Exposure of Patient-Derived Mesenchymal Stromal Cells to TGFB1 Supports Fibrosis Induction in a Pediatric Acute Megakaryoblastic Leukemia Model

Abstract

Bone marrow fibrosis (BMF) is a rare complication in acute leukemia. In pediatrics, it predominantly occurs in acute megakaryoblastic leukemia (AMKL) and especially in patients with trisomy 21, called myeloid leukemia in Down syndrome (ML-DS). Defects in mesenchymal stromal cells (MSC) and cytokines specifically released by the myeloid blasts are thought to be the main drivers of fibrosis in the bone marrow niche (BMN). To model the BMN of pediatric patients with AMKL in mice, we first established MSCs from pediatric patients with AMKL (n ¼ 5) and ML-DS (n ¼ 9). Healthy donor control MSCs (n ¼ 6) were generated from unaffected children and adolescents ≤18 years of age. Steady-state analyses of the MSCs revealed that patient-derived MSCs exhibited decreased adipogenic differentiation potential and enrichment of proliferation-associated genes. Importantly, TGFB1 exposure in vitro promoted early profibrotic changes in all three MSC entities. To study BMF induction for longer periods of time, we created an in vivo humanized artificial BMN subcutaneously in immunodeficient NOD.Cg-Prkdc scid Il2rg tm1Wjl /SzJ mice, using a mixture of MSCs, human umbilical vein endothelial cell, and Matrigel. Injection of AMKL blasts as producers of TGFB1 into this BMN after 8 weeks induced fibrosis grade I/II in a dose-dependent fashion over a time period of 4 weeks. Thus, our study developed a humanized mouse model that will be instrumental to specifically examine leukemogenesis and therapeutic targets for AMKL blasts in future.Implications: TGFB1 supports fibrosis induction in a pediatric AMKL model generated with patient-derived MSCs.

Far from Health: The Bone Marrow Microenvironment in AML, A Leukemia Supportive Shelter

“…The BMM in children with Down syndrome (DS)-acute megakaryoblastic leukemia (AMKL) is characterized by marrow fibrosis [ 138 , 139 ], and TGF-β has been revealed as the main mediator of bone marrow fibrosis [ 140 ]. Based on pediatric patient-derived samples, Hack et al showed that TGF-β supports fibrosis and thus significantly contributes to leukemogenesis in pediatric DS-AMKL [ 141 ].…”

“…Given that MKs and leukemic blasts abundantly express TGF-β, resulting in markedly increased TGF-β levels in the DS-AMKL BMM, and TGF-β has been shown to induce early-stage marrow fibrosis in DS-AMKL [ 141 ], TGF-β appears to play a pivotal role in the leukemogenesis of AMKL (FAB-M7) in children with and without trisomy-21. Exosomes released in AML have been revealed to contain high concentrations of TGF-β and to impact leukemogenesis and the therapeutic response [ 134 , 142 ].…”