Immutep narrows efti strategy as TACTI-004 review finds manufacturing differences

Immutep Limited (ASX: IMM; NASDAQ: IMMP) on September 11, 2026 furnished Form 6-K, accession 0001193125-26-389402, with Exhibit 99.1 outlining a focused registration-directed development strategy for eftilagimod alfa, or efti. The company intends to concentrate on head and neck squamous cell carcinoma in patients with negative PD-L1 expression, defined as a Combined Positive Score below 1, and the neoadjuvant setting of soft tissue sarcoma.

The strategy follows manufacturing findings from the ongoing root cause analysis after TACTI-004 was discontinued. Immutep has identified subtle analytical and structural differences between efti made at 200 L and 2,000 L scale, including a difference in N-glycan structure. For IMMP investors, the announcement connects a narrower clinical focus with a return to manufacturing at the scale used in earlier studies, while leaving the cause of the unexpected TACTI-004 outcome unresolved.

A new 200 L manufacturing run has been contracted, and preparations for the next clinical trials have commenced. Immutep targets study starts in the second half of calendar 2027, subject to trial design, regulatory interactions, manufacturing timelines, partnering and resources. That makes the September 11 announcement a development strategy and manufacturing update, with both clinical and supply steps still ahead.

Two settings define the efti strategy

The proposed head and neck cancer focus is specifically HNSCC with PD-L1 CPS below 1. The second focus is neoadjuvant soft tissue sarcoma, meaning treatment before surgery. These are the two settings Immutep intends to prioritize for future registration-directed clinical development; the announcement does not establish final trial designs.

Immutep describes the focus as a staged risk-benefit approach consistent with prior FDA interactions. It cites Fast Track designation for HNSCC and Orphan Drug Designation for STS, granted in April 2026. Those designations provide context for the company's selection of indications, while the next studies remain subject to further regulatory interactions and final decisions.

Manufacturing findings leave the root cause open

The company considers the differences between the two manufacturing scales potentially relevant because TACTI-004 showed a markedly different immune activation profile from previous trials, alongside an unexpected clinical outcome. The N-glycan finding is an example of the subtle structural differences identified so far. Immutep has not presented the analysis as complete or established that manufacturing differences fully explain the trial result.

Based on the available root cause analysis data to date, Immutep believes clinical factors cannot explain the unexpected outcome. It lists a suboptimal protocol, substantial imbalance between trial arms and safety findings among the factors considered. It also believes trial-execution factors, including invalid randomisation or general trial conduct, do not explain the result. These are the company's current conclusions from an ongoing investigation; it says it will provide another update when the analysis is complete.

A new 200 L run draws on earlier batch experience

Immutep has contracted a new manufacturing run at 200 L scale. It says ten GMP batches were previously manufactured at that scale and used in successful Phase I/II studies, including TACTI-mel, TACTI-002 and INSIGHT-003. TACTI-004, by contrast, was conducted exclusively with efti manufactured at 2,000 L scale.

That history explains the company's emphasis on the smaller manufacturing scale, but the new contract is a step toward future supply. The announcement does not report completion of the run or release of clinical material. Earlier study experience also leaves the proposed registration-directed trials to establish their own results.

Trial timing depends on supply, design and resources

Preparations have begun for the next trials, with study starts targeted for the second half of 2027. The company expressly ties that target to final trial-design decisions, regulatory interactions, manufacturing timelines, partnering and resources. Each condition matters to the timetable, so the stated period remains a target rather than confirmation that studies have started.

Licensing partner Dr. Reddy’s Laboratories has been consulted and supports the approach, according to Immutep. The company is also in preliminary discussions with other parties about the proposed pathway. The disclosure describes support and early discussions, without announcing a new partnership or an expanded license.

Separately, Immutep says IMP761, its agonist anti-LAG-3 program for autoimmune disease, continues in line with previously disclosed plans. The central development questions for efti remain the completion of the root cause analysis, progress on the contracted manufacturing run and the decisions needed to turn the two-indication strategy into clinical studies.