Observations on the antigenicity and clinical effects of a candidate antipregnancy vaccine: beta-subunit of human chorionic gonadotropin linked to tetanus toxoid.

Vaccines for control of fertility are likely to have an important impact on family planning methods. They are designed to act by mobilization of an internal physiological process and do not require external medication on a continuous basis. A number of birth control vaccines are at different stages of development, the most advanced being a vaccine inducing antibodies against human chorionic gonadotrophin (hCG). This vaccine consists of a heterospecies dimer (HSD, beta hCG associated with alpha-subunit of ovine luteinizing hormone, beta hCG:alpha oLH) linked to tetanus toxoid (TT) or diphtheria toxoid (DT) as carriers. The vaccine has recently passed an important milestone; it has completed the first leg of phase II efficacy trials. Women of proven fertility leading active sexual life were protected from becoming pregnant at antibody titres > or = 50 ng of hCG bioneutralization capacity per ml. This vaccine has previously been demonstrated to be reversible in its effect. It is free from any notable side-effects on endocrine, cardiovascular and other body functions. Ovulation was not disturbed and menstrual regularity was maintained. A logistic disadvantage of the present vaccine is the requirement for multiple injections. This is expected to be overcome by encapsulation of the requisite doses of the vaccine in biodegradable microspheres, which could be given at a single contact point for sustained antibody titres lasting over a year. A live recombinant vaccine has also been made that elicits high anti-hCG titres in monkeys for nearly 2 years following primary immunization and a booster at 8-9 months.

A birth control vaccine is on the horizon for family planning.

The possibility of inducing antibodies against reproductive tract antigens by deliberate immunization was indicated as early as 1899 by the pioneering work of Landsteiner (14) and Metchinikoff (15). These leaders of immunology did obtain antisera toxic to sperm. However, the practical utility of this lead for control of fertility could not materialize owing to several factors. Crude tissue extracts induced antibodies reactive to unwanted tissues with potential toxicity hazards. Not enough was known of the immune processes and the manner in which these could be modulated to advantage. Furthermore, for antigens localized on sperm, it would be necessary to ensure the right type of immune reactions in the genital tract for preventing fertilization; antibodies in systemic circulation alone may not suffice.

Birth control vaccines inducing antibodies against chorionic gonadotropin.

Contraception as a socially aceptable custom is by and large a 20th century phenomenon and is now perceived by many as a solution to a pressing world problem - that of overpopulation. As Shakespeare states in quotations above, we can define accurately what we would like to accomplish, but the achievement is often easier said than done. Such sentiments describe very well the state of the art as far as contraception is concerned. Most thinking people, and indeed many governments, see a reduction of the birth rate as the most significant way to achieve economic progress and to raise the standard of living in their countries commensurate with the expectations of their citizens. It is clear that we, the peoples of the world, have a choice, either we can reproduce until resources become insufficient to support us or we can take steps to control reproduction and achieve the desirable goal of zero population growth. Zero growth is defined as that state where the number of births and deaths are equal.

C.R. Prasad

Papers

Acute toxicity and pharmacology of β-human chorionic gonadotrophin conjugated tetanus toxoid (Pr-β-HCG-TT)