Abstract PO-040: Integration of anti-TIGIT and anti-Lag3 with NBTXR3-mediated immunoradiation therapy improves abscopal effect and induces long-term memory against cancer

Abstract Introduction: TIGIT and Lag3 are inhibitory receptors expressed on cytotoxic CD8+ T cells and NK cells and directly inhibit the activation and proliferation of these cells. We proposed that blockade of TIGIT and Lag3 could improve antitumor immune response in a mouse model of anti-PD1-resistant mice. Methods: 129Sv/Ev mice were inoculated with 50,000 anti-PD1-resistant 344SQR cells in the right leg on day 0 (primary tumor) and with 50,000 cells in the left leg on day 4 (secondary tumor). Primary tumors were injected with NBTXR3 (radioenhancer nanoparticles) on day 7 and irradiated with 12 Gy on days 8, 9, and 10. Anti-PD1 (200 mg), anti-Lag3 (200 mg), and anti-TIGIT (200 mg) were given to mice by intraperitoneal injections on days 5, 8, 11, 14, 21, 28, 35, and 42. On day 21, primary tumors, secondary tumors, and blood samples were harvested and analyzed with flow cytometry to evaluate changes in immune cell populations. Mice in which tumors were completely eradicated were re-challenged with another 50,000 344SQR cells in the right flank at least two months post radiation; no further treatment was given to these mice, and tumor growth was monitored. Results: The addition of anti-TIGIT, anti-Lag3, or anti-TIGIT+anti-LAG3 to NBTXR3+XRT+anti-PD1 therapy significantly improved control of both primary and secondary tumors, and the addition of anti-TIGIT plus anti-LAG3 also led to fewer spontaneous lung metastases. The addition of either anti-TIGIT or anti-Lag3 to NBTXR3+XRT+anti-PD1 extended the mouse survival time relative to NBTXR3+XRT+anti-PD1. None of the 8 mice in either the NBTXR3+XRT+anti-PD1+anti-TIGIT group or the NBTXR3+XRT+anti-PD1+anti-Lag3 group survived more than 32 days; in contrast, 3 of the 8 mice that received NBTXR3+XRT+anti-PD1+anti-TIGIT+anti-Lag3 survived until the end of the experiment. These surviving mice were found to have developed memory against 344SQR cells, and no further tumor growth was observed after re-challenge. Flow cytometry analysis showed that adding anti-TIGIT+anti-Lag3 to NBTXR3+XRT+anti-PD1 increased the percentages of proliferating CD8+ T cells in primary tumors, secondary tumors, and blood, and increased the percentage of NK cells in the secondary tumors. Conclusions: Blockade of TIGIT and Lag3 with NBTXR3+XRT+anti-PD1 improved CD8+ T-cell proliferation, augmented the antitumor response at both irradiated and unirradiated (abscopal) tumors, and induced potent long-term antitumor memory in mice. Citation Format: Yun Hu, Sebastien Paris, Hampartsoum Barsoumian, Duygu Sezen, Ke Wen He, Mark Wasley, Fatemeh Masrorpour, Peng Liang Yang, Nahum Puebla-Osorio, Maria Angelica Cortez, James Welsh. Integration of anti-TIGIT and anti-Lag3 with NBTXR3-mediated immunoradiation therapy improves abscopal effect and induces long-term memory against cancer [abstract]. In: Proceedings of the AACR Virtual Special Conference on Radiation Science and Medicine; 2021 Mar 2-3. Philadelphia (PA): AACR; Clin Cancer Res 2021;27(8_Suppl):Abstract nr PO-040.