Effect of immunization with six sperm peptide vaccines on fertility of female mice

Spermatozoon is an exciting target for contraceptive vaccine development. Several sperm antigens (native or recombinant) and sperm peptides cause various degrees of contraceptive effect in female mice. No single antigen/ peptide has shown to cause a complete block in fertility in the mouse model. To enhance the efficacy of the vaccine, six sperm peptides were selected for the present study namely mFA-12,19, mFA-1117136, YLP12, P10G, A9D and SP56. These have been shown to cause > 50% to > 80% reduction in fertility when used individually for immunization. The present study was undertaken to test the hypothesis that the vaccination with all the six peptides together will enhance the contraceptive efficacy by an additive effect resulting in a complete block of fertility in the mouse model. Six vaccines were prepared by conjugating the six synthetic peptides with the recombinant binding subunit of cholera toxin (rCTB). Female CD-1 mice were immunized intramuscularly with all the six peptide vaccines. Each animal received a total of five injections at 2- to 3- week intervals of all of the six vaccines and each vaccine was injected at a separate site. Approximately four weeks after the last injection, the animals were mated. Immunization of each mouse with all six peptides resulted in a dose-dependent inhibition of fertility. At 150 micro g dose, there was an overall 45% reduction compared to controls. Several mice produced antibodies (> or = 2SD units) against these peptides in the serum and the genital tract but the titers were low, and many animals did not respond to several peptides. No animal produced antibodies to all six peptides in serum or the genital tract. When the antibody titers against all six peptides disappeared after > 10 months from circulation and the genital tract, all the animals regained fertility. These findings indicate that the immunization with the six sperm peptide vaccines induce antibodies in serum and the genital tract that cause a reversible long-term contraceptive effect in female mice. The inhibition in fertility was up to 45% rather than a complete block that seems to be due to low antibody titers, especially in the genital tract. It was interesting to note that even with such low titers there was a significant reduction in fertility after immunization with multipeptide vaccine. Multipeptide vaccination is an exciting approach and the present preliminary data warrant further studies.