No abstract

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

Chronic myeloid leukemia (CML) is currently treated with tyrosine kinase inhibitors, but these do not effectively eliminate the CML stem cells. As a consequence, CML stem cells persist and cause relapse in most patients upon drug discontinuation. Furthermore, no effective therapy exists for the advanced stages of the disease. Interleukin-1 receptor accessory protein (IL1RAP; IL1R3) is a coreceptor of interleukin-1 receptor type 1 and has been found upregulated on CML stem cells. Here, we show that primitive (CD34CD38) CML cells, in contrast to corresponding normal cells, express a functional interleukin-1 (IL-1) receptor complex and respond with NF-κB activation and marked proliferation in response to IL-1. IL1RAP antibodies that inhibit IL-1 signaling could block these effects. In vivo administration of IL1RAP antibodies in mice transplanted with chronic and blast phase CML cells resulted in therapeutic effects mediated by murine effector cells. These results provide novel insights into the role of IL1RAP in CML and a strong rationale for the development of an IL1RAP antibody therapy to target residual CML stem cells.

Key Points• IL1RAP is overexpressed on candidate AML stem cells and is a promising target for antibody-based therapy.IL1RAP, a co-receptor for interleukin (IL)-1 and IL-33 receptors, was previously found to be highly upregulated on candidate chronic myeloid leukemia stem cells, allowing for leukemia-selective killing using IL1RAP-targeting antibodies. We analyzed IL1RAP expression in a consecutive series of 29 patients with acute myeloid leukemia (AML) and, based on the level of expression in mononuclear cells (MNCs), we divided the samples into 3 groups: IL1RAP low (n 5 6), IL1RAP intermediate (n 5 11), and IL1RAP high (n 5 12). Within the CD341CD382 population, the intermediate and high groups expressed higher levels of IL1RAP than did corresponding normal cells. With the aim to target AML stem cells, an anti-IL1RAP monoclonal antibody was generated followed by isotype switching for improved antibody-dependent, cell-mediated cytotoxicity activity. Using this antibody, we achieved selective killing of AML MNC, CD341CD381, and CD341CD382 cells. Our findings demonstrate that IL1RAP is a promising new therapeutic target in AML. (Blood. 2013;121(18):3709-3713)