Inoculation of Lactobacillus expressing hCG beta in the vagina induces an anti-hCG beta antibody response in murine vaginal mucosa.

Objectives: To test the possibility of vaccination with lactobacillus expressing hCG beta antigen administered by vaginal mucosal immunization.

Methods: A plasmid pIlac-hCG beta was constructed and then transfected into Lactobacillus casei CECT5276, which stably expressed hCG beta protein. RIA was used to detect hCG beta in the culture supernatant and cell lysate. Western blotting was performed to evaluate the expressed protein of interest. Female BALB/c mice aged 6-8 weeks received inoculations in the vagina of the recombinant L. casei CECT5276. ELISA was used to determine the anti-hCG beta IgA antibody in vaginal lavage fluid from the BALB/c mice after vaginal mucosal immunization.

Results: The pIlac alone appeared to have a higher efficiency than pIlac-hCG beta, and the highest transfection efficiency of both plasmids was at pulse voltages of 1200 V and 1500 V. About 78.5% of the hCG beta protein was excreted into the culture supernatant. Excretion of hCG beta was most efficient when the pH of the culture medium was adjusted to around 7.0 and the concentration of lactose was around 1%. The hCG beta protein in the vaginal lavage fluid of these BALB/c mice was positive on the third day after vaginal inoculation. Anti-hCG beta IgA antibody continued to be found in the vaginal lavage fluid for 2 weeks following a booster vaginal inoculation. The splenic lymphocytes of the mice immunized with hCG beta through the vagina underwent a proliferative reaction to hCG antigen restimulation in vitro. Interferon gamma (IFN-gamma) and interleukin (IL)-4 were secreted at higher levels after vaginal mucosal immunization of L. casei expressing hCG beta than after vaginal mucosal immunization of L. casei alone.

Conclusions: Vaginal immunization of lactobacillus expressing hCG beta induced an anti-hCG beta antibody response in the murine vaginal mucosa. Induction of the antigen-specific antibodies in the reproductive tract following vaginal inoculation of recombinant lactobacillus will lead to the development of a safe, efficient, and easy-to-use form of immunocontraception.