FOXP3 expression accurately defines the population of intratumoral regulatory T cells that selectively accumulate in metastatic melanoma lesions.
Regulatory T (T(reg)) cells are often found in human tumors; however, their functional characteristics have been difficult to evaluate due to low cell numbers and the inability to adequately distinguish between activated and T(reg) cell populations. Using a novel approach, we examined the intracellular cytokine production capacity of tumor-infiltrating T cells in the single-cell suspensions of enzymatically digested tumors to differentiate T(reg) cells from effector T cells. Similar to T(reg) cells in the peripheral blood of healthy individuals, tumor-infiltrating FOXP3(+)CD4 T cells, unlike FOXP3(-) T cells, were unable to produce IL-2 and IFN-gamma upon ex vivo stimulation, indicating that FOXP3 expression is a valid biological marker for human T(reg) cells even in the tumor microenvironment. Accordingly, we enumerated FOXP3(+)CD4 T(reg) cells in intratumoral and peritumoral sections of metastatic melanoma tumors and found a significant increase in proportion of FOXP3(+)CD4 T(reg) cells in the intratumoral compared with peritumoral areas. Moreover, their frequencies were 3- to 5-fold higher in tumors than in peripheral blood from the same patients or healthy donors, respectively. These findings demonstrate that the tumor-infiltrating CD4 T(reg) cell population is accurately depicted by FOXP3 expression, they selectively accumulate in tumors, and their frequency in peripheral blood does not properly reflect tumor microenvironment.
Ahmadzadeh
Mojgan
M
Surgery Branch, National Cancer Institute, National Institutes of Health, Bethesda, MD, USA.
Felipe-Silva
Aloisio
A
Heemskerk
Bianca
B
Powell
Daniel J
DJ
Wunderlich
John R
JR
Merino
Maria J
MJ
Rosenberg
Steven A
SA
D016207:Cytokines / Q000096:biosynthesis; D051858:Forkhead Transcription Factors / Q000032:analysis*; D006801:Humans; D018655:Lymphocyte Count; D009101:Multiple Myeloma / Q000276:immunology / Q000473:pathology*; D009362:Neoplasm Metastasis / Q000276:immunology / Q000473:pathology; D050378:T-Lymphocytes, Regulatory / Q000737:chemistry / Q000276:immunology*
D016207:Cytokines; C418974:FOXP3 protein, human; D051858:Forkhead Transcription Factors