Immune response of male baboons to testis-specific LDH-C₄

Four sexually mature male baboons (Papio sp.) were immunized with a chimeric peptide containing a B-cell epitope of the testis-specific lactate dehydrogenase (LDH-C₄) and a promiscuous T-cell epitope of tetanus toxin. LDH-C₄ is the testis-specific isozyme of lactate dehydrogenase, and antibodies to this protein reduce fertility significantly in female nonhuman primates. Animals were immunized on Day 0 and received booster injections at Days 29, 61, and 344 after priming. Serum specific antibodies were determined at regular intervals during the initial 6 months and after the last booster. Testis biopsies were taken at Days 61, 127, and 183 after the primary immunization. Sperm-zona binding was assessed prior to and three times after the last booster. The present study demonstrated that this epitope of LDH-C₄ did not cause autoimmune disease and that sperm from these immunized males had a diminished zona binding capacity. These results suggest that a safe male immunocontraceptive based on development of anti-sperm antibodies may be feasible.