NT-I7 in Combination With Nivolumab in Advanced Gastric, Gastro-Esophageal Junction or Esophageal Adenocarcinoma

Inclusion Criteria: 1. Dose Escalation: Have histologically or cytologically confirmed locally advanced or metastatic solid tumor and can be either CPI-pretreated or CPI-naive. Phase 2: Have histologically or cytologically confirmed locally advanced or metastatic carcinoma of Gastric or Gastro-Esophageal Junction (GEJ) or Esophageal Adenocarcinoma (EAC) and who progressed on or intolerant to 2 or more prior lines of standard therapy including chemotherapy, immunotherapy, and targeted therapy. 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 may have biopsiable disease. Optional for participants to provide a) pre-treatment tumor tissue sample and b) on-treatment tumor biopsy. 4. At least 20 participants enrolled in the Phase 2 must agree to provide tumor tissue sample prior to the start of treatment. 5. 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. 6. 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 chemotherapy or any anti-cancer therapy with half-life \<1 week within 4 weeks or 5 half-lives, whichever is shorter, prior to first dose of study treatment. 3. Has received prior radiotherapy within 2 weeks of start of study treatment. 4. 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. 5. 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). 6. History of severe hypersensitivity reactions to monoclonal antibodies (mAbs) or intravenous immunoglobulin preparation. 7. Clinically significant cardiac disease. 8. Has a history of allergy or intolerance (unacceptable adverse events \[AEs\]) to study drug components or polysorbate-80-containing injections. Note: Polysorbate 80 is a buffer used to make NT-I7. 9. 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. 10. Has had an allogenic tissue/solid organ transplant or bone marrow transplant. 11. Subjects who were intolerable and discontinued from prior immune checkpoint inhibitors.