General Inclusion Criteria:

          -  Male participants; age ≥ 18 years

          -  Metastatic castrate-resistant prostate cancer while on anti-androgen treatment with
             castrate levels of testosterone (≤1.7 nmol/L or 50 ng/dL)

          -  Measurable or non-measurable disease as per radiographic evaluation

          -  Participants with measurable disease may require a fresh tumor biopsy at study entry

          -  Performance status of 0 or 1

          -  Life expectancy of at least 3 months

          -  Adequate hematologic and end-organ function

          -  Inclusion Criteria for Participants receiving an enzalutamide-containing treatment

               -  Disease progression after prior treatment with abiraterone

          -  Inclusion Criteria for Participants receiving a docetaxel-containing treatment

               -  Disease progression after prior androgen synthesis inhibitor therapy

          -  Inclusion Criteria for all other Participants

               -  Disease progression after prior androgen synthesis inhibitor treatment and up to
                  2 prior lines of taxane chemotherapy

        General Exclusion Criteria:

          -  Prior treatment with immune checkpoint blockade therapy

          -  Prior anticancer treatment including approved agents, systemic radiotherapy, or
             investigational therapy, within 2-4 weeks prior first study treatment

          -  ECG (Electrocardiogram) result with QTcF ≥480 msec

          -  Prior stem cell or solid organ transplantation

          -  Prior treatment with drugs that stimulate the immune system within 4 weeks prior to
             first study treatment

          -  Prior treatment with drugs that suppress the immune system within 2 weeks prior to
             first study treatment

          -  Received a live, attenuated vaccine within 4 weeks prior to first study treatment, or
             may need to receive a vaccine during study treatment

          -  Presence of metastases in the brain or cancer spreading into the cerebrospinal fluid -
             CSF (leptomeningeal disease)

          -  Prior pulmonary fibrosis, pneumonia, or pneumonitis

          -  Cancer other than prostate within 2 years prior to study entry, except for some
             cancers with a low risk of spreading like non-melanoma skin

          -  Prior treatment with an agent targeting the adenosine pathway

          -  No oral or IV antibiotics within 2 weeks prior to first study treatment

          -  No severe infection within 4 weeks prior to first study treatment

          -  No clinically significant cardiac disease

          -  Inability to swallow oral medications

          -  HIV, Hepatitis B, and C test results negative prior to first study treatment

          -  Exclusion Criteria for Participants receiving an enzalutamide-containing treatment

               -  Prior treatment with docetaxel, cabazitaxel, or other taxane chemotherapy (prior
                  docetaxel [up to 6 cycles] for hormone-sensitive prostate cancer is allowed if
                  the last dose was at least 6 months prior to study treatment initiation)

               -  Prior treatment with enzalutamide or similar therapy other than abiraterone

               -  Active or history of autoimmune disease or immune deficiency

               -  History of severe allergic reactions to antibody therapy

               -  Concomitant use of a medication prohibited by the protocol (including certain
                  transporter substrates as well as known strong CYP3A4 inducers and CYP3A4
                  inhibitors) within 4 weeks prior to and throughout study treatment

          -  Exclusion Criteria for Participants receiving a docetaxel-containing treatment

               -  Prior treatment with docetaxel, cabazitaxel, or other taxane chemotherapy

               -  Active or history of autoimmune disease or immune deficiency

               -  History of severe allergic reactions to antibody therapy

               -  Concomitant use of a medication prohibited by the protocol (including certain
                  transporter substrates as well as known strong CYP3A4 inducers and CYP3A4
                  inhibitors) within 4 weeks prior to and throughout study treatment

          -  Exclusion Criteria for all other Participants

               -  Prior treatment with 3 or more lines of taxane chemotherapy

               -  Active or history of autoimmune disease or immune deficiency

               -  History of severe allergic reactions to antibody therapy

               -  Concomitant use of a medication prohibited by the protocol (including certain
                  transporter substrates as well as known strong CYP3A4 inducers and CYP3A4
                  inhibitors) within 4 weeks prior to and throughout study treatment