Abstract 55P
Background
In the clinic, immune checkpoint immunotherapy (ICI) is used to re-activate immune reactions against tumor neoantigens, leading to striking remission in cancer patients’ tumors. However, complete or durable responses to ICI treatment only occur in a minority of patients. While the level of tumor mutational burden (TMB) can be used as a predictive marker for responsiveness, we questioned whether the subcellular localization of the neoantigens within the tumor cell additionally plays a role. Using 3 human datasets with 1722 patients treated with ICI, we previously highlighted that patients bearing a high proportion of tumor neoantigens at the membrane of cancer cells responded better to anti-PD1. To decipher underlying immunological mechanisms, we developed a melanoma mouse model that expresses membrane-bound or soluble antigens and analyzed local and systemic anti-tumor immune responses upon anti-PD1 immunotherapy.
Methods
We engineered B16F10 melanoma cells to express membrane-bound or soluble OVA and analyzed intratumoral immune cell infiltration upon implantation in C57BL6 mice. We then compared tumor growth upon anti-PD1 treatment in the wild-type mice or in mice depleted for specific immune cells population. In addition, we compared systemic responses upon tumor implantation via ex vivo antigen-specific restimulation of the splenocytes.
Results
We demonstrated that mice bearing tumors with membrane-bound OVA have increased local and systemic anti-tumor immune reactions compared to soluble OVA, which rendered these tumors highly susceptible to ICI, leading to complete tumor rejection in mice. We additionally observed that tumor rejection was dependent on the level of antigen expressed in the cancer cells, with an increased rejection rate observed for the high dose membrane-bound OVA tumors compared to low ones. We surprisingly found that tumor rejection was independent of immunoglobulin G (IgG), of NK cells and of BatF3+ cross-presenting dendritic cells, and mostly relied on CD8+ T cells cytotoxicity, and partially on CD4+ T cells.
Conclusions
In this study, we show that the subcellular localization of tumor neoantigens plays an important role in the immunogenicity of tumors and subsequent responsiveness to anti-PD1 immunotherapy.
Legal entity responsible for the study
Priscilla S. Briquez, Jeffrey A. Hubbell.
Funding
This work was funded by the Chicago Immunoengineering Innovation Center of the University of Chicago and NIH R01CA219304 (to M.A.S).
Disclosure
All authors have declared no conflicts of interest.