Chronic myeloid leukemia (CML) is genetically characterized by the Philadelphia (Ph) chromosome, formed through a reciprocal translocation between chromosomes 9 and 22 and giving rise to the constitutively active tyrosine kinase P210 BCR/ABL1. Therapeutic strategies aiming for a cure of CML will require full eradication of Ph chromosome-positive (Ph + ) CML stem cells. Here we used geneexpression profiling to identify IL-1 receptor accessory protein (IL1RAP) as up-regulated in CML CD34 + cells and also in cord blood CD34 + cells as a consequence of retroviral BCR/ABL1 expression. To test whether IL1RAP expression distinguishes normal (Ph − ) and leukemic (Ph + ) cells within the CML CD34 + CD38 − cell compartment, we established a unique protocol for conducting FISH on small numbers of sorted cells. By using this method, we sorted cells directly into drops on slides to investigate their Ph-chromosome status. Interestingly, we found that the CML CD34 + CD38 − IL1RAP + cells were Ph + , whereas CML CD34 + CD38 − IL1RAP − cells were almost exclusively Ph − . By performing long-term culture-initiating cell assays on the two cell populations, we found that Ph + and Ph − candidate CML stem cells could be prospectively separated. In addition, by generating an anti-IL1RAP antibody, we provide proof of concept that IL1RAP can be used as a target on CML CD34 + CD38 − cells to induce antibody-dependent cell-mediated cytotoxicity. This study thus identifies IL1RAP as a unique cell surface biomarker distinguishing Ph + from Ph − candidate CML stem cells and opens up a previously unexplored avenue for therapy of CML.antibody-dependent cell-mediated cytotoxicity | cancer | biomarker | therapeutic antibody

Serial quantification of BCR–ABL1 mRNA is an important therapeutic indicator in chronic myeloid leukaemia, but there is a substantial variation in results reported by different laboratories. To improve comparability, an internationally accepted plasmid certified reference material (CRM) was developed according to ISO Guide 34:2009. Fragments of BCR–ABL1 (e14a2 mRNA fusion), BCR and GUSB transcripts were amplified and cloned into pUC18 to yield plasmid pIRMM0099. Six different linearised plasmid solutions were produced with the following copy number concentrations, assigned by digital PCR, and expanded uncertainties: 1.08±0.13 × 106, 1.08±0.11 × 105, 1.03±0.10 × 104, 1.02±0.09 × 103, 1.04±0.10 × 102 and 10.0±1.5 copies/μl. The certification of the material for the number of specific DNA fragments per plasmid, copy number concentration of the plasmid solutions and the assessment of inter-unit heterogeneity and stability were performed according to ISO Guide 35:2006. Two suitability studies performed by 63 BCR–ABL1 testing laboratories demonstrated that this set of 6 plasmid CRMs can help to standardise a number of measured transcripts of e14a2 BCR–ABL1 and three control genes (ABL1, BCR and GUSB). The set of six plasmid CRMs is distributed worldwide by the Institute for Reference Materials and Measurements (Belgium) and its authorised distributors (https://ec.europa.eu/jrc/en/reference-materials/catalogue/; CRM code ERM-AD623a-f).

The 8p11 myeloproliferative syndrome (EMS), also referred to as stem cell leukemia/lymphoma, is a chronic myeloproliferative disorder that rapidly progresses into acute leukemia. Molecularly, EMS is characterized by fusion of various partner genes to the