Inclusion Criteria:

          -  Patients must have signed an informed-consent form indicating that the patient
             understands the purpose of and procedures required for the study and is willing to
             participate in the study.

          -  Patients must have a history of prostate adenocarcinoma (adenocarcinoma must be the
             primary histology; secondary components of variant histologies are acceptable)
             confirmed on biopsy and treated with primary radical prostatectomy (RP) or definitive
             radiation (RT). Prior salvage RT is acceptable.

          -  Patients must have experienced biochemical recurrence (BCR) plus have minimum PSA
             values noted below:

               -  Following primary RP: Any detectable rising PSA after RP (or after salvage RT if
                  performed), minimum PSA 1.0 at time of screening

               -  Following primary RT: PSA rise to ≥2 ng/mL above the nadir

               -  No evidence of metastases on conventional imaging (CT or MRI plus bone scan)

          -  PSA doubling time (PSADT) <10 months --PSADT: calculated as per Prostate Cancer
             Working Group 3 (PCWG3) and the Memorial Sloan Kettering Cancer Center calculator:
             (https://www.mskcc.org/nomograms/prostate/psa_doubling_time)

        With linear regression model of normal logarithm of PSA and time, based on:

          -  At least 3 consecutive PSA values with each value ≥0.2 ng/mL

          -  Interval between first and last PSA values is ≥8 weeks but ≤12 months.

             -Archival tissue is mandatory, either prostatectomy specimen or (in patients who
             received primary RT) diagnostic core biopsies. Patients must consent to
             next-generation sequencing performed on this tissue.

          -  If diagnostic core biopsies are only available tissue, at least 3 cores must be
             involved by tumor

               -  Easteron Cooperative Oncology Group (ECOG) performance status 0-1

               -  Age ≥18 years

               -  Adequate organ and marrow function:

               -  System Laboratory Value

          -  Hematological

          -  White blood cell (WBC) ≥ 2000/µL

          -  Absolute Neutrophil Count (ANC) ≥ 1500/μL

          -  Platelets (Plt) ≥ 100 x103/μL

          -  Hemoglobin (Hgb) > 9.0 g/dL (with or without transfusion)

             -Renal

          -  Serum Creatinine ≤ 2 x ULN

          -  Hepatic

          -  Bilirubin1 ≤ 1.5× upper limit of normal (ULN)

          -  Aspartate aminotransferase (AST) ≤ 3 × ULN

          -  Alanine aminotransferase (ALT) ≤ 3 × ULN

               -  Except subjects with Gilbert Syndrome, who can have total bilirubin < 3.0 mg/dL

               -  Baseline testosterone ≥100 ng/dL

               -  Recovery from acute toxicity related to prior therapy, including surgery and
                  radiation, or no treatment-related toxicity ≥ grade 2.

               -  History of prior malignancy or concurrent separate malignancy is not an exclusion
                  criterion so long as the non-prostate malignancy is stable and does not require
                  any treatment.

               -  Able to understand and sign informed consent and adhere to study procedures.

               -  Male patients whose female partners are of reproductive potential must agree to
                  use a contraception during the trial period

        Exclusion Criteria:

          -  Current use of ADT or plan to initiate ADT during trial period

          -  Major surgery or radiation therapy within 14 days of starting study treatment

          -  Subjects with active autoimmune disease. Patients with a history of autoimmune disease
             that has not required systemic immunosuppressive therapy or does not threaten vital
             organ function including central nervous system, heart, lungs, kidneys, skin, and
             gastrointestinal tract will be allowed.

          -  Known history of immune deficiencies or chronic viral infections including HIV,
             hepatitis B (HBV), and hepatitis C (HCV) (patients with prior therapy for HBV or HCV
             is permitted if viral clearance was documented).

          -  Concurrent medical condition requiring use of systemic corticosteroids with prednisone
             >10 mg per day or equivalent. Use of inhaled, nasal, and topical steroids (applied to
             small body areas) is allowed.

          -  Current use (within past 4 weeks) of other prohibited medications including
             anti-cancer therapies, hormonal therapies, 5-alpha reductase inhibitors, and
             alternative medications known to alter PSA (e.g. phytoestrogens and saw palmetto).

          -  Prior treatment with immune checkpoint inhibitors. (Prior cancer vaccines are
             allowed.)

          -  Serious intercurrent medical or psychiatric illness that, in the judgment of the
             investigator, would interfere with patient's ability to carry out the treatment
             program