Mosca, Matthieu; Gurvan Hermange; Amandine Tisserand; Robert Noble; Christophe Marzac; Caroline Marty; Cecile Le Sueur; Hugo Campario; Gaelle Vertenoeil; Mira El-Khoury; Cyril Catelain; Philippe Rameau; Cyril Gella; Julien Lengte; Nicole Casadevall; Remi Favier; Eric Solary; Bruno Cassinat; Jean-Jacques Kiladjian; Stefan N. Constantinescu; Florence Pasquier; Michael E. Hochberg; Hana Raslova; Jean-Luc Villeval; Francois Girodon; William Vainchenker; Paul-Henry Cournede and Isabelle Plo

Classical BCR-ABL-negative myeloproliferative neoplasms (MPN) are clonal disorders of hematopoietic stem cells (HSC) caused mainly by recurrent mutations in genes encoding JAK2 (JAK2), calreticulin (CALR), or the thrombopoietin receptor (MPL). Interferon alpha (IFNα) has demonstrated some efficacy in inducing molecular remission in MPN. In order to determine factors that influence molecular response rate, we evaluated the long-term molecular efficacy of IFNα in MPN patients by monitoring the fate of cells carrying driver mutations in a prospective observational and longitudinal study of 48 patients over more than 5 years. We measured several times per year the clonal architecture of early and late hematopoietic progenitors (84,845 measurements) and the global variant allele frequency in mature cells (409 measurements). Using mathematical modeling and hierarchical Bayesian inference, we further inferred the dynamics of IFNα-targeted mutated HSC. Our data support the hypothesis that IFNα targets JAK2V617F HSC by inducing their exit from quiescence and differentiation into progenitors. Our observations indicate that treatment efficacy is higher in homozygous than heterozygous JAK2V617F HSC and increases with high IFNα dosage in heterozygous JAK2V617F HSC. Besides, we found that the molecular responses of CALRm HSC to IFNα were heterogeneous, varying between type 1 and type 2 CALRm, and high dosage of IFNα correlates with worse outcomes. Together, our work indicates that the long-term molecular efficacy of IFNα implies an HSC exhaustion mechanism and depends on both the driver mutation type and IFNα dosage.