Immutep Limited (ASX:IMM) has disclosed Phase I clinical data for IMP761, its first-in-class LAG-3 agonist antibody, presented as a late-breaking abstract at ACR Convergence 2026 in Orlando, Florida, showing statistically significant and exposure-dependent inhibition of T-cell-driven immune responses in healthy volunteers.

Key Points

  • IMP761 demonstrated statistically significant, exposure-dependent suppression of immune responses after a single infusion in healthy volunteers across seven dose levels (0.03 mg/kg to 14 mg/kg)
  • No serious or severe adverse events reported; pharmacokinetic profile supports a four-week dosing interval
  • The multiple ascending dose (MAD) portion of the Phase I study is ongoing, with no new safety signals observed to date
  • Results from the MAD portion are anticipated to be reported in H1 CY2027 and are expected to inform dose selection for a potential future Phase II program

Phase I Study Design and KLH Challenge Model

The ongoing Phase I study is a randomised, placebo-controlled, double-blind first-in-human study (NCT06637865) conducted by the Centre for Human Drug Research (CHDR) in Leiden, the Netherlands, evaluating IMP761 in 60 healthy volunteers using the keyhole limpet haemocyanin (KLH) challenge model. Volunteers are immunised with KLH three times and then given small intradermal injections of KLH, producing a measurable T-cell-driven local immune reaction. According to the filing, the model is an established method to test whether a drug can dampen a T-cell-driven immune response to a foreign antigen.

Tolerability, Pharmacokinetics, and Pre-Clinical Rheumatoid Arthritis Findings

IMP761 was well tolerated across all seven dose levels evaluated, with no serious or severe adverse events reported. The pharmacokinetic profile disclosed in the filing supports a four-week dosing interval for the MAD portion of the study. In complementary pre-clinical studies using samples from rheumatoid arthritis patients, IMP761 demonstrated statistically significant reductions in T-cell activation and proliferation, according to the filing. The data disclosed at ACR Convergence 2026 builds on results previously presented at EULAR 2026.

CSO Commentary and Next Steps for IMP761 Development

Immutep Chief Scientific Officer Dr. Frédéric Triebel stated that the results from the large double-blinded trial "clearly show the immunosuppressive effect of IMP761 on a strong antigen-driven T-cell response in tissues, without safety concerns." The filing states that analysis of the MAD portion of the Phase I study, with a focus on pharmacokinetics, is ongoing. Results from that portion are anticipated in H1 CY2027 and are expected to inform dose selection for a potential future Phase II program. IMP761 is described as the only LAG-3 agonist antibody currently in clinical development, to the company's knowledge.