Development and Characterization of Monoclonal Antisperm Antibodies: Potential for Contraception

There is an expressed need to develop a greater variety of safe contraceptive methods which would find acceptance worldwide, particularly in developing countries. Immunization against spermatozoa might be such a method as judged by the accumulated evidence from studies on human females and in a number of female animal species. Two extraction techniques were used for sperm membrane antigen isolation. The first technique involved NP-40 detergent for antigen extraction from human motile sperm and the second technique employed homogenized human testis for antigen extraction. Using these immunogens, sperm membrane-specific monoclonal antibodies (MAbs) were developed. When these antisperm MAbs were subjected to evaluation against an extensive panel of human tissues, no cross-reactivity to somatic tissues was observed, but staining was seen on sperm cells in testis, caput- and cauda epididymis, and vas deferens. Four of these antisperm MAbs were against epididymal antigens, three were against seminal vesicle factors, and seven were against testis specific antigens. These evaluations indicated sperm specificity of these antibodies, fulfilling one of the important criteria for contraceptive vaccine development set forth in a World Health Organization (WHO) monoclonal antibody workshop report. The results of immunofluorescence (IF) and immunochemical staining (ICS) studies on methanol-fixed sperm indicated that these antibodies recognized antigens on the plasma membrane overlaying different regions of the sperm, i.e., acrosome, postacrosome, equatorial, midpiece, and tail. When these anti-sperm MAbs were tested on fresh, capacitated, and acrosome reacted spermatozoa, a differential reactivity with fresh sperm as compared to acrosome reacted sperm was observed. The wide species cross-reactivity of these antisperm antibodies indicated shared antigens in these species, raising the possibility of employing experimental animal models to test contraceptive vaccines. These antisperm MAbs demonstrated the multiplicity of antigens having a role in the process of fertilization. Eight of these antisperm MAbs were able to inhibit at least one sperm functional test in vitro, which satisfied another criterion for immunocontraceptive vaccine development. Since one MAb (DH22) was capable of binding to the acrosomal cap region of acrosome reacted sperm, this MAb could be used as a marker to identify acrosomal reacted sperm among the different matured stages found in a sperm population. Purification and biochemical characterization of these sperm antigens to which these antisperm MAbs were directed, would be of interest to better understand their immunocontraceptive potential