Philadelphia-like B-cell acute lymphoblastic Leukaemia: Disease features and outcomes in the era of immunotherapy.

Philadelphia chromosome (Ph)-like acute lymphoblastic leukaemia (ALL) is a high-risk subtype with a gene expression profile similar to Ph-positive ALL, due to activation of tyrosine kinase signalling. To understand the clinical implications of Ph-like ALL, this single-centre retrospective study evaluates outcomes in 268 adults, largely Hispanic ALL patients treated between 2013 and 2024, with a subgroup analysis of 139 haematopoietic stem cell transplantation (HSCT) patients. ALL subtypes included 68 (25.4%) Ph-like, 89 (33.2%) Ph-positive, and 111 (41.4%) Ph-negative. Ph-like patients were the youngest age at diagnosis (p = 0.007), most likely to have refractory disease (p < 0.001), and least likely to achieve minimal residual disease (MRD) negativity after induction (p = 0.031). Relative to Ph-negative ALL, Ph-like achieved worse event-free survival (EFS) (HR = 1.66; 95% CI 1.12-2.46; p = 0.012), whereas Ph-positive had improved EFS (HR = 0.60; 95% CI 0.38-0.93; p = 0.024) and cumulative incidence of relapse (CIR) (HR = 0.59; 95% CI 0.35-0.99; p = 0.046). Within the transplant subgroup, Ph status did not impact disease-free survival (DFS), CIR, or overall survival (OS). However, patients who received blinatumomab within 1-year pre-HSCT had improved DFS (HR = 0.43; 95% CI 0.20-0.94; p = 0.034) and CIR (HR = 0.26; 95% CI 0.09-0.75; p = 0.13). In conclusion, our data suggest that Ph-like is less likely to respond to standard induction therapy and HSCT may result in similar survival outcomes to Ph-negative ALL.

T cells lacking HDAC11 have increased effector functions and mediate enhanced alloreactivity in a murine model.

Histone acetylation and the families of enzymes responsible for controlling these epigenetic marks have been implicated in regulating T-cell maturation and phenotype. Here, we demonstrate a previously undefined role of histone deacetylase 11 (HDAC11) in regulating T-cell effector functions. Using EGFP-HDAC11 transgenic reporter mice, we found that HDAC11 expression was lower in effector relative to naive and central memory T-cell populations, and activation of resting T cells resulted in its decreased expression. Experiments using HDAC11 knockout (KO) mice revealed that T cells from these mice displayed enhanced proliferation, proinflammatory cytokine production, and effector molecule expression. In addition, HDAC11KO T cells had increased expression of Eomesodermin (Eomes) and TBX21 (Tbet), transcription factors previously shown to regulate inflammatory cytokine and effector molecule production. Conversely, overexpression of HDAC11 resulted in decreased expression of these genes. Chromatin immunoprecipitation showed the presence of HDAC11 at the Eomes and Tbet gene promoters in resting T cells, where it rapidly disassociated following T-cell activation. In vivo, HDAC11KO T cells were refractory to tolerance induction. HDAC11KO T cells also mediated accelerated onset of acute graft-versus-host disease (GVHD) in a murine model, characterized by increased proliferation of T cells and expression of interferon-γ, tumor necrosis factor, and EOMES. In addition, adoptive transfer of HDAC11KO T cells resulted in significantly reduced tumor burden in a murine B-cell lymphoma model. Taken together, these data demonstrate a previously unknown role of HDAC11 as a negative epigenetic regulator of T-cell effector phenotype and function.

A novel role for histone deacetylase 6 in the regulation of the tolerogenic STAT3/IL-10 pathway in APCs.

APCs are critical in T cell activation and in the induction of T cell tolerance. Epigenetic modifications of specific genes in the APC play a key role in this process, and among them histone deacetylases (HDACs) have emerged as key participants. HDAC6, one of the members of this family of enzymes, has been shown to be involved in regulation of inflammatory and immune responses. In this study, to our knowledge we show for the first time that genetic or pharmacologic disruption of HDAC6 in macrophages and dendritic cells results in diminished production of the immunosuppressive cytokine IL-10 and induction of inflammatory APCs that effectively activate Ag-specific naive T cells and restore the responsiveness of anergic CD4(+) T cells. Mechanistically, we have found that HDAC6 forms a previously unknown molecular complex with STAT3, association that was detected in both the cytoplasmic and nuclear compartments of the APC. By using HDAC6 recombinant mutants we identified the domain comprising amino acids 503-840 as being required for HDAC6 interaction with STAT3. Furthermore, by re-chromatin immunoprecipitation we confirmed that HDAC6 and STAT3 are both recruited to the same DNA sequence within the Il10 gene promoter. Of note, disruption of this complex by knocking down HDAC6 resulted in decreased STAT3 phosphorylation--but no changes in STAT3 acetylation--as well as diminished recruitment of STAT3 to the Il10 gene promoter region. The additional demonstration that a selective HDAC6 inhibitor disrupts this STAT3/IL-10 tolerogenic axis points to HDAC6 as a novel molecular target in APCs to overcome immune tolerance and tips the balance toward T cell immunity.

Graft Versus Host Disease Prophylaxis in Matched Donor Stem Cell Transplantation: Post-transplantation Cyclophosphamide Combinations Versus Methotrexate/Tacrolimus.

BACKGROUND: The use of post-transplant cyclophosphamide (PTCy) is highly effective in preventing graft versus host disease (GVHD) for haploidentical allogeneic hematopoietic stem cell transplantation (allo-HSCT). There is limited data on the role of PTCy as GVHD prophylaxis in matched-sibling and fully matched-unrelated donor (MSD/MUD) allo-HSCT. METHODS: Our single-center retrospective study aims to compare outcomes of PTCy alone or in combination with mycophenolate mofetil and tacrolimus (PTCy/MMF/TAC) relative to methotrexate and tacrolimus (MTX/TAC). The primary endpoint of our study was GVHD-free, relapse free survival (GRFS). Secondary endpoints were overall survival (OS), disease free survival (DFS), and incidence of severe acute and chronic GVHD. We identified 74 adult patients who underwent MSD/MUD allo-HSCT at our institution from 2015 to 2023. RESULTS: Within our cohort, 33.8% (n = 25) received MTX/TAC, while 54.0% (n = 40) received PTCy/MMF/TAC, and 12.2% (n = 9) received PTCy alone. Patients receiving PTCY had the longest time to neutrophil engraftment relative to MTX/TAC (15 days vs. 12 days, P = .010). PTCy/MMF/TAC was associated with improved GRFS relative to MTX/TAC (hazard ratio [HR] = HR 0.42, 95% CI 0.19-0.93, P = .031), which persisted when controlling for age. Incidence of chronic GVHD was lower in the PTCy/MMF/TAC group compared to MTX/TAC (1-year 9.0% vs. 30.1%, HR 0.19, 95% CI 0.06-0.59, P = .005). However, OS and DFS were comparable across all groups. CONCLUSIONS: Our results demonstrate decreased rates of severe chronic GVHD resulting in improved GRFS when using PTCy/TAC/MTX as GVHD prophylaxis compared to MTX/TAC in MSD/MUD.

Combination Therapy With Asciminib and Ponatinib as a Bridge to Brexucabtagene Autoleucel and Maintenance in a Patient With Relapsed Refractory Philadelphia Positive B-Cell Acute Lymphoblastic Leukemia.

Tyrosine kinase inhibitors (TKIs) have changed the prognosis of Philadelphia-positive B-cell acute lymphoblastic leukemia (ALL); however, relapsed and refractory disease after multiple TKIs continues to be a clinical challenge. Brexucabtagene autoleucel (brexu-cel) is a novel FDA-approved therapy for relapsed and refractory ALL. Given the lengthy manufacturing time, bridging therapy is commonly employed prior to brexu-cel. Here we describe a case of a 75-year-old Hispanic male patient with relapsed/refractory Philadelphia-positive B-cell ALL with extramedullary disease involving abdominal lymph nodes and skin. He was initially treated with chemotherapy in combination with imatinib, and later received dasatinib and subsequently blinatumomab and nilotinib. As the patient progressed, he received ponatinib with low-dose salvage chemotherapy and did not show kinase domain mutation. In a final effort, a novel combination of ponatinib with asciminib was used as a bridge therapy before brexu-cel and later as maintenance therapy after brexu-cel. This novel combination was able to control disease prior to brexu-cel for 2 months and maintained remission for at least 10 months. This report shows that the novel combination of ponatinib and asciminib is tolerable and effective as a bridge and maintenance therapy after brexu-cel.

Case report: Pulse cyclophosphamide for treatment of multi-agent-refractory hepatic graft-versus-host disease.

Graft-versus-host disease (GVHD) is a common complication in patients receiving allogeneic hematopoietic stem cell transplantation (HSCT). GVHD is characterized as either acute or chronic based on symptomatology and histopathological findings. Despite advancements in disease-targeting therapeutics, steroid-refractory GVHD remains a significant contributor to mortality in HSCT recipients, highlighting the gaps in our understanding of its pathophysiology and treatment strategies. We present the case of a 46-year-old woman diagnosed with acute undifferentiated leukemia, who exhibited persistently elevated levels of serum total bilirubin (T.Bili), alkaline phosphatase (ALP), and liver function tests (LFTs) beginning on [day +201] post-haploidentical peripheral blood stem cell (PBSC) transplantation. The patient received fludarabine/total body irradiation (Flu/TBI) as a myeloablative conditioning regimen and post-transplant cyclophosphamide/tacrolimus/mycophenolate mofetil (PTCy/Tac/MMF) as GVHD prophylaxis. A liver biopsy confirmed the diagnosis of GVHD, while other possible etiologies were excluded by corresponding tests. Initial treatment with prednisone and tacrolimus, and the later addition of ruxolitinib, all showed poor response indicated by worsening T.Bili, ALP, and LFTs at the same time. Based on a multidisciplinary comprehensive assessment, we decided to administer 1,000 mg/m2 (1,600 mg) of cyclophosphamide ("pulse Cy"), which resulted in a dramatic improvement in T.Bili and transaminases starting from the very next day. A durable response to pulse cyclophosphamide was observed, as all indicators normalized ("complete response") within 55 days without relapses. The patient remains in good health with no recurrence of hepatic GVHD. To our knowledge, this is the first case in which Grade IV hepatic GVHD, refractory to multiple agents including steroids, tacrolimus, and ruxolitinib, demonstrated a complete response to pulse cyclophosphamide. The success highlights the potential therapeutic role of cyclophosphamide, a potent and cost-effective chemotherapy agent, in treating multi-agent-refractory GVHD. Large-scale clinical trials are warranted to validate its efficacy in this setting.

Concordance of Next-Generation Sequencing and Multiparametric Flow Cytometry Methods for Detecting Measurable Residual Disease in Adult Acute Lymphoblastic Leukemia: Optimizing Prediction of Clinical Outcomes From a Single-Center Study.

INTRODUCTION: Detection of measurable residual disease (MRD) in adults with acute lymphoblastic leukemia (ALL) is a vital biomarker in risk prediction and treatment selection. Next-generation sequencing (NGS) offers greater sensitivity relative to multiparametric flow cytometry (MFC) and may be a better predictive tool for identifying ALL patients at risk of relapse. PATIENTS AND METHODS: This single-center retrospective study compares MRD detection by NGS versus MFC in 52 adult B- and T-ALL patients treated at our institution between 2018 and 2023. Pretreatment bone marrow samples were used for assay calibration, while post-treatment MRD assessment was completed up to 4.5 months after the first complete remission (CR1) using an MRD cutoff of 10-6 for distinguishing relapse risk. RESULTS: The 2-year cumulative incidence of relapse (CIR) among patients who were MRD positive using MFC and NGS was 39.5% and 46.2%, respectively. Unlike MFC, post-CR1 MRD positivity with NGS significantly predicted CIR (HR = 9.47, P = .028). In patients who were MRD negative by MFC, low levels of MRD detected by NGS distinguished patients at high risk of relapse (HR 10.3, P = .026, 2-year CIR 51.6%). CONCLUSION: Our data suggests that assessment of post-CR1 MRD using a highly sensitive NGS assay can identify ALL patients undergoing frontline therapy at increased risk of relapse and guide the use of adjuvant therapy.

Donor matters: Donor selection impact on hematopoietic stem cell transplantation outcomes in Hispanic patients with B-cell acute lymphocytic leukemia: Insights from a myeloablative HSCT study.

BACKGROUND: Hematopoietic stem cell transplantation (HSCT) is a pivotal treatment for high-risk acute lymphocytic leukemia (ALL), although limited by suitable human leukocyte antigen (HLA)-matched sibling donors (MSD). This study evaluates the impact of donor selection on outcomes in post-HSCT Hispanic B-cell ALL patients. METHODOLOGY: This single-center retrospective study evaluates outcomes in 88 adult Hispanic B-cell ALL patients who underwent haploidentical, MSD, or MUD myeloablative HSCT between 2013 and 2023. RESULTS: Compared to Haploidentical transplants, MSD exhibited worse cumulative incidence of relapse (CIR) (HR = 3.39; P = 0.014) and disease-free survival (DFS) (HR = 2.44; P = 0.048) whereas MUD outcomes did not differ. This effect persisted even when controlling for pre-HSCT stage and Minimal residual disease (MRD) status. In addition, Ph-like was a significant predictor of worse DFS (HR = 3.60; P=0.014) and CIR (HR = 2.97; P=0.035) on multivariate analysis. Older donor age correlated with worse GVHD-free, relapse-free survival (GRFS) in haploidentical transplants (HR = 1.05; P=0.036). CONCLUSION: Our data highlights improved outcomes with younger, haploidentical donors among Hispanic B-cell ALL patients undergoing myeloablative HSCT. This underscores the importance of donor selection in optimizing outcomes for ALL patients.

Histone deacetylase inhibitor LAQ824 augments inflammatory responses in macrophages through transcriptional regulation of IL-10.

APCs are important in the initiation of productive Ag-specific T cell responses and the induction of T cell anergy. The inflammatory status of the APC at the time of encounter with Ag-specific T cells plays a central role in determining such divergent T cell outcomes. A better understanding of the regulation of proinflammatory and anti-inflammatory genes in its natural setting, the chromatin substrate, might provide novel insights to overcome anergic mechanisms mediated by APCs. In this study, we show for the first time, to our knowledge, that treatment of BALB/c murine macrophages with the histone deacetylase inhibitor LAQ824 induces chromatin changes at the level of the IL-10 gene promoter that lead to enhanced recruitment of the transcriptional repressors HDAC11 and PU.1. Such an effect is associated with diminished IL-10 production and induction of inflammatory cells able of priming naive Ag-specific T cells, but more importantly, capable of restoring the responsiveness of anergized Ag-specific CD4(+) T cells.

Unique challenges to diagnosing sweet syndrome following induction chemotherapy for relapsed Acute Myeloid Leukemia (AML): A case and brief-review.

Background: Sweet Syndrome (SS) is a rare inflammatory skin condition characterized by the sudden appearance of tender, erythematous or violaceous papules, plaques, and nodules typically found on the face, neck, shoulder, upper extremities, and trunk. Often, SS is difficult to diagnose because of its various non-specific manifestations, including fever, arthralgia, myalgia and ocular involvement. In most cases described in literature, cutaneous and pulmonary symptoms of SS present in a concomitant manner. Several reported cases of pulmonary SS have shown that if left untreated, acute respiratory distress syndrome can ensue and progress to fatal respiratory failure. Case report: A 58-year-old female with acute myeloid leukemia (AML) secondary to chronic lymphocytic leukemia (CLL) presented with new nodular lesions, dyspnea, and fevers. Chest X-ray revealed pulmonary infiltrates. The patient developed new facial lesions and worsening hypoxic respiratory failure. Further infectious workup was negative. She was found to have SS with pulmonary involvement and initiated on high-dose intravenous (IV) steroids with marked clinical improvement. Conclusions: Major and minor criteria for the diagnosis of lung-associated SS should be carefully evaluated, especially when a biopsy is unavailable. The following case report describes the clinical course and outcomes from treatment for this patient.

Real world experience: Examining outcomes using letermovir for CMV prophylaxis in high-risk allogeneic hematopoietic stem cell patients in the setting of using T-cell depletion as GVHD prophylaxis.

BACKGROUND: Cytomegalovirus (CMV) infection significantly impacts the morbidity and mortality of patients undergoing allogeneic hematopoietic stem cell transplant (HSCT). Despite monitoring and pharmacologic prophylaxis with drugs such as valganciclovir or ganciclovir, rates of early CMV reactivation have continually persisted, contributing to increased rates of morbidity and mortality in allogeneic-HSCT patients. This study evaluates the outcomes of letermovir in preventing CMV reactivation and CMV-related complications in HSCT recipients with initiation of therapy at +21 days in high-risk patients. METHODS: We retrospectively analyzed adult patients at University of Southern California (USC) Norris Cancer Hospital who received allogeneic-HSCT from 2018 to 2020 with subsequent serial CMV monitoring and treatment. CMV reactivation was determined in patients if they had clinically significant serum CMV viremia (viremia requiring treatment) or organ involvement by day+100. Primary endpoint assessed was day+100 rates of CMV reactivation. Secondary end-points included 1-year OS, 1-year RFS, and incidence of GVHD. Descriptive statistics were used to compare characteristics between groups used in this study, with a significance level of α = 0.05. RESULTS: Between 2018 and 2020, 116 adult HSCT recipients were reviewed. 51% were male and 49% were female; donor sources consisted of 27% match related donor (MRD) 28% match-unrelated donor (MUD), and 45% haploidentical donor. Of the 116 patients, 92 were identified as high-risk for CMV reactivation. 71 patients received letermovir prophylaxis, and 21 patients received no prophylaxis. In high-risk patients, after adjusting for GVHD status and transplant type, patients that received letermovir had no statistically significant difference of having D + 100 CMV reactivation compared to patients that did not receive letermovir. 1.02 (95% CI: 0.35, 3.20) (p = 0.97). Moreover, there were no statistically significant difference observed between letermovir treatment and 1-year OS, 1-year RFS, and incidence of GVHD. CONCLUSION: Patients in the high-risk letermovir group had outcomes that were comparable to the lower risk "non-letermovir" group. There was no significant difference in CMV D + 100 reactivation between high-risk patients who did not receive letermovir compared to the patients who did. While other studies have shown that early initiation of letermovir may be associated with improved outcomes, our study shows that the use of letermovir with initiation at 21 days may not necessarily translate to improved secondary outcomes such as overall survival. Further prospective studies evaluating the time of initiating therapy and outcomes are needed.

Modulation of antigen-presenting cells by HDAC inhibitors: implications in autoimmunity and cancer.

There is a growing body of evidence to support the use of histone deacetylase inhibitors (HDACi) in the treatment of diverse conditions from autoimmunity to cancer. In this context, HDACi have been ascribed many immunomodulatory effects, assigning novel and promising roles to these compounds. This review summarizes the current observations arising from both pre-clinical and clinical studies in these pathological conditions. However, it is left to be explained how a single agent can have both pro- and anti-inflammatory effects in either physiological or pathological conditions. This question is explored in greater detail by focusing on the effects of HDACi on antigen-presenting cells (APCs), key regulators of immune activation. In particular, HDACi modulation of molecules involved in antigen processing and presentation, as well as co-stimulatory and adhesion molecules, and cytokines will be discussed in the context of both professional and non-professional APCs. Professional APCs encompass classic immune cells; however, it is increasingly evident that other somatic cells, including cancer cells, are not immunologically inert and can display functions similar to professional APCs, a challenging feature that needs to be explored as a potential therapeutic target. In this way, professional and non-professional APCs can regulate their particular micro-environmental niche, affecting either a pro- or anti-inflammatory milieu.

Unique Challenges to Diagnosing Human Herpesvirus-6 (HHV-6) Encephalitis Following Post-Hematopoietic Stem Cell Transplant: A Case and Brief Review.

A patient with an ultimate diagnosis of human herpesvirus-6 (HHV-6) encephalitis developed central nervous system (CNS) symptoms 13 days after undergoing myeloablative haploidentical allogeneic hematopoietic stem cell transplant (HSCT). Due to the patient's body habitus, magnetic resonance (MR) imaging was not obtained until the onset of retrograde amnesia on day +24. MR imaging and other clinical findings eliminated all skepticism of HHV-6 encephalitis and HHV-6 antivirals were initiated on day +28, leading to gradual recovery. This case demonstrates some of the factors that may complicate the diagnosis of post-alloHSCT HHV-6 encephalitis. Because HHV-6 encephalitis and viremia can occur without warning, a single negative study should not exclude future development, especially if CNS symptoms are present. Acute graft-versus-host disease and cord blood transplantation are both significant risk factors for HHV-6 encephalitis. Human leukocyte antigen (HLA) mismatch, engraftment complications, or certain HLA alleles have also been associated with HHV-6 encephalitis. Chromosomally integrated HHV-6 must also be ruled out to prevent inappropriate and potentially harmful administration of antivirals. Due to the severe short- and long-term sequelae of HHV-6 encephalitis, appropriate treatment should be administered as soon as possible.

Harnessing features of adaptive NK cells to generate iPSC-derived NK cells for enhanced immunotherapy.

Select subsets of immune effector cells have the greatest propensity to mediate antitumor responses. However, procuring these subsets is challenging, and cell-based immunotherapy is hampered by limited effector-cell persistence and lack of on-demand availability. To address these limitations, we generated a triple-gene-edited induced pluripotent stem cell (iPSC). The clonal iPSC line was engineered to express a high affinity, non-cleavable version of the Fc receptor CD16a and a membrane-bound interleukin (IL)-15/IL-15R fusion protein. The third edit was a knockout of the ecto-enzyme CD38, which hydrolyzes NAD+. Natural killer (NK) cells derived from these uniformly engineered iPSCs, termed iADAPT, displayed metabolic features and gene expression profiles mirroring those of cytomegalovirus-induced adaptive NK cells. iADAPT NK cells persisted in vivo in the absence of exogenous cytokine and elicited superior antitumor activity. Our findings suggest that unique subsets of the immune system can be modeled through iPSC technology for effective treatment of patients with advanced cancer.

Harnessing Natural Killer Cell Antitumor Immunity: From the Bench to Bedside.

Natural killer (NK) cells are critical effector lymphocytes mediating tumor immune surveillance and clearance. They do so by direct tumor killing using cytolytic granules and death receptors, and by interfacing with and potentiating adaptive immune responses through the production of cytokines. From a therapeutic perspective, NK cells have been shown to exert graft-versus-leukemia activity in the context of hematopoietic stem cell transplantation and are important in the clinical efficacy of antibodies. Advances in basic and translational NK cell biology have led to multiple potential strategies to augment their in vivo activity to improve antitumor responses. Despite their potent effects, NK cells have been shown to be safe for adoptive cell therapy in both the autologous and allogeneic settings, with promising, but so far limited, clinical efficacy. This review will provide an overview of strategies being pursued to improve NK cell activity and efficacy, focusing on cell source, NK cell activation, and in vivo persistence.

Histone deacetylase 11: A novel epigenetic regulator of myeloid derived suppressor cell expansion and function.

Myeloid-derived suppressor cells (MDSCs), a heterogeneous population of cells capable of suppressing anti-tumor T cell function in the tumor microenvironment, represent an imposing obstacle in the development of cancer immunotherapeutics. Thus, identifying elements essential to the development and perpetuation of these cells will undoubtedly improve our ability to circumvent their suppressive impact. HDAC11 has emerged as a key regulator of IL-10 gene expression in myeloid cells, suggesting that this may represent an important targetable axis through which to dampen MDSC formation. Using a murine transgenic reporter model system where eGFP expression is controlled by the HDAC11 promoter (Tg-HDAC11-eGFP), we provide evidence that HDAC11 appears to function as a negative regulator of MDSC expansion/function in vivo. MDSCs isolated from EL4 tumor-bearing Tg-HDAC11-eGFP display high expression of eGFP, indicative of HDAC11 transcriptional activation at steady state. In striking contrast, immature myeloid cells in tumor-bearing mice display a diminished eGFP expression, implying that the transition of IMC to MDSC's require a decrease in the expression of HDAC11, where we postulate that it acts as a gate-keeper of myeloid differentiation. Indeed, tumor-bearing HDAC11-knockout mice (HDAC11-KO) demonstrate a more suppressive MDSC population as compared to wild-type (WT) tumor-bearing control. Notably, the HDAC11-KO tumor-bearing mice exhibit enhanced tumor growth kinetics when compare to the WT control mice. Thus, through a better understanding of this previously unknown role of HDAC11 in MDSC expansion and function, rational development of targeted epigenetic modifiers may allow us to thwart a powerful barrier to efficacious immunotherapies.

Divergent roles of histone deacetylase 6 (HDAC6) and histone deacetylase 11 (HDAC11) on the transcriptional regulation of IL10 in antigen presenting cells.

The anti-inflammatory cytokine IL-10 is a key modulator of immune responses. A better understanding of the regulation of this cytokine offers the possibility of tipping the balance of the immune response toward either tolerance, or enhanced immune responses. Histone deacetylases (HDACs) have been widely described as negative regulators of transcriptional regulation, and in this context, the primarily nuclear protein HDAC11 was shown to repress il-10 gene transcriptional activity in antigen-presenting cells (APCs). Here we report that another HDAC, HDAC6, primarily a cytoplasmic protein, associates with HDAC11 and modulates the expression of IL-10 as a transcriptional activator. To our knowledge, this is the first demonstration of two different HDACs being recruited to the same gene promoter to dictate divergent transcriptional responses. This dynamic interaction results in dynamic changes in the expression of IL-10 and might help to explain the intrinsic plasticity of the APC to determine T-cell activation versus T-cell tolerance.

The antimelanoma activity of the histone deacetylase inhibitor panobinostat (LBH589) is mediated by direct tumor cytotoxicity and increased tumor immunogenicity.

Melanoma is the deadliest skin cancer, and its incidence has been increasing faster than any other cancer. Although immunogenic, melanoma is not effectively cleared by host immunity. In this study, we investigate the therapeutic, antimelanoma potential of the histone deacetylase inhibitor (HDACi) panobinostat (LBH589) by assessing both its cytotoxic effects on melanoma cells as well as enhancement of immune recognition of melanoma. Utilizing murine and human melanoma cell lines, we analyzed the effects of LBH589 on proliferation and survival. In addition, we analyzed the expression of several immunologically relevant surface markers and melanoma differentiation antigens, and the ability of LBH589-treated melanoma to activate antigen-specific T cells. Finally, we assessed the in-vivo effects of LBH589 in a mouse melanoma model. Low nanomolar concentrations of LBH589 inhibit the growth of all melanoma cell lines tested, but not normal melanocytes. This inhibition is characterized by increased apoptosis as well as a G1 cell cycle arrest. In addition, LBH589 augments the expression of major histocompatibility complex and costimulatory molecules on melanoma cells leading to an increased ability to activate antigen-specific T cells. Treatment also increases expression of melanoma differentiation antigens. In vivo, LBH589 treatment of melanoma-bearing mice results in a significant increase in survival. However, in immunodeficient mice, the therapeutic effect of LBH589 is lost. Taken together, LBH589 exerts a dual effect upon melanoma cells by affecting not only growth/survival but also by increasing melanoma immunogenicity. These effects provide the framework for future evaluation of this HDAC inhibitor in melanoma treatment.