Increased Number of IL-17 Producing CD4⁺ T Cells in Low Risk Myelodysplastic Syndrome (MDS)

Immunological responses are increasingly recognized as important in the initiation and progression of MDS. Indeed, autoimmune diseases commonly occur in association with low risk MDS. Different studies, including our own, have shown that Foxp3⁺ Tregs play a role in the inhibition of tumour immune surveillance in high risk MDS; however, less clear are the potential factors which are inducing inflammatory response in low risk MDS that may also predispose to autoimmunity. CD4⁺IL 17 producing T cells (Th17) are considered as important pro-inflammatory T cells and contribute to the pathogenesis of a number of autoimmune diseases as well as some malignancies. The aim of this study was to investigate the potential role of Th17 cells in low risk MDS. We show for the first time that Th17 cells are markedly increased in low risk MDS in comparison to high risk disease and healthy age matched controls. We also describe an inverse relationship between numbers of Th17 cells and naturally occurring Tregs in MDS.

88 patients with newly diagnosed MDS, and 15 age matched healthy donors, were recruited. Analysis of Th17 cells was performed in a subset of 43 patients. WHO classifications were as follows: 19% had RA, 33% had RCMD, 32% had RAEB I & II and 16% had 5q- syndrome. A clear difference was observed in the median percentage and absolute number of Th17 cells between patients with low risk (based on IPSS) compared to high risk MDS (p<0.01). In low risk, but not high risk MDS, CD4⁺ cells had greater median number of committed Th17 cells than healthy donors (p<0.01). The absolute number of polyclonal Foxp3⁺ Tregs inversely correlated with Th17 cells, with higher Tregs in the high risk MDS when compared to low risk MDS or healthy donors (p<0.001), consistent with our previous report. Analysis according to IPSS, BM blast percentage or WHO classification revealed the same patterns of Th17 and Tregs expression, with the higher risk phenotypes being associated with significantly higher Treg number and lower risk phenotypes with greater Th17 cells. This finding was specific for Th17 as there was no significant difference in the number of circulating Th1 and Th2 cells between MDS subtypes.

Co-culture of Tregs from patients with MDS with their own T effectors lead to suppression of supernatant IFNγ levels. Importantly, Tregs did not have an inhibitory effect on IL17 production and indicates that reduced Th17 number in the presence of high Tregs does not indicate active suppression of the Th17 phenotype.

To investigate differences in serum cytokines between low and high risk MDS and healthy donors, serum samples from patients were analyzed by Luminex for multiple cytokines. The cytokines IL12(p<0.01) IL7(p<0.005) IFNγ(p<0.01) and RANTES (p<0.005) were significantly higher in patients with low risk compared to high risk MDS and healthy controls. The inhibitory cytokine IL10 and soluble IL2 receptor were present at higher levels in the serum of patients with high risk MDS (p<0.01 and p<0.005 respectively). To confirm that the peripheral blood cytokines are a true reflection of cytokine concentration in the bone marrow, the concentration of 30 different cytokines was measured by Luminex in 10 matched bone marrow and peripheral blood samples from these patients and there was no significant difference between these two sets of samples. In addition, the level of apoptosis, assessed by TUNEL assay, was also higher in the bone marrow of low risk patients.

In conclusion, the “unfavourable” Th17 to Tregs ratio in low risk MDS may explain the higher risk of autoimmunity and bone marrow apoptosis. These findings may help identify subtype of low risk MDS patients likely to respond to immunosuppressive therapy.