Construction and evaluation of an engineered autonomously lysing Salmonella system coupled with self-assembled nanoparticles as a vaccine platform for antigen delivery

Live attenuated Salmonella vectors hold great promise for antigen delivery due to their ability to elicit broad mucosal and systemic immunity, but their clinical translation is hindered by safety concerns (e.g., virulence reversion, persistent colonization) and suboptimal antigen release kinetics. Here, we devised and constructed a novel, programmed lysis system in Salmonella based on regulated delayed gene expression and integrated it with self-assembled nanoparticles to create a versatile vaccine platform. This programmed lysis system involved a tse1 gene from Pseudomonas aeruginosa (P. aeruginosa) encoding a peptidoglycan-cleaving lytic effector and a controllable promoter PpagC regulated by Mg²⁺ concentration, and Streptococcus pneumoniae (S. pneumoniae) antigen PspA was used to evaluate this system, which was fused with ferritin (FR) or dihydrolipoyl acetyltransferase (E2p) to self-assembled nanoparticles. The results confirmed Mg²⁺-responsive programmed lysis both in vitro and in vivo and the successful synthesis and assembly of antigen-displaying nanoparticles in S. Typhimurium. Animal studies demonstrated that all engineered autonomously lysing Salmonella strains colonized gut-associated lymphoid tissues equivalently to the control. Notably, this Salmonella vaccine platform showed no significant histopathological signs of virulence in liver or spleen tissues relative to PBS-treated controls. Immunization with the control and this Salmonella vaccine platform elicited robust anti-PspA IgG responses and conferred significant protection against challenge with wild-type S. pneumoniae. Moreover, the nanoparticle-fused constructs (FR and E2p) also induced significant mucosal IgA responses, and the anti-PspA-specific IgG response induced by this Salmonella vaccine platform was significantly higher than that elicited by the non-nanoparticle controls in long-term immune responses. Collectively, our findings establish a programmable lysis-based Salmonella vaccine platform that achieves an optimal balance between the biosafety of attenuated Salmonella and the efficacy of antigen delivery, providing a versatile strategy for next-generation live vector vaccines.