rBCG::PUMA exhibits enhanced immunogenicity compared to BCG in mice

Tuberculosis (TB), caused by Mycobacterium tuberculosis, remains a major global public health threat. The limited efficacy of the current Bacillus Calmette-Guérin (BCG) vaccine against adult pulmonary TB highlights the urgent need for improved vaccine strategies. To address this, we engineered a recombinant BCG strain, designated rBCG::PUMA, which expresses the pro-apoptotic gene PUMA to enhance immunogenicity.

In mouse models, rBCG::PUMA infection was associated with significantly increased macrophage apoptosis in vitro (p < 0.05). It also elicited a markedly enhanced Th1-biased immune response characterized by elevated levels of IFN-γ, TNF-α, IL-2, and IL-12p70 (p < 0.05), together with reduced secretion of IL-4 and IL-10 (p < 0.05). Immunization with rBCG::PUMA promoted a stronger cellular immune profile, including increased CD8⁺ central memory T cells (TCM) at week 8 post-immunization and elevated CD4⁺ effector memory T cells (TEM), and was associated with sustained upregulation of macrophage costimulatory molecules at week 12 (P < 0.05). Regarding humoral responses, rBCG::PUMA significantly increased titers of PPD-specific total IgG and IgG subclass antibodies (p < 0. 01), accompanied by a persistently Th1-skewed IgG2b/IgG1 ratio. The overall safety profile of rBCG::PUMA was comparable to that of the parental BCG strain.

Enhancement of the apoptotic pathway via PUMA was associated with broader and enhanced immunogenicity of rBCG::PUMA in mice compared with conventional BCG. This included improved cellular immunity, enhanced generation of memory T cell subsets, enhanced macrophage costimulatory activity, and stronger humoral responses, while maintaining a favorable safety profile. However, this study did not include a Mycobacterium tuberculosis challenge model; therefore, protective efficacy remains to be determined. These findings provide a preliminary immunological basis for further evaluation of rBCG::PUMA as a promising immunogenic platform and support the concept of apoptosis-targeted vaccine design.