Systemic Immune Activation Linked to Improved Outcomes with Eftilagimod Alfa in Metastatic Breast Cancer Study

New findings from Immutep's Phase 2b AIPAC-003 study are providing additional insight into the mechanism of action of eftilagimod alfa (efti), an antigen-presenting cell activator being investigated in combination with paclitaxel for patients with metastatic breast cancer. According to the company, translational analyses presented at the 2026 American Society of Clinical Oncology Annual Meeting found that systemic immune activation following treatment was associated with improved clinical outcomes.¹

The results build on previously reported efficacy findings from the AIPAC-003 trial and offer a potential biomarker strategy for identifying patients most likely to benefit from treatment. Researchers reported that activation of both innate and adaptive immune responses correlated with longer progression-free survival and overall survival, supporting the immunomodulatory effects of the investigational therapy.¹

What did the AIPAC-003 analysis show?

The translational analysis evaluated blood samples collected from patients enrolled in the randomized Phase 2b study. Investigators examined changes in immune cell populations and activation markers following treatment with efti and paclitaxel.¹

According to the findings, patients who experienced higher levels of systemic immune activation demonstrated improved clinical outcomes compared with those showing less robust immune responses. Specifically, enhanced activation of antigen-presenting cells, T cells, and other immune components appeared to be associated with prolonged disease control and survival.¹

Researchers noted that the findings provide additional evidence supporting the proposed mechanism of action of efti, which functions as a soluble LAG-3 protein designed to activate antigen-presenting cells and stimulate broader antitumor immune responses.²

How does eftilagimod alfa work?

Unlike immune checkpoint inhibitors that primarily remove inhibitory signals from T cells, efti is intended to activate the immune system upstream by targeting major histocompatibility complex class II molecules on antigen-presenting cells.²

This approach is designed to enhance both innate and adaptive immune responses, potentially improving the ability of the immune system to recognize and attack cancer cells. Investigators reported that the latest biomarker analyses demonstrated increases in immune activation markers consistent with this proposed mechanism.¹

The findings also contribute to a growing body of research exploring how immune activation signatures may help predict treatment outcomes across multiple cancer types.

Why are biomarkers important in immuno-oncology?

One of the persistent challenges in cancer immunotherapy is identifying which patients are most likely to benefit from treatment. While biomarkers such as PD-L1 expression have helped guide the use of certain checkpoint inhibitors, many immunotherapies still lack reliable predictive markers.³

The AIPAC-003 findings suggest that monitoring systemic immune activation could potentially provide a way to assess treatment response earlier and more accurately. According to investigators, patients demonstrating stronger immune activation after receiving efti appeared more likely to experience favorable outcomes.¹

If validated in future studies, such biomarkers could help clinicians optimize treatment selection and potentially improve patient management strategies.

What could the findings mean for future development?

The results arrive as Immutep continues evaluating efti across multiple oncology indications and combination regimens. While the current findings remain exploratory, they provide important biological evidence supporting the therapy's mechanism of action and may help guide future clinical development efforts.¹

Researchers emphasized that additional studies will be needed to confirm the predictive value of systemic immune activation markers. However, the observed association between immune activation and improved survival outcomes offers further support for the potential role of antigen-presenting cell activation as a therapeutic strategy in cancer treatment.

As interest grows in combination immunotherapy approaches, biomarker-driven insights such as those generated from AIPAC-003 may become increasingly important for understanding which patients are most likely to benefit from novel immune-based therapies.³

References

1. Systemic immune activation with eftilagimod alfa associated with statistically significant increased overall survival in late-stage cancer patients. (2026 May 28). BioSpace. https://www.biospace.com/press-releases/systemic-immune-activation-with-eftilagimod-alfa-associated-with-statistically-significant-increased-overall-survival-in-late-stage-cancer-patients
2. Brignone, C., Grygar, C., Marcu, M., Schäkel, K., & Triebel, F. (2007 Sep). A soluble form of lymphocyte activation gene-3 (IMP321) induces activation of a large range of human effector cytotoxic cells. Journal of immunology https://doi.org/10.4049/jimmunol.179.6.4202
3. Ribas A, Wolchok JD. (2018 Mar). Cancer immunotherapy using checkpoint blockade. Science. https://www.science.org/doi/10.1126/science.aar4060