Tumor-targeted delivery of Tetanus toxoid by Listeria improves immunotherapy against ovarian cancer in mice.

Ovarian cancer is known for its poor neoantigen expression and strong immunosuppression. Here, we utilized an attenuated non-pathogenic bacterium delivering a highly immunogenic Tetanus Toxoid protein (Listeria-TT), as a neoantigen surrogate, inside tumors through infection in a metastatic mouse ovarian cancer model (Id8p53-/- Luc). Gemcitabine (GEM) was added to reduce immune suppression. Listeria-TT+GEM treatments resulted in tumors expressing TT and reactivation of pre-existing CD4 and CD8 memory T cells to TT (generated early in life), which were then attracted to the TT-expressing tumors and producing granzyme B and perforin. This correlated with a strong reduction in the ovary tumors and metastases, and a significant improvement of the survival time compared to all control groups. Moreover, two treatment cycles with Listeria-TT+GEM doubled the survival time compared to untreated mice. Checkpoint inhibitors have little effect on ovarian cancer partly because of low neoantigen expression. We evaluated if delivery of TT by Listeria to the TME improved the effect of anti-PD1 antibodies. We found that Listeria-TT+GEM+PD1 was significantly more effective (efficacy and survival) than PD1 or Listeria-TT+GEM alone, and that more treatment cycles with Listeria-TT+GEM+PD1 significantly increased the survival time compared to Listeria-TT+GEM alone. In summary, the results of this study suggest that our approach may benefit ovarian cancer patients.