Prognostic importance of tumour-infiltrating memory T cells in oesophageal squamous cell carcinoma

Memory T cells survive for many months and years and are critically important for host defence in humans. In tumour immunity, they have been also suggested to play a significant role in tumour progression and metastasis. However, the role of memory T cells in actual human cancer remains largely unknown. In this study, the clinical importance of tumour-infiltrating CD45RO+ memory T cells was investigated in human oesophageal squamous cell carcinoma (OSCC). CD45RO+ T cells were evaluated by immunohistochemistry in primary OSCC tumours from 105 patients. Patients were classified into two groups as CD45RO+hi or CD45RO+lo based on the number of cells stained positively for CD45RO. No significant difference was observed between CD45RO status and several clinicopathological prognostic factors. However, the postoperative overall and disease-free survival for CD45RO+hi patients was significantly better than for CD45RO+lo patients. Furthermore, there were significant correlations of CD45RO status in the primary tumour with postoperative lymph node and pulmonary recurrence, suggesting that memory T cells may control postoperative metastatic recurrence. Most importantly, CD45RO+ memory T cell status has a significant prognostic value for OSCC independently of conventional tumournodemetastasis (TNM) classification. Our study may provide a rationale for developing a novel immunotherapy in intentional induction of memory T cells for the treatment of oesophageal cancer.