CAR T cell therapy selectively eradicates mutant calreticulin cells in myelofibrosis xenografts and human organoid models.

Myeloproliferative neoplasms (MPNs) are a group of chronic myeloid blood cancers, with a significant subset driven by mutations in calreticulin (CALR). Current immunotherapies have limited success in myeloid neoplasms due to a lack of amenable targets and an immunologically hostile tumor microenvironment (TME). The calreticulin mutant protein (mutCALR) uniquely binds and activates the thrombopoietin receptor (TpoR), leading to the display of a mutCALR-TpoR complex on the extracellular membrane of disease-driving cells. This complex represents a critical therapeutic vulnerability, offering a specific target for advanced immunotherapeutic strategies where standard treatments fall short in achieving deep, durable remissions and disease eradication.

Researchers developed a novel CAR T cell therapy designed to specifically target the mutCALR-TpoR complex expressed on the surface of disease-driving cells. The therapy's efficacy was evaluated in vitro using patient samples from individuals with myelofibrosis, focusing on the selective depletion of mutCALR+ stem cells. In vivo studies utilized mutCALR leukemia xenograft models to assess improvements in survival. To more accurately simulate the complex environment of myelofibrotic marrow, a human "chimeroid" organoid model was developed, allowing for the evaluation of CAR T cell potency within a fibrotic tumor microenvironment. Furthermore, a method was devised to boost the cell surface expression of mutCALR in CD34+ cells isolated from patients with accelerated/blast phase MPNs (defined as >10% blasts), aiming to enhance CAR T cell targeting efficiency.