Eleison Pharmaceuticals (ELSN) S-1 IPO registration

Exhibit 23.1

CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

We hereby consent to the incorporation by reference in the Prospectus constituting a part of this Registration Statement of Eleison Pharmaceuticals Inc. (the “Company”) on Form S-1 of our report dated December 13, 2021, which includes an explanatory paragraph relating to the Company’s ability to continue as a going concern, relating to the financial statements of the Company as of and for the years ended December 31, 2020 and 2019. We also consent to the reference to us under the caption “Experts” in the Prospectus.

/s/ WithumSmith+Brown, PC

WithumSmith+Brown, PC

East Brunswick, New Jersey

January 24, 2022