Formulation of a potential antipregnancy vaccine based on the beta-subunit of human chorionic gonadotropin (beta-hCG). II. Use of compounds of the muramyl dipeptide (MDP) family as adjuvants

Earlier tests of an antipregnancy vaccine consisting of the beta-subunit of human chorionic gonadotropin (beta-hCG) linked by reaction with a carbodiimide reagent to tetanus toxoid (TT) and adsorbed on Al(OH)3 resulted in antibody responses that were judged inadequate in some women. Experiments were therefore conducted to evaluate the effectiveness of additional adjuvants in increasing the antibody response. Muramyl dipeptide (MDP) and several of its analogs were formulated with the vaccine and tested in rabbits. Some of the analogs, and notably N-acetyl-normuramyl-L-alanyl-D-isoglutamine, elicited substantial increments in the ability of the antisera to bind [125I]hCG and in its ability to neutralize hCG in the rat uterine weight assay. The effectiveness of these peptides was greatest when formulated in a water-in-oil emulsion. Increments of 10 fold were attained using a vegetable oil as the oil component. The MDP analogs were much less effective as adjuvants when formulated in oil-in-water emulsions or in aqueous suspensions of the antigen. It is concluded that selected MDP analogs incorporated in a water-in-vegetable oil emulsion can markedly increase the circulating antibody response to the beta-hCG-TT vaccine.