The primary objectives of the study are to determine the safety and activity of multiple doses of MDX-010 in patients with hormone-refractory prostate cancer (HRPC), and to determine the safety and activity profile of a single dose of cytotoxic chemotherapy (docetaxel) in combination with MDX-010

Inclusion Criteria:

• Clinical diagnosis of adenocarcinoma of the prostate.
• Metastatic prostate cancer (positive bone scan or measurable disease).
• Progressive disease after androgen deprivation.
• No prior chemotherapy or immunotherapy (tumor vaccine, cytokine, or growth factor given to control prostate cancer).

Exclusion Criteria:

• Other prior malignancy, except for adequately treated basal or squamous cell skin cancer or superficial bladder cancer, or any other cancer from which the patient has been disease-free for greater than or equal to 5 years.
• Previous occurrence of autoimmune disease.
• Active infection requiring therapy including HIV or chronic hepatitis.