• There is a role for the posttranslational modification, neddylation, in regulation of immune responses mediated by dendritic cells.• A role for neddylation in NF-kB signaling in dendritic cells was identified.Posttranslational protein modifications (PTMs) are necessary for cells to function properly. The role of PTMs in regulating immune responses, specifically those mediated by dendritic cells (DCs), which are critical for both innate and adaptive immunity, is not well understood. Utilizing multiple but complementary approaches, we determined the role of an important but less understood type of PTM, namely, neddylation, in regulating DC functions. Inhibition of neddylation suppressed the release of proinflammatory cytokines by DCs in response to Toll-like receptor, nucleotide oligomerization domain-like receptor, and noninfectious CD40L stimulation. These effects were more profound than those mediated by the proteasome inhibitor bortezomib or a commonly used antiinflammatory agent, dexamethasone. Targeting neddylation also suppressed the ability of DCs to stimulate murine allogeneic T cells in vitro and in vivo and human allogeneic T-cell responses in vitro. Mechanistic studies demonstrated that inhibition of neddylation reduced both canonical and noncanonical nuclear factor-kB (NF-kB) activity. Neddylation inhibition prevented the degradation of inhibitor-kB and thus reduced the translocation and activation of NF-kB, but without perturbation of the mitogen-activated protein kinase/extracellular signal-regulated kinase pathway. Thus, blocking neddylation could be a novel strategy for mitigating immune-mediated disease processes. (Blood. 2013;122(12):2062-2073

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BACKGROUND Acute graft-versus-host disease (GVHD) remains a significant barrier to a more widespread application of allogeneic hematopoietic stem cell transplantation (HSCT). Vorinostat (suberoylanilide hydroxamic acid) is a histone deacetylases (HDAC) inhibitor that has been shown to attenuate GVHD in pre-clinical models. We aimed to study the safety and activity of vorinostat in combination with standard immunoprophylaxis for GVHD prevention in patients undergoing related donor reduced intensity conditioning HSCT. METHODS In this prospective, single-arm phase 1/2 study of vorinostat, we recruited patients with high-risk hematologic malignances at two centers in the USA. We enrolled patients aged 18 years or older who were candidates for a reduced intensity conditioning HSCT and had an available 8/8- or 7/8-Human Leukocyte Antigen (HLA) matched related donor. Disease status had to be adequately controlled at the time of transplant. All patients received a conditioning regimen consisting of fludarabine 40 mg/m2 daily for four days (total dose 160 mg/m2) and busulfan 3·2 mg/kg daily for two days (total dose 6·4 mg/kg). GVHD prophylaxis consisted of mycophenolate mofetil 1 gram three times daily from day 0 and through day 28 and tacrolimus beginning on day −3 pre-HSCT and tapered beginning on day 56 and discontinued by day 180 post-HSCT in the absence of GVHD. The investigational agent, vorinostat, was initiated on day −10 through day 100 post-HSCT. The primary endpoint of the study was grade 2–4 acute GVHD by day 100. We expected to reduce the incidence to 25% from 42% based on similarly treated patients from the study centers and published literature. Patients were assessed for both toxicity and the primary endpoint if at least 21 days of vorinostat were administered. Patients who received less than 21 days of therapy were still assessed for toxicity and were replaced in accordance to the protocol. The trial is registered with ClinicalTrials.gov, NCT00810602. FINDINGS Between March 2008 and February 2013, we enrolled 50 patients evaluable for both toxicity and response. All patients engrafted neutrophils and platelets at expected times post-HSCT. The median percentages of chimerism in whole-blood at day 100 and 1-year were 98% (interquartile range [IQR], 98–100) and 100% (IQR, 100–100), respectively. The primary endpoint of the study was met with a day 100 cumulative incidence of grade 2–4 acute GVHD of 22% (95% cumulative incidence: 13%, 36%). Eight additional patients enrolled were assessed for toxicity only, in accordance with the protocol, because they received less than 21 days of study drug. The most common non-hematologic adverse events were all grade 3 and included electrolyte disturbances (N=15), hyperglycemia (N=10), infections (N=4), mucositis (N=4), and elevated liver enzymes (N=3). There was one grade 4 hypokalemia event and two grade 4 infections. Non-symptomatic thrombocytopenia which occurred after engraftment was the most common hematologic grade 3 or 4 adverse event (N=9), but was transien...

Key Points• HDAC inhibition reduced proinflammatory cytokines and increased regulatory T-cell number and function after allo-HCT.• HDAC inhibition enhanced signal transducer and activator of transcription 3 acetylation and induced indoleamine-2,3-dioxygenase after allo-HCT.We examined immunological responses in patients receiving histone deacetylase (HDAC) inhibition (vorinostat) for graft-versus-host disease prophylaxis after allogeneic hematopoietic cell transplant. Vorinostat treatment increased histone acetylation in peripheral blood mononuclear cells (PBMCs) from treated patients, confirming target HDAC inhibition. HDAC inhibition reduced proinflammatory cytokine levels in plasma and from PBMCs and decreased ex vivo responses of PBMCs to proinflammatory TLR-4 stimuli, but did not alter the number or response of conventional T cells to nonspecific stimuli. However, the numbers of regulatory T cells (Tregs) were increased, which revealed greater demethylation of the Foxp3 T regulatory-specific demethylation region. Vorinostat-treated patients showed increased expression of CD45RA and CD31 on Tregs, and these Tregs demonstrated greater suppression on a per cell basis. Consistent with preclinical findings, HDAC inhibition also increased signal transducer and activator of transcription 3 acetylation and induced indoleamine-2,3-dioxygenase. Our data demonstrate that HDAC inhibition reduces inflammatory responses of PBMC but enhances Tregs after allo-HCT. (Blood. 2015;125(5):815-819)

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