Increased number of CD25+ FoxP3+ regulatory T cells in oral squamous cell carcinomas detected by chromogenic immunohistochemical double staining

BACKGROUND: The role of tumor-infiltrating regulatory T cells (Treg) compromising antitumor effects of immune cells in oral squamous cell carcinoma (OSCC) is largely unknown. PURPOSE: The presence of CD25(+) FoxP3(+) Treg as well as of CD3(+) FoxP3(+) and of CD8(+) FoxP3(+) tumor-infiltrating lymphocytes (TIL) was verified in OSCC and compared with non-cancerous lymphoepithelial tissue. RESULTS: Three double stainings (CD3/FoxP3, CD8/FoxP3 and CD25/FoxP3) were performed on tissue sections of 15 OSCC and compared with 15 human tonsils. RESULTS: OSCC biopsy samples provide evidence for a strong infiltration of TIL, in particular, naturally occurring CD25(+) FoxP3(+) Treg. Whereas a comparison of OSCC and control tissue did not show significant changes in the number of CD3(+) FoxP3(+) TIL and of CD8(+) FoxP3(+) TIL, a significantly higher frequency of CD25(+) FoxP3(+) TIL (Treg) could be observed in OSCC (P < 0.001, two-sided t-test). Given the small number of specimens, a significant correlation with tumor stage could not be verified. CONCLUSION: Chromogenic double staining of CD4/FoxP3 is a promising tool for the detection of Treg in paraffin-embedded tissue of OSCC.