This study is an open, single arm, dose increasing study to evaluate the safety and efficacy of the combination of mRNA personalized tumor vaccine encoding neoantigen (hereinafter referred to as tumor vaccine) and Sintilimab injection (hereinafter referred to as Sintilimab) in the treatment of advanced malignant solid tumors.

Inclusion Criteria:

• Are ≥18 years old, without limitation of sex at time of consent.
• Patients with malignant solid tumors confirmed by histopathology or cytology and having at least one measurable lesion.
• Fresh biopsy specimens can be provided for vaccine preparation.
• Patients with malignant solid tumors who develop secondary drug resistance after receiving PD-1/PD-L1 drug therapy, including but not limited to gastric cancer, esophageal cancer, and other gastrointestinal tumors of MSI-H

Exclusion Criteria:

• It is known that it is allergic to any tumor vaccine and Sintilimab preparations; Or have experienced severe allergic reactions to other monoclonal antibodies in the past;
• The predicted number of new antigens is less than 10;
• Those who are pregnant or breastfeeding;
• Those with an expected survival period of less than 3 months;