Previously described contraceptive vaccine candidates represent recombinant protein or synthetic peptide immunogens. However, the S19 carbohydrate epitope and other SAGA-1-specific carbohydrate epitopes are components of the sperm glycocalyx, the extracellular matrix of carbohydrate that coats the surface of human spermatozoa. Carbohydrate immunogens provide opportunity for improved immunocontraceptive effects over peptide immunogens as carbohydrate epitopes are more accessible to antibody binding. This is due to the generally protruding character of the carbohydrate chain of a glycoprotein into an aqueous environment, as opposed to short chain peptides or conformational epitopes, which may be obscured or lost depending on the binding conditions.
As more fully described in the parent application, the improvement of available contraceptive methods receives substantially continuous attention. Currently available spermicides employ detergents, specifically, varieties of Nonoxynol-9. The use of this detergent spermicide has been implicated in increasing frequency of urogenital, cervical, and vaginal inflamation in women employing the same. As an alternative, the use of antibodies as "spermicides" has been suggested. See generally Alexander, Scientific American, September: 136-141 (1995).
One antibody studied in terms of its sperm-binding potential is the S19 monoclonal antibody. This monoclonal antibody is described, but not enablingly disclosed, in Anderson et al., J. Reprod. Immunol., 10:1031-257 (1987). This antibody strongly agglutinates human sperm, inhibits tight binding between human sperm and the zona pellucida and blocks sperm penetration of cervical mucus. Mahoney et al., J. Reprod. Immunol., 19:269-285.
The monoclonal antibody of S19 is expressed by the hybridoma cell line deposited at the ATTC, in 10801 University Blvd., Manassas, Va. 20110-2209, USA on Jun. 26, 1996, under accession number HB-12144. This deposit was made pursuant to the Budapest Treaty, and all restrictions thereon will be irrevocably removed upon issuance of a patent on the pending parent application, which has been allowed. Notwithstanding the early publication identifying the existence of the antibody, the same was not made available, or otherwise publicly used or sold, until after the filing of the parent application in June of 1996. The experiments described in Mahoney et al., Supra, were conducted under the control of inventor John Herr, and thus, the S19 monoclonal antibody is the subject of the claims of the parent patent to issue.
While work has continued on topical contraceptives, interest continues in developing a contraceptive vaccine, based on the use of sperm antigens. Decreased fertility rates have been obtained through the immunization of test animals with sperm surface antigens such as LDH-C4, O'Hern et al., Biol. Reprod. 52:331-339 (1995), PH-20, Primakoff et al., Nature 335:543-546 (1988), RSA-1, O'Rand et al., J. Reprod. Immunol. 25:89-102 (1993) and fertilin, Ramarao et al., Mol. Reprod. Dev., 43:70-75 (1995). Unfortunately, as observed in the parent case, the highest rate of efficacy observed in vaccines of this type is about 75% inhibition of fertility. While impressive as an experimental development, this is far below the threshold necessary to provide an acceptable and safe contraceptive vaccine at a level comparable to oral contraceptives and other methods commercially available.