1.10 Combined TLR/CD40 Stimulation Potentiates an Immunogenic Neoantigen Vaccine

T. Hoki1, T. Yamauchi1, C. A. Eppolito1, A. J. Francois1, K. Odunsi1,2,3, F. Ito1,4,5  1Roswell Park Cancer Institute,Center For Immunotherapy,Buffalo, NY, USA 2Roswell Park Cancer Institute,Department Of Gynecologic Oncology,Buffalo, NY, USA 3Roswell Park Cancer Institute,Department Of Immunology,Buffalo, NY, USA 4State University Of New York At Buffalo,Department Of Surgery, University At Buffalo Jacobs School Of Medicine And Biomedical Sciences,Buffalo, NY, USA 5Roswell Park Cancer Institute,Department Of Surgical Oncology,Buffalo, NY, USA

Cancer neoantigens are derived from nonsynonymous, tumor-specific mutations that create de novo epitopes for T cells, and bypass central thymic tolerance. Although they are highly immunogenic and induce immune responses in humans, the overall success of vaccination studies that target cancer neoantigens has so far been limited. To boost cell-mediated immunity against epithelial tumors, signaling through CD40 has been used with promising results. Toll-like receptor (TLR) agonists have also been implemented as adjuvants. Furthermore, combinatorial stimulation of TLRs and CD40 generates expansion of CD8+ T cells targeting nonmutated self-antigens compared with either agonist alone. However, therapeutic efficacy of combined TLR/CD40 stimulation in the setting of neoantigen vaccine remains elusive. 

To this end, we used murine MC38 colon adenocarcinoma cells that harbor a single-epitope mutation within the Adpgk protein with the neo-epitope presented in MHC-I H-2Db molecules. C57BL/6 mice were inoculated subcutaneously with MC38 cells. MC38 tumor-bearing mice were treated with soluble Adpgk mutant epitope in combination with TLR agonist, anti-CD40 antibody or both. 

Therapeutic vaccination with the Adpgk mutant peptide combined with TLR agonist and an anti-CD40 antibody (TLR/CD40) significantly slowed tumor growth and improved survival. This was associated with expansion and terminal differentiation of CD8+ T cells in the periphery as well as in the tumor microenvironment. Significantly increased terminally differentiated neoantigen-specific CD8+ T cells in blood and spleen were identified using the tetramer staining assay.

These studies provide the rational basis for the use of TLR and CD40 agonists together as essential adjuvants to optimize vaccines designed to elicit therapeutic immunity against cancer neoantigens.