Summary
The research article discusses myeloproliferative neoplasms (MPN), a type of cancer that affects the blood and bone marrow. It focuses on the Calreticulin (CALR) mutation found in 20% to 25% of MPN patients (with ET and MF) and, which is a potential target for new drug therapies. The authors describe a novel approach using CRISPR/Cas9 to edit genes in human blood stem cells, allowing for the study of CALR mutant MPN in a human setting. The edited cells exhibited features similar to those seen in people with CALR mutant MPN, such as an abnormal response to thrombopoietin, immune cell imbalance, and bone marrow damage. The study also found that the mutated cells were more sensitive to certain drugs, providing a new tool to study CALR mutant MPN and develop new treatments.
Abstract
Calreticulin (CALR) mutations present the main oncogenic drivers in JAK2 wildtype (WT) myeloproliferative neoplasms (MPN), including essential thrombocythemia and myelofibrosis, where mutant (MUT) CALR is increasingly recognized as a suitable mutation-specific drug target. However, our current understanding of its mechanism-of-action is derived from mouse models or immortalized cell lines, where cross-species differences, ectopic over-expression and lack of disease penetrance are hampering translational research. Here, we describe the first human gene-engineered model of CALR MUT MPN using a CRISPR/Cas9 and adeno-associated viral vector-mediated knock-in strategy in primary human hematopoietic stem and progenitor cells (HSPCs) to establish a reproducible and trackable phenotype in vitro and in xenografted mice.
Our humanized model recapitulates many disease hallmarks: thrombopoietin-independent megakaryopoiesis, myeloid-lineage skewing, splenomegaly, bone marrow fibrosis, and expansion of megakaryocyte-primed CD41+ progenitors. Strikingly, introduction of CALR mutations enforced early reprogramming of human HSPCs and the induction of an endoplasmic reticulum stress response. The observed compensatory upregulation of chaperones revealed novel mutation-specific vulnerabilities with preferential sensitivity of CALR mutant cells to inhibition of the BiP chaperone and the proteasome. Overall, our humanized model improves purely murine models and provides a readily usable basis for testing of novel therapeutic strategies in a human setting.
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