MSB-2311

MSB2311 is a novel pH-dependent humanized anti-programmed death-ligand 1 (PD-L1) monoclonal antibody. This phase I study primarily aimed to determine the maximum tolerated dose (MTD)/recommended phase 2 dose level (RP2D) of MSB2311 in patients with advanced solid tumors or lymphoma. MSB2311 was intravenously administered at 3, 10, and 20 mg/kg every 3 weeks (Q3W) and 10 mg/kg every 2 weeks (Q2W) using 3 + 3 design. During expansion phase, eligible patients with either PD-L1 overexpression, Epstein-Barr Virus positive, microsatellite instability high/mismatch repair deficient, or high tumor mutation burden tumors were treated at RP2D. A total of 37 Chinese patients were treated, including 31 with solid tumors and 6 lymphoma. No dose limiting toxicity was reported and MTD was not reached. The trial was expanded at 20 mg/kg Q3W or 10 mg/kg Q2W, both of which were determined as RP2D. Most common drug-related treatment-emergent adverse events were anemia (43.2%), aspartate aminotransferase increase (27.0%), proteinuria (21.6%), alanine aminotransferase increase and hypothyroidism (18.9% each), thyroid stimulating hormone increased and hyperglycemia (16.2% each). Out of 20 efficacy evaluable patients with biomarker positive solid tumors, 6 achieved confirmed partial response with the median duration of response of 11.0 months (95% CI 7.0-11.4) and 4 had stable disease, resulting an objective response rate of 30.0% (95% CI 11.9, 54.3) and disease control rate of 50.0% (95% CI 27.2, 72.8). One partial response was also observed among 6 patients with lymphoma. MSB2311 demonstrated a manageable safety profile and promising antitumor activity in patients with advanced solid tumors and lymphomas.