First-in-Human Dose-Escalation Study of Fianlimab, an Antilymphocyte Activation Gene-3 Antibody, with Cemiplimab in Patients with Advanced Malignancies

Purpose: Preclinical data indicate that fianlimab (antilymphocyte activation gene-3) plus cemiplimab (anti–PD-1) enhances antitumor activity. Here, we report prespecified final analyses of the dose-escalation part of a first-in-human, phase 1 study (NCT03005782) of fianlimab as monotherapy and in combination with cemiplimab in patients with advanced malignancies. Patients and Methods: Adult patients received 1 to 40 mg/kg of fianlimab plus 350 mg of cemiplimab every 3 weeks (Q3W) across various dose-escalation schedules. Primary objectives were the rate of dose-limiting toxicities, adverse events (including immune mediated), deaths, laboratory abnormalities, and pharmacokinetics. Secondary outcomes were objective response rate, best overall response, duration of response, and antidrug antibody variables. Results: Seventy-eight patients were enrolled (fianlimab + cemiplimab, n = 47; fianlimab monotherapy, n = 31). One patient treated with 3 mg/kg fianlimab + cemiplimab experienced dose-limiting toxicities, including increased blood creatine phosphokinase and myasthenic syndrome. No maximum tolerated dose was reached. Any-grade treatment-emergent adverse events occurred in 90% of patients with fianlimab monotherapy, in 87% of patients with fianlimab + cemiplimab, and in 87% of patients who transitioned from monotherapy to combination therapy. Fianlimab pharmacokinetics were dose proportional and similar in monotherapy and combination therapy. Across patients who received fianlimab + cemiplimab, five achieved a partial response, three of whom experienced a response after transitioning from monotherapy to combination therapy. Fianlimab 1,600 mg Q3W (20 mg/kg in an 80-kg individual) is the selected dose for phase 2 and phase 3 studies. Conclusions: Fianlimab as monotherapy and in combination with cemiplimab demonstrated acceptable safety and preliminary antitumor activity, which is generally consistent with previous reports of cemiplimab.