Abstract 2367: STING agonist ADU-S100 improves the antitumor response of CLDN18.2/CD3 BiTEs by enhancing stem-like tumor-reactive CD8+ T cells in pancreatic adenocarcinoma

Abstract Background: Immunotherapy with CLDN18. 2/CD3 BiTEs (bispecific T-cell engagers) has shown clinical activity in pancreatic adenocarcinoma. However, only few patients benefit from the treatment, and most responders develop acquired resistance. STING agonists may promote the development of stem-like central memory CD8+ T cells and enhance antitumor responses. This study aimed to investigate the synergistic effect and related mechanism of STING agonist plus CLDN18. 2/CD3 BiTEs regimen. Methods: Single-cell RNA sequencing and flow cytometry were used to examine the tumor immune landscape in humanized PDX mouse models. By qPCR, western blot and flow cytometry, an orthotopic transplantation mouse model of pancreatic cancer and an in vitro tumor-PBMC coculture system were established to reveal the potential molecular mechanism of STING agonist ADU-S100 in optimizing the effects of CLDN18. 2/CD3 BiTEs (IBI389). Results: In PDAC organoids, IBI389 induced potent, specific cytotoxicity, the CLDN18. 2 BiTEs significantly engaged human CD3+ T cells with tumor cells in an organoid-PBMC coculture system in vitro, resulting in the formation of the immunological synapse (IS). IBI389 monotherapy significantly suppressed tumor growth and improved survival in vivo in hCD3e C57BL/6 and humanized hCD34+ PDX mouse models. Further, single-cell RNA sequencing and flow cytometry analysis revealed that the intertumoral TCF1+PD-1+ stem-like T cells and STING signaling activity of T cells were enriched in the early stage of tumor development and sharply decreased in the late stage during CLDN18. 2 BiTEs administration. Furthermore, we discovered that the STING agonist ADU-S100 could significantly induce the enrichment of TCF1+PD-1+ stem-like CD8+ T cells in vitro and in vivo, increasing IBI389’s therapeutic effects. Furthermore, humanized PDX mice that were given the combination of IBI389 and ADU-S100 and survived after complete tumor rejection were rechallenged with PDX tumors. Humanized PDX tumors and hCD3e KPC orthotopic tumors from mice treated with the combination contained increased numbers of TCF1+PD-1+ stem-like CD8+ T cells, CD4+CD127+ memory T cells, CD8+CD127+ memory T cells, and fewer numbers of CD4+PD-1+Tim-3+ exhausted T cells, CD8+PD-1+Tim-3+ exhausted T cells and CD4+CD25+ Treg cells. Conclusions: Pancreatic tumors appear to evade immune response by inducing immune-suppressive tumor microenvironment development. In mice, the combination of STING agonist ADU-S100 and CLDN18. 2 BiTEs increased the proportion of memory and stem-like CD4+ and CD8+ T cells while decreasing the proportion of regulatory and exhausted T cells in pancreatic tumors, eradicating all detectable tumors. This data may be utilized to formulate immune-based combination therapies for PDAC. Citation Format: Tianxing Zhou, Jingrui Yan, Bin Wang, Yongjie Xie, Chao Yang, Jun Yu, Jihui Hao. STING agonist ADU-S100 improves the antitumor response of CLDN18. 2/CD3 BiTEs by enhancing stem-like tumor-reactive CD8+ T cells in pancreatic adenocarcinoma abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 2367.