A Clinical Study to Evaluate the Efficacy and Safety of HLX26 (Anti-LAG-3 Monoclonal Antibody Injection) Combined With Serplulimab and Chemotherapy in Previously Untreated Advanced NSCLC Patients

This study is a phase II study to evaluate the efficacy, safety and tolerability of HLX26 in combination with Serplulimab and chemotherapy in the treatment of patients with Non-small cell lung cancer. The trial was divided into period 1 (safety run-in phase) and period 2 (dose expansion phase). The first phase is an open-label study, patients will receive varying doses (800 mg, 600 mg or lower) of HLX26 combined with a fixed dose (300 mg) of serplulimab and chemotherapy, administered by intravenous infusion every 3 weeks. Observation period of DLT lasts for 3 weeks after the first administration of HLX26. Safety review committee (SRC) will responsible for the safety of combination treatment. After confirmation of the safety, the efficacy of HLX26 combined with Serplulimab and chemotherapy will be evaluated in period 2. The second phase (dose expansion phase) is a randomized, double-blind, placebo-controlled study to evaluate the safety and efficacy of 2 dose levels of HLX26 combined with fixed-dose (300 mg) of serplulimab and chemotherapy in patients with NSCLC. If the tolerability observation of the 600mg dose group is completed in the first phase, the SRC will review the safety data obtained from the study and decide whether to enter into the second phase; if 2 of the 6 subjects in the 600mg dose group in the first phase occur DLT event, we will continue to explore the safe dose of HLX26 and enroll another 3-6 subjects. Once the maximum tolerated dose (MTD) is found, two doses, MTD and MTD-1, will be selected to enter the dose expansion phase. (The SRC will review the safety and tolerability results obtained in the study to determine the MTD, and will select the dose of MTD-1 below the MTD and within the effective dose range). In the second stage, there are 3 groups and 40 people in each group. The interactive network/voice response system (IWRS) is used to randomly assign qualified subjects to the following three groups in a 1:1:1 allocation ratio: \> Group A: HLX26 MTD intravenous infusion + serplulimab 300 mg intravenous infusion, Q3W; chemotherapy \> Group B: HLX26 MTD-1 intravenous infusion + serplulimab 300 mg intravenous infusion, Q3W; chemotherapy \> Group C: placebo + serplulimab 300 mg intravenous infusion, Q3W; chemotherapy The chemotherapy will be decided by investigator per patients' pathological type. nsqNSCLC patients will receive pemetrexed and carboplatin as chemotherapy and sqNSCLC patients will receive nab-paclitaxel or paclitaxel and carboplatin.