Development of antifertility vaccine using sperm specific proteins

Sperm proteins are known to be associated with normal fertilization as auto- or iso-antibodies to these proteins may cause infertility. Therefore, sperm proteins have been considered to be the potential candidate for the development of antifertility vaccine. Some of the sperm proteins proved to be promising antigens for contraceptive vaccine includes lactate dehydrogenase (LDH-C4), protein hyaluronidase (PH-20), and Eppin. Immunization with LDH-C4 reduced fertility in female baboons but not in female cynomolgus macaques. Active immunization with PH-20 resulted in 100 per cent inhibition of fertility in male guinea pigs but it induced autoimmune orchitis. Immunization with Eppin elicited high antibody titres in 78 per cent of immunized monkeys and induced infertility but the immunopathological effect of immunization was not examined. Human sperm antigen (80 kDa HSA) is a sperm specific, highly immunogenic and conserved sperm protein. Active immunization with 80 kDa HSA induced immunological infertility in male and female rats. Partial N-terminal amino acid sequence of 80 kDa HSA (Peptide NT) and its peptides (Peptides 1, 2, 3 and 4) obtained by enzymatic digestion did not show homology with any of the known proteins in gene bank. Peptides NT, 1, 2 and 4 were found to mimic immunobiological activity of native protein. Passive administration of antibodies to peptides NT, 1, 2 and 4 induced infertility in male and female rats and peptide 1 was found to be most effective in suppressing fertility. Active immunization with keyhole limpet haemocynin (KLH) conjugated synthetic peptide 1 impaired fertility in all the male rabbits and six of the seven male marmosets. The fertility was restored following decline in antibody titre. All these findings on 80 kDA HAS suggest that the synthetic Peptide-1 of 80 kDa HSA is the promising candidate for development of male contraceptive vaccine.