Abstract 5116: Inflammasome unleashing during anti-PD-1 therapy modulates CD8+ T cell exhaustion through Th17 cells
Authors: Russo Sofia , Malcuori Mateo , Charbonnier David , Segovia Mercedes , Hill Marcelo 
Published: April 2023

Abstract
PD-1/PD-L1 blockade has greatly improved overall and progression free survival in a variety of cancers. However, only a minority of patients with advanced disease benefit from this approach. We have recently showed that inflammasome unleashing by inhibition of the intracellular cation channel TMEM176B with Boritinib (BayK8644) augments anti-PD-1 efficacy. However, the mechanisms involved were not completely understood. We hypothesized that inflammasome activation triggered by Boritinib may recruit Th17 cells to modulate CD8+ T cell exhaustion. To test this hypothesis, we have analyzed Th17 cells and subsets of exhausted CD8+ T cells in the tumor microenvironment of WT mice treated with anti-PD1 ± Boritinib. Combining Boritinib with anti-PD-1 led to an increased frequency of Th17 cells in the tumor microenvironment compared to anti-PD-1 alone. Furthermore, CD73 expression was down-regulated whereas IFN-γ was up-regulated in Th17 cells in the tumor microenvironment of Boritinib + anti-PD-1 treated mice, suggesting an effector phenotype of these cells. In addition, combination of anti-PD-1 with Boritinib results in an increased frequency of progenitor exhausted CD8+ T cells (CD44+PD-1+TCF1+TOX+) and transitory exhausted CD8+ T cells (CD44+PD-1+TCF1−TOX−CX3CR1+) in the tumor microenvironment compared to anti-PD-1 alone. Similar results were obtained using Tmem176b−/− mice treated with anti-PD-1, suggesting an on-target effect of Boritinib. To assess a potential role of Th17 cells in the anti-tumor immunity triggered by Boritinib + anti-PD-1, we treated WT and Il17a−/− mice. We found that Il17 is necessary for the anti-tumor effect of Boritinib + anti-PD-1, since Il17a−/− mice showed a reduced overall survival compared to WT mice. Under this combined therapy, IL-17 may impact on exhausted CD8+ T cells subsets since we found that transitory and terminally exhausted CD8+ T cells in the tumor microenvironment of Il17a−/− mice had less granzyme B than in WT mice. To directly show the role of Th17 cells in the anti-PD-1 anti-tumor immunity we adoptively transferred in vitro differentiated effector Th17 cells. Adoptive transfer of effector Th17 cells into tumor-bearing mice treated with anti-PD-1 resulted in better survival than mice treated with anti-PD-1 alone. To characterize the downstream mechanisms, we performed an in vivo cytotoxicity assay. We found that mice adoptively transferred with effector Th17 cells exhibited greater cytotoxicity by CD8+ T cells than mice treated with anti-PD-1 alone. Furthermore, this could be explained by an increased frequency in progenitor exhausted CD8+ T cells. Thus, effector Th17 cells potentiate CD8+ T cells on anti-PD-1 treatment. In conclusion, combination of anti-PD-1 with Boritinib augments the efficacy of the former by unleashing the inflammasome which results in an increased frequency of Th17 cells leading to modulation of exhausted CD8+ T cells.
Citation Format: Sofia Russo, Mateo Malcuori, David Charbonnier, Mercedes Segovia, Marcelo Hill. Inflammasome unleashing during anti-PD-1 therapy modulates CD8+ T cell exhaustion through Th17 cells. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 5116.