Techniques for time-efficient isolation of human skin dendritic cell subsets and assessment of their antigen uptake capacity

Distinct human Langerhans cell subsets orchestrate reciprocal functions and require different developmental regulation

Langerhans cells (LCs) play a pivotal role in skin homeostasis, and the heterogeneity of LCs has long been considered. In this study, we have identified two steady-state (LC1 and LC2) and two activated LC subsets in the epidermis of human skin and in LCs derived from CD34⁺ hemopoietic stem cells (HSC-LCs) by utilizing single-cell RNA sequencing and mass cytometry. Analysis of HSC-LCs at multiple time-points during differentiation revealed that EGR1 and Notch signaling were among the top pathways regulating the bifurcation of LC1 and LC2. LC1 were characterized as classical LCs, mainly related to innate immunity and antigen processing. LC2 were similar to monocytes or myeloid dendritic cells, involving in immune responses and leukocyte activation. LC1 remained stable under inflammatory microenvironment, whereas LC2 were prone to being activated and demonstrated elevated expression of immuno-suppressive molecules. We revealed distinct human LC subsets that require different developmental regulation and orchestrate reciprocal functions.

Antigen Uptake After Intradermal Microinjection Depends on Antigen Nature and Formulation, but Not on Injection Depth

The skin is an attractive alternative administration route for allergy vaccination, as the skin is rich in dendritic cells (DCs) and is easily accessible. In the skin multiple subsets of DCs with distinct roles reside at different depths. In this study antigen (=allergen for allergy) formulations were injected in ex vivo human skin in a depth-controlled manner by using a hollow microneedle injection system. Biopsies were harvested at the injection site, which were then cultured for 72 h. Subsequently, the crawled-out cells were collected from the medium and analyzed with flow cytometry. Intradermal administration of ovalbumin (OVA, model antigen) solution at various depths in the skin did not affect the migration and maturation of DCs. OVA was taken up efficiently by the DCs, and this was not affected by the injection depth. In contrast, Bet v 1, the major allergen in birch pollen allergy, was barely taken up by dermal DCs (dDCs). Antigens were more efficiently taken up by CD14⁺ dDCs than CD1a⁺ dDCs, which in turn were more efficient at taken up antigen than Langerhans cells. Subsequently, both OVA and Bet v 1 were formulated in cationic and anionic liposomes, which altered antigen uptake drastically following intradermal microinjection. While OVA uptake was reduced by formulation in liposomes, Bet v 1 uptake in dDCs was increased by encapsulation in both cationic and anionic liposomes. This highlights the potential use of liposomes as adjuvant in intradermal allergy vaccine delivery. In conclusion, we observed that antigen uptake after intradermal injection was not affected by injection depth, but varied between different antigens and formulation.

Monocytes Acquire the Ability to Prime Tissue-Resident T Cells via IL-10-Mediated TGF-β Release

Using non-human primates (NHPs), mice, and human primary cells, we found a role for interleukin-10 (IL-10) in the upregulation of the tissue-resident memory T cell (T_RM) marker CD103. In NHPs, intravenous, but not subcutaneous, immunization with peptide antigen and an adjuvant combining an agonistic anti-CD40 antibody plus poly(IC:LC) induced high levels of CD103⁺ T_RMs in the lung, which correlated with early plasma IL-10 levels. Blocking IL-10 reduced CD103 expression on human T cells stimulated in vitro with the adjuvant combination as well as diminished CD103 on lung-resident T cells in vivo in mice. Monocyte-produced IL-10 induced the release of surface-bound transforming growth factor β (TGF-β), which in turn upregulated CD103 on T cells. Early TGF-β imprinted increased sensitivity to TGF-β restimulation, indicating an early commitment of the T cell lineage toward T_RMs during the priming stage of activation. IL-10-mediated TGF-β signaling may therefore have a critical role in the generation of T_RM following vaccination.

Innate Molecular and Cellular Signature in the Skin Preceding Long-Lasting T Cell Responses after Electroporated DNA Vaccination

DNA vaccines delivered with electroporation (EP) have shown promising results in preclinical models and are evaluated in clinical trials. In this study, we aim to characterize early mechanisms occurring in the skin after intradermal injection and EP of the auxoGTUmultiSIV DNA vaccine in nonhuman primates. First, we show that EP acts as an adjuvant by enhancing local inflammation, notably via granulocytes, monocytes/macrophages, and CD1a^int-expressing cell recruitment. EP also induced Langerhans cell maturation, illustrated by CD86, CD83, and HLA-DR upregulation and their migration out of the epidermis. Second, we demonstrate the crucial role of the DNA vaccine in soluble factors release, such as MCP-1 or IL-15. Transcriptomic analysis showed that EP played a major role in gene expression changes postvaccination. However, the DNA vaccine is required to strongly upregulate several genes involved in inflammatory responses (e.g., Saa4), cell migration (e.g., Ccl3, Ccl5, or Cxcl10), APC activation (e.g., Cd86), and IFN-inducible genes (e.g., Ifit3, Ifit5, Irf7, Isg15, orMx1), illustrating an antiviral response signature. Also, AIM-2, a cytosolic DNA sensor, appeared to be strongly upregulated only in the presence of the DNA vaccine and trends to positively correlate with several IFN-inducible genes, suggesting the potential role of AIM-2 in vaccine sensing and the subsequent innate response activation leading to strong adaptive T cell responses. Overall, these results demonstrate that a combined stimulation of the immune response, in which EP and the auxoGTUmultiSIV vaccine triggered different components of the innate immunity, led to strong and persistent cellular recall responses.

Phenotypic and functional consequences of different isolation protocols on skin mononuclear phagocytes

Mononuclear phagocytes are present in skin and mucosa and represent one of the first lines of defense against invading pathogens, which they detect via an array of pathogen-binding receptors expressed on their surface. However, their extraction from tissue is difficult, and the isolation technique used has functional consequences on the cells obtained. Here, we compare mononuclear phagocytes isolated from human skin using either enzymatic digestion or spontaneous migration. Cells isolated via enzymatic digestion are in an immature state, and all subsets are easily defined. However, cells isolated by spontaneous migration are in a mature state, and CD141 cross-presenting DCs (cDC1) are more difficult to define. Different pathogen-binding receptors are susceptible to cleavage by blends of collagenase, demonstrating that great care must be taken in choosing the correct enzyme blend to digest tissue if carrying out pathogen-interaction assays. Finally, we have optimized mononuclear phagocyte culture conditions to enhance their survival after liberation from the tissue.

Phenotypic and Functional Properties of Human Steady State CD14+ and CD1a+ Antigen Presenting Cells and Epidermal Langerhans Cells

Cutaneous antigen presenting cells (APCs) are critical for the induction and regulation of skin immune responses. The human skin contains phenotypically and functionally distinct APCs subsets that are present at two separated locations. While CD1ahigh LCs form a dense network in the epidermis, the CD14+ and CD1a+ APCs reside in the dermal compartment. A better understanding of the biology of human skin APC subsets is necessary for the improvement of vaccine strategies that use the skin as administration route. In particular, progress in the characterization of uptake and activatory receptors will certainly improve APC-targeting strategies in vaccination. Here we performed a detailed analysis of the expression and function of glycan-binding and pattern-recognition receptors in skin APC subsets. The results demonstrate that under steady state conditions human CD1a+ dermal dendritic cells (DCs) were phenotypically most mature as measured by the expression of CD83 and CD86, whereas the CD14+ cells showed a higher expression of the CLRs DC-SIGN, mannose receptor and DCIR and had potent antigen uptake capacity. Furthermore, steady state LCs showed superior antigen cross-presentation as compared to the dermal APC subsets. Our results also demonstrate that the TLR3 ligand polyribosinic-polyribocytidylic acid (pI:C) was the most potent stimulator of cytokine production by both LCs and dDCs. These studies warrant further exploration of human CD1a+ dDCs and LCs as target cells for cancer vaccination to induce anti-tumor immune responses.

Identification of skin immune cells in non-human primates

The skin is a valuable target for vaccine delivery because it contains many immune cell populations, notably antigen presenting cells. Skin immune cells have been extensively described in mice and humans but not in non-human primates, which are pertinent models for immunological research in vaccination. The aim of this work was to describe immune cell populations in the epidermis, dermis and skin draining lymph nodes in cynomolgus macaques by a single 12-parameter flow cytometry protocol. Given that skin cells share several markers, we defined a gating strategy to identify accurately immune cells and to limit contamination of one immune cell population by another. The epidermis contained CD1a(+)CD1c(-) Langerhans cells (LCs), CD3(+) T cells and putative NK cells. The dermis contained CD1a(+)CD1c(-) cells, which were similar to LCs, CD1a(+)CD1c(+) dermal dendritic cells (DDCs), CD163(high)CD11b(+) resident macrophages, CD3(+) T cells and putative NK cells. The skin also contained CD66(+) polymorphonuclear cells in some animals. Thus, immune cell populations in the macaque are similar to those in humans despite some differences in phenotype. In skin draining lymph nodes, we identified migratory LCs, CD1a(+)CD1c(+) DDCs and macrophages. The simultaneous identification of these different immune cells with one panel of markers avoids the use of large amounts of precious sample and may improve the understanding of immune mechanisms in the skin after treatment or vaccination.

Dissociation of skeletal muscle for flow cytometric characterization of immune cells in macaques

The majority of vaccines and several treatments are administered by intramuscular injection. The aim is to engage and activate immune cells, although they are rare in normal skeletal muscle. The phenotype and function of resident as well as infiltrating immune cells in the muscle after injection are largely unknown. While methods for obtaining and characterizing murine muscle cell suspensions have been reported, protocols for nonhuman primates (NHPs) have not been well defined. NHPs comprise important in vivo models for studies of immune cell function due to their high degree of resemblance with humans. In this study, we developed and systematically compared methods to collect vaccine-injected muscle tissue to be processed into single cell suspensions for flow cytometric characterization of immune cells. We found that muscle tissue processed by mechanical disruption alone resulted in significantly lower immune cell yields compared to enzymatic digestion using Liberase. Dendritic cell subsets, monocytes, macrophages, neutrophils, B cells, T cells and NK cells were readily detected in the muscle by the classic human markers. The methods for obtaining skeletal muscle cell suspension established here offer opportunities to increase the understanding of immune responses in the muscle, and provide a basis for defining immediate post-injection vaccine responses in primates.

Cross-presentation through langerin and DC-SIGN targeting requires different formulations of glycan-modified antigens

Dendritic cells (DCs) and Langerhans cells (LC) are professional antigen presenting cells (APCs) that initiate humoral and cellular immune responses. Targeted delivery of antigen towards DC- or LC-specific receptors enhances vaccine efficacy. In this study, we compared the efficiency of glycan-based antigen targeting to both the human DC-specific C-type lectin receptor (CLR) DC-SIGN and the LC-specific CLR langerin. Since DC-SIGN and langerin are able to recognize the difucosylated oligosaccharide Lewis Y (Le(Y)), we prepared neoglycoconjugates bearing this glycan epitope to allow targeting of both lectins. Le(Y)-modified liposomes, with an approximate diameter of 200nm, were significantly endocytosed by DC-SIGN(+) DCs and mediated efficient antigen presentation to CD4(+) and CD8(+) T cells. Surprisingly, although langerin bound to Le(Y)-modified liposomes, LCs exposed to Le(Y)-modified liposomes could not endocytose liposomes nor mediate antigen presentation to T cells. However, LCs mediated an enhanced cross-presentation when antigen was delivered through langerin using Le(Y)-modified synthetic long peptides. In contrast, Le(Y)-modified synthetic long peptides were recognized by DC-SIGN, but did not trigger antigen internalization nor antigen cross-presentation. These data demonstrate that langerin and DC-SIGN have different size requirements for antigen uptake. Although using glycans remains an interesting option in the design of anti-cancer vaccines targeting multiple CLRs, aspects such as molecule size and conformation need to be taken in consideration.

Macrophage- and neutrophil-derived TNF-α instructs skin langerhans cells to prime antiviral immune responses

Dendritic cells are major APCs that can efficiently prime immune responses. However, the roles of skin-resident Langerhans cells (LCs) in eliciting immune responses have not been fully understood. In this study, we demonstrate for the first time, to our knowledge, that LCs in cynomolgus macaque skin are capable of inducing antiviral-specific immune responses in vivo. Targeting HIV-Gag or influenza hemagglutinin Ags to skin LCs using recombinant fusion proteins of anti-Langerin Ab and Ags resulted in the induction of the viral Ag-specific responses. We further demonstrated that such Ag-specific immune responses elicited by skin LCs were greatly enhanced by TLR ligands, polyriboinosinic polyribocytidylic acid, and R848. These enhancements were not due to the direct actions of TLR ligands on LCs, but mainly dependent on TNF-α secreted from macrophages and neutrophils recruited to local tissues. Skin LC activation and migration out of the epidermis are associated with macrophage and neutrophil infiltration into the tissues. More importantly, blocking TNF-α abrogated the activation and migration of skin LCs. This study highlights that the cross-talk between innate immune cells in local tissues is an important component for the establishment of adaptive immunity. Understanding the importance of local immune networks will help us to design new and effective vaccines against microbial pathogens.

Human plasmacytoid dendritic cells efficiently capture HIV-1 envelope glycoproteins via CD4 for antigen presentation

Advances in HIV-1 vaccine clinical trials and preclinical research indicate that the virus envelope glycoproteins (Env) are likely to be an essential component of a prophylactic vaccine. Efficient Ag uptake and presentation by dendritic cells (DCs) is important for strong CD4(+) Th cell responses and the development of effective humoral immune responses. In this study, we examined the capacity of distinct primary human DC subsets to internalize and present recombinant Env to CD4(+) T cells. Consistent with their specific receptor expression, skin DCs bound and internalized Env via C-type lectin receptors, whereas blood DC subsets, including CD1c(+) myeloid DCs, CD123(+) plasmacytoid DCs (PDCs), and CD141(+) DCs exhibited a restricted repertoire of C-type lectin receptors and relied on CD4 for uptake of Env. Despite a generally poor capacity for Ag uptake compared with myeloid DCs, the high expression of CD4 on PDCs allowed them to bind and internalize Env very efficiently. CD4-mediated uptake delivered Env to EEA1(+) endosomes that progressed to Lamp1(+) and MHC class II(+) lysosomes where internalized Env was degraded rapidly. Finally, all three blood DC subsets were able to internalize an Env-CMV pp65 fusion protein via CD4 and stimulate pp65-specific CD4(+) T cells. Thus, in the in vitro systems described in this paper, CD4-mediated uptake of Env is a functional pathway leading to Ag presentation, and this may therefore be a mechanism used by blood DCs, including PDCs, for generating immune responses to Env-based vaccines.

Dendritic cell recruitment in response to skin antigen tests in HIV-1-infected individuals correlates with the level of T-cell infiltration

OBJECTIVES

To study whether in-vivo recruitment of dendritic cells in response to antigen administration in the skin is altered during HIV-1 infection.

DESIGN

Skin punch biopsies were collected from HIV-1-positive as well as seronegative individuals at 48 h after intradermal injection of inactivated antigens of mumps virus, Candida albicans, or purified protein derivate (PPD) from Mycobacterium tuberculosis.

METHODS

Cryosections were analyzed by in-situ staining and computerized imaging.

RESULTS

Control skin biopsies showed that there was no difference in the number of skin-resident dendritic cells between seronegative and HIV-1-positive individuals. Antigen injection resulted in substantial infiltration of dendritic cells compared to the frequencies found in donor-matched control skin. In HIV-1-positive individuals, CD123(+)/CD303(+) plasmacytoid dendritic cells and CD11c myeloid dendritic cells, including the CD141(+) cross-presenting subset, were recruited at lower levels compared to healthy controls in response to PPD and mumps but not C. albicans. The level of dendritic cell recruitment correlated with the frequencies of T cells infiltrating the respective antigen sites. Ki67(+) cycling T cells at the injection sites were much more frequent in response to each of the antigens in the HIV-1-positive individuals, including those with AIDS, compared to healthy controls.

CONCLUSION

Multiple dendritic cell subsets infiltrate the dermis in response to antigen exposure. There was no obvious depletion or deficiency in mobilization of dendritic cells in response to antigen skin tests during chronic HIV-1 infection. Instead, the levels of antigen-specific memory T cells that accumulate at the antigen site may determine the level of dendritic cell infiltration.

Comparative analysis of the interaction of Helicobacter pylori with human dendritic cells, macrophages, and monocytes

Helicobacter pylori may cause chronic gastritis, gastric cancer, or lymphoma. Myeloid antigen-presenting cells (APCs) are most likely involved in the induction and expression of the underlying inflammatory responses. To study the interaction of human APC subsets with H. pylori, we infected monocytes, monocyte-derived dendritic cells (DCs), and monocyte-derived (classically activated; M1) macrophages with H. pylori and analyzed phenotypic alterations, cytokine secretion, phagocytosis, and immunostimulation. Since we detected CD163(+) (alternatively activated; M2) macrophages in gastric biopsy specimens from H. pylori-positive patients, we also included monocyte-derived M2 macrophages in the study. Upon H. pylori infection, monocytes secreted interleukin-1β (IL-1β), IL-6, IL-10, and IL-12p40 (partially secreted as IL-23) but not IL-12p70. Infected DCs became activated, as shown by the enhanced expression of CD25, CD80, CD83, PDL-1, and CCR7, and secreted IL-1β, IL-6, IL-10, IL-12p40, IL-12p70, and IL-23. However, infection led to significantly downregulated CD209 and suppressed the constitutive secretion of macrophage migration inhibitory factor (MIF). H. pylori-infected M1 macrophages upregulated CD14 and CD32, downregulated CD11b and HLA-DR, and secreted mainly IL-1β, IL-6, IL-10, IL-12p40, and IL-23. Activation of DCs and M1 macrophages correlated with increased capacity to induce T-cell proliferation and decreased phagocytosis of dextran. M2 macrophages upregulated CD14 and CD206 and secreted IL-10 but produced less of the proinflammatory cytokines than M1 macrophages. Thus, H. pylori affects the functions of human APC subsets differently, which may influence the course and the outcome of H. pylori infection. The suppression of MIF in DCs constitutes a novel immune evasion mechanism exploited by H. pylori.

Human epidermal Langerhans cells maintain immune homeostasis in skin by activating skin resident regulatory T cells

Recent studies have demonstrated that the skin of a normal adult human contains 10-20 billion resident memory T cells, including various helper, cytotoxic, and regulatory T cell subsets, that are poised to respond to environmental antigens. Using only autologous human tissues, we report that both in vitro and in vivo, resting epidermal Langerhan cells (LCs) selectively and specifically induced the activation and proliferation of skin resident regulatory T (Treg) cells, a minor subset of skin resident memory T cells. In the presence of foreign pathogen, however, the same LCs activated and induced proliferation of effector memory T (Tem) cells and limited Treg cells' activation. These underappreciated properties of LCs, namely maintenance of tolerance in normal skin, and activation of protective skin resident memory T cells upon infectious challenge, help clarify the role of LCs in skin.

Reversal of iC3b-inhibited dendritic cell differentiation via inhibition of the extracellular signal-regulated mitogen-activated protein kinase promotes CD4(+) T cell proliferation

OBJECTIVES

To investigate the roles of ERK1/2 and p38 MAPK cascades in the differentiation of iC3b-combined CD14(+) monocyte into CD1a(+) MDDC, and to study how these cells influence CD4(+) T cell proliferation.

METHODS

CD14(+) monocyte was co-cultured with iC3b with or without inhibitors specific for ERK1/2 or p38 MAPK pathways for 2days, then the expressions of CD14, CD1a, phophso-ERK1/2, phophso-p38, IL-10 and IL-12 p70 were detected, and CD4(+) T cell proliferation was measured via (3)H-TdR as well.

RESULTS

Maturation of CD1a(+) DC was inhibited by iC3b along with downregulated expressions of CD1a, phophso-p38 and IL-12p70 and upregulated expressions of phophso-ERK1/2 and IL-10, and the CD4(+) T cell proliferation was restrained accordingly. When pretreated with inhibitor specific for ERK1/2 pathway, the inhibited maturation of imDC was reversed prominently with a higher level expression of CD1a and IL-12p70, whereas expressions of phophso-ERK1/2 and IL-10 were lowered, and accordingly the CD4(+) T cell proliferation restored significantly.

CONCLUSIONS

iC3b inhibited the differentiation of CD14(+) monocytes into CD1a(+) MDDCs via ERK1/2 pathway, and restoration of CD1a(+) MDDCs maturation occurred with the treatment of inhibitors specific for ERK1/2 pathway. Meanwhile, treatment of the inhibitor for the ERK1/2 cascade reversed the inhibited CD4(+) T cell proliferation, implying a potential possibility for clinical intervention.

The role of the lymphatic system in vaccine trafficking and immune response

The development and improvement of vaccines has been a significant endeavor on the part of the medical community for more than the last two centuries, and the success of these efforts is obvious when one considers the millions of lives that have been saved. Recent work in the field of vaccines, however, indicates that vaccines may be developed for even more challenging diseases than those previously addressed. It will be important in achieving this feat to account for the physical and chemical processes related to vaccine trafficking, rather than solely relying on our knowledge of the pathogen and our empirical experience. A thorough understanding of the lymphatic system is essential considering the role it plays in antigen trafficking and all immunological activity. This review describes the results of recent work that provides insight into the physiological processes of the lymphatic system and its various components with an emphasis on vaccine antigen trafficking from the administration site to secondary lymphoid tissues and the ensuing immune response. The review also discusses current challenges in designing vaccines and presents modern strategies for designing vaccines to better interface with the lymphatic system.

Plasmacytoid dendritic cells infiltrate the skin in positive tuberculin skin test indurations

Plasmacytoid dendritic cells (pDCs) are rarely present in normal skin but have been shown to infiltrate lesions of infections or autoimmune disorders. Here, we report that several DC subsets including CD123(+) BDCA-2/CD303(+) pDCs accumulate in the dermis in indurations induced by the tuberculin skin test (TST), used to screen immune sensitization by Mycobacterium tuberculosis. Although the purified protein derivate (PPD) used in the TST did not itself induce pDC recruitment or IFN-α production, the positive skin reactions showed high expression of the IFN-α-inducible protein MxA. In contrast, the local immune response to PPD was associated with substantial cell death and high expression of the cationic antimicrobial peptide LL37, which together can provide a means for pDC activation and IFN-α production. In vitro, pDCs showed low uptake of PPD compared with CD11c(+) and BDCA-3/CD141(+) myeloid DC subsets. Furthermore, supernatants from pDCs activated with LL37-DNA complexes reduced the high PPD uptake in myeloid DCs, as well as decreased their capacity to activate T-cell proliferation. Infiltrating pDCs in the TST reaction site may thus have a regulatory effect upon the antigen processing and presentation functions of surrounding potent myeloid DC subsets to limit potentially detrimental and excessive immune stimulation.