Mesenchymal stromal cells from JAK2V617F myeloproliferative neoplasms support healthy and malignant haematopoiesis in a humanised scaffold model in vivo
Myeloproliferative Neoplasms (MPN) are malignancies of hematopoietic stem and progenitor cells (HSPCs) that lead to the overproduction of mature blood cells. These disorders include Essential Thrombocythemia (ET), Polycythaemia Vera (PV), and Primary Myelofibrosis (PMF), primarily driven by somatic mutations such as JAK2V617F. Research indicates that mesenchymal stromal cells (MSCs) support fibrosis in PMF, though their role in ET and PV remains less clear. Furthermore, in vivo studies of ET/PV HSPCs remain a challenge due to low engraftment levels in xenograft models. Overall design: We employed a 3D scaffold model to create an MPN humanised xenograft mouse model, enabling in vivo functional studies of primary MPN progenitor cells and the supportive role of human MSCs. Using this model, we first demonstrated robust haematopoietic support of healthy (HD) HSPCs by PV and ET MSCs. We then investigated the role of MSCs in sustaining JAK2V617F mutant cells by using a CRISPR-Cas9 editing model, along with primary PV and ET HSPCs. Our results showed consistent engraftment of CRISPR-edited JAK2V617F mutant HSPCs and PV and ET patient-derived HSPCs in scaffolds seeded with HD, PV, and ET stroma, providing the first in vivo evidence that PV and ET MSCs can sustain both healthy and MPN-associated haematopoiesis. Furthermore, HD MSCs were also capable of sustaining PV and ET HSPCs in vivo. Overall, we present the first humanised MPN xenograft model that offers valuable insights into how human BM MSCs interact with JAK2V617F mutant clones.