Safety and Efficacy of Personalized Neoantigen Vaccine in Advanced Gastric Cancer

This trial is an investigator-initiated, single-center, open-label, single-arm exploratory study of mRNA neoantigen tumor vaccine in the treatment of advanced gastric cancer, including two phases: dose escalation and dose expansion. To evaluate the safety and tolerability of neoantigen tumor vaccine in subjects with advanced gastric cancer by conducting dose escalation trial in subjects diagnosed with advanced gastric cancer, and preliminarily evaluate the efficacy of neoantigen tumor vaccine in subjects with advanced gastric cancer. According to the characteristics of safety and efficacy data in the dose escalation phase, the dose expansion is performed at the intended clinical dose based on the investigator's judgment, and the treatment is performed in combination with PD-1/L1 to further evaluate the efficacy and safety profile of neoantigen tumor vaccine at a specific dose. Both the dose escalation phase and dose expansion phase include a screening period (Week -4 \~ Week -2), a baseline period (Week -1 \~ Day -1), a treatment period (Day 1 \~ Week 8 or 16), and a follow-up period. Subjects who signed and provided the formal informed consent entered the screening period. The treatment period included the initial treatment period (Day 1 \~ Week 8) and the enhanced treatment period (Week 12 \~ Week 16). The investigator determined whether to enter the enhanced treatment period based on the comprehensive judgment of the subject's efficacy, safety, compliance and other factors from Week 8 to Week 12. In the dose escalation phase, 18 subjects are expected to be enrolled at 100 μg, 200 μg and 400 μg (6 subjects in 100 μg, 6 subjects in 200 μg and 6 subjects in 400 μg). The low dose group was enrolled first, and the next dose group was started when the number of subjects met the requirements. If any subject withdrew early, the low dose group was given priority. The investigator will choose the optimal clinical dose for dose expansion, which can be one dose group or m