CD4⁺CD25^high Foxp3⁺ Regulatory T-Cells Are Correlated with Different Risk Factors in Myelodysplastic Syndrome (MDS).

Regulatory T-cells (Tregs) are important in the immune surveillance of malignancies. In MDS Tregs may inhibit effective immune responses against the dysplastic clone thereby facilitating disease progression. We studied the number (CD4⁺ and CD8⁺), function and clonality of CD4⁺Tregs in the peripheral blood of 75 MDS patients with different subtypes of MDS and 9 healthy volunteers as controls. The number of Tregs was also compared between different cytogenetic abnormalities. The phenotype of the expanded Tregs was analysed by assessment of the naïve vs memory subpopulations (CD25^highFoxp3⁺CD27⁺CD45RO⁻ and CD25^highFoxp3⁺CD27⁺CD45RO⁺ respectively) in low and high risk MDS. The absolute number of CD4⁺CD25^highFoxp3⁺ and CD4⁺/CD8⁺CD25⁺Foxp3⁺ was calculated. The median number of CD4⁺CD25^highFoxp3⁺ Tregs in 5q-syndrome was 0.7×10⁷/l (range, 0.2–2.2x10⁷), Refractory Anemia (RA) 0.7×10⁷/l (range, 0.5–1.6x10⁷), Refractory Cytopenia with Multilineage Dysplasia (RCMD) 1.3×10⁷/l (range, 0.2–2.6x10⁷), Refractory Anemia with Excess Blast (RAEB) 2.2×10⁷/l (range, 0.6–7.0x10⁷) and Myelodysplastic/Myeloproliferative Disease (MDS/MPD) 3.1×10⁷/l (range, 0.8–5.0x10⁷). CD4⁺Tregs were higher in patients with ≥5% BM blasts vs <5% BM blasts (p<0.001), in high vs low/intermediate IPSS (p<0.001), disease progression vs stable disease (p<0.001). CD4⁺ Tregs were lower in 5q- syndrome, RCMD and RA. However, these did not differ significantly from normal controls (p=0.6), whereas RAEB and MDS/MPD had higher CD4⁺ Tregs than normal donors (p<0.001, p=0.02). The number of Tregs has also been correlated with cytogenetic abnormalities (based on IPSS definition). In patients with isolated 5q- Tregs were significantly lower than those with complex (p=0.004) or intermediate risk karyotypes (p<0.001). There was no difference in the number of CD8⁺ Tregs between MDS subtypes (p=0.28), IPSS (p=0.19), or disease progression (p=0.19). The percentage of naïve Tregs was significantly higher in high risk patients compared with low risk and healthy volunteers (p=0.032). The ratio of naïve to memory Tregs was also significantly higher in the high risk than low risk (p=0.016) or control groups (p=0.032). The spectratype of CD4⁺CD25⁺ TCR amplicons showed a polyclonal pattern and the overall complexity of Vβ spectratypes was not different between low and high risk group (p=0.54). By contrast the spectratype of CD8⁺Tcells was skewed on average in 6/24 Vβ subfamilies indicating the clonal expansion of these cells. Functionality of the expanded Tregs was demonstrated by inhibition of IFN-γ secretion by effector T-cells, confirmed by both intracellular staining and ELISA. We demonstrate that expansion of Tregs occurs frequently in high risk MDS and disease progression. By contrast, in low risk MDS the Treg population tends to be lower, thereby permitting the emergence of autoimmune responses. Although the increased number of Tregs in high IPSS MDS is an important indication of immune suppression, Karyotype and bone marrow blast percentage can influence the number of Tregs independently.