Abstract A151: Immunotherapy against cancer using iNKT ligands in combination with an attenuated Listeria monocytogenes in humanized mouse models

Listeria monocytogenes (Lm) is a gram-positive bacterium associated with gastrointestinal infections. Initially, infects epithelial cells in the small intestine, then migrates to other organs where it is taken up mainly by phagocytic cells. Once phagocytized, Lm may then be processed in the phagosome to generate peptides presented on MHC Class II for activation of Lm-specific CD4+ T-cell responses. Lm can also escape the phagosome, leading to secretion of protein antigens into the cytosol. These are processed and presented by MHC Class I molecules to CD8+ T-cells, generating strong protective immunity that can clear the infection and prevent subsequent reinfection. Lm has been exploited for its use as a vaccine vector, particularly for the delivery of tumor-associated antigens. Our previous work showed that the efficacy of Lm as an anti-umor therapeutic vaccine could be significantly improved by incorporation of synthetic glycolipid activators of CD1d-restricted invariant natural killer T-cells (iNKT-cells) into the bacteria. Using an attenuated Lm strain expressing the tumor-associated antigen Mage-B, this approach gave improvements in prevention of metastasis in the 4T1 breast carcinoma model in BALB/c mice, and also gave modest reductions in the size of primary tumors. Currently, our efforts are directed at further improving this approach to more effectively target primary tumors, and also at validating the effects in a more humanized experimental models. To this end, we are using two models: 1. human CD1d knock-in (hCD1dKI) mouse line in which the mouse CD1d protein has been replaced by human CD1d, and 2. VaKI mouse, which is a new model made by our lab that is a hCD1dKI mouse that has as a transgene the α-chain of the human iNKT TCR (Vα24Jα18) and is deficient of endogenous murine iNKT-cells due to a murine Jα18 KO. These mice models have diminished percentages of iNKT-cells closely resembling what is seen in most humans, and thus mount iNKT-cell responses that are comparable to those seen in humans. We found that incorporation of iNKT-cell activating glycolipids into Lm leads to improved iNKT-cell-dependent immune responses in our models, and induces synergistic antitumor immune mechanisms against implanted primary syngeneic tumors (B16 F10 and MC38). Besides, administration of iNKT-cell activating glycolipids in association with Lm did not induce anergy or exhaustion of the responding cells, thus enabling repeated treatment to boost antitumor immune responses. Citation Format: Noemi Alejandra Saavedra-Avila, Shalu Sharma, Christopher T. Johndrow, Tony Ng, Claudia Gravekamp, Steven A. Porcelli. Immunotherapy against cancer using iNKT ligands in combination with an attenuated Listeria monocytogenes in humanized mouse models [abstract]. In: Proceedings of the Fourth CRI-CIMT-EATI-AACR International Cancer Immunotherapy Conference: Translating Science into Survival; Sept 30-Oct 3, 2018; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2019;7(2 Suppl):Abstract nr A151.