T-Cell Responses to Neoantigens Post Treatment With Ipilimumab in Men With Metastatic Castration-Resistant Prostate Cancer

Inclusion Criteria: 1. Signed written Informed Consent for this protocol. 2. Agreed to participate in laboratory protocol PA13-0291 for the testing of biomarkers as described in this clinical protocol. 3. Patients included in the study must be \>/= 18 years old. 4. Histologically or cytologically confirmed carcinoma of the prostate. 5. Subjects must have metastatic prostate cancer mass tissue collection within 3 months of study entry. 6. Evidence of metastatic disease on previous bone scan, CT scan and/or MRI. 7. Asymptomatic or minimally symptomatic. 8. Tumor progression while on hormone therapy with castrate levels serum testosterone (\</= 1.7 nmol/L or 50 ng/dL) defined as biopsy-proven, PSA and/or radiographic criteria according to the Prostate Cancer Working Group 2 (PCWG2).Castrate levels of testosterone must be maintained by surgical or medical means throughout the conduct of the study. 9. ECOG performance status \</= 1. 10. Patients must have normal organ and marrow function as defined below: a) WBC \>/= 2500/uL.; b) ANC \>/= 1000/uL.; c) Platelets \>/= 75 x 10\^3/uL.; d) Hemoglobin \>/= 9 g/dL.; e) Creatinine \</= 2.5 x ULN.; f) ALT \</= 2.5 x ULN for patients without liver metastases. For patients with liver metastasis ALT \</= 5 x ULN is allowed.; g) Bilirubin \</= 2.5 x ULN (except for patients with Gilbert's Syndrome, who must have a total bilirubin \</= 3mg/dL). 11. Patient agrees to use adequate contraception (barrier method of birth control) prior to study entry, during therapy and up to 3 months after last dose of ipilimumab. Exclusion Criteria: 1. Treatment with any of the following medications or interventions concomitantly or within 28 days of starting ipilimumab: a.) Systemic corticosteroids. Use of inhaled, intranasal, intra-articular and topical steroids is acceptable, as is a short course (i.e. \</= 1 day) of corticosteroids to prevent a reaction to the IV contrast used for CT scans.; b.) External beam radiation therapy or major surgery requiring general anesthetic.; c.) Any systemic therapy for prostate cancer (with the exception of bisphosphonates and RANK-ligand inhibitors for bone metastases which are allowed) including chemotherapy, secondary hormonal therapies (such as megestrol acetate, diethylstilbestrol, ketoconazole, abiraterone, enzalutamide) and non-steroidal anti-androgens (such as bicalutamide, flutamide or nilutamide).; d.) Immune modulators, cytokines or vaccines for the management of cancer or non-cancer-related illnesses.; 2. (Exclusion Criteria #2 Cont.): e.) Any non-oncology vaccine therapy used for prevention of infectious diseases (for up to one month before any dose of ipilimumab).; f.) Any other investigational product. 3. Use of controlled schedule III controlled substances for cancer-related pain control. 4. Autoimmune disease: Patients with a history of inflammatory bowel disease (including Crohn's disease and ulcerative colitis) and autoimmune disorders such as rheumatoid arthritis, systemic progressive sclerosis \[scleroderma\], Systemic Lupus Erythematosus or autoimmune vasculitis \[e.g., Wegener's Granulomatosis\] are excluded from this study. 5. Any underlying medical or psychiatric condition, which in the opinion of the Investigator, will make the administration of study drug hazardous or obscure the interpretation of AEs, such as a condition associated with frequent diarrhea. 6. Patients with known brain metastases. 7. Uncontrolled intercurrent illness including, but not limited to, ongoing or active infection, history of congestive heart failure, unstable angina pectoris, cardiac arrhythmia, or psychiatric illness/social situations that would limit compliance with study requirements. 8. Known HIV, Hepatitis B, or Hepatitis C. 9. Untreated symptomatic spinal cord compressions. 10. Other malignancies requiring active therapy or known to be associated with altered immune response. 11. Patients who have had a history of acute diverticulitis, intra-abdominal abscess, GI obstruction and abdominal carcinomatosis which are known risk factors for bowel perforation.