This is a phase Ib/II, open-label, multicenter study to evaluate the safety, tolerability, pharmacokinetics (PK), and preliminary efficacy of JS015 combination therapy in patients with advanced solid tumors. The Recommended dose for phase II trial （RP2D） will be determined based on the safety, tolerability, pharmacokinetics and efficacy.

Inclusion Criteria:

1. Patients who meet the following criteria for each indication cohort:

1. Esophageal cancer cohort, patients with histologically or cytologically confirmed esophageal squamous cell carcinoma with locally advanced unresectable or with distant metastasis, who progressed during or after prior first-line PD-(L)1 antibody and platinum-based chemotherapy;
2. Gastric cancer cohort, patients with histologically or cytologically confirmed gastric/gastroesophageal junction adenocarcinoma with locally advanced unresectable or distant metastases, HER2-negative, who progressed during or after prior first-line PD-(L)1 antibody and platinum-based chemotherapy;
3. 1L gastric cancer cohort, patients with histologically or cytologically confirmed gastric/gastroesophageal junction adenocarcinoma with HER2-negative results and no prior systemic antitumor therapy;
4. Colorectal cancer cohort, patients with histologically confirmed adenocarcinoma of the colon or rectum, who progressed during or after first-line 5-FU-based combination therapy;
5. Pancreatic cancer cohort, patients with histologically or cytologically confirmed locally advanced unresectable or distant metastatic pancreatic ductal adenocarcinoma, who have not received any previous systemic antitumor therapy 2 . Eastern Cooperative Oncology Group (ECOG) 0 or 1; 3. Life expectancy >=12 weeks; 4. At least one measurable lesion according to RECIST 1.1; 5. Adequate organ function;

Exclusion Criteria:

1. Leptomeningeal metastases and /or active brain metastases;
2. Pleural, peritoneal, or pericardial effusion with clinical symptoms or requiring repeated management (puncture, drainage, etc.);
3. History of interstitial lung disease or a previous history of noninfectious pneumonia with corticosteroid therapy, or evidence of active pneumonia on screening imaging;
4. History of immunodeficiency;
5. History of serious cardiovascular and/or cerebrovascular diseases;
6. History of abdominal or tracheo-esophageal fistula, gastrointestinal (GI) perforation, or intra-abdominal abscess within 6 months before the first dose of administration