Vaccine Therapy Plus Interleukin-12 in Treating Patients With Metastatic Prostate Cancer That Has Not Responded to Hormone Therapy

DISEASE CHARACTERISTICS: Histologically confirmed metastatic adenocarcinoma of the prostate HLA-A2 positive Progressive measurable systemic disease PSA at least 5 ng/mL with 2 consecutive rising PSA levels at least 1 week apart and no measurable disease OR Objective evidence of disease progression by a 20% increase in the sum of longest diameter of all target lesions or evidence of new lesions by CT or bone scan regardless of PSA status Lesions must be at least 1 cm to be considered measurable Progressive systemic disease after discontinuation of anti-androgen therapy Previously treated with orchiectomy (testosterone less than 50 ng/mL) OR luteinizing hormone-releasing hormone (LHRH) analogue therapy with or without anti-androgens If on LHRH analogue therapy, must continue therapy during study Brain metastases allowed if previously treated, clinically stable, and weaned from prior corticosteroids PATIENT CHARACTERISTICS: Age: Over 18 Performance status: Karnofsky 70-100% Life expectancy: At least 12 weeks Hematopoietic: Absolute neutrophil count greater than 1,500/mm^3 Hemoglobin greater than 9 g/dL Platelet count greater than 100,000/mm^3 No active gastrointestinal bleeding Hepatic: Bilirubin less than 1.5 times upper limit of normal (ULN) SGPT normal Hepatitis B surface antigen negative Renal: Creatinine less than 1.5 times ULN Calcium less than 11 mg/dL Cardiovascular: No significant cardiovascular disease No cardiac arrhythmia requiring therapy Other: Fertile patients must use effective barrier contraception No intrinsic immunosuppression HIV negative No serious concurrent infection No psychiatric illness that would preclude study compliance No clinically significant autoimmune disease No uncontrolled peptic ulcer disease No history of inflammatory bowel disease PRIOR CONCURRENT THERAPY: Biologic therapy: At least 4 weeks since prior biologic therapy Chemotherapy: Not specified Endocrine therapy: See Disease Characteristics At least 4 weeks since prior flutamide At least 6 weeks since prior bicalutamide or nilutamide No concurrent systemic corticosteroids except physiologic replacement doses Radiotherapy: Not specified Surgery: See Disease Characteristics Other: No concurrent immunosuppressive drugs (e.g., cyclosporine)