Major Inclusion Criteria:

        • Able to understand and comply with study procedures, understand the risks involved, and
        provide written informed consent.

        Dose Escalation:

          -  Histologically and / or cytological confirmed solid tumors: colorectal, endometrial,
             gastric including, gastroesophageal junction adenocarcinoma (GC), head and neck
             (esophageal, hepatocellular (HCC), non-small cell lung cancer, mesothelioma, ovarian,
             and renal cell carcinoma (RCC), either refractory or relapsed to standard therapy or
             for which no effective standard therapy is available.

          -  No restriction to number of prior therapies for Dose Escalation Segment except for
             gastric and renal cell carcinoma.

        Cohort Extension:

          -  Histologically and/or cytological confirmed solid tumors with an approved labelled
             indication for PD-1 inhibitors.

          -  Tumor biopsy at study entry and during therapy. Tumor sites used to satisfy this
             criterion must not have received any prior radiation therapy. Sites for biopsy must be
             distinct from target lesions used for efficacy assessment.

          -  Measurable disease according to RECIST v1.1.

        Dose and Disease Expansion:

          -  MSI-H or dMMR per local laboratory and failed at least one prior line of standard of
             care chemotherapy per local standards.

          -  Carcinoma of Unknown Primary

        Major Exclusion Criteria:

          -  History of severe hypersensitivity to mAbs, excipients of the drug product or other
             components

          -  Prior malignancy active within the previous 2 years except for locally curable cancers
             that have been cured, such as basal or squamous cell skin cancer, superficial bladder
             cancer or carcinoma in situ of the cervix or breast

          -  Any active autoimmune disease or a documented history of autoimmune disease, or
             history of syndrome that required systemic steroids or immunosuppressive medications,
             except for subjects with vitiligo or resolved childhood asthma/atopy

          -  Prior therapy with an anti-PD-1, anti-PD-L1, anti-PDL-2, or anti-CTLA-4 antibody (or
             any other antibody targeting T cell co-stimulation pathways) (except NSCLC)

          -  Known significant mental illness or other conditions such as active alcohol or other
             substance abuse that, in the opinion of the Investigator, predisposes the subject to
             high risk of noncompliance with the protocol treatment or assessments.