Harnessing human dendritic cell subsets for medicine

CD34+ -derived Langerhans cell-like cells are different from epidermal Langerhans cells in their response to thymic stromal lymphopoietin

Thymic stromal lymphopoietin (TSLP) endows human blood-derived CD11c⁺ dendritic cells (DCs) and Langerhans cells (LCs) obtained from human epidermis with the capacity to induce pro-allergic T cells. In this study, we investigated the effect of TSLP on umbilical cord blood CD34⁺-derived LC-like cells. These cells are often used as model cells for LCs obtained from epidermis. Under the influence of TSLP, both cell types differed in several ways. As defined by CD83, CD80 and CD86, TSLP did not increase maturation of LC-like cells when compared with freshly isolated LCs and epidermal émigrés. Differences were also found in the production of chemokine (C-C motif) ligand (CCL)17. LCs made this chemokine only when primed by TSLP and further stimulated by CD40 ligation. In contrast, LC-like cells released CCL17 in response to CD40 ligation, irrespective of a prior treatment with TSLP. Moreover, the CCL17 levels secreted by LC-like cells were at least five times higher than those from migratory LCs. After maturation with a cytokine cocktail consisting of tumour necrosis factor-α, interleukin (IL)-1β, IL-6 and prostaglandin (PG)E₂ LC-like cells released IL-12p70 in response to CD40 ligation. Most importantly and in contrast to LC, TSLP-treated LC-like cells did not induce a pro-allergic cytokine pattern in helper T cells. Due to their different cytokine secretion and the different cytokine production they induce in naïve T cells, we conclude that one has to be cautious to take LC-like cells as a paradigm for ‘real’ LCs from the epidermis.

Human dendritic cell culture and bacterial infection

Dendritic cells (DC) play a key role in the development of natural immunity to microbes. The DC form a bridge between the innate and adaptive immune system by providing key instructions particularly to antigen naïve T-cells. The interaction of DC with T lymphocytes involves three signals: (1) antigen processing and presentation in context of MHC Class I and/or II, (2) expression of T cell co-stimulatory molecules, and (3) cytokine production. Studying the interactions of DCs with specific pathogens allows for better understanding of how protective immunity is generated, and may be particularly useful for assessing vaccine components. In this chapter, we describe methods to generate human monocyte-derived DCs and assess their maturation, activation, and function, using interaction with the gram-negative bacterial pathogen Neisseria meningitidis as a model.

Targeting skin dendritic cells to improve intradermal vaccination

Vaccinations in medicine are typically administered into the muscle beneath the skin or into the subcutaneous fat. As a consequence, the vaccine is immunologically processed by antigen-presenting cells of the skin or the muscle. Recent evidence suggests that the clinically seldom used intradermal route is effective and possibly even superior to the conventional subcutaneous or intramuscular route. Several types of professional antigen-presenting cells inhabit the healthy skin. Epidermal Langerhans cells (CD207/langerin(+)), dermal langerin(neg), and dermal langerin(+) dendritic cells (DC) have been described, the latter subset so far only in mouse skin. In human skin langerin(neg) dermal DC can be further classified based on their reciprocal expression of CD1a and CD14. The relative contributions of these subsets to the generation of immunity or tolerance are still unclear. Yet, specializations of these different populations have become apparent. Langerhans cells in human skin appear to be specialized for induction of cytotoxic T lymphocytes; human CD14(+) dermal DC can promote antibody production by B cells. It is currently attempted to rationally devise and improve vaccines by harnessing such specific properties of skin DC. This could be achieved by specifically targeting functionally diverse skin DC subsets. We discuss here advances in our knowledge on the immunological properties of skin DC and strategies to significantly improve the outcome of vaccinations by applying this knowledge.

Intradermal immunization triggers epidermal Langerhans cell mobilization required for CD8 T-cell immune responses

The potential of the skin immune system for the generation of both powerful humoral and cellular immune responses is now well established. However, the mechanisms responsible for the efficacy of skin antigen-presenting cells (APCs) during intradermal (ID) vaccination still remain to be elucidated. We have previously demonstrated in clinical trials that preferential targeting of Langerhans cells (LCs) by transcutaneous immunization shapes the immune response toward vaccine-specific CD8 T cells. Others have shown that ID inoculation of a vaccine, which targets dermal APCs, mobilizes both the cellular and humoral arms of immunity. Here, we investigated the participation of epidermal LCs in response to ID immunization. When human or mouse skin was injected ID with a particle-based vaccine, we observed significant modifications in the morphology of epidermal LCs and their mobilization to the dermis. We further established that this LC recruitment after ID administration was essential for the induction of antigen-specific CD8 T cells, but was, however, dispensable for the generation of specific CD4 T cells and neutralizing antibodies. Thus, epidermal and dermal APCs shape the outcome of the immune responses to ID vaccination. Their combined potential provides new avenues for the development of vaccination strategies against infectious diseases.

Day-4 myeloid dendritic cells pulsed with whole tumor lysate are highly immunogenic and elicit potent anti-tumor responses

“Day-7” myeloid DCs are commonly used in the clinic. However, there is a strong need to develop DCs faster that have the same potent immunostimulatory capacity as “Day-7” myeloid DCs and at the same time minimizing time, labor and cost of DC preparations. Although “2 days” DCs can elicit peptide-specific responses, they have not been demonstrated to engulf, process and present complex whole tumor lysates, which could be more convenient and personalized source of tumor antigens than defined peptides. In this preclinical study, we evaluated the T-cell stimulatory capacity of Day-2, Day-4, and Day-7 cultured monocyte-derived DCs loaded with SKOV3 cell whole lysate prepared by freeze-thaw or by UVB-irradiation followed by freeze-thaw, and matured with lipopolysaccharide (LPS) and interferon (IFN)-gamma. DCs were evaluated for antigen uptake, and following maturation with LPS and IFN-gamma, DCs were assessed for expression of CD80, CD40, CD86, ICAM-1 and CCR7, production of IL-12p70 and IP-10, and induction of tumor-specific T-cell responses. Day-4 and Day-7 DCs exhibited similar phagocytic abilities, which were superior to Day-2 DCs. Mature Day-7 DCs expressed the highest CD40 and ICAM-1, but mature Day-4 DCs produced the most IL-12p70 and IP-10. Importantly, Day-4 and Day-7 DCs derived from ovarian cancer patients stimulated equally strongly tumor-specific T-cell responses. This is the first study demonstrating the highly immunogenic and strong T-cell stimulatory properties of Day-4 myeloid DCs, and provided important preclinical data for rapid development of potent whole tumor lysate-loaded DC vaccines that are applicable to many tumor types.

Immunotherapy of lung adenocarcinoma patient with Peptide-pulsed dendritic cells: a case report

Immunotherapy with ex vivo generated dendritic cells (DCs) is reported to be of low toxicity and of diverse effectiveness in cancer treatment. The synthetic antigens are frequently used for immunotherapy especially for patients with stable disease after prior treatment. We described the effect of peptide-loaded DCs-based immunotherapy on patient with recurrent surgically resected adenocarcinoma with bronchoalveolar feature with co-existing of Takayasu arteritis and chronic hepatitis B. In January 2010, 61-year-old patient received subcutaneously four bi-weekly vaccinations of DCs loaded with MUC1 and MAGE-3 epitopes. Additionally, he received three bi-weekly booster vaccinations after 7 months from the first course of immunotherapy. Delayed-type hypersensitivity test was positive only for MAGE-3 antigen. The evidence expansion of MAGE-3-specific CD8(+) cells after first vaccination and after third vaccination during boosters injections was observed (from 0.08% before vaccination to 0.5% after first vaccination; from 0.05% before booster vaccination to 0.24% after third injection). Computed tomography scans performed after first course and after booster course of vaccination until April 2011 did not shown any presence of lung tumour or metastases. Based on clinical factors (no completed wedge-resection and recurrent character of cancer) as well as on the presence of the tumour-antigen-specific immunological response, we could speculated that immunotherapy prolonged disease free-survival in our patient. Over 16 months from first vaccination, the patient remains without symptoms of cancer.

Dendritic cell and macrophage heterogeneity in vivo

Macrophage and dendritic cell (DC) are hematopoietic cells found in all tissues in the steady state that share the ability to sample the environment but have distinct function in tissue immunity. Controversies remain on the best way to distinguish macrophages from DCs in vivo. In this Perspective, we discuss how recent discoveries in the origin of the DC and macrophage lineage help establish key functional differences between tissue DC and macrophage subsets. We also emphasize the need to further understand the functional heterogeneity of the tissue DC and macrophage lineages to better comprehend the complex role of these cells in tissue homeostasis and immunity.

A quantitative proteomic approach for detecting protein profiles of activated human myeloid dendritic cells

Dendritic cells (DC) direct the magnitude, polarity and effector function of the adaptive immune response. DC express toll-like receptors (TLR), antigen capturing and processing machinery, and costimulatory molecules, which facilitate innate sensing and T cell activation. Once activated, DC can efficiently migrate to lymphoid tissue and prime T cell responses. Therefore, DC play an integral role as mediators of the immune response to multiple pathogens. Elucidating the molecular mechanisms involved in DC activation is therefore central in gaining an understanding of host response to infection. Unfortunately, technical constraints have limited system-wide 'omic' analysis of human DC subsets collected ex vivo. Here we have applied novel proteomic approaches to human myeloid dendritic cells (mDCs) purified from 100 mL of peripheral blood to characterize specific molecular networks of cell activation at the individual patient level, and have successfully quantified over 700 proteins from individual samples containing as little as 200,000 mDCs. The proteomic and network readouts after ex vivo stimulation of mDCs with TLR3 agonists are measured and verified using flow cytometry.

Wnt5a skews dendritic cell differentiation to an unconventional phenotype with tolerogenic features

Dendritic cells (DCs) are critical regulators of immune responses that integrate signals from the innate and adaptive immune system and orchestrate T cell responses toward either immunity or tolerance. Growing evidence points to the Wnt signaling pathway as a pivotal piece in the immune balance and focuses on DCs as a direct target for their immunoregulatory role. Our results show that the increase in Wnt5a signaling during the differentiation of human DCs from monocytes alters their phenotype and compromises their subsequent capacity to mature in response to TLR-dependent stimuli. These Wnt5a-DCs produce scant amounts of IL-12p70 and TNF-α but increased levels of IL-10. Consequently, these Wnt5a-DCs have a reduced capacity to induce Th1 responses that promote IL-10 secretion by CD4 T cells. Changes in the transcriptional profile of Wnt5a-DCs correlate with their unconventional phenotype caused presumably by increased IL-6/IL-10 signaling during the process of DC differentiation. The effect of Wnt5a is not a consequence of β-catenin accumulation but is dependent on noncanonical Ca(2+)/calmodulin-dependent protein kinase II/NF-κB signaling. Our results therefore suggest that under high levels of Wnt5a, typical of the inflammatory state and sepsis, monocytes could differentiate into unconventional DCs with tolerogenic features.

Stromal regulation of human gastric dendritic cells restricts the Th1 response to Helicobacter pylori

BACKGROUND & AIMS

Mucosal dendritic cells (DCs) play a key role in initiating the T-helper (Th)1 response to Helicobacter pylori. To further elucidate the mucosal response to H pylori, we examined whether gastric stromal factors condition DCs to support tolerance to H pylori, analogous to intestinal stromal factor-driven macrophage tolerance to commensal bacteria.

METHODS

To model mucosal DC development, we isolated and cultured cell-depleted human stroma/extracellular matrix from fresh gastric and intestinal mucosa to generate stroma-conditioned media. We then analyzed the capacity of stroma-conditioned media-treated monocyte-derived DCs and primary human gastric and intestinal DCs pulsed in vitro with H pylori to induce T-cell proliferation and interferon gamma secretion.

RESULTS

Stromal factors in gastric mucosa suppressed H pylori-stimulated DC activation and the ability of DCs to drive a Th1 proliferative and cytokine response to H pylori. The ability of gastric stromal factors to down-regulate DC function was similar to that of intestinal stromal factors and was independent of transforming growth factor β, prostaglandin E₂, interleukin (IL)-10, and thymic stromal lymphopoietin. Stroma-conditioned media-induced reduction in DC-stimulated Th1 responses was associated with reduced DC release of IL-12.

CONCLUSIONS

Gastric stromal factors down-regulate DC responsiveness to H pylori, resulting in a dampened gastric Th1 response. We speculate that stroma-induced down-regulation of DC function contributes to the permissiveness of both gastric and intestinal mucosa to colonization by persistent residential microbes.

Heat-shock protein 70-dependent dendritic cell activation by 5-aminolevulinic acid-mediated photodynamic treatment of human glioblastoma spheroids in vitro

BACKGROUND

T-cell responses contribute to the anti-tumoural effect of photodynamic therapy (PDT). For such responses to occur, dendritic cells (DCs) have to migrate to the tumour, take up tumour antigens and respond to danger signals with maturation, before they engage in T-cell activation. Here, we have studied the effect of 5-aminolevulinic acid (ALA)-mediated PDT on DCs in vitro in a human spheroid model of glioblastoma (GB).

METHODS

Spheroids of the GB cell lines U87 and U251 were treated with ALA/PDT, and effects on attraction, uptake of tumour antigens and maturation of DCs were studied. To block heat-shock protein-70 (HSP-70) on the spheroids, neutralising antibodies were used.

RESULTS

5-Aminolevulinic acid /PDT-treated GB spheroids attracted DCs that acquired tumour antigens from the spheroids effectively. Moreover, co-culture with ALA/PDT-treated spheroids induced DC maturation as indicated by the upregulation of CD83 and co-stimulatory molecules as well as increased T-cell stimulatory activity of the DCs. Heat-shock protein-70 was upregulated on the spheroids after ALA/PDT treatment. Uptake of tumour antigens and DC maturation induced by the ALA/PDT-treated spheroids were inhibited when HSP-70 was blocked.

CONCLUSION

ALA/PDT treatment of glioma spheroids promotes the three initial steps of the afferent phase of adaptive immunity, which is at least partially mediated by HSP-70.

Immunological mechanisms of vaccination

Vaccines represent one of the greatest triumphs of modern medicine. Despite the common origins of vaccinology and immunology more than 200 years ago, the two disciplines have evolved along such different trajectories that most of the highly successful vaccines have been made empirically, with little or no immunological insight. Recent advances in innate immunity have offered new insights about the mechanisms of vaccine-induced immunity and have facilitated a more rational approach to vaccine design. Here we will discuss these advances and emerging themes on the immunology of vaccination.

Impact of aging on dendritic cell functions in humans

Aging is a paradox of reduced immunity and chronic inflammation. Dendritic cells are central orchestrators of the immune response with a key role in the generation of immunity and maintenance of tolerance. The functions of DCs are compromised with age. There is no major effect on the numbers and phenotype of DC subsets in aged subjects; nevertheless, their capacity to phagocytose antigens and migrate is impaired with age. There is aberrant cytokine secretion by various DC subsets with CDCs secreting increased basal level of pro-inflammatory cytokines but the response on stimulation to foreign antigens is decreased. In contrast, the response to self-antigens is increased suggesting erosion of peripheral self tolerance. PDC subset also secretes reduced IFN-α in response to viruses. The capacity of DCs to prime T cell responses is also affected. Aging thus has a profound affect on DC functions. Present review summarizes the effect of advancing age on DC functions in humans in the context of both immunity and tolerance.

Therapeutic vaccines and immune-based therapies for the treatment of chronic hepatitis B: perspectives and challenges

The treatment of chronic hepatitis B virus (HBV) infection has greatly improved over the last 10 years, but alternative treatments are still needed. Therapeutic vaccination is a promising new strategy for controlling chronic infection. However, this approach has not been as successful as initially anticipated for chronic hepatitis B. General impairment of the immune responses generated during persistent HBV infection, with exhausted T cells not responding correctly to therapeutic vaccination, is probably responsible for the poor clinical responses observed to date. Intensive research efforts are now focusing on increasing the efficacy of therapeutic vaccination without causing liver disease. Here we describe new approaches to use with therapeutic vaccination, in order to overcome the inhibitory mechanisms impairing immune responses. We also describe innovative strategies for generating functional immune responses and inducing sustained control of this persistent infection.

Epicutaneous allergen administration: is this the future of allergen-specific immunotherapy?

IgE-mediated allergies, such as allergic rhinoconjunctivitis and asthma, have become highly prevalent, today affecting up to 30% of the population in industrialized countries. Allergen-specific immunotherapy (SIT) either subcutaneously or via the sublingual route is effective, but only few patients (<5%) choose immunotherapy, as treatment takes several years and because allergen administrations are associated with local and, in some cases, even systemic allergic side-effects because of allergen accidentally reaching the circulation. In order to resolve these two major drawbacks, the ideal application site of SIT should have two characteristics. First, it should contain a high number of potent antigen-presenting cells to enhance efficacy and shorten treatment duration. Secondly, it should be nonvascularized in order to minimize inadvertent systemic distribution of the allergen and therefore systemic allergic side-effects. The epidermis, a nonvascularized multilayer epithelium, that contains high numbers of potent antigen-presenting Langerhans cells (LC) could therefore be an interesting administration route. The present review will discuss the immunological rational, history and actual clinical experience with epicutaneous allergen-specific immunotherapy.

Co-administration of IL-1+IL-6+TNF-α with Mycobacterium tuberculosis infected macrophages vaccine induces better protective T cell memory than BCG

BCG has been administered globally for more than 75 years, yet tuberculosis (TB) continues to kill more than 2 million people annually. Further, BCG protects childhood TB but is quite inefficient in adults. This indicates that BCG fails to induce long-term protection. Hence there is a need to explore alternative vaccination strategies that can stimulate enduring T cell memory response. Dendritic cell based vaccination has attained extensive popularity following their success in various malignancies. In our previous study, we have established a novel and unique vaccination strategy against Mycobacterium tuberculosis (M. tb) and Salmonella typhimurium by utilizing infected macrophages (IM). In short-term experiments (30 days), substantial degree of protection was observed. However, remarkable difference was not observed in long-term studies (240 days) due to failure of the vaccine to generate long-lasting memory T cells. Hence, in the present study we employed T cell memory augmenting cytokines IL-1+IL-6+TNF-α and IL-7+IL-15 for the induction of the enhancement of long-term protection by the vaccine. We co-administered the M. tb infected macrophages vaccine with IL-1+IL-6+TNF-α (IM-1.6.α) and IL-7+IL-15 (IM-7.15). The mice were then rested for a reasonably large period (240 days) to study the bona fide T cell memory response before exposing them to aerosolized M. tb. IM-1.6.α but not IM-7.15 significantly improved memory T cell response against M. tb, as evidenced by recall responses of memory T cells, expansion of both central as well as effector memory CD4 and CD8 T cell pools, elicitation of mainly Th1 memory response, reduction in the mycobacterial load and alleviated lung pathology. Importantly, the protection induced by IM-1.6.α was significantly better than BCG. Thus, this study demonstrates that not only antigen-pulsed DCs can be successfully employed as vaccines against cancer and infectious diseases but also macrophages infected with M. tb can be utilized with great efficacy especially in protection against TB.

Insight into the immunobiology of human skin and functional specialization of skin dendritic cell subsets to innovate intradermal vaccination design

Dendritic cells (DC) are the key initiators and regulators of any immune response which determine the outcome of CD4(+) and CD8(+) T-cell responses. Multiple distinct DC subsets can be distinguished by location, phenotype, and function in the homeostatic and inflamed human skin. The function of steady-state cutaneous DCs or recruited inflammatory DCs is influenced by the surrounding cellular and extracellular skin microenvironment. The skin is an attractive site for vaccination given the extended local network of DCs and the easy access to the skin-draining lymph nodes to generate effector T cells and immunoglobulin-producing B cells for long-term protective immunity. In the context of intradermal vaccination we describe in this review the skin-associated immune system, the characteristics of the different skin DC subsets, the mechanism of antigen uptake and presentation, and how the properties of DCs can be manipulated. This knowledge is critical for the development of intradermal vaccine strategies and supports the concept of intradermal vaccination as a superior route to the conventional intramuscular or subcutaneous methods.

Dendritic cells in cancer immunotherapy

DC initiate and regulate T-cell immunity and are thus the key to optimization of all types of vaccines. Insights into DC biology offer many opportunities to enhance immunogenicity. In this Viewpoint, I discuss some recent developments and findings that are of immediate relevance for the clinical development of cancer vaccines. In addition, I emphasize my personal view that we should explore the potential of adoptively transferred DC (i.e. DC vaccination) as cancer vaccines by performing two-armed trials that address critical variables and by delivering antigens via mRNA-transfected DC.

Designing vaccines based on biology of human dendritic cell subsets

The effective vaccines developed against a variety of infectious agents, including polio, measles, and hepatitis B, represent major achievements in medicine. These vaccines, usually composed of microbial antigens, are often associated with an adjuvant that activates dendritic cells (DCs). Many infectious diseases are still in need of an effective vaccine including HIV, malaria, hepatitis C, and tuberculosis. In some cases, the induction of cellular rather than humoral responses may be more important because the goal is to control and eliminate the existing infection rather than to prevent it. Our increased understanding of the mechanisms of antigen presentation, particularly with the description of DC subsets with distinct functions, as well as their plasticity in responding to extrinsic signals, represent opportunities to develop novel vaccines. In addition, we foresee that this increased knowledge will permit us to design vaccines that will reprogram the immune system to intervene therapeutically in cancer, allergy, and autoimmunity.

New views on natural killer cell-based immunotherapy for melanoma treatment

Natural killer (NK) cell-based immunotherapies treat hematopoietic malignancies, but are less effective against solid tumors. Here, we review recent data on NK cell recognition of melanoma at various stages of the disease and propose a combinatorial strategy to exploit fully the potential of NK cells. Depending on the stage of melanoma progression, NK cell-based therapies could be combined with pharmacological and T cell-based immunotherapies, to: (i) prevent lymph node metastases by redistributing cytotoxic NK cells; (ii) boost NK cell activity using chemotherapy to upregulate activating ligands on tumor cells; and (iii) target visceral metastases by transfer of autologous or allogeneic NK cells.

Two-way traffic on the bridge from innate to adaptive immunity

Conventional wisdom suggests that information is usually transmitted from the dendritic cell (DC) to the T cell. In this issue, Schwarz and Schwarz demonstrate that UV-induced T regulatory cells (Tregs) can influence the biology of naïve DC. They report that IL-10-secreting Tregs prime DC to activate additional Tregs when injected into naïve mice. It may be possible to use DCs that have been "educated" by Tregs to induce immune tolerance in vivo.

Langerhans cells and dermal dendritic cells capture protein antigens in the skin: possible targets for vaccination through the skin

Dendritic cells capture and process antigen and present it to T lymphocytes in the lymphoid organs. Dendritic cells of the skin, including epidermal Langerhans cells, langerin(+) and langerin(negative) dermal dendritic cells are ideally positioned to take up pathogens that enter the body through the skin or vaccines that are administered into (intradermal) or onto (epicutaneous) the skin. The antigen uptake properties of skin dendritic cells have not thoroughly been studied yet. We therefore investigated the uptake of the fluorochrome-conjugated model antigen ovalbumin (OVA) by skin dendritic cells in the mouse. OVA was readily taken up by immature Langerhans cells both in situ and in cell suspensions. When offered to Langerhans cells in situ either by "bathing" skin explants in OVA-containing culture medium or by intradermal injection they retained the captured OVA for at least 2-3 days when migrating into the culture medium and, importantly, into the draining lymph nodes. Also langerin(+) and - to a larger extent - langerin(negative) skin dendritic cells took up and transported OVA to the lymph nodes. Interestingly, mature Langerhans cells were still capable of ingesting substantial amounts of OVA, indicating that predominantly receptor-mediated endocytosis is operative in these cells. Unlike macropinocytosis, this pathway of endocytosis is not shut down upon dendritic cell maturation. These observations indicate that in intradermal vaccination schemes, Langerhans cells from the epidermis are prominently involved. They were recently shown to possess the capacity to induce functional cytotoxic T lymphocytes. Furthermore, the potential to markedly enhance antigen uptake and processing by targeting antigen to c-type lectin receptors on Langerhans cells was also recently demonstrated. Our data provide a rationale and an incentive to explore in more detail antigen targeting to Langerhans cells with the aim of harnessing it for immunotherapy.

Adjuvanted influenza vaccine administered intradermally elicits robust long-term immune responses that confer protection from lethal challenge

Background

The respiratory illnesses caused by influenza virus can be dramatically reduced by vaccination. The current trivalent inactivated influenza vaccine is effective in eliciting systemic virus-specific antibodies sufficient to control viral replication. However, influenza protection generated after parenteral immunization could be improved by the induction of mucosal immune responses.

Methodology/Principal Findings

Transcutaneous immunization, a non-invasive vaccine delivery method, was used to investigate the quality, duration and effectiveness of the immune responses induced in the presence of inactivated influenza virus co-administered with retinoic acid or oleic acid. We observed an increased migration of dendritic cells to the draining lymph nodes after dermal vaccination. Here we demonstrate that this route of vaccine delivery in combination with certain immunomodulators can induce potent immune responses that result in long-term protective immunity. Additionally, mice vaccinated with inactivated virus in combination with retinoic acid show an enhanced sIgA antibody response, increased number of antibody secreting cells in the mucosal tissues, and protection from a higher influenza lethal dose.

Conclusions/Significance

The present study demonstrates that transdermal administration of inactivated virus in combination with immunomodulators stimulates dendritic cell migration, results in long-lived systemic and mucosal responses that confer effective protective immunity.

Targeting of antigens to skin dendritic cells: possibilities to enhance vaccine efficacy

Vaccinations in medicine are commonly administered through the skin. Therefore, the vaccine is immunologically processed by antigen-presenting cells of the skin. There is recent evidence that the clinically less often used intradermal route is effective; in cases even superior to the conventional subcutaneous or intramuscular route. Professional antigen-presenting cells of the skin comprise epidermal Langerhans cells (CD207/langerin(+)), dermal langerin(-) and dermal langerin(+) dendritic cells (DCs). In human skin, langerin(-) dermal DCs can be further subdivided on the basis of their reciprocal CD1a and CD14 expression. The relative contributions of these subsets to the generation of immunity or tolerance are still unclear. Langerhans cells in human skin seem to be specialized for induction of cytotoxic T lymphocytes. Likewise, mouse Langerhans cells are capable of cross-presentation and of protecting against experimental tumours. It is desirable to harness these properties for immunotherapy. A promising strategy to dramatically improve the outcome of vaccinations is 'antigen targeting'. Thereby, the vaccine is delivered directly and selectively to defined types of skin DCs. Targeting is achieved by means of coupling antigen to antibodies that recognize cell surface receptors on DCs. This approach is being widely explored. Little is known, however, about the events that take place in the skin and the DCs subsets involved therein. This topic will be discussed in this article.