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CD36 defines CML cells less sensitive to imatinib
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Figure 2. Differentially expressed proteins on primitive CML cells. (A) Representative histograms showing the specific expression of CD36 and LEPR but not ITGB3 and TFRC on leukemic CD34+CD38low cells compared to corresponding cells in NBM. (B) Dot plot showing consistent overexpression of CD36 in the CD34+CD38low cell fraction in CML samples (n=16) compared to NBM samples (n=5). (C) Overexpression of LEPR in the CD34+CD38low cell fraction in a cohort of ten CML patients with high IL1RAP expression as compared to NBM samples (n=4). **P<0.01. CML: chronic myeloid leukemia; NBM: normal bone marrow; MFI: mean fluorescence inten- sity; LEPR: leptin receptor.
IL1RAP+CD36− CML cells. Both populations are enriched for BCR/ABL1 positive cells, given that IL1RAP expression marks these cells.11,13 The two cell populations exhibited similar growth and survival after three days in cell culture (n=3, P=0.48, Figure 3E). Interestingly, the CD36 expressing cell population showed significantly decreased imatinib sensitivity as compared to cells lacking CD36 (n=3, P=0.019, Figure 3F). By contrast, the two cell populations exhibited a similar sensitivity to nilotinib, suggesting that the decreased in vitro sensitivity of CD36 expressing cells to imatinib can be overcome by the second generation TKI nilotinib (Online Supplementary Figure S7). In order to deter- mine if the difference in response to imatinib was caused by differences in quiescence, cell cycle status was evaluated in three CML patient samples. No difference in cell cycle sta- tus was observed between CD36 positive and negative cells within the CD34+CD38lowIL1RAP+ population, with the
majority of cells being in G0 or G1 phase (Figure 3G,H). As anticipated, more mature CD34+CD38+ cells were cycling to a higher degree (Online Supplementary Figure S8). These findings suggest that within the CD34+CD38lowIL1RAP+ compartment, CD36 defines cells that are quiescent and less sensitive to imatinib treatment. Morever, within the primitive CD34+CD38lowIL1RAP+ fraction, CD36 positive and CD36 negative cells showed similar expression of other putative CML stem cell markers, such as CD25 and CD26 (Online Supplementary Figure S9).
CD36 expression declines during TKI treatment
In order to investigate whether TKI treatment affects CD36 expression, we first cultured primary CML cells in vitro. However, CD36 expression rapidly decreased during in vitro culture even without the presence of TKI (Online Supplementary Figure S10A-S10C). Subsequently, in a more
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