Inclusion Criteria:

• Histologically documented prostate cancer that is progressing following castration. The disease should not be progressing so as to require palliative treatment within 12 weeks of enrollment based on clinical assessment by the investigator. All patients must have assessable disease by radionuclide and/or radiographic studies.
• Castrate levels of testosterone (<50 ng/ml).
• Karnofsky performance status >60%.
• Patients whose initial hormone treatment (exclusive of neoadjuvant hormone therapy) was a combined androgen blockade approach, e.g. an orchiectomy plus an anti-androgen, or gonadotropin releasing hormone analog and an anti-androgen, must show progression of disease following withdrawal of the anti-androgen prior to enrollment.

• Adequate organ function:

  • Hematologic:

    • ANC >1,500/mm3
    • Platelet count >100,000/mm3
  • Hepatic: Bilirubin <1.5 mg/dL and AST<1.5X's the ULN
  • Renal: Creatinine <1.5 mg/dL or creatinine clearance > 60 mL/min.
  • Coagulation: Prothrombin time < institutional UNL.
• Patients must have recovered from the acute toxicities of any prior therapy, and not received chemotherapy, radiation therapy or other investigational anticancer therapeutic drugs for at least 4 weeks prior to entry into the trial.
• Patients must be at least 18 years of age.
• Subjects will be informed as to the potential risk of procreation while participating in this trial and will be advised to use effective contraception during the entire study period.
• Patients must sign an informed consent indicating that they are aware of the investigational nature of this study in keeping with the policies of the institution.

Exclusion Criteria:

• Clinically significant cardiac disease (New York Heart Association Class III or IV), or severe debilitating pulmonary disease.
• Active CNS or epidural primary tumor or active CNS or epidural metastases.
• An active uncontrolled infection or an infection requiring intravenous antibiotic treatment.
• Participation in another therapeutic clinical trial with an experimental drug, concurrently or within the 4 weeks prior to dosing in this study.
• Lack of recovery from the myelosuppressive effects of prior radiation therapy or chemotherapy.
• Patients who have undergone diagnostic ProstaScint, Myoscint, or Oncoscint scans, or have undergone any other prior administration of a murine protein for diagnostic or therapeutic purposes, without regard to HAMA test results.
• Patients with a history of autoimmune hepatitis or history of autoimmune disease.
• Prior radiation therapy encompassing >25% of the bone marrow
• Prior systemic administration of a therapeutic radiolabeled monoclonal antibody.
• Patients who are unwilling to use a condom (even if they have undergone a prior vasectomy) while having intercourse, while taking the drug and for 4 weeks after stopping treatment.