Critical Role for Skin-Derived Migratory DCs and Langerhans Cells in TFH and GC Responses after Intradermal Immunization

Vaccinia Virus: Mechanisms Supporting Immune Evasion and Successful Long-Term Protective Immunity

Vaccinia virus is the most successful vaccine in human history and functions as a protective vaccine against smallpox and monkeypox, highlighting the importance of ongoing research into vaccinia due to its genetic similarity to other emergent poxviruses. Moreover, vaccinia's ability to accommodate large genetic insertions makes it promising for vaccine development and potential therapeutic applications, such as oncolytic agents. Thus, understanding how superior immunity is generated by vaccinia is crucial for designing other effective and safe vaccine strategies. During vaccinia inoculation by scarification, the skin serves as a primary site for the virus-host interaction, with various cell types playing distinct roles. During this process, hematopoietic cells undergo abortive infections, while non-hematopoietic cells support the full viral life cycle. This differential permissiveness to viral replication influences subsequent innate and adaptive immune responses. Dendritic cells (DCs), key immune sentinels in peripheral tissues such as skin, are pivotal in generating T cell memory during vaccinia immunization. DCs residing in the skin capture viral antigens and migrate to the draining lymph nodes (dLN), where they undergo maturation and present processed antigens to T cells. Notably, CD8+ T cells are particularly significant in viral clearance and the establishment of long-term protective immunity. Here, we will discuss vaccinia virus, its continued relevance to public health, and viral strategies permissive to immune escape. We will also discuss key events and populations leading to long-term protective immunity and remaining key gaps.

Microneedle patch with pure drug tips for delivery of liraglutide: pharmacokinetics in rats and minipigs

Transdermal delivery of peptide drugs is almost impossible with conventional penetration enhancers because of epidermal barrier function. Microneedle (MN) patches can bypass the epidermal barrier and have been developed for trans- and intradermal delivery of peptide drugs and vaccines. However, dissolving MN patches are limited by low drug loading capacities due to their small size and admixture of drug and water-soluble excipients. Furthermore, few in vivo pharmacokinetic studies, especially in large animals such as pigs, have been performed to assess post-application systemic drug exposure. Here, we developed a dissolving MN patch with pure liraglutide at the needle tips. The MN patch could load up to 2.21 ± 0.14 mg of liraglutide in a patch size of 0.9 cm2, which was nearly two orders of magnitude higher than that obtained with conventional MN patches of the same size. Raman imaging confirmed that liraglutide was localized at the MN tips. The MN had sufficient mechanical strength to penetrate the epidermis and could deliver up to 0.93 ± 0.04 mg of liraglutide into skin with a dosing variability of less than 6.8%. The MN patch delivery enabled faster absorption of liraglutide than that provided by subcutaneous (S.C.) injection, and achieved relative bioavailability of 69.8% and 46.3% compared to S.C. injection in rats and minipigs, respectively. The MN patch also exhibited similar patterns of anti-hyperglycemic effect in diabetic rats and individual variability in pharmacokinetic parameters as S.C. injection. The liraglutide MN application was well tolerated; no skin irritation was observed in minipigs except for mild erythema occurring within 4 h after once daily administration for 7 days at the same site. Our preclinical study suggests that MN patch with pure drug needle tips might offer a safe and effective alternative to S.C. injection for administration of liraglutide.

A mechanistic marker-based screening tool to predict clinical immunogenicity of biologics

BACKGROUND

The efficacy and safety of therapeutic proteins are undermined by immunogenicity driven by anti-drug antibodies. Immunogenicity risk assessment is critically necessary during drug development, but current methods lack predictive power and mechanistic insight into antigen uptake and processing leading to immune response. A key mechanistic step in T-cell-dependent immune responses is the migration of mature dendritic cells to T-cell areas of lymphoid compartments, and this phenomenon is most pronounced in the immune response toward subcutaneously delivered proteins.

METHODS

The migratory potential of monocyte-derived dendritic cells is proposed to be a mechanistic marker for immunogenicity screening. Following exposure to therapeutic protein in vitro, dendritic cells are analyzed for changes in activation markers (CD40 and IL-12) in combination with levels of the chemokine receptor CXCR4 to represent migratory potential. Then a transwell assay captures the intensity of dendritic cell migration in the presence of a gradient of therapeutic protein and chemokine ligands.

RESULTS

Here, we show that an increased ability of the therapeutic protein to induce dendritic cell migration along a gradient of chemokine CCL21 and CXCL12 predicts higher immunogenic potential. Expression of the chemokine receptor CXCR4 on human monocyte-derived dendritic cells, in combination with activation markers CD40 and IL-12, strongly correlates with clinical anti-drug antibody incidence.

CONCLUSIONS

Mechanistic understanding of processes driving immunogenicity led to the development of a predictive tool for immunogenicity risk assessment of therapeutic proteins. These predictive markers could be adapted for immunogenicity screening of other biological modalities.

Comparative Evaluation of Intradermal vis-à-vis Intramuscular Pre-Exposure Prophylactic Vaccination against Rabies in Cattle

Rabies is a progressively fatal viral disease affecting a wide variety of warm-blooded animals and human beings. With cattle being major part of Indian livestock population, rabies can result in significant financial losses. Immunization of livestock vulnerable to exposure is the best way to control rabies. The present study was undertaken to investigate the efficacy of a rabies pre-exposure prophylactic vaccine administered through different routes and to sequentially monitor the levels of rabies virus-neutralizing antibody (RVNA) titers in cattle. Thirty cattle were divided into five groups of six animals each. Group I and III animals were immunized with 1 mL and 0.2 mL of rabies vaccine through intramuscular (IM) and intradermal (ID) routes, respectively, on day 0, with a booster dose on day 21; Group II and IV animals were immunized with 1 mL and 0.2 mL of rabies vaccine, respectively, without the booster dose; unvaccinated animals served as a control (Group V). Serum samples were collected on days 0, 14, 28, and 90 to estimate RVNA titers using the rapid fluorescent focus inhibition test (RFFIT). The titers were above an adequate level (≥0.5 IU/mL) on day 14 and maintained up to 90 days in all animals administered the rabies vaccine through the IM and ID route with or without a booster dose. The study indicated that both routes of vaccination are safe and effective in providing protection against rabies. Hence, both routes can be considered for pre-exposure prophylaxis. However, the ID route proved to be more economical due to its dose-sparing effect.

The immunological effects of intradermal particle-based vaccine delivery using a novel microinjection needle studied in a human skin explant model

For intradermal (ID) immunisation, novel needle-based delivery systems have been proposed as a better alternative to the Mantoux method. However, the penetration depth of needles in the human skin and its effect on immune cells residing in the different layers of the skin has not been analyzed. A novel and user-friendly silicon microinjection needle (Bella-mu^TM) has been developed, which allows for a perpendicular injection due to its short needle length (1.4-1.8 mm) and ultrashort bevel. We aimed to characterize the performance of this microinjection needle in the context of the delivery of a particle-based outer membrane vesicle (OMV) vaccine using an ex vivo human skin explant model. We compared the needles of 1.4 and 1.8 mm with the conventional Mantoux method to investigate the depth of vaccine injection and the capacity of the skin antigen-presenting cell (APC) to phagocytose the OMVs. The 1.4 mm needle deposited the antigen closer to the epidermis than the 1.8 mm needle or the Mantoux method. Consequently, activation of epidermal Langerhans cells was significantly higher as determined by dendrite shortening. We found that five different subsets of dermal APCs are able to phagocytose the OMV vaccine, irrespective of the device or injection method. ID delivery using the 1.4 mm needle of a OMV-based vaccine allowed epidermal and dermal APC targeting, with superior activation of Langerhans cells. This study indicates that the use of a microinjection needle improves the delivery of vaccines in the human skin.

Skin-Based Vaccination: A Systematic Mapping Review of the Types of Vaccines and Methods Used and Immunity and Protection Elicited in Pigs

The advantages of skin-based vaccination include induction of strong immunity, dose-sparing, and ease of administration. Several technologies for skin-based immunisation in humans are being developed to maximise these key advantages. This route is more conventionally used in veterinary medicine. Skin-based vaccination of pigs is of high relevance due to their anatomical, physiological, and immunological similarities to humans, as well as being a source of zoonotic diseases and their livestock value. We conducted a systematic mapping review, focusing on vaccine-induced immunity and safety after the skin immunisation of pigs. Veterinary vaccines, specifically anti-viral vaccines, predominated in the literature. The safe and potent skin administration to pigs of adjuvanted vaccines, particularly emulsions, are frequently documented. Multiple methods of skin immunisation exist; however, there is a lack of consistent terminology and accurate descriptions of the route and device. Antibody responses, compared to other immune correlates, are most frequently reported. There is a lack of research on the underlying mechanisms of action and breadth of responses. Nevertheless, encouraging results, both in safety and immunogenicity, were observed after skin vaccination that were often comparable to or superior the intramuscular route. Further research in this area will underlie the development of enhanced skin vaccine strategies for pigs, other animals and humans.

Comparative immunogenicity analysis of intradermal versus intramuscular immunization with a recombinant human adenovirus type 5 vaccine against Ebola virus

The proper route for vaccine delivery plays an important role in activating a robust immune response. Several viral vector-based vaccines against Ebola disease administered intramuscularly have been found to have excellent immunogenicity and protectiveness. In this study, we evaluated different vaccine routes for Ad5-EBOV delivery by comparing humoral and cellular responses, germinal center reactions, dendritic cell activation and antigen expression. Mice injected intramuscularly with the vaccine exhibited an advantage in antigen expression, leading to more robust germinal center and humoral responses, while intradermal injection recruited more migrating DCs and induced a more polyfunctional cellular response. Our study provides more data for future use of viral vector-based vaccines.

Antigen transfer and its effect on vaccine-induced immune amplification and tolerance

Antigen transfer refers to the process of intercellular information exchange, where antigenic components including nucleic acids, antigen proteins/peptides and peptide-major histocompatibility complexes (p-MHCs) are transmitted from donor cells to recipient cells at the thymus, secondary lymphoid organs (SLOs), intestine, allergic sites, allografts, pathological lesions and vaccine injection sites via trogocytosis, gap junctions, tunnel nanotubes (TNTs), or extracellular vesicles (EVs). In the context of vaccine inoculation, antigen transfer is manipulated by the vaccine type and administration route, which consequently influences, even alters the immunological outcome, i.e., immune amplification and tolerance. Mainly focused on dendritic cells (DCs)-based antigen receptors, this review systematically introduces the biological process, molecular basis and clinical manifestation of antigen transfer.

Refining the DC-targeting vaccination for preventing emerging infectious diseases

The development of safe, long-term, effective vaccines is still a challenge for many infectious diseases. Thus, the search of new vaccine strategies and production platforms that allow rapidly and effectively responding against emerging or reemerging pathogens has become a priority in the last years. Targeting the antigens directly to dendritic cells (DCs) has emerged as a new approach to enhance the immune response after vaccination. This strategy is based on the fusion of the antigens of choice to monoclonal antibodies directed against specific DC surface receptors such as CD40. Since time is essential, in silico approaches are of high interest to select the most immunogenic and conserved epitopes to improve the T- and B-cells responses. The purpose of this review is to present the advances in DC vaccination, with special focus on DC targeting vaccines and epitope mapping strategies and provide a new framework for improving vaccine responses against infectious diseases.

mTORC1 signaling in antigen-presenting cells of the skin restrains CD8+ T cell priming

How mechanistic target of rapamycin complex 1 (mTORC1), a key regulator of cellular metabolism, affects dendritic cell (DC) metabolism and T cell-priming capacity has primarily been investigated in vitro, but how mTORC1 regulates this in vivo remains poorly defined. Here, using mice deficient for mTORC1 component raptor in DCs, we find that loss of mTORC1 negatively affects glycolytic and fatty acid metabolism and maturation of conventional DCs, particularly cDC1s. Nonetheless, antigen-specific CD8⁺ T cell responses to infection are not compromised and are even enhanced following skin immunization. This is associated with increased activation of Langerhans cells and a subpopulation of EpCAM-expressing cDC1s, of which the latter show an increased physical interaction with CD8⁺ T cells in situ. Together, this work reveals that mTORC1 limits CD8⁺ T cell priming in vivo by differentially orchestrating the metabolism and immunogenicity of distinct antigen-presenting cell subsets, which may have implications for clinical use of mTOR inhibitors.

Information flow in the spatiotemporal organization of immune responses

Immune responses must be rapid, tightly orchestrated, and tailored to the encountered stimulus. Lymphatic vessels facilitate this process by continuously collecting immunological information (ie, antigens, immune cells, and soluble mediators) about the current state of peripheral tissues, and transporting these via the lymph across the lymphatic system. Lymph nodes (LNs), which are critical meeting points for innate and adaptive immune cells, are strategically located along the lymphatic network to intercept this information. Within LNs, immune cells are spatially organized, allowing them to efficiently respond to information delivered by the lymph, and to either promote immune homeostasis or mount protective immune responses. These responses involve the activation and functional cooperation of multiple distinct cell types and are tailored to the specific inflammatory conditions. The natural patterns of lymph flow can also generate spatial gradients of antigens and agonists within draining LNs, which can in turn further regulate innate cell function and localization, as well as the downstream generation of adaptive immunity. In this review, we explore how information transmitted by the lymph shapes the spatiotemporal organization of innate and adaptive immune responses in LNs, with particular focus on steady state and Type-I vs. Type-II inflammation.

Mechanisms underpinning poor antibody responses to vaccines in ageing

Vaccines are a highly effective intervention for conferring protection against infections and reducing the associated morbidity and mortality in vaccinated individuals. However, ageing is often associated with a functional decline in the immune system that results in poor antibody production in older individuals after vaccination. A key contributing factor of this age-related decline in vaccine efficacy is the reduced size and function of the germinal centre (GC) response. GCs are specialised microstructures where B cells undergo affinity maturation and diversification of their antibody genes, before differentiating into long-lived antibody-secreting plasma cells and memory B cells. The GC response requires the coordinated interaction of many different cell types, including B cells, T follicular helper (Tfh) cells, T follicular regulatory (Tfr) cells and stromal cell subsets like follicular dendritic cells (FDCs). This review discusses how ageing affects different components of the GC reaction that contribute to its limited output and ultimately impaired antibody responses in older individuals after vaccination. An understanding of the mechanisms underpinning the age-related decline in the GC response is crucial in informing strategies to improve vaccine efficacy and extend the healthy lifespan amongst older people.

Langerhans cells and cDC1s play redundant roles in mRNA-LNP induced protective anti-influenza and anti-SARS-CoV-2 immune responses

Nucleoside modified mRNA combined with Acuitas Therapeutics' lipid nanoparticles (LNPs) has been shown to support robust humoral immune responses in many preclinical animal vaccine studies and later in humans with the SARS-CoV-2 vaccination. We recently showed that this platform is highly inflammatory due to the LNPs' ionizable lipid component. The inflammatory property is key to support the development of potent humoral immune responses. However, the mechanism by which this platform drives T follicular helper (Tfh) cells and humoral immune responses remains unknown. Here we show that lack of Langerhans cells or cDC1s neither significantly affected the induction of PR8 HA and SARS-CoV-2 RBD-specific Tfh cells and humoral immune responses, nor susceptibility towards the lethal challenge of influenza and SARS-CoV-2. However, the combined deletion of these two DC subsets led to a significant decrease in the induction of PR8 HA and SARS-CoV-2 RBD-specific Tfh cell and humoral immune responses. Despite these observed defects, these mice remained protected from lethal influenza and SARS-CoV-2 challenges. We further found that IL-6, unlike neutrophils, was required to generate normal Tfh cells and antibody responses, but not for protection from influenza challenge. In summary, here we bring evidence that the mRNA-LNP platform can support the induction of protective immune responses in the absence of certain innate immune cells and cytokines.

Langerhans cells and cDC1s play redundant roles in mRNA-LNP induced protective anti-influenza and anti-SARS-CoV-2 responses

Nucleoside modified mRNA combined with Acuitas Therapeutics' lipid nanoparticles (LNP) have been shown to support robust humoral immune responses in many preclinical animal vaccine studies and later in humans with the SARS-CoV-2 vaccination. We recently showed that this platform is highly inflammatory due to the LNPs' ionizable lipid component. The inflammatory property is key to support the development of potent humoral immune responses. However, the mechanism by which this platform drives T follicular helper cells (Tfh) and humoral immune responses remains unknown. Here we show that lack of Langerhans cells or cDC1s neither significantly affected the induction of PR8 HA and SARS-CoV-2 RBD-specific Tfh cells and humoral immune responses, nor susceptibility towards the lethal challenge of influenza and SARS-CoV-2. However, the combined deletion of these two DC subsets led to a significant decrease in the induction of PR8 HA and SARS-CoV-2 RBD-specific Tfh cell and humoral immune responses. Despite these observed defects, the still high antibody titers were sufficient to confer protection towards lethal viral challenges. We further found that IL-6, but not neutrophils, was required to generate Tfh cells and antibody responses. In summary, here we bring evidence that the mRNA-LNP platform can support protective adaptive immune responses in the absence of specific DC subsets through an IL-6 dependent and neutrophil independent mechanism.

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.

Recent Progress in Dendritic Cell-Based Cancer Immunotherapy

Simple Summary

Cancer immunotherapy has now attracted much attention because of the recent success of immune checkpoint inhibitors. However, they are only beneficial in a limited fraction of patients most probably due to lack of sufficient CD8+ cytotoxic T-lymphocytes against tumor antigens in the host. In this regard, dendritic cells are useful tools to induce host immune responses against exogenous antigens. In particular, recently characterized cross-presenting dendritic cells are capable of inducing CD8+ cytotoxic T-lymphocytes against exogenous antigens such as tumor antigens and uniquely express the chemokine receptor XCR1. Here we focus on the recent progress in DC-based cancer vaccines and especially the use of the XCR1 and its ligand XCL1 axis for the targeted delivery of cancer vaccines to cross-presenting dendritic cells.

Abstract

Cancer immunotherapy aims to treat cancer by enhancing cancer-specific host immune responses. Recently, cancer immunotherapy has been attracting much attention because of the successful clinical application of immune checkpoint inhibitors targeting the CTLA-4 and PD-1/PD-L1 pathways. However, although highly effective in some patients, immune checkpoint inhibitors are beneficial only in a limited fraction of patients, possibly because of the lack of enough cancer-specific immune cells, especially CD8⁺ cytotoxic T-lymphocytes (CTLs), in the host. On the other hand, studies on cancer vaccines, especially DC-based ones, have made significant progress in recent years. In particular, the identification and characterization of cross-presenting DCs have greatly advanced the strategy for the development of effective DC-based vaccines. In this review, we first summarize the surface markers and functional properties of the five major DC subsets. We then describe new approaches to induce antigen-specific CTLs by targeted delivery of antigens to cross-presenting DCs. In this context, the chemokine receptor XCR1 and its ligand XCL1, being selectively expressed by cross-presenting DCs and mainly produced by activated CD8⁺ T cells, respectively, provide highly promising molecular tools for this purpose. In the near future, CTL-inducing DC-based cancer vaccines may provide a new breakthrough in cancer immunotherapy alone or in combination with immune checkpoint inhibitors.

Dual function of Langerhans cells in skin TSLP-promoted TFH differentiation in mouse atopic dermatitis

BACKGROUND

Atopic dermatitis (AD) is among the most common chronic inflammatory skin diseases, usually occurring early in life, and often preceding other atopic diseases such as asthma. TH2 has been believed to play a crucial role in cellular and humoral response in AD, but accumulating evidence has shown that follicular helper T cell (TFH), a critical player in humoral immunity, is associated with disease severity and plays an important role in AD pathogenesis.

OBJECTIVES

This study aimed at investigating how TFHs are generated during the pathogenesis of AD, particularly what is the role of keratinocyte-derived cytokine TSLP and Langerhans cells (LCs).

METHODS

Two experimental AD mouse models were employed: (1) triggered by the overproduction of TSLP through topical application of MC903, and (2) induced by epicutaneous allergen ovalbumin (OVA) sensitization.

RESULTS

This study demonstrated that the development of TFHs and germinal center (GC) response were crucially dependent on TSLP in both the MC903 model and the OVA sensitization model. Moreover, we found that LCs promoted TFH differentiation and GC response in the MC903 model, and the depletion of Langerin+ dendritic cells (DCs) or selective depletion of LCs diminished the TFH/GC response. By contrast, in the model with OVA sensitization, LCs inhibited TFH/GC response and suppressed TH2 skin inflammation and the subsequent asthma. Transcriptomic analysis of Langerin+ and Langerin- migratory DCs revealed that Langerin+ DCs became activated in the MC903 model, whereas these cells remained inactivated in OVA sensitization model.

CONCLUSIONS

Together, these studies revealed a dual functionality of LCs in TSLP-promoted TFH and TH2 differentiation in AD pathogenesis.

Route of Vaccine Administration Alters Antigen Trafficking but Not Innate or Adaptive Immunity

Although intramuscular (i.m.) administration is the most commonly used route for licensed vaccines, subcutaneous (s.c.) delivery is being explored for several new vaccines under development. Here, we use rhesus macaques, physiologically relevant to humans, to identify the anatomical compartments and early immune processes engaged in the response to immunization via the two routes. Administration of fluorescently labeled HIV-1 envelope glycoprotein trimers displayed on liposomes enables visualization of targeted cells and tissues. Both s.c. and i.m. routes induce efficient immune cell infiltration, activation, and antigen uptake, functions that are tightly restricted to the skin and muscle, respectively. Antigen is also transported to different lymph nodes depending on route. However, these early differences do not translate into significant differences in the magnitude or quality of antigen-specific cellular and humoral responses over time. Thus, although some distinct immunological differences are noted, the choice of route may instead be motivated by clinical practicality.

Dendritic Cell Regulation of T Helper Cells

As the professional antigen-presenting cells of the immune system, dendritic cells (DCs) sense the microenvironment and shape the ensuing adaptive immune response. DCs can induce both immune activation and immune tolerance according to the peripheral cues. Recent work has established that DCs comprise several phenotypically and functionally heterogeneous subsets that differentially regulate T lymphocyte differentiation. This review summarizes both mouse and human DC subset phenotypes, development, diversification, and function. We focus on advances in our understanding of how different DC subsets regulate distinct CD4⁺ T helper (Th) cell differentiation outcomes, including Th1, Th2, Th17, T follicular helper, and T regulatory cells. We review DC subset intrinsic properties, local tissue microenvironments, and other immune cells that together determine Th cell differentiation during homeostasis and inflammation.

Innate cell microenvironments in lymph nodes shape the generation of T cell responses during type I inflammation

Microanatomical organization of innate immune cells within lymph nodes (LNs) is critical for the generation of adaptive responses. In particular, steady-state LN-resident dendritic cells (Res cDCs) are strategically localized to intercept lymph-draining antigens. Whether myeloid cell organization changes during inflammation and how that might affect the generation of immune responses are unknown. Here, we report that during type I, but not type II, inflammation after adjuvant immunization or viral infection, antigen-presenting Res cDCs undergo CCR7-dependent intranodal repositioning from the LN periphery into the T cell zone (TZ) to elicit T cell priming. Concurrently, inflammatory monocytes infiltrate the LNs via local blood vessels, enter the TZ, and cooperate with Res cDCs by providing polarizing cytokines to optimize T cell effector differentiation. Monocyte infiltration is nonuniform across LNs, generating distinct microenvironments with varied local innate cell composition. These spatial microdomains are associated with divergent early T cell effector programming, indicating that innate microenvironments within LNs play a critical role in regulating the quality and heterogeneity of T cell responses. Together, our findings reveal that dynamic modulation of innate cell microenvironments during type I inflammation leads to optimized generation of adaptive immune responses to vaccines and infections.

Immunogenicity Challenges Associated with Subcutaneous Delivery of Therapeutic Proteins

The subcutaneous route of administration has provided convenient and non-inferior delivery of therapeutic proteins compared to intravenous infusion, but there is potential for enhanced immunogenicity toward subcutaneously administered proteins in a subset of patients. Unwanted anti-drug antibody response toward proteins or monoclonal antibodies upon repeated administration is shown to impact the pharmacokinetics and efficacy of multiple biologics. Unique immunogenicity challenges of the subcutaneous route have been realized through various preclinical and clinical examples, although subcutaneous delivery has often demonstrated comparable immunogenicity to intravenous administration. Beyond route of administration as a treatment-related factor of immunogenicity, certain product-related risk factors are particularly relevant to subcutaneously administered proteins. This review attempts to provide an overview of the mechanism of immune response toward proteins administered subcutaneously (subcutaneous proteins) and comments on product-related risk factors related to protein structure and stability, dosage form, and aggregation. A two-wave mechanism of antigen presentation in the immune response toward subcutaneous proteins is described, and interaction with dynamic antigen-presenting cells possessing high antigen processing efficiency and migratory activity may drive immunogenicity. Mitigation strategies for immunogenicity are discussed, including those in general use clinically and those currently in development. Mechanistic insights along with consideration of risk factors involved inspire theoretical strategies to provide antigen-specific, long-lasting effects for maintaining the safety and efficacy of therapeutic proteins.

Effective and Safe Stimulation of Humoral and Cell-Mediated Immunity by Intradermal Immunization with a Cyclic Dinucleotide/Nanoparticle Combination Adjuvant

Intradermal (ID) immunization is an attractive route of vaccination because it targets tissue rich in dendritic cells, has dose-sparing potential, and allows needle-free delivery. However, few adjuvants are effective, nonreactogenic, and compatible with needle-free delivery devices. In this study, we demonstrate that a combination adjuvant composed of cyclic-di-AMP (cdAMP) and the plant-derived nanoparticle adjuvant Nano-11 significantly enhanced the immune response to ID-injected vaccines in mice and pigs with minimal local reaction at the injection site. The cdAMP/Nano-11 combination adjuvant increased Ag uptake by lymph node-resident and migratory skin dendritic cell subpopulations, including Langerhans cells. ID immunization with cdAMP/Nano-11 expanded the population of germinal center B cells and follicular helper T cells in the draining lymph node and Ag-specific Th1 and Th17 cells in the spleen. It elicited an enhanced immune response with a significant increase of IgG1 and IgG2a responses in mice at a reduced dose compared with i.m. immunization. An increased IgG response was observed following needle-free ID immunization of pigs. Nano-11 and cdAMP demonstrated a strong synergistic interaction, as shown in the activation of mouse, human, and porcine APC, with increased expression of costimulatory molecules and secretion of TNF and IL-1β. The combination adjuvant induced robust activation of both NF-κB and IFN regulatory factor signaling pathways and the NLRP3 inflammasome. We conclude that the combination of Nano-11 and cdAMP is a promising adjuvant for ID delivery of vaccines that supports a balanced immune response.

The role of Langerhans cells in epidermal homeostasis and pathogenesis of psoriasis

The skin is the main barrier between the human body and the outside world, which not only plays the role of a physical barrier but also functions as the first line of defence of immunology. Langerhans cells (LCs), as dendritic cells (DC) that play an important role in the immune system, are mainly distributed in the epidermis. This review focuses on the role of these epidermal LCs in regulating skin threats (such as microorganisms, ultraviolet radiation and allergens), especially psoriasis. Since human and mouse skin DC subsets share common ontogenetic characteristics, we can further explore the role of LCs in psoriatic inflammation.

Harnessing the Complete Repertoire of Conventional Dendritic Cell Functions for Cancer Immunotherapy

The onset of checkpoint inhibition revolutionized the treatment of cancer. However, studies from the last decade suggested that the sole enhancement of T cell functionality might not suffice to fight malignancies in all individuals. Dendritic cells (DCs) are not only part of the innate immune system, but also generals of adaptive immunity and they orchestrate the de novo induction of tolerogenic and immunogenic T cell responses. Thus, combinatorial approaches addressing DCs and T cells in parallel represent an attractive strategy to achieve higher response rates across patients. However, this requires profound knowledge about the dynamic interplay of DCs, T cells, other immune and tumor cells. Here, we summarize the DC subsets present in mice and men and highlight conserved and divergent characteristics between different subsets and species. Thereby, we supply a resource of the molecular players involved in key functional features of DCs ranging from their sentinel function, the translation of the sensed environment at the DC:T cell interface to the resulting specialized T cell effector modules, as well as the influence of the tumor microenvironment on the DC function. As of today, mostly monocyte derived dendritic cells (moDCs) are used in autologous cell therapies after tumor antigen loading. While showing encouraging results in a fraction of patients, the overall clinical response rate is still not optimal. By disentangling the general aspects of DC biology, we provide rationales for the design of next generation DC vaccines enabling to exploit and manipulate the described pathways for the purpose of cancer immunotherapy in vivo. Finally, we discuss how DC-based vaccines might synergize with checkpoint inhibition in the treatment of malignant diseases.

Antigen presentation by dendritic cells and their instruction of CD4+ T helper cell responses

Dendritic cells are powerful antigen-presenting cells that are essential for the priming of T cell responses. In addition to providing T-cell-receptor ligands and co-stimulatory molecules for naive T cell activation and expansion, dendritic cells are thought to also provide signals for the differentiation of CD4+ T cells into effector T cell populations. The mechanisms by which dendritic cells are able to adapt and respond to the great variety of infectious stimuli they are confronted with, and prime an appropriate CD4+ T cell response, are only partly understood. It is known that in the steady-state dendritic cells are highly heterogenous both in phenotype and transcriptional profile, and that this variability is dependent on developmental lineage, maturation stage, and the tissue environment in which dendritic cells are located. Exposure to infectious agents interfaces with this pre-existing heterogeneity by providing ligands for pattern-recognition and toll-like receptors that are variably expressed on different dendritic cell subsets, and elicit production of cytokines and chemokines to support innate cell activation and drive T cell differentiation. Here we review current information on dendritic cell biology, their heterogeneity, and the properties of different dendritic cell subsets. We then consider the signals required for the development of different types of Th immune responses, and the cellular and molecular evidence implicating different subsets of dendritic cells in providing such signals. We outline how dendritic cell subsets tailor their response according to the infectious agent, and how such transcriptional plasticity enables them to drive different types of immune responses.

New GMP manufacturing processes to obtain thermostable HIV-1 gp41 virosomes under solid forms for various mucosal vaccination routes

The main objective of the MACIVIVA European consortium was to develop new Good Manufacturing Practice pilot lines for manufacturing thermostable vaccines with stabilized antigens on influenza virosomes as enveloped virus-like particles. The HIV-1 gp41-derived antigens anchored in the virosome membrane, along with the adjuvant 3M-052 (TLR7/8 agonist) on the same particle, served as a candidate vaccine for the proof of concept for establishing manufacturing processes, which can be directly applied or adapted to other virosomal vaccines or lipid-based particles. Heat spray-dried powders suitable for nasal or oral delivery, and freeze-dried sublingual tablets were successfully developed as solid dosage forms for mucosal vaccination. The antigenic properties of vaccinal antigens with key gp41 epitopes were maintained, preserving the original immunogenicity of the starting liquid form, and also when solid forms were exposed to high temperature (40 °C) for up to 3 months, with minimal antigen and adjuvant content variation. Virosomes reconstituted from the powder forms remained as free particles with similar size, virosome uptake by antigen-presenting cells in vitro was comparable to virosomes from the liquid form, and the presence of excipients specific to each solid form did not prevent virosome transport to the draining lymph nodes of immunized mice. Virosome integrity was also preserved during exposure to <−15 °C, mimicking accidental freezing conditions. These “ready to use and all-in-one” thermostable needle-free virosomal HIV-1 mucosal vaccines offer the advantage of simplified logistics with a lower dependence on the cold chain during shipments and distribution.

Rejuvenating conventional dendritic cells and T follicular helper cell formation after vaccination

Germinal centres (GCs) are T follicular helper cell (Tfh)-dependent structures that form in response to vaccination, producing long-lived antibody secreting plasma cells and memory B cells that protect against subsequent infection. With advancing age the GC and Tfh cell response declines, resulting in impaired humoral immunity. We sought to discover what underpins the poor Tfh cell response in ageing and whether it is possible to correct it. Here, we demonstrate that older people and aged mice have impaired Tfh cell differentiation upon vaccination. This deficit is preceded by poor activation of conventional dendritic cells type 2 (cDC2) due to reduced type 1 interferon signalling. Importantly, the Tfh and cDC2 cell response can be boosted in aged mice by treatment with a TLR7 agonist. This demonstrates that age-associated defects in the cDC2 and Tfh cell response are not irreversible and can be enhanced to improve vaccine responses in older individuals.

Prédire la réponse à la vaccination contre la grippe

La vaccination est l’un des progrès majeurs de la médecine moderne. Mais afin d’améliorer l’efficacité des vaccins existants et d’en élaborer de nouveaux, nous devons mieux connaître les mécanismes d’action à l’origine de l’immunité protectrice et les stratégies vaccinales permettant d’induire une défense durable. La voie cutanée est une stratégie de vaccination importante, en raison de la richesse qu’elle présente en cellules de l’immunité innée qui ont un rôle clé dans la qualité, l’intensité et la persistance des réponses adaptatives qu’elles induisent. L’intégration des données biologiques obtenues au cours d’un essai clinique de vaccination antigrippale nous donne un aperçu de l’impact de la voie d’immunisation et de la signature innée sur la qualité des réponses immunitaires.

Mechanisms of innate events during skin reaction following intradermal injection of seasonal influenza vaccine

The skin plays a crucial role in host defences against microbial attack and the innate cells must provide the immune system with sufficient information to organize these defences. This unique feature makes the skin a promising site for vaccine administration. Although cellular innate immune events during vaccination have been widely studied, initial events remain poorly understood. Our aim is to determine molecular biomarkers of skin innate reaction after intradermal (i.d.) immunization. Using an ex vivo human explant model from healthy donors, we investigated by NanoLC-MS/MS analysis and MALDI-MSI imaging, to detect innate molecular events (lipids, metabolites, proteins) few hours after i.d. administration of seasonal trivalent influenza vaccine (TIV). This multimodel approach allowed to identify early molecules differentially expressed in dermal and epidermal layers at 4 and 18 h after TIV immunization compared with control PBS. In the dermis, the most relevant network of proteins upregulated were related to cell-to-cell signalling and cell trafficking. The molecular signatures detected were associated with chemokines such as CXCL8, a chemoattractant of neutrophils. In the epidermis, the most relevant networks were associated with activation of antigen-presenting cells and related to CXCL10. Our study proposes a novel step-forward approach to identify biomarkers of skin innate reaction. SIGNIFICANCE: To our knowledge, there is no study analyzing innate molecular reaction to vaccines at the site of skin immunization. What is known on skin reaction is based on macroscopic (erythema, redness…), microscopic (epidermal and dermal tissues) and cellular events (inflammatory cell infiltrate). Therefore, we propose a multimodal approach to analyze molecular events at the site of vaccine injection on skin tissue. We identified early molecular networks involved biological functions such cell migration, cell-to-cell interaction and antigen presentation, validated by chemokine expression, in the epidermis and dermis, then could be used as early indicator of success in immunization.

CXCR5-negative natural killer cells ameliorate experimental autoimmune myasthenia gravis by suppressing follicular helper T cells

Background

Recent studies have demonstrated that natural killer (NK) cells can modulate other immune components and are involved in the development or progression of several autoimmune diseases. However, the roles and mechanisms of NK cells in regulating experimental autoimmune myasthenia gravis (EAMG) remained to be illustrated.

Methods

To address the function of NK cells in experimental autoimmune myasthenia gravis in vivo, EAMG rats were adoptively transferred with splenic NK cells. The serum antibodies, and splenic follicular helper T (Tfh) cells and germinal center B cells were determined by ELISA and flow cytometry. The roles of NK cells in regulating Tfh cells were further verified in vitro by co-culturing splenocytes or isolated T cells with NK cells. Moreover, the phenotype, localization, and function differences between different NK cell subtypes were determined by flow cytometry, immunofluorescence, and ex vivo co-culturation.

Results

In this study, we found that adoptive transfer of NK cells ameliorated EAMG symptoms by suppressing Tfh cells and germinal center B cells. Ex vivo studies indicated NK cells inhibited CD4⁺ T cells and Tfh cells by inducing the apoptosis of T cells. More importantly, NK cells could be divided into CXCR5^- and CXCR5⁺ NK subtypes according to the expression of CXCR5 molecular. Compared with CXCR5^- NK cells, which were mainly localized outside B cell zone, CXCR5⁺ NK were concentrated in the B cell zone and exhibited higher expression levels of IL-17 and ICOS, and lower expression level of CD27. Ex vivo studies indicated it was CXCR5^- NK cells not CXCR5⁺ NK cells that suppressed CD4⁺ T cells and Tfh cells. Further analysis revealed that, compared with CXCR5^- NK cells, CXCR5⁺ NK cells enhanced the ICOS expression of Tfh cells.

Conclusions

These findings highlight the different roles of CXCR5^- NK cells and CXCR5⁺ NK cells. It was CXCR5^- NK cells but not CXCR5⁺ NK cells that suppressed Tfh cells and inhibited the autoimmune response in EAMG models.

Dendritic cell subsets in T cell programming: location dictates function

Dendritic cells (DCs) can be viewed as translators between innate and adaptive immunity. They integrate signals derived from tissue infection or damage and present processed antigen from these sites to naive T cells in secondary lymphoid organs while also providing multiple soluble and surface-bound signals that help to guide T cell differentiation. DC-mediated tailoring of the appropriate T cell programme ensures a proper cascade of immune responses that adequately targets the insult. Recent advances in our understanding of the different types of DC subsets along with the cellular organization and orchestration of DC and lymphocyte positioning in secondary lymphoid organs over time has led to a clearer understanding of how the nature of the T cell response is shaped. This Review discusses how geographical organization and ordered sequences of cellular interactions in lymph nodes and the spleen regulate immunity.

Transcriptional control of dendritic cell development and functions

Dendritic cells (DCs) are major regulators of adaptive immunity, as they are not only capable to induce efficient immune responses, but are also crucial to maintain peripheral tolerance and thereby inhibit autoimmune reactions. DCs bridge the innate and the adaptive immune system by presenting peptides of self and foreign antigens as peptide MHC complexes to T cells. These properties render DCs as interesting target cells for immunomodulatory therapies in cancer, but also autoimmune diseases. Several subsets of DCs with special properties and functions have been described. Recent achievements in understanding transcriptional programs on single cell level, together with the generation of new murine models targeting specific DC subsets, advanced our current understanding of DC development and function. Thus, DCs arise from precursor cells in the bone marrow with distinct progenitor cell populations splitting the monocyte populations and macrophage populations from the DC lineage, which upon lineage commitment can be separated into conventional cDC1, cDC2, and plasmacytoid DCs (pDCs). The DC populations harbor intrinsic programs enabling them to react for specific pathogens in dependency on the DC subset, and thereby orchestrate T cell immune responses. Similarities, but also varieties, between human and murine DC subpopulations are challenging, and will require further investigation of human specimens under consideration of the influence of the tissue micromilieu and DC subset localization in the future.

Dendritic cell subsets and locations

Dendritic cells (DCs) are a unique class of immune cells that act as a bridge between innate and adaptive immunity. The discovery of DCs by Cohen and Steinman in 1973 laid the foundation for DC biology, and the advances in the field identified different versions of DCs with unique properties and functions. DCs originate from hematopoietic stem cells, and their differentiation is modulated by Flt3L. They are professional antigen-presenting cells that patrol the environmental interphase, sites of infection, or infiltrate pathological tissues looking for antigens that can be used to activate effector cells. DCs are critical for the initiation of the cellular and humoral immune response and protection from infectious diseases or tumors. DCs can take up antigens using specialized surface receptors such as endocytosis receptors, phagocytosis receptors, and C type lectin receptors. Moreover, DCs are equipped with an array of extracellular and intracellular pattern recognition receptors for sensing different danger signals. Upon sensing the danger signals, DCs get activated, upregulate costimulatory molecules, produce various cytokines and chemokines, take up antigen and process it and migrate to lymph nodes where they present antigens to both CD8 and CD4 T cells. DCs are classified into different subsets based on an integrated approach considering their surface phenotype, expression of unique and conserved molecules, ontogeny, and functions. They can be broadly classified as conventional DCs consisting of two subsets (DC1 and DC2), plasmacytoid DCs, inflammatory DCs, and Langerhans cells.

Peptide-Based Vaccination for Antibody Responses Against HIV

HIV-1 is responsible for a global pandemic of 35 million people and continues to spread at a rate of >2 million new infections/year. It is widely acknowledged that a protective vaccine would be the most effective means to reduce HIV-1 spread and ultimately eliminate the pandemic, whereas a therapeutic vaccine might help to mitigate the clinical course of the disease and to contribute to virus eradication strategies. However, despite more than 30 years of research, we do not have a vaccine capable of protecting against HIV-1 infection or impacting on disease progression. This, in part, denotes the challenge of identifying immunogens and vaccine modalities with a reduced risk of failure in late stage development. However, progress has been made in epitope identification for the induction of broadly neutralizing antibodies. Thus, peptide-based vaccination has become one of the challenges of this decade. While some researchers reconstitute envelope protein conformation and stabilization to conserve the epitope targeted by neutralizing antibodies, others have developed strategies based on peptide-carrier vaccines with a similar goal. Here, we will review the major peptide-carrier based approaches in the vaccine field and their application and recent development in the HIV-1 field.

The regenerative potential of skin and the immune system

Skin has the natural ability to heal and replace dead cells regulated by a network of complex immune processes. This ability is conferred by the population of resident immune cells that act in coordination with other players to provide a homeostatic environment under constant challenge. Other than providing structure and integrity, the epidermis and dermis also house distinct immune properties. The dermal part is represented by fibroblasts and endothelial cells followed by an array of immune cells which includes dendritic cells (DCs), macrophages, mast cells, NK-cells, neutrophils, basophils, eosinophils, αβ T lymphocytes, B-cells and platelets. On the other hand, the functionally active immune cells in the epidermis comprise keratinocytes, DCs, NKT-cells, γδ T cells and αβ T cells (CD4+ and CD8+). Keratinocytes create a unique microenvironment for the cells of the immune system by promoting immune recognition and cellular differentiation. T lymphocytes exhibit tissue-specific tropism toward the epidermis and the lymphatic drainage system important for their function in immune regulation. This diversity in immune regulators makes the skin a unique organ to overcome pathogenic or foreign invasion. In addition, the highly coordinated molecular events make the skin an attractive model to understand and explore its regenerative potential.

The Role of the Immune System in Cutaneous Squamous Cell Carcinoma

Cutaneous squamous cell carcinoma (cSCC) is the second most common skin cancer. In immunosuppressed populations it is a source of considerable morbidity and mortality due to its enhanced recurrence and metastatic potential. In common with many malignancies, leucocyte populations are both protective against cancer development and also play a role in 'sculpting' the nascent tumor, leading to loss of immunogenicity and tumor progression. UV radiation and chronic viral carriage may represent unique risk factors for cSCC development, and the immune system plays a key role in modulating the response to both. In this review, we discuss the lessons learned from animal and ex vivo human studies of the role of individual leucocyte subpopulations in the development of cutaneous SCC. We then discuss the insights into cSCC immunity gleaned from studies in humans, particularly in populations receiving pharmacological immunosuppression such as transplant recipients. Similar insights in other malignancies have led to exciting and novel immune therapies, which are beginning to emerge into the cSCC clinical arena.

Innate gene signature distinguishes humoral versus cytotoxic responses to influenza vaccination

BACKGROUND

Systems vaccinology allows cutting-edge analysis of innate biomarkers of vaccine efficacy. We have been exploring novel strategies to shape the adaptive immune response, by targeting innate immune cells through novel immunization routes.

METHODS

This randomized phase I/II clinical study (n=60 healthy subjects aged 18-45 years old) used transcriptomic analysis to discover early biomarkers of immune response quality after transcutaneous (t.c.), intradermal (i.d.), and intramuscular (i.m.) administration of a trivalent influenza vaccine (TIV season 2012-2013) (1:1:1 ratio). Safety and immunogenicity (hemagglutinin inhibition (HI), microneutralization (MN) antibodies and CD4, CD8 effector T cells) were measured at baseline Day (D)0 and at D21. Blood transcriptome was analyzed at D0 and D1.

RESULTS

TIV-specific CD8+GranzymeB+(GRZ) T cells appeared in more individuals immunized by the t.c. and i.d. routes, while immunization by the i.d. and i.m. routes prompted high levels of HI antibody titers and MN against A/H1N1 and A/H3N2 influenza viral strains. The early innate gene signature anticipated immunological outcome by discriminating two clusters of individuals with either distinct humoral or CD8 cytotoxic responses. Several pathways explained this dichotomy confirmed by nine genes and serum level of CXCL10 were correlated with either TIV-specific cytotoxic CD8+GRZ+ T-cell or antibody responses. A logistic regression analysis demonstrated that these nine genes and serum levels of CXCL10 (D1/D0) best foreseen TIV-specific CD8+GRZ+ T-cell and antibody responses at D21.

CONCLUSION

This study provides new insight into the impact of immunization routes and innate signature in the quality of adaptive immune responses.

Modulation of Vaccine-Induced CD4 T Cell Functional Profiles by Changes in Components of HIV Vaccine Regimens in Humans

To date, six vaccine strategies have been evaluated in clinical trials for their efficacy at inducing protective immune responses against HIV infection. However, only the ALVAC-HIV/AIDSVAX B/E vaccine (RV144 trial) has demonstrated protection, albeit modestly (31%; P = 0.03). One potential correlate of protection was a low-frequency HIV-specific CD4 T cell population with diverse functionality. Although CD4 T cells, particularly T follicular helper (Tfh) cells, are critical for effective antibody responses, most studies involving HIV vaccines have focused on humoral immunity or CD8 T cell effector responses, and little is known about the functionality and frequency of vaccine-induced CD4 T cells. We therefore assessed responses from several phase I/II clinical trials and compared them to responses to natural HIV-1 infection. We found that all vaccines induced a lower magnitude of HIV-specific CD4 T cell responses than that observed for chronic infection. Responses differed in functionality, with a CD40 ligand (CD40L)-dominated response and more Tfh cells after vaccination, whereas chronic HIV infection provoked tumor necrosis factor alpha (TNF-α)-dominated responses. The vaccine delivery route further impacted CD4 T cells, showing a stronger Th1 polarization after dendritic cell delivery than after intramuscular vaccination. In prime/boost regimens, the choice of prime and boost influenced the functional profile of CD4 T cells to induce more or less polyfunctionality. In summary, vaccine-induced CD4 T cell responses differ remarkably between vaccination strategies, modes of delivery, and boosts and do not resemble those induced by chronic HIV infection. Understanding the functional profiles of CD4 T cells that best facilitate protective antibody responses will be critical if CD4 T cell responses are to be considered a clinical trial go/no-go criterion.IMPORTANCE Only one HIV-1 candidate vaccine strategy has shown protection, albeit marginally (31%), against HIV-1 acquisition, and correlates of protection suggested that a multifunctional CD4 T cell immune response may be important for this protective effect. Therefore, the functional phenotypes of HIV-specific CD4 T cell responses induced by different phase I and phase II clinical trials were assessed to better show how different vaccine strategies influence the phenotype and function of HIV-specific CD4 T cell immune responses. The significance of this research lies in our comprehensive comparison of the compositions of the T cell immune responses to different HIV vaccine modalities. Specifically, our work allows for the evaluation of vaccination strategies in terms of their success at inducing Tfh cell populations.

Determination of T Follicular Helper Cell Fate by Dendritic Cells

T follicular helper (Tfh) cells are a specialized subset of CD4⁺ T cells that collaborate with B cells to promote and regulate humoral responses. Unlike other CD4⁺ effector lineages, Tfh cells require interactions with both dendritic cells (DCs) and B cells to complete their differentiation. While numerous studies have assessed the potential of different DC subsets to support Tfh priming, the conclusions of these studies depend heavily on the model and method of immunization used. We propose that the location of different DC subsets within the lymph node (LN) and their access to antigen determine their potency in Tfh priming. Finally, we provide a three-step model that accounts for the ability of multiple DC subsets and related lineages to support the Tfh differentiation program.

The adjuvant GLA-AF enhances human intradermal vaccine responses

Adjuvants are key to shaping the immune response to vaccination, but to date, no adjuvant suitable for human use has been developed for intradermal vaccines. These vaccines could be self-administered and sent through the mail as they do not require long needles or technical expertise in immunization. In the event of a pandemic outbreak, this approach could alleviate the congregation of patients in health centers and thus reduce the potential of these centers to enhance the spread of lethal infection. A reliable and potent vaccine system for self-administration would provide an effective countermeasure for delivery through existing product distribution infrastructure. We report results from preclinical and clinical trials that demonstrate the feasibility of an adjuvanted, intradermal vaccine that induced single shot protection in ferrets and seroprotection in humans against one of the more lethal strains of pandemic flu, Indonesia H5N1. In the human trial, the vaccine was safe and clinical responses were above approvable endpoints for a protective flu vaccine. Inclusion of a modern TLR4 (Toll-like receptor 4) agonist-based adjuvant was critical to the development of the response in the intradermal groups. In humans, this is the first report of a safe and effective intradermal adjuvant, GLA-AF (aqueous formulation of glucopyranosyl lipid adjuvant), and provides a future path for developing a vaccine-device combination for distribution by mail and self-administration in case of a pandemic.

Migratory CD11b+ conventional dendritic cells induce T follicular helper cell-dependent antibody responses

T follicular helper (Tfh) cells are a subset of CD4⁺ T cells that promote antibody production during vaccination. Conventional dendritic cells (cDCs) efficiently prime Tfh cells; however, conclusions regarding which cDC instructs Tfh cell differentiation have differed between recent studies. We found that these discrepancies might exist because of the unusual sites used for immunization in murine models, which differentially bias which DC subsets access antigen. We used intranasal immunization as a physiologically relevant route of exposure that delivers antigen to all tissue DC subsets. Using a combination of mice in which the function of individual DC subsets is impaired and different antigen formulations, we determined that CD11b⁺ migratory type 2 cDCs (cDC2s) are necessary and sufficient for Tfh induction. DC-specific deletion of the guanine nucleotide exchange factor DOCK8 resulted in an isolated loss of CD11b⁺ cDC2, but not CD103⁺ cDC1, migration to lung-draining lymph nodes. Impaired cDC2 migration or development in DC-specific Dock8 or Irf4 knockout mice, respectively, led to reduced Tfh cell priming, whereas loss of CD103⁺ cDC1s in Batf3^-/- mice did not. Loss of cDC2-dependent Tfh cell priming impaired antibody-mediated protection from live influenza virus challenge. We show that migratory cDC2s uniquely carry antigen into the subanatomic regions of the lymph node where Tfh cell priming occurs-the T-B border. This work identifies the DC subset responsible for Tfh cell-dependent antibody responses, particularly when antigen dose is limiting or is encountered at a mucosal site, which could ultimately inform the formulation and delivery of vaccines.

Interleukin-32 promotes detachment and activation of human Langerhans cells in a human skin explant model

BACKGROUND

Cross-talk between skin keratinocytes (KCs) and Langerhans cells (LCs) plays a fundamental role in the body's first line of immunological defences. However, the mechanism behind the interaction between these two major epidermal cells is unknown. Interleukin (IL)-32 is produced in inflammatory skin disorders. We questioned the role of IL-32 in the epidermis.

OBJECTIVES

We aimed to determine the role of IL-32 produced by KCs on surrounding LCs.

METHODS

We used an ex vivo human explant model from healthy donors and investigated the role of IL-32 on LC activation using imaging, flow cytometry, reverse transcriptase quantitative polymerase chain reaction and small interfering (si)RNA treatment.

RESULTS

Modified vaccinia virus ankara (MVA) infection induced KC death alongside the early production of the proinflammatory cytokine IL-32. We demonstrated that IL-32 produced by MVA-infected KCs induced modest but significant morphological changes in LCs and downregulation of adhesion molecules, such as epithelial cell adhesion molecule and very late antigen-4, and CXCL10 production. The treatment of KCs with IL-32-specific siRNA, and anti-IL-32 blocking antibody significantly inhibited LC activation, demonstrating the role of IL-32 in LC activation. We also found that some Toll-like receptor ligands induced a very high level of IL-32 production by KCs, which initiated LC activation.

CONCLUSIONS

We propose, for the first time, that IL-32 is a molecular link between KCs and LCs in healthy skin, provoking LC migration from the epidermis to the dermis prior to their migration to the draining lymph nodes.

Preclinical evaluation of mRNA trimannosylated lipopolyplexes as therapeutic cancer vaccines targeting dendritic cells

Clinical trials with direct administration of synthetic mRNAs encoding tumor antigens demonstrated safety and induction of tumor-specific immune responses. Their proper delivery to dendritic cells (DCs) requires their protection against RNase degradation and more specificity for dose reduction. Lipid-Polymer-RNA lipopolyplexes (LPR) are attractive mRNA delivery systems and their equipment with mannose containing glycolipid, specific of endocytic receptors present on the membrane of DCs is a valuable strategy. In this present work, we evaluated the capacity of LPR functionalized with a tri-antenna of α-d-mannopyranoside (triMN-LPR) concerning (i) their binding to CD209/DC-SIGN and CD207/Langerin expressing cell lines, human and mouse DCs and other hematopoietic cell populations, (ii) the nature of induced immune response after in vivo immunization and (iii) their therapeutic anti-cancer vaccine efficiency. We demonstrated that triMN-LPR provided high induction of a local inflammatory response two days after intradermal injection to C57BL/6 mice, followed by the recruitment and activation of DCs in the corresponding draining lymph nodes. This was associated with skin production of CCR7 and CXCR4 at vaccination sites driving DC migration. High number of E7-specific T cells was detected after E7-encoded mRNA triMN-LPR vaccination. When evaluated in three therapeutic pre-clinical murine tumor models such as E7-expressing TC1 cells, OVA-expressing EG7 cells and MART-1-expressing B16F0 cells, triMN-LPR carrying mRNA encoding the respective antigens significantly exert curative responses in mice vaccinated seven days after initial tumor inoculation. These results provide evidence that triMN-LPR give rise to an efficient stimulatory immune response allowing for therapeutic anti-cancer vaccination in mice. This mRNA formulation should be considered for anti-cancer vaccination in Humans.

Redefining the Role of Langerhans Cells As Immune Regulators within the Skin

Langerhans cells (LC) are a unique population of tissue-resident macrophages that form a network of cells across the epidermis of the skin, but which have the ability to migrate from the epidermis to draining lymph nodes (LN). Their location at the skin barrier suggests a key role as immune sentinels. However, despite decades of research, the role of LC in skin immunity is unclear; ablation of LC results in neither fatal susceptibility to skin infection nor overt autoimmunity due to lack of immune regulation. Our understanding of immune processes has traditionally been centered on secondary lymphoid organs as sites of lymphocyte priming and differentiation, which is exemplified by LC, initially defined as a paradigm for tissue dendritic cells that migrate to draining LN on maturation. But, more recently, an awareness of the importance of the tissue environment in shaping effector immunity has emerged. In this mini-review, we discuss whether our lack of understanding of LC function stems from our lymph node-centric view of these cells, and question whether a focus on LC as immune regulators in situ in the skin may reveal clearer answers about their function in cutaneous immunology.

Ontogeny and function of murine epidermal Langerhans cells

Langerhans cells (LCs) are epidermis-resident antigen-presenting cells that share a common ontogeny with macrophages but function as dendritic cells (DCs). Their development, recruitment and retention in the epidermis is orchestrated by interactions with keratinocytes through multiple mechanisms. LC and dermal DC subsets often show functional redundancy, but LCs are required for specific types of adaptive immune responses when antigen is concentrated in the epidermis. This Review will focus on those developmental and functional properties that are unique to LCs.

Intradermal vaccination with hollow microneedles: A comparative study of various protein antigen and adjuvant encapsulated nanoparticles

In this study, we investigated the potential of intradermal delivery of nanoparticulate vaccines to modulate the immune response of protein antigen using hollow microneedles. Four types of nanoparticles covering a broad range of physiochemical parameters, namely poly (lactic-co-glycolic) (PLGA) nanoparticles, liposomes, mesoporous silica nanoparticles (MSNs) and gelatin nanoparticles (GNPs) were compared. The developed nanoparticles were loaded with a model antigen (ovalbumin (OVA)) with and without an adjuvant (poly(I:C)), followed by the characterization of size, zeta potential, morphology, and loading and release of antigen and adjuvant. An in-house developed hollow-microneedle applicator was used to inject nanoparticle suspensions precisely into murine skin at a depth of about 120μm. OVA/poly(I:C)-loaded nanoparticles and OVA/poly(I:C) solution elicited similarly strong total IgG and IgG1 responses. However, the co-encapsulation of OVA and poly(I:C) in nanoparticles significantly increased the IgG2a response compared to OVA/poly(I:C) solution. PLGA nanoparticles and liposomes induced stronger IgG2a responses than MSNs and GNPs, correlating with sustained release of the antigen and adjuvant and a smaller nanoparticle size. When examining cellular responses, the highest CD8⁺ and CD4⁺ T cell responses were induced by OVA/poly(I:C)-loaded liposomes. In conclusion, the applicator controlled hollow microneedle delivery is an excellent method for intradermal injection of nanoparticle vaccines, allowing selection of optimal nanoparticle formulations for humoral and cellular immune responses.