A STRATEGY FOR IDENTIFYING CANDIDATE SPERM ANTIGENS FOR IMMUNOCONTRACEPTION - ISOLATION OF HUMAN TESTIS CDNA CLONES USING POLYCLONAL ANTISERA DIRECTED AGAINST HAMSTER ACROSOMAL MEMBRANE PREPARATION

Components of the mammalian sperm acrosome that have been conserved du ring evolution are probably essential for fertilization and are theref ore potential antigens for the development of an immunocontraceptive v accine. In order to identify such protein components, a series of spec ific polyclonal antisera were generated by immunizing rabbits with pur ified acrosomal membrane fractions from hamster epididymal spermatozoa . Antisera were finally selected using immunological and in-vitro fert ilization assays, and used to then screen a human testis lambda gt11 c DNA library. As a result of this screening over 70 clones were identif ied, selected and purified. The cDNAs were amplified by polymerase cha in reaction (PCR) and the inserts characterized by restriction enzyme digestion and oligonucleotide probing techniques. The functional activ ity of beta-galactosidase fusion proteins expressed by these clones wa s tested by a hamster in-vitro fertilization assay (IVF). Fusion prote in from three clones (HA5-2, HA6-2 and HB4-1) inhibited significantly fertilization and reduced sperm-zona binding compared to controls. To date, sequence data has been obtained from HB4-1 (1.75 kb). The first 1132 nucleotides displayed > 96% homology to human testis-specific lac tate dehydrogenase (LDH-C4) gene, the product of which is a known cand idate antigen for a contraceptive vaccine. This finding suggests that a strategy involving the screening across species for conserved moieti es of the mammalian acrosome may be useful for identifying candidate a ntigens for immunocontraception.