6-K

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 6-K

REPORT OF FOREIGN PRIVATE ISSUER

PURSUANT TO RULE 13a-16 OR 15d-16

UNDER THE SECURITIES EXCHANGE ACT OF 1934

Date as October 13, 2025

Commission File Number 001-35428

IMMUTEP LIMITED

(ExactName as Specified in its Charter)

N/A

(Translation ofRegistrant’s Name)

Level 32, Australia Square

264 George Street, Sydney

NSW 2000, Australia

(Address of principal executive office)

Indicate by check mark whether the registrant files or will file annual reports under cover of Form 20-F or Form 40-F.

Form 20-F ☒   Form 40-F ☐

Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(1): ☐

Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(7): ☐

Indicate by check mark whether by furnishing the information contained in this Form, the registrant is also thereby furnishing the information to the Commission pursuant to Rule 12g3-2(b) under the Securities Exchange Act of 1934.

Yes ☐   No ☒

If “Yes” is marked, indicated below the file number assigned to the registrant in connection with Rule 12g3-2(b): Not applicable.

EXHIBIT INDEX

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, thereunto duly authorized.

Date: October 13, 2025

EX-99.1

Exhibit 99.1

Immutep Announces Successful Completion of FDA Project Optimus Requirements

SYDNEY, AUSTRALIA – October 13, 2025 – Immutep Limited (ASX: IMM; NASDAQ: IMMP) (“Immutep” or “the Company”), a late-stage immunotherapy company targeting cancer and autoimmune diseases, today announces that positive and straightforward feedback has been received from the US Food and Drug Administration (“FDA”) regarding the successful completion of Project Optimus requirements and agreement on 30mg as the optimal biological dose for eftilagimod alfa (efti).

Immutep’s Chief Development Officer, Christian Mueller, said, “We are very thankful for the FDA’s positive feedback and productive discussions over the past few years. The alignment on efti’s optimal biologic dose has strategic relevance to our efti oncology programs and is a major de-risking event and building block towards future BLA filings. We are excited to successfully conclude this chapter of efti’s clinical development and are intently focused on bringing this novel immunotherapy to market to help address the needs of cancer patients worldwide.”

The agreement with the FDA on efti’s optimal biological dosing carries strategic importance in the ongoing and future clinical development of this first-in-class immunotherapy, including the global TACTI-004 (KEYNOTE-F91) Phase III trial evaluating efti in combination with MSD’s (Merck & Co., Inc., Rahway, NJ, USA) anti-PD-1 therapy KEYTRUDA^®^ (pembrolizumab), and chemotherapy as first-line treatment for advanced or metastatic non-small cell lung cancer (1L NSCLC), regardless of PD-L1 expression. With the conclusion of Project Optimus, this registrational study is now in process of opening sites in the United States.

About Eftilagimod Alfa (Efti)

Efti is a novel immunotherapy that directly activates antigen-presenting cells or APCs (e.g. dendritic cells, monocytes) via the MHC Class II pathway to fight cancer. As an MHC Class II agonist, its activation of APCs engages the adaptive and innate immune system to initiate a broad anti-cancer immune response. This includes priming and activating cytotoxic T cells as well as generating important co-stimulatory signals & cytokines that further boost the immune system’s ability to combat cancer.

Efti is under evaluation for a variety of solid tumours including non-small cell lung cancer (NSCLC) in a pivotal Phase III trial called TACTI-004 (KEYNOTE-F91), as well as head and neck squamous cell carcinoma (HNSCC), soft tissue sarcoma, and breast cancer. Its favourable safety profile enables various combinations like with anti-PD-[L]1 immunotherapy, radiotherapy, and/or chemotherapy. Efti has received Fast Track designation in first line HNSCC and in first line NSCLC from the United States Food and Drug Administration (FDA).

About Immutep

Immutep is a late-stage biotechnology company developing novel immunotherapies for cancer and autoimmune disease*.* The Company is a pioneer in the understanding and advancement of therapeutics related to Lymphocyte Activation Gene-3 **** (LAG-3), and its diversified product portfolio harnesses LAG-3’s ability to stimulate or suppress the immune response. Immutep is dedicated to leveraging its expertise to bring innovative treatment options to patients in need and to maximise value for shareholders. For more information, please visit www.immutep.com.

KEYTRUDA^®^ is a registeredtrademark of Merck Sharp & Dohme LLC, a subsidiary of Merck & Co., Inc., Rahway, NJ, USA.

Australian Investors/Media:

Eleanor Pearson, Sodali & Co.

+61 2 9066 4071; [email protected]

U.S. Investors/Media:

Chris Basta, VP, Investor Relations and Corporate Communications

+1 (631) 318 4000; [email protected]

This announcement was authorised for release by the Board of Immutep Limited.