Sipuleucel-T will be administered as standard of care. Oral Indoximod/placebo will be self-administered twice daily for 6 months starting after the last infusion of sipuleucel-T. Patients will be treated for a minimum of 12 weeks of Indoximod/placebo before disease progression can be declared and Indoximod/placebo will not be discontinued for increasing prostate specific antigen (PSA) in the absence of symptomatic clinical progression.