PRODUCTION IN ESCHERICHIA-COLI, PURIFICATION AND IMMUNOGENICITY OF ACROSOMAL PROTEIN SP-10, A CANDIDATE CONTRACEPTIVE VACCINE

The testis-specific human sperm antigen, SP-10, has been designated a 'primary vaccine candidate' by the World Health Organization Taskforce on Contraceptive Vaccines. Molecular cloning and sequencing of the cD NAs coding for human (h) and baboon (b) SP-10 have been reported. To p roduce large amounts of pure antigen for ongoing studies of the immuno genicity and anti-fertility effects of SP-10, we used an efficient Esc herichia coli expression system. The full-length open reading frames f or hSP-10 and bSP-10 were placed under the inducible T7 bacteriophage RNA polymerase/promoter system. An in-frame fusion was made such that a His(6) stretch was produced at the C terminus of SP-10. Upon inducti on of gene expression, large amounts of hSP-10 or bSP-10 were synthesi zed and the recombinant (re-) protein segregated into an insoluble fra ction. The protein was then solubilized in 6 M guanidine-HCl and purif ied by immobilized metal affinity chromatography (IMAC). The yield of purified bSP-10 preparation was approx. 20 mu g/ml of culture. Immunor eactivity of the purified re-SP-10 with MHS-10, a monoclonal antibody specific to SP-10, and rabbit polyclonal sera raised against SP-10, in dicated that the synthesized antigen was suitable for immunization stu dies. Four female baboons were then immunized with the re-bSP-10 antig en. Immunoblots using pre-immune and immune sera from these animals in dicated that all four baboons produced antibodies that reacted with na tive SP-10 extracted from human sperm in a manner identical to that of MHS-10, the positive control. Immune sera also stained the acrosome r egion of human and baboon sperm heads by immunofluorescence. These res ults demonstrated that the full-length re-bSP-10 antigen was immunogen ic in female baboons and generated an immune response which recognized the native antigen on the sperm head, indicating that the recombinant antigen is a suitable vaccine immunogen.