Inclusion Criteria:  Histologically confirmed AEG, Siewert type I or II; Potentially resectable cT3-4a, any N, M0 (AJCC 8 TNM classification); Have a performance status of 0 or 1 on the ECOG Performance Scale; Age 18-75 years old, both men and women; Be willing and able to provide written informed consent/assent for the trial; Demonstrate adequate organ function , all screening labs should be performed within 10 days of treatment initiation; Female subject of childbearing potential should have a negative urine or serum pregnancy within 72 hours prior to receiving the first dose of study medication. If the urine test is positive or cannot be confirmed as negative, a serum pregnancy test will be required; Be willing to provide tissue from a newly obtained core or excisional biopsy of a tumor lesion through repeated biopsies. Newly-obtained is defined as a specimen obtained up to 4 weeks (28 days) prior to initiation of treatment on Day 1. Subjects for whom newly-obtained samples cannot be provided (e.g. inaccessible or subject safety concern) may submit an archived specimen only upon agreement from the Sponsor.  Exclusion Criteria:  Prior therapy (operation, radiotherapy, immunotherapy, or chemotherapy) for AEG; Ineligibility or contraindication for esophagectomy; Has a diagnosis of immunodeficiency or is receiving chronic systemic steroid therapy (in dosing exceeding 10 mg daily of prednisone equivalent) or any other form of immunosuppressive therapy within 7 days prior to the first dose of study drug; Has active autoimmune disease that has required systemic treatment in the past 2 years (i.e. with use of disease modifying agents, corticosteroids or immunosuppressive drugs); Has severe hypersensitivity and adverse events (≥Grade 3) to nivolumab and/or any PD-1/PD-L1 inhibitors.