Person:

Robson, Simon

Induced regulatory T-cells (iT-reg) and T helper type 17 (Th17) in the mouse share common CD4 progenitor cells and exhibit overlapping phenotypic and functional features. Here, we show that human Th17 cells endowed with suppressor activity (supTh17) can be derived following exposure of iT-reg populations to Th17 polarizing conditions. In contrast to “pathogenic” Th17, supTh17 display immune suppressive function and express high levels of CD39, an ectonucleotidase that catalyzes the conversion of pro-inflammatory extracellular nucleotides ultimately generating nucleosides. Accordingly, supTh17 exhibit nucleoside triphosphate diphosphohydrolase activity, as demonstrated by the efficient generation of extracellular AMP, adenosine and other purine derivatives. In addition supTh17 cells are resistant to the effects of adenosine as result of the low expression of the A2A receptor and accelerated adenosine catalysis by adenosine deaminase (ADA). These supTh17 can be detected in the blood and in the lamina propria of healthy subjects. However, these supTh17 cells are diminished in patients with Crohn’s disease. In summary, we describe a human Th17 subpopulation with suppressor activity, which expresses high levels of CD39 and consequently produces extracellular adenosine. As these uniquely suppressive CD39+ Th17 cells are decreased in patients with inflammatory bowel disease, our findings might have implications for the development of novel anti-inflammatory therapeutic approaches in these and potentially other immune disorders.

Purinergic signaling and associated ectonucleotidases, such as CD39 and CD73, have been implicated in the pathogenesis of inflammatory bowel disease (IBD). CD39 is known to be a Treg memory cell marker, and here we determine the phenotype and function of CD73+CD4+ T lymphocytes in patients with IBD. We describe elevated levels of CD73+CD4+ T cells in the peripheral blood and intestinal lamina propria of patients with active IBD. The functional phenotype of these CD73+CD4+ T cells was further determined by gene expression, ecto-enzymatic activity, and suppressive assays. Increased numbers of CD73+CD4+ T cells in the periphery and lamina propria were noted during active inflammation, which returned to baseline levels following anti-TNF treatment. Peripheral CD73+CD4+ T cells predominantly expressed CD45RO, and were enriched with IL-17A+ cells. The CD73+CD4+ cell population expressed higher levels of RORC, IL-17A, and TNF, and lower levels of FOXP3 and/or CD25, than CD73−CD4+ T cells. Expression of CD73 by peripheral CD4+ T cells was increased by TNF, and decreased by an anti-TNF monoclonal antibody (infliximab). In vitro, these peripheral CD73+CD4+ T cells did not suppress proliferation of CD25− effector cells, and expressed higher levels of pro-inflammatory markers. We conclude that the CD73+CD4+ T-cell population in patients with active IBD are enriched with cells with a T-helper type 17 phenotype, and could be used to monitor disease activity during treatment.

CD39 (ENTPD1) is expressed by subsets of pathogenic human CD4+ T cells, such as T helper type 17 (Th17) cells. These Th17 cells are considered important in intestinal inflammation, such as seen in Crohn’s disease. Recently, CD161 (NKR-P1A) has been shown to be a phenotypic marker of human Th17 cells. In this study, we report that co-expression of CD161 and CD39 not only identifies these cells but also promotes Th17 generation. We note that human CD4+CD39+CD161+ T cells can be induced under stimulatory conditions that promote Th17 in vitro. Furthermore, CD4+CD39+CD161+ cells purified from blood and intestinal tissues, from both healthy controls and patients with Crohn’s disease, are of the Th17 phenotype and exhibit pro-inflammatory functions. CD39 is co-expressed with CD161, and this association augments acid sphingomyelinase (ASM) activity upon stimulation of CD4+ T cells. These pathways regulate mTOR and STAT3 signaling to drive the Th17 phenotype. Inhibition of ASM activity by pharmacological blockers or knockdown of ASM abrogates STAT3 signaling, thereby limiting IL-17 production in CD4+ T cells obtained from both controls and patients with active Crohn’s disease. Increased levels of CD39+CD161+ CD4+ T cells in blood or lamina propria are noted in patients with Crohn’s disease; and levels directly correlate with clinical disease activity. Hence, co-expression of CD39 and CD161 by CD4+ T cells might serve as a biomarker to monitor Th17 responsiveness. Collectively, CD39 and CD161 modulate human Th17 responses in Crohn's disease through alterations in purinergic nucleotide-mediated responses and ASM catalytic bioactivity, respectively.