Inspired by infertility that occurs in some women who develop antibodies against their partner’s sperm, scientists at the University of North Carolina (UNC) are adapting new contraceptives that may offer women a non-hormonal option to prevent pregnancy.

UNC researchers have so far engineered and tested ultra-potent monoclonal antibodies that effectively trapped and blocked more than 99.9% of human sperm. The antibody was isolated from an infertile woman and targets a unique surface antigen present on human sperm; the sperm quickly clump together upon exposure to the contraceptive antibodies.

“Using our highly multivalent IgG platform, we engineered antibodies that were more than 10 to 16 times more potent at agglutinating sperm and reducing sperm permeation through mucus than the best-known antibody,” said Bhawana Shrestha, a doctoral student in the Department of Microbiology and Immunology at the UNC School of Medicine.

In studying the effect of the antibodies in sheep, which have reproductive tracts like human females, the UNC researchers noted that a high dose of 333 micrograms of antibody – both naturally-occurring and newly-engineered antibodies – effectively stopped all human sperm motility; and at a low dose of 33.3 micrograms, the modified antibodies also immobilised 97% to 99% of sperm.

As monoclonal antibodies make for expensive drugs, Professor Samuel Lai, of the Division of Pharmacoengineering and Molecular Pharmaceutics at the UNC Eshelman School of Pharmacy, thinks that second-generation molecules of the same antibodies will be a more affordable solution.

Mucommune, a startup spun out of the Lai Lab, has licensed such a molecule for development of an antibody-based contraceptive – an intravaginal ring that steadily releases the antibodies; or a dissolvable film placed in the vagina where it spreads antibodies before sex.

“There’s a major unmet need for alternative, non-hormonal contraceptives for women […] by avoiding exogenous hormones and creating a women-controlled contraceptive method, we believe the antibodies developed here could meet the contraceptive needs for millions of women, help to reduce the number of unintended pregnancies and alleviate the health care costs of unintended pregnancies which some estimate to be in excess of USD$20 billion a year,” Lai said.

Mucommune will focus on safety and manufacturing to prepare for human clinical trials using said molecule, estimated to start in 2023.

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