Abstract: Objective To detect the changes in the number and phenotype of tumor infiltrating immune cells in rectal cancer tissues before and after neoadjuvant concurrent chemoradiotherapy (CRT) and analyze their correlation with the clinicopathological parameters of the patients. Methods The protein expressions of CD3, CD4, CD8, CD56 and Foxp3 in biopsy specimens and postoperative pathological specimens collected from 20 rectal cancer patients before and after neoadjuvant CRT were detected using ElivisionTM Plus immunohistochemistry, and the results were statistically analyzed. Results Compared with the measurements before the therapy, neoadjuvant CRT resulted in significant increments in CD3 (21.8% vs 48.8% , P< 0.001), CD4 (16.5% vs 42.2%, P<0.001), CD8 (8.3% vs 33.4%, P<0.001) and CD56 (0 vs 7.6%, P=0.012), obvious reduction in Foxp3 expression (26.0% vs 15.3%, P=0.005), but no significant changes in CD4/CD8 ratio of (2.7 vs 5.1). Multivariate analysis showed that the increase of CD3- positive cells (HR=0.16, P=0.028) and CD8- positive cells (HR=0.03, P=0.001) was positively correlated with the disease-free survival of the patients after the operation. Conclusion Neoadjuvant CRT can significantly increase the proportions of infiltrating immune cells positive for CD3, CD4, CD8 and CD56 and decrease the proportion of Treg lymphocytes in the tumor tissues in patients with rectal cancer. The patients with increased CD3- and CD8- positive T lymphocytes may have longer disease-free survival after the surgery

Key words: rectal cancer; neoadjuvant concurrent chemoradiotherapy; tumor infiltrating immune cells; immunohistochemistry; prognosis