Stabilization of Foxp3 by Targeting JAK2 Enhances Efficacy of CD8 Induced Regulatory T Cells in the Prevention of Graft-versus-Host Disease.

CD8+ induced regulatory T cells (iTregs) have been identified to suppress alloreactive immune responses and expressed regulatory T cell (Treg) ontological markers as similar as CD4+ iTregs. However, adoptive transfer of CD8+ iTreg-based therapy is hampered by the instability of Treg specific-transcription factor, Foxp3. As CD8+ iTregs were previously demonstrated to possess superior tumor-killing ability to CD4+ iTregs, adoptive transfer of stabilized CD8+ iTregs would be a potential therapy to prevent tumor relapse during graft-versus-leukemia disease (GVHD) treatment. In the current study, we generated alloantigen reactive CD8+ iTregs from JAK2-/- T cells and adoptively transferred them to MHC-mismatched and haploidentical murine models of allogeneic bone marrow transplantation. JAK2-/- CD8+ iTregs not only attenuated GVHD but also preserved graft-versus-leukemia effect. Mechanistic analysis revealed that JAK2-/- CD8+ iTregs upregulated natural Treg marker (neuropilin-1), and augmented DNA demethylation of CNS2 region within Foxp3 gene. These properties licensed JAK2-/- CD8+ iTregs to retain high Foxp3 expression resulting in less conversion to type 1 CTLs; as a result, JAK2-/- CD8+ iTregs were able to maintain their suppressive and cytolytic function. Thus, our findings provide a strong rationale and means to stabilize CD8+ iTregs by targeting JAK2, and the stabilized CD8+ iTregs exhibit therapeutic potential for alleviating GVHD and preserving the graft-versus-leukemia effect.

Ruxolitinib: in the treatment of myelofibrosis.

Ruxolitinib is a selective inhibitor of Janus kinases (JAK) 1 and 2, which are involved in the signalling pathway of various cytokines and growth factors essential to haematopoiesis. JAK 1 and 2 are implicated in the development of myelofibrosis, as well as other haematological malignancies. Ruxolitinib is the first agent approved for the treatment of myelofibrosis. In a randomized, double-blind, placebo-controlled, multicentre trial (COMFORT-I) in patients with myelofibrosis, significantly more ruxolitinib than placebo recipients achieved a ≥ 35% reduction in spleen volume (primary endpoint) at 24 weeks. In a randomized, open-label, multicentre trial (COMFORT-II) in patients with myelofibrosis, significantly more ruxolitinib than best available therapy recipients achieved the same primary endpoint at 48 weeks. Significantly more ruxolitinib than placebo recipients achieved a ≥ 50% reduction in Total Symptom Score at 24 weeks in COMFORT-I. Ruxolitinib generally improved health-related quality-of-life scores, while best available therapy was generally associated with worsened scores at 48 weeks in COMFORT-II. In COMFORT-I, overall survival data appeared to favour ruxolitinib over placebo; of note, most placebo recipients had crossed over to receive ruxolitinib. In COMFORT-II, a significant difference in overall survival between ruxolitinib and best available therapy was not shown; this trial was not powered to detect such a difference. In clinical trials in patients with myelofibrosis, ruxolitinib was generally associated with an acceptable tolerability profile. In the placebo-controlled trial, the most commonly reported grade 3 or 4 adverse events in ruxolitinib recipients were thrombocytopenia, anaemia and neutropenia. These haematological adverse events were mainly managed with dosage interruptions/reductions and/or transfusions, and rarely resulted in discontinuation.