A Comparative Study of the T Cell Stimulatory and Polarizing Capacity of Human Primary Blood Dendritic Cell Subsets

Dendritic cells (DCs) are central players of immune responses; they become activated upon infection or inflammation and migrate to lymph nodes, where they can initiate an antigen-specific immune response by activating naive T cells. Two major types of naturally occurring DCs circulate in peripheral blood, namely, myeloid and plasmacytoid DCs (pDCs). Myeloid DCs (mDCs) can be subdivided based on the expression of either CD1c or CD141. These human DC subsets differ in surface marker expression, Toll-like receptor (TLR) repertoire, and transcriptional profile, suggesting functional differences between them. Here, we directly compared the capacity of human blood mDCs and pDCs to activate and polarize CD4 + T cells. CD141 + mDCs show an overall more mature phenotype over CD1c + mDC and pDCs; they produce less IL-10 and more IL-12 than CD1c + mDCs. Despite these differences, all subsets can induce the production of IFN-in naive CD4 + T cells. CD1c + and CD141 + mDCs especially induce a strong T helper 1 profile. Importantly, naive CD4 + T cells are not polarized towards regulatory T cells by any subset. These findings further establish all three human blood DCs-despite their differences-as promising candidates for immunostimulatory effectors in cancer immunotherapy

Targeting uptake receptors on human plasmacytoid dendritic cells triggers antigen cross-presentation and robust type I IFN secretion

Item does not contain fulltextPlasmacytoid dendritic cells (pDCs) play a crucial role in initiating immune responses by secreting large amounts of type I IFNs. Currently, the role for human pDCs as professional APCs in the cross-presentation of exogenous Ags is being re-evaluated. Human pDCs are equipped with a broad repertoire of Ag uptake receptors and an efficient Ag-processing machinery. In this study, we set out to investigate which receptor can best be deployed to deliver Ag to pDCs for Ag (cross-)presentation. We show that targeting nanoparticles to pDCs via the C-type lectins DEC-205, DC immunoreceptor, blood DC Ag-2, or the FcR CD32 led to uptake, processing, and (cross-) presentation of encapsulated Ag to both CD4(+) and CD8(+) T cells. This makes these receptors good candidates for potential in vivo targeting of pDCs by nanocarriers. Notably, the coencapsulated TLR7 agonist R848 efficiently activated pDCs, resulting in phenotypical maturation as well as robust IFN-alpha and TNF-alpha production. Taken together, their cross-presentation capacity and type I IFN production to further activate components of both the innate and adaptive immune system mark pDCs as inducers of potent antitumor responses. These findings pave the way to actively recruit human pDCs for cellular cancer immunotherapy

A Comparative Study of the T Cell Stimulatory and Polarizing Capacity of Human Primary Blood Dendritic Cell Subsets

Dendritic cells (DCs) are central players of immune responses; they become activated upon infection or inflammation and migrate to lymph nodes, where they can initiate an antigen-specific immune response by activating naive T cells. Two major types of naturally occurring DCs circulate in peripheral blood, namely, myeloid and plasmacytoid DCs (pDCs). Myeloid DCs (mDCs) can be subdivided based on the expression of either CD1c or CD141. These human DC subsets differ in surface marker expression, Toll-like receptor (TLR) repertoire, and transcriptional profile, suggesting functional differences between them. Here, we directly compared the capacity of human blood mDCs and pDCs to activate and polarize CD4+ T cells. CD141+ mDCs show an overall more mature phenotype over CD1c+ mDC and pDCs; they produce less IL-10 and more IL-12 than CD1c+ mDCs. Despite these differences, all subsets can induce the production of IFN-γ in naive CD4+ T cells. CD1c+ and CD141+ mDCs especially induce a strong T helper 1 profile. Importantly, naive CD4+ T cells are not polarized towards regulatory T cells by any subset. These findings further establish all three human blood DCs—despite their differences—as promising candidates for immunostimulatory effectors in cancer immunotherapy

GBF1- and ACBD3-independent recruitment of PI4KIIIβ to replication sites by rhinovirus 3A proteins

PI4KIIIβ recruitment to Golgi membranes relies on GBF1/Arf and ACBD3. Enteroviruses like poliovirus and coxsackievirus recruit PI4KIIIβ to their replication sites via their 3A proteins. Here, we show that human rhinovirus (HRV) 3A also recruited PI4KIIIβ to replication sites. Unlike other enterovirus 3A proteins, HRV 3A failed to bind GBF1. Although previously HRV 3A was shown to interact with ACBD3, our data suggest that PI4KIIIβ recruitment occurred independently of both GBF1 and ACBD3

Human type 1 and type 2 conventional dendritic cells express indoleamine 2,3‐dioxygenase 1 with functional effects on T cell priming

Dendritic cells (DCs) are key regulators of the immune system that shape T cell responses. Regulation of T cell induction by DCs may occur via the intracellular enzyme indoleamine 2,3‐dioxygenase 1 (IDO), which catalyzes conversion of the essential amino acid tryptophan into kynurenine. Here, we examined the role of IDO in human peripheral blood plasmacytoid DCs (pDCs), and type 1 and type 2 conventional DCs (cDC1s and cDC2s). Our data demonstrate that under homeostatic conditions, IDO is selectively expressed by cDC1s. IFN‐γ or TLR ligation further increases IDO expression in cDC1s and induces modest expression of the enzyme in cDC2s, but not pDCs. IDO expressed by conventional DCs is functionally active as measured by kynurenine production. Furthermore, IDO activity in TLR‐stimulated cDC1s and cDC2s inhibits T cell proliferation in settings were DC‐T cell cell‐cell contact does not play a role. Selective inhibition of IDO1 with epacadostat, an inhibitor currently tested in clinical trials, rescued T cell proliferation without affecting DC maturation status or their ability to cross‐present soluble antigen. Our findings provide new insights into the functional specialization of human blood DC subsets and suggest a possible synergistic enhancement of therapeutic efficacy by combining DC‐based cancer vaccines with IDO inhibition

Lipid peroxidation causes endosomal antigen release for cross-presentation

Dingjan I, Verboogen DRJ, Paardekooper LM, et al. Lipid peroxidation causes endosomal antigen release for cross-presentation. SCIENTIFIC REPORTS. 2016;6(1): 22064.Dendritic cells (DCs) present foreign antigen in major histocompatibility complex (MHC) class I molecules to cytotoxic T cells in a process called cross-presentation. An important step in this process is the release of antigen from the lumen of endosomes into the cytosol, but the mechanism of this step is still unclear. In this study, we show that reactive oxygen species (ROS) produced by the NADPH-oxidase complex NOX2 cause lipid peroxidation, a membrane disrupting chain-reaction, which in turn results in antigen leakage from endosomes. Antigen leakage and cross-presentation were inhibited by blocking ROS production or scavenging radicals and induced when using a ROS-generating photosensitizer. Endosomal antigen release was impaired in DCs from chronic granulomatous disease (CGD) patients with dysfunctional NOX2. Thus, NOX2 induces antigen release from endosomes for cross-presentation by direct oxidation of endosomal lipids. This constitutes a new cellular function for ROS in regulating immune responses against pathogens and cancer

Human type 1 and type 2 conventional dendritic cells express indoleamine 2,3-dioxygenase 1 with functional effects on T cell priming

Dendritic cells (DCs) are key regulators of the immune system that shape T cell responses. Regulation of T cell induction by DCs may occur via the intracellular enzyme indoleamine 2,3-dioxygenase 1 (IDO), which catalyzes conversion of the essential amino acid tryptophan into kynurenine. Here, we examined the role of IDO in human peripheral blood plasmacytoid DCs (pDCs), and type 1 and type 2 conventional DCs (cDC1s and cDC2s). Our data demonstrate that under homeostatic conditions, IDO is selectively expressed by cDC1s. IFN-γ or TLR ligation further increases IDO expression in cDC1s and induces modest expression of the enzyme in cDC2s, but not pDCs. IDO expressed by conventional DCs is functionally active as measured by kynurenine production. Furthermore, IDO activity in TLR-stimulated cDC1s and cDC2s inhibits T cell proliferation in settings were DC-T cell cell-cell contact does not play a role. Selective inhibition of IDO1 with epacadostat, an inhibitor currently tested in clinical trials, rescued T cell proliferation without affecting DC maturation status or their ability to cross-present soluble antigen. Our findings provide new insights into the functional specialization of human blood DC subsets and suggest a possible synergistic enhancement of therapeutic efficacy by combining DC-based cancer vaccines with IDO inhibition

Human plasmacytoid dendritic cells efficiently cross-present exogenous Ags to CD8+ T cells despite lower Ag uptake than myeloid dendritic cell subsets

Item does not contain fulltextIn human peripheral blood, 4 populations of dendritic cells (DCs) can be distinguished, plasmacytoid dendritic cells (pDCs) and CD16(+), CD1c(+), and BDCA-3(+) myeloid DCs (mDCs), each with distinct functional characteristics. DCs have the unique capacity to cross-present exogenously encountered antigens (Ags) to CD8(+) T cells. Here we studied the ability of all 4 blood DC subsets to take up, process, and present tumor Ags to T cells. Although pDCs take up less Ags than CD1c(+) and BDCA3(+) mDCs, pDCs induce potent Ag-specific CD4(+) and CD8(+) T-cell responses. We show that pDCs can preserve Ags for prolonged periods of time and on stimulation show strong induction of both MHC class I and II, which explains their efficient activation of both CD4(+) and CD8(+) T cells. Furthermore, pDCs cross-present soluble and cell-associated tumor Ags to cytotoxic T lymphocytes equally well as BDCA3(+) mDCs. These findings, and the fact that pDCs outnumber BDCA3(+) mDCs, both in peripheral blood and lymph nodes, together with their potent IFN-I production, known to activate both components of the innate and adaptive immune system, put human pDCs forward as potent activators of CD8(+) T cells in antitumor responses. Our findings may therefore have important consequences for the development of antitumor immunotherapy