HIV Interferes with Mycobacterium tuberculosis Antigen Presentation in Human Dendritic Cells

Selective 5-Lipoxygenase Expression in Langerhans Cells and Impaired Dendritic Cell Migration in 5-LO-Deficient Mice Reveal Leukotriene Action in Skin

Dendritic cells (DCs) are specialized antigen presentation cells that play critical roles in the initiation and regulation of immune responses. The molecular determinants of DC differentiation and maturation are target of extensive investigation. VentX is a human homeobox transcriptional factor that regulates proliferation and differentiation of hematopoietic cells. In the current study, we report that ablation of VentX expression in monocytes significantly impaired their differentiation into DCs. Conversely, overexpression of VentX in monocytic THP1 cells accelerated their differentiation toward DCs. We showed that VentX regulates DC differentiation, in part, through modulating IL6 expression. Clinically, we found that VentX expression was elevated in intestinal lamina propria DCs (LPDCs) of inflamed mucosa from inflammatory bowel disease patients. Knockdown experiments suggested that VentX is essential for the maturation of LPDCs. In addition, corticosteroid treatment markedly decreased VentX expression in LPDCs and enforced expression of VentX counteracted the effects of corticosteroid on DCs maturation. Our data suggest that VentX is a critical transcriptional regulator of DC differentiation and maturation, and a potential target of immune regulation and therapy.

Cardiovascular diseases (CVDs) are one of the leading causes of mortality worldwide.1 It has been so for decades, notwithstanding a wide array of – mostly preventive – treatment modalities targeting known risk factors, such as hyperlipidemia, type 2 diabetes mellitus, hypertension, or obesity. Recent technical and conceptual advances have unveiled important contributions of the immune system in the pathophysiology of a variety of CVDs such as atherosclerosis, ischemic stroke, chronic heart failure, and other myocardial conditions like myocardial ischemia and reperfusion, viral myocarditis, and cardiac transplantation.2–4 In many of these disorders, so-called danger-associated molecular patterns (DAMPs), released from necrotic tissue and dying cells, can lead to the activation of certain immune cell populations such as monocytes/ macrophages, granulocytes, and T cells, thus aggravating ongoing inflammatory processes at the lesion site. Dendritic cells (DCs) are key modulators of immunity, pivotal in directing innate and adaptive immune responses against microbial, viral, but also modified self-antigens present at the sites of injury. Given the tissue trauma underlying various CVDs, it is not surprising that recent observations have allocated a regulatory role for DCs in CVD-associated immune responses. Interestingly, nondiseased arteries of young individuals were seen to host a network of resident vascular DCs (CD1a+ S100+ lag+ CD31− CD83− CD86−),5 representing a phenotype related to Langerhans cells in the skin. In agreement, monocyte-derived CD11c+ CD68+ dendritic cells could be detected in the atherosclerosis-prone lesser curvature and aortic sinus in inbred atherosclerosis-susceptible (C57Bl/6), but not resistant mouse strains (balb/c).6 Murine vascular resident DCs express an immature phenotype with low expression of costimulatory molecules, and are present in the subendothelial space with occasional probing into the vascular lumen. DCs have …

Chronic Ethanol Consumption Impairs Cellular Immune Responses Against HCV NS5 Protein Due to Dendritic Cell Dysfunction

Antigen presenting cells (APCs), especially dendritic cells (DCs), play a major role in the hierarchy of the induction of immune reactions. DCs are widely accepted as the most potent APCs capable of inducing protective adaptive immune responses in addition to tolerance to self-antigens. The role of DCs is currently being investigated in the context of many disease and therapeutic settings. In response to a variety of microbial and endogenous stimuli, resting DCs in peripheral tissues undergo a complex maturation process that might involve the regulation of genes that control distinct DC functions. The different functional properties of DCs are also linked to the existence of several subpopulations in humans and animals that differ in response to stimuli. In this special issue, several articles addressed some recent findings highlighting the interactions between key immune effectors both in vitro and in vivo and in different disease settings. V. R. Yanofsky et al. provided an in-depth analysis of DC biology, with a particular focus on skin DCs and their role in cutaneous carcinoma. C. Y. J. Chung et al. provided an overview of the role of DCs in the immunopathogenesis of autoimmunity, as well as recent concepts of DC-based therapeutic opportunities in autoimmune diseases. On the other hand, P. Ruiz et al. described the different treatments and some of the novel immunotherapeutic strategies undertaken to induce transplantation tolerance in general. More specifically, M. Michael et al. discussed the current knowledge of Treg biology and its potential for cell-based immunotherapy in allogeneic stem cell transplantation. The review by A. K. Gloudemans et al. summarized the latest literature on the role of mucosal IgA in protection against allergic airway disease, the mechanisms described to induce secretory IgA, and the role of (mucosal) DCs in this process. D.-Y. Chen et al. examined the effect of dextromethorphan (DXM), a common cough suppressant, on the activation and function of DCs. Interestingly, DXM decreased the LPS-induced surface expression of CD80, CD83, and HLA-DR and the secretion of IL-6 and IL-12 in human monocyte-derived DCs. These findings provide a new insight into the impact of DXM treatment on DCs and suggest that DXM has the potential to be used in treating DC-related acute and chronic diseases. Similarly, L. Adalid-Peralta et al. showed that cysticerci may modulate DCs to favor a suppressive environment, which may help parasite establishment, minimizing the excessive inflammation, which may lead to tissue damage. In the same line, R. N. Ramos et al. described that cytokines such as IL-10 and TGF-beta, as well as cell surface molecules like PD-L1 and ICOS, seem to be significantly involved in the redirection of DCs towards tolerance induction, and tumor cells may modulate distinct DC subpopulations through the involvement of these molecules. Another work from X. Gu et al. suggested that regulation of B7-H1 expression on hepatic stellate cells by IFN-γ represents an important mechanism that regulates immune responses in the liver favoring tolerogenicity rather than immunogenicity. Finally, A. Brosbol-Ravnborg et al. described how vitamin D3 and TLR agonists acted in synergy to alter secretion of cytokines from human DCs in a direction that may provide an anti-inflammatory environment. From a therapeutic perspective, C. Penna et al. elegantly showed that a combined treatment, including dexamethasone preconditioning followed by an inoculation of short-term LPS-stimulated type II collagen-loaded DCs, provides an improved strategy for attenuating arthritis severity. On the other hand, data from S. O. Akefeldt et al. suggested that targeting MCL1 and BCL2A1 in infiltrating DC may affect the clinical outcomes in rheumatoid arthritis (RA) and Langerhans cell histiocytosis (LCH). P. Cordiali-Fei et al. showed that in patients with limited systemic sclerosis, Treg cells were inversely correlated to disease duration, suggesting that their levels may represent a marker of disease progression. Interestingly, C. Donas et al. showed that Trichostatin A (TSA) could potentially be used to enhance the differentiation and suppressive function of CD4+Foxp3+ Treg cells. Finally, L. de la Cruz-Merino et al. reviewed some important aspects about the role of tumor-infiltrating lymphocytes (TIL) and their subtypes, tumor-associated macrophages (TAM), and myeloid-derived suppressive cells (MDSC) that will eventually be incorporated into diagnostic and therapeutic algorithms of breast cancer. The work from W. Maes et al. discussed based on an animal model the value of local elimination of Tregs within the tumor microenvironment which might represent an important tool from both fundamental and clinical perspectives. All in all, articles published in this special issue clearly show that DCs and Tregs are currently being considered as attractive targets towards manipulation of the immune system for therapeutic purposes in different human disease settings. Mohamad Mohty Arnon Nagler Nicolaus Kroger Beatrice Gaugler

Exovesicles from Human Activated Dendritic Cells Fuse with Resting Dendritic Cells, Allowing Them to Present Alloantigens

“Won’t Get Fooled Again” (by Tuberculosis)

Neutrophil Elastase Converts Human Immature Dendritic Cells into Transforming Growth Factor-β1-Secreting Cells and Reduces Allostimulatory Ability

HIV coinfection is the greatest risk factor for transition of latent Mycobacterium tuberculosis infection into active tuberculosis (TB). Epidemiological data reveal both the reduction and the impairment of M. tuberculosis-specific CD4 T cells, although the cellular link and actual mechanisms resulting in immune impairment/suppression need further characterization. M. tuberculosis-specific CD4 T cells play a central role in development of protective immunity against TB, in which they participate in the activation of macrophages through the dendritic cell (DC)-T cell axis. Using an in vitro priming system for generating Ag-specific T cells, we explored if HIV-M. tuberculosis-infected (coinfected) human DCs can dysregulate the M. tuberculosis-specific CD4 T cell phenotype and functionality and subsequently mediate the failure to control M. tuberculosis infection in macrophages. After coculture with coinfected DCs, M. tuberculosis Ag-specific CD4 T cells lost their ability to enhance control of M. tuberculosis infection in infected macrophages. Coinfection of DCs reduced proliferation of M. tuberculosis Ag-specific CD4 T cells without affecting their viability, led to increased expression of coinhibitory factors CTLA-4, PD-1, and Blimp-1, and decreased expression of costimulatory molecules CD40L, CD28, and ICOS on the T cells. Expression of the regulatory T cell markers FOXP3 and CD25, together with the immunosuppressive cytokines TGF-β and IL-10, was also significantly increased by coinfection compared with M. tuberculosis single infection. Our data suggest a pattern in which HIV, through its effect on DCs, impairs the ability of M. tuberculosis-specific CD4 T cells to maintain a latent TB within human macrophages, which could play an early role in the subsequent development of TB.

The immunoregulatory cytokine, interleukin-10 (IL-10), has been shown to inhibit the maturation of human myeloid dendritic cells (DC). In the present study, we demonstrate that IL-10 has paradoxical effects on the maturation of murine myeloid bone marrow-derived DC. On the one hand, IL-10 inhibits the maturation of murine myeloid DC. The addition of IL-10 to granulocyte-macrophage colony-stimulating factor (GM-CSF)-supported murine BM-derived DC cultures reduced the frequency of major histocompatibility complex (MHC) class IIbright cells. These IL-10-pretreated DC have a reduced capacity to stimulate T cells in an allogeneic mixed leucocyte reaction. On the other hand, however, and in contrast to the effects of IL-10 on human DC, we found that the addition of IL-10 from the initiation of the culture onwards induced an up-regulation of the expression of the costimulatory molecules CD40, CD80 and CD86 on murine myeloid DC, as compared to DC generated with GM-CSF only. Moreover, a subpopulation of IL-10-pretreated MHC class IIdim DC lacked the capacity to take up dextran-fluorescein isothiocyanate (FITC), a feature of DC maturation. Taken together, our data demonstrate that the generation of murine myeloid DC in the presence of IL-10 results in a population of incompletely matured MHC class IIdim CD80+ CD86+ DC. These DC lack T-cell stimulatory capacity, suggesting a role for IL-10 in conferring tolerogenic properties on murine myeloid DC.

It is becoming clear that ionizing radiation positively influences certain immune parameters, which opens the possibility for combining radio- and immunotherapies in cancer treatment. The presence of functionally competent dendritic cells (DCs) is crucial in mounting a successful antitumor immune response. While it has been shown that DCs are relatively radioresistant, few and contradictory data are available on how ionizing radiation alters the functional integrity of these cells. Therefore, our objective was to investigate the effect of whole-body irradiation on the function of splenic DCs. C57Bl/6 mice were irradiated with 0.1, 0.25, and 2 Gy X-rays and changes in the phenotype of splenic DCs were compared to unirradiated controls. An increase was seen in DC surface markers influencing DC-T cell interactions. In vivo cytokine production was determined by direct intracellular cytokine staining. Irradiation with 2 Gy induced a 1.6-fold increase in IL-1α production, while the combination of irradiation and lipopolysaccharide (LPS) treatment induced a 3.9-fold increase, indicating a strong synergism between irradiation and LPS stimulation. Interaction of DCs with effector and regulatory T cells was investigated in a mixed lymphocyte reaction. While DCs from control animals induced stronger proliferation of regulatory T cells, DCs from animals irradiated with 2 Gy induced stronger proliferation of effector T cells. Antigen uptake and presentation was investigated by measuring the capacity of DCs to internalize and present ovalbumine (OVA)-derived peptides on their major histocompatibility complex (MHCI) molecules. Irradiation with 2 Gy did not influence antigen uptake or presentation, while low doses stimulated antigen uptake and reduced the level of antigen presentation. In conclusion, high-dose in vivo irradiation induced increased expression of T cell costimulatory markers, enhanced production of proinflammatory cytokines and a stronger stimulation of effector T cell proliferation than that of regulatory T cells. However, it did not influence DC antigen uptake or presentation. On the other hand, low-dose irradiation increased antigen uptake and lowered antigen presentation of DCs, indicating that low- and high-dose irradiation act on different pathways in DCs.

Sex differences in cancer susceptibility and mortality are well documented. In general, men have a higher cancer incidence and poorer outcomes when compared to women. Of immunologic relevance, and in contrast to cancer, women account for almost 80% of the autoimmune cases reported. These findings suggest male sex is a ‘risk factor’ for cancer but protective against autoimmunity and also highlight the potential involvement of sex hormones in regulating the immune response. Several recent publications have put a spotlight on androgen-mediated immune regulation and its impact on anti-tumor immunity. Guan and colleagues demonstrated that blockade of sex hormones in prostate tumor-bearing mice resulted in improved adaptive immune responses via direct modulation of CD8+ T cell-intrinsic androgen receptor signaling. Androgen-deprivation led to increased interferon gamma (IFNγ) expression by T cells and improved overall anti-tumor immunity. Additionally, others have shown using non-reproductive cancer mouse models (melanoma, bladder, colon and liver) that androgen receptor signaling promotes T cell exhaustion, and inhibits the activity and stemness of anti-tumor CD8+ T cells. Importantly, there is a clear role for androgen-mediated immune regulation in non-reproductive human cancer given a recent publication showing improved progression-free survival and overall survival in female versus male melanoma patients who were treated with neoadjuvant BRAF/MEK-targeted therapy. Follow-up preclinical mouse models showed significantly higher expression of the androgen receptor in tumors of both male and female BRAF/MEK-treated mice versus control and pharmacological inhibition of androgen receptor signaling improved responses to BRAF/MEK-targeted therapy in both male and female mice. Taken together, these publications stress the importance of understanding androgen-mediated immune control in both male and female cancer patients and the broad applicability of this signaling pathway in tissues including, but also beyond, the reproductive tract. There is mounting evidence to support a role androgen signaling in T cell biology. However, professional antigen presenting cells such as dendritic cells (DCs) are an essential part of generating robust anti-tumor T cell immunity were not addressed in these studies. Notably, DCs have been reported to be sensitive to androgens. Castration studies in mice found that removal of testosterone increased antigen presentation and expression of co-stimulatory molecules on DCs. In addition, hypogonadal men are at elevated risk of developing autoimmunity. Isolation of DCs from these patients showed a significant increase in DC maturation. HIV infected DCs derived from males produced significantly less type I interferon compared to female patients, resulting in weaker CD8 T cell responses against the virus. These data establish that androgens can shape DC function, yet they fall short in identifying the mechanisms of how androgens regulate DCs and the impact this may have on anti-tumor immunity. In our initial interrogation of a single-cell RNA sequencing dataset of human prostate cancer patients, we found that human tumors with low androgen receptor activity had increased IFNγ pathway activity and that IFNγ activity was positively associated with an increase in antigen presentation. Importantly, IFNγ is a cytokine that strongly induces antigen processing and presentation by antigen presenting cells and androgen deprivation therapy increases T cell derived IFNγ in tumor bearing mice suggesting that androgen receptor activity may also regulate antigen presentation. Furthermore, our analysis showed that elevated androgen receptor activity correlated with lower antigen presentation, conceivably through suppression of DC function. We hypothesized that inhibition of androgen receptor-mediated suppression of DC function would improve antigen presentation and anti-tumor T cell responses. Here we demonstrate using a B16 melanoma model that male and female DCs, both bone marrow-derived and those sorted from murine steady-state skin and melanoma tumors, express androgen receptor. Interestingly, there is a striking upregulation of androgen receptor expression specifically on type 1 conventional DCs (cDC1s) following uptake of tumor-derived antigen in vivo. cDC1s are a subset of DC that is particularly specialized in cross-presentation of exogenous antigens on MHCI. In this way, cDC1s are dominant drivers of CD8+ T cell responses and, via this function, have been shown to be essential for anti-tumor immunity. Further by inhibiting androgen receptor signaling in vitro using the clinically relevant inhibitor, enzalutamide, we find that bone marrow-derived DCs have increased phagocytic activity as shown by fluorescent bead uptake. Next, we injected male mice with B16 melanoma tumors and, after allowing the tumors to establish, we treated them with degarelix to reduce testosterone levels and enzalutamide to further inhibit androgen receptor signaling. On day 15 we sacrificed the mice, measured the tumors and interrogated DC function by flow cytometry. Strikingly, we found that inhibition of androgen receptor signaling in vivo significantly increased tumor-derived antigen uptake by cDC1s and, importantly, this correlated with improved tumor control as seen by significantly smaller tumors upon androgen receptor inhibition. These data provide insight into the regulation of DCs within the tumor microenvironment and how suppressing inhibitory hormone molecules may lead to better antigen presentation and more effective downstream T cell responses. Cancer immunotherapy is designed to generate an autoimmune-like response against an individual’s cancer. Given the striking sexual dimorphism in both autoimmunity and cancer, there is a clear and pressing need to investigate the impact of sex hormones on the effectiveness and function of cancer immunotherapy. And while myeloid cell targeted therapies and DC-based anti-tumor vaccines hold great promise for boosting anti-tumor T cells responses, current clinical use and efficacy has been limited pointing to an urgent need for improved vaccine and therapeutic design. This will rely on a better understanding of DC activation in this context. Our data indicates that there is a role for androgen receptor signaling in DC function and highlights the potential impact of DC-intrinsic androgen receptor inhibition on optimal DC vaccine design and the generation of more productive DC targeted immunotherapies. Citation Format: Kasidy Brown, Fanny Polesso, Victoria Schuster, Amy Moran, Megan Ruhland. Dendritic cell intrinsic androgen receptor signaling reduces dendritic cell function and anti-tumor immunity. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr NG01.

Class 3 semaphorins (Semas) are soluble proteins that are well recognized for their role in guiding axonal migration during neuronal development. In the immune system, Sema3A has been shown to influence murine dendritic cell (DC) migration by signaling through a neuropilin (NRP)-1/plexin-A1 coreceptor axis. Potential roles for class 3 Semas in human DCs have yet to be described. We tested the hypothesis that Sema3A, -3C, and -3F, each with a unique NRP-1 and/or NRP-2 binding specificity, influence human DC migration. In this report, we find that although NRP-1 and NRP-2 are expressed in human immature DCs (imDCs), NRP-2 expression increases as cells mature further, whereas expression of NRP-1 declines dramatically. Elevated levels of RNA encoding plexin-A1 and -A3 are present in both imDCs and mature DC (mDCs), supporting the relevance of Sema/NRP/plexin signaling pathways in these cells. Sema3A, -3C, and -3F bind to human DCs, with Sema3F binding predominantly through NRP-2. The binding of these Semas leads to reorganization of actin filaments at the plasma membrane and increased transwell migration in the absence or presence of chemokine CCL19. Microfluidic chamber assays failed to demonstrate consistent changes in speed of Sema3C-treated DCs, suggesting increased cell deformability as a possible explanation for enhanced transwell migration. Although monocytes express RNA encoding Sema3A, -3C, and -3F, only RNA encoding Sema3C increases robustly during DC differentiation. These data suggest that Sema3A, -3C, and -3F, likely with coreceptors NRP-1, NRP-2, and plexin-A1 and/or -A3, promote migration and possibly other activities of human DCs during innate and adaptive immune responses.

The role of dendritic cells in asthma

Staphylococcus aureus is a human pathogen responsible for high morbidity and mortality worldwide. Recurrent infections with this bacterium are common, suggesting that S. aureus thwarts the development of sterilizing immunity. S. aureus strains that cause disease in humans produce up to five different bicomponent toxins (leukocidins) that target and lyse neutrophils, innate immune cells that represent the first line of defense against S. aureus infections. However, little is known about the role of leukocidins in blunting adaptive immunity. Here, we explored the effects of leukocidins on human dendritic cells (DCs), antigen-presenting cells required for the development of adaptive immunity. Using an ex vivo infection model of primary human monocyte-derived dendritic cells, we found that S. aureus, including strains from different clonal complexes and drug resistance profiles, effectively kills DCs despite efficient phagocytosis. Although all purified leukocidins could kill DCs, infections with live bacteria revealed that S. aureus targets and kills DCs primarily via the activity of leukocidin LukAB. Moreover, using coculture experiments performed with DCs and autologous CD4+ T lymphocytes, we found that LukAB inhibits DC-mediated activation and proliferation of primary human T cells. Taken together, the data determined in the study reveal a novel immunosuppressive strategy of S. aureus whereby the bacterium blunts the development of adaptive immunity via LukAB-mediated injury of DCs.IMPORTANCE Antigen-presenting cells such as dendritic cells (DCs) fulfill an indispensable role in the development of adaptive immunity by producing proinflammatory cytokines and presenting microbial antigens to lymphocytes to trigger a faster, specific, and long-lasting immune response. Here, we studied the effect of Staphylococcus aureus toxins on human DCs. We discovered that the leukocidin LukAB hinders the development of adaptive immunity by targeting human DCs. The ability of S. aureus to blunt the function of DCs could help explain the high frequency of recurrent S. aureus infections. Taken together, the results from this study suggest that therapeutically targeting the S. aureus leukocidins may boost effective innate and adaptive immune responses by protecting innate leukocytes, enabling proper antigen presentation and T cell activation.