Abstract 5155: CD8+ T cells and CD4+central memory T cells as biomarkers of perioperative anti-PD-1 therapy in combination with concurrent chemoradiotherapy for locally advanced G/GEJ adenocarcinoma

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Abstract Background: Gastric or gastroesophageal junction (G/GEJ) adenocarcinoma is one of the most common lethal malignancies in the world. Near half of the G/GEJ adenocarcinoma are locally advanced at diagnosis and with poor prognosis. Several clinical trials including SHARED (ChiCTR1900024428), which conducted in our center, demonstrated that perioperative anti-PD-1 therapy in combination with concurrent chemoradiotherapy for locally advanced G/GEJ cancers, could raise the pCR rate over 30%. However, the biomarkers for patients with pCR are nor clear. Methods: Baseline tumor biopsies and post-treatment surgical tissues were collected for next-generation sequencing (NGS) and mass cytometry (CyTOF). The overall survival (OS) was measured from the date of surgery to the date of death or the last follow-up visit. Results: 34 patients with locally advanced G/GEJ cancer received anti-PD-1 therapy (Sintilimab) in combination with concurrent chemoradiotherapy in our center. Our results met the pre-specified primary endpoint, with a pCR rate of 38.2% (13/34) and median DFS of 17.0 months. Tumor mutation burden (TMB) analyzed by NGS was higher in the pCR group than those not achieving pCR (non-pCR). Deletion of cytoband 7q35, where TPK1 locates, was significantly enriched in pCR groups. The RNA sequencing data revealed an enrichment of dendritic cells (DC), CD8+ T cells and cytotoxic cell signatures in the pCR group. Conversely, the signature for CD4+ central memory T cells (TCM) was observed to be lower in the pCR group. On the other hand, CyTOF data also demonstrated that the proportion of CD8+ T cells, CD8+ effector memory T cells (TEM) were both higher in pCR group at baseline, while CD4+ TCM was lower. Moreover, the proportion of specific subtype characterized by CD127+CD27+CD45RO+CXCR5-CD4+ TCM was significantly lower in pCR patients and significantly reduced after treatment. As continuous variable, only CD8+ T cells correlated with OS. Conclusions: It seemed that CD8+ T cells and CD4+ TCM cells could be predictive biomarkers of perioperative anti-PD-1 therapy in combination with cCRT for locally advanced G/GEJ. Furthermore, we found a new CD4+ TCM subtype defined with CD127+CD27+CD45RO+CXCR5- could be novel biomarkers. Citation Format: Yue Wang, Yawei Chen, Ju Yang, Xiaoyu Zhou, Yutao Wei, Qin Liu, Yang Yang, Wenxian Guan, Baorui Liu, Jia Wei. CD8+ T cells and CD4+central memory T cells as biomarkers of perioperative anti-PD-1 therapy in combination with concurrent chemoradiotherapy for locally advanced G/GEJ 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(6_Suppl):Abstract nr 5155.