Scientists at Johns Hopkins University are working on a new form of contraception for women that promises to be safe, long-lasting, convenient to use and, at the same time, to provide protection against sexually transmitted diseases.
The contraceptive agent is a substance made by the human body itself -- an antibody found naturally in infertile women that prevents sperm from reaching the egg. This antibody is cloned and coupled with other cloned human antibodies that protect against a variety of sexually transmitted diseases.
The combination of antibodies would be delivered by a polymer vaginal ring designed to release the antibodies at a low but effective rate for up to several months. The vaginal ring under study is one made of the same kinds of polymers, or chemical compounds, that are used in controlled release systems for many drugs.
The technique is reversible -- if the source of the antibodies is removed, normal fertility should return, according to the researchers.
"Women need better prophylactic methods as well as contraceptive methods and this research may provide an answer," Dr. Richard Cone, the principal investigator, said yesterday.
Antibodies also might be incorporated into a skin lotion or lubricant for use by men in place of a condom to help protect both partners, he said.
The need to tie contraception to the prevention of sexually transmitted disease, particularly AIDS, was stressed by Judy Norsigian, a member of the National Research Council's Committee on Contraception in October at a "Crisis in Contraception" conference at the Johns Hopkins medical complex.
"As we enter an era in which HIV-positivity is becoming more and more important . . . we have to look much more carefully at barrier methods of contraception," Norsigian said. "We cannot look at contraception alone -- in isolation -- any more."
Laboratory studies at the Hopkins Department of Biophysics by Cone and Kevin Whaley, a research scientist, have demonstrated that small doses of the antibody cloned from an infertile woman may provide protection against pregnancy for weeks or even months by preventing sperm from swimming in cervical mucus.
Animal studies at Hopkins have shown that human antibodies against genital herpes virus delivered to the vaginas of mice prevent herpes infections, the researchers said. Similar experiments are under way to develop antibodies that could block the transmission of an AIDS-like disease in cats.
Mark Saltzman, a chemical engineer at the Johns Hopkins School of Engineering with long experience in the design of polymer implants for the release of drugs, has been developing the antibody delivery system.
"Our model is taking the form of a vaginal ring made of polymerof ethylene vinyl-acetate, the same type of polymer long used to make some types of intrauterine devices," Saltzman said.
One of the beauties of the polymer device is that it delivers the antibodies where they are needed, said Cone. "It isn't necessary to flood the entire body with them just to protect the reproductive tract," he said.
Antibodies have many of the most desired properties for long-term contraceptives, the researchers said. Since antibodies occur naturally in all bodily secretions, they should be non-toxic. Antibodies are more potent than the detergents, like nonoxynol-9, now used in vaginal contraceptives. And, the use of antibodies will not cause hormonal changes in the body.
The idea of incorporating a combination of antibodies in a vaginal ring raises many exciting possibilities, Saltzman said.
"We've made a lot of progress putting different sorts of antibodies into polymers and showing that they remain active as they are released," he said. "We can design polymers that release them at basically any rate we want. Potentially, we can mix and match any set of antibodies to provide protection against whatever spectrum of pathogens one might come in contact with."
The research in the use of antibodies in polymer technology is being supported by the National Institutes of Health. Saltzman also is a member of a team investigating the use of the same type of polymer in controlled release into the brain of drugs that show promise in treating Alzheimer's disease, brain cancer and other brain disorders.