A Switch in Regulatory T-Cell Memory Phenotype Is Associated with Poor Survival in Lower Risk Myleodysplastic Syndrome Patients

Abstract 1703

Myleodysplastic syndrome (MDS) is a heterogeneous group of clonal hematopoietic diseases marked by various cytopenias including neutropenia and anemia. Hematologic improvement in response to T-cell depleting agents and immunosuppressants in a subset of MDS patients suggests that hematopoietic impairment may result from autoreactive T-cell activation. Conversely, suppression of the T-cell compartment may be permissible to the development of malignant myeloid clones. The suspicion that T-cell homeostatic balance may be disrupted in MDS has spawned numerous studies investigating mechanisms of immune suppression and autoimmune regulation. T-cell autoimmunity is regulated in part by regulatory T-cells (Tregs), which express T cell receptors (TCRs) that recognize self-antigens and function to maintain immune homeostasis. Indeed, higher numbers of Tregs have been found in higher risk MDS patients, and those MDS subtypes with higher blast percentages. However, the role of Tregs in lower risk patients is less clear, but may still represent an important component of pathogenesis in early disease.

Because of the autoimmune nature of low risk MDS, we hypothesized that alterations in the Treg compartment may play a role in lower risk MDS disease progression. To address this, we analyzed Treg phenotype and numbers in MDS patients largely classified as low risk by the International Prognostic Scoring System (IPSS) and 41 age-matched controls using cell surface markers as analyzed by flow cytometry. Tregs were identified as CD3⁺CD4⁺CD25⁺CD127^dim. The use of CD127 as a Treg marker was validated by intracellular staining with FoxP3. Naïve and memory phenotypes within the Treg compartment were analyzed using CD45RA and CD27 expression. Naïve Tregs (Treg^N) were characterized as CD45RA⁺CD27⁺, central memory Tregs (Treg^CM) as CD45RA⁻CD27⁺, and effector memory Tregs (Treg^EM) as CD45RA⁻CD27⁻. Two distinct subgroups of MDS patients were identified: one with elevated total numbers of Tregs, and a second with a marked shift in Treg memory phenotype away from the common Treg^CM phenotype and toward the rare Treg^EM phenotype. These two subgroups of patients were distinct from each other, and appeared to be independent of MDS WHO subtype, IPSS score, karyotype, neutropenic state, and thrombocytopenic state. MDS patients with a shift toward Treg^EMwere associated with anemia (p=0.0433). This association was not found in MDS patients with total increases in Treg numbers.

Next, we sought to determine if there are differences in overall survival (OS) of MDS patients with either increased total numbers of Tregs or in patients with a shift toward Treg^EM phenotype. Patients with greater than 50 Tregs/μl did have reduced OS compared to patients with less Tregs, but this difference was not statistically significant (p=0.1387). In contrast, a highly significant difference was observed in MDS patients with a shift toward the Treg^EM phenotype (p=0.0200), with patients having greater than 2.5Treg^EM/μl displaying the worst OS (Figure 1).

Figure 1

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Overall Survival in lower risk MDS patients with Low, Intermediate, or High absolute numbers of TregEM cells

Figure 1

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Overall Survival in lower risk MDS patients with Low, Intermediate, or High absolute numbers of TregEM cells

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Lastly, because an increased Treg^EM compartment is associated with reduced OS in MDS patients, we sought to compare the suppressive capacities of Treg^N, Treg^CM, and Treg^EM cells to better understand the functional consequences of Treg memory shift. CD4⁺ T-cells were isolated by negative selection, and then Treg^N, Treg^CM, and Treg^EM cells were sorted using CD45RA and CD27 expression. Conventional CD4⁺ responder cells were then labeled with Carboxyfluorescein succinimidyl ester (CFSE) and co-cultured with increasing ratios of each isolated Treg population. Cellular division in response to CD3/CD28 stimulation was measured 5 days later by analyzing CFSE dilution. Treg^CM appear to be the least suppressive, while Treg^N and Treg^EM cells were more potently suppressive. These results indicate that a shift in Treg phenotype toward Treg^EM may result in a more suppressive Treg compartment without obvious increases in total Treg numbers. Taken together, this data suggests that in lower risk MDS, the phenotypic makeup of the Treg compartment may be more important than total Treg numbers. In addition, this data suggests that increased Treg^EM cells may be a novel prognostic indicator in low risk MDS.