Phase II Study of Sipuleucel-T and Indoximod for Patients With Refractory Metastatic Prostate Cancer

Inclusion Criteria: * Histologically documented adenocarcinoma of the prostate with metastatic disease as evidenced by soft tissue and/or bony metastases on baseline computed tomography (CT) scan of the abdomen and pelvis and/or bone scan * Castration-resistant based on a current or historical evidence of disease progression despite surgical or medical castration as demonstrated by one or more of the following: * PSA progression (defined as two consecutive prostate specific antigen (PSA) measurements at least 14 days apart ≥ 2.0 ng/ml and ≥ 50% above the minimum PSA during castration therapy or above pre-treatment value if no response) * progression of measurable disease based on Response Evaluation Criteria In Solid Tumors (RECIST) criteria (≥ 50% increase in the sum of the cross products of all measurable lesions or the development of any new lesions * progression of non-measureable disease * Serum PSA ≥ 2.0 ng/ml at study enrollment * Castration levels of testosterone defined as ≤ 30 ng/dL at study enrollment. Must be at least 3 months from surgical castration or must have received medical castration therapy for at least 3 months and be receiving such therapy at the time of confirmed disease progression * Asymptomatic or minimally symptomatic disease as demonstrated by Eastern Cooperative Oncology Group (ECOG) Performance Status 0 or 1 and no need for opiate pain medications to control pain/symptoms * Age 18 years and old * Adequate bone marrow, renal and hepatic function within 14 days of study enrollment defined as: * Bone marrow: WBC \> 3,000/uL; absolute neutrophil count \> 1,500/uL; platelets \> 100,000/uL * Renal: creatinine within institutional upper limit of normal (ULN) OR creatinine clearance \> 60 mL/min/1.73 m2 for patients with creatinine levels above ULN * Hepatic: total bilirubin \< 1.5 X institutional ULN; aspartate aminotransferase (AST ((SGOT)) and alanine aminotransferase (ALT((SGPT)) \< 2.5 X institutional ULN Exclusion Criteria: * Chronic steroid dependence (should stop all steroid supplementation 4 weeks prior to enrollment) * Human immunodeficiency virus (HIV)-positive patients and those with other acquired/inherited immunodeficiency * History of gastrointestinal disease causing malabsorption or obstruction such as, but not limited to Crohn's disease, celiac sprue, tropical sprue, bacterial overgrowth/blind loop syndrome, gastric bypass surgery, strictures, adhesions, achalasia, bowel obstruction, or extensive small bowel resection * Inability to take medications by mouth * History of allergic reactions attributed to compounds of similar chemical or biologic composition * Active autoimmune disease, chronic inflammatory condition, conditions requiring concurrent use of any systemic immunosuppressants or steroids. Mild-intermittent asthma requiring only occasional beta-agonist inhaler use or mild localized eczema will not be excluded. * Previous allo-transplant of any kind * History of prior treatment with anti-CTLA4 blocking antibody