Inhibition of histone methylation arrests ongoing graft-versus-host disease in mice by selectively inducing apoptosis of alloreactive effector T cells

Abstract

Histone methylation is thought to be important for regulating Ag-driven T-cell responses. However, little is known about the effect of modulating histone methylation on inflammatory T-cell responses. We demonstrate that in vivo administration of the histone methylation inhibitor 3-deazaneplanocin A (DZNep) arrests ongoing GVHD in mice after allogeneic BM transplantation. DZNep IntroductionPathogenic T-cell responses can be detrimental to the host. For example, GVHD is a life-threatening complication after allogeneic BM transplantation (BMT). 1-3 GVHD is caused by donor T cells that attack normal tissues of the recipient. 1-3 Standard immunosuppressive therapy for GVHD lacks efficacy and impairs the antitumor activity. 1,2,4 New approaches are needed to control GVHD.Epigenetic modifications are thought to be important for T-cell immune responses. 5,6 These modifications include histone methylation, DNA methylation, and histone acetylation. 7-10 Histone methylation is the modification of certain amino acids of a histone by adding methyl groups. [8][9][10] Depending on the site and degree of methylation, histone methylation can be activating or repressive. For example, trimethylation of histone H3 at lysine 4 (H3K4me3), H3K36me3, and H3K79me3 are associated with transcriptional activation, whereas H3K9me3, H3K27me3, and H4K20me3 are related to gene repression. 8,9 Recent studies have reported that histone methylation may play important roles in regulating the expression of genes associated with survival, proliferation, and differentiation of Ag-activated T cells. 11,12 Unlike histone methylation, DNA methylation results in global silencing of gene expression, 10 whereas histone acetylation is associated with a relaxing chromatin structure that facilitates transcription. 10 It has been shown that the DNA methylation inhibitor 5-Aza-2-deoxycytidine (5-AzaC) and the histone deacetylase (HDAC) inhibitor suberoylanilide hydroxamic acid (SAHA) may prevent GVHD in mice through a mechanism of modulating regulatory T cells (Tregs) 13,14 and APCs, 15-17 respectively. However, global modifications of DNA and chromatin structures are found to be associated with toxicities and adverse effects. 10 Thus, novel epigenetic approaches capable of targeting a specific set of genes in alloreactive T cells are desirable for controlling GVHD while minimizing adverse effects.3-Deazaneplanocin A (DZNep) possesses the potent ability to selectively inhibit some histone methylation, such as H3K27me3, H3K4me3, and H4K20me3. 18,19 DZNep is an inhibitor of S-adenosyl-L-homocysteine (AdoHcy) hydrolase. AdoHcy hydrolase catalyzes the reversible hydrolysis of AdoHcy to adenosine and homocysteine. 20,21 When this enzyme is inhibited, AdoHcy accumulates in cells, leading to inhibition of the histone methyltransferease (HMT) activity and the subsequent histone methylation inhibition. 20 DZNep acts through a different pathway than DNA methylation inhibitors and HDAC inhibitors. 10,18,19 An Inside Blood analysis of this article appears at the fron...

The histone methyltransferase Ezh2 is a crucial epigenetic regulator of allogeneic T-cell responses mediating graft-versus-host disease

“…Similar to Ezh2 deficiency, DZNep treatment reduced cellular Ezh2, decreased H3K27me3, activated Bim, and caused apoptosis in alloreactive T cells. 10 However, although Bim was clearly important for DZNep treatment-reduced GVHD, 10 deletion of Bim in Ezh2-deficient T cells only partially rescued their survival and expansion. Two possibilities may explain this discrepancy.…”

“…In contrast, DZNep treatment caused a reduction of multiple histone methylation pathways (eg, H3K4me3, H3K27me3, H3K36me3, H4K20me3). 10,11 Because each of these histone methylation pathways may have distinct roles in T-cell immune responses, 9 it is likely that the reduction of Ezh2 function in activated T cells only represents one subset of multiple effects by DZNep treatment. Second, conditional knockout results in complete and permanent inactivation of Ezh2.…”

“…16 Naïve T cells expressed low levels of Ezh2 but rapidly upregulated Ezh2 upon TCR ligation and alloantigen stimulation. 10,16,18 However, whether Ezh2 plays important roles in regulating T-cell immune responses in vivo has not been previously determined. In the present study, we used conditional inactivation models to isolate the stage-specific alterations in allogeneic T-cell responses engendered by Ezh2 ablation and its effect on GVHD and graft-versus-leukemia (GVL) activity.…”

“…8,9 We have recently demonstrated that inhibition of histone methylation using 3-Deazaneplanocin A (DZNep) arrested ongoing GVHD through induction of apoptosis in alloreactive T cells. 10 DZNep reduced multiple histone methylation marks, including trimethylation of histone H3 at lysine 4 (H3K4me3), H3K27me3, H3K36me3, and H4K20me3, [10][11][12] each of which is catalyzed by a specific HMT. 9,13 However, the key HMT that regulates allogeneic T-cell responses remains unclear.…”

Programming of donor T cells using allogeneic δ-like ligand 4–positive dendritic cells to reduce GVHD in mice

“…GVHD in BDF1 mice was induced by transfer of donor B6 CD4 1 plus CD8 1 T cells. 31 In the C3H.SW anti-B6 mouse model of GVHD directed against minor histocompatibility antigens, B6 recipients were irradiated using 1000 cGray from an radiograph source, followed by transfer of C3H.SW TCD-BM with or without CH3.SW CD8 1 T cells. In GVL experiments, we injected A20 TGL cells (1 3 10 6 ) 2 hours before HSCT, which reflects the residual disease in human transplant recipients as described, 32,33 and monitored leukemic growth using bioluminescence imaging.…”