PS1485 TRAMETINIB RESTORES IMMUNE TOLERANCE IN ITP PATIENTS BY MODULATING IRF4‐MEDIATED TH1 AND TREG CELLS
Authors: H. Wang, N. An, Y. Liu, X. Hu, M. Hou
Journal: HemaSphere (2019)

Background: Helper T lymphocyte subsets and their secreted cytokine disorders in immune thrombocytopenia (ITP), including platelet autoreactive CD4 + effector T cells, are excessively activated. While the CD4 + CD25 + Foxp3 + regulatory T cells (Tregs) are numerically and functionally impaired. Recent studies have shown that interferon regulatory factor 4 (IRF4), a key transcription factor, repress PD‐1 expression in activated T cells. The deletion in mice resulted in progressive establishment of CD4 + T cell dysfunction and long‐term allograft survival. Trametinib, a MEK1/2 inhibitor, has been reported to target IRF4 upon in vitro CD4 + T cell activation. And it also could inhibit CD4 + T cell proliferation as well as Th1 and Th17 cell differentiation, whereas, it promotes the differentiation of inducible Tregs. Therefore, whether the treatment of trametinib has potential in ITP is still unknown. Aims: Our study aimed to evaluate the potential of trametinib in regulating the immune homeostasis in ITP, and further to explore the role of IRF4 in the pathogenesis of ITP. Whether trametinib could be a new therapeutic strategy in the management of ITP, it is our long‐term concern. Methods: A total of 20 patients with ITP and 10 healthy volunteers consenting were enrolled. All blood samples were collected after obtaining the informed consent from each participant. The mRNA expression of IRF4, Foxp3 and T‐bet in the peripheral blood mononuclear cells (PBMCs) of the ITP patients and healthy control was detected by q‐PCR. We sorted CD4 + T cells and the naïve CD4 + T cells from PBMCs in ITP patients and cultured for 3 days with anti‐CD3 antibodies, anti‐CD28 antibodies, and rhIL‐2, stimulated with 100 nM trametinib, and 0.1% DMSO as negative control. PBMCs apoptosis and the ratio of Th1 and Tregs were detected by Flow cytometry. Results: The IRF4 mRNA expression was significantly increased in the ITP patients’ PBMCs compared to healthy control. (Figure A) When treated with 100 nM trametinib as previously reported, the apoptosis of PBMCs (Figure B) and percentages of CD4 + T cells had no big difference between ITP patients and healthy control. However, 100 nM trametinib could increase the percentage of CD4 + CD25 + Foxp3 + Tregs, while the ratio of Th1 cells in PBMCs and CD4 + T cells levels was significantly decreased. (Figure C) The results of q‐PCR were further confirmed. The IRF4 and T‐bet expressions were decreased, while the Foxp3 level was significantly increased. (Figure D) We further isolated the naïve CD4 + T cells and treated with trametinib. The results showed trametinib could directly activate and induce the differentiation of Tregs from naïve CD4 + T cells. (Figure E) Summary/Conclusion: Our results demonstrated that trametinib could regulate CD4 + T cells homeostasis in ITP. Trametinib could increase the percentage of Tregs by reducing the expression of IRF4, meanwhile, the ratio of pro‐inflammatory Th1 cells was decreased. A new target of IRF4 in T cells could be a novel era and a potential therapeutic strategy not only for transplant rejection but also for other autoimmune disorders. Therefore, we propose that trametinib administration has become a promising therapeutic strategy for the management of ITP patients. image