3089 – ELUCIDATING THE MECHANISM OF ACTION OF INTERFERON-Α THERAPY IN THE TREATMENT OF MYELOPROLIFERATIVE NEOPLASMS

The majority of patients with Bcr-Abl negative myeloproliferative neoplasms (MPN) have a JAK2-V617F mutation. JAK-inhibitors have been shown to normalize blood count and reduce splenomegaly, but does not substantially reduce the mutant allele burden. Interferon-alpha (IFNα) treatment is currently the only option for MPN patients that achieves molecular remission. However, long-term treatment with IFNα is required to achieve this and patients frequently exhibit adverse side-effects. Thus it is important to understand the mechanism of action of IFNα in achieving molecular remission. Previous studies in JAK2-mutant MPN mouse model have shown that IFNα treatment leads to the depletion of the mutant hematopoietic stem cells (HSCs). Our previous findings have shown that IFNα can drive wildtype dormant HSCs into cycling and leads to attrition of HSC function. To assess the inherent proliferative index of MPN-stem cells and the effect of IFNα treatment on mutant-HSC dormancy, a BrdU pulse-chase experiment was performed on a JAK2 mutant mouse model. The kinetics of BrdU label loss was assessed and the label-dilution was observed to be significantly faster in the JAK2-mutant HSCs compared to wildtype HSCs. This suggests that the mutant HSCs have an inherently high cycling compared to wildtype HSCs. However, BrdU-high residual label-retaining mutant-HSCs were observed even at 20 weeks post-induction of mutation. This suggests that a sub-fraction of mutant-HSCs stay quiescent and might contribute as a reservoir of mutant HSCs that propagate the disease. The mutant mice will be further treated with IFNα, post-labelling with BrdU, to assess if the JAK2-mutant HSCs can be further driven into cycle more than wild-type HSCs. The proportion of residual label-retaining HSCs will also be analyzed following JAK-inhibitor treatment.