DISEASE CHARACTERISTICS: Histologically confirmed prostate carcinoma For Phase I: progressive, androgen-independent disease required, i.e.: Elevated PSA despite castrate testosterone levels (below 50 ng/dl) documented on 3 successive occasions For Phase II: progressive disease after surgery or radiotherapy without prior hormonal therapy also eligible HLA-A1- or HLA-A2-positive disease required Measurable or evaluable disease required No active CNS metastases