Perturbations of Both Nonregulatory and Regulatory FOXP3+ T Cells in Patients with Malignant Melanoma

Background: 'FOXP3+ regulatory T cells' (Tregs) are reported to be increased in tumour-bearing hosts including patients with melanoma, leading to tumour immune suppression. However, this idea is challenged by recent evidence that the 'FOXP3+ Treg' fraction in fact contains activated 'nonregulatory' T cells. Also, FOXP3+ T cells are reported to have functionally and kinetically distinct subsets.

Objectives: To investigate whether either or both of regulatory and 'nonregulatory' FOXP3+ T cells are perturbed in patients with melanoma.

Methods: FOXP3+ T cells were classified into three subsets, namely CD45RO+FOXP3(low) nonregulatory T cells, CD45RO+FOXP3(high) effector Tregs, and CD45RO-FOXP3(low) naïve Tregs, according to their expression levels of FOXP3 and CD45RO. The percentage and cytokine production of these FOXP3+ T-cell subsets were assessed by flow cytometry.

Results: Both regulatory and nonregulatory T cells were increased in patients with melanoma. Moreover, we found three unexpected perturbations in FOXP3+ T-cell subsets: (i) patients with melanoma showed higher frequencies of FOXP3(low) nonregulatory T cells, which decreased and normalized after tumour removal; (ii) FOXP3(low) naïve Tregs containing higher frequencies of interferon-γ+ cells increased with tumour progression; and (iii) CD45RO+FOXP3(high) effector Tregs were pronouncedly infiltrated around tumour tissues.

Conclusions: These findings demonstrate that patients with melanoma have distinct and differential perturbation of both regulatory and nonregulatory FOXP3+ T cells. The degree of perturbation is associated with tumour burden and progression, suggesting that the perturbation reflects fundamental pathophysiological processes in patients with melanoma. The presented analysis provides a practical approach to investigate the immunological environment of cancer patients.