1 UNITED STATES SECURITIES AND EXCHANGE COMMISSION WASHINGTON, D.C. 20549 FORM 8-K CURRENT REPORT FILED PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 DATE OF REPORT (DATE OF EARLIEST EVENT REPORTED): APRIL 23, 2001 ARONEX PHARMACEUTICALS, INC. (EXACT NAME OF REGISTRANT AS SPECIFIED IN ITS CHARTER) DELAWARE 0-20111 76-0196535 (STATE OR OTHER JURISDICTION OF (COMMISSION FILE NUMBER) (I.R.S. EMPLOYER IDENTIFICATION NO.) INCORPORATION OR ORGANIZATION) 8707 TECHNOLOGY FOREST PLACE THE WOODLANDS, TEXAS 77381-1191 (ADDRESS OF PRINCIPAL EXECUTIVE OFFICES AND ZIP CODE) (281) 367-1666 (REGISTRANT'S TELEPHONE NUMBER, INCLUDING AREA CODE) 2 ITEM 5. OTHER EVENTS On April 24, 2001, Aronex Pharmaceuticals, Inc. (the "Company") publicly disseminated a press release announcing that it had entered into an Agreement and Plan of Merger (the "Merger Agreement") dated as of April 23, 2001 with Antigenics Inc. ("Antigenics") and its wholly owned merger subsidiary, which provides for, and sets forth the terms and conditions of, the merger (the "Merger") of the merger subsidiary to be formed by Antigenics with and into the Company. As a result of the Merger, the Company will become a wholly owned subsidiary of Antigenics. The Merger Agreement and a form of Stockholder Voting Agreement executed by the Company's directors, officers and one of its largest stockholders is attached hereto as Exhibits 2.1 and 2.2, respectively. A copy of the Company's press release announcing the execution of the Merger Agreement is attached hereto as Exhibit 99.1. The press release is incorporated by reference into this Item 5 and the foregoing description of the Merger Agreement, Merger and press release is qualified in its entirety by reference to all of the attached exhibits. ITEM 7. EXHIBITS Exhibit 2.1+ -- Agreement and Plan of Merger dated as of April 23, 2001 among Aronex Pharmaceuticals, Inc., Antigenics Inc. and NASA Merger Corp. (incorporated by reference to Exhibit 2.1 to the Antigenics Inc. Current Report on Form 8-K as filed with the Securities and Exchange Commission on April 24, 2001 (the "Antigenics Form 8-K")). Exhibit 2.2+ -- Form of Stockholder Voting Agreement in connection with the Merger Agreement (incorporated by reference to Exhibit 2.2 to the Antigenics Form 8-K). Exhibit 99.1* -- The Company's Press Release dated April 24, 2001. + Incorporated herein by reference. * Filed herewith. -2- 3 SIGNATURES Pursuant to the requirements of the Securities Exchange Act of 1934, the Registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized. ARONEX PHARMACEUTICALS, INC. Date: April 24, 2001 By: /s/ Geoffrey F. Cox, Ph.D. --------------------------------- Geoffrey F. Cox, Ph.D. Chairman of the Board and Chief Executive Officer -3- 4 EXHIBIT INDEX EXHIBIT NUMBER DESCRIPTION - ------ ----------- 2.1+ -- Agreement and Plan of Merger dated as of April 23, 2001 among Aronex Pharmaceuticals, Inc., Antigenics Inc. and NASA Merger Corp. (incorporated by reference to Exhibit 2.1 to the Antigenics Inc. Current Report on Form 8-K as filed with the Securities and Exchange Commission on April 24, 2001 (the "Antigenics Form 8-K")). 2.2+ -- Form of Stockholder Voting Agreement in connection with the Merger Agreement (incorporated by reference to Exhibit 2.2 to the Antigenics Form 8-K). 99.1* -- The Company's Press Release dated April 24, 2001. + Incorporated herein by reference. * Filed herewith.