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.