DISEASE CHARACTERISTICS: Histologically proven hormone refractory adenocarcinoma of the prostate that is asymptomatic Must have soft tissue and/or bony metastases No visceral organ metastases (e.g., liver, lung, brain) or cytologically positive effusions (e.g., pleural effusions or ascites) At least 25% of tumor cells staining positive for prostatic acid phosphatase by immunohistochemistry PSA at least 5 ng/mL Tumor progression after hormonal therapy No cancer related pain and no regular requirement for analgesics

PATIENT CHARACTERISTICS: Age: 18 and over Performance status: ECOG 0 or 1 Life expectancy: At least 16 weeks Hematopoietic: WBC at least 2,000/mm3 Absolute neutrophil count at least 1,000/mm3 Platelet count at least 100,000/mm3 Hemoglobin at least 9.0 g/dL Hepatic: Bilirubin no greater than 2 times upper limit of normal (ULN) ALT and AST no greater than 5 times ULN Hepatitis B surface antigen and hepatitis C antibody negative Renal:

Creatinine no greater than 2.0 mg/dL Other: HIV1, HIV2, and HTLV-1 negative No active bacterial, viral, or fungal infection No other malignancy except:

Basal cell or squamous cell skin cancer within the past 3 years OR Stage I or II other cancers within the past 5 years No psychologic, familial, sociologic, geographic, or other medical condition that would preclude study

PRIOR CONCURRENT THERAPY: Biologic therapy: No prior biologic therapy Chemotherapy: No more than 1 prior chemotherapy regimen Endocrine therapy: See Disease Characteristics More than 1 year since prior corticosteroids except replacement systemic steroids and inhaled, intranasal, or topical corticosteroids No concurrent antiandrogen therapy Concurrent LHRH agonists allowed Radiotherapy: No prior radiopharmaceutical therapy At least 4 weeks since other prior radiotherapy and recovered Surgery: At least 4 weeks since prior surgery and recovered Other: No concurrent herbal therapy Concurrent bisphosphonates allowed if started at least 30 days before enrollment and continued for duration of study