<i>Listeria</i> delivers tetanus toxoid protein to pancreatic tumors and induces cancer cell death in mice

Abstract

Pancreatic ductal adenocarcinoma (PDAC) is a highly metastatic disease. Tumors are poorly immunogenic and immunosuppressive, preventing T cell activation in the tumor microenvironment. Here, we present a microbial-based immunotherapeutic treatment for selective delivery of an immunogenic tetanus toxoid protein (TT_856-1313) into PDAC tumor cells by attenuated <i>Listeria monocytogenes</i>. This treatment reactivated preexisting TT-specific memory T cells to kill infected tumor cells in mice. Treatment of KrasG12D,p53R172H, Pdx1-Cre (KPC) mice with <i>Listeria</i>-TT resulted in TT accumulation inside tumor cells, attraction of TT-specific memory CD4 T cells to the tumor microenvironment, and production of perforin and granzyme B in tumors. Low doses of gemcitabine (GEM) increased immune effects of <i>Listeria</i>-TT, turning immunologically cold into hot tumors in mice. In vivo depletion of T cells from <i>Listeria</i>-TT + GEM-treated mice demonstrated a CD4 T cell-mediated reduction in tumor burden. CD4 T cells from TT-vaccinated mice were able to kill TT-expressing Panc-02 tumor cells in vitro. In addition, peritumoral lymph node-like structures were observed in close contact with pancreatic tumors in KPC mice treated with <i>Listeria</i>-TT or <i>Listeria</i>-TT + GEM. These structures displayed CD4 and CD8 T cells producing perforin and granzyme B. Whereas CD4 T cells efficiently infiltrated the KPC tumors, CD8 T cells did not. <i>Listeria</i>-TT + GEM treatment of KPC mice with advanced PDAC reduced tumor burden by 80% and metastases by 87% after treatment and increased survival by 40% compared to nontreated mice. These results suggest that <i>Listeria</i>-delivered recall antigens could be an alternative to neoantigen-mediated cancer immunotherapy.