Hematopoietic expression of a chimeric murine‐human <scp>CALR</scp> oncoprotein allows the assessment of <scp>anti‐CALR</scp> antibody immunotherapies in vivo
Sarada Achyutuni, Harini Nivarthi, Andrea Majoros, Eva Hug, Christina M. Schueller, Ruochen Jia, Cecília Varga, Michael Schuster, Martin Senekowitsch, Dimitrios Tsiantoulas, Anoop Kavirayani, Christoph J. Binder, Christoph Bock, Oleh Zagrijtschuk, Róbert Královics
Abstract
Myeloproliferative neoplasms (MPNs) are characterized by a pathologic expansion of myeloid lineages. Mutations in JAK2, CALR and MPL genes are known to be three prominent MPN disease drivers. Mutant CALR (mutCALR) is an oncoprotein that interacts with and activates the thrombopoietin receptor (MPL) and represents an attractive target for targeted therapy of CALR mutated MPN. We generated a transgenic murine model with conditional expression of the human mutant exon 9 (del52) from the murine endogenous Calr locus. These mice develop essential thrombocythemia like phenotype with marked thrombocytosis and megakaryocytosis. The disease exacerbates with age showing prominent signs of splenomegaly and anemia. The disease is transplantable and mutCALR stem cells show proliferative advantage when compared to wild type stem cells. Transcriptome profiling of hematopoietic stem cells revealed oncogenic and inflammatory gene expression signatures. To demonstrate the applicability of the transgenic animals for immunotherapy, we treated mice with monoclonal antibody raised against the human mutCALR. The antibody treatment lowered platelet and stem cell counts in mutant mice. Secretion of mutCALR did not constitute a significant antibody sink. This animal model not only recapitulates human MPN but also serves as a relevant model for testing immunotherapeutic strategies targeting epitopes of the human mutCALR.