EZH2-driven immune evasion defines high-risk pediatric AML with t(16;21) FUS::ERG gene fusion

Abstract

ABSTRACTDespite decades of research, acute myeloid leukemia (AML) remains a remarkably lethal malignancy. While pediatric AML (pAML) carries a more favorable prognosis than adult AML, the past 25 years of large clinical trials have produced few improvements in pAML survival. Nowhere is this more evident than in patients carrying a t(16;21)(p11;q22) translocation, which yields theFUS::ERGfusion transcript. Patients withFUS::ERG-positive AML are often primary refractory, and most responders quickly relapse. In COG clinical trials, allogeneic stem cell transplantation was of no benefit toFUS::ERGpAML patients; 100% of transplanted patients succumbed to their disease. Expression of major histocompatibility complex (MHC) class I & II and costimulatory molecules is absent at diagnosis inFUS::ERGAML, mirroring the epigenetic mechanism of post-transplant relapse seen in adult AML and its associated dismal outcomes. Here we show that this class-defining immune-repressive phenotype is driven by overexpression of theEZH2histone lysine methyltransferasein vitroand in multiple clinical cohorts. We show that treatment with the FDA-approved EZH2 inhibitor tazemetostat along with IFN-γ reverses this phenotype, re-establishes MHC presentation, and severely impairs the viability ofFUS::ERGAML cells. EZH2 inhibitors may thus provide the first targeted therapeutic option for patients with this high-risk subtype of pAML, with particular benefit as a bridge to successful allogeneic stem cell transplantation.STATEMENT OF SIGNIFICANCEFUS::ERGpAML patients have dismal outcomes. Here we show a ubiquitous immune-evasive phenotype, defined by elevated EZH2 levels and loss of MHC class I and II receptors, present in these patients at diagnosis. Treatment with the EZH2 inhibitor tazemetostat and IFN-γ reverses this phenotype in patient-derived cell lines.