Hypomethylation and up-regulation ofPD-1in T cells by azacytidine in MDS/AML patients: A rationale for combined targeting of PD-1 and DNA methylation

// Andreas D. Ørskov 1, * , Marianne B. Treppendahl 1, * , Anni Skovbo 2, 3 , Mette S. Holm 4 , Lone S. Friis 1, 5 , Marianne Hokland 2 , Kirsten Grønbæk 1 1 Department of Hematology, Rigshospitalet, Copenhagen University Hospital, Copenhagen, Denmark 2 Department of Biomedicine, Aarhus University, Aarhus, Denmark 3 FACS Core Facility, Aarhus University, Aarhus, Denmark 4 Department of Hematology, Aarhus University Hospital, Aarhus, Denmark 5 Department of Hematology, Odense University Hospital, Odense, Denmark * These authors have contributed equally to this work. Correspondence to: Kirsten Grønbæk, e-mail: kirsten.groenbaek@regionh.dk Keywords: myelodysplastic syndromes, hypomethylating agents, DNA methylation, programmed death-1, T cells Received: November 29, 2014      Accepted: February 09, 2015      Published: March 18, 2015 ABSTRACT The hypomethylating agents (HMAs) are standard therapy for patients with higher-risk myelodysplastic syndrome (MDS); however, the majority of the patients will lose their response to HMAs over time due to unknown mechanisms. It has recently been shown that T cell expression of the immunoinhibitory receptor PD-1 is regulated by DNA methylation. In 12 of 27 patients (44%) PD-1 promoter demethylation was observed in sorted peripheral blood T cells isolated over consecutive cycles of treatment with 5-azacytidine (5-aza). The PD-1 promoter demethylation correlated with an increase in PD-1 expression. Moreover, demethylation of the PD-1 promoter correlated with a significantly worse overall response rate (8% vs. 60%, p = 0.014), and a trend towards a shorter overall survival ( p = 0.11) was observed. A significantly higher baseline methylation level of the PD-1 promoter was observed in T cells of non-responding patients compared to healthy controls ( p = 0.023). Accordingly, in addition to their beneficial function, HMAs induce PD-1 expression on T cells in the MDS microenvironment, thereby likely hampering the immune response against the MDS blasts. Thus, we suggest that activation of the PD-1 checkpoint during HMA treatment can be a possible resistance mechanism, which may be overcome by combination therapy with a PD-1 pathway inhibitor.