Reactivation of pre-existing T cell memory by a LADS-TT vaccine induces potent anti-tumor immunity in cervical and colon carcinoma models

Tetanus toxoid (TT) is a highly immunogenic recall antigen that can reactivate preexisting TT-specific memory T cells. We have previously developed a Listeria -based Live Attenuated Double Substitution (LADS) vaccine platform, engineered to deliver foreign antigens, which is capable of suppressing and preventing tumor formation. In this study, we constructed several LADS-TT strains, which exhibited significantly attenuated virulence (median lethal dose, LD ₅₀  = 1×10 ^9.7 CFU) compared to the wild-type strain (LD ₅₀  = 1×10 ^5.25 CFU). The LADS-TT strains demonstrated a favorable safety profile and tumor tissue tropism. Notably, the strain encoding the long TT fragment (LADS-TT-L) elicited a potent anti-tumor response in a murine cervical cancer model, resulting in a significant reduction in tumor volume compared to LADS, LADS-TT-M (medium fragment) and LADS-TT-S (short fragment) strains. Furthermore, the optimized LADS-TT-L vaccination regimen induced robust anti-tumor efficacy in both murine cervical cancer and colon carcinoma models. This efficacy was associated with the generation of key cytokines and the activation of memory CD8⁺ and CD4⁺ T cells. In conclusion, LADS-TT-L mediates potent anti-tumor immunity by inducing a Th1-type immune response, characterized by cytokine production and the activation of memory T cells within the tumor microenvironment. Our findings highlight a promising strategy for cancer therapy and the prevention of infection diseases.