University of North Carolina at Chapel Hill Graduate School
Doi
Abstract
Nearly half of all pregnancies in the United States are unintended, due to poor adoption of existing methods of contraception, the majority of which are hormonal methods. Naturally occurring sperm-binding antibodies prevents fertilization in immune infertile women by trapping motile sperm in mucus through agglutination and mucin-crosslinking, thereby preventing sperm from reaching the egg. Indeed, vaginal delivery of sperm agglutinating IgM in the highly fertile rabbit model reduced embryo formation by 95%. This led us to explore the direct vaginal delivery of sperm-binding monoclonal antibodies as a strategy for effective non-hormonal contraception. In this dissertation, I worked to 1) Engineer a panel of multivalent IgGs possessing 4-10 Fabs against a unique surface antigen universally present on human sperm, 2) Assess the agglutination and trapping potency of all multivalent IgGs in vitro and in vivo, 3) Develop self-dissolving intravaginal film comprising of hexavalent sperm-binding IgG (6 Fabs per molecule; termed as “FIF”) produced in cGMP-compliant Nicotiana-expression system and 4) Evaluate the potency of FIF-Film in reducing progressively motile sperm in the sheep vagina. Our results indicated that all multivalent IgGs produced at comparable yields and possessed identical thermal stability and homogeneity to the parent IgG. All multivalent IgGs were markedly more potent and faster at agglutinating sperm than the parent IgG, while preserving Fc-mediated crosslinking of individual spermatozoa in mucus. Especially, the highly multivalent IgGs (HM-IgGs; 6-10 Fabs per molecule) were at least 10- to 16-fold more potent and faster at agglutinating sperm than the parent IgG. The increased potencies translated to effective (>99.9%) reduction of progressively motile sperm in the sheep vagina using just 33 micrograms of the 10-Fab HM-IgG per sheep. Similarly, the polyvinyl alcohol-based water-soluble contraceptive film formulated with Nicotiana-expressed 6-Fab HM-IgG enabled complete agglutination of all progressively motile sperm within 2 mins in the sheep vagina. These results not only underscore the potential of multivalent contraceptive antibodies to provide safe, effective, on-demand non-hormonal contraception but also represent a promising platform for generating potent agglutinating mAb for diverse medical applications such as anti-bacterial therapeutics.Doctor of Philosoph
