Identification of HIV transmitting CD11c+ human epidermal dendritic cells

Herpes simplex virus type-1 infection and spread in a novel porcine corneal explant model is restricted to the epithelium

Herpes Keratitis (HK) is a debilitating infection of the cornea that remains the leading cause of infectious blindness in developed countries. Caused primarily by herpes simplex virus type 1 (HSV-1), it is associated with recurrent inflammation, leading to corneal scarring. This study investigated the initial events during acute HSV-1 infection in the cornea by adapting our human anogenital mucosal explant model to a HSV-1 infected porcine corneal explant model. We infected these corneas topically via high-density microarray patches (HD-MAPs) dipped in GFP-labelled HSV-1. Virus infection and spread was detected by both GFP protein and RNAscope, adapted for HSV-1 DNA. The punctures were consistent, usually in the epithelium but some extended into the underlying stroma. However, HSV-1 was restricted to the corneal epithelium, without spread through the anterior limiting membrane (ALM) or Bowman's layer into the stroma nor to the uppermost epithelial layer. This layer expressed SPRR1A similarly to the stratum granulosum of skin which is refractory to HSV-1 infection. In corneas where infected epithelial cells extended to the ALM, SPRR1A was also observed in this layer, suggesting it may contribute to its barrier function. Such studies of HSV-1 infection and spread will help improve therapy for HK and vaccine design to prevent it.

Neuroimmunology of psoriasis: Possible roles for calcitonin gene-related peptide in its pathogenesis

The nervous system has a complex interplay with the immune system, especially at barrier sites such as the skin. This allows it to play a role in a variety of cutaneous inflammatory disorders such as psoriasis, exerting effects on various immune cells via effector molecules such as neuropeptides. In this review, we discuss the role of calcitonin gene-related peptide in modulating the immune system and inflammation, with a focus on psoriasis.

Recent Advances in Our Understanding of Human Inflammatory Dendritic Cells in Human Immunodeficiency Virus Infection

Anogenital inflammation is a critical risk factor for HIV acquisition. The primary preventative HIV intervention, pre-exposure prophylaxis (PrEP), is ineffective in blocking transmission in anogenital inflammation. Pre-existing sexually transmitted diseases (STIs) and anogenital microbiota dysbiosis are the leading causes of inflammation, where inflammation is extensive and often asymptomatic and undiagnosed. Dendritic cells (DCs), as potent antigen-presenting cells, are among the first to capture HIV upon its entry into the mucosa, and they subsequently transport the virus to CD4 T cells, the primary HIV target cells. This increased HIV susceptibility in inflamed tissue likely stems from a disrupted epithelial barrier integrity, phenotypic changes in resident DCs and an influx of inflammatory HIV target cells, including DCs and CD4 T cells. Gaining insight into how HIV interacts with specific inflammatory DC subsets could inform the development of new therapeutic strategies to block HIV transmission. However, little is known about the early stages of HIV capture and transmission in inflammatory environments. Here, we review the currently characterised inflammatory-tissue DCs and their interactions with HIV.

Massive endocytosis mechanisms are involved in uptake of HIV-1 particles by monocyte-derived dendritic cells

Introduction

HIV-1 exploits dendritic cells (DCs) to spread throughout the body via specific recognition of gangliosides present on the viral envelope by the CD169/Siglec-1 membrane receptor. This interaction triggers the internalization of HIV-1 within a structure known as the sac-like compartment. While the mechanism underlying sac-like compartment formation remains elusive, prior research indicates that the process is clathrin-independent and cell membrane cholesterol-dependent and involves transient disruption of cortical actin. Here, we investigate the potential involvement of massive endocytosis (MEND) in this process.

Methods

We used live cell confocal imaging to measure the dimensions and dynamics of the compartment. We assessed the role of actin and cholesterol in fixed and live cells using confocal microscopy and evaluated the effect of PI3K and protein palmytoilation inhibitors during viral uptake.

Results

Our data demonstrate extensive plasma membrane invagination based on sac-like compartment dimensions (2.9 μm in diameter and 20 μm3 in volume). We showed that the cholesterol concentration doubles within the regions of viral uptake, suggesting lipid-phase separation, and that development of the sac-like compartment is accompanied by transient depolarization of cortical actin. Moreover, we observed that protein palmitoylation and PI3K inhibition reduce the sac-like compartment formation rate from 70% to 20% and 40%, respectively.

Conclusions

Our results indicate the involvement of MEND mechanisms during sac-like compartment formation.

The spatial biology of HIV infection

HIV infection implicates a spectrum of tissues in the human body starting with viral transmission in the anogenital tract and subsequently persisting in lymphoid tissues and brain. Though studies using isolated cells have contributed significantly towards our understanding of HIV infection, the tissue microenvironment is characterised by a complex interplay of a range of factors, all of which can influence the course of infection but are otherwise missed in ex vivo studies. To address this knowledge gap, it is necessary to investigate the dynamics of infection and the host immune response in situ using imaging-based approaches. Over the last decade, emerging imaging techniques have continually redefined the limits of detection, both in terms of the scope and the scale of the targets. In doing so, this has opened up new questions that can be answered by in situ studies. This review discusses the high-dimensional imaging modalities that are now available and their application towards understanding the spatial biology of HIV infection.

Breaching the Barrier: Investigating Initial Herpes Simplex Viral Infection and Spread in Human Skin and Mucosa

Herpes simplex virus (HSV) is sexually transmitted via the anogenital mucosa where it initially infects epidermal keratinocytes and mononuclear phagocytes (MNPs). It then spreads to the dorsal root ganglion via sensory nerve endings, to remain latent for life with periodic reactivation. Currently, there is no cure or vaccine. Initial or recurrent HSV infection can produce serious complications and mediate acquisition of HIV. This review outlines the initial events after the HSV infection of human anogenital mucosa to determine the optimal window to target the virus before it becomes latent. After infection, HSV spreads rapidly within the mid-layers of epidermal keratinocytes in the explanted human inner foreskin. Infected cells produce chemokines, which modulate nectin-1 distribution on the surface of adjacent keratinocytes, facilitating viral spread. Epidermal Langerhans cells and dendritic cells become infected with HSV followed by a "viral relay" to dermal MNPs, which then present viral antigen to T cells in the dermis or lymph nodes. These data indicate the need for interruption of spread within 24 h by diffusible vaccine-induced mediators such as antiviral cytokines from resident immune cells or antibodies. Intradermal/mucosal vaccines would need to target the relevant dermal MNPs to induce HSV-specific CD4+ and CD8+ T cells.

Neonatal Fc receptor is a functional receptor for classical human astrovirus

Human astrovirus (HAstV) is a global cause of gastroenteritis in infants, the elderly, and the immunocompromised. However, the molecular mechanisms that control its susceptibility are not fully understood, as the functional receptor used by the virus has yet to be identified. Here, a genome-wide CRISPR-Cas9 library screen in Caco2 cells revealed that the neonatal Fc receptor (FcRn) can function as a receptor for classical HAstV (Mamastrovirus genotype 1). Deletion of FCGRT or B2M, which encode subunits of FcRn, rendered Caco2 cells and intestinal organoid cells resistant to HAstV infection. We also showed that human FcRn expression renders non-susceptible cells permissive to viral infection and that FcRn binds directly to the HAstV spike protein. Therefore, our findings provide insight into the entry mechanism of HAstV into susceptible cells. We anticipate that this information can be used to develop new therapies targeting human astroviruses, providing new strategies to treat this global health issue.

Human genital dendritic cell heterogeneity confers differential rapid response to HIV-1 exposure

Dendritic cells (DCs) play critical roles in HIV pathogenesis and require further investigation in the female genital tract, a main portal of entry for HIV infection. Here we characterized genital DC populations at the single cell level and how DC subsets respond to HIV immediately following exposure. We found that the genital CD11c+HLA-DR+ myeloid population contains three DC subsets (CD1c+ DC2s, CD14+ monocyte-derived DCs and CD14+CD1c+ DC3s) and two monocyte/macrophage populations with distinct functional and phenotypic properties during homeostasis. Following HIV exposure, the antiviral response was dominated by DCs' rapid secretory response, activation of non-classical inflammatory pathways and host restriction factors. Further, we uncovered subset-specific differences in anti-HIV responses. CD14+ DCs were the main population activated by HIV and mediated the secretory antimicrobial response, while CD1c+ DC2s activated inflammasome pathways and IFN responses. Identification of subset-specific responses to HIV immediately after exposure could aid targeted strategies to prevent HIV infection.

Langerhans cells and skin immune diseases

Langerhans cells (LCs) are the key antigen-presenting cells in the epidermis in normal conditions and respond differentially to environmental and/or endogenous stimuli, exerting either proinflammatory or anti-inflammatory effects. Current knowledge about LCs mainly originates from studies utilizing mouse models, whereas with the development of single-cell techniques, there has been significant progress for human LCs, which has updated our understanding of the phenotype, ontogeny, differentiation regulation, and function of LCs. In this review, we delineated the progress of human LCs and summarized LCs' function in inflammatory skin diseases, providing new ideas for precise regulation of LC function in the prevention and treatment of skin diseases.

Herpes simplex virus spreads rapidly in human foreskin, partly driven by chemokine-induced redistribution of Nectin-1 on keratinocytes

HSV infects keratinocytes in the epidermis of skin via nectin-1. We established a human foreskin explant infection model to investigate HSV entry and spread. HSV1 entry could only be achieved by the topical application of virus via high density microarray projections (HD-MAPs) to the epidermis, which penetrated beyond one third of its thickness, simulating in vivo microtrauma. Rapid lateral spread of HSV1 to a mean of 13 keratinocytes wide occurred after 24 hours and free virus particles were observed between keratinocytes, consistent with an intercellular route of spread. Nectin-1 staining was markedly decreased in foci of infection in the epidermis and in the human keratinocyte HaCaT cell line. Nectin-1 was redistributed, at the protein level, in adjacent uninfected cells surrounding infection, inducible by CCL3, IL-8 (or CXCL8), and possibly CXCL10 and IL-6, thus facilitating spread. These findings provide the first insights into HSV1 entry and spread in human inner foreskin in situ.

Epithelial dendritic cells vs. Langerhans cells: Implications for mucosal vaccines

Next-generation vaccines may be delivered via the skin and mucosa. The stratified squamous epithelium (SSE) represents the outermost layer of the skin (epidermis) and type II mucosa (epithelium). Langerhans cells (LCs) have been considered the sole antigen-presenting cells (APCs) to inhabit the SSE; however, it is now clear that dendritic cells (DCs) are also present. Importantly, there are functional differences in how LCs and DCs take up and process pathogens as well as their ability to activate and polarize T cells, though whether DCs participate in neuroimmune interactions like LCs is yet to be elucidated. A correct definition and functional characterization of APCs in the skin and anogenital tissues are of utmost importance for the design of better vaccines and blocking pathogen transmission. Here, we provide a historical perspective on the evolution of our understanding of the APCs that inhabit the SSE, including a detailed review of the most recent literature.

Nerve-myeloid cell interactions in persistent human pain: a reappraisal using updated cell subset classifications

ABSTRACT

The past 20 years have seen a dramatic shift in our understanding of the role of the immune system in initiating and maintaining pain. Myeloid cells, including macrophages, dendritic cells, Langerhans cells, and mast cells, are increasingly implicated in bidirectional interactions with nerve fibres in rodent pain models. However, our understanding of the human setting is still poor. High-dimensional functional analyses have substantially changed myeloid cell classifications, with recently described subsets such as epidermal dendritic cells and DC3s unveiling new insight into how myeloid cells interact with nerve fibres. However, it is unclear whether this new understanding has informed the study of human chronic pain. In this article, we perform a scoping review investigating neuroimmune interactions between myeloid cells and peripheral nerve fibres in human chronic pain conditions. We found 37 papers from multiple pain states addressing this aim in skin, cornea, peripheral nerve, endometrium, and tumour, with macrophages, Langerhans cells, and mast cells the most investigated. The directionality of results between studies was inconsistent, although the clearest pattern was an increase in macrophage frequency across conditions, phases, and tissues. Myeloid cell definitions were often outdated and lacked correspondence with the stated cell types of interest; overreliance on morphology and traditional structural markers gave limited insight into the functional characteristics of investigated cells. We therefore critically reappraise the existing literature considering contemporary myeloid cell biology and advocate for the application of established and emerging high-dimensional proteomic and transcriptomic single-cell technologies to clarify the role of specific neuroimmune interactions in chronic pain.

Associations of cortical SPP1 and ITGAX with cognition and common neuropathologies in older adults

INTRODUCTION

The secreted phosphoprotein 1 (SPP1) gene expressed by CD11c+ cells is known to be associated with microglia activation and neuroinflammatory diseases. As most studies rely on mouse models, we investigated these genes and proteins in the cortical brain tissue of older adults and their role in Alzheimer's disease (AD) and related disorders.

METHODS

We leveraged protein measurements, single-nuclei, and RNASeq data from the Religious Orders Study and Rush Memory and Aging Project (ROSMAP) of over 1200 samples for association analysis.

RESULTS

Expression of SPP1 and its encoded protein osteopontin were associated with faster cognitive decline and greater odds of common neuropathologies. At single-cell resolution,  integrin subunit alpha X (ITGAX) was highly expressed in microglia, where specific subpopulations were associated with AD and cerebral amyloid angiopathy.

DISCUSSION

The study provides evidence of SPP1 and ITGAX association with cognitive decline and common neuropathologies identifying a microglial subset associated with disease.

The integrated stress response signaling during the persistent HIV infection

Human immunodeficiency virus-1 (HIV) infection is a chronic disease under antiretroviral therapy (ART), during which active HIV replication is effectively suppressed. Stable viral reservoirs are established early in infection and cannot be eradicated in people with HIV (PWH) by ART alone, which features residual immune inflammation with disease-associated secondary comorbidities. Mammalian cells are equipped with integrated stress response (ISR) machinery to detect intrinsic and extrinsic stresses such as heme deficiency, nutrient fluctuation, the accumulation of unfolded proteins, and viral infection. ISR is the part of the innate immunity that defends against pathogen infection or environmental alteration, thereby maintaining homeostasis to avoid diseases. Here, we describe how this machinery responds to the off-target effects of ART and persistent HIV infection in both the peripheral compartments and the brain. The latter may be important for us to better understand the mechanisms of stable HIV reservoirs and HIV-associated neurocognitive disorders.

Lymph node dendritic cells harbor inducible replication-competent HIV despite years of suppressive ART

Although gut and lymph node (LN) memory CD4 T cells represent major HIV and simian immunodeficiency virus (SIV) tissue reservoirs, the study of the role of dendritic cells (DCs) in HIV persistence has long been limited to the blood due to difficulties to access lymphoid tissue samples. In this study, we show that LN migratory and resident DC subpopulations harbor distinct phenotypic and transcriptomic profiles. Interestingly, both LN DC subpopulations contain HIV intact provirus and inducible replication-competent HIV despite the expression of the antiviral restriction factor SAMHD1. Notably, LN DC subpopulations isolated from HIV-infected individuals treated for up to 14 years are transcriptionally silent but harbor replication-competent virus that can be induced upon TLR7/8 stimulation. Taken together, these results uncover a potential important contribution of LN DCs to HIV infection in the presence of ART.

Redefining the human corneal immune compartment using dynamic intravital imaging

The healthy human cornea is a uniquely transparent sensory tissue where immune responses are tightly controlled to preserve vision. The cornea contains immune cells that are widely presumed to be intraepithelial dendritic cells (DCs). Corneal immune cells have diverse cellular morphologies and morphological alterations are used as a marker of inflammation and injury. Based on our imaging of corneal T cells in mice, we hypothesized that many human corneal immune cells commonly defined as DCs are intraepithelial lymphocytes (IELs). To investigate this, we developed functional in vivo confocal microscopy (Fun-IVCM) to investigate cell dynamics in the human corneal epithelium and stroma. We show that many immune cells resident in the healthy human cornea are T cells. These corneal IELs are characterized by rapid, persistent motility and interact with corneal DCs and sensory nerves. Imaging deeper into the corneal stroma, we show that crawling macrophages and rare motile T cells patrol the tissue. Furthermore, we identify altered immune cell behaviors in response to short-term contact lens wear (acute inflammatory stimulus), as well as in individuals with allergy (chronic inflammatory stimulus) that was modulated by therapeutic intervention. These findings redefine current understanding of immune cell subsets in the human cornea and reveal how resident corneal immune cells respond and adapt to chronic and acute stimuli.

Microenvironmental and cell intrinsic factors governing human cDC2 differentiation and monocyte reprogramming

cDC2s occur abundantly in peripheral tissues and arise from circulating blood cDC2s. However, the factors governing cDC2 differentiation in tissues, especially under inflammatory conditions, remained poorly defined. We here found that psoriatic cDC2s express the efferocytosis receptor Axl and exhibit a bone morphogenetic protein (BMP) and p38MAPK signaling signature. BMP7, strongly expressed within the lesional psoriatic epidermis, cooperates with canonical TGF-β1 signaling for inducing Axl+cDC2s from blood cDC2s in vitro. Moreover, downstream induced p38MAPK promotes Axl+cDC2s at the expense of Axl+CD207+ Langerhans cell differentiation from blood cDC2s. BMP7 supplementation allowed to model cDC2 generation and their further differentiation into LCs from CD34+ hematopoietic progenitor cells in defined serum-free medium. Additionally, p38MAPK promoted the generation of another cDC2 subset lacking Axl but expressing the non-classical NFkB transcription factor RelB in vitro. Such RelB+cDC2s occurred predominantly at dermal sites in the inflamed skin. Finally, we found that cDC2s can be induced to acquire high levels of the monocyte lineage identity factor kruppel-like-factor-4 (KLF4) along with monocyte-derived DC and macrophage phenotypic characteristics in vitro. In conclusion, inflammatory and psoriatic epidermal signals instruct blood cDC2s to acquire phenotypic characteristics of several tissue-resident cell subsets.

TRPV1 activation in human Langerhans cells and T cells inhibits mucosal HIV-1 infection via CGRP-dependent and independent mechanisms

Upon its mucosal transmission, HIV type 1 (HIV-1) rapidly targets genital antigen-presenting Langerhans cells (LCs), which subsequently transfer infectious virus to CD4+ T cells. We previously described an inhibitory neuroimmune cross talk, whereby calcitonin gene-related peptide (CGRP), a neuropeptide secreted by peripheral pain-sensing nociceptor neurons innervating all mucosal epithelia and associating with LCs, strongly inhibits HIV-1 transfer. As nociceptors secret CGRP following the activation of their Ca2+ ion channel transient receptor potential vanilloid 1 (TRPV1), and as we reported that LCs secret low levels of CGRP, we investigated whether LCs express functional TRPV1. We found that human LCs expressed mRNA and protein of TRPV1, which was functional and induced Ca2+ influx following activation with TRPV1 agonists, including capsaicin (CP). The treatment of LCs with TRPV1 agonists also increased CGRP secretion, reaching its anti-HIV-1 inhibitory concentrations. Accordingly, CP pretreatment significantly inhibited LCs-mediated HIV-1 transfer to CD4+ T cells, which was abrogated by both TRPV1 and CGRP receptor antagonists. Like CGRP, CP-induced inhibition of HIV-1 transfer was mediated via increased CCL3 secretion and HIV-1 degradation. CP also inhibited direct CD4+ T cells HIV-1 infection, but in CGRP-independent manners. Finally, pretreatment of inner foreskin tissue explants with CP markedly increased CGRP and CCL3 secretion, and upon subsequent polarized exposure to HIV-1, inhibited an increase in LC-T cell conjugate formation and consequently T cell infection. Our results reveal that TRPV1 activation in human LCs and CD4+ T cells inhibits mucosal HIV-1 infection, via CGRP-dependent/independent mechanisms. Formulations containing TRPV1 agonists, already approved for pain relief, could hence be useful against HIV-1.

Unveiling uterine aging: Much more to learn

Uterine aging is an important factor that impacts fertility, reproductive health, and uterus-related diseases; however, it remains poorly explored. Functionally, these disturbances have been associated with an abnormal hormonal response in the endometrium and decreased endometrial receptivity. Based on emerging evidence, these alterations are mediated via the senescence of endometrial stem cells and impaired decidualization of endometrial stromal cells. Multiple molecular activities may participate in uterine aging, including oxidative stress, inflammation, fibrosis, DNA damage response, and cellular senescence. Over the past decade, several protective strategies targeting these biological processes have afforded promising results, including stem cell therapy, anti-aging drugs, and herbal medicines. However, the currently available evidence is fragmented and scattered. Here, we summarize the most recent findings regarding uterine aging, including functional and structural alterations and potential cellular and molecular mechanisms, and discuss potential protective interventions against uterine aging. Thereby, we hope to provide a comprehensive understanding of the pathophysiological processes and underlying mechanisms associated with uterine aging, as well as improve fecundity and reproductive outcomes in females of advanced reproductive age.

Immune activation of vaginal human Langerhans cells increases susceptibility to HIV-1 infection

Vaginal inflammation increases the risk for sexual HIV-1 transmission but underlying mechanisms remain unclear. In this study we assessed the impact of immune activation on HIV-1 susceptibility of primary human vaginal Langerhans cells (LCs). Vaginal LCs isolated from human vaginal tissue expressed a broad range of TLRs and became activated after exposure to both viral and bacterial TLR ligands. HIV-1 replication was restricted in immature vaginal LCs as only low levels of infection could be detected. Notably, activation of immature vaginal LCs by bacterial TLR ligands increased HIV-1 infection, whereas viral TLR ligands were unable to induce HIV-1 replication in vaginal LCs. Furthermore, mature vaginal LCs transmitted HIV-1 to CD4 T cells. This study emphasizes the role for vaginal LCs in protection against mucosal HIV-1 infection, which is abrogated upon activation. Moreover, our data suggest that bacterial STIs can increase the risk of HIV-1 acquisition in women.

HIV Latency and Nanomedicine Strategies for Anti-HIV Treatment and Eradication

Antiretrovirals (ARVs) reduce Human Immunodeficiency Virus (HIV) loads to undetectable levels in infected patients. However, HIV can persist throughout the body in cellular reservoirs partly due to the inability of some ARVs to cross anatomical barriers and the capacity of HIV-1 to establish latent infection in resting CD4⁺ T cells and monocytes/macrophages. A cure for HIV is not likely unless latency is addressed and delivery of ARVs to cellular reservoir sites is improved. Nanomedicine has been used in ARV formulations to improve delivery and efficacy. More specifically, researchers are exploring the benefit of using nanoparticles to improve ARVs and nanomedicine in HIV eradication strategies such as shock and kill, block and lock, and others. This review will focus on mechanisms of HIV-1 latency and nanomedicine-based approaches to treat HIV.

Dendritic Cells - Winning the Fight against HIV

HIV is a virus that targets and hijacks the immune cells of the host. It multiplies by attacking the helper T-lymphocytes. HIV has remained one of the most difficult and dangerous infections in the world due to the inability to find a successful treatment and a lack of access to medical care. When the virus reaches the body, dendritic cells are the first cells it encounters. DCs have been identified as one of the most effective mediators of immune responses, implying a promising strategy against viral infection. The current state of knowledge about the function of dendritic cells and their subsets is critical for using their full potential as a candidate for the development of an HIV vaccine. Despite extensive efforts, a reliable vaccine with the fewest side effects has yet to be found, and further research is needed to find a dependable and efficient vaccine. The extent to which dendritic cell-based therapy is used to treat HIV was investigated in this study. As the virus attacks the host immune system, the dendritic cells can trigger an immune response against HIV-1 infection.

Women for science and science for women: Gaps, challenges and opportunities towards optimizing pre-exposure prophylaxis for HIV-1 prevention

Preventing new HIV infections remains a global challenge. Young women continue to bear a disproportionate burden of infection. Oral pre-exposure prophylaxis (PrEP), offers a novel women-initiated prevention technology and PrEP trials completed to date underscore the importance of their inclusion early in trials evaluating new HIV PrEP technologies. Data from completed topical and systemic PrEP trials highlight the role of gender specific physiological and social factors that impact PrEP uptake, adherence and efficacy. Here we review the past and current developments of HIV-1 prevention options for women with special focus on PrEP considering the diverse factors that can impact PrEP efficacy. Furthermore, we highlight the importance of inclusion of female scientists, clinicians, and community advocates in scientific efforts to further improve HIV prevention strategies.

Cytokines and chemokines: The vital role they play in herpes simplex virus mucosal immunology

Herpes simplex viruses (HSV) types 1 and 2 are ubiquitous infections in humans. They cause orofacial and genital herpes with occasional severe complications. HSV2 also predisposes individuals to infection with HIV. There is currently no vaccine or immunotherapy for these diseases. Understanding the immunopathogenesis of HSV infections is essential to progress towards these goals. Both HSV viruses result in initial infections in two major sites - in the skin or mucosa, either after initial infection or recurrence, and in the dorsal root or trigeminal ganglia where the viruses establish latency. HSV1 can also cause recurrent infection in the eye. At all of these sites immune cells respond to control infection. T cells and resident dendritic cells (DCs) in the skin/mucosa and around reactivating neurones in the ganglia, as well as keratinocytes in the skin and mucosa, are major sources of cytokines and chemokines. Cytokines such as the Type I and II interferons synergise in their local antiviral effects. Chemokines such as CCL2, 3 and 4 are found in lesion vesicle fluid, but their exact role in determining the interactions between epidermal and dermal DCs and with resident memory and infiltrating CD4 and CD8 T cells in the skin/mucosa is unclear. Even less is known about these mechanisms in the ganglia. Here we review the data on known sources and actions of these cytokines and chemokines at cellular and tissue level and indicate their potential for preventative and therapeutic interventions.

An in situ analysis pipeline for initial host-pathogen interactions reveals signatures of human colorectal HIV transmission

The initial immune response to HIV determines transmission. However, due to technical limitations we still do not have a comparative map of early mucosal transmission events. By combining RNAscope, cyclic immunofluorescence, and image analysis tools, we quantify HIV transmission signatures in intact human colorectal explants within 2 h of topical exposure. We map HIV enrichment to mucosal dendritic cells (DCs) and submucosal macrophages, but not CD4⁺ T cells, the primary targets of downstream infection. HIV⁺ DCs accumulate near and within lymphoid aggregates, which act as early sanctuaries of high viral titers while facilitating HIV passage to the submucosa. Finally, HIV entry induces recruitment and clustering of target cells, facilitating DC- and macrophage-mediated HIV transfer and enhanced infection of CD4⁺ T cells. These data demonstrate a rapid response to HIV structured to maximize the likelihood of mucosal infection and provide a framework for in situ studies of host-pathogen interactions and immune-mediated pathologies.

Langerin-expressing dendritic cells in pulmonary immune-related diseases

Dendritic cells (DCs) are “frontline” immune cells dedicated to antigen presentation. They serve as an important bridge connecting innate and adaptive immunity, and express various receptors for antigen capture. DCs are divided into various subclasses according to their differential expression of cell surface receptors and different subclasses of DCs exhibit specific immunological characteristics. Exploring the common features of each sub-category has became the focus of many studies. There are certain amounts of DCs expressing langerin in airways and peripheral lungs while the precise mechanism by which langerin⁺ DCs drive pulmonary disease is unclear. Langerin-expressing DCs can be further subdivided into numerous subtypes based on the co-expressed receptors, but here, we identify commonalities across these subtypes that point to the major role of langerin. Better understanding is required to clarify key disease pathways and determine potential new therapeutic approaches.

Blimp-1 is a prognostic indicator for progression of cervical intraepithelial neoplasia grade 2

BACKGROUND

Progression of cervical intraepithelial neoplasia (CIN) to higher grade disease is associated with persistent human papillomavirus (HPV) infection and an absence of immune-mediated regression. However, the immune microenvironment that distinguishes progression from persistent or regressing lesions has not been well defined.

METHODS

A total of 69 patients under the age of 25 with high-risk HPV-positive cytology and biopsy-confirmed p16-positive CIN2 were included in the study. Biopsies were stained using 20 antibodies to a range of immune markers. Based on a 2-year follow-up, samples were analysed in "progressor" (CIN3 +) or "persister/regressor" (CIN1, 2 or normal) groups.

RESULTS

Progression was most strongly associated with Blimp-1 positive cell staining in the lesion (P = 0.0019) and with low numbers of infiltrating CD4 cells in the dermal region beneath the lesion (P = 0.0022). The presence of CD4, CD8 and T bet-positive cells in the dermal region most strongly correlated with CD11c cells in the persister/regressor but not the progressor group.

CONCLUSION

High numbers of Blimp-1 + cells in CIN2 lesions may predict progression to more severe disease. Measurement of Blimp-1 may have diagnostic utility for the determination of the need to treat women with cervical pre-cancer.

HIGHLIGHTS

CIN2 progression is associated with high numbers of Blimp-1 positive cells in the lesion. Detection of Blimp-1 in the lesion may have utility as a prognostic test to inform the need to treat CIN2.

Characterisation of the immune microenvironment of cutaneous squamous cell carcinoma in immunosuppression

Cutaneous squamous cell carcinoma (cSCC) is a common cancer. Systemic immunosuppression with drugs such as Prednisone results in more aggressive disease. We hypothesise that more aggressive disease in immunosuppression is the result of immune changes in the tumour microenvironment. We characterised T cell, phagocytic and antigen presenting cell subsets in cSCC, and determined if these infiltrates were altered by immunosuppressive therapy. We found a dominant 'CD8 profile' in the centre of cSCC lesions, with CD8 cells correlating with Tbet, FoxP3, OX40 and 'M2-like' macrophages, whereas a 'Tbet and granulocyte profile' with associated inflammation predominated at the margin of the tumour. Individuals on systemic immunosuppressive therapy had lesions that were comparable in size, stage and number of vessels to immune competent individuals however the number of CD11c positive cells in the lesion centre was significantly reduced. We conclude that cSCC lesions are immunologically heterogeneous across the lesion and that systemically immunosuppressed individuals have reduced CD11c positive cells in the centre of the lesion. The role and detailed phenotype of CD11c positive cells in cSCC lesions warrants further investigation.

Immune parameters of HIV susceptibility in the female genital tract before and after penile-vaginal sex

Background

In women, most HIV infections are acquired through penile-vaginal sex. Inflammation in the female genital tract (FGT) increases the risk of HIV acquisition and transmission, likely through recruitment of HIV target cells and disruption of epithelial barrier integrity. Although sex may have important immune and epithelial effects, the impact of receptive penile-vaginal sex on the immune correlates of HIV susceptibility in the female genital tract is not well described.

Methods

STI-free heterosexual couples were recruited to the Sex, Couples and Science (SECS) Study, with the serial collection of cervical secretions (CVS), endocervical cytobrushes, blood and semen before and up to 72 h after either condomless (n = 29) or condom-protected (n = 8) penile-vaginal sex. Immune cells were characterized by flow cytometry, and immune factors including cytokines and soluble E-cadherin (sE-cad; a marker of epithelial disruption) were quantified by multiplex immunoassay. Co-primary endpoints were defined as levels of IP-10 and IL-1α, cytokines previously associated with increased HIV susceptibility.

Results

Here we show that cervicovaginal levels of vaginal IP-10, sE-cad and several other cytokines increase rapidly after sex, regardless of condom use. The proportion of endocervical HIV target cells, including Th17 cells, activated T cells, and activated or mature dendritic cells (DCs) also increase, particularly after condomless sex. Although most of these immune changes resolve within 72 h, increases in activated cervical CD4 + T cells and Tcm persist beyond this time.

Conclusions

Penile-vaginal sex induces multiple genital immune changes that may enhance HIV susceptibility during the 72 h post-sex window that is critical for virus acquisition. This has important implications for the mucosal immunopathogenesis of HIV transmission.

Women who acquire HIV most commonly do so during penile-vaginal sex. Although the risk of HIV acquisition is higher when there is pre-existing inflammation in the female genital tract, the impact of receptive penile-vaginal sex itself on immune markers of HIV susceptibility in the genital tract has not been widely studied. We recruited heterosexual couples, without HIV or sexually-transmitted infections, and studied the impact of a single episode of penile-vaginal sex on immune cells and proteins in the female genital tract. We found that some markers within the cervix and vagina increased immediately after sex, then returned to normal. We noticed differences in these changes depending on whether the sex was condom-protected and whether the male partner was circumcised. Our findings might help us to understand how sex impacts the immune system and how this might contribute to HIV acquisition.

Mohammadi et al. evaluate immune markers and cell types associated with HIV susceptibility in the female genital tract before and after penile-vaginal sex. The authors report that these immune parameters increase rapidly and transiently after sex, with condom use affecting some of the changes observed.

Evolving Strategies to Eliminate the CD4 T Cells HIV Viral Reservoir via CAR T Cell Immunotherapy

Although the advent of ART has significantly reduced the morbidity and mortality associated with HIV infection, the stable pool of HIV in latently infected cells requires lifelong treatment adherence, with the cessation of ART resulting in rapid reactivation of the virus and productive HIV infection. Therefore, these few cells containing replication-competent HIV, known as the latent HIV reservoir, act as the main barrier to immune clearance and HIV cure. While several strategies involving HIV silencing or its reactivation in latently infected cells for elimination by immune responses have been explored, exciting cell based immune therapies involving genetically engineered T cells expressing synthetic chimeric receptors (CAR T cells) are highly appealing and promising. CAR T cells, in contrast to endogenous cytotoxic T cells, can function independently of MHC to target HIV-infected cells, are efficacious and have demonstrated acceptable safety profiles and long-term persistence in peripheral blood. In this review, we present a comprehensive picture of the current efforts to target the HIV latent reservoir, with a focus on CAR T cell therapies. We highlight the current challenges and advances in this field, while discussing the importance of novel CAR designs in the efforts to find a HIV cure.

Role of Dendritic Cells in Viral Brain Infections

To gain access to the brain, a so-called immune-privileged organ due to its physical separation from the blood stream, pathogens and particularly viruses have been selected throughout evolution for their use of specific mechanisms. They can enter the central nervous system through direct infection of nerves or cerebral barriers or through cell-mediated transport. Indeed, peripheral lymphoid and myeloid immune cells can interact with the blood-brain and the blood-cerebrospinal fluid barriers and allow viral brain access using the "Trojan horse" mechanism. Among immune cells, at the frontier between innate and adaptive immune responses, dendritic cells (DCs) can be pathogen carriers, regulate or exacerbate antiviral responses and neuroinflammation, and therefore be involved in viral transmission and spread. In this review, we highlight an important contribution of DCs in the development and the consequences of viral brain infections.

CGRP inhibits human Langerhans cells infection with HSV by differentially modulating specific HSV-1 and HSV-2 entry mechanisms

Herpes simplex virus (HSV) is widespread globally, with both HSV-1 and HSV-2 responsible for genital herpes. During sexual transmission, HSV targets epithelial cells, sensory peripheral pain neurons secreting the mucosal neuropeptide calcitonin gene-related peptide (CGRP), and mucosal immune cells including Langerhans cells (LCs). We previously described a neuro-immune crosstalk, whereby CGRP inhibits LCs-mediated human immunodeficiency virus type 1 (HIV-1) transmission. Herein, to further explore CGRP-mediated anti-viral function, we investigated whether CGRP affects LCs infection with HSV. We found that both HSV-1 and HSV-2 primary isolates productively infect monocyte-derived LCs (MDLCs) and inner foreskin LCs. Moreover, CGRP significantly inhibits infection with both HSV subtypes of MDLCs and langerin^high, but not langerin^low, inner foreskin LCs. For HSV-1, infection is mediated via the HSV-1-specific entry receptor 3-O sulfated heparan sulfate (3-OS HS) in a pH-depended manner, and CGRP down-regulates 3-OS HS surface expression, as well as abrogates pH dependency. For HSV-2, infection involves langerin-mediated endocytosis in a pH-independent manner, and CGRP up-regulates surface expression of atypical langerin double-trimer oligomers. Our results show that CGRP inhibits mucosal HSV infection by differentially modulating subtype-specific entry receptors and mechanisms in human LCs. CGRP could turn out useful for prevention of LCs-mediated HSV infection and HSV/HIV-1 co-infection.

PDE4B Is a Homeostatic Regulator of Cyclic AMP in Dendritic Cells

Chronic decreases in the second messenger cyclic AMP (cAMP) occur in numerous settings, but how cells compensate for such decreases is unknown. We have used a unique system-murine dendritic cells (DCs) with a DC-selective depletion of the heterotrimeric GTP binding protein Gαs-to address this issue. These mice spontaneously develop Th2-allergic asthma and their DCs have persistently lower cAMP levels. We found that phosphodiesterase 4B (PDE4B) is the primary phosphodiesterase expressed in DCs and that its expression is preferentially decreased in Gαs-depleted DCs. PDE4B expression is dynamic, falling and rising in a protein kinase A-dependent manner with decreased and increased cAMP concentrations, respectively. Treatment of DCs that drive enhanced Th2 immunity with a PDE4B inhibitor ameliorated DC-induced helper T cell response. We conclude that PDE4B is a homeostatic regulator of cellular cAMP concentrations in DCs and may be a target for treating Th2-allergic asthma and other settings with low cellular cAMP concentrations.

HIV-1 Trans Infection via TNTs Is Impeded by Targeting C5aR

Nonadjacent immune cells communicate through a complex network of tunneling nanotubes (TNTs). TNTs can be hijacked by HIV-1, allowing it to spread between connected cells. Dendritic cells (DCs) are among the first cells to encounter HIV-1 at mucosal sites, but they are usually efficiently infected only at low levels. However, HIV-1 was demonstrated to productively infect DCs when the virus was complement-opsonized (HIV-C). Such HIV-C-exposed DCs mediated an improved antiviral and T-cell stimulatory capacity. The role of TNTs in combination with complement in enhancing DC infection with HIV-C remains to be addressed. To this aim, we evaluated TNT formation on the surface of DCs or DC/CD4+ T-cell co-cultures incubated with non- or complement-opsonized HIV-1 (HIV, HIV-C) and the role of TNTs or locally produced complement in the infection process using either two different TNT or anaphylatoxin receptor antagonists. We found that HIV-C significantly increased the formation of TNTs between DCs or DC/CD4+ T-cell co-cultures compared to HIV-exposed DCs or co-cultures. While augmented TNT formation in DCs promoted productive infection, as was previously observed, a significant reduction in productive infection was observed in DC/CD4+ T-cell co-cultures, indicating antiviral activity in this setting. As expected, TNT inhibitors significantly decreased infection of HIV-C-loaded-DCs as well as HIV- and HIV-C-infected-DC/CD4+ T-cell co-cultures. Moreover, antagonizing C5aR significantly inhibited TNT formation in DCs as well as DC/CD4+ T-cell co-cultures and lowered the already decreased productive infection in co-cultures. Thus, local complement mobilization via DC stimulation of complement receptors plays a pivotal role in TNT formation, and our findings herein might offer an exciting opportunity for novel therapeutic approaches to inhibit trans infection via C5aR targeting.

CAR/CXCR5-T cell immunotherapy is safe and potentially efficacious in promoting sustained remission of SIV infection

During chronic human immunodeficiency virus (HIV) or simian immunodeficiency virus (SIV) infection prior to AIDS progression, the vast majority of viral replication is concentrated within B cell follicles of secondary lymphoid tissues. We investigated whether infusion of T cells expressing an SIV-specific chimeric antigen receptor (CAR) and the follicular homing receptor, CXCR5, could successfully kill viral-RNA+ cells in targeted lymphoid follicles in SIV-infected rhesus macaques. In this study, CD4 and CD8 T cells from rhesus macaques were genetically modified to express antiviral CAR and CXCR5 moieties (generating CAR/CXCR5-T cells) and autologously infused into a chronically infected animal. At 2 days post-treatment, the CAR/CXCR5-T cells were located primarily in spleen and lymph nodes both inside and outside of lymphoid follicles. Few CAR/CXCR5-T cells were detected in the ileum, rectum, and lung, and no cells were detected in the bone marrow, liver, or brain. Within follicles, CAR/CXCR5-T cells were found in direct contact with SIV-viral RNA+ cells. We next infused CAR/CXCR5-T cells into ART-suppressed SIV-infected rhesus macaques, in which the animals were released from ART at the time of infusion. These CAR/CXCR5-T cells replicated in vivo within both the extrafollicular and follicular regions of lymph nodes and accumulated within lymphoid follicles. CAR/CXR5-T cell concentrations in follicles peaked during the first week post-infusion but declined to undetectable levels after 2 to 4 weeks. Overall, CAR/CXCR5-T cell-treated animals maintained lower viral loads and follicular viral RNA levels than untreated control animals, and no outstanding adverse reactions were noted. These findings indicate that CAR/CXCR5-T cell treatment is safe and holds promise as a future treatment for the durable remission of HIV.

Applications of Antibody-Based Antigen Delivery Targeted to Dendritic Cells In Vivo

Recombinant immunoglobulins, derived from monoclonal antibodies recognizing the defined surface epitopes expressed on dendritic cells, have been employed for the past two decades to deliver antigens to dendritic cells in vivo, serving as critical tools for the investigation of the corresponding T cell responses. These approaches originated with the development of the recombinant chimeric antibody against a multilectin receptor, DEC-205, which is present on subsets of murine and human conventional dendritic cells. Following the widespread application of antigen targeting through DEC-205, similar approaches then utilized other epitopes as entry points for antigens delivered by specific antibodies to multiple types of dendritic cells. Overall, these antigen-delivery methodologies helped to reveal the mechanisms underlying tolerogenic and immunogenic T cell responses orchestrated by dendritic cells. Here, we discuss the relevant experimental strategies as well as their future perspectives, including their translational relevance.

OMIP 082: A 25-color phenotyping to define human innate lymphoid cells, natural killer cells, mucosal-associated invariant T cells, and γδ T cells from freshly isolated human intestinal tissue

We developed a 25-color flow cytometry panel to comprehensively interrogate innate lymphoid cells (ILC), mucosal-associated invariant T (MAIT) cells, natural killer (NK) cells and γδ T cells in human tissues. The ability to isolate and interrogate these cells from fresh human tissue is crucial in understanding the role these cells play at immune-privileged mucosal surfaces like the intestine in health and disease settings. However, liberating these cells from tissue is extremely challenging as many key surface identification markers are susceptible to enzymatic cleavage. Choosing the correct enzyme-antibody clone combination within a high-parameter panel is, therefore, a critical consideration. Here, we present a comprehensive, in-depth analysis of the effect different common digestive enzyme blends have on key surface markers used to identify these cell types. In addition, we compared multiple antibody clones for surface markers that are highly susceptible to enzymatic cleavage, such as CD127 and NKp44, to achieve the most consistent and superior staining patterns among donors.

HIV transmitting mononuclear phagocytes; integrating the old and new

In tissue, mononuclear phagocytes (MNP) are comprised of Langerhans cells, dendritic cells, macrophages and monocyte-derived cells. They are the first immune cells to encounter HIV during transmission and transmit the virus to CD4 T cells as a consequence of their antigen presenting cell function. To understand the role these cells play in transmission, their phenotypic and functional characterisation is important. With advancements in high parameter single cell technologies, new MNPs subsets are continuously being discovered and their definition and classification is in a state of flux. This has important implications for our knowledge of HIV transmission, which requires a deeper understanding to design effective vaccines and better blocking strategies. Here we review the historical research of the role MNPs play in HIV transmission up to the present day and revaluate these studies in the context of our most recent understandings of the MNP system.

Native CGRP Neuropeptide and Its Stable Analogue SAX, But Not CGRP Peptide Fragments, Inhibit Mucosal HIV-1 Transmission

Background

The vasodilator neuropeptide calcitonin gene-related peptide (CGRP) plays both detrimental and protective roles in different pathologies. CGRP is also an essential component of the neuro-immune dialogue between nociceptors and mucosal immune cells. We previously discovered that CGRP is endowed with anti-viral activity and strongly inhibits human immunodeficiency virus type 1 (HIV-1) infection, by suppressing Langerhans cells (LCs)-mediated HIV-1 trans-infection in-vitro and mucosal HIV-1 transmission ex-vivo. This inhibition is mediated via activation of the CGRP receptor non-canonical NFκB/STAT4 signaling pathway that induces a variety of cooperative mechanisms. These include CGRP-mediated increase in the expression of the LC-specific pathogen recognition C-type lectin langerin and decrease in LC-T-cell conjugates formation. The clinical utility of CGRP and modalities of CGRP receptor activation, for inhibition of mucosal HIV-1 transmission, remain elusive.

Methods

We tested the capacity of CGRP to inhibit HIV-1 infection in-vivo in humanized mice. We further compared the anti-HIV-1 activities of full-length native CGRP, its metabolically stable analogue SAX, and several CGRP peptide fragments containing its binding C-terminal and activating N-terminal regions. These agonists were evaluated for their capacity to inhibit LCs-mediated HIV-1 trans-infection in-vitro and mucosal HIV-1 transmission in human mucosal tissues ex-vivo.

Results

A single CGRP intravaginal topical treatment of humanized mice, followed by HIV-1 vaginal challenge, transiently restricts the increase in HIV-1 plasma viral loads but maintains long-lasting higher CD4+ T-cell counts. Similarly to CGRP, SAX inhibits LCs-mediated HIV-1 trans-infection in-vitro, but with lower potency. This inhibition is mediated via CGRP receptor activation, leading to increased expression of both langerin and STAT4 in LCs. In contrast, several N-terminal and N+C-terminal bivalent CGRP peptide fragments fail to increase langerin and STAT4, and accordingly lack anti-HIV-1 activities. Finally, like CGRP, treatment of human inner foreskin tissue explants with SAX, followed by polarized inoculation with cell-associated HIV-1, completely blocks formation of LC-T-cell conjugates and HIV-1 infection of T-cells.

Conclusion

Our results show that CGRP receptor activation by full-length CGRP or SAX is required for efficient inhibition of LCs-mediated mucosal HIV-1 transmission. These findings suggest that formulations containing CGRP, SAX and/or their optimized agonists/analogues could be harnessed for HIV-1 prevention.

A model of impaired Langerhans cell maturation associated with HPV induced epithelial hyperplasia

Langerhans cells (LC) are skin-resident antigen-presenting cells that regulate immune responses to epithelial microorganisms. Human papillomavirus (HPV) infection can promote malignant epithelial transformation. As LCs are considered important for controlling HPV infection, we compared the transcriptome of murine LCs from skin transformed by K14E7 oncoprotein and from healthy skin. We identified transcriptome heterogeneity at the single cell level amongst LCs in normal skin, associated with ontogeny, cell cycle, and maturation. We identified a balanced co-existence of immune-stimulatory and immune-inhibitory LC cell states in normal skin that was significantly disturbed in HPV16 E7-transformed skin. Hyperplastic skin was depleted of immune-stimulatory LCs and enriched for LCs with an immune-inhibitory gene signature, and LC-keratinocyte crosstalk was dysregulated. We identified reduced expression of interleukin (IL)-34, a critical molecule for LC homeostasis. Enrichment of an immune-inhibitory LC gene signature and reduced levels of epithelial IL-34 were also found in human HPV-associated cervical epithelial cancers.

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Single cell atlas of Langerhans cells in cutaneous skin

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Stimulatory and inhibitory Langerhans cell states are in balance

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Inhibitory Langerhans cell states dominate HPV-transformed hyperplastic skin

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Langerhans cell imbalance is associated with disrupted IL-34 signaling

Unboxing dendritic cells: Tales of multi-faceted biology and function

Often referred to as the bridge between innate and adaptive immunity, dendritic cells (DCs) are professional antigen-presenting cells (APCs) that constitute a unique, yet complex cell system. Among other APCs, DCs display the unique property of inducing protective immune responses against invading microbes, or cancer cells, while safeguarding the proper homeostatic equilibrium of the immune system and maintaining self-tolerance. Unsurprisingly, DCs play a role in many diseases such as autoimmunity, allergy, infectious disease and cancer. This makes them attractive but challenging targets for therapeutics. Since their initial discovery, research and understanding of DC biology have flourished. We now recognize the presence of multiple subsets of DCs distributed across tissues. Recent studies of phenotype and gene expression at the single cell level have identified heterogeneity even within the same DC type, supporting the idea that DCs have evolved to greatly expand the flexibility of the immune system to react appropriately to a wide range of threats. This review is meant to serve as a quick and robust guide to understand the basic divisions of DC subsets and their role in the immune system. Between mice and humans, there are some differences in how these subsets are identified and function, and we will point out specific distinctions as necessary. Throughout the text, we are using both fundamental and therapeutic lens to describe overlaps and distinctions and what this could mean for future research and therapies.

How dendritic cells sense and respond to viral infections

The ability of dendritic cells (DCs) to sense viral pathogens and orchestrate a proper immune response makes them one of the key players in antiviral immunity. Different DC subsets have complementing functions during viral infections, some specialize in antigen presentation and cross-presentation and others in the production of cytokines with antiviral activity, such as type I interferons. In this review, we summarize the latest updates concerning the role of DCs in viral infections, with particular focus on the complex interplay between DC subsets and severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). Despite being initiated by a vast array of immune receptors, DC-mediated antiviral responses often converge towards the same endpoint, that is the production of proinflammatory cytokines and the activation of an adaptive immune response. Nonetheless, the inherent migratory properties of DCs make them a double-edged sword and often viral recognition by DCs results in further viral dissemination. Here we illustrate these various aspects of the antiviral functions of DCs and also provide a brief overview of novel antiviral vaccination strategies based on DCs targeting.

Many Langerhans make light work of skin immunity

The concept of functional specialization is fundamental to the immune system but has not been previously observed in human Langerhans cells. In this issue of Immunity, Liu et al. use single-cell approaches to define two distinct epidermal subsets converging on a common activation and migration pathway.

Flow-FISH as a Tool for Studying Bacteria, Fungi and Viruses

Many techniques are currently in use to study microbes. These can be aimed at detecting, identifying, and characterizing bacterial, fungal, and viral species. One technique that is suitable for high-throughput analysis is flow cytometry-based fluorescence in situ hybridization, or Flow-FISH. This technique employs (fluorescently labeled) probes directed against DNA or (m)RNA, for instance targeting a gene or microorganism of interest and provides information on a single-cell level. Furthermore, by combining Flow-FISH with antibody-based protein detection, proteins of interest can be measured simultaneously with genetic material. Additionally, depending on the type of Flow-FISH assay, Flow-FISH can also be multiplexed, allowing for the simultaneous measurement of multiple gene targets and/or microorganisms. Together, this allows for, e.g., single-cell gene expression analysis or identification of (sub)strains in mixed cultures. Flow-FISH has been used in mammalian cells but has also been extensively employed to study diverse microbial species. Here, the use of Flow-FISH for studying microorganisms is reviewed. Specifically, the detection of (intracellular) pathogens, studying microorganism biology and disease pathogenesis, and identification of bacterial, fungal, and viral strains in mixed cultures is discussed, with a particular focus on the viruses EBV, HIV-1, and SARS-CoV-2.

Comprehensive RNA sequencing in primary murine keratinocytes and fibroblasts identifies novel biomarkers and provides potential therapeutic targets for skin-related diseases

BACKGROUND

Keratinocytes and fibroblasts represent the major cell types in the epidermis and dermis of the skin and play a significant role in maintenance of skin homeostasis. However, the biological characteristics of keratinocytes and fibroblasts remain to be elucidated. The purpose of this study was to compare the gene expression pattern between keratinocytes and fibroblasts and to explore novel biomarker genes so as to provide potential therapeutic targets for skin-related diseases such as burns, wounds, and aging.

METHODS

Skin keratinocytes and fibroblasts were isolated from newborn mice. To fully understand the heterogeneity of gene expression between keratinocytes and fibroblasts, differentially expressed genes (DEGs) between the two cell types were detected by RNA-seq technology. Quantitative real-time polymerase chain reaction (qRT-PCR) was used to detect the known genes of keratinocytes and fibroblasts and verify the RNA-seq results.

RESULTS

Transcriptomic data showed a total of 4309 DEGs (fold-change > 1.5 and q-value < 0.05). Among them, 2197 genes were highly expressed in fibroblasts and included 10 genes encoding collagen, 16 genes encoding transcription factors, and 14 genes encoding growth factors. Simultaneously, 2112 genes were highly expressed in keratinocytes and included 7 genes encoding collagen, 14 genes encoding transcription factors, and 8 genes encoding growth factors. Furthermore, we summarized 279 genes specifically expressed in keratinocytes and 33 genes specifically expressed in fibroblasts, which may represent distinct molecular signatures of each cell type. Additionally, we observed some novel specific biomarkers for fibroblasts such as Plac8 (placenta-specific 8), Agtr2 (angiotensin II receptor, type 2), Serping1 (serpin peptidase inhibitor, clade G, member 1), Ly6c1 (lymphocyte antigen 6 complex, locus C1), Dpt (dermatopontin), and some novel specific biomarkers for keratinocytes such as Ly6a (lymphocyte antigen 6 complex, locus A) and Lce3c (late cornified envelope 3C), Ccer2 (coiled-coil glutamate-rich protein 2), Col18a1 (collagen, type XVIII, alpha 1) and Col17a1 (collagen type XVII, alpha 1). In summary, these data provided novel identifying biomarkers for two cell types, which can provide a resource of DEGs for further investigations.

Optimal Isolation Protocols for Examining and Interrogating Mononuclear Phagocytes From Human Intestinal Tissue

The human intestine contains numerous mononuclear phagocytes (MNP), including subsets of conventional dendritic cells (cDC), macrophages (Mf) and monocytes, each playing their own unique role within the intestinal immune system and homeostasis. The ability to isolate and interrogate MNPs from fresh human tissue is crucial if we are to understand the role of these cells in homeostasis, disease settings and immunotherapies. However, liberating these cells from tissue is problematic as many of the key surface identification markers they express are susceptible to enzymatic cleavage and they are highly susceptible to cell death. In addition, the extraction process triggers immunological activation/maturation which alters their functional phenotype. Identifying the evolving, complex and highly heterogenous repertoire of MNPs by flow cytometry therefore requires careful selection of digestive enzyme blends that liberate viable cells and preserve recognition epitopes involving careful selection of antibody clones to enable analysis and sorting for functional assays. Here we describe a method for the anatomical separation of mucosa and submucosa as well as isolating lymphoid follicles from human jejunum, ileum and colon. We also describe in detail the optimised enzyme digestion methods needed to acquire functionally immature and biologically functional intestinal MNPs. A comprehensive list of screened antibody clones is also presented which allows for the development of high parameter flow cytometry panels to discriminate all currently identified human tissue MNP subsets including pDCs, cDC1, cDC2 (langerin⁺ and langerin^-), newly described DC3, monocytes, Mf1, Mf2, Mf3 and Mf4. We also present a novel method to account for autofluorescent signal from tissue macrophages. Finally, we demonstrate that these methods can successfully be used to sort functional, immature intestinal DCs that can be used for functional assays such as cytokine production assays.

Targeting human langerin promotes HIV-1 specific humoral immune responses

The main avenue for the development of an HIV-1 vaccine remains the induction of protective antibodies. A rationale approach is to target antigen to specific receptors on dendritic cells (DC) via fused monoclonal antibodies (mAb). In mouse and non-human primate models, targeting of skin Langerhans cells (LC) with anti-Langerin mAbs fused with HIV-1 Gag antigen drives antigen-specific humoral responses. The development of these immunization strategies in humans requires a better understanding of early immune events driven by human LC. We therefore produced anti-Langerin mAbs fused with the HIV-1 gp140z Envelope (αLC.Env). First, we show that primary skin human LC and in vitro differentiated LC induce differentiation and expansion of naïve CD4⁺ T cells into T follicular helper (Tfh) cells. Second, when human LC are pre-treated with αLC.Env, differentiated Tfh cells significantly promote the production of specific IgG by B cells. Strikingly, HIV-Env-specific Ig are secreted by HIV-specific memory B cells. Consistently, we found that receptors and cytokines involved in Tfh differentiation and B cell functions are upregulated by LC during their maturation and after targeting Langerin. Finally, we show that subcutaneous immunization of mice by αLC.Env induces germinal center (GC) reaction in draining lymph nodes with higher numbers of Tfh cells, Env-specific B cells, as well as specific IgG serum levels compared to mice immunized with the non-targeting Env antigen. Altogether, we provide evidence that human LC properly targeted may be licensed to efficiently induce Tfh cell and B cell responses in GC.

In recent years, the place of innovative vaccines based on the induction/regulation and modulation of the immune response with the aim to elicit an integrated T- and B cell immune responses against complex antigens has emerged besides “classical” vaccine vectors. Targeting antigens to dendritic cells is a vaccine technology concept supported by more than a decade of animal models and human pre-clinical experimentation. Recent investigations in animals underscored that Langerhans cells (LC) are an important target to consider for the induction of antibody responses by DC targeting vaccine approaches. Nonetheless, the development of these immunization strategies in humans remains elusive. We therefore developed and produced an HIV vaccine candidate targeting specifically LC through the Langerin receptor. We tested the ability of our vaccine candidate of targeting LC from skin explant and of inducing in vitro the differentiation of T follicular helper (Tfh) cells. Using complementary in vitro models, we demonstrated that Tfh cells induced by human LC are functional and the targeting of LC by our vaccine candidate promotes the secretion of anti-HIV IgG by memory B cells from HIV-infected individuals. In this study human LC exhibit key cellular functions able to drive potent anti-HIV-1 humoral responses providing mechanistic evidence of the Tfh- and B cell stimulating functions of primary skin targeted LC. Finally, we demonstrated in Xcr1^DTA mice the significant advantage of LC targeting for inducing Tfh and germinal center (GC)-B cells and anti-HIV-1 antibodies. Therefore, the targeting of the human Langerin receptor appears to be a promising strategy for developing efficient HIV-1 vaccine.

Mucosal Dendritic Cell Subsets Control HIV-1's Viral Fitness

Dendritic cell (DC) subsets are abundantly present in genital and intestinal mucosal tissue and are among the first innate immune cells that encounter human immunodeficiency virus type 1 (HIV-1) after sexual contact. Although DCs have specific characteristics that greatly enhance HIV-1 transmission, it is becoming evident that most DC subsets also have virus restriction mechanisms that exert selective pressure on the viruses during sexual transmission. In this review we discuss the current concepts of the immediate events following viral exposure at genital mucosal sites that lead to selection of specific HIV-1 variants called transmitted founder (TF) viruses. We highlight the importance of the TF HIV-1 phenotype and the role of different DC subsets in establishing infection. Understanding the biology of HIV-1 transmission will contribute to the design of novel treatment strategies preventing HIV-1 dissemination.