Clinical impact of tumor-infiltrating CD45RO⁺ memory T cells on human gastric cancer.

Memory T cells survive for months and even years and are critical for host defense in humans. They have been recently suggested to play a significant role in tumor immunity. In this study, we aimed to investigate the clinical impact of tumor-infiltrating memory T cells on human gastric cancer. We evaluated CD45RO(+)T cells infiltrating into primary gastric cancer tissues by immunohistochemistry in 101 patients with gastric cancer. Patients were classified into 2 groups (CD45RO(+Hi) and CD45RO(+Lo)) based on the number of positively stained T cells. There was no significant correlation observed between CD45RO status and post-operative prognosis in early gastric cancer. By contrast, in advanced cancer, the post-operative overall and disease-free survival of patients with CD45RO(+Hi) were significantly improved compared to those of patients with CD45RO(+Lo). In addition, CD45RO status in the primary tumors significantly correlated with the development of post-operative recurrence, particularly peritoneal recurrence. Furthermore, the local expression of interferon-γ (IFN-γ) in the CD45RO(+Hi) tumors was significantly higher than that in the CD45RO(+Lo) tumors, suggesting that CD45RO(+) T cells induced local immune activation. Multivariate analysis indicated that the CD45RO(+) status was an independent prognostic factor in advanced gastric cancer. In conclusion, tumor-infiltrating CD45RO(+) memory T cells are functional and have significant prognostic value in human gastric cancer. Our data suggest that adaptive immune response is clinically critical in gastric cancer.