This is a Phase 1/2 study of GB263T in participants with advanced NSCLC and other solid tumor. The study will consist of a dose-escalation and expansion stage to determine RP2D (Phase 1), and an extension stage (Phase 2) where participants will be enrolled into indication-specific cohorts.

Inclusion Criteria:

1. ≥18 years of age.
2. Subjects with histologically or cytologically confirmed metastatic or unresectable advanced NSCLC or other solid tumors who have progressed on prior standard therapy, have been intolerant to prior standard therapy, or have refused all other currently available therapeutic options.
3. Subjects must have evaluable disease according to Response Evaluation Criteria in Solid Tumors (RECIST) v1.1.
4. ECOG PS 0-1.
5. An expected survival time is ≥3 months.
6. Adequate organ function.
7. Subjects in Phase II must agree to provide pre-treatment tumor tissue samples.

Exclusion Criteria:

1. Subjects who have had prior chemotherapy, targeted cancer therapy, immunotherapy, or any investigational anti-cancer treatment within 2 weeks or five half-lives of the treatment (whichever is longer), prior to the first administration of the study drug.
2. Toxicity (excluding alopecia, peripheral neuropathy, and hypothyroidism) that did not return to class 0 or class 1 of NCI CTCAE V5.0 from prior antitumor therapy prior to the first administration of the study drug.
3. Prior radical radiation therapy completed within 4 weeks prior to the first administration of the study drug.
4. Subjects with untreated symptomatic brain metastases.
5. History of interstitial lung disease (ILD).
6. Uncontrolled pleural effusion, pericardial effusion, or ascites requiring recurrent drainage procedures.
7. Received live virus vaccination within 30 days of first dose of study treatment.