The effects of immunity induced by BCG priming and tuberculosis fusion protein AMM vaccine boosting

Objective: To investigate the boosting efficiency of a subunit vaccine consisting of the fusion protein Ag85B-Mpt64 _190-198-Mth8.4 (AMM), dimethyl-dioctyldecyl ammonium bromide (DDA) and BCG polysaccharide nucleic acid (BCG-PSN) on the primed inoculation with BCG. Methods: The AMM subunit vaccine was composed of fusion protein AMM, adjuvant DDA and BCG-PSN. The first mouse experimental group was immunized with BCG first, then boosted with the AMM subunit vaccine in the 10th week. The second experimental group was boosted with the AMM subunit vaccine in the 8th week and the 10th week respectively with a two weeks interval after the primed with BCG. Two control groups were treated respectively with physiological saline alone and BCG alone. After the primed inoculation, ELISPOT and ELISA were used for the detection of the cell-mediated and humoral immune response in week 14 and week 22 respectively. Furthermore, the immunized mice were challenged with live BCG to mimic tuberculosis infection in the 22nd week after the primed inoculation. Subsequently the T cell typing and humoral response were detected by flow cytometry and ELISA, respectively. Results: (1) The level of secreting IFN-γ: 14 weeks after the primed inoculation, with the stimulation of the specific antigen-Ag85B, the number of cells secreting IFN-γ in the second experimental group (135±14) was more than BCG alone immunized group (19±16), t=10.98, P<0.01. In the 22nd week, the number of cells secreting IFN-γ in the second experimental group (208±11) was still more than BCG alone group (57±18), t=6.43, P<0.01. (2) The level of humoral immune response: the IgG1 antibody titer in the second experimental group was obviously higher than that in the first experimental group. However, the ratio of IgG2a to IgG1, as the index reflecting the Thl-type immune response, in the experimental group 2 was lower than that in the experimental group 1. (3) The contents of CD4 ⁺ CD25 ⁺ T cells after challenged with live BCG strain: the first and the second experimental groups were both higher than the BCG alone group (t ₁=3.08, t ₂=3.16, (P<0.05). Conclusion: Boosting the BCG-primed mice with tuberculosis AMM subunit vaccine twice can induce higher level of cell-mediated and humoral immune response than BCG alone, which could activate the regulative immune response at the same time.