An engineered antibody could be a potent non-hormonal contraceptive for women, ensnaring sperm and inactivating them before they can fertilize the egg.<\/p>\n
The antibody was developed from a natural one discovered in an immune-infertile woman by a Japanese group in the 1980s. The engineered antibody was produced in tobacco plants and has six fragment-antigen binding (Fab) arms with an affinity for a glycoprotein found almost exclusively on sperm.<\/p>\n
This PVA film was impregnated with the engineered antibody and it dissolves in aqueous environments releasing its cargo<\/p>\n
It is effective in trapping and aggregating sperm, showing over 10-fold greater potency compared with the parent IgG antibody with two Fabs. \u2018We want sperm to be clumped together so that most remain in the vaginal tract, so few if any can ascend through the cervix and reach the egg,\u2019 says Sam Lai at the University of North Carolina, who led this research.<\/p>\n
The study generated vaginal films, suitable for human use, loaded with engineered antibodies and inserted them into sheep to assess their effect on human sperm motility. The film dissolves in the vagina releasing the antibodies. \u2018Within two minutes we were able to completely agglutinate all the sperm,\u2019 says Lai.<\/p>\n
The strategy offers an alternative to hormonal contraceptives. \u2018Often women don\u2019t want to be on hormonal pills continuously. They have side effects that are disagreeable to many women,\u2019 says Deborah Anderson, a mucosal immunologist at Boston University, US. Another approach is to use spermicides, such as nonoxynol-9. These kill sperm, but their detergent properties can damage mucosal surfaces and increase a woman\u2019s risk of sexually transmitted infections, including HIV.<\/p>\n
Nearly half of all pregnancies in the US, and in many developing countries, are unintended. This is because millions of women avoid available contraceptive methods.<\/p>\n
\u2018The more methods available, and diverse methods, the more likely it is that an individual woman or a couple will find something that works for them,\u2019 says\u00a0<\/span>Richard Anderson, a professor of clinical reproductive science at the University of Edinburgh. Presently, there are no antibody-based contraceptives, though this approach has been pursued for years, he notes. \u2018These never worked, but that is largely because they were systemic, rather than local.\u2019 There were also concerns that vaccination with sperm antigens might lead to permanent infertility in women given such a a jab.<\/p>\n There is an ongoing\u00a0<\/span>exploratory trial\u00a0<\/span>using the natural anti-sperm antibody that began in 2021. \u2018We made our clinical grade antibody about three years ago,\u2019 says Boston University\u2019s Anderson. Her group pursued\u00a0<\/span>the natural antibody\u00a0<\/span>after being advised that \u2018heavily engineered antibodies haven\u2019t been used in clinical applications yet\u2019.\u00a0<\/span>She views the engineered antibody as a second-generation option.<\/p>\n Her trial aims to recruit 15 women with tubal ligation \u2013 and therefore not at risk of pregnancy \u2013 who would then use the antibody film before sex with their partner. They would then report to the clinic for a physician to sample and count motile sperm.<\/p>\n \u2018The data looks promising so far,\u2019 says Anderson. She hopes to begin a phase 3 fertility study in three years and have a commercial product within five years. \u2018This will be an on-demand product that women will use just before sex to prevent unintended pregnancy,\u2019 Anderson says. \u2018It is discrete, it is woman controlled and we hope less expensive than lots of other methods.\u2019 She says it could cost as little as $1 (\u00a30.75) per dose.<\/p>\n