Abstract
Pro-inflammatory IL-17-producing T cells termed Th17 are actively involved in the pathogenesis of GVHD. The development and function of Th17 cells is dependent on activation of STAT3, RORgt and IRF4 transcription factors. Aberrant activation of Rho-associated kinase 2 (ROCK2) leads to induction of IL-17 and IL-21 secretion via IRF4-dependent mechanism. KD025, is a potent and selective ROCK2 inhibitor, which when given to healthy human subjects down-regulated the ability of T cells to secrete IL-21 and IL-17, but not interferon (IFN)-g, in response to TCR stimulation in vitro (Figure 1). KD025 inhibits STAT3 phosphorylation which supports RORgt, Th17 generation, and IL-21 production. Concurrently, KD025 increases STAT5 phosphorylation and Treg suppressor function in a dose-responsive fashion. KD025 treatment therefore shifts Th17/Treg balance. Th17 cells have been linked to in vivo pro-inflammatory responses, antibody production, and fibrosis. Conversely, Tregs can offset these pathogenic responses. Given the profile of KD025, we tested the effects of this inhibitor on cGVHD pathogenesis in a multi-organ system rodent model of disease that is driven by IL-21 responses and is associated with lung, liver and intestinal fibrosis. We observed that Th17/Rorc deficient T cells are unable to mediate cGVHD pathogenesis. In mice with established cGVHD, therapy was initiated with 30, 100, or 150 mg/kg/dose of KD025 daily from d28-56. Treated mice had a dose dependent decrease in the development of pathogenic pulmonary function as determined by whole body plethysmography (Figure 2) which correlated with a marked reduction of antibody deposition in the lungs of treated mice to levels comparable to non-cGVHD controls. KD025 administration also resulted in a 2-fold decrease in collagen deposition in the lungs of mice treated with the highest dose of KD025. The spleens of mice treated with 150 mg/kg dose of KD025 had a decrease in the frequency of germinal centers compared to the vehicle treated mice. To determine the selective role of STAT3 on T cells, mice were transplanted with wildtype (WT) bone marrow (BM) and WT or inducible STAT3 deficient T cells. In parallel cohorts, the role of STAT3 in BM-derived B cells, precursors of germinal center B cells, was examined using WT vs inducible STAT3 deficient BM cells + WT T cells. We demonstrate here that mice transplanted with inducible STAT3 deficient T cells or BM cells had pulmonary function comparable to the healthy negative controls, suggesting that STAT3 is a potential therapeutic target in both T and B cells is necessary for the development of cGVHD and providing mechanistic insight into how KD025 may ameliorate active cGVHD. Studies are in progress to test KD025 administration in a murine scleroderma model using a minor histocompatibility antigen disparate donor-recipient strain that we have shown to be dependent upon STAT3 expressing donor T cells and a STAT3 inhibitor in both cGVHD models described here. Together, these data demonstrate that KD025 is effective at decreasing STAT3-dependent production of IL-21 and IL-17 and the use of KD025 is a potentially novel therapeutic intervention for the treatment of cGVHD.
Fig 1 Oral administration of KD025 down-regulates the IL-17 and IL-21 secretion in human PBMCs upon stimulation ex vivo. Human PBMCs were purified from healthy human subjects before and after oral administration of KD025 at doses 40, 120, 240, 320 and stimulated ex vivo. Cytokine secretion was determined after 48 hours by ELISA. Fig 1. Oral administration of KD025 down-regulates the IL-17 and IL-21 secretion in human PBMCs upon stimulation ex vivo. Human PBMCs were purified from healthy human subjects before and after oral administration of KD025 at doses 40, 120, 240, 320 and stimulated ex vivo. Cytokine secretion was determined after 48 hours by ELISA.
Fig 2 KD025 is an effective therapy for established murine cGVHD. Mice were given KD025 (150 mg/kg) d.28-56. PFTs indicate normal resistance, elastance and better compliance. Lung Ig deposition and fibrosis were comparable to BM controls. Fig 2. KD025 is an effective therapy for established murine cGVHD. Mice were given KD025 (150 mg/kg) d.28-56. PFTs indicate normal resistance, elastance and better compliance. Lung Ig deposition and fibrosis were comparable to BM controls.
Disclosures
No relevant conflicts of interest to declare.
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