Intratumoral CD8+ t cell as a potential positive predictor for treatment of chemo-immunotherapy in PD-L1 negative advanced gastric cancer patients.

e16029 Background: It was demonstrated that CPS PDL1 positive patients of advanced gastric cancer (GC) could benefit from specific immune checkpoint inhibitors (ICI) for first-line, and second-line or subsequent therapy. However, whether the application of ICI could lead to better clinical outcome in advanced GC patients who were negative for PDL1 remains further explore. Some studies showed that patients with specific tumor immune microenvironment (TME) are more sensitive to immunotherapy. Therefore, TME may be a potential positive predictor for PDL1 negative patients treated with immunotherapy. Methods: We retrospectively enrolled 26 advanced GC patients who were treated by chemoimmunotherapy in Shenzhen Hospital of Peking University and evaluated for clinical characteristics. Peritumoral and intratumoral Tumour-infiltrating lymphocytes (TIL) were detected by mIHC (multiplex immunofluorescence) among these patients. The correlation between PFS and clinical characteristics including TIL was analyzed by univariate survival analysis and multivariate Cox proportional hazards analysis. Results: In 26 patients, 5 patients (19.2%) experienced complete response (CR), 9 patients (34.6%) experienced partial response (PR), while 7 patients (26.9%) experienced stable disease (SD). Compared with non-responders, higher intratumoral infiltrating CD8+ T cells instead of other subtypes were detected in CPS PDL1 negative Patients who respond to chemoimmunotherapy. Further analysis revealed that CD8+ TIL was a predictive biomarker for PFS to chemo-immunotherapy in CPS PDL1 negative patients. Conclusions: For CPS PDL1 negative advanced GC patients, intratumoral CD8+ TIL may be a potential positive predictor for treatment of chemo-immunotherapy.