Natural killer receptor ligand expression on acute myeloid leukemia impacts survival and relapse after chemotherapy

Natural killer (NKs) cells provide rapid responses to viral-infected and malignant cells, including acute myeloid leukemia (AML) blasts. The balance among inhibitory and activating signals, delivered by multiple interactions between ligands on target cells and NK receptors, determines the posture of the NK cell response to either one of target cell elimination or tolerance. The aim of this work was to study the influence of the differential expression of activating and inhibitory NK receptor ligands (NKRLs) by leukemic blasts on clinical outcome in newly diagnosed AML patients. Leukemic cells and clinical data from 66 patients undergoing induction chemotherapy were obtained from the Australasian Leukemia Lymphoma Group tissue bank. Expression of 6 activating (MICA, MICAB, CD155, CD112, ULBP1, and ULBP2/5/6) and 3 inhibitory (HLA class I, PD-L1, and PD-L2) NKRLs was analyzed by flow cytometry. AML blasts displayed heterogeneous expression of NKRLs. MICA, CD112, and ULBP1 were most frequently expressed. ULBP1 expression was significantly associated with improved 2-year overall survival (51.4% vs 11.4%), relapse-free survival (42.5% vs 10.0%), and reduced relapse (44.1% vs 78.6%). We calculated a net score of activating minus inhibitory ligands and demonstrated that the expression of an overall activating NK ligand phenotype was associated with superior 2-year overall survival (59.6% vs 24.4%) and reduced relapse (31.5% vs 68.2%). Our study provides clinical evidence for the role of NK cell-mediated immunoediting against AML, mediated by the expression of NKRLs on blasts, and supports investigation into strategies to enhance NK cell function to improve outcomes in patients with AML.