Inclusion Criteria:

          -  Histologically confirmed adenocarcinoma of the prostate (clinical stage T1c-T3b, N0,
             M0) without involvement of lymph nodes, bone, or visceral organs

          -  Initial prostate biopsy is available for central pathologic review, and is confirmed
             to show at least 2 positive cores and a Gleason sum of ≥7

          -  Radical prostatectomy has been scheduled at Johns Hopkins Hospital

          -  Age ≥18 years

          -  ECOG performance status 0-1, or Karnofsky score ≥ 70% (see Appendix A)

          -  Adequate bone marrow, hepatic, and renal function:

               -  WBC >3,000 cells/mm3

               -  ANC >1,500 cells/mm3

               -  Hemoglobin >9.0 g/dL

               -  Platelet count >100,000 cells/mm3

               -  Serum creatinine <1.5 × upper limit of normal (ULN)

               -  Serum bilirubin <1.5 × ULN

               -  ALT <3 × ULN

               -  AST <3 × ULN

               -  Alkaline phosphatase <3 × ULN

          -  The etiology of abnormal bilirubin and transaminase levels should be evaluated prior
             to study entry.

          -  Willingness to provide written informed consent and HIPAA authorization for the
             release of personal health information, and the ability to comply with the study
             requirements (note: HIPAA authorization will be included in the informed consent)

          -  Willingness to use barrier contraception from the time of first dose of MGA271 until
             the time of prostatectomy.

        Exclusion Criteria:

          -  Presence of known lymph node involvement or distant metastases

          -  Other histologic types of prostate cancers such as ductal, sarcomatous, lymphoma,
             small cell, and neuroendocrine tumors

          -  Prior radiation therapy, hormonal therapy, biologic therapy, or chemotherapy for
             prostate cancer

          -  Prior immunotherapy/vaccine therapy for prostate cancer

          -  Prior use of experimental agents for prostate cancer

          -  Concomitant treatment with other hormonal therapy or 5α-reductase inhibitors

          -  Current use of systemic corticosteroids or use of systemic corticosteroids within 4
             weeks of enrollment (inhaled corticosteroids for asthma or COPD are permitted as are
             other non-systemic steroids such as topical corticosteroids)

          -  History or presence of autoimmune disease requiring systemic immunosuppression
             (including but not limited to: inflammatory bowel disease, systemic lupus
             erythematosus, vasculitis, rheumatoid arthritis, scleroderma, multiple sclerosis,
             hemolytic anemia, Sjögren syndrome, and sarcoidosis)

          -  History of malignancy within the last 3 years, with the exception of non-melanoma skin
             cancers and superficial bladder cancer

          -  Uncontrolled major active infectious, cardiovascular, pulmonary, hematologic, or
             psychiatric illnesses that would make the patient a poor study candidate

          -  Known prior or current history of HIV and/or hepatitis B/C