BET-bromodomain and EZH2 inhibitor-treated chronic GVHD mice have blunted germinal centers with distinct transcriptomes

Despite advances in the field, chronic graft-versus-host-disease (cGVHD) remains a leading cause of morbidity and mortality following allogenic hematopoietic stem cell transplant. Because treatment options remain limited, we tested efficacy of anticancer, chromatin-modifying enzyme inhibitors in a clinically relevant murine model of cGVHD with bronchiolitis obliterans (BO). We observed that the novel enhancer of zeste homolog 2 (EZH2) inhibitor JQ5 and the BET-bromodomain inhibitor JQ1 each improved pulmonary function; impaired the germinal center (GC) reaction, a prerequisite in cGVHD/BO pathogenesis; and JQ5 reduced EZH2-mediated H3K27me3 in donor T cells. Using conditional EZH2 knockout donor cells, we demonstrated that EZH2 is obligatory for the initiation of cGVHD/BO. In a sclerodermatous cGVHD model, JQ5 reduced the severity of cutaneous lesions. To determine how the 2 drugs could lead to the same physiological improvements while targeting unique epigenetic processes, we analyzed the transcriptomes of splenic GCB cells (GCBs) from transplanted mice treated with either drug. Multiple inflammatory and signaling pathways enriched in cGVHD/BO GCBs were reduced by each drug. GCBs from JQ5- but not JQ1-treated mice were enriched for proproliferative pathways also seen in GCBs from bone marrow-only transplanted mice, likely reflecting their underlying biology in the unperturbed state. In conjunction with in vivo data, these insights led us to conclude that epigenetic targeting of the GC is a viable clinical approach for the treatment of cGVHD, and that the EZH2 inhibitor JQ5 and the BET-bromodomain inhibitor JQ1 demonstrated clinical potential for EZH2i and BETi in patients with cGVHD/BO.

Targeting PI3K signaling to ameliorate chronic graft versus host disease

The phosphoinositide 3-kinase (PI3K) pathway is a key signaling pathway necessary for T cell activation, differentiation and metabolism. T effector cells rely on increased PI3K signaling to fuel glycolysis for their metabolic needs, while T regulatory cells downregulate PI3K and favor lipid oxidation. The metabolic processes of lymphocytes modulating chronic graft versus host disease (cGVHD) have remained largely unexamined and represent a novel therapeutic strategy for this disease. Here, we investigated the role of PI3K signaling in a murine model of cGVHD that is etiologically linked to up regulated germinal centers (GCs) and characterized by multisystem organ disease; including fibrosis of the lung, which results in pulmonary dysfunction. We hypothesized that inhibition of PI3K signaling would alter the activation and/or function of GC-facilitating T follicular helper (TFH) cells resulting in lessened disease. The findings in this study are that mice treated with a PI3Kd inhibitor had decreased pulmonary dysfunction similar to that of the control, non-cGVHD mice. The frequencies of splenic TFH cells as well as GC B cells were decreased by a PI3K delta inhibitor compared to non-treated cGVHD controls. In a similar manner, mice that received PI3K kinase delta dead Tregs also had decreased TFH frequency as well as reduced pulmonary dysfunction. Our results indicate the differential requirement for signaling through PI3K delta and suggest that targeting this pathway may be a potential new therapy for treatment of cGVHD. Additional studies are required to validate the potential therapeutic use.