CD200 expression marks leukemia stem cells (LSC) in human AML part 2

The leukemia stem cell (LSC) populations of acute myeloid leukemia (AML) exhibit phenotypic, genetic and functional heterogeneity that contribute to therapy failure and relapse. Progress towards understanding the mechanistic basis for therapy resistance in LSCs has been hampered by difficulties in isolating cell fractions that enrich for the entire heterogeneous population of LSCs within individual AML samples. We previously reported that CD200 gene expression is upregulated in LSC-containing AML fractions. We demonstrate that CD200 is present on a greater proportion of CD45dim blasts compared to more differentiated CD45high cells in AML patient samples. In 75% of AML cases examined, CD200 was expressed on 10% of CD45dim blasts; of these, CD200 identified LSCs within the blast population in 90% of samples tested in xenotransplantation assays. Notably, CD200 expression captured both CD34- and CD34- LSCs within individual AML samples. Highly purified CD45dimCD200+ LSC-containing blasts were enriched in primitive HSC/progenitor-like signatures, while CD45dimCD200- nonengrafting blasts were enriched in myeloid-like signature. Moreover, analysis of CD45dimCD200+ blasts from NPM1-mutated AMLs also demonstrated an enrichment of primitive gene expression signatures compared to unfractionated (bulk) cells. CD45dim blasts were sorted into CD200+ and CD200- fractions from AML samples functionally validated to contain CD200+ LSCs (Metadata1) before RNA extraction and sequencing. RNA from unfractionated (bulk) cells was extracted and subjected to gene expression analysis using Illumina HumanHT-12 v4 microarrays (Ng et al. Nature. 2016;540:433-437) (Metadata2) or sequencing (Metadata3).