Immunomodulatory Effects of Azacitidine Treatment In High Risk Myelodysplastic Syndrome

Abstract 1860

Immune editing is recognized as being important in the pathogenesis of myelodysplastic syndrome (MDS). In low risk MDS, inappropriate immune reactions are thought to contribute to the initiation and progression of the disease. IL-17 producing CD4+ T-helper cells have been associated with various autoimmune diseases and are found in increased frequencies in low-risk MDS. These increased Th17 frequencies are accompanied by a reduced FoxP3+ T-regulatory (Treg) frequency. On the other hand, in high-risk MDS, the elevated number of bone marrow blasts was associated with increased numbers of Treg. These increased Treg may inhibit immune responses directed against the dysplastic blasts and as such permit progression of the disease. The demethylating agents ‘5-aza-2’-deoxycytidine and ‘5-azacitidine (Aza) have shown significant clinical benefits in the treatment of MDS. Although aberrant DNA methylation patterns appear to play a role in the pathogenesis of MDS, clinical responses to DNA demethylating agents could not be related to changes in DNA methylation patterns. Cytokine production and FoxP3 expression are also regulated by epigenetic mechanisms, and FoxP3 expression is increased upon in vitro treatment with Aza. Since cytokines and FoxP3+ Treg may play a role in the pathogenesis of MDS, we set out to investigate the effects of Aza (Vidaza®) treatment on CD4+ T-helper subset frequencies in high-risk MDS patients. Nine patients treated with 75 mg/m²/day subcutaneously for 7 consecutive days in a 28 day cycle were included in this study. Peripheral blood samples were drawn before, 15 days after start of treatment and at the end of the third cycle. There was no change in absolute or relative CD3+ and CD3+CD4+ T-cell numbers during treatment. The proportion of Treg was slightly but not significantly increased (paired student's T-test, p=0.08) on day 15 (11.9 % of CD4+) compared to levels before treatment (9.6 % of CD4+) while numbers dropped to pretreatment levels after the third cycle(9.6 % of CD4+). Cytokine producing cells were enumerated after stimulation with phorbol-12-myristate-13-acetate (PMA) and ionomycin in the presence of Brefeldin A. No significant changes in IFNγ (23.8%, 22.5% and 17.9% of CD4+ cells pretreatment, 15d post treatment and after the third cycle respectively) TNFα (38.3, 35.9 and 39.3% of CD4+ cells) or IL-4 (0.6, 1.0 and 0.6% of CD4+ cells) producing cells were observed. However, the proportion of IL-17 producing cells progressively decreased during treatment (1.1, 0.7 and 0.6% of CD4+ cells; ANOVA, p=0.006). In conclusion, Aza may modulate the immune response and in particular reduce IL-17 responses. This effect of Aza may provide a rationale for expanding the group of patients eligible for Aza treatment with low risk MDS patients, because low risk MDS has been associated with elevated, potential pathogenic, Th17 cells.