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)