Molecular adjuvant C3d3 improved the anti-hCGβ humoral immune response in vaginal inoculation with live recombinant Lactobacillus expressing hCGβ-C3d3 fusion protein

To enhance the contraceptive efficiency of human chorionic gonadotrophin (hCG)-beta contraceptive vaccine, we coupled hCG-beta gene with molecular adjuvant C3d3, and cloned into live Lactobacilli (Lb.) to express fusion protein hCGβ-C3d3. The recombinant Lb. could survive in BALB/c murine vagina for at least 3 weeks. After inoculating BALB/c and C57BL/6 mice via vagina, we found that the antibody titer peaks induced by the Lb.hCGβ-C3d3 inoculation were higher significantly than the Lb.hCGβ. T and B cells in spleen and vagina were significantly increased, and anti-hCGβ IgG and IgA antibody-secreting cells in uterus and vagina were significantly increased compared to the control in different strain mice. Our study shows that the C3d3 can display apparent adjuvant efficiency to induce more powerful humoral response to the hCGβ antigen in vaginal mucosal immunization.