Eftilagimod Alpha (Soluble LAG3 Protein) Combined with Pembrolizumab as Second-Line Therapy for Patients with Metastatic Head and Neck Squamous Cell Carcinoma.

Purpose: Eftilagimod alpha (efti), a soluble LAG3 protein, activates antigen-presenting cells (APC) and downstream T cells. TACTI-002 (part C) evaluated whether combining efti with pembrolizumab led to strong antitumor responses in patients with second-line recurrent or metastatic head and neck squamous cell carcinoma (R/M HNSCC) while demonstrating good tolerability.

Patients and methods: In this multinational phase II trial using Simon's two-stage design, patients who were PD-L(1)-naïve with R/M HNSCC who had failed first-line platinum-based therapy, unselected for PD-L1, received intravenous pembrolizumab (200 mg, once every 2 weeks) combined with subcutaneous efti (30 mg once every 2 weeks for 24 weeks and once every 3 weeks thereafter). The primary endpoint was objective response rate per RECIST 1.1 modified for immune-based therapy by investigator assessment. Additional endpoints included duration of response, progression-free survival, overall survival, and tolerability. Pharmacodynamic effects (absolute lymphocyte count) and Th1 cytokine biomarkers (IFNγ/CXCL10)] were evaluated in liquid biopsies.

Results: Between March 2019 and January 2021, 39 patients were enrolled; 37 were evaluated for response. All patients received prior chemotherapy, and 40.5% were pretreated with cetuximab; 53.1% of patients had PD-L1 combined positive score <20. With a median follow-up of 38.8 months, the objective response rate was 29.7%, including 13.5% complete responders. The median duration of response was not reached. Rapid and sustained absolute lymphocyte count increase was observed in patients who had an objective response. Th1 biomarkers increased sustainably after first treatment. No unexpected safety signals were observed.

Conclusions: Efti plus pembrolizumab was safe and showed encouraging antitumor activity and pharmacodynamic effects in patients with second-line head and neck squamous cell carcinoma (HNSCC), thus supporting further evaluation of this combination in earlier treatment lines.