Key Inclusion Criteria:

          1. Dose escalation cohorts: Advanced stage (unresectable or metastatic) solid tumor
             malignancy, confirmed histologically or cytologically as defined in the protocol

          2. Dose expansion cohorts: Advanced stage (unresectable or metastatic) head and neck
             squamous cell carcinoma, confirmed histologically or cytologically as defined in the
             protocol

          3. Mandatory biopsies: Able and willing to provide tumor tissue at baseline and while on
             treatment, with at least 1 soft tissue lesion amenable to biopsy by ultrasound or
             computed tomography (CT)-guided biopsy

             All Cohorts:

          4. Has no prior history of immune checkpoint blockade (ICB) therapy

          5. Has exhausted all approved available treatment options for their disease, with no
             standard therapy likely to convey clinical benefit as defined in the protocol

        Key Exclusion Criteria:

          1. Has previously received GITR-targeted therapy

          2. Has received any previous systemic biologic therapy within 5 half-lives of first dose
             of study therapy as defined in the protocol

          3. Has any condition that requires ongoing/continuous corticosteroid therapy (>10 mg
             prednisone/day or anti-inflammatory equivalent) within 14 days prior to the first dose
             of study therapy

          4. Has ongoing or recent (within 5 years) evidence of significant autoimmune disease that
             required treatment with systemic immunosuppressive treatments as defined in the
             protocol

          5. Has a known history of, or any evidence of, interstitial lung disease, or active,
             non-infectious pneumonitis in the past 5 years. A history of radiation pneumonitis in
             the radiation field is permitted as long as pneumonitis resolved ≥6 months prior to
             first dose of study therapy

          6. Has uncontrolled infection with human immunodeficiency virus, hepatitis B or hepatitis
             C infection, or diagnosis of immunodeficiency

          7. Has received a live vaccine within 4 weeks of planned start of study medication. For
             dose escalation only: Has received a COVID-19 vaccination within 1 week of planned
             start of study medication or for which the planned COVID-19 vaccinations would not be
             completed 1 week prior to start of study.

          8. Has had prior allogeneic stem cell transplantation or received organ transplants at
             any time, or autologous stem cell transplantation

        Note: Other protocol-defined Inclusion/ Exclusion criteria apply