⁃ Written informed consent by the participants or the participant's legally authorized representative prior to screening.

• Participants with Eastern Cooperative Oncology Group (ECOG) performance status of 0 to 1 at study enrollment and an estimated life expectancy of at least 3 months.

• Disease must have at least 1 measurable lesion by Response Evaluation Criteria in Solid Tumors (RECIST) version 1.1. Tumor lesions situated in a previously irradiated area are not considered measurable unless there has been demonstrated progression in the lesion. Imaging tests outside the screening period are valid if performed not more than 2 weeks before consent signature and otherwise fulfil protocol criteria.

• Participants with adequate organ function defined by the following:

⁃ Participants must not have required blood transfusion or growth factor support ≤ 14 days before sample collection at screening:

∙ Absolute neutrophil count ≥ 1.5 × 109 /L.

∙ Platelet count ≥ 100 × 109 /L.

∙ Hemoglobin ≥ 9 g/dL.

∙ Alanine aminotransferase and AST ≤ 2.5 × ULN or \< 5 × ULN if hepatic metastases present.

∙ Serum total bilirubin ≤ 1.5 × ULN (or \< 3 × ULN for participants with Gilbert's syndrome).

∙ Alkaline phosphatase ≤ 2.5 × ULN or \< 5 × ULN if bone metastases present.

∙ Prothrombin time ≤ 1.5 × ULN.

∙ International normalized ratio (INR) ≤ 2.0 or activated partial thromboplastin time (aPTT) ≤ 1.5 × ULN. Exception: INR 2 to ≤ 3 is acceptable for participants on a stable dose of anticoagulants.

∙ Estimated creatinine clearance \> 50 mL/min according to the Cockcroft Gault formula

• Participants with highly effective contraception (that is, methods with a failure rate of less than 1% per year) for both male and female participants if the risk of conception exists.

• Dose escalation Phase specific Inclusion Criterion:

⁃ Participants with histologically or cytologically proven locally unresectable advanced or metastatic solid tumors, which are refractory or intolerant to standard therapy or for which no standard therapy exists.

⁃ Participants who have histologically or cytologically confirmed diagnosis of relapsed or refractory, locally unresectable advanced or metastatic NSCLC, HNSCC, ESCC, who received at least one line of systemic treatment including anti-PD-1 or anti-PD-L1 therapy.

• Only participants who have evaluable PD L1 expression results are eligible.

• NSCLC cohort:

∙ Documented histologically or cytologically squamous or non-squamous stage IV NSCLC.

‣ Documented evidence of tumors expressing PD L1 (TPS ≥ 1%) for the determination of PD L1 expression in NSCLC.

‣ No sensitive epidermal growth factor receptor (EGFR) mutation and anaplastic lymphoma kinase (ALK) rearrangement.

‣ No known actionable genomic alterations of ROS1 rearrangement, BRAF V600E mutation, MET mutation, NTRK1/2/3 gene fusion, and/or RET rearrangement.

• HNSCC cohort:

⁃ • Documented histologically or cytologically squamous cell carcinoma of the head and neck. Nasopharynx is excluded.

⁃ • Refractory or intolerant to platinum based chemotherapy or concurrent chemoradiation.

‣ PD L1 expression: Documented evidence of Combined Positive Score (CPS) ≥ 1 for PD L1.

• ESCC cohort:

∙ Documented histologically or cytologically squamous carcinoma.

‣ PD L1 expression: Documented evidence of CPS ≥ 1 for PD L1.