Flow cytometric immunophenotypic alterations of persistent clonal haematopoiesis in remission bone marrows of patients with NPM1-mutated acute myeloid leukaemia

Abstract

Clonal haematopoiesis (CH) in patients with acute myeloid leukaemia (AML) may persist beyond attaining complete remission. From a consecutive cohort of 67 patients with nucleophosmin 1-mutated (NPM1^mut ) AML, we identified 50 who achieved NPM1^mut clearance and had parallel multicolour flow cytometry (MFC) and next generation sequencing (NGS). In total, 13 (26%) cleared all mutations, 37 (74%) had persistent CH frequently involving DNA methyltransferase 3α (DNMT3A,70%), tet methylcytosine dioxygenase 2 (TET2, 27%), isocitrate dehydrogenase 2 (IDH2, 19%) and IDH1 (11%). A small number (<1%) of aberrant CD34⁺ myeloblasts, but immunophenotypically different from original AML blasts [herein referred to as a pre-leukaemic (PL) phenotype], was detected in 17 (49%) patients with CH, but not in any patients with complete clearance of all mutations (P = 0·0037). A PL phenotype was associated with higher mutation burden (P = 0·005). Persistent IDH2 and serine and arginine-rich splicing factor 2 (SRSF2) mutations were exclusively observed in PL⁺ CH⁺ cases (P = 0·016). Persistent dysplasia was seen exclusively in cases with a PL⁺ phenotype (29% vs. none; P = 0·04). The PL⁺ phenotype did not correlate with age, intensity of induction therapy or relapse-free survival. Post-remission CH in the setting of NPM1^mut clearance is common and may result in immunophenotypic changes in myeloid progenitors. It is important to not misinterpret these cells as AML measurable residual disease (MRD).

Keywords: AML; Clonal hematopoiesis; MRD; NPM1.