The goal of this clinical research study is to learn how ipilimumab in combination with Lupron (leuprolide acetate) affects the body's own defense (immune) system before having surgery to remove prostate cancer. The safety of the drug combination will also be studied.

The Study Drugs:

Ipilimumab is designed to cause an immune response in your body by blocking 2 specific molecules that usually block an immune response. This may help to kill cancer cells.

Leuprolide acetate is designed to lower the level of testosterone (a male hormone) in the blood. This may slow the growth of cancer cells.

Study Drug Administration:

If you are found to be eligible to take part in this study, you will receive a leuprolide acetate injection in your muscle. This is considered Week 0. One week later, you will begin treatment with ipilimumab. Ipilimumab will be given by vein over 90 minutes during Weeks 1 and 4 (about 21 days apart). During the infusion, your blood pressure will be measured every 30 minutes, and again an hour after you are finished receiving the drug.

Study Visits:

At Weeks 0, 1, 4 and 7, the following tests and procedures will be performed:

• You will have a physical exam, including measurement of your vital signs and weight.
• You will be asked about any drugs or treatments you may be receiving.
• You will be asked about any side effects you may have experienced.
• Your performance status will be recorded.
• Blood (about 7-10 tablespoons) will be drawn for routine tests. This blood will also be tested to measure your protein, PSA and testosterone levels, to check the function of your thyroid and adrenal glands, and to test for an immune response.

Surgery:

About 4 weeks after your second treatment with ipilimumab, you will have surgery to remove your prostate gland. You will be asked to sign a separate consent form that describes the surgery and its risks. A sample of the leftover prostate gland tissue from surgery will be tested for an immune response. On that day, the following tests and procedures will be performed:

Between 14 and 24 weeks after your surgery, you will return to the clinic for your post-operative follow-up visit. The following tests and procedures will be performed:

• You will have a physical exam, including measurement of your vital signs and weight.
• Your performance status will be recorded.
• You will be asked about any drugs or treatments you may be receiving.
• You will be asked about any side effects you have experienced since your last visit.
• Blood (about 7-10 tablespoons) will be drawn for routine tests. This blood will also be used to measure your protein, testosterone and PSA levels, to check the function of your thyroid and adrenal glands, and to test for an immune response.
• You will have a bone scan, and either a CT or MRI scan of your chest, abdomen, and pelvis to check the status of the disease.

Length of Study:

You will only receive 2 treatments with ipilimumab on this study. You will be on study until 24 weeks after surgery. You will be taken off study if intolerable side effects occur, if the disease gets worse, or if the study doctor thinks it is in your best interest to be taken off study.

This is an investigational study. Ipilimumab is not FDA approved or commercially available. Ipilimumab is currently being used for research purposes only. Leuprolide acetate is FDA approved for management of metastatic prostate cancer but is not approved for use before definitive surgery. It is commercially available to treat prostate cancer.

Up to 20 patients will take part in this study. All will be enrolled at MD Anderson.

Inclusion Criteria:

1. Willing and able to give written informed consent;
2. Histologic Documentation: Histologic documentation of prostatic adenocarcinoma. Patients with small cell, neuroendocrine, or transitional cell carcinomas are not eligible. All eligible patients must have a known Gleason sum based on biopsy or TURP at the time of registration.
3. Locally Resectable Disease: Patients must have disease (localized or locally advanced) which is deemed by the surgeon to be resectable. Lymph node metastasis or lymph nodes suspicious of harboring metastasis should be deemed surgically resectable by the surgeon.
4. Determination of high-risk status: Patients must have either: 1) a Prostate biopsy Gleason sum >/= 8 OR 2) PSA >/= 20.
5. Prior Treatment: No prior treatment for prostate cancer including prior surgery (excluding TURP), pelvic lymph node dissection, radiation therapy, or chemotherapy. Patients who have initiated leuprolide acetate within 1 week of signing consent will be eligible.
6. Patients must be appropriate candidates for radical prostatectomy. Evidence of underlying cardiac disease should be evaluated prior to enrollment to ensure that patients are not at high risk of cardiac complications.
7. ECOG performance status of 0 or 1;
8. Required values for initial laboratory tests: a) WBC >/= 3000/uL; b) ANC >/= 1500/uL, c) Platelets >/= 100 x 10^3/uL; d) Hemoglobin >/= 9 g/dL; e) Creatinine </= 2.0 x ULN; f) AST </= 2.5 x ULN; g) Bilirubin 0 - 1.0 mg/dL, except patients with Gilbert's Syndrome, who must have a total bilirubin less than 3.0 mg/mL;
9. Men >/= 18 years of age
10. Patients must agree to practice barrier birth control methods while on therapy, prior to surgery.

Exclusion Criteria:

1. Any other malignancy from which the patient has been disease-free for less than 5 years, with the exception of adequately treated and cured basal or squamous cell skin cancer.
2. Autoimmune disease: Patients with a history of Inflammatory Bowel Disease (including Crohn's disease and ulcerative colitis) are excluded from this study as are patients with a history of autoimmune disease (e.g., rheumatoid arthritis, systemic progressive sclerosis [scleroderma], Systemic Lupus Erythematosus, autoimmune vasculitis [e.g., Wegener's Granulomatosis]).
3. Known HIV or chronic hepatitis.
4. Any underlying medical condition, which in the opinion of the Investigator, will make the administration of study drug hazardous or obscure the interpretation of adverse events, such as a condition associated with frequent diarrhea.
5. Patients who have had a history of acute diverticulitis, intra-abdominal abscess, GI obstruction, abdominal carcinomatosis which are known risks factors for bowel perforation, should be excluded from the study.
6. Any non-oncology vaccine therapy used for prevention of infectious diseases (for up to one month prior to or after any dose of ipilimumab.
7. Concomitant therapy with any of the following: IL-2, interferon or other non-study immunotherapy regimens; cytotoxic chemotherapy; immunosuppressive agents; other investigation therapies; or chronic use of systemic corticosteroids (used in the management of cancer or non-cancer-related illnesses);
8. Previous treatment with other investigational products within 30 days;
9. Previous enrollment in another MDX-010 (BMS-734016) clinical trial or prior treatment with a CD137 agonist or CTLA-4 inhibitor or agonist
10. Concurrent use of 5-alpha-reductase inhibitors (finasteride, dutasteride).
11. Prisoners or patients who are compulsorily detained (involuntarily incarcerated) for treatment of either a psychiatric or physical (e.g., infectious disease) illness must not be enrolled in this study.

Two participants are not included in the demographics, excluded from the study due to screening failure or withdraw prior to being assigned any treatment.

Adverse event collection from baseline until 30 days after the last dose of drug, approximately 14 weeks post surgery.

Two participants of nineteen registered on the study were excluded prior to any treatment assignment due to screen failure and withdrawal, therefore are not included in adverse event reporting.