CD4(+) T Cells Expressing Latency-Associated Peptide and Foxp3 Are an Activated Subgroup of Regulatory T Cells Enriched in Patients with Colorectal Cancer

Latency-associated peptide (LAP) - expressing regulatory T cells (Tregs) are important for immunological self-tolerance and immune homeostasis. In order to investigate the role of LAP in human CD4(+)Foxp3(+) Tregs, we designed a cross-sectional study that involved 42 colorectal cancer (CRC) patients. The phenotypes, cytokine-release patterns, and suppressive ability of Tregs isolated from peripheral blood and tumor tissues were analyzed. We found that the population of LAP-positive CD4(+)Foxp3(+) Tregs significantly increased in peripheral blood and cancer tissues of CRC patients as compared to that in the peripheral blood and tissues of healthy subjects. Both LAP(+) and LAP(−) Tregs had a similar effector/memory phenotype. However, LAP(+) Tregs expressed more effector molecules, including tumor necrosis factor receptor II, granzyme B, perforin, Ki67, and CCR5, than their LAP(−) negative counterparts. The in vitro immunosuppressive activity of LAP(+) Tregs, exerted via a transforming growth factor-β–mediated mechanism, was more potent than that of LAP(−) Tregs. Furthermore, the enrichment of LAP(+) Treg population in peripheral blood mononuclear cells (PBMCs) of CRC patients correlated with cancer metastases. In conclusion, we found that LAP(+) Foxp3(+) CD4(+) Treg cells represented an activated subgroup of Tregs having more potent regulatory activity in CRC patients. The increased frequency of LAP(+) Tregs in PBMCs of CRC patients suggests their potential role in controlling immune response to cancer and presents LAP as a marker of tumor-specific Tregs in CRC patients.