Advances in understanding the mechanism of action of adult vaccines.

The occurrence of herpes zoster (HZ) correlates with declining memory T cells that had responded to earlier infection with varicella-zoster virus (VZV). There are especially lower T cell responses to the single immunodominant VZV protein glycoprotein E (gE) in people over 50 years of age, although antibody responses to VZV persist. Therefore, a live attenuated zoster vaccine (ZVL) aimed at restoring T cell responses was developed. Surprisingly, a recombinant zoster vaccine (RZV) consisting of gE combined with the AS01B adjuvant system proved superior in efficacy and durability. In this issue of the JCI, Laing, Ford, and colleagues showed that both vaccines stimulated preimmunization naive CD4+ T cells, not just memory CD4+ T cells, to gE, and recruited these naive responses into the overall memory response. However, compared with ZVL, RZV stimulated this response to a much greater degree. These results will help guide development of more effective and durable vaccines for older individuals.

Highly Networked SARS-CoV-2 Peptides Elicit T Cell Responses with Enhanced Specificity.

Identifying SARS-CoV-2-specific T cell epitope-derived peptides is critical for the development of effective vaccines and measuring the duration of specific SARS-CoV-2 cellular immunity. In this regard, we previously identified T cell epitope-derived peptides within topologically and structurally essential regions of SARS-CoV-2 spike and nucleocapsid proteins by applying an immunoinformatics pipeline. In this study, we selected 30 spike- and nucleocapsid-derived peptides and assessed whether these peptides induce T cell responses and avoid major mutations found in SARS-CoV-2 variants of concern. Our peptide pool was highly specific, with only a single peptide driving cross-reactivity in people unexposed to SARS-COV-2, and immunogenic, inducing a polyfunctional response in CD4+ and CD8+ T cells from COVID-19 recovered individuals. All peptides were immunogenic and individuals recognized broad and diverse peptide repertoires. Moreover, our peptides avoided most mutations/deletions associated with all four SARS-CoV-2 variants of concern while retaining their physicochemical properties even when genetic changes are introduced. This study contributes to an evolving definition of individual CD4+ and CD8+ T cell epitopes that can be used for specific diagnostic tools for SARS-CoV-2 T cell responses and is relevant to the development of variant-resistant and durable T cell-stimulating vaccines.

Emergence and antibody evasion of BQ, BA.2.75 and SARS-CoV-2 recombinant sub-lineages in the face of maturing antibody breadth at the population level.

BACKGROUND: The Omicron era of the COVID-19 pandemic commenced at the beginning of 2022 and whilst it started with primarily BA.1, it was latter dominated by BA.2 and the related sub-lineage BA.5. Following resolution of the global BA.5 wave, a diverse grouping of Omicron sub-lineages emerged derived from BA.2, BA.5 and recombinants thereof. Whilst emerging from distinct lineages, all shared similar changes in the Spike glycoprotein affording them an outgrowth advantage through evasion of neutralising antibodies. METHODS: Over the course of 2022, we monitored the potency and breadth of antibody neutralization responses to many emerging variants in the Australian community at three levels: (i) we tracked over 420,000 U.S. plasma donors over time through various vaccine booster roll outs and Omicron waves using sequentially collected IgG pools; (ii) we mapped the antibody response in individuals using blood from stringently curated vaccine and convalescent cohorts. (iii) finally we determine the in vitro efficacy of clinically approved therapies Evusheld and Sotrovimab. FINDINGS: In pooled IgG samples, we observed the maturation of neutralization breadth to Omicron variants over time through continuing vaccine and infection waves. Importantly, in many cases, we observed increased antibody breadth to variants that were yet to be in circulation. Determination of viral neutralization at the cohort level supported equivalent coverage across prior and emerging variants with isolates BQ.1.1, XBB.1, BR.2.1 and XBF the most evasive. Further, these emerging variants were resistant to Evusheld, whilst increasing neutralization resistance to Sotrovimab was restricted to BQ.1.1 and XBF. We conclude at this current point in time that dominant variants can evade antibodies at levels equivalent to their most evasive lineage counterparts but sustain an entry phenotype that continues to promote an additional outgrowth advantage. In Australia, BR.2.1 and XBF share this phenotype and, in contrast to global variants, are uniquely dominant in this region in the later months of 2022. INTERPRETATION: Whilst the appearance of a diverse range of omicron lineages has led to primary or partial resistance to clinically approved monoclonal antibodies, the maturation of the antibody response across both cohorts and a large donor pools importantly observes increasing breadth in the antibody neutralisation responses over time with a trajectory that covers both current and known emerging variants. FUNDING: This work was primarily supported by Australian Medical Foundation research grants MRF2005760 (SGT, GM & WDR), Medical Research Future Fund Antiviral Development Call grant (WDR), the New South Wales Health COVID-19 Research Grants Round 2 (SGT & FB) and the NSW Vaccine Infection and Immunology Collaborative (VIIM) (ALC). Variant modeling was supported by funding from SciLifeLab's Pandemic Laboratory Preparedness program to B.M. (VC-2022-0028) and by the European Union's Horizon 2020 research and innovation programme under grant agreement no. 101003653 (CoroNAb) to B.M.

Multiple COVID-19 vaccine doses in CLL and MBL improve immune responses with progressive and high seroconversion.

Patients with chronic lymphocytic leukemia (CLL) or monoclonal B-lymphocytosis (MBL) have impaired response to COVID-19 vaccination. A total of 258 patients (215 with CLL and 43 with MBL) had antispike antibody levels evaluable for statistical analysis. The overall seroconversion rate in patients with CLL was 94.2% (antispike antibodies ≥50 AU/mL) and 100% in patients with MBL after multiple vaccine doses. After 3 doses (post-D3) in 167 patients with CLL, 73.7% were seropositive, 17.4% had antispike antibody levels between 50 and 999 AU/mL, and 56.3% had antispike antibody levels ≥1000 AU/mL, with a median rise from 144.6 to 1800.7 AU/mL. Of patients who were seronegative post-D2, 39.7% seroconverted post-D3. For those who then remained seronegative after their previous dose, seroconversion occurred in 40.6% post-D4, 46.2% post-D5, 16.7% post-D6, and 0% after D7 or D8. After seroconversion, most had a progressive increase in antispike antibody levels. Neutralization was associated with higher antispike antibody levels, more vaccine doses, and earlier severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants; neutralizing antibody against early clade D614G was detected in 65.3%, against Delta in 52.0%, and against Omicron in 36.5%. SARS-CoV-2-specific T-cell production of interferon γ and interleukin 2 occurred in 73.9% and 60.9%, respectively, of 23 patients tested. After multiple vaccine doses, by multivariate analysis, immunoglobulin M ≥0.53 g/L, immunoglobulin subclass G3 ≥0.22 g/L and absence of current CLL therapy were independent predictors of positive serological responses. Multiple sequential COVID-19 vaccination significantly increased seroconversion and antispike antibody levels in patients with CLL or MBL.

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.

Tissue resident memory T cells inhabit the deep human conjunctiva.

Mucosal linings of the body, including the conjunctiva, are enriched in tissue-resident memory T cells (TRMs) whose defining feature is their continual tissue protection that does not rely on migration to lymphoid organs to elicit immune responses. Hitherto, conjunctival TRMs have only been identified in the superficial epithelium. This work aims to develop a more complete understanding of the conjunctival immunological capacity by investigating the presence of TRMs within the deeper, more stable layers of the healthy human conjunctiva. Using immunofluorescence microscopy and antibodies against CD3, CD4, CD69 and HLA-DR on bulbar conjunctival biopsies obtained from 7 healthy adults (age range = 32-77 years; females = 4), we identified CD69+TRM subsets in all layers of the human conjunctiva: the superficial epithelium, the basal epithelium, the adenoid, and the fibrous layers. Interestingly, the adenoid layer showed significantly higher densities of both CD4 and CD8 TRMs when compared to the fibrous layer and conjunctival epithelia. Additionally, CD4 TRMs predominated significantly over CD8 TRMs in the adenoid layer. The abundance of deep conjunctival CD69+TRMs within the healthy human may suggest the presence of defence mechanisms capable of inducing long-term immunogenic memory. Understanding this spatial distribution of conjunctival CD69+TRMs is essential to improving mucosal vaccine design.

COVID-19 vaccine failure in chronic lymphocytic leukaemia and monoclonal B-lymphocytosis; humoural and cellular immunity.

Chronic lymphocytic leukaemia (CLL) is associated with immunocompromise and high risk of severe COVID-19 disease and mortality. Monoclonal B-cell lymphocytosis (MBL) patients also have immune impairment. We evaluated humoural and cellular immune responses in 181 patients with CLL (160) and MBL (21) to correlate failed seroconversion [<50 AU/ml SARS-CoV-2 II IgG assay, antibody to spike protein; Abbott Diagnostics)] following each of two vaccine doses with clinical and laboratory parameters. Following first and second doses, 79.2% then 45% of CLL, and 50% then 9.5% of MBL patients respectively remained seronegative. There was significant association between post dose two antibody level with pre-vaccination reduced IgM (p < 0.0001), IgG2 (p < 0.035), and IgG3 (p < 0.046), and CLL therapy within 12 months (p < 0.001) in univariate analysis. By multivariate analysis, reduced IgM (p < 0.0002) and active therapy (p < 0.0002) retained significance. Anti-spike protein levels varied widely and were lower in CLL than MBL patients, and both lower than in normal donors. Neutralisation activity showed anti-spike levels <1000 AU/ml were usually negative for both an early viral clade and the contemporary Delta variant and 72.9% of CLL and 53.3% of MBL failed to reach levels ≥1000 AU/ml. In a representative sample, ~80% had normal T-cell responses. Failed seroconversion occurred in 36.6% of treatment-naïve patients, in 78.1% on therapy, and in 85.7% on ibrutinib.

Herpes Simplex Virus type 1 infects Langerhans cells and the novel epidermal dendritic cell, Epi-cDC2s, via different entry pathways.

Skin mononuclear phagocytes (MNPs) provide the first interactions of invading viruses with the immune system. In addition to Langerhans cells (LCs), we recently described a second epidermal MNP population, Epi-cDC2s, in human anogenital epidermis that is closely related to dermal conventional dendritic cells type 2 (cDC2) and can be preferentially infected by HIV. Here we show that in epidermal explants topically infected with herpes simplex virus (HSV-1), both LCs and Epi-cDC2s interact with HSV-1 particles and infected keratinocytes. Isolated Epi-cDC2s support higher levels of infection than LCs in vitro, inhibited by acyclovir, but both MNP subtypes express similar levels of the HSV entry receptors nectin-1 and HVEM, and show similar levels of initial uptake. Using inhibitors of endosomal acidification, actin and cholesterol, we found that HSV-1 utilises different entry pathways in each cell type. HSV-1 predominantly infects LCs, and monocyte-derived MNPs, via a pH-dependent pathway. In contrast, Epi-cDC2s are mainly infected via a pH-independent pathway which may contribute to the enhanced infection of Epi-cDC2s. Both cells underwent apoptosis suggesting that Epi-cDC2s may follow the same dermal migration and uptake by dermal MNPs that we have previously shown for LCs. Thus, we hypothesize that the uptake of HSV and infection of Epi-cDC2s will stimulate immune responses via a different pathway to LCs, which in future may help guide HSV vaccine development and adjuvant targeting.

Identification of SARS-CoV-2 Nucleocapsid and Spike T-Cell Epitopes for Assessing T-Cell Immunity.

Developing optimal T-cell response assays to severe acute respiratory syndrome coronavirus type 2 (SARS-CoV-2) is critical for measuring the duration of immunity to this disease and assessing the efficacy of vaccine candidates. These assays need to target conserved regions of SARS-CoV-2 global variants and avoid cross-reactivity to seasonal human coronaviruses. To contribute to this effort, we employed an in silico immunoinformatics analysis pipeline to identify immunogenic peptides resulting from conserved and highly networked regions with topological importance from the SARS-CoV-2 nucleocapsid and spike proteins. A total of 57 highly networked T-cell epitopes that are conserved across geographic viral variants were identified from these viral proteins, with a binding potential to diverse HLA alleles and 80 to 100% global population coverage. Importantly, 18 of these T-cell epitope derived peptides had limited homology to seasonal human coronaviruses making them promising candidates for SARS-CoV-2-specific T-cell immunity assays. Moreover, two of the NC-derived peptides elicited effector/polyfunctional responses of CD8+ T cells derived from SARS-CoV-2 convalescent patients.IMPORTANCE The development of specific and validated immunologic tools is critical for understanding the level and duration of the cellular response induced by SARS-CoV-2 infection and/or vaccines against this novel coronavirus disease. To contribute to this effort, we employed an immunoinformatics analysis pipeline to define 57 SARS-CoV-2 immunogenic peptides within topologically important regions of the nucleocapsid (NC) and spike (S) proteins that will be effective for detecting cellular immune responses in 80 to 100% of the global population. Our immunoinformatics analysis revealed that 18 of these peptides had limited homology to circulating seasonal human coronaviruses and therefore are promising candidates for distinguishing SARS-CoV-2-specific immune responses from pre-existing coronavirus immunity. Importantly, CD8+ T cells derived from SARS-CoV-2 survivors exhibited polyfunctional effector responses to two novel NC-derived peptides identified as HLA-binders. These studies provide a proof of concept that our immunoinformatics analysis pipeline identifies novel immunogens which can elicit polyfunctional SARS-CoV-2-specific T-cell responses.

AFid: a tool for automated identification and exclusion of autofluorescent objects from microscopy images.

MOTIVATION: Autofluorescence is a long-standing problem that has hindered the analysis of images of tissues acquired by fluorescence microscopy. Current approaches to mitigate autofluorescence in tissue are lab-based and involve either chemical treatment of sections or specialized instrumentation and software to 'unmix' autofluorescent signals. Importantly, these approaches are pre-emptive and there are currently no methods to deal with autofluorescence in acquired fluorescence microscopy images. RESULTS: To address this, we developed Autofluorescence Identifier (AFid). AFid identifies autofluorescent pixels as discrete objects in multi-channel images post-acquisition. These objects can then be tagged for exclusion from downstream analysis. We validated AFid using images of FFPE human colorectal tissue stained for common immune markers. Further, we demonstrate its utility for image analysis where its implementation allows the accurate measurement of HIV-Dendritic cell interactions in a colorectal explant model of HIV transmission. Therefore, AFid represents a major leap forward in the extraction of useful data from images plagued by autofluorescence by offering an approach that is easily incorporated into existing workflows and that can be used with various samples, staining panels and image acquisition methods. We have implemented AFid in ImageJ, Matlab and R to accommodate the diverse image analysis community. AVAILABILITY AND IMPLEMENTATION: AFid software is available at https://ellispatrick.github.io/AFid. SUPPLEMENTARY INFORMATION: Supplementary data are available at Bioinformatics online.

Vaccines for Herpes Simplex: Recent Progress Driven by Viral and Adjuvant Immunology.

Herpes simplex viruses (HSV) types 1 and 2 are ubiquitous. They both cause genital herpes, occasionally severe disease in the immunocompromised, and facilitate much HIV acquisition globally. Despite more than 60 years of research, there is no licensed prophylactic HSV vaccine and some doubt as to whether this can be achieved. Nevertheless, a previous HSV vaccine candidate did have partial success in preventing genital herpes and HSV acquisition and another immunotherapeutic candidate reduced viral shedding and recurrent lesions, inspiring further research. However, the entry pathway of HSV into the anogenital mucosa and the subsequent cascade of immune responses need further elucidation so that these responses could be mimicked or improved by a vaccine, to prevent viral entry and colonization of the neuronal ganglia. For an effective novel vaccine against genital herpes the choice of antigen and adjuvant may be critical. The incorporation of adjuvants of the vaccine candidates in the past, may account for their partial efficacy. It is likely that they can be improved by understanding the mechanisms of immune responses elicited by different adjuvants and comparing these to natural immune responses. Here we review the history of vaccines for HSV, those in development and compare them to successful vaccines for chicken pox or herpes zoster. We also review what is known of the natural immune control of herpes lesions, via interacting innate immunity and CD4 and CD8 T cells and the lessons they provide for development of new, more effective vaccines.

Mechanisms of Immune Control of Mucosal HSV Infection: A Guide to Rational Vaccine Design.

Herpes Simplex Virus (HSV) is a highly prevalent sexually transmitted infection that aside from causing cold sores and genital lesions, causes complications in the immunocompromised and has facilitated a large proportion of HIV acquisition globally. Despite decades of research, there is no prophylactic HSV vaccine ready for use in humans, leaving many questioning whether a prophylactic vaccine is an achievable goal. A previous HSV vaccine trial did have partial success in decreasing acquisition of HSV2-promising evidence that vaccines can prevent acquisition. However, there is still an incomplete understanding of the immune response pathways elicited by HSV after initial mucosal infection and how best to replicate these responses with a vaccine, such that acquisition and colonization of the dorsal root ganglia could be prevented. Another factor to consider in the rational design of an HSV vaccine is adjuvant choice. Understanding the immune responses elicited by different adjuvants and whether lasting humoral and cell-mediated responses are induced is important, especially when studies of past trial vaccines found that a sufficiently protective cell-mediated response was lacking. In this review, we discuss what is known of the immune control involved in initial herpes lesions and reactivation, including the importance of CD4 and CD8 T cells, and the interplay between innate and adaptive immunity in response to primary infection, specifically focusing on the viral relay involved. Additionally, a summary of previous and current vaccine trials, including the components used, immune responses elicited and the feasibility of prophylactic vaccines looking forward, will also be discussed.

Vaccine priming is restricted to draining lymph nodes and controlled by adjuvant-mediated antigen uptake.

The innate immune mechanisms by which adjuvants enhance the potency and protection of vaccine-induced adaptive immunity are largely unknown. We introduce a model to delineate the steps of how adjuvant-driven innate immune activation leads to priming of vaccine responses using rhesus macaques. Fluorescently labeled HIV-1 envelope glycoprotein (Env) was administered together with the conventional aluminum salt (alum) adjuvant. This was compared to Env given with alum with preabsorbed Toll-like receptor 7 (TLR7) ligand (alum-TLR7) or the emulsion MF59 because they show superiority over alum for qualitatively and quantitatively improved vaccine responses. All adjuvants induced rapid and robust immune cell infiltration to the injection site in the muscle. This resulted in substantial uptake of Env by neutrophils, monocytes, and myeloid and plasmacytoid dendritic cells (DCs) and migration exclusively to the vaccine-draining lymph nodes (LNs). Although less proficient than monocytes and DCs, neutrophils were capable of presenting Env to memory CD4+ T cells. MF59 and alum-TLR7 showed more pronounced cell activation and overall higher numbers of Env+ cells compared to alum. This resulted in priming of higher numbers of Env-specific CD4+ T cells in the vaccine-draining LNs, which directly correlated with increased T follicular helper cell differentiation and germinal center formation. Thus, strong innate immune activation promoting efficient vaccine antigen delivery to infiltrating antigen-presenting cells in draining LNs is an important mechanism by which superior adjuvants enhance vaccine 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.

Understanding natural herpes simplex virus immunity to inform next-generation vaccine design.

Incremental advances in our knowledge of how natural immune control of herpes simplex virus (HSV) develops have yielded insight as to why previous vaccine attempts have only been partially successful, however, our understanding of these pathways, particularly in humans, is still incomplete. Further elucidation of the innate immune events that are responsible for stimulating these effector responses is required to accurately inform vaccine design. An enhanced understanding of the mechanism of action of novel adjuvants will also facilitate the rational choice of adjuvant to optimise such responses. Here we review the reasons for the hitherto partial HSV vaccine success and align these with our current knowledge of how natural HSV immunity develops. In particular, we focus on the innate immune response and the role of dendritic cells in inducing protective T-cell responses and how these pathways might be recapitulated in a vaccine setting.

Design and evaluation of surface and adjuvant modified PLGA microspheres for uptake by dendritic cells to improve vaccine responses.

Designing strategies for targeting antigens to dendritic cells is a major goal in vaccinology. Here, PLGA (poly lactic-co-glycolic acid) microspheres and with several surface modifications that affect to their uptake by human blood primary dendritic cells and monocytes have been evaluated. Higher uptake was found by all the cell types when cationic microspheres (PLGA modified with polyethylene imine) were used. These cationic particles were in vivo evaluated in mice. In addition, MPLA(1) or poly(I:C)(2) and α-GalCer(3) were also encapsulated to address their adjuvant effect. All the microspheres were able to produce humoral immune responses, albeit they were higher for cationic microspheres. Moreover, surface charge seemed to have a role on biasing the immune response; cationic microspheres induced higher IFN-γ levels, indicative of Th1 activation, while unmodified ones mainly triggered IL4 and IL17A release, showing Th2 activation. Thus, we have shown here the potential and versatility of these MS, which may be tailored to needs.

Human Anti-CD40 Antibody and Poly IC:LC Adjuvant Combination Induces Potent T Cell Responses in the Lung of Nonhuman Primates.

Nonlive vaccine platforms that induce potent cellular immune responses in mucosal tissue would have broad application for vaccines against infectious diseases and tumors. Induction of cellular immunity could be optimized by targeted activation of multiple innate and costimulatory signaling pathways, such as CD40 or TLRs. In this study, we evaluated immune activation and elicitation of T cell responses in nonhuman primates after immunization with peptide Ags adjuvanted with an agonistic anti-CD40Ab, with or without the TLR3 ligand poly IC:LC. We found that i.v. administration of the anti-CD40Ab induced rapid and transient innate activation characterized by IL-12 production and upregulated costimulatory and lymph node homing molecules on dendritic cells. Using fluorescently labeled Abs for in vivo tracking, we found that the anti-CD40Ab bound to all leukocytes, except T cells, and disseminated to multiple organs. CD4(+) and CD8(+) T cell responses were significantly enhanced when the anti-CD40Ab was coadministered with poly IC:LC compared with either adjuvant given alone and were almost exclusively compartmentalized to the lung. Notably, Ag-specific T cells in the bronchoalveolar lavage were sustained at ∼5-10%. These data indicate that systemic administration of anti-CD40Ab may be particularly advantageous for vaccines and/or therapies that require T cell immunity in the lung.

Relay of herpes simplex virus between Langerhans cells and dermal dendritic cells in human skin.

The mechanism by which immunity to Herpes Simplex Virus (HSV) is initiated is not completely defined. HSV initially infects mucosal epidermis prior to entering nerve endings. In mice, epidermal Langerhans cells (LCs) are the first dendritic cells (DCs) to encounter HSV, but it is CD103(+) dermal DCs that carry viral antigen to lymph nodes for antigen presentation, suggesting DC cross-talk in skin. In this study, we compared topically HSV-1 infected human foreskin explants with biopsies of initial human genital herpes lesions to show LCs are initially infected then emigrate into the dermis. Here, LCs bearing markers of maturation and apoptosis formed large cell clusters with BDCA3(+) dermal DCs (thought to be equivalent to murine CD103(+) dermal DCs) and DC-SIGN(+) DCs/macrophages. HSV-expressing LC fragments were observed inside the dermal DCs/macrophages and the BDCA3(+) dermal DCs had up-regulated a damaged cell uptake receptor CLEC9A. No other infected epidermal cells interacted with dermal DCs. Correspondingly, LCs isolated from human skin and infected with HSV-1 in vitro also underwent apoptosis and were taken up by similarly isolated BDCA3(+) dermal DCs and DC-SIGN(+) cells. Thus, we conclude a viral antigen relay takes place where HSV infected LCs undergo apoptosis and are taken up by dermal DCs for subsequent antigen presentation. This provides a rationale for targeting these cells with mucosal or perhaps intradermal HSV immunization.