Fidelity of mutational burden in immature and mature cells before and after 6 cycles of AZA in clinical responders and nonresponders. (A) Schematic showing AZA treatment regime and sorting strategy to assess VAF in multiple cell types before and after AZA treatment. Those cell types colored white were not characterized in this figure. (B-C) VAFs in individual cell types, pre- and post-AZA treatment in 9 patients with MDS, for the indicated variants for each patient with corresponding clinical parameters (neutrophils, ×10⁹/L; platelets [Plts], ×10⁹/L; hemoglobin [Hb], g/L; and blasts, % blasts in BM). VAFs refer to alleles: in diploid cells a VAF of 0.5 indicates that every cell carries a mutated allele. VAFs >0.5 can occur where there is loss of heterozygosity or in the case of X-linked genes in male patients where each cell carries only 1 copy of the allele. For each patient the International Working Group [IWG] (2006) assessment post-AZA is shown.¹⁹ Responders (B) (complete remission [CR], marrow complete remission [mCR], and hematological improvement [HI]) are indicated in purple and nonresponders (C) (all stable disease [SD]) are indicated in lime. Variant names are abbreviated as gene names; multiple occurrences of the same gene in a single patient indicate multiple variants detected. Full variant IDs are provided in the supplemental Table 2.