Comprehensive Genetic Analysis Revealed Myeloid/Natural Killer (NK) Cell Precursor Acute Leukemia As a Novel Distinctive Leukemia Entity

Introduction: Myeloid/Natural killer (NK) cell precursor acute leukemia (MNKPL) is a rare hematologic malignancy prevalent in East Asia. MNKPL is characterized by extramedullary involvement, immature lymphoblastoid morphology without myeloperoxidase (MPO) reactivity, the CD7+/CD33+/CD34+/CD56+/HLA−DR+ phenotype. MNKPL is classified as mixed phenotype acute leukemia, and not otherwise specified rare types (MPAL NOS rare types) in WHO classification. However, its characteristic clinical feature and undetermined genetic feature suggests that MNPKL leaves open the possibility of a new independent disease concept. Here, we report clinical features and genetic alterations in patients with MNKPL. Methods: The Leukemia and Lymphoma Committee of the Japanese Society of Pediatric Hematology and Oncology (JSPHO) sent out questionnaires to 110 JSPHO affiliated hospitals and collected cases of MNPKL diagnosed during the period 2000-2013. Besides, the cases published as literature were recruited. The data of clinical features, cell surface antigen profiling, overall survival (OS), and event-free survival (EFS) defined as relapse or death were also collected as a secondary survey. The protocol of this retrospective study was approved by the review boards of JSPHO and Ehime Prefectural Central Hospital. Comprehensive genetic analysis including 13 whole-exome sequences (WES), 2 target sequence, 6 RNA sequence (RNA-seq), and 8 DNA methylation analysis was performed. We also performed single-cell RNA-seq using 1 sample of MNKPL patients and a normal bone marrow sample as the reference. The research protocol was approved by the review board of TMDU. Results: Sixteen children or young adults ( In genetic analysis, median 388 somatic mutations in MNKPL were identified by WES. The recurrent mutations were observed in NOTCH1 (n=5), MAML3 (n=4), NRAS, MAP3K4, RECQL4, CREBBP, ASXL2, and KMT2D (n=3, respectively), and MAML2, MAP3K1, FLT3, CARD11, MSH4, FANCI, WT1, ZNF384, and ERG (n=2, respectively). The distinct expression pattern, higher expression of RUNX3 and NOTCH1, and lower expression of BCL11B were identified in MNKPL samples which were compared to MPAL, AML, and T cell ALL in RNA-seq. The distinct methylation profile, hypomethylation of RUNX3 regulatory region, and hypermethylation of BCL11B regulatory region were identified in DNA methylation analysis. Single-cell RNA-seq analysis also showed distinct 4 subsets of MNKPL. Discussion and Conclusions: NK cells are the founding member of a family of innate lymphoid cells (ILC). Genetic abnormality of NOTCH1 pathway is a hallmark of MNPKL. RUNX3 is required for NK cell survival and proliferation in response to IL-15 signaling. RUNX3 high expression and hypomethylation of RUNX3 regulatory region also characterize MNKPL. Currently, MNKPL is classified as MPAL NOS, our genetic analysis revealed that MNKPL is a distinct group from MPAL. The prognosis of MNKPL was not satisfactory even though HCT was performed. The development of new therapeutic approaches based on these genetic analyses is highly expected. Disclosures Saito: Toshiba Corporation: Research Funding. Nakazawa: Toshiba Corporation: Research Funding.