Inclusion Criteria:

          1. Have histologically or cytologically confirmed locally locally advanced or metastatic
             carcinoma of Gastric or Gastro-esophageal Junction (GEJ) or Esophageal Adenocarcinoma
             (EAC) who progressed on or intolerant to 2 or more prior lines of chemotherapy and/or
             targeted therapy in the advanced/metastatic setting. Participants with
             HER2-overexpresing tumor who progressed on trastuzumab-based therapy and at least 1
             other line of therapy are also eligible.

             Note: GEJ adenocarcinomas are defined as tumors that have their center within 5 cm
             proximal and distal of the anatomical cardia, as described in the Siewert
             classification system (Siewert et al, 2000)

          2. Have at least one measurable lesion according to RECIST 1.1.

          3. Participants enrolling in the dose escalation phase must have biopsiable disease.
             Participants must agree to provide a) pre- treatment tumor tissue sample and b)
             on-treatment tumor biopsy.

          4. Participants enrolled in the Phase 2 must agree to provide tumor tissue sample prior
             to the start of treatment.

          5. PD-L1 expression status must be determined by the study-designated central lab prior
             to randomization (CPS <5 versus CPS ≥ 5) for participants enrolled in Phase 2.

          6. Female participants are either postmenopausal for at least 1 year, are surgically
             sterile for at least 6 weeks; if a female participant is of childbearing potential,
             she must agree to remain abstinent (refrain from heterosexual intercourse) or to
             follow instructions for one highly effective method of contraception for the duration
             of study treatment and for 5 months after the last dose of study treatment.

          7. Non-sterile male participants who are sexually active with female partners of
             childbearing potential must agree to remain abstinent (refrain from heterosexual
             intercourse) or to follow instructions for one highly effective method of
             contraception for the duration of study treatment and for 3 months after the last dose
             of study treatment.

        Exclusion Criteria:

          1. Pregnant, or breastfeeding or expecting to conceive or father children within the
             study duration from screening through 5 months (for female participants) or 3 months
             (for male participants) after the last dose of study treatment.

          2. Receiving any investigational therapy or any approved therapy for investigational use
             within 4 weeks or 5 half-lives, whichever is longer, prior to first dose of study
             treatment.

          3. Has previously received checkpoint inhibitor (CPI) treatment for gastric cancer or GEJ
             or EAC.

          4. Has received prior radiotherapy within 2 weeks of start of study treatment.

          5. Has received treatment with complementary medications (excluding, herbal supplements,
             or traditional Chinese medications) to treat the disease under study within 2 weeks
             prior to the first dose of study treatment.

          6. Subjects are eligible if CNS metastases are asymptomatic and do not require immediate
             treatment or have been treated and subjects have neurologically returned to baseline
             (except for residual signs or symptoms related to the CNS treatment).

          7. History of severe hypersensitivity reactions to monoclonal antibodies (mAbs) or
             intravenous immunoglobulin preparation.

          8. Clinically significant cardiac disease.

          9. Has a history of allergy or intolerance (unacceptable adverse events [AEs]) to study
             drug components or polysorbate-80-containing infusions.

             Note: Polysorbate 80 is a buffer used to make NT-I7.

         10. Has received a live vaccine within 4 weeks prior to the first dose of study drug.
             Seasonal influenza vaccines for injection are generally killed virus vaccines and are
             allowed.

         11. Has had an allogenic tissue/solid organ transplant or bone marrow transplant.