Differential Dynamics of CALR Mutant Allele Burden in Myeloproliferative Neoplasms during Interferon Alfa Treatment

Abstract

Discovery of somatic mutations in the calreticulin gene (CALR) has identified a subgroup of Philadelphia-negative chronic myeloproliferative neoplasms (MPN) with separate haematological characteristics and prognosis. CALR mutations serve as novel markers both of diagnostic value and as targets for monitoring molecular responses during therapy. Interferon-α (IFN) selectively targets the malignant clone in a subset of MPN patients and can induce both haematological and molecular remissions in CALR mutated essential thrombocythemia (ET) patients. We investigated the response to IFN in a cohort of 21 CALR mutated MPN patients including ET, prefibrotic primary myelofibrosis (pre-PMF), and primary myelofibrosis (PMF) with a median follow-up of 31 months. For evaluation of a molecular response, we developed highly sensitive quantitative PCR (qPCR) assays for monitoring the mutant allele burden of the two most prevalent CALR mutations (type 1 and type 2). Thirteen patients (62%) experienced a decrease in the mutant allele burden with a median decline of 29% from baseline. However, only four patients, including patients with ET, pre-PMF, and PMF diagnosis, achieved molecular responder (MR) status with >50% reduction in mutant allele burden according to European LeukemiaNet (ELN) guidelines. MR patients displayed significant differences in the dynamics of the CALR mutant load with regard to time to response and dynamics in mutant allele burden after discontinuation of IFN treatment. Furthermore, we highlight the prognostic value of the CALR mutant allele burden by showing a close association with leucocyte- and platelet counts, hemoglobin concentration, in addition to plasma lactate dehydrogenase (LDH) irrespective of molecular response and treatment status.

Inflammatory Signaling Pathways in Preleukemic and Leukemic Stem Cells

“…Data from clinical studies in PV, ET, and MF patients show that treatment with IFN-α can cause cycling and differentiation of pathologic stem cells, and lead to a decrease of JAK2 allelic burden ( 9 , 27 ). Similar results have been obtained in patients with calreticulin-mutated ET and MF ( 28 ). IFN treatment resulted in transfusion independence, decreased spleen size, and improved symptoms and quality of life in a significant proportion of MPN patients ( 29 ).…”

Synergic Crosstalk between Inflammation, Oxidative Stress, and Genomic Alterations in BCR–ABL-Negative Myeloproliferative Neoplasm

“…Such findings are in agreement with other results from CD34+ cells of MPN subjects, where JAK2V617F-but not mutant CALR-caused an increase of IFNa-controlled genes [90]. A possible hypothesis regarding these results is that CALR-mutated MPN subjects require greater amounts of IFNa to attain an analogous molecular response [91], as confirmed by Czech et al, who reported higher doses of IFN were needed to achieve the same response in CALR mutant 32D cells than in JAK2V617F mutant 32D cells [90].…”

Emerging translational science discoveries, clonal approaches, and treatment trends in chronic myeloproliferative neoplasms

“…[33][34][35][36]43,44 Recently, two groups reported hematological responses also in CALR-positive MPN patients, including patients with MF. [45][46][47][48] Koschmieder et al assessed the degree of molecular response in patients with JAK2 V617Fvs CALRmutant ET or MF treated with pegIFNa. In a retrospective analysis, while the percentage of complete hematological response was similar in the two groups, partial molecular remission (PMR) was significantly higher in JAK2 V617Fvs CALR-mutant patients (61 vs 20%), and nonresponse was higher in CALR-vs JAK2 V617F -mutant patients (70% vs 22%).…”

“…Clearly, IFNa is able to induce molecular remissions in a substantial fraction of patients, and murine models have shown explicit sensitivity of JAK2 V617F ‐positive HSCs to IFN . Recently, two groups reported hematological responses also in CALR ‐positive MPN patients, including patients with MF . Koschmieder et al assessed the degree of molecular response in patients with JAK2 V617F ‐ vs CALR ‐mutant ET or MF treated with pegIFNa.…”