Early safety and efficacy from a phase I open-label clinical trial of CD137(4-1BB) agonistic antibody LVGN6051 as monotherapy and in combination with pembrolizumab.

2521 Background: LVGN6051, a monoclonal antibody against CD137 (also known as 4-1BB or TNFRSF9) with an engineered Fc capable of selectively binding to the Fcγ receptor IIB, acts as a conditional CD137 agonist, resulting in immune activation optimally in tumor microenvironment ( Qi, Nat. Commun. 2019 ). In preclinical models, LVGN6051 demonstrated robust anti-tumor efficacy and safety as a single agent and in combination with anti-PD-1 antibodies. Therefore, we have initiated this first-in-human study of LVGN6051 alone or in combination with pembrolizumab for the treatment of advanced or metastatic malignancy. Methods: This study includes accelerated dose escalation monotherapy up to 2 mg/kg of LVGN6051, and traditional 3 + 3 design for higher doses of LVGN6051 alone or in combination with pembrolizumab. Then, this study will enroll patients with specific types of malignancies following Simon’s two-stage design. Both agents are administered once every 3 weeks. Primary objectives of this study were to define the safety profile and to establish the recommended phase 2 dose (RP2D) of LVGN6051 alone or in combination with pembrolizumab. Pharmacokinetics, immunogenicity, pharmacodynamics and clinical efficacy will be also evaluated. Results: At the cut-off date on January 18, 2021, 16 subjects have been enrolled into the monotherapy cohorts (n=12, no DLT observed up to 7 mg/kg), and the combination cohort (n=4, ongoing at LVGN6051 2 mg/kg and pembrolizumab 200 mg, one DLT observed). No treatment-related adverse event (TRAE) was observed in monotherapy. Treatment-emergent adverse events (TEAE) in combination included increased ALT/AST, thrombocytopenia, and fatigue. In the combination cohort, one patient with predominant hepatic metastases and history of intermittent grade 2 hepatic impairment experienced grade 3 increased ALT/AST (DLT) on cycle 1 day 15 that were resolved to her baseline without corticosteroids on cycle 1 day 18. TRAE included increased ALT/AST, thrombocytopenia, neutropenia, nausea and fatigue. Seven of 10 evaluable patients in the monotherapy cohorts demonstrated stable disease with the longest treatment being 8+ months. Tumor reductions by >10% were observed in melanoma and neuroendocrine tumor on monotherapy. One patient with metastatic head and neck squamous cell carcinoma who had progressed on an anti-PD-L1 based therapy showed an immune partial response (iPR) for 6+ months to the combination therapy. Conclusions: Preliminary evidence showed that LVGN6051 was well tolerated and tumor shrinkages were observed. While we continue assessing its safety profile, antitumor activity was observed in the LVGN6051 and pembrolizumab cohort. The favorable safety profile and preliminary antitumor activity warrant further evaluation in patients with advanced malignancies. Clinical trial information: NCT04130542.