Increased megakaryocytic proliferation, pro-platelet deposition and expression of fibrosis-associated factors in children with chronic myeloid leukaemia with bone marrow fibrosis

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Paediatric chronic myeloid leukaemia (ped-CML) is rare and ped-CML with fibre accumulation in the bone marrow (MF) is thought to be even rarer. In adults (ad-CML), fibrosis represents an adverse prognostic factor. So far, the pro-fibrotic changes in the bone marrow microenvironment have not been investigated in detail in ped-CML. From a total of 66 ped-CML in chronic phase, biopsies were analysable and 10 had MF1/2 (MF1, n = 8/10; MF2, n = 2/10). We randomly selected 16 ped-CML and 16 ad-CML cases with and without fibrosis (each n = 8) as well as 18 non-neoplastic controls. Bone marrow samples were analysed with a real-time PCR-based assay (including 127 genes for paediatric cases) and by immunohistochemistry. We found increased expression of megakaryocytic genes in ped-CML. The number of megakaryocytes and pro-platelets are increased in CML patients, but the most significant increase was noted for ped-CML-MF1/2. Anti-fibrotic MMP9 expression was lower in children than in adults. Cell mobilisationrelated CXCL12 was decreased in young and adult patients with CML but not the corresponding receptor CXCR4. In summary, fibre accumulation in ped-CML-MF1/2 is associated with increased megakaryocytic proliferation and increased interstitial pro-platelet deposition. Deregulated expression of matrix-modulating factors shifts the bone marrow microenvironment towards fibrosis.

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