Hematopoietic stem progenitor cells with malignancy‐related gene mutations in patients with acquired aplastic anemia are characterized by the increased expression of CXCR4

The phenotypic changes in hematopoietic stem progenitor cells (HSPCs) with somatic mutations of malignancy‐related genes in patients with acquired aplastic anemia (AA) are poorly understood. As our initial study showed increased CXCR4 expression on HLA allele‐lacking (HLA[−]) HSPCs that solely support hematopoiesis in comparison to redundant HLA(+) HSPCs in AA patients, we screened the HSPCs of patients with various types of bone marrow (BM) failure to investigate their CXCR4 expression. In comparison to healthy individuals (n = 15, 12.3%–49.9%, median 43.2%), the median CXCR4(+) cell percentages in the HSPCs of patients without somatic mutations were low: 29.3% (14.3%–37.3%) in the eight patients without HLA(−) granulocytes, 8.8% (4.1%–9.8%) in the five patients with HLA(−) cells accounting for >90% of granulocytes, and 7.8 (2.1%–8.7%) in the six patients with paroxysmal nocturnal hemoglobinuria. In contrast, the median percentage was much higher (78% [61.4%–88.7%]) in the five AA patients without HLA(−) granulocytes possessing somatic mutations (c‐kit, t[8;21], monosomy 7 [one for each], ASXL1 [n = 2]), findings that were comparable to those (66.5%, 63.1%–88.9%) in the four patients with advanced myelodysplastic syndromes. The increased expression of CXCR4 may therefore reflect intrinsic abnormalities of HSPCs caused by somatic mutations that allow them to evade restriction by BM stromal cells.