Role of LAP + CD4 + T cells in the tumor microenvironment of colorectal cancer.

Aim: To investigate the abundance and potential functions of LAP ⁺ CD4 ⁺ T cells in colorectal cancer (CRC).
Methods: Proportions of LAP ⁺ CD4 ⁺ T cells were examined in peripheral blood and tumor/paratumor tissues of CRC patients and healthy controls using flow cytometry. Expression of phenotypic markers such as forkhead box (Fox)p3, cytotoxic T-lymphocyte-associated protein (CTLA)-4, chemokine CC receptor (CCR)4 and CCR5 was measured using flow cytometry. LAP ^- CD4 ⁺ and LAP ⁺ CD4 ⁺ T cells were isolated using a magnetic cell-sorting system and cell purity was analyzed by flow cytometry. Real-time quantitative polymerase chain reaction was used to measure expression of cytokines interleukin (IL)-10 and transforming growth factor (TGF)-β.
Results: The proportion of LAP ⁺ CD4 ⁺ T cells was significantly higher in peripheral blood from patients (9.44% ± 3.18%) than healthy controls (1.49% ± 1.00%, P < 0.001). Among patients, the proportion of LAP ⁺ CD4 ⁺ T cells was significantly higher in tumor tissues (11.76% ± 3.74%) compared with paratumor tissues (3.87% ± 1.64%, P < 0.001). We also observed positive correlations between the proportion of LAP ⁺ CD4 ⁺ T cells and TNM stage ( P < 0.001), distant metastasis ( P < 0.001) and serum level of carcinoembryonic antigen ( P < 0.05). Magnetic-activated cell sorting gave an overall enrichment of LAP ⁺ CD4 ⁺ T cells (95.02% ± 2.87%), which was similar for LAP ^- CD4 ⁺ T cells (94.75% ± 2.76%). In contrast to LAP ^- CD4 ⁺ T cells, LAP ⁺ CD4 ⁺ T cells showed lower Foxp3 expression but significantly higher levels of CTLA-4, CCR4 and CCR5 ( P < 0.01). LAP ⁺ CD4 ⁺ T cells expressed significantly larger amounts of IL-10 and TGF-β but lower levels of IL-2, IL-4, IL-17 and interferon-γ, compared with LAP ^- CD4 ⁺ T cells.
Conclusion: LAP ⁺ CD4 ⁺ T cells accumulated in the tumor microenvironment of CRC patients and were involved in immune evasion mediated by IL-10 and TGF-β.
Competing Interests: Conflict-of-interest statement: The authors declare no conflicts of interest.