PRIOR CONCURRENT THERAPY: Biologic therapy: At least 6 weeks since prior biologic therapy and recovered No other concurrent immunotherapy Chemotherapy: At least 6 weeks since prior chemotherapy and recovered No concurrent chemotherapy Endocrine therapy: See Disease Characteristics Greater than 4 weeks since prior flutamide At least 6 weeks since prior bicalutamide Concurrent gonadal androgen suppression with LHRH analogues allowed unless androgen refractory disease At least 6 weeks since prior steroids No concurrent steroids Radiotherapy: See Disease Characteristics At least 6 weeks since prior radiotherapy to the prostate (12 weeks since strontium 89) and recovered No concurrent radiotherapy Surgery: Prior surgical castration allowed Other: No concurrent immunosuppressants (e.g., azathioprine or cyclosporine)