The Tumor Recall Response of Antitumor Immunity Primed by a Live, Recombinant Listeria monocytogenes Vaccine Comprises Multiple Effector Mechanisms

Listeria monocytogenes, a facultative intracellular bacterium, can induce a potent antitumor immune response if engineered to express a model tumor antigen also expressed by the tumor cells. The effectiveness of this approach is dependent on L. monocytogenes-induced tumor-specific CD4+ and CD8+ T-cells. CD8+ T-cells may mediate tumor eradication largely through direct CTL activity, but the role of CD4+ T-cells and other cells of the immune system is less clear. Here we investigate their role and the role of the cytokines they produce in the ability of L. monocytogenes-induced antitumor immunity to protect against tumor challenge. Our results suggest that a complex cytokine response, involving type 2 as well as type 1 cytokines, is responsible for the ability of Lm-NP-immunized mice to resist tumor challenge, potentially mediating tumor cell killing through multiple effector pathways.