Resident Memory T Cell in Metastatic Lymph Nodes Is Associated With Favorable Prognosis in Gastric Cancer Patients

Infiltration of resident memory T cells (TRMs) in the main tumor has been reported as a favorable prognostic factor. However, the role of TRMs in the lymph nodes (LNs) remains unclear. Thus, we examined the prognostic impact of TRMs infiltration within LNs of patients with gastric cancer (GC). Among 151 patients with metastasis to LN station No. 3, we classified them into two groups (CD103^hi and CD103^lo) based on the number of CD103⁺ T cells using immunohistochemical staining and analyzed the association between these groups and survival outcomes. We also examined the phenotype of CD8⁺ CD103⁺ T cells in the metastatic LNs using flow cytometry. Among patients with LN metastasis, metastasis to LN station No. 3 was significantly associated with a poor prognosis. There was a significant correlation between the number of CD8⁺ CD103⁺ T cells between the main lesion and the metastatic LNs. CD103^hi was associated with a favorable prognosis (5-year overall survival [OS], log-rank p = 0.001; 5-year recurrence free survival [RFS], log-rank p = 0.001). Among adjuvant chemotherapy cases, patients with CD103^hi exhibited significantly better OS and RFS than those with CD103^lo (OS, log-rank p < 0.001; RFS, log-rank p < 0.001). Flow cytometry revealed that PD-1 expression in CD8⁺ CD103⁺ T cells was higher in metastatic than in normal LNs. Among patients with CD103^hi, those with high PD-1 expression exhibited significantly better OS than those with low PD-1 expression. In conclusion, the infiltration of TRMs into LNs is a critical prognostic factor in GC.