Histone deacetylase inhibitors affect dendritic cell differentiation and immunogenicity

Histone deacetylases as regulators of inflammation and immunity

Histone deacetylases (HDACs) remove an acetyl group from lysine residues of target proteins to regulate cellular processes. Small-molecule inhibitors of HDACs cause cellular growth arrest, differentiation and/or apoptosis, and some are used clinically as anticancer drugs. In animal models, HDAC inhibitors are therapeutic for several inflammatory diseases, but exacerbate atherosclerosis and compromise host defence. Loss of HDAC function has also been linked to chronic lung diseases in humans. These contrasting effects might reflect distinct roles for individual HDACs in immune responses. Here, we review the current understanding of innate and adaptive immune pathways that are regulated by classical HDAC enzymes. The objective is to provide a rationale for targeting (or not targeting) individual HDAC enzymes with inhibitors for future immune-related applications.

Valproic acid exhibits biphasic effects on apoptotic cell death of activated lymphocytes through differential modulation of multiple signaling pathways

Valproic acid (VPA), a histone deacetylase (HDAC) inhibitor, possesses potent anti-tumor activity against a variety of malignant cells. However, its action on lymphocytes and the underlying mechanism are not completely understood. In this study, we aimed to analyze the effects of VPA on the proliferation, activation, and apoptosis of murine lymphocytes activated with concanavalin A (ConA). Our results showed that VPA inhibited the proliferation of ConA-activated lymphocytes in a dose-dependent manner. Low-dose VPA (≤ 1.1 mM) enhanced CD69 expression on the activated lymphocytes, whereas at high doses (≥ 3.3 mM) it decreased CD69 expression. Furthermore, VPA reduced activation-induced apoptotic cell death at low doses, but at high doses it promoted apoptotic cell death of activated lymphocytes dramatically. It was found that the Bax/Bcl-2 ratio and phosphorylation of histone H2A.X was decreased at low doses of VPA but was increased at high doses. The phosphorylation of STAT3 was also differentially regulated by different doses of VPA. VPA, at 5 mM induced the phosphorylation of p38 but not JNK and extracellular signal-regulated kinase (ERK)1/2. In addition, VPA induced a dose-dependent increase in the acetylation of histone H3. These results demonstrate that VPA exhibits dose-dependent biphasic effect on apoptosis of activated lymphocytes probably through differential modulation of several apoptosis-related signaling pathways.

Exogenous control of the expression of Group I CD1 molecules competent for presentation of microbial nonpeptide antigens to human T lymphocytes

Group I CD1 (CD1a, CD1b, and CD1c) glycoproteins expressed on immature and mature dendritic cells present nonpeptide antigens (i.e., lipid or glycolipid molecules mainly of microbial origin) to T cells. Cytotoxic CD1-restricted T lymphocytes recognizing mycobacterial lipid antigens were found in tuberculosis patients. However, thanks to a complex interplay between mycobacteria and CD1 system, M. tuberculosis possesses a successful tactic based, at least in part, on CD1 downregulation to evade CD1-dependent immunity. On the ground of these findings, it is reasonable to hypothesize that modulation of CD1 protein expression by chemical, biological, or infectious agents could influence host's immune reactivity against M. tuberculosis-associated lipids, possibly affecting antitubercular resistance. This scenario prompted us to perform a detailed analysis of the literature concerning the effect of external agents on Group I CD1 expression in order to obtain valuable information on the possible strategies to be adopted for driving properly CD1-dependent immune functions in human pathology and in particular, in human tuberculosis.

The therapeutic potential of HDAC inhibitors in the treatment of multiple sclerosis

Multiple sclerosis (MS) is a devastating autoimmune disorder of the central nervous system (CNS) for which there is no efficacious cure. Thanks to numerous preclinical and clinical studies, drugs able to mitigate the inexorable course of the disease have been made available recently. Still, there is a terrible need for compounds capable of reducing the severity of the autoimmune attack and of blocking progression of the disorder. Also, besides the classic immunosuppressive strategies, it is now appreciated that compounds directly targeting neuronal death can be of relevance to the treatment of MS patients. Acetylation homeostasis is a key regulator of both immune cell activation and neuronal survival. Of note, potent histone deacetylase inhibitors (HDACi) endowed with antiinflammatory and neuroprotective properties have been identified. Efficacy of HDACi in experimental models of MS has been reported consistently. In this review, we provide an appraisal of the literature on HDACi and MS, also discussing the mechanisms by which HDACi can suppress the autoimmune attack to the CNS.

HDAC inhibition in rheumatoid arthritis and juvenile idiopathic arthritis

Rheumatoid arthritis (RA) and juvenile idiopathic arthritis (JIA) are heterogeneous autoimmune diseases characterized by chronic joint inflammation. Methotrexate is used as the gold standard to treat rheumatoid arthritis, yet there are many patients in whom the disease cannot be controlled or who experience unacceptable intolerance. Most of the biologics currently used are effective, but mostly if combined with methotrexate. Long-term possible side effects, such as impaired host defense mechanisms against infection and lymphoma, are distinct disadvantages and a major concern of anticytokine therapies. Parenteral administration is a problem, particularly in children. Thus, there is a need to explore new treatment options. Here we review the properties of histone deacetylase inhibitors (HDACi) as they apply to rheumatoid arthritis by looking at effects on cytokine production, T-cell differentiation and the function of macrophages, dendritic cells, osteoblasts, osteoclasts and synovial fibroblasts. We also review the safety and efficacy of givinostat (ITF 2357) in the treatment of systemic onset juvenile idiopathic arthritis (SOJIA) and its influence on the cytokine networks in SOJIA. Givinostat is an orally active HDACi which was given to children with SOJIA. After 12 wk of treatment, there were significant benefits, particularly in reducing the pain and arthritic component of the disease and decreasing the neutrophilia. CD40L, IL-1α and IFNγ in whole blood lysates decreased at wks 2 and 4 compared with baseline levels. The clinical data are consistent with those from animal models of rheumatoid arthritis and suggest that trials with HDACi are promising as a safe oral alternative to anticytokines and methotrexate.

Investigational histone deacetylase inhibitors for non-Hodgkin lymphomas

IMPORTANCE OF THE FIELD

Histone deacetylase inhibitors (HDIs) have been shown effective as single agents for cutaneous T-cell lymphomas, peripheral T-cell lymphomas, and B-cell lymphomas, such as follicular lymphoma and mantle cell lymphoma. Of interest, HDIs in combination with other drugs can be a treatment for Epstein-Barr virus-associated lymphoproliferative disorders. Our data of gene expression profiles in PBMCs of responders to vorinostat was discussed.

AREAS COVERED IN THIS REVIEW

This review summarizes recent clinical trials of HDIs in non-Hodgkin lymphomas, the effects of HDIs in in vitro and mouse models, and the possibility of future combination treatments.

WHAT THE READER WILL GAIN

The HDI dosing schedule is crucial to optimize outcomes and avoid irreversible adverse effects. Responses to HDIs are slow, highlighting the need to continue treatment until the maximum response is achieved. HDIs cause hyperacetylation of histone and nonhistone proteins, resulting in various effects on neoplastic cells and immune responses in their microenvironment.

TAKE HOME MESSAGE

Even though HDIs are not potent as single agents, they are likely to provide promising therapeutic options when combined with other agents, i.e., BCL2/BCL-XL antagonists and proteasome inhibitors. Future studies should seek to identify biomarkers that predict patient responses to HDIs.

Histone deacetylase inhibitors: potential targets responsible for their anti-cancer effect

The histone deacetylase inhibitors (HDACi) have demonstrated anticancer efficacy across a range of malignancies, most impressively in the hematological cancers. It is uncertain whether this clinical efficacy is attributable predominantly to their ability to induce apoptosis and differentiation in the cancer cell, or to their ability to prime the cell to other pro-death stimuli such as those from the immune system. HDACi-induced apoptosis occurs through altered expression of genes encoding proteins in both intrinsic and extrinsic apoptotic pathways; through effects on the proteasome/aggresome systems; through the production of reactive oxygen species, possibly by directly inducing DNA damage; and through alterations in the tumor microenvironment. In addition HDACi increase the immunogenicity of tumor cells and modulate cytokine signaling and potentially T-cell polarization in ways that may contribute the anti-cancer effect in vivo. Here, we provide an overview of current thinking on the mechanisms of HDACi activity, with attention given to the hematological malignancies as well as scientific observations arising from the clinical trials. We also focus on the immune effects of these agents.

The short chain fatty acid sodium butyrate regulates the induction of CD1a in developing dendritic cells

Dendritic cells (DCs) are professional antigen-presenting cells with attributes for priming/activating T cells and mediating immune responses. Considering the importance of DCs in the initiation of immune responses, it will be of interest to study their mechanisms of regulation. Histone-modifying enzymes, such as histone deacetylases (HDACs), are critical in controlling chromatin organization. The aim of our study was to investigate DC differentiation under the influence of sodium butyrate (NaB), a short chain fatty acid that is a histone deacetylase inhibitor. Monocytes from healthy individuals were differentiated into immature DCs with IL-4 and GM-CSF in the presence or absence of NaB. DC differentiation was evaluated by CD14 and CD1a expression by flow cytometry. We observed that monocytes stimulated to differentiate in the presence of NaB displayed colony formation and dendritic cell morphology, lost CD14 and showed decreased secretion of IL-1β. The acquisition of CD1a, however, was impaired. Being a natural short chain fatty acid, NaB may regulate CD1a acquisition independently of its HDAC inhibitory activity. We observed that the addition of peroxisome proliferator-activated receptor γ (PPAR-γ) antagonist (GW9662) did not reverse NaB effect, suggesting this was not the pathway involved. On the other hand, CD1a can also be induced by toll like receptors 2 (TLR 2) agonists, such as Pam3Cys, and NaB inhibited this effect. Our data suggest that the histone deacetylase inhibitor NaB instead of impairing DC differentiation inhibits the acquisition of CD1a induced both by cytokines and by TLR 2 agonist stimulus. Furthermore, this occurs at the transcriptional level as NaB led to a decrease in mRNA levels of CD1a and upregulation of CD1d.

Epigenetics and rheumatoid arthritis: the role of SENP1 in the regulation of MMP-1 expression

The aggressive phenotype of RA synovial fibroblasts (RASF) is characterised by the increased expression of matrix metalloproteinase (MMP)-1 as well as the small ubiquitin like modifier (SUMO)-1 and decreased expression of SUMO-specific protease SENP1. Since we showed an increased activity of acetyltransferases in this autoimmune disease, we wanted to analyze whether this affects the expression of MMP-1 and can be reversed by the reconstitution of SENP1. In RASF, the acetylation of histone H4 was significantly increased in the distal region of the MMP-1 promoter by 274 +/- 36% compared to OASF. Most interestingly, overexpression of SENP1 in RASF decreased acetylation specifically in this region by 51 +/- 0.5% and globally by 73 +/- 11%. Furthermore, the overexpression of SENP1 resulted in a downregulation of MMP-1 at both the mRNA (58 +/- 7%) and protein levels (28 +/- 6%), significantly reduced the invasiveness of RASF (from 34 +/- 9% to 2 +/- 2%) and led to an accumulation of histone deacetylase 4 (HDAC4) on the MMP-1 promoter (197 +/- 36%). Interestingly, SENP1 failed to modulate the expression of MMP-1 in the cells silenced for HDAC4. This is the first study linking the SUMOylation pathway and the production of MMP-1 to an epigenetic control mechanism mediated through histone acetylation which has a functional consequence for the invasiveness of RASF.

Association of histone deacetylase genes with schizophrenia in Korean population

Histone deacetylases (HDACs) are pivotal enzymes in the epigenetic modification or regulatory mechanisms of gene transcription. Based on previous assertions that the pathophysiology of schizophrenia is associated with epigenetics, we hypothesized that polymorphisms of HDAC genes might be related to schizophrenia. We recruited 278 patients with schizophrenia and 234 normal controls from a Korean population. Clinical information of the group with schizophrenia was obtained from medical records, the Brief Psychiatric Rating Scale (BPRS), the Scale for the Assessment of Negative Symptoms (SANS), and the Operational Criteria Checklist (OPCRIT). Three single-nucleotide polymorphisms (SNPs) in HDAC genes were selected, including rs2530223 of HDAC3, rs1063639 of HDAC4, and rs1555048 of HDAC10. For the analysis of genetic data, SNPStats, SNPAnalyzer, and Helixtree programs were used. In the present study, rs1063639 of the HDAC4 gene showed associations with schizophrenia in the codominant and dominant models. In the analysis of clinical phenotypes, smoking status was associated with rs2530223 of HDAC3 in the codominant and recessive models. The results suggest that HDAC3 and HDAC4 genes might play a role in the pathophysiology of schizophrenia in a Korean population.

Blockade of dendritic cell development by bacterial fermentation products butyrate and propionate through a transporter (Slc5a8)-dependent inhibition of histone deacetylases

Mammalian colon harbors trillions of bacteria, yet there is no undue inflammatory response by the host against these bacteria under normal conditions. The bacterial fermentation products acetate, propionate, and butyrate are believed, at least in part, to be responsible for these immunosuppressive effects. Dendritic cells play an essential role in presentation of antigens to T lymphocytes and initiation of adaptive immune responses. Here we report that butyrate and propionate block the generation of dendritic cells from bone marrow stem cells, without affecting the generation of granulocytes. This effect is dependent on the Na(+)-coupled monocarboxylate transporter Slc5a8, which transports butyrate and propionate into cells, and on the ability of these two bacterial metabolites to inhibit histone deacetylases. Acetate, which is also a substrate for Slc5a8 but not an inhibitor of histone deacetylases, does not affect dendritic cell development, indicating the essential role of histone deacetylase inhibition in the process. The blockade of dendritic cell development by butyrate and propionate is associated with decreased expression of the transcription factors PU.1 and RelB. Butyrate also elicits its biologic effects through its ability to activate the G-protein-coupled receptor Gpr109a, but this mechanism is not involved in butyrate-induced blockade of dendritic cell development. The participation of Slc5a8 and the non-involvement of Gpr109a in butyrate effects have been substantiated using bone marrow cells obtained from Slc5a8(-/-) and Gpr109a(-/-) mice. These findings uncover an important mechanism underlying the anti-inflammatory functions of the bacterial fermentation products butyrate and propionate.

MS-275, an histone deacetylase inhibitor, reduces the inflammatory reaction in rat experimental autoimmune neuritis

Experimental autoimmune neuritis (EAN) is a T cell-mediated autoimmune inflammatory demyelinating disease of the peripheral nervous system and serves as the animal model of human inflammatory demyelinating polyradiculoneuropathies. MS-275, a potent histone deacetylase inhibitor currently undergoing clinical investigations for various malignancies, has been reported to demonstrate promising anti-inflammatory activities. In our present study, MS-275 administration (3.5 mg/kg i.p.) to EAN rats once daily from the appearance of first neurological signs greatly reduced the severity and duration of EAN and attenuated local accumulation of macrophages, T cells and B cells, and demyelination of sciatic nerves. Further, significant reduction of mRNA levels of pro-inflammatory interleukin-1beta, interferon-gamma, interleukine-17, inducible nitric oxide synthase and matrix metalloproteinase-9 was observed in sciatic nerves of MS-275 treated EAN rats. In lymph nodes, MS-275 depressed pro-inflammatory cytokines as well, but increased expression of anti-inflammatory cytokine interleukine-10 and of foxhead box protein3 (Foxp3), a unique transcription factor of regulatory T cells. In addition, MS-275 treatment increased proportion of infiltrated Foxp3(+) cells and anti-inflammatory M2 macrophages in sciatic nerves of EAN rats. In summary, our data demonstrated that MS-275 could effectively suppress inflammation in EAN, through suppressing inflammatory T cells, macrophages and cytokines, and inducing anti-inflammatory immune cells and molecules, suggesting MS-275 as a potent candidate for treatment of autoimmune neuropathies.

Protein acetylation in the cardiorenal axis: the promise of histone deacetylase inhibitors

Acetylation of histone and nonhistone proteins provides a key mechanism for controlling signaling and gene expression in heart and kidney. Pharmacological inhibition of protein deacetylation with histone deacetylase (HDAC) inhibitors has shown promise in preclinical models of cardiovascular and renal disease. Efficacy of HDAC inhibitors appears to be governed by pleiotropic salutary actions on a variety of cell types and pathophysiological processes, including myocyte hypertrophy, fibrosis, inflammation and epithelial-to-mesenchymal transition, and occurs at compound concentrations below the threshold required to elicit toxic side effects. We review the roles of acetylation/deacetylation in the heart and kidney and provide rationale for extending HDAC inhibitors into clinical testing for indications involving these organs.

Epigenetics in atherosclerosis and inflammation

Atherosclerosis is a multifactorial disease with a severe burden on western society. Recent insights into the pathogenesis of atherosclerosis underscore the importance of chronic inflammation in both the initiation and progression of vascular remodelling. Expression of immunoregulatory molecules by vascular wall components within the atherosclerotic lesions is accordingly thought to contribute to the ongoing inflammatory process. Besides gene regulatory proteins (transcription factors), epigenetic mechanisms also play an essential and fundamental role in the transcriptional control of gene expression. These epigenetic mechanisms change the accessibility of chromatin by DNA methylation and histone modifications. Epigenetic modulators are thus critically involved in the regulation of vascular, immune and tissue-specific gene expression within the atherosclerotic lesion. Importantly, epigenetic processes are reversible and may provide an excellent therapeutic target. The concept of epigenetic regulation is gradually being recognized as an important factor in the pathogenesis of atherosclerosis. Recent research provides an essential link between inflammation and reprogramming of the epigenome. In this review we therefore discuss the basis of epigenetic regulation – and the contribution thereof in the regulation of inflammatory processes in general and during atherosclerosis in particular. Moreover we highlight potential therapeutic interventions based on epigenetic mechanisms.

Ovarian cancer cells induce peripheral mature dendritic cells to differentiate into macrophagelike cells in vitro

AIMS

Precursors of dendritic cells (DCs) are able to differentiate into macrophages induced by some tumor-associated molecules; however, whether peripheral mature DCs could differentiate into macrophages remains unknown. This study was designed to find out whether ovarian cancer cells could induce peripheral mature DCs to differentiate into macrophages.

MAIN METHODS

Mature DCs were cultured from monocytes with granulocyte-macrophage colony-stimulating factor and interleukin 4 (IL-4) for 6 days and lipopolysaccharide for another 24 hours and then were cocultured for 48 hours with ovarian cancer ascites or cell-free supernatants of SKOV3 and CAOV3 cell lines. In some experiments, mature DCs were cultured in the absence or presence of IL-10 or leukemia inhibitory factor (LIF) for the same time. In neutralization experiments, neutralizing monoclonal antibodies to IL-10 or LIF were added to the cultures. Cell phenotypes and phagocytosis were analyzed using flow cytometry; allogeneic T-cell proliferation assay was used to examine stimulatory activity of cells.

RESULTS AND CONCLUSIONS

Mature DCs cocultured with ovarian cancer ascites or supernatants of SKOV3 and CAOV3 differentiated into a group of macrophagelike cells that exhibited increased expression of surface marker CD14+CD1a-, decreased expression of CD83, poorer T-cell costimulatory properties, and greater endocytosis of fluorescein isothiocyanate-dextran in vitro. Interleukin 10 but not LIF mediated this differentiation pathway.

Immunomodulatory effects of deacetylase inhibitors: therapeutic targeting of FOXP3+ regulatory T cells

Classical zinc-dependent histone deacetylases (HDACs) catalyse the removal of acetyl groups from histone tails and also from many non-histone proteins, including the transcription factor FOXP3, a key regulator of the development and function of regulatory T cells. Many HDAC inhibitors are in cancer clinical trials, but a subset of HDAC inhibitors has important anti-inflammatory or immunosuppressive effects that might be of therapeutic benefit in immuno-inflammatory disorders or post-transplantation. At least some of these effects result from the ability of HDAC inhibitors to enhance the production and suppressive functions of FOXP3(+) regulatory T cells. Understanding which HDACs contribute to the regulation of the functions of regulatory T cells may further stimulate the development of new class- or subclass-specific HDAC inhibitors with applications beyond oncology.

The HDAC inhibitor panobinostat (LBH589) inhibits mesothelioma and lung cancer cells in vitro and in vivo with particular efficacy for small cell lung cancer

Lung cancer is the leading cause of cancer deaths in the United States. Current therapies are inadequate. Histone deacetylase inhibitors (HDACi) are a recently developed class of anticancer agents that cause increased acetylation of core histones and nonhistone proteins leading to modulation of gene expression and protein activity involved in cancer cell growth and survival pathways. We examined the efficacy of the HDACi panobinostat (LBH589) in a wide range of lung cancers and mesotheliomas. Panobinostat was cytotoxic in almost all 37 cancer cell lines tested. IC(50) and LD(50) values were in the low nmol/L range (4-470 nmol/L; median, 20 nmol/L). Small cell lung cancer (SCLC) cell lines were among the most sensitive lines, with LD(50) values consistently <25 nmol/L. In lung cancer and mesothelioma animal models, panobinostat significantly decreased tumor growth by an average of 62% when compared with vehicle control. Panobinostat was equally effective in immunocompetent and severe combined immunodeficiency mice, indicating that the inhibition of tumor growth by panobinostat was not due to direct immunologic effects. Panobinostat was, however, particularly effective in SCLC xenografts, and the addition of the chemotherapy agent etoposide augmented antitumor effects. Protein analysis of treated tumor biopsies revealed elevated amounts of cell cycle regulators such as p21 and proapoptosis factors, such as caspase 3 and 7 and cleaved poly[ADP-ribose] polymerase, coupled with decreased levels of antiapoptotic factors such as Bcl-2 and Bcl-X(L). These studies together suggest that panobinostat may be a useful adjunct in the treatment of thoracic malignancies, especially SCLC.

Cutting edge: Negative regulation of dendritic cells through acetylation of the nonhistone protein STAT-3

Histone deacetylase (HDAC) inhibition modulates dendritic cell (DC) functions and regulates experimental graft-vs-host disease and other immune-mediated diseases. The mechanisms by which HDAC inhibition modulates immune responses remain largely unknown. STAT-3 is a transcription factor shown to negatively regulate DC functions. In this study we report that HDAC inhibition acetylates and activates STAT-3, which regulates DCs by promoting the transcription of IDO. These findings demonstrate a novel functional role for posttranslational modification of STAT-3 through acetylation and provide mechanistic insights into HDAC inhibition-mediated immunoregulation by induction of IDO.

Apicidin, the Histone Deacetylase Inhibitor, Suppresses TH1 Polarization of Murine Bone Marrow-Derived Dendritic Cells

Apicidin is a fungal metabolite shown to exhibit anti-proliferative, anti-invasive, and anti-inflammatory properties by the inhibition of histone deacetylase (HDAC). However, the effects of apicidin on the maturation and immunostimulatory function of dendritic cells (DCs) remain unknown. In this study, we investigated whether apicidin modulates surface molecule expression, cytokine production, endocytosis capacity, and underlying signaling pathways in murine bone marrow-derived DCs. We observed that apicidin significantly attenuated surface molecule expression in LPS-stimulated DCs, suppressed production of interleukin (IL)-12 and proinflammatory cytokines (IL-6 and TNF-α) by DCs, and reduced IFN-γ production by T cells. The apicidin-treated DCs were found to be highly efficient in antigen capture via mannose receptor-mediated endocytosis. Apicidin also inhibited LPS-induced MAPK activation and NF-κB nuclear translocation in DCs. Moreover, the apicidin-treated DCs were incapable of inducing Th1 responses and normal cell-mediated immune responses. These novel findings not only provide new insights into the immunopharmacological role of apicidin in terms of its effects on DCs, but also broaden current perspectives of the immunopharmacological functions of apicidin, and have implications for the development of therapeutic adjuvants for the treatment of DC-related acute and chronic diseases.

Enumeration of blood dendritic cells in patients with multiple myeloma at presentation and through therapy

Multiple myeloma (MM) is a clonal B-cell malignancy characterised by excess bone marrow plasma cells, serum and/or urine paraprotein, immune paraesis, renal failure and lytic bone lesions. Dendritic cells (DC) are key players in the adaptive and innate immune responses, but reside in tissues, so are difficult to quantify in vivo. By enumerating the blood DC pool, we aim to examine the influence of MM disease and accompanying therapy on the DC system. We have shown, using the BDCA DC detection kit, that blood pDC and mDC numbers are suppressed at diagnosis in MM, and uniquely, monoclonal gammopathy of uncertain significance (MGUS) and patients with plasmacytoma. B-cell numbers were also significantly reduced in MM, MGUS and patients with plasmacytoma (p<or=0.005). Standard chemotherapy did not improve the number of mDC1 or pDC seen in the blood of patients with MM. The number of blood mDC1 improved transiently following auto hemopoietic stem cell transplantation, as numbers returned to within the normal range at engraftment and were maintained until D100. The number of blood mDC1 in patients taking thalidomide was also significantly higher than at relapse. These studies suggest that the defects in the B cell and blood DC pool is present in MGUS and plasmacytoma as well as patients with MM and can recover following therapy.

Blocking TH17-polarizing cytokines by histone deacetylase inhibitors in vitro and in vivo

Histone deacetylase (HDAC) inhibitors are small molecules inducing cell-cycle arrest, differentiation, and apoptosis, currently undergoing clinical trials as anticancer drugs. In addition, emerging evidence suggests HDAC inhibitors may have anti-inflammatory and immunomodulatory properties as well, although the molecular mechanisms remain poorly defined. Given the central role of dendritic cells (DC) in the induction and maintenance of the inflammatory and immune response, we investigated the effects of HDAC inhibitors on the maturation and activation of human monocyte-derived DC in the presence of LPS and IFN-gamma. Our results show that the production of T(H)1- and T(H)17-inducing cytokines, namely IL-12 and IL-23, was inhibited by trichostatin A (72% and 52%, respectively) and suberoylanilide hydroxamic acid (86% and 83%). Strikingly, HDAC inhibitors were effective if added simultaneously as well as after the proinflammatory challenge, and their effect was not associated to a reduction of expression or function of LPS/IFN-gamma receptors. These findings were confirmed in two different murine models. In addition, HDAC inhibitors selectively blocked the production of T(H)1-attracting chemokines CXCL9, CXCL10, and CXCL11. The reduction of T(H)1- and T(H)17-inducing cytokines as well as T(H)1-attracting chemokines may represent relevant mechanisms through which HDAC inhibitors at nonproapoptotic doses exert their immunomodulatory properties.

Histone deacetylase inhibition modulates indoleamine 2,3-dioxygenase-dependent DC functions and regulates experimental graft-versus-host disease in mice

Histone deacetylase (HDAC) inhibitors are antitumor agents that also have antiinflammatory properties. However, the mechanisms of their immunomodulatory functions are not known. We investigated the mechanisms of action of 2 HDAC inhibitors, suberoylanilide hydroxamic acid (SAHA) and ITF 2357, on mouse DC responses. Pretreatment of DCs with HDAC inhibitors significantly reduced TLR-induced secretion of proinflammatory cytokines, suppressed the expression of CD40 and CD80, and reduced the in vitro and in vivo allostimulatory responses induced by the DCs. In addition, injection of DCs treated ex vivo with HDAC inhibitors reduced experimental graft-versus-host disease (GVHD) in a murine allogeneic BM transplantation model. Exposure of DCs to HDAC inhibitors increased expression of indoleamine 2,3-dioxygenase (IDO), a suppressor of DC function. Blockade of IDO in WT DCs with siRNA and with DCs from IDO-deficient animals caused substantial reversal of HDAC inhibition-induced in vitro suppression of DC-stimulated responses. Direct injection of HDAC inhibitors early after allogeneic BM transplantation to chimeric animals whose BM-derived cells lacked IDO failed to protect from GVHD, demonstrating an in vivo functional role for IDO. Together, these data show that HDAC inhibitors regulate multiple DC functions through the induction of IDO and suggest that they may represent a novel class of agents to treat immune-mediated diseases.

Immunotherapy with dendritic cells for cancer

Dendritic cells are professional antigen-presenting cells with a key role in both immunity induction and tolerance maintenance. Dendritic cells are highly specialized in antigen capture, processing and presentation, and express co-stimulation signals which activate T lymphocytes and NK cells. Dendritic cells generated in culture and loaded with an antigen efficiently induce antigen-specific immunity after injection. More recently, methods have been developed that target antigens to dendritic cells in vivo, bypassing the need for ex vivo cell manipulations. Numerous ongoing studies aim to evaluate the effectiveness of dendritic cell vaccines in preventing tumor relapses and extending patients' survival. Further implementation of this form of immunotherapy is expected following the identification of the mechanisms controlling dendritic cell immunogenicity, and from a better understanding of the cell dynamics whereby immune responses are orchestrated. Here, we discuss these new insights together with an overview of the dendritic cell-based clinical studies carried out to date.