services, for us or one or more of our respective affiliates in the ordinary course of business for which they receive compensation.

In order to facilitate the offering of our securities, any underwriters may engage in transactions that stabilize, maintain or otherwise affect the price of the securities or any other securities the prices of which may be used to determine payments on such securities. Specifically, any underwriters may overallot in connection with the offering, creating a short position for their own accounts. In addition, to cover overallotments or to stabilize the price of the securities or of any such other securities, the underwriters may bid for, and purchase, the securities or any such other securities in the open market. Finally, in any offering of our securities through a syndicate of underwriters, the underwriting syndicate may reclaim selling concessions allowed to an underwriter or a dealer for distributing the securities in the offering if the syndicate repurchases previously distributed securities in transactions to cover syndicate short positions, in stabilization transactions or otherwise. Any of these activities may stabilize or maintain the market price of the securities above independent market levels. Any such underwriters are not required to engage in these activities and may end any of these activities at any time.

We agreed to keep this prospectus effective untilmay engage in at the earlier of (i) the date on which the securities may be resold by the selling stockholders without registration and without regard to any volume or manner-of-sale limitations by reason ofmarket offerings into an existing trading market in accordance with Rule 144, without the requirement for the Company to be in compliance with the current public information under Rule 144415(a)(4) under the Securities ActAct. In addition, we may enter into derivative transactions with third parties, or any other rule of similar effect or (ii) all of thesell securities have been sold pursuant tonot covered by this prospectus to third parties in privately negotiated transactions. If the applicable prospectus supplement so indicates, in connection with those derivatives, the third parties may sell securities covered by this prospectus and the applicable prospectus supplement, including in short sale transactions. If so, the third party may use securities pledged by us or Rule 144 under the Securities Actborrowed from us or others to settle those sales or to close out any other rulerelated open borrowings of similar effect.stock, and may use securities received in settlement of those derivatives to close out any related open borrowings of stock. The resale securitiesthird party in such sale transactions will be sold only through registered or licensed brokers or dealersan underwriter and, if required under applicable state securities laws. In addition,not identified in certain states, the resale securities covered hereby may notthis prospectus, will be sold unless they have been registered or qualified for salenamed in the applicable stateprospectus supplement (or a post-effective amendment). In addition, we may otherwise loan or pledge securities to a financial institution or other third party that in turn may sell the securities short using this prospectus and an exemption from the registrationapplicable prospectus supplement. Such financial institution or qualification requirement is available and is complied with.other third party may transfer its economic short position to investors in our securities or in connection with a concurrent offering of other securities.

Under applicable rules and regulations under the Exchange Act, any person engaged in the distribution of the resale securities may not simultaneously engage in market making activities with respect to the Common Stock for the applicable restricted period, as defined in Regulation M, prior to the commencement of the distribution. In addition, the selling stockholders will be subject to applicable provisionsRule 15c6-1 of the Exchange Act, andtrades in the rules and regulations thereunder, including Regulation M, which may limit the timing of purchases and salessecondary market generally are required to settle in two business days (or such shorter settlement cycle that is in effect under Rule 15c6-1 of the Common Stock byExchange Act from time to time), unless the selling stockholders orparties to any other person. We will make copies of thissuch trade expressly agree otherwise. The applicable prospectus availablesupplement may provide that the original issue date for your securities may be more than two scheduled business days after the trade date for your securities. Accordingly, in such a case, if you wish to the selling stockholders and have informed them of the need to deliver a copy of this prospectus to each purchaser at ortrade securities on any date prior to the timesecond business day before the original issue date for your securities, you will be required, by virtue of the sale (including by compliance with Rule 172 underfact that your securities initially are expected to settle in more than two scheduled business days after the Securities Act).

LEGAL MATTERStrade date for your securities, to make alternative settlement arrangements to prevent a failed settlement.

The validityspecific terms of any lock-up provisions in respect of any given offering will be described in the sharesapplicable prospectus supplement. The anticipated date of Common Stockdelivery of offered securities will be set forth in thisthe applicable prospectus has been passed upon for us by supplement relating to each offer.

LEGAL MATTERS

Mintz, Levin, Cohn, Ferris, Glovsky and Popeo, P.C., New York, New York.York, will pass upon the validity of the securities offered hereby unless otherwise indicated in the applicable prospectus supplement. Any underwriters will also be advised about the validity of the securities and other legal matters by their own counsel, which will be named in the applicable prospectus supplement.

EXPERTS

OurThe consolidated financial statements appearingof SELLAS Life Sciences Group, Inc. (the “Company”) incorporated in ourthe Prospectus Supplement by reference from the Annual Report on Form 10-K of the Company for the year ended December 31, 2019,2023, have been audited by Moss Adams LLP, an independent registered public accounting firm, as stated in their report which is incorporated herein by reference. Such consolidated financial statements have been so incorporated in reliance upon the report of such firm (which report expresses an unqualified opinion and includes an explanatory paragraph regarding the Company’srelated to a going concern uncertainty)emphasis), which is incorporated herein by reference. Such consolidated financial statements are incorporated by reference in reliance upon the report of such firm given upon their authority as experts in accounting and auditing.

WHERE YOU CAN FIND ADDITIONALMORE INFORMATION

We are subject to the information requirements of the Exchange Acta reporting company and we therefore file periodicannual, quarterly and current reports, proxy statements and other information with the SEC. This prospectus is part of the registration statement on Form S-3 we filed with the SEC relatingunder the Securities Act and does not contain all the information set forth or incorporated by reference in the registration statement. Whenever a reference is made in this prospectus to any of our business, financial statementscontracts, agreements or other documents, the reference may not be complete and you should refer to the exhibits that are a part of the registration statement or the exhibits to the reports or other matters.  Thedocuments incorporated by reference into this prospectus for a copy of such contract, agreement or other document. You may read and copy the registration statement, as well as our reports, proxy statements and other information, we file may be inspected and copied at prescribed rates at the SEC'sSEC’s Public Reference Room located at 100 F Street, N.E., Washington, D.C. 20549. You may obtainPlease call the SEC at 1-800-SEC-0330 for more information onabout the operation of the SEC's Public Reference Room by calling the SEC at 1-800-SEC-0330.public reference room. The SEC also maintains a websitean Internet site that contains reports, proxy and information statements and other information regarding issuers like us that file electronically with the SEC.SEC, including SELLAS Life Sciences Group, Inc. The address of the SEC'sSEC’s Internet site can be found at www.sec.gov. We maintain a website is http://www.sec.gov.

This prospectus constitutes part of a registration statement filed under the Securities Act with respect to the shares of Common Stock covered hereby.  As permitted by the SEC's rules, this prospectus omits some of the information, exhibits and undertakings included in the registration statement.  You may read and copy the information omitted from this prospectus but contained in the registration statement, as well as the periodic reports and other information we file with the SEC, at the public reference room and website of the SEC referred to above.  You may also access our filings with the SECwww.sellaslife.com. Information found on, our website, which is located at http://www.sellaslifesciences.com/.  The information contained onor accessible through, our website is not a part of, and is not incorporated into, this prospectus, or any prospectus supplement, and you should not consider it part of this prospectus.prospectus or any prospectus supplement.

Statements contained in this prospectus as to the contents of any contract or other document are not necessarily complete, and in each instance we refer you to the copy of the contract or other document filed or incorporated by reference as an exhibit to the registration statement or as an exhibit to our Exchange Act filings, each such statement being qualified in all respects by such reference.

INFORMATION INCORPORATEDINCORPORATION BY REFERENCE

The SEC allows us to incorporate by reference the information we file with it, which means that we can disclose important information to you by referring you to another document that we have filed separately with the SEC. You should read the information incorporated by reference because it is an important part of this prospectus.prospectus and the applicable prospectus supplement. Information in this prospectus supersedes information incorporated by reference that we filed with the SEC prior to the date of this prospectus, while information that we file later with the SEC will automatically update and supersede the information in this prospectus.prospectus and the applicable prospectus supplement. We incorporate by reference into this prospectus and the registration statement of which this prospectus is a part the information or documents listed below that we have filed with the SEC (Commission File No. 001-33958):

We also incorporate by reference any future filings (other than the portions of current reports furnished under Item 2.02 or Item 7.01 of Form 8-K and exhibits filed on such form that are related to such items unless such Form 8-K expressly provides to the contrary) made with the SEC pursuant to Sections 13(a), 13(c), 14 or 15(d) of the Exchange Act, including those made after the date of the initial filing of the registration statement of which this prospectus is a part and prior to effectiveness of such registration statement, until we file a post-effective amendment that indicates the termination of the offering of the Common Stockcommon stock made by this prospectus and will become a part of this prospectus from the date that such documents are filed with the SEC. Information in such future filings updates and supplements the information provided in this prospectus.prospectus and any applicable prospectus supplement. Any statements in any such future filings will automatically be deemed to modify and supersede any information in any document we previously filed with the SEC that is incorporated or deemed to be incorporated herein by reference to the extent that statements in the later filed document modify or replace such earlier statements.

We will furnish without charge to each person, including any beneficial owner, to whom a prospectus and applicable prospectus supplement is delivered, upon written or oral request, a copy of any or all of the documents incorporated by reference into this prospectus but not delivered with the prospectus and applicable prospectus supplement, including exhibits that are specifically incorporated by reference into such documents. You should direct any requests for documents to SELLAS Life Sciences Group, Inc., Attention: Corporate Secretary, 7 Times Square, Suite 2503, New York, New YorkNY 10036. Our phone number is (917) 438-4353.(646) 200-5278.

You should rely only on information contained in, or incorporated by reference into, this prospectus and any prospectus supplement. We have not authorized anyone to provide you with information different from that contained in this prospectus or incorporated by reference into this prospectus. We are not making offers to sell the securities in any jurisdiction in which such an offer or solicitation is not authorized or in which the person making such offer or solicitation is not qualified to do so or to anyone to whom it is unlawful to make such offer or solicitation.

PART II

- INFORMATION NOT REQUIRED IN THE PROSPECTUS

Item 14.Other Expenses of Issuance and Distribution.Distribution

The following table sets forth all costsan estimate of the fees and expenses payable by the Registrant,us, other than underwriting discounts and commissions, in connection with the sale and distribution of the securities being registered under this registration statement.hereby. All the amounts shown are estimates, except for the Securities and Exchange Commission, or SEC registration fee.

(1)       These fees are calculated based on the securities offered and the number of issuances and accordingly cannot be estimated at this time.

Item 15.Indemnification of Directors and Officers.Officers

As permitted by Section 102 of the Delaware General Corporation Law,DGCL, we have adopted provisions in our amended and restated certificate of incorporation and amended and restated bylaws, each as amended, which limit or eliminate the personal liability of our directors for a breach of their fiduciary duty of care as a director. The duty of care generally requires that, when acting on behalf of the corporation, directors exercise an informed business judgment based on all material information reasonably available to them. Consequently, a director will not be personally liable to us or our stockholders for monetary damages for breach of fiduciary duty as a director, except for liability for:

These limitations of liability do not affect the availability of equitable remedies such as injunctive relief or rescission. Our amended and restated certificate of incorporation also authorizes us to indemnify our officers, directors and other agents to the fullest extent permitted under Delaware law.

As permitted by Section 145 of the Delaware General Corporation Law,DGCL, our amended and restated bylaws, as amended, provide that:

Our amended and restated certificate of incorporation and bylaws, each as amended, which are filed as Exhibits 3.1 and 3.3, provide for the indemnification provisions described above and elsewhere herein. We have entered into separate indemnification agreements with our directors and officers that may be broader than the specific indemnification provisions contained in the Delaware General Corporation Law.DGCL. These indemnification agreements generally require us, among other things, to indemnify our officers and directors against liabilities that may arise by reason of their status or service as directors or officers, other than liabilities arising from willful misconduct. These indemnification agreements also generally require us to advance any expenses incurred by the directors or officers as a result of any proceeding against them as to which they could be indemnified. In addition, we have purchased a policy of directors’ and officers’ liability insurance that insures our directors and officers against the cost of defense, settlement or payment of a judgment in some circumstances. These indemnification provisions and the indemnification agreements may be sufficiently broad to permit indemnification of our officers and directors for liabilities, including reimbursement of expenses incurred, arising under the Securities Act.

We have entered into indemnification agreements with our directors and executive officers, in addition to the indemnification provided for in our amended and restated certificate of incorporation and amended and restated bylaws, and intend to enter into indemnification agreements with any new directors and executive officers in the future.

We have purchased and currently intend to maintain insurance on behalf of each and every person who is or was a director or officer of our company against any loss arising from any claim asserted against him or her and incurred by him or her in any such capacity, subject to certain exclusions.

Item 16.Exhibits.

See Exhibit IndexThe following the signature page toexhibits are filed as part of this Registration Statement.Statement on Form S-3 or are incorporated herein by reference.

* Filed herewith.

** To be filed by amendment or as an exhibit to a current report on Form 8-K and incorporated by reference, if applicable.

*** To be filed separately under electronic form type 305B2 under Rule 305(b)(2) of the Trust Indenture Act, if applicable.

Item 17.  Undertakings.Undertakings

The undersigned registrant hereby undertakes:

(1) To file, during any period in which offers or sales are being made, a post-effective amendment to this registration statement:

(i) To include any prospectus required by Section 10(a)(3) of the Securities Act of 1933;

(ii) To reflect in the prospectus any facts or events arising after the effective date of the registration statement (or the most recent post-effective amendment thereof) which, individually or in the aggregate, represent a fundamental change in the information set forth in the registration statement. Notwithstanding the foregoing, any increase or decrease in volume of securities offered (if the total dollar value of securities offered would not exceed that which was registered) and any deviation from the low or high end of the estimated maximum offering range may be reflected in the form of prospectus filed with the SEC pursuant to Rule 424(b) if, in the aggregate, the changes in volume and price represent no more than a 20% change in the maximum aggregate offering price set forth in the “Calculation of Registration Fee” table in the effective registration statement; and

(iii) To include any material information with respect to the plan of distribution not previously disclosed in the registration statement or any material change to such information in the registration statement;

provided however, that paragraphs (a)(1)(i), (1)(ii), and (1)(iii) of this section do not apply if the information required to be included in a post-effective amendment by those paragraphs is contained in reports filed with or furnished to the CommissionSEC by the registrant pursuant to sectionSection 13 or sectionSection 15(d) of the Securities Exchange Act of 1934 (15 U.S.C. 78m or 78o(d)) that are incorporated by reference in the registration statement, or is contained in a form of prospectus filed pursuant to Rule 424(b) that is part of the registration statement.

(2) That, for the purpose of determining any liability under the Securities Act of 1933, each such post-effective amendment shall be deemed to be a new registration statement relating to the securities offered therein, and the offering of such securities at that time shall be deemed to be the initial bona fide offering thereof.

The(3) To remove from registration by means of a post-effective amendment any of the securities being registered which remain unsold at the termination of the offering.

(4) That, for the purpose of determining liability under the Securities Act of 1933 to any purchaser:

(i) Each prospectus filed by the registrant pursuant to Rule 424(b)(3) shall be deemed to be part of the registration statement as of the date the filed prospectus was deemed part of and included in the registration statement; and

(ii) Each prospectus required to be filed pursuant to Rule 424(b)(2), (b)(5), or (b)(7) as part of a registration statement in reliance on Rule 430B relating to an offering made pursuant to Rule 415(a)(1)(i), (vii), or (x) for the purpose of providing the information required by Section 10(a) of the Securities Act of 1933 shall be deemed to be part of and included in the registration statement as of the earlier of the date such form of prospectus is first used after effectiveness or the date of the first contract of sale of securities in the offering described in the prospectus. As provided in Rule 430B, for liability purposes of the issuer and any person that is at that date an underwriter, such date shall be deemed to be a new effective date of the registration statement relating to the securities in the registration statement to which that prospectus relates, and the offering of such securities at that time shall be deemed to be the initial bona fide offering thereof. Provided, however, that no statement made in a registration statement or prospectus that is part of the registration statement or made in a document incorporated or deemed incorporated by reference into the registration statement or prospectus that is part of the registration statement will, as to a purchaser with a time of contract of sale prior to such effective date, supersede or modify any statement that was made in the registration statement or prospectus that was part of the registration statement or made in any such document immediately prior to such effective date.

(5) That, for the purpose of determining liability of the registrant under the Securities Act of 1933 to any purchaser in the initial distribution of the securities, the undersigned registrant undertakes that in a primary offering of securities of the undersigned registrant pursuant to this registration statement, regardless of the underwriting method used to sell the securities to the purchaser, if the securities are offered or sold to such purchaser by means of any of the following communications, the undersigned registrant will be a seller to the purchaser and will be considered to offer or sell such securities to such purchaser: (i) any preliminary prospectus or prospectus of the undersigned registrant relating to the offering required to be filed pursuant to Rule 424; (ii) any free writing prospectus relating to the offering prepared by or on behalf of the undersigned registrant or used or referred to by the undersigned registrant; (iii) the portion of any other free writing prospectus relating to the offering containing material information about the undersigned registrant or its securities provided by or on behalf of the undersigned registrant; and (iv) any other communication that is an offer in the offering made by the undersigned registrant to the purchaser.

The undersigned registrant hereby undertakes that,(6) That, for purposes of determining any liability under the Securities Act of 1933, each filing of the registrant’s annual report pursuant to sectionSection 13(a) or section 15(d) of the Securities Exchange Act of 1934 (and, where applicable, each filing of an employee benefit plan’s annual report pursuant to sectionSection 15(d) of the Securities Exchange Act of 1934) that is incorporated by reference in the registration statement shall be deemed to be a new registration statement relating to the securities offered therein, and the offering of such securities at that time shall be deemed to be the initial bona fide offering thereof.

(7) To file an application for the purpose of determining the eligibility of the trustee to act under subsection (a) of Section 310 of the Trust Indenture Act in accordance with the rules and regulations prescribed by the SEC under Section 305(b)(2) of the Trust Indenture Act.

Insofar as indemnification for liabilities arising under the Securities Act of 1933 may be permitted to directors, officers and controlling persons of the registrant pursuant to the foregoing provisions, or otherwise, the registrant has been advised that in the opinion of the Securities and Exchange CommissionSEC such indemnification is against public policy as expressed in the Securities Act of 1933 and is, therefore, unenforceable. In the event that a claim for indemnification against such liabilities (other than the payment by the registrant of expenses incurred or paid by a director, officer or controlling person of the registrant in the successful defense of any action, suit or proceeding) is asserted by such director, officer or controlling person in connection with the securities being registered, the registrant will, unless in the opinion of its counsel the matter has been settled by controlling precedent, submit to a court of appropriate jurisdiction the question whether such indemnification by it is against public policy as expressed in the Securities Act of 1933 and will be governed by the final adjudication of such issue.

The undersigned registrant hereby undertakes that:

SIGNATURES

SIGNATURES

Pursuant to the requirements of the Securities Act of 1933, the registrant certifies that it has reasonable grounds to believe that it meets all of the requirements for filing on Form S-3 and has duly caused this registration statement to be signed on its behalf by the undersigned, thereunto duly authorized, in the cityCity of New York, New York, on this August 14, 2020.March 28, 2024.

POWER OF ATTORNEY

We, the undersigned officers and directors of SELLAS Life Sciences Group, Inc.,KNOW ALL PERSONS BY THESE PRESENTS, that each person whose signature appears below hereby severally constituteconstitutes and appointappoints Angelos M. Stergiou and John T. Burns, and each of them singly, as oursuch person’s true and lawful attorneys,attorneys-in-fact and agents, with full power to them,of substitution and to each of them singly, to signresubstitution, for ussuch person and in our namessuch person’s name, place and stead, in the capacities indicated below, the registration statement on Form S-3 filed herewith, and any and all pre-effectivecapacities, to sign any and all amendments (including, without limitation, post-effective amendmentsamendments) to saidthis registration statement and(or any registration statement filedfor the same offering that is to be effective upon filing pursuant to Rule 462(b) under the Securities Act of 1933, as amended, in connection with the registration under the Securities Act of 1933, as amended, of equity securities of the Company,1933), and to file or cause to be filed the same, with all exhibits thereto, and otherall documents in connection therewith, with the Securities and Exchange Commission, granting unto each said attorneys,attorney-in-fact and each of them,agent, full power and authority to do and perform each and every act and thing requisite and necessary to be done in connection therewith,and about the premises, as fully to all intents and purposes as each of ussuch person might or could do in person, and hereby ratifying and confirming all that any said attorneys,attorney-in-fact and each of them,agent, or theirany substitute or substitutes shallof any of them, may lawfully do or cause to be done by virtue of this Power of Attorney.hereof.

Pursuant to the requirements of the Securities Act of 1933, this Registration Statement on Form S-3registration statement has been signed below by the following persons in the capacities and on the dates indicated.

EXHIBIT LIST