Somatic HLA mutations expose the role of class I–mediated autoimmunity in aplastic anemia and its clonal complications | Aplastic Anemia and MDS International Foundation

Somatic HLA mutations expose the role of class I–mediated autoimmunity in aplastic anemia and its clonal complications

Journal Title: 
Blood Advances
Primary Author: 
Daria V. Babushok
Author(s): 
Daria V. Babushok, Jamie L. Duke, Hongbo M. Xie, Natasha Stanley, Jamie Atienza, Nieves Perdigones, Peter Nicholas, Deborah Ferriola, Yimei Li, Hugh Huang, Wenda Ye, Jennifer J. D. Morrissette, Jane Kearns, David L. Porter, Gregory M. Podsakoff
Original Publication Date: 
Monday, October 23, 2017

Acquired aplastic anemia (aAA) is an acquired deficiency of early hematopoietic cells, characterized by inadequate blood production, and a predisposition to myelodysplastic syndrome (MDS) and leukemia. Although its exact pathogenesis is unknown, aAA is thought to be driven by human leukocyte antigen (HLA)–restricted T cell immunity, with earlier studies favoring HLA class II-mediated pathways. Using whole-exome sequencing (WES), we recently identified 2 patients with aAA with somatic mutations in HLA class I genes. We hypothesized that HLA class I mutations are pathognomonic for autoimmunity in aAA, but were previously underappreciated because the major histocompatibility complex (MHC) region is notoriously difficult to analyze by WES. Using a combination of targeted deep sequencing of HLA class I genes and single nucleotide polymorphism array (SNP-A) genotyping, we screened 66 patients with aAA for somatic HLA class I loss. We found somatic HLA loss in 11 patients (17%), with 13 loss-of-function mutations in HLA-A*33:03, HLA-A*68:01, HLA-B*14:02, and HLA-B*40:02 alleles. Three patients had more than 1 mutation targeting the same HLA allele. Interestingly, HLA-B*14:02 and HLA-B*40:02 were significantly overrepresented in patients with aAA compared with ethnicity-matched controls. Patients who inherited the targeted HLA alleles, regardless of HLA mutation status, had a more severe disease course with more frequent clonal complications as assessed by WES, SNP-A, and metaphase cytogenetics, and more frequent secondary MDS. The finding of recurrent HLA class I mutations provides compelling evidence for a predominant HLA class I-driven autoimmunity in aAA and establishes a novel link between immunogenetics and clonal evolution of patients with aAA.

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