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Leukemia. 2018 Feb;32(2):429-437. doi: 10.1038/leu.2017.214. Epub 2017 Jul 5.

The calreticulin (CALR) exon 9 mutations are promising targets for cancer immune therapy.

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Department of Hematology, Zealand University Hospital, Roskilde, Denmark.
Center for Cancer Immune Therapy, Department of Hematology, Copenhagen University Hospital at Herlev, Herlev, Denmark.
Department of Oncology, Copenhagen University Hospital at Herlev, Herlev, Denmark.
Department of Hematology, Rigshospitalet, Copenhagen, Denmark.
Department of Immunology and Microbiology, University of Copenhagen, Copenhagen, Denmark.


The calreticulin (CALR) exon 9 mutations are found in ∼30% of patients with essential thrombocythemia and primary myelofibrosis. Recently, we reported spontaneous immune responses against the CALR mutations. Here, we describe that CALR-mutant (CALRmut)-specific T cells are able to specifically recognize CALRmut cells. First, we established a T-cell culture specific for a CALRmut epitope. These specific T cells were able to recognize several epitopes in the CALRmut C terminus. Next, we established a CALRmut-specific CD4+ T-cell clone by limiting dilution. These CD4+ T cells recognized autologous CALRmut monocytes and hematopoietic stem cells, and T-cell recognition of target cells was dependent on the presence of CALR. Furthermore, we showed that the CALRmut response was human leukocyte antigen (HLA)-DR restricted. Finally, we demonstrated that the CALRmut-specific CD4+ T cells, despite their phenotype, were cytotoxic to autologous CALRmut cells, and that the cytotoxicity was mediated by degranulation of the T cells. In conclusion, the CALR exon 9 mutations are targets for specific T cells and thus are promising targets for cancer immune therapy such as peptide vaccination in patients harboring CALR exon 9 mutations.

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