Targeting JAK2 reduces GVHD and xenograft rejection through regulation of T cell differentiation

Abstract

Janus kinase 2 (JAK2) signal transduction is a critical mediator of the immune response. JAK2 is implicated in the onset of graft-versus-host disease (GVHD), which is a significant cause of transplant-related mortality after allogeneic hematopoietic cell transplantation (allo-HCT). Transfer of JAK2 donor T cells to allogeneic recipients leads to attenuated GVHD yet maintains graft-versus-leukemia. Th1 differentiation among JAK2 T cells is significantly decreased compared with wild-type controls. Conversely, iTreg and Th2 polarization is significantly increased among JAK2 T cells. Pacritinib is a multikinase inhibitor with potent activity against JAK2. Pacritinib significantly reduces GVHD and xenogeneic skin graft rejection in distinct rodent models and maintains donor antitumor immunity. Moreover, pacritinib spares iTregs and polarizes Th2 responses as observed among JAK2 T cells. Collectively, these data clearly identify JAK2 as a therapeutic target to control donor alloreactivity and promote iTreg responses after allo-HCT or solid organ transplantation. As such, a phase I/II acute GVHD prevention trial combining pacritinib with standard immune suppression after allo-HCT is actively being investigated (https://clinicaltrials.gov/ct2/show/NCT02891603).

Metabolic reprogramming augments potency of human pSTAT3–inhibited iTregs to suppress alloreactivity

“…The final purity of the iTreg (CD4 + , CD127 -, CD25 + , Foxp3 + ) (28,29) product was >90% ( Figure 1A). iTreg function was tested in standard suppression assays against DC-allostimulated T cells (22,23,30). Neither S3I-201 nor DMSO was added to the 5-day suppression assay cultures.…”

“…Skin is an important and clinically relevant GVHD-target organ (33,34). To test the activity of pSTAT3-inhibited iTregs in vivo, we used our established human skin graft/NSG mouse xenogeneic model (22,23). NSG mice received a 1-cm 2 split thickness human skin graft.…”

“…Thus, the iTregs were autologous to the PBMCs and allogeneic to the skin. The skin grafts were monitored daily for signs of rejection, including ulceration, necrosis, and scabbing (22,23). Skin grafts that were >75% nonviable were considered rejected.…”

“…Compared with DMSO-treated iTregs, pSTAT3 inhibition significantly increased the frequency of IL-9 + , CLA + iTregs ( Figure 3 Human pSTAT3-inhibited iTregs significantly reduce skin graft infiltration by pathogenic Th2 cells. To assess effects of pSTAT3-inhibited human iTregs on T cells within the graft, NSG mice were transplanted with human skin (22,23) and then inoculated with allogeneic human PBMCs alone or in combination with pSTAT3-inhibited or vehicle-treated iTregs. On day +21, the mice were humanely euthanized, and the skin grafts were harvested, preserved, and later analyzed by IHC to determine the content of T cell subsets.…”

“…Our human skin graft/NSG mouse xenotransplantation model is well suited to study human iTregs as the cells readily engraft in the immunodeficient mouse and skin is a clinically relevant organ in GVHD (22,23). Skin is also a critical driver of alloreactivity and a well-established tissue to test experimental tolerance induction (24)(25)(26).…”