Diverging fates of cells of origin in acute and chronic leukaemia.
Bottom Line: During disease-maintenance, CML LT-HSCs persist to function as cancer stem cells (CSCs) that maintain leukaemia and require signalling by the transcription factor STAT5.In contrast, B-ALL LT-HSCs differentiate into CSCs that correspond to pro-B cells.This transition step requires a transient IL-7 signal and is lost in IL-7Rα-deficient cells.
Affiliation: Research Institute of Molecular Pathology (I.M.P.), Vienna, Austria. email@example.comShow MeSH
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Mentions: Long-term cultivation of CSCs from CML has so far not been reported. When we cultivated ex vivo purified BCR/ABLp210+ LT-HSCs in serum-free medium plus defined growth factors (SCF/Tpo/IGF-II and FGF-1; Zhang & Lodish, 2005, 2008), the cells formed ‘cobblestone structures’ consisting of adherent and suspension cells (Supporting Information Fig S6C). Efficient cultivation was only achieved when the large (forward scatter, FSChigh) cells representing approximately 7–8% of the CSC-pool were re-plated (Supporting Information Fig S6C). Small (FSClow) BCR/ABLp210+ CSCs were unable to proliferate in vitro (Movies S1 and S2). Using this method, BCR/ABLp210+ CSCs were expanded >1014-fold within 67 days (Fig 6A). Wildtype LT-HSCs increased only about 100-fold and stopped to proliferate after 14 days. BCR/ABLp210+ CSCs expressed multiple markers indicative for HSCs (Supporting Information Tables SIIA and SIIB) and retained the ability to induce a fatal CML-like disease (n = 3) upon injection into lethally irradiated mice even after 103-fold expansion (Fig 6B). This CML recapitulated the phenotype observed in primary transplants and was dominated by Gr-1+/Mac-1+ leukaemic cells (Fig 6B). However, this leukaemogenic capacity was lost after 107-fold expansion (data not shown). We also tested whether our cultivation system extends to CSCs from caSTAT5+-induced disease. Purified caSTAT5+ LT-HSCs from moribund mice were maintained in SCF/Tpo/IGF-II and FGF-1 under serum-free conditions—enabling sustained proliferation (Supporting Information Fig S6D). Comparable to BCR/ABLp210 CSCs, the caSTAT5+ CSCs expressed HSC-surface markers in vitro (Supporting Information Tables SIIIA and SIIIB) and were able to induce CML in secondary transplants (data not shown). In summary, we show that BCR/ABLp210+ and caSTAT5+ CSCs may be expanded in vitro—retaining key features such as HSC surface marker expression, self-renewal and the ability to induce leukaemia upon transplantation.
Affiliation: Research Institute of Molecular Pathology (I.M.P.), Vienna, Austria. firstname.lastname@example.org