ER Stress Sensor PERK Boosts T Cell Pathogenicity in Gvhd through Regulating ERAD

Allogeneic hematopoietic cell transplantation (allo-HCT) is currently a curative strategy for treatment of patients with hematological malignancies. Donor derived T cells mediate graft-versus leukemia (GVL) responses, but also induce graft-versus host disease (GVHD) that is a major cause for the morbidity and mortality of patients after allo-HCT. Thus, control of GVHD while maintaining GVL effect is an ultimate goal in the field. Endoplasmic Reticulum (ER) stress has been reported to play an important role in the activation and function of various immune cells and the development of multiple human diseases. Activation of unfolded protein responses (UPR) controls the quality of the proteome pool in ER stressed cells and maintains the intracellular protein homeostasis. ER-associated protein degradation (ERAD) is a cellular pathway that targets misfolded proteins of ER for ubiquitination and subsequent degradation via proteasome. In the current study, we investigated how allogenic T cells manage ER stress and how ER stress regulates T cell-driven GVHD.

To address the question, we initially analyzed the publicly available RNA sequencing (RNA seq) data and found that Eif2ak3 (encoding PERK) were dramatically increased in allogenic T cells. We next established syngeneic and allogeneic murine models of HCT and observed that PERK and ERAD-associated genes were significantly upregulated in donor T cells transferred into allogeneic recipients as compared with those of syngeneic controls. Upon allogenic stimulation, T cells increased phosphorylation of PERK (p-PERK). To further assess the role of PERK in T cell-driven GVHD, we purified T cells from WT and PERK^flox/floxCD4Cre (PERK-cKO) mice and transferred into lethally irradiated BALB/c mice and proved that PERK deficiency in donor T cells significantly attenuated GVHD while preserving GVL effect. The outcome was associated with reduced proliferation of CD4⁺ but not CD8⁺ T cells and Th1 and Th17 differentiation, and increased Treg generation via downregulating Nrf2 levels in PERK-deficient T cells.

Mechanistically, we found that PERK interacted with SEL1L in activated T cells. Interestingly, PERK differentially regulated the pro-inflammatory cytokines secretion in T cells upon allogenic versus anti-CD3 polyclonal stimulation. PERK increased the generation of Th1 and Th17 and augmented GVHD while downregulating SEL1L levels. In contrast, PERK inhibited the pro-inflammatory cytokine production by T cells after anti-CD3 stimulation while upregulating SEL1L levels. Furthermore, we demonstrated that PERK enhanced mitochondrial membrane potential (MMP) in CD4⁺ T cells upon allogeneic stimulation through SEL1L-mediated ERAD pathway, thus decreasing the protein levels of PINK1 and inhibiting the autophagy of allogenic T cells.

Pharmacologically, treatment of allo-HCT recipients with PERK specific inhibitor, AMG44, significantly reduced GVHD severity while maintaining the GVL activity. For translational research, we also assessed the effect of AMG44 in GVHD induced by human PBMCs in NSG HLA-A2-transgenic mice. We found that AMG44 administration significantly reduced GVHD severity reflected by prolonged survival, reduced GVHD scores and body weight loss. More importantly, the treatment with AMG44 preserved the GVL effect against B-cell lymphoma.

In summary, our findings validate PERK as a potential novel therapeutic target for the prevention of GVHD while preserving GVL responses. The study elucidates a new mechanism by which PERK differentially regulated T-cell allogeneic and polyclonal responses through modulating ERAD pathway.