REVERSIBLE CONTRACEPTIVE EFFECT OF PH-20 IMMUNIZATION IN MALE GUINEA-PIGS

Sperm proteins are currently being studied as antigens on which to bas e a contraceptive vaccine. Sperm plasma membrane proteins offer the th eoretical possibility of immunizing either males or females and achiev ing a contraceptive effect. In this study, we investigated the sperm p lasma membrane protein PH-20 as an antigen for inducing infertility in males. We found that infertility can reproducibly be induced in male guinea pigs immunized with purified PH-20: 100% (29 of 29) of PH-20-im munized males became infertile, whereas all 22 controls were fertile. The males were extremely responsive to PH-20 immunization: infertility could be induced with a single injection of only 5 mu g PH-20. Among males that received their initial injection when they were similar to 300 g (body weight), 14 of 15 had regained fertility at about 1 yr aft er initial injection. Surprisingly, in another group of males that rec eived their first injection when they were similar to 650 g (body weig ht), only 1 of 5 had regained fertility about 1 yr after initial injec tion. Anti-PH-20 titers in antisera (2 mo after initial injection) wer e generally in the range 1.1-4.2 x 10(4) in twice-injected males and t he range 1.8-9.4 x 10(3) in once-injected males. Over the next 6-11 mo , twice-injected males' titers decreased greater than or equal to 4-fo ld, whereas once-injected males' titers decreased slightly (1.1- to 1. 8-fold). After 6-11 mo, anti-PH-20 titers were in the range 1.0-4.8 x 10(3), and the precise residual titer did not correlate with fertility /infertility. The results show that immunization of males with PH-20, even at low doses, results in a reproducible, completely effective con traceptive action.