Impact of tumor-infiltrating T cells on survival in patients with malignant pleural mesothelioma

Objective: The aim of the study was to determine the impact of tumor-infiltrating lymphocytes on survival in patients with malignant pleural mesothelioma treated with induction chemotherapy followed by extrapleural pneumonectomy. Methods: We performed an immunohistochemical analysis of 32 extrapleural pneumonectomy specimens to assess the distribution of T-cell subtypes (CD3(+), CD4(+), and CD8(+)), regulatory subtypes (CD25(+) and FOXP3(+)), and memory subtype (CD45RO(+)) within the tumor. Results: Patients with high levels of CD8(+) tumor-infiltrating lymphocytes demonstrated better survival than those with low levels (3-year survival: 83% vs 28%; P = .06). Moreover, high levels of CD8(+) tumor- infiltrating lymphocytes were associated with a lower incidence of mediastinal node disease (P = .004) and longer progression- free survival (P = .05). Higher levels of CD8(+) tumor- infiltrating lymphocytes were observed in patients treated with cisplatin and pemetrexed than in those treated with cisplatin and vinorelbine (P = .02). Patients presenting high levels of CD4(+) or CD25(+) tumor-infiltrating lymphocytes or low levels of CD45RO(+) also demonstrated a trend toward shorter survival. However, the presence of FOXP3(+) tumor- infiltrating lymphocytes did not affect survival. After multivariate adjustment, high levels of CD8(+) tumor- infiltrating lymphocytes remained an independent prognostic factor associated with delayed recurrence (hazard ratio = 0.38; confidence interval = 0.09-0.87; P = .02) and better survival (hazard ratio = 0.39; confidence interval = 0.09-0.89; P = .02). Conclusion: The presence of high levels of CD8(+) tumor-infiltrating lymphocytes is associated with better prognosis in patients undergoing extrapleural pneumonectomy for malignant pleural mesothelioma. The stimulation of CD8(+) lymphocytes can be a potential therapeutic strategy to improve outcome.