A Trial to Evaluate Safety, Tolerability, Pharmacokinetics and Preliminary Efficacy of BA1203 in Advanced Solid Tumors.

1. Able and willing to provide written informed consent and to comply with the study protocol;
2. Subject with histologically or cytologically confirmed advanced and/or metastatic solid tumors who have progressed on all standard therapies, are intolerant to Standard-Of-Care (SOC), and/or are non-amenable to SOC;
3. At least one measurable lesion according to Response Evaluation Criteria for Solid Tumors version 1.1 (RECIST v1.1);
4. Patients with colorectal cancer must have a microsatellite instability (MSI) test report, and patients with other tumor types must have a prior Programmed Death-Ligand 1 (PD-L1) histopathological examination report; if unavailable, tumor tissue specimens must be provided for the above tests.;
5. Life expectancy >=12 weeks;
6. Eastern Cooperative Oncology Group (ECOG) performance status of 0 or 1;
7. Adequate major organ function;
8. Women of Childbearing Potential must have a negative pregnancy test within 7 days prior to the first dose: Agreement to remain abstinent (refrain from heterosexual intercourse) or use highly effective contraceptive methods;
9. Men: Agreement to remain abstinent (refrain from heterosexual intercourse) or use highly effective contraceptive methods and refrain from donating sperm.

Exclusion Criteria:

1. Patients with primary central nervous system tumors or new or symptomatic central nervous system metastases.
2. Patients with a known history of another malignancy within 5 years prior to signing the informed consent.
3. Patients with significant cardiovascular and cerebrovascular diseases.
4. Presence of any of the following within 8 weeks before the first dose: symptomatic radiation pneumonitis, radiation esophagitis, or radiation-induced colitis/proctitis; interstitial lung disease; pulmonary disease with severe obstructive ventilatory impairment; unhealed peptic ulcer; cirrhosis-related complications; chronic enteritis; ischemic necrotizing enteritis; gastrointestinal obstruction; tendency to gastrointestinal bleeding or high risk of gastrointestinal perforation; pancreatitis requiring treatment; arterial or venous thrombotic disease; chronic nephritis; or nephrotic syndrome.
5. Any active autoimmune disease, or autoimmune or inflammatory disease requiring immunosuppressive therapy.
6. History of Stevens-Johnson syndrome, toxic epidermal necrolysis, or drug-induced hypersensitivity syndrome (DIHS).
7. History of allogeneic hematopoietic stem cell transplantation or organ transplantation, or currently awaiting transplantation.
8. Immune-related adverse events during prior antitumor therapy that make the patient no longer suitable for continued immunotherapy.
9. Prior treatment with Programmed Cell Death Protein 1 / Interleukin-2 or Programmed Cell Death Protein 1 / Interleukin-15 agents.