Phase Ib Study of Utomilumab (PF-05082566), a 4-1BB/CD137 Agonist, in Combination with Pembrolizumab (MK-3475) in Patients with Advanced Solid Tumors.

This phase Ib study (NCT02179918) evaluated the safety, antitumor activity, pharmacokinetics, and pharmacodynamics of utomilumab, a fully human IgG2 mAb agonist of the T-cell costimulatory receptor 4-1BB/CD137 in combination with the humanized, PD-1-blocking IgG4 mAb pembrolizumab in patients with advanced solid tumors. Utomilumab (0.45-5.0 mg/kg) and pembrolizumab (2 mg/kg) were administered intravenously every 3 weeks. Utomilumab dose escalation was conducted using the time-to-event continual reassessment method. Twenty-three patients received combination treatment with no dose-limiting toxicities. Treatment-emergent adverse events were mostly grades 1 to 2, without any treatment-related discontinuations. Six patients (26.1%) had confirmed complete or partial responses. Pharmacokinetics and immunogenicity of utomilumab and pembrolizumab were similar when administered alone or in combination. A trend toward higher levels of activated memory/effector peripheral blood CD8 T cells was observed in responders versus nonresponders. The safety, tolerability, and clinical activity demonstrated by utomilumab in combination with pembrolizumab support further investigation in patients with advanced solid tumors. .