A DNA vaccine for the treatment of prostate cancer, comprising a plasmid vector comprising a nucleotide sequence encoding SSX-2 operably linked to a transcription regulatory element, wherein upon administration to a mammal a cytotoxic immune reaction against cells expressing SSX-2 is induced. In one embodiment, the SSX-2 encoded is a xenoantigen highly homologous to the autoantigen SSX-2 of the mammal. Also disclosed are methods for inducing immune reaction to SSX-2, or treating prostate cancer in a mammal, using the DNA vaccine and pharmaceutical compositions comprising the vaccine. In one embodiment, xenoantigen vaccination is followed by boosting with autoantigen SSX-2 from the same animal species as the mammal being treated.