The driver mutations JAK2V617F, MPLW515L/K and CALR influence disease phenotype of myeloproliferative neoplasms (MPNs) and might sustain a condition of chronic inflammation.
The recent discovery of frameshift mutations in CALR in approximately 70 % of MPN patients lacking the JAK2 and MPL mutations offers a reliable diagnostic marker for the latter group.
Somatic mutations of Janus kinase 2 (JAK2V617F), calreticulin (CALR), and myeloproliferative leukemia virus oncogene (MPL) are the major clonal molecules that drive the pathogenesis of myeloproliferative neoplasms (MPN).
Although the role of mutated CALR in the development of MPNs has begun to be clarified, there are still no data available on the function of wild-type (WT) CALR during physiological hematopoiesis.
Moreover, the combination of BMN673, ruxolitinib, and hydroxyurea was highly effective in vivo against JAK2(V617F)<sup>+</sup> murine MPN-like disease and also against JAK2(V617F)<sup>+</sup>, CALR(del52)<sup>+</sup>, and MPL(W515L)<sup>+</sup> primary MPN xenografts.
Collectively, our studies demonstrate that occasional patients with CALR mutation-positive ET or MF carry other MPN-initiating genetic mutations (including JAK2 V617F), acquire "secondary mutations" before or after the CALR mutation, or evolve over time to being CALR mutation-homozygous.
Considering these results, we propose that mutant CALR promotes myeloproliferative neoplasm development by activating c-MPL and its downstream pathway.
We initially focused on identifying HLA class I neoepitopes derived from calreticulin (CALR) exon 9 mutations, found in ~ 80% of JAK2wt myeloproliferative neoplasms (MPN).
CALR mutations were present in 44% of ET (15/34), 14% of persistent thrombocytosis suggestive of MPN (3/21) and none of the secondary thrombocytosis (0/98).
Calreticulin mutation represents the second most frequent mutation after JAK2 V617F in myeloproliferative disorder and is considered to be a driving mutation.
Recent advances in the biology of MPNs have greatly facilitated their molecular diagnosis since most patients present with mutation(s) in the JAK2, MPL, or CALR genes.
Since association with MPL is required for the oncogenicity of mutant CALR, we propose a model in which the constitutive activation of the MPL downstream pathway by mutant CALR multimers induces the development of MPN.
Genotyping for CALR mutations represents a novel useful tool for establishing a clonal myeloproliferative disorder in JAK2 and MPL wt patients with thrombocytosis and may have prognostic and therapeutic relevance.