ATP-Hydrolysing Treg in Patients with Acute Myeloid Leukemia

Abstract 4255

We have previously shown that the frequency and suppressor function of regulatory T cells (Treg) is increased in newly-diagnosed patients with acute myeloid leukemia (AML). Here, we show that CD4+CD39+ ATP-hydrolyzing T cells are involved in the production of immunosuppressive adenosine and that this mechanism of suppression characterizes Treg present in the blood and bone marrow of AML patients.

Peripheral blood and bone marrow samples were obtained from AML patients prior to any treatment (n=20) and healthy controls (NC, n=20). The frequency and phenotype as well as cytokine profiles of CD4+CD39+ T cells were determined using multicolor flow cytometry, real-time PCR and western blots. Adenosine production was measured by mass spectrometry. Co-cultures of CD4+CD39+ Treg with conventional T cells were tested for suppression of proliferation.

In NC and patients with AML, CD4+CD39+ Treg contained two subsets of ATP-hydrolyzing T cells in equal proportions (Fig.1): FOXP3+CD25+ and FOXP3negCD25neg.Both subsets were increased in frequency (p < 0.04) in AML relative to NC (Fig.2). In the presence of other immune cells or exosomes positive for CD73 (hydrolyzes AMP to adenosine) both subsets produced immunosuppressive adenosine. In co-cultures, CD4+CD39+FOXP3negCD25neg T cells converted to FOXP3+CD25+ T cells.

View largeDownload slide

View largeDownload slide

Close modal

Our data suggest that Treg with the ability to produce adenosine are a major subset of suppressor cells in the blood and bone marrow of AML patients. Co-culture experiments indicate that the ability of these cells to suppress immune responses is regulated at the level of FOXP3 and CD25 expression by factors present in their microenvironment.