The development of more effective Mycobacterium tuberculosis vaccines has become a global priority. Previously, researchers demonstrated that recombinant BCG expressing the LTAK63 adjuvant (rBCG-LTAK63) provided better protection against tuberculosis challenge in mice than BCG. They assessed the immune response before and after challenge to elucidate the immune effector mechanisms induced by rBCG-LTAK63. Intraperitoneal immunization with BCG or rBCG-LTAK63 was used to test the ability to induce an innate immune response: both showed increased cellular infiltration in the peritoneum, with high numbers of neutrophils at 24 h and macrophages at 7 days. The rBCG-LTAK63-immunized mice produced more Nitric Oxide after 24 hours and more Hydrogen Peroxide after 7 days. The number of lymphocytes was higher in the rBCG-LTAK63 group than in the BCG group. Immunophenotyping of lymphocytes revealed that immunization with rBCG-LTAK63 increased CD4+ and CD8+ T cells. 90 days after subcutaneous immunization with rBCG-LTAK63, a higher long-term Th1/Th17 cytokine profile was observed. Immune responses at 15 days after challenge revealed that rBCG-LTAK63-immunized mice had more TNF—secreting CD4+ T cells and multifunctional IL-2+ TNF-+ CD4+ T cells than BCG-immunized mice.
In comparison to BCG, the findings indicate that immunization with rBCG-LTAK63 induces stronger innate and long-term immune responses. These findings are consistent with the increased resistance to tuberculosis.