A groundbreaking advancement in cancer immunotherapy has emerged from collaborative research led by scientists at University College London (UCL) and the University of Oxford, who have engineered a novel CAR T cell therapy aimed at eradicating the malignant stem cells that drive myeloproliferative neoplasms (MPNs), a challenging group of blood cancers. This innovative therapy harnesses the immune system’s capacity for precision targeting to selectively annihilate cells harboring a mutation in the calreticulin (CALR) gene, a mutation present in nearly one-third of MPN cases, while sparing normal, healthy blood cells.
Myeloproliferative neoplasms originate from genetic mutations arising within hematopoietic stem cells, the progenitors of blood cell lineages. Over time, these mutated stem cells can lead to progressive bone marrow fibrosis, or scarring, impairing the marrow’s ability to produce healthy blood. This pathological scarring culminates in myelofibrosis, a debilitating condition characterized by anemia and bone marrow failure. Moreover, a significant subset of patients experience disease evolution to an accelerated phase resembling acute leukemia, marked by high mortality rates and limited therapeutic options. Currently, there are no universally curative treatments available for most MPN patients.
Chimeric antigen receptor (CAR) T cell therapy represents a transformative advance in hematologic oncology, enabling the reprogramming of patient-derived cytotoxic T lymphocytes to identify and attack malignant cells with extraordinary specificity. While CAR T cells have revolutionized treatment for certain leukemias and lymphomas, their application to MPNs has faced challenges due to the difficulty of isolating unique markers on malignant stem cells without affecting normal hematopoiesis. This new study, published in Science Translational Medicine, reports the successful design of CAR T cells that target the aberrant CALR protein expressed on the surface of mutant stem cells, thus providing an exploitable vulnerability.
The research team employed a comprehensive suite of experimental models, including patient-derived samples, sophisticated three-dimensional organoids mimicking human bone marrow architecture, and in vivo murine models, to validate the efficacy and selectivity of the CALR-targeted CAR T cells. These CAR T cells demonstrated potent cytotoxicity against CALR-mutant cells, effectively depleting disease-driving populations while leaving non-mutant blood cells unharmed. This selective depletion is crucial to preserving normal hematopoiesis and minimizing adverse effects.
Significantly, the three-dimensional bone marrow organoid model employed in the study recapitulated the fibrotic and complex microenvironment of myelofibrosis. The ability of CAR T cells to infiltrate this dense, scarred environment and execute targeted killing provides encouraging evidence for their potential clinical effectiveness in the hostile tumor milieu typically resistant to therapy. Organotypic models like these bridge the gap between in vitro studies and human clinical trials by faithfully replicating disease conditions, offering invaluable insights into real-world therapeutic dynamics.
Further insights emerged concerning the efficacy of CAR T cell therapy in the more aggressive, accelerated phase of MPN, where target protein expression diminishes. The team found that treatment with eltrombopag, a thrombopoietin receptor agonist used clinically to elevate platelet counts, enhanced CALR display on mutant cells. This upregulation significantly improved CAR T cell recognition and killing efficiency, suggesting an adjunctive therapeutic strategy to overcome immune evasion in advanced disease stages.
In vivo experiments using xenotransplant mouse models of myelofibrosis revealed that CALR-specific CAR T cells not only controlled leukemic proliferation but also conferred a meaningful survival advantage. These data strongly support the translational potential of this therapy and underpin plans for a Phase I clinical trial at University College London Hospital (UCLH), anticipated to commence within one to two years, pending regulatory approvals and funding acquisition.
Standard treatment paradigms for MPNs currently involve JAK inhibitors, which ameliorate symptoms by modulating cytokine signaling pathways but fail to eradicate the underlying malignant stem cells. Consequently, most patients eventually develop resistance and disease progression ensues. Allogeneic bone marrow transplantation remains the sole potentially curative option, albeit limited by donor availability, patient fitness, and a high mortality risk from transplantation complications. The advent of CAR T cell therapy tailored to CALR mutations may revolutionize this therapeutic landscape by offering a targeted, less toxic alternative.
Dr. Alex Rampotas, the study’s lead author, highlighted the therapeutic promise of this strategy, emphasizing its precision and potential to induce durable remissions. By exploiting the CALR mutation as a neoantigenic “flag,” the CAR T cells can discriminate malignant clones from normal counterparts, “turbo-boosting” the immune response to root out the disease at its source. This selective eradication stands to restore normal blood cell production, shifting treatment goals from symptomatic relief to genuine disease modification.
Professor Beth Psaila, a senior author from Oxford, underscored the importance of the advanced organoid models in elucidating the complex interactions within fibrotic bone marrow and facilitating the evaluation of novel immunotherapies. These models enable single-cell resolution analyses in human tissue contexts, accelerating the refinement of CAR T cell therapies and potentially guiding personalized treatment approaches in myelofibrosis and related blood cancers.
MPNs are categorized as rare diseases, yet their cumulative incidence in the UK approaches 4,000 new diagnoses annually, equating to about eight cases per 100,000 population. Among these, CALR-mutated MPNs comprise approximately one-third, translating to hundreds of new patients yearly who could benefit from such specialized therapies. Given the chronic nature of MPNs, this strategy also holds promise to transform long-term disease management for the substantial patient population living with these cancers.
The research consortium is actively engaged in securing resources and navigating regulatory pathways to initiate clinical testing of the CALR-targeted CAR T cells. Should early-phase trials demonstrate safety and efficacy, broader clinical deployment and patient access could feasibly occur within the early to mid-2030s. This timeline reflects realistic developmental trajectories for sophisticated cellular therapeutics but underscores the urgency for continued support in this promising frontier.
This study exemplifies the forefront of personalized cancer immunotherapy, where genetic mutations define bespoke immune interventions capable of surgically excising malignant stem cells. By coupling molecular insights with innovative cell engineering and physiologically relevant models, the research charts a course toward transformative treatments with the potential to rewrite prognoses for patients grappling with myeloproliferative neoplasms.
Subject of Research: Cells
Article Title: CAR T cell therapy selectively depletes disease-driving mutant calreticulin cells in xenotransplants and human organoid models of myelofibrosis
News Publication Date: 1-Jul-2026
Web References: www.science.org/doi/10.1126/scitranslmed.adz3553
References: DOI 10.1126/scitranslmed.adz3553, Science Translational Medicine
Keywords: CAR T cell therapy, myeloproliferative neoplasms, myelofibrosis, calreticulin mutation, hematopoietic stem cells, immunotherapy, bone marrow organoids, leukemia, eltrombopag, blood cancer, targeted therapy
