Mycobacterium indicus pranii is a potent immunomodulator for a recombinant vaccine against human chorionic gonadotropin

The objective of this work was to identify a human use-permissible adjuvant to enhance significantly the antibody response to a recombinant anti-hCG vaccine. Previous Phase II efficacy trials in sexually active women have demonstrated the prevention of pregnancy at hCG bioneutralization titers of 50 ng/ml or more. Mycobacterium indicus pranii (MIP), a non-pathogenic Mycobacterium employed as an autoclaved suspension in aqueous buffer, significantly increased antibody titers in the FVB strain of mice. Three other genetic strains of mice: SJL, C3H, and C57Bl/6 responded with antibody titers several-fold higher than 50 ng/ml, which is the protective threshold in women, although there were differences in the peak titers attained. In addition, the duration of the antibody response was lengthened. The vaccine hCGβ-LTB, given together with MIP, induces both a Th1 and Th2 response, which is reflected in the production of not only IgG1, but also a high proportion of IgG2a and IgG2b antibodies.