TYK2 Is Essential for IFNα-Induced Resolution of MPN Features in a Murine Jak2V617F PMF Model

Interferon (IFN)-α exhibits antiviral and antiproliferative effects on normal and neoplastic cells. It is an effective treatment option for myeloproliferative neoplasms (MPNs). The intracellular signaling of IFN-α is triggered by binding of IFN-α to its specific receptors on the cell surface, followed by the activation of tyrosine kinase-2 (TYK2) and Janus kinase-1 (JAK1), both of which are receptor-associated Janus kinases (JAKs). Activated JAKs activate many signaling molecules, including signal transducers and activators of transcription (STATs). Antiviral activity of IFN-α was abrogated in Stat1 deficient-embryonic fibroblasts, however, Tyk2 deficient-cells were resistant to viral infection in the presence of IFN-α, indicating the essential role of STAT1 for the antiviral activity of IFN-α, and TYK2 is not required for that. The antiproliferative effect is another major activity of IFN-α, however, the precise antiproliferative mechanism of IFN-α is not completely understood. We assessed the effect of ropeginterferon-α-2b, a monopegylated IFN-α-2b, on MPN model mice (Jak2V617F mice), and investigated the role of TYK2 in the antiproliferative effect of IFN-α.

Jak2VF mice exhibited leukocytosis and thrombocytosis, and TYK2 deficiency had no effect on MPN phenotypes induced by Jak2VF. IFN-α treatment was associated with a significant reduction in leukocyte and platelet counts in Jak2V617F mice. In contrast, leukocyte and platelet counts remained unchanged after IFN-α treatment in Jak2V617F and Tyk2^-/- mice. The proportions of BM progenitor cells as MEP and megakaryocyte lineage cells as MKP were markedly decreased by IFN-α treatment in Jak2V617F mice, whereas IFN-α had no effect on their proportions in Jak2V617F;Tyk2^-/- mice. Next, we assessed the effects of IFN-a on cytokine-dependent colony formation. The colony numbers of CFU-GM and CFU-Meg from Jak2V617F mice decreased by about half in the presence of IFN-a. In contrast, cytokine-dependent colony formation was not affected by the presence of IFN-a in Jak2V617F;Tyk2^-/- mice. GSEA revealed significant enrichment of genes regulating antiproliferation in IFN-α-treated Jak2VF GMPs, but not in IFN-α-treated GMPs from Jak2V617F;Tyk2^-/- mice. Collectively, these results indicate that TYK2 plays an essential role in the antiproliferative effect of IFN-α on Jak2VF progenitors.

IFN-α was reported to induce HSCs to enter the cell cycle. The significant reduction in quiescent cells and increase in cycling LT-HSCs in Jak2VF compared to WT HSCs after IFN-α treatment was reported (Mullally et al. Blood 2013). Consistent with previous reports, the proportion of long-term HSCs in BM from Jak2VF mice was decreased by 8-weeks-IFN-α treatment, however, this IFN-α effect was not observed when TYK2 was absent. In the pool of phenotypic long-term HSCs, there are subsets of stem cells with an intrinsic megakaryocytic bias and a propensity to commit directly to the megakaryocytic lineage. In the JAK2VF mutant fraction of HSCs from recipient mice transplanted with JAK2VF and WT BM cells, IFN-α treated mice were reported to show an increase in the percentage of CD41^high, megakaryocyte-skewed HSCs (Rao et al. Blood 2021). Consistent with this report, IFN-α treatment increased the proportion of CD41^highHSCs and decreased that of CD41^lowHSCs in BM from Jak2VF mice, and again, IFN-α-induced megakaryocytic bias of HSCs was not observed in TYK2 deficient HSCs. IFN-α had similar effect on Jak2VF-HSCs in recipient mice transplanted with Jak2VF and WT BM cells, and this IFN-α effect was not observed when TYK2 was absent. These observations indicate that TYK2 is essential for the effects of IFN-α on HSCs.

These results indicate that TYK2 is indispensable for the effects of IFN-α on improvement of MPN features.