索利吉克斯美国存托股招股说明书（2026年6月26日版）

Soligenix, Inc. Up to $2,500,000 COMMON STOCK Thisprospectus supplement(the“Prospectus Supplement”)amends and supplements theinformation in the prospectus supplement dated May 28, 2026 (the “May Prospectus”), which amendedand supplemented the prospectus supplement dated January 23, 2026 (the “January Prospectus”), filed as apart of our registration statement on Form S-3 (File No. 333-274265) (the “Registration Statement”) andthe prospectus dated December 15, 2023 contained therein (the “December Prospectus” and, together withthe January Prospectus and the May Prospectus, the “Prior Prospectus”), relating to the offering, issuanceand sale by us of our common stock, par value $0.001 per share, from time to time, that may be issued andsold under the At Market Issuance Sales Agreement (the “Sales Agreement”), dated January 23, 2026, byand between us and Rodman & Renshaw LLC, as sales agent. This Prospectus Supplement should be readin conjunction with the Prior Prospectus, and is qualified by reference thereto, except to the extent that the We are filing this Prospectus Supplement to amend the Prior Prospectus to update the maximumdollar amount of shares we are eligible to sell under the Sales Agreement and this Prospectus Supplement.Under the Prior Prospectus, we were eligible to offer and sell shares of common stock having an aggregateoffering price of up to $6,406,000. As of the date hereof, we have sold shares of common stock having anaggregate price of approximately $6,234,000 under the Prior Prospectus. This Prospectus Supplementrelates to the offer and sale of up to $2,500,000 of our common stock under the Sales Agreement, whichreplaces all amounts left unsold under the Prior Prospectus. As of the date hereof, the current aggregatemarket value of our outstanding common stock held by non-affiliates, or public float, is $30,702,784, Pursuant to General Instruction I.B.6, as of the date hereof, we currently may offer and sellcommon stock having an aggregate offering price of up to $2,500,000 under the Sales Agreement pursuantto this Prospectus Supplement, which amount is in addition to the common stock that we have sold to datein accordance with the Sales Agreement under the Prior Prospectus. If our public float increases such thatwe may sell additional amounts under the Sales Agreement and the Registration Statement of which thisProspectus Supplement and the Prior Prospectus are a part, we will file another prospectus supplementprior to making additional sales. Pursuant to General Instruction I.B.6 of Form S-3, in no event will we sellsecurities in a public primary offering with a value exceeding one-third of the aggregate market value of Our common stock is listed on the Nasdaq Capital Market under the symbol “SNGX.” On June25, 2026, the last reported sale price of our common stock on the Nasdaq Capital Market was $0.395 per We are a smaller reporting company as defined under Rule 405 of the Securities Act of 1933, asamended, and as such, we have elected to comply with certain reduced public company reportingrequirements. See the section entitled “Summary — Implications of Being a Smaller Reporting Company” Investing in our common stock involves a high degree of risk. Before buying any shares, youshould read the discussion of material risks of investing in our common stock in “Risk Factors”beginning on page S-7 of the Prior Prospectus, and in our most recent Annual Report on Form 10-Kand in the risks discussed under similar headings in the documents incorporated by reference in this Neither the Securities and Exchange Commission nor any state securities commission hasapproved or disapproved of these securities or passed upon the adequacy or accuracy of the Prior Rodman & Renshaw LLC The date of this Prospectus Supplement is June 26, 2026.