Background & Aims: Regulatory T cells (Tregs) express the forkhead box transcription factor (FoxP3) and suppress the antitumor immune response. We investigated whether the intratumoral densities of FoxP3+ and effector CD3+ lymphocytes are associated with prognosis of patients with colon cancer. Methods: FoxP3 and CD3 expression and location were determined in stage II and III colon carcinomas (n = 160) and normal mucosa (n = 25) by immunohistochemistry; CD4 and FoxP3 were localized by dual immunofluorescence microscopy. T-cell markers were compared with pathological variables, DNA mismatch repair status, and patient survival using Cox proportional hazards models. Results: FoxP3+ and CD3+ T-cell densities were increased in carcinomas compared with autologous normal mucosa (P < .0001). An increase in intraepithelial FoxP3+ cells was associated with poor tumor differentiation (P = .038), female sex (P = .028), and advanced patient age (P = .042). FoxP3+ cell density was not prognostic, yet patients with tumors with reduced intraepithelial CD3+ T-cell densities had reduced disease-free survival (DFS) rates (hazard ratio [HR], 1.87 [95% confidence interval, 1.10-3.16]; P = .018). A low intraepithelial CD3+/FoxP3+ cell ratio predicted reduced DFS (46.2% vs 66.7% survival at 5 years; HR, 2.17 [95% confidence interval, 1.11-4.23]; P = .0205). The prognostic impact of these markers was maintained when tumors were stratified by mismatch repair status. By multivariate analysis, a low CD3+/FoxP3+ cell ratio (P = .0318) and low numbers of CD3+ T cells (P = .0397) predicted shorter DFS times and were stronger prognostic variables than tumor stage or number of lymph node metastases. Conclusions: A low intraepithelial CD3+/FoxP3+ cell ratio and reduced numbers of CD3+ T cells were associated with shorter patient survival time, indicating the importance of an effector to Treg cell ratio in colon cancer prognosis.
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