Alpha-galactosylceramide is an effective mucosal adjuvant for repeated intranasal or oral delivery of HIV peptide antigens

Liposome-based dry powder vaccine immunization targeting the lungs induces broad protection against pneumococcus

Streptococcus pneumoniae is an important human pathogen. Currently used conjugate vaccines are effective against invasive disease, but protection is restricted to serotypes included in the formulation, leading to serotype replacement. Furthermore, protection against non-invasive disease is reported to be considerably lower. The development of a serotype-independent vaccine is thus important and Pneumococcal surface protein A (PspA) is a promising vaccine candidate. PspA shows some diversity and can be classified in 6 clades and 3 families, with families 1 and 2 being the most frequent in clinical isolates. The ideal vaccine should thus induce protection against the two most common families of PspA. The aim of this work was to develop a liposome-based vaccine containing PspAs from family 1 and 2 and to characterize its immune response. Liposomes (LP) composed of dipalmitoylphosphatidylcholine (DPPC) and 3β-[N-(N',N'-dimethylaminoethane)-carbamoyl]cholesterol (DC-Chol) with or without α-galactosylceramide (α-GalCer) were produced by microfluidics, encapsulating PspA from clade 1 (PspA1, family 1) and/or clade 4 (PspA4Pro, family 2) followed by spray-drying with trehalose to form nanocomposite microparticles carriers (NCMP). LP/NCMPs showed good stability and preservation of protein activity. LP/NCMPs containing PspA1 and/or PspA4Pro were used for immunization of mice targeting the lungs. High serum IgG antibody titers against both PspA1 and PspA4Pro were detected in animals immunized with LP/NCMPs containing α-GalCer, with a balance of IgG1 and IgG2a titers. IgG in sera from immunized mice bound to pneumococcal strains from different serotypes and expressing different PspA clades, indicating broad recognition. Mucosal IgG and IgA were also detected. Importantly, immunization with LP/NCMPs induced full protection against strains expressing PspAs from family 1 and 2. Furthermore, CD4+ resident memory T cells were detected in the lungs of the immunized animals that survived the challenge.

A phase 1/2 clinical trial of invariant natural killer T cell therapy in moderate-severe acute respiratory distress syndrome

Invariant natural killer T (iNKT) cells, a unique T cell population, lend themselves for use as adoptive therapy due to diverse roles in orchestrating immune responses. Originally developed for use in cancer, agenT-797 is a donor-unrestricted allogeneic ex vivo expanded iNKT cell therapy. We conducted an open-label study in virally induced acute respiratory distress syndrome (ARDS) caused by the severe acute respiratory syndrome-2 virus (trial registration NCT04582201). Here we show that agenT-797 rescues exhausted T cells and rapidly activates both innate and adaptive immunity. In 21 ventilated patients including 5 individuals receiving veno-venous extracorporeal membrane oxygenation (VV-ECMO), there are no dose-limiting toxicities. We observe an anti-inflammatory systemic cytokine response and infused iNKT cells are persistent during follow-up, inducing only transient donor-specific antibodies. Clinical signals of associated survival and prevention of secondary infections are evident. Cellular therapy using off-the-shelf iNKT cells is safe, can be rapidly scaled and is associated with an anti-inflammatory response. The safety and therapeutic potential of iNKT cells across diseases including infections and cancer, warrants randomized-controlled trials.

Oral administration of DNA alginate nanovaccine induced immune-protection against Helicobacter pylori in Balb/C mice

BACKGROUND

Helicobacter pylori (H. Pylori), is an established causative factor for the development of gastric cancer and the induction of persistent stomach infections that may lead to peptic ulcers. In recent decades, several endeavours have been undertaken to develop a vaccine for H. pylori, although none have advanced to the clinical phase. The development of a successful H. pylori vaccine is hindered by particular challenges, such as the absence of secure mucosal vaccines to enhance local immune responses, the absence of identified antigens that are effective in vaccinations, and the absence of recognized indicators of protection.

METHODS

The DNA vaccine was chemically cloned, and the cloning was verified using PCR and restriction enzyme digestion. The efficacy of the vaccination was investigated. The immunogenicity and immune-protective efficacy of the vaccination were assessed in BALB/c mice. This study demonstrated that administering a preventive Alginate/pCI-neo-UreH Nanovaccine directly into the stomach effectively triggered a robust immune response to protect against H. pylori infection in mice.

RESULTS

The level of immune protection achieved with this nano vaccine was similar to that observed when using the widely accepted formalin-killed H. pylori Hel 305 as a positive control. The Alginate/pCI-neo-UreH Nanovaccine composition elicited significant mucosal and systemic antigen-specific antibody responses and strong intestinal and systemic Th1 responses. Moreover, the activation of IL-17R signaling is necessary for the defensive Th1 immune responses in the intestines triggered by Alginate/pCI-neo-UreH.

CONCLUSION

Alginate/pCI-neo-UreH is a potential Nanovaccine for use in an oral vaccine versus H. pylori infection, according to our findings.

NKT Agonist-Antigen Conjugates as Cancer Vaccines

Natural killer T (NKT) cells are a population of innate-like T cells capable of enhancing both innate and adaptive immune responses. Co-delivering an NKT cell agonist and antigen can provide molecular signals to antigen-presenting cells, such as dendritic and B cells, that facilitate strong antigen-specific adaptive immune responses. Accordingly, there has been a significant number of developmental NKT cell-dependent vaccine therapies developed, particularly in the last decade, with many incorporating cancer antigens. In this review, we summarize studies that chemically conjugate the NKT cell agonist and antigen as an effective strategy for agonist-antigen co-delivery to drive antitumor responses.

Non-Invasive Vaccines: Challenges in Formulation and Vaccine Adjuvants

Given the limitations of conventional invasive vaccines, such as the requirement for a cold chain system and trained personnel, needle-based injuries, and limited immunogenicity, non-invasive vaccines have gained significant attention. Although numerous approaches for formulating and administrating non-invasive vaccines have emerged, each of them faces its own challenges associated with vaccine bioavailability, toxicity, and other issues. To overcome such limitations, researchers have created novel supplementary materials and delivery systems. The goal of this review article is to provide vaccine formulation researchers with the most up-to-date information on vaccine formulation and the immunological mechanisms available, to identify the technical challenges associated with the commercialization of non-invasive vaccines, and to guide future research and development efforts.

Current Progress and Challenges in the Study of Adjuvants for Oral Vaccines

Over the past 20 years, a variety of potential adjuvants have been studied to enhance the effect of oral vaccines in the intestinal mucosal immune system; however, no licensed adjuvant for clinical application in oral vaccines is available. In this review, we systematically updated the research progress of oral vaccine adjuvants over the past 2 decades, including biogenic adjuvants, non-biogenic adjuvants, and their multi-type composite adjuvant materials, and introduced their immune mechanisms of adjuvanticity, aiming at providing theoretical basis for developing feasible and effective adjuvants for oral vaccines. Based on these insights, we briefly discussed the challenges in the development of oral vaccine adjuvants and prospects for their future development.

Recent Developments in Oral Delivery of Vaccines Using Nanocarriers

As oral administration of vaccines is the preferred route due to its high patient compliance and ability to stimulate both cellular and humoral immune responses, it is also associated with several challenges that include denaturation of vaccine components in the acidic environment of the stomach, degradation from proteolytic enzymes, and poor absorption through the intestinal membrane. To achieve effective delivery of such biomolecules, there is a need to investigate novel strategies of formulation development that can overcome the barriers associated with conventional vaccine delivery systems. Nanoparticles are advanced drug delivery carriers that provide target-oriented delivery by encapsulating vaccine components within them, thus making them stable against unfavorable conditions. This review provides a detailed overview of the different types of nanocarriers and various approaches that can enhance oral vaccine delivery.

Oral vaccination using microdevices to deliver α-GalCer adjuvanted vaccine afford a mucosal immune response

Oral vaccination has in the recent years gained a lot of attraction, mainly due to optimized patient compliance and logistics. However, the development of oral vaccines, especially oral subunit vaccines is challenging. Micro technology can be utilized to overcome some of these challenges, by facilitating protection and effective delivery of the vaccine components in the gastrointestinal tract (GI tract). One such technology is Microcontainers (MCs), which can be realized to be mucoadhesive and to target specific regions of the GI tract via oral delivery. Here, we test MCs, for oral delivery of the C. trachomatis vaccine candidate CTH522, in combination with effective mucosal adjuvants. The adjuvants alpha- galactosylceramide (α-GalCer), C-di-GMP and cholera toxin B were compared in vivo, to identify the most prominent adjuvant for formulation with CTH522. Formulations were administered both purely oral and as boosters following a subcutaneous (s.c.) prime with CTH522 in combination with the CAF®01 adjuvant. CTH522 formulated with α-GalCer showed to be the most efficient combination for the oral vaccine, based on the immunological analysis. Lyophilized formulation of CTH522 and α-GalCer was loaded into MCs and these were subsequently coated with Eudragit L100-55 and evaluated in vivo in mice for the ability of MCs to mediate intestinal vaccine delivery and increase immunogenicity of the vaccine. Mice receiving oral prime and boosters did show a significantly enhanced mucosal immune responses compared to naive mice. This indicates the MCs are indeed capable of delivering the vaccine formulation intact and able to stimulate the immune cells. Mice orally boosted with MCs following a s.c. prime with CAF01, demonstrated improved systemic and local Th17 responses, along with increased local IFN-γ and IgA levels compared to both the s.c. prime alone and the homologous oral prime-boost immunization. However, due to the relatively weak observed effect of the MC delivery on the immune responses, it was hypothesized that the MCs are proportionally too large for the GI tract of mice, and thus cleared before an effective immune response can be induced. To investigate this, MCs were loaded with BaSO4, and orally administered to mice. Analysis with X-ray and CT showed a transit time of approximately 1-1.5 h from the stomach to the cecum, corresponding to the standard transit time in mice, and an extremely narrow absorption window. This indicates that mice is not a suitable animal model for evaluation of MCs. These data should be taken into consideration in future in vivo trials with this and similar technologies, where larger animals might be a necessity for proof-of-concept studies.

A Glycolipid α-GalCer Derivative, 7DW8-5 as a Novel Mucosal Adjuvant for the Split Inactivated Influenza Vaccine

Influenza virus infects the host and transmits through the respiratory tract (i.e., the mouth and nose); therefore, the development of intranasal influenza vaccines that mimic the natural infection, coupled with an efficient mucosal adjuvant, is an attractive alternative to current parenteral vaccines. However, with the withdrawal of cholera toxin and Escherichia coli heat-labile endotoxin from clinical use due to side effects, there are no approved adjuvants for intranasal vaccines. Therefore, safe and effective mucosal adjuvants are urgently needed. Previously, we reported that one derivative of α-Galactosylceramide (α-GalCer), 7DW8-5, could enhance the protective efficacy of split influenza vaccine by injection administration. However, the mucosal adjuvanticity of 7DW8-5 is still unclear. In this study, we found that 7DW8-5 promotes the production of secret IgA antibodies and IgG antibodies and enhances the protective efficacy of the split influenza vaccine by intranasal administration. Furthermore, co-administration of 7DW8-5 with the split influenza vaccine significantly reduces the virus shedding in the upper and lower respiratory tract after lethal challenge. Our results demonstrate that 7DW8-5 is a novel mucosal adjuvant for the split influenza vaccine.

The role of unconventional T cells in COVID-19

COVID-19 is a respiratory disease caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). It was first documented in late 2019, but within months, a worldwide pandemic was declared due to the easily transmissible nature of the virus. Research to date on the immune response to SARS-CoV-2 has focused largely on conventional B and T lymphocytes. This review examines the emerging role of unconventional T cell subsets, including γδ T cells, invariant natural killer T (iNKT) cells and mucosal associated invariant T (MAIT) cells in human SARS-CoV-2 infection.Some of these T cell subsets have been shown to play protective roles in anti-viral immunity by suppressing viral replication and opsonising virions of SARS-CoV. Here, we explore whether unconventional T cells play a protective role in SARS-CoV-2 infection as well. Unconventional T cells are already under investigation as cell-based immunotherapies for cancer. We discuss the potential use of these cells as therapeutic agents in the COVID-19 setting. Due to the rapidly evolving situation presented by COVID-19, there is an urgent need to understand the pathogenesis of this disease and the mechanisms underlying its immune response. Through this, we may be able to better help those with severe cases and lower the mortality rate by devising more effective vaccines and novel treatment strategies.

Mucosal Vaccination With Recombinant Tm-WAP49 Protein Induces Protective Humoral and Cellular Immunity Against Experimental Trichuriasis in AKR Mice

Trichuriasis is one of the most common neglected tropical diseases of the world's poorest people. A recombinant vaccine composed of Tm-WAP49, an immunodominant antigen secreted by adult Trichuris stichocytes into the mucosa of the cecum to which the parasite attaches, is under development. The prototype is being evaluated in a mouse model of Trichuris muris infection, with the ultimate goal of producing a mucosal vaccine through intranasal delivery. Intranasal immunization of mice with Tm-WAP49 formulated with the adjuvant OCH, a truncated analog of alpha-GalCer with adjuvanticity to stimulate natural killer T cells (NKT) and mucosal immunity, induced significantly high levels of IgG and its subclasses (IgG1 and IgG2a) in immunized mice. This also resulted in a significant reduction of worm burden after challenge with T. muris-infective eggs. The addition of QS-21 adjuvant to this vaccine formulation further reduced worm counts. The improved protection from the dual-adjuvanted vaccine correlated with higher serum antibody responses (IgG, IgG1, IgG2a, IgA) as well as with the induction of antigen-specific IgA in the nasal mucosa. It was also associated with the robust cellular responses including functional subsets of CD4 T cells producing IL-4, and cytotoxic CD8 T cells expressing granzyme B. The worm reduction achieved by mucosal immunization was higher than that induced by subcutaneous immunization. Intranasal immunization also induced a significantly higher nasal mucosa-secreted antigen-specific IgA response, as well as higher functional cellular responses including CD4⁺IL4⁺ (Th1) and CD8⁺GnzB⁺ (Th2) T cells, and antigen-specific INFγ-producing T cells in both spleen and MLNs and antibody-producing B cells (CD19⁺B220⁺/B220⁺GL7⁺). Mucosal immunization further induced long-term T lymphocyte memory with increased central (CD62L⁺CD44⁺) and effector (CD62L^-CD44⁺) memory subsets of both CD4 and CD8 T cells at 60 days after the last immunization. In summary, intranasal immunization with recombinant Tm-WAP49 protein induced strong protection versus murine trichuriasis. It represents a promising vaccination approach against intestinal nematodes.

6″-Modifed α-GalCer-peptide conjugate vaccine candidates protect against liver-stage malaria

Self-adjuvanting vaccines consisting of peptide epitopes conjugated to immune adjuvants are a powerful way of generating antigen-specific immune responses. We previously showed that a Plasmodium-derived peptide conjugated to a rearranged form of α-galactosylceramide (α-GalCer) could stimulate liver-resident memory T (T_RM) cells that were effective killers of liver-stage Plasmodium berghei ANKA (Pba)-infected cells. To investigate if similar or even superior T_RM responses can be induced by modifying the α-GalCer adjuvant, we created new conjugate vaccine cadidates by attaching an immunogenic Plasmodium-derived peptide antigen to 6″-substituted α-GalCer analogues. Vaccine synthesis involved developing an efficient route to α-galactosylphytosphingosine (α-GalPhs), from which the prototypical iNKT cell agonist, α-GalCer, and its 6″-deoxy-6″-thio and -amino analogues were derived. Attaching a cathepsin B-cleavable linker to the 6″-modified α-GalCer created pro-adjuvants bearing a pendant ketone group available for peptide conjugation. Optimized reaction conditions were developed that allow for the efficient conjugation of peptide antigens to the pro-adjuvants via oxime ligation to create new glycolipid-peptide (GLP) conjugate vaccines. A single dose of the vaccine candidates induced acute NKT and Plasmodium-specific CD8⁺ T cell responses that generated potent hepatic T_RM responses in mice. Our findings demonstrate that attaching antigenic peptides to 6″-modifed α-GalCer generates powerful self-adjuvanting conjugate vaccine candidates that could potentially control hepatotropic infections such as liver-stage malaria.

Candidate vaccines comprised of peptide antigen conjugated to 6″-modified α-GalCer analogues generate potent hepatic T_RM responses in mice with a single dose inducing protective immunity against malaria in a Plasmodium sporozoite challenge model.

Role of NKT Cells during Viral Infection and the Development of NKT Cell-Based Nanovaccines

Natural killer T (NKT) cells, a small population of T cells, are capable of influencing a wide range of the immune cells, including T cells, B cells, dendritic cells and macrophages. In the present review, the antiviral role of the NKT cells and the strategies of viruses to evade the functioning of NKT cell have been illustrated. The nanoparticle-based formulations have superior immunoadjuvant potential by facilitating the efficient antigen processing and presentation that favorably elicits the antigen-specific immune response. Finally, the immunoadjuvant potential of the NKT cell ligand was explored in the development of antiviral vaccines. The use of an NKT cell-activating nanoparticle-based vaccine delivery system was supported in order to avoid the NKT cell anergy. The results from the animal and preclinical studies demonstrated that nanoparticle-incorporated NKT cell ligands may have potential implications as an immunoadjuvant in the formulation of an effective antiviral vaccine that is capable of eliciting the antigen-specific activation of the cell-mediated and humoral immune responses.

Potent Neutralizing Antibodies Elicited by RBD-Fc-Based COVID-19 Vaccine Candidate Adjuvanted by the Th2-Skewing iNKT Cell Agonist

The development of a safe and effective COVID-19 vaccine is of paramount importance to terminate the current pandemic. An adjuvant is crucial for improving the efficacy of the subunit COVID19 vaccine. α-Galactosylceramide (αGC) is a classical iNKT cell agonist which causes the rapid production of Th1- and Th2-associated cytokines; we, therefore, expect that the Th1- or Th2-skewing analogues of αGC can better enhance the immunogenicity of the receptor-binding domain in the spike protein of SARS-CoV-2 fused with the Fc region of human IgG (RBD-Fc). Herein, we developed a universal synthetic route to the Th1-biasing (α-C-GC) and Th2-biasing (OCH and C20:2) analogues. Immunization of mice demonstrated that αGC-adjuvanted RBD-Fc elicited a more potent humoral response than that observed with Alum and enabled the sparing of antigens. Remarkably, at a low dose of the RBD-Fc protein (2 μg), the Th2-biasing agonist C20:2 induced a significantly higher titer of the neutralizing antibody than that of Alum.

Advances in Oral Subunit Vaccine Design

Many pathogens invade the host at the intestinal surface. To protect against these enteropathogens, the induction of intestinal secretory IgA (SIgA) responses is paramount. While systemic vaccination provides strong systemic immune responses, oral vaccination is the most efficient way to trigger protective SIgA responses. However, the development of oral vaccines, especially oral subunit vaccines, is challenging due to mechanisms inherent to the gut. Oral vaccines need to survive the harsh environment in the gastrointestinal tract, characterized by low pH and intestinal proteases and need to reach the gut-associated lymphoid tissues, which are protected by chemical and physical barriers that prevent efficient uptake. Furthermore, they need to surmount default tolerogenic responses present in the gut, resulting in suppression of immunity or tolerance. Several strategies have been developed to tackle these hurdles, such as delivery systems that protect vaccine antigens from degradation, strong mucosal adjuvants that induce robust immune responses and targeting approaches that aim to selectively deliver vaccine antigens towards specific immune cell populations. In this review, we discuss recent advances in oral vaccine design to enable the induction of robust gut immunity and highlight that the development of next generation oral subunit vaccines will require approaches that combines these solutions.

Polyethylenimine: An Intranasal Adjuvant for Liposomal Peptide-Based Subunit Vaccine against Group A Streptococcus

Group A Streptococcus (GAS) and GAS-related infections are a worldwide challenge, with no commercial GAS vaccine available. Polyethylenimine (PEI) attaches to the cells' surface and delivers cargo into endosomal and cytosolic compartments. We hypothesized that this will confer mucosal adjuvant properties for peptide antigens against group A Streptococcus (GAS). In this study, we successfully demonstrated the development of PEI incorporated liposomes for the delivery of a lipopeptide-based vaccine (LCP-1) against GAS. Outbred mice were administrated with the vaccine formulations intranasally, and immunological investigation showed that the PEI liposomes elicited significant mucosal and systemic immunity with the production of IgA and IgG antibodies. Antibodies were shown to effectively opsonize multiple isolates of clinically isolated GAS. This proof-of-concept study showed the capability for PEI liposomes to act as a safe vehicle for the delivery of GAS peptide antigens to elicit immune responses against GAS infection, making PEI a promising addition to liposomal mucosal vaccines.

Immunization with a recombinant BibA surface protein confers immunity and protects mice against group B Streptococcus (GBS) vaginal colonization

Streptococcus agalactiae or group B Streptococcus (GBS) is a Gram-positive bacterium divided into ten distinct serotypes that colonizes the vaginal and rectal tracts of approximately 30% of women worldwide. GBS is the leading cause of invasive infection in newborns, causing sepsis, pneumoniae and meningitis. The main strategy to prevent GSB infection in newborns includes the use of intrapartum antibiotic therapy, which does not prevent late-onset diseases and may select resistant bacterial strains. We still do not have a vaccine formulation specific for this pathogen approved for human use. Conserved surface proteins are potential antigens that could be targets for recognition by antibodies and activation of cell opsonization. We used a serotype V GBS (GBS-V)-derived recombinant surface protein, rBibA, and evaluated the potential protective role of the induced antigen-specific antibodies after parenteral or mucosal immunizations in C57BL/6 mice. In vitro and in vivo assays demonstrated that vaccine formulations containing BibA combined with different adjuvants induced serum IgG and/or secreted IgA antibodies, leading to enhanced opsonophagocytosis of GBS-V cells and reduced invasion of epithelial cells. One BibA-based vaccine formulation adjuvanted with a nontoxic derivative of the heat-labile toxin produced by enterotoxigenic Escherichia coli (ETEC) strains was capable of inducing protection against vaginal colonization and lethal parenteral challenge with GBS-V. Serum collected from vaccinated mice conferred passive protection against vaginal colonization in naïve mice challenged with GBS-V. Taken together, the present data demonstrate that the BibA protein is a promising antigen for development of a vaccine to protect against GBS infection.

Intranasal Therapeutic Peptide Vaccine Promotes Efficient Induction and Trafficking of Cytotoxic T Cell Response for the Clearance of HPV Vaginal Tumors

Human papillomavirus (HPV)-induced cancers continue to affect millions of women around the world, and the five year survival rate under the current standard of care for these cancers is less than 60% in some demographics. Therefore there is still an unmet need to develop an effective therapy that can be easily administered to treat established HPV cervical cancer lesions. We sought to investigate the potential of an intranasal HPV peptide therapeutic vaccine incorporating the combination of α-Galactosylceramide (α-GalCer) and CpG-ODN adjuvants (TVAC) against established HPV genital tumors in a syngeneic C57BL/6J mouse model. We obtained evidence to show that TVAC, delivered by the mucosal intranasal route, induced high frequencies of antigen-specific CD8 T cells concurrent with significant reduction in the immunosuppressive regulatory T cells and myeloid derived suppressor cells in the tumor microenvironment (TME), correlating with sustained elimination of established HPV genital tumors in over 85% of mice. Inclusion of both the adjuvants in the vaccine was necessary for significant increase of antigen-specific CD8 T cells to the tumor and antitumor efficacy because vaccination incorporating either adjuvant alone was inefficient. These results strongly support the utility of the TVAC administered by needle-free intranasal route as a safe and effective strategy for the treatment of established genital HPV tumors.

Perturbation of mucosal-associated invariant T cells and iNKT cells in HIV infection

PURPOSE OF REVIEW

To analyze the possible role that the 'unconventional' T-cell populations mucosal-associated invariant T cell (MAIT) and iNKT cells play during HIV infection and following antiretroviral therapy (ART) treatment.

RECENT FINDINGS

A substantial body of evidence now demonstrates that both MAIT and iNKT cells are depleted in blood during HIV infection. The depletion and dysfunction of MAIT and iNKT cells are only partially restored by suppressive ART, potentially contributing to HIV-related comorbidities.

SUMMARY

The deficiency and dysfunction of MAIT and iNKT T-cell subsets likely impact on immunity to important coinfections including Mycobacterium tuberculosis. This underscores the importance of research on restoring these unconventional T cells during HIV infection. Future studies in this field should address the challenge of studying tissue-resident cells, particularly in the gut, and better defining the determinants of MAIT/iNKT cell dysfunction. Such studies could have a significant impact on improving the immune function of HIV-infected individuals.

An oral alpha-galactosylceramide adjuvanted Helicobacter pylori vaccine induces protective IL-1R- and IL-17R-dependent Th1 responses

Helicobacter pylori causes chronic gastric infection that can lead to peptic ulcers and is an identified risk factor for gastric cancer development. Although much effort has been put into the development of a Helicobacter pylori vaccine over the last three decades, none has yet reached clinical application. Specific challenges pertaining to effective H. pylori vaccine development include the lack of proven vaccine-effective antigens and safe mucosal adjuvants to enhance local immune responses as well as the lack of accepted correlates of protection. Herein, we demonstrate that prophylactic intragastric immunisation with a whole-cell killed H. pylori antigen administered together with the non-toxic oral adjuvant α-galactosylceramide (α-GalCer) induced effective immune protection against H. pylori infection in mice, which was of similar magnitude as when using the “gold standard” cholera toxin as adjuvant. We further describe that this α-GalCer-adjuvanted vaccine formulation elicited strong intestinal and systemic Th1 responses as well as significant antigen-specific mucosal and systemic antibody responses. Finally, we report that the protective intestinal Th1 responses induced by α-GalCer are dependent on CD1d, IL-1R as well as IL-17R signalling. In summary, our results show that α-GalCer is a promising adjuvant for inclusion in an oral vaccine against H. pylori infection.

Infection by Helicobacter pylori is highly prevalent in humans and can lead to chronic inflammation and gastric cancer, but to date no effective vaccine has been approved for clinical use owing to the lack of appropriate antigens and of safe mucosal adjuvants that can produce protective and durable immunity to the bacterium. Sukanya Raghavan, Ed Lavelle and colleagues now show that prophylactic intragastric administration of an inactivated whole-cell H. pylori preparation, together with the oral adjuvant α-galactosylceramide, reduced H. pylori infection in mice by eliciting a protective mucosal and systemic T_H1 response. The immunisation triggered antigen-specific antibodies and interferon-γ that prevented effective colonisation of H. pylori after challenge in a process dependent on the CD1d, IL-1 receptor and IL-17 receptor pathways. The reported enhanced immune response to this orally adjuvanted vaccine formulation paves the way for further studies of its safety and efficacy.

Therapeutic Potential of Invariant Natural Killer T Cells in Autoimmunity

Tolerance against self-antigens is regulated by a variety of cell types with immunoregulatory properties, such as CD1d-restricted invariant natural killer T (iNKT) cells. In many experimental models of autoimmunity, iNKT cells promote self-tolerance and protect against autoimmunity. These findings are supported by studies with patients suffering from autoimmune diseases. Based on these studies, the therapeutic potential of iNKT cells in autoimmunity has been explored. Many of these studies have been performed with the potent iNKT cell agonist KRN7000 or its structural variants. These findings have generated promising results in several autoimmune diseases, although mechanisms by which iNKT cells modulate autoimmunity remain incompletely understood. Here, we will review these preclinical studies and discuss the prospects for translating their findings to patients suffering from autoimmune diseases.

Lipid-Based Particles: Versatile Delivery Systems for Mucosal Vaccination against Infection

Vaccination is the process of administering immunogenic formulations in order to induce or harness antigen (Ag)-specific antibody and T cell responses in order to protect against infections. Important successes have been obtained in protecting individuals against many deleterious pathological situations after parenteral vaccination. However, one of the major limitations of the current vaccination strategies is the administration route that may not be optimal for the induction of immunity at the site of pathogen entry, i.e., mucosal surfaces. It is now well documented that immune responses along the genital, respiratory, or gastrointestinal tracts have to be elicited locally to ensure efficient trafficking of effector and memory B and T cells to mucosal tissues. Moreover, needle-free mucosal delivery of vaccines is advantageous in terms of safety, compliance, and ease of administration. However, the quest for mucosal vaccines is challenging due to (1) the fact that Ag sampling has to be performed across the epithelium through a relatively limited number of portals of entry; (2) the deleterious acidic and proteolytic environment of the mucosae that affect the stability, integrity, and retention time of the applied Ags; and (3) the tolerogenic environment of mucosae, which requires the addition of adjuvants to elicit efficient effector immune responses. Until now, only few mucosally applicable vaccine formulations have been developed and successfully tested. In animal models and clinical trials, the use of lipidic structures such as liposomes, virosomes, immune stimulating complexes, gas-filled microbubbles and emulsions has proven efficient for the mucosal delivery of associated Ags and the induction of local and systemic immune reponses. Such particles are suitable for mucosal delivery because they protect the associated payload from degradation and deliver concentrated amounts of Ags via specialized sampling cells (microfold cells) within the mucosal epithelium to underlying antigen-presenting cells. The review aims at summarizing recent development in the field of mucosal vaccination using lipid-based particles. The modularity ensured by tailoring the lipidic design and content of particles, and their known safety as already established in humans, make the continuing appraisal of these vaccine candidates a promising development in the field of targeted mucosal vaccination.

The Influence of Invariant Natural Killer T Cells on Humoral Immunity to T-Dependent and -Independent Antigens

Vaccination with CD1d-binding glycolipid adjuvants and co-administered protein, lipid, and carbohydrate antigens leads to invariant natural killer T (NKT) cell-dependent enhancement of protective B cell responses. NKT cell activation boosts the establishment of protein antigen-specific B cell memory and long-lived plasma cell (LLPC) compartments. NKT cells may exert a similar effect on some carbohydrate-specific B cells, but not lipid-specific B cells. The mechanisms of action of NKT cells on B cell responsiveness and subsequent differentiation into memory B cells and LLPC is dependent on CD1d expression by dendritic cells and B cells that can co-present glycolipids on CD1d and antigen-derived peptide on MHCII. CD1d/glycolipid-activated NKT cells are able to provide help to B cells in a manner dependent on cognate and non-cognate interactions. More recently, a glycolipid-expanded subset of IL-21-secreting NKT cells known as NKT follicular helper cells has been suggested to be a driver of NKT-enhanced humoral immunity. This review summarizes established and recent findings on how NKT cells impact humoral immunity and suggests possible areas of investigation that may allow the incorporation of NKT-activating agents into vaccine adjuvant platforms.

Prophylactic Sublingual Immunization with Mycobacterium tuberculosis Subunit Vaccine Incorporating the Natural Killer T Cell Agonist Alpha-Galactosylceramide Enhances Protective Immunity to Limit Pulmonary and Extra-Pulmonary Bacterial Burden in Mice

Infection by Mycobacterium tuberculosis (Mtb) remains a major global concern and the available Bacillus Calmette-Guerin (BCG) vaccine is poorly efficacious in adults. Therefore, alternative vaccines and delivery strategies focusing on Mtb antigens and appropriate immune stimulating adjuvants are needed to induce protective immunity targeted to the lungs, the primary sites of infections and pathology. We present here evidence in support of mucosal vaccination by the sublingual route in mice using the subunit Mtb antigens Ag85B and ESAT-6 adjuvanted with the glycolipid alpha-galactosylceramide (α-GalCer), a potent natural killer T (NKT) cell agonist. Vaccinated animals exhibited strong antigen-specific CD4 and CD8 T cells responses in the spleen, cervical lymph nodes and lungs. In general, inclusion of the α-GalCer adjuvant significantly enhanced these responses that persisted over 50 days. Furthermore, aerosolized Mtb infection of vaccinated mice resulted in a significant reduction of bacterial load of the lungs and spleens as compared to levels seen in naïve controls or those vaccinated with subunit proteins, adjuvant , or BCG alone. The protection induced by the Mtb antigens and-GalCer vaccine through sublingual route correlated with a TH1-type immunity mediated by antigen-specific IFN-γ and IL-2 producing T cells.

Intranasal Vaccination Affords Localization and Persistence of Antigen-Specific CD8⁺ T Lymphocytes in the Female Reproductive Tract

Immunization strategies generating large numbers of antigen-specific T cells in the female reproductive tract (FRT) can provide barrier protection against sexually-transmitted pathogens, such as the human immunodeficiency virus (HIV) and human papillomaviruses (HPV). The kinetics and mechanisms of regulation of vaccine-induced adaptive T cell-mediated immune responses in FRT are less well defined. We present here evidence for intranasal delivery of the model antigen ovalbumin (OVA) along with alpha-galactosylceramide adjuvant as a protein vaccine to induce significantly higher levels of antigen-specific effector and memory CD8⁺ T cells in the FRT, relative to other systemic and mucosal tissues. Antibody blocking of the CXCR3 receptor significantly reduced antigen-specific CD8⁺ T cells subsequent to intranasal delivery of the protein vaccine suggesting an important role for the CXCR3 chemokine-receptor signaling for T cell trafficking. Further, intranasal vaccination with an adenoviral vector expressing OVA or HIV-1 envelope was as effective as intramuscular vaccination for generating OVA- or ENV-specific immunity in the FRT. These results support the application of the needle-free intranasal route as a practical approach to delivering protein as well as DNA/virus vector-based vaccines for efficient induction of effector and memory T cell immunity in the FRT.

Synthetic TRP2 long-peptide and α-galactosylceramide formulated into cationic liposomes elicit CD8+ T-cell responses and prevent tumour progression

The lipid antigen α-galactosylceramide (α-GalCer) is a potent activator of invariant natural killer T-cells (iNKT cells) and can stimulate cytotoxic and anti-tumour immune responses. However optimal responses appear to be induced by α-GalCer when cell-based vaccines are delivered intravenously. Here we investigated if co-delivery of protein and peptide antigens along with α-GalCer in a liposomal formulation could stimulate therapeutic anti-tumour immune responses. Cationic liposomes were inherently immune-stimulatory and induced cytotoxic immune responses when delivered both by intravenous and subcutaneous injection. However, only vaccine delivered intravenously stimulated therapeutic anti-tumour immune responses to a peptide antigen. Surface modification with polyethylene glycol (PEG) did not improve immune responses to either intravenously or subcutaneously delivered vaccines. Immune responses to short and long peptide sequences (CD8 and CD4 epitopes) of the self-antigen tyrosinase-related protein 2 (TRP2) as a vaccine antigen, co-delivered with α-GalCer in either cationic liposomes or PBS were further examined. Enhanced production of IFN-γ, increased cytotoxic T-cell responses and tumour survival were observed when a long TRP2-peptide was delivered with α-GalCer in cationic liposomes.

Enhancement of Mucosal Immunogenicity of Viral Vectored Vaccines by the NKT Cell Agonist Alpha-Galactosylceramide as Adjuvant

Gene-based vaccination strategies, specifically viral vectors encoding vaccine immunogens are effective at priming strong immune responses. Mucosal routes offer practical advantages for vaccination by ease of needle-free administration, and immunogen delivery at readily accessible oral/nasal sites to efficiently induce immunity at distant gut and genital tissues. However, since mucosal tissues are inherently tolerant for induction of immune responses, incorporation of adjuvants for optimal mucosal vaccination strategies is important. We report here the effectiveness of alpha-galactosylceramide (α-GalCer), a synthetic glycolipid agonist of natural killer T (NKT) cells, as an adjuvant for enhancing immunogenicity of vaccine antigens delivered using viral vectors by mucosal routes in murine and nonhuman primate models. Significant improvement in adaptive immune responses in systemic and mucosal tissues was observed by including α-GalCer adjuvant for intranasal immunization of mice with vesicular stomatitis virus vector encoding the model antigen ovalbumin and adenoviral vectors expressing HIV env and Gag antigens. Activation of NKT cells in systemic and mucosal tissues along with significant increases in adaptive immune responses were observed in rhesus macaques immunized by intranasal and sublingual routes with protein or adenovirus vectored antigens when combined with α-GalCer adjuvant. These results support the utility of α-GalCer adjuvant for enhancing immunogenicity of mucosal vaccines delivered using viral vectors.

Unique potential of 4-1BB agonist antibody to promote durable regression of HPV+ tumors when combined with an E6/E7 peptide vaccine

Antibody modulation of T-cell coinhibitory (e.g., CTLA-4) or costimulatory (e.g., 4-1BB) receptors promotes clinical responses to a variety of cancers. Therapeutic cancer vaccination, in contrast, has produced limited clinical benefit and no curative therapies. The E6 and E7 oncoproteins of human papilloma virus (HPV) drive the majority of genital cancers, and many oropharyngeal tumors. We discovered 15-19 amino acid peptides from HPV-16 E6/E7 for which induction of T-cell immunity correlates with disease-free survival in patients treated for high-grade cervical neoplasia. We report here that intranasal vaccination with these peptides and the adjuvant alpha-galactosylceramide elicits systemic and mucosal T-cell responses leading to reduced HPV(+) TC-1 tumor growth and prolonged survival in mice. We hypothesized that the inability of these T cells to fully reject established tumors resulted from suppression in the tumor microenvironment which could be ameliorated through checkpoint modulation. Combining this E6/E7 peptide vaccine with checkpoint blockade produced only modest benefit; however, coadministration with a 4-1BB agonist antibody promoted durable regression of established genital TC-1 tumors. Relative to other therapies tested, this combination of vaccine and α4-1BB promoted the highest CD8(+) versus regulatory FoxP3(+) T-cell ratios, elicited 2- to 5-fold higher infiltration by E7-specific CTL, and evoked higher densities of highly cytotoxic TcEO (T cytotoxic Eomesodermin) CD8 (>70-fold) and ThEO (T helper Eomesodermin) CD4 (>17-fold) T cells. These findings have immediate clinical relevance both in terms of the direct clinical utility of the vaccine studied and in illustrating the potential of 4-1BB antibody to convert therapeutic E6/E7 vaccines already in clinical trials into curative therapies.

iNKT Cells and Their Potential Lipid Ligands during Viral Infection

Invariant natural killer T (iNKT) cells are a unique population of lipid-reactive CD1d-restricted innate-like T lymphocytes. Despite being a minor population, they serve as an early source of cytokines and promote immunological crosstalk thus bridging innate and adaptive immunity. Diseases ranging from allergy, autoimmunity, and cancer, as well as infectious diseases, including viral infection, have been reported to be influenced by iNKT cells. However, it remains unclear how iNKT cells are activated during viral infection, as virus-derived lipid antigens have not been reported. Cytokines may activate iNKT cells during infections from influenza and murine cytomegalovirus, although CD1d-dependent activation is evident in other viral infections. Several viruses, such as dengue virus, induce CD1d upregulation, which correlates with iNKT cell activation. In contrast, herpes simplex virus type 1 (HSV-1), human immunodeficiency virus (HIV), Epstein–Barr virus, and human papilloma virus promote CD1d downregulation as a strategy to evade iNKT cell recognition. These observations suggest the participation of a CD1d-dependent process in the activation of iNKT cells in response to viral infection. Endogenous lipid ligands, including phospholipids as well as glycosphingolipids, such as glucosylceramide, have been proposed to mediate iNKT cell activation. Pro-inflammatory signals produced during viral infection may stimulate iNKT cells through enhanced CD1d-dependent endogenous lipid presentation. Furthermore, viral infection may alter lipid composition and inhibit endogenous lipid degradation. Recent advances in this field are reviewed.

CD1d-dependent endogenous and exogenous lipid antigen presentation

Invariant natural killer T (iNKT) cells recognize endogenous and exogenous lipids in the context of CD1d molecules, and through the activation and maturation of dendritic cells and B cells, can significantly enhance priming of antigen-specific T and B cell responses. Recent findings have provided important insights into the recognition of several novel endogenous lipids by iNKT cells, and into the mechanisms controlling their generation and loading onto CD1d molecules. In this review we discuss these latest findings and describe the role of autophagy in iNKT cell development and activation.

Regulation of NKT Cell Localization in Homeostasis and Infection

Natural killer T (NKT) cells are a specialized subset of T lymphocytes that regulate immune responses in the context of autoimmunity, cancer, and microbial infection. Lipid antigens derived from bacteria, parasites, and fungi can be presented by CD1d molecules and recognized by the canonical T cell receptors on NKT cells. Alternatively, NKT cells can be activated through recognition of self-lipids and/or pro-inflammatory cytokines generated during infection. Unlike conventional T cells, only a small subset of NKT cells traffic through the lymph nodes under homeostatic conditions, with the largest NKT cell populations localizing to the liver, lungs, spleen, and bone marrow. This is thought to be mediated by differences in chemokine receptor expression profiles. However, the impact of infection on the tissue localization and function of NKT remains largely unstudied. This review focuses on the mechanisms mediating the establishment of peripheral NKT cell populations during homeostasis and how tissue localization of NKT cells is affected during infection.

The Response of CD1d-Restricted Invariant NKT Cells to Microbial Pathogens and Their Products

Invariant natural killer T (iNKT) cells become activated during a wide variety of infections. This includes organisms lacking cognate CD1d-binding glycolipid antigens recognized by the semi-invariant T cell receptor of iNKT cells. Additional studies have shown that iNKT cells also become activated in vivo in response to microbial products such as bacterial lipopolysaccharide, a potent inducer of cytokine production in antigen-presenting cells (APCs). Other studies have shown that iNKT cells are highly responsive to stimulation by cytokines such as interleukin-12. These findings have led to the concept that microbial pathogens can activate iNKT cells either directly via glycolipids or indirectly by inducing cytokine production in APCs. iNKT cells activated in this manner produce multiple cytokines that can influence the outcome of infection, usually in favor of the host, although potent iNKT cell activation may contribute to an uncontrolled cytokine storm and sepsis. One aspect of the response of iNKT cells to microbial pathogens is that it is short-lived and followed by an extended time period of unresponsiveness to reactivation. This refractory period may represent a means to avoid chronic activation and cytokine production by iNKT cells, thus protecting the host against some of the negative effects of iNKT cell activation, but potentially putting the host at risk for secondary infections. These effects of microbial pathogens and their products on iNKT cells are not only important for understanding the role of these cells in immune responses against infections but also for the development of iNKT cell-based therapies.

Intranasal and oral vaccination with protein-based antigens: advantages, challenges and formulation strategies

Most pathogens initiate their infections at the human mucosal surface. Therefore, mucosal vaccination, especially through oral or intranasal administration routes, is highly desired for infectious diseases. Meanwhile, protein-based antigens provide a safer alternative to the whole pathogen or DNA based ones in vaccine development. However, the unique biopharmaceutical hurdles that intranasally or orally delivered protein vaccines need to overcome before they reach the sites of targeting, the relatively low immunogenicity, as well as the low stability of the protein antigens, require thoughtful and fine-tuned mucosal vaccine formulations, including the selection of immunostimulants, the identification of the suitable vaccine delivery system, and the determination of the exact composition and manufacturing conditions. This review aims to provide an up-to-date survey of the protein antigen-based vaccine formulation development, including the usage of immunostimulants and the optimization of vaccine delivery systems for intranasal and oral administrations.

Sublingual injection of microparticles containing glycolipid ligands for NKT cells and subunit vaccines induces antibody responses in oral cavity

Natural Killer T (NKT) cells are a unique type of innate immune cells which exert paradoxical roles in animal models through producing either Th1 or Th2 cytokines and activating dendritic cells. Alpha-galactosylceramide (αGalCer), a synthetic antigen for NKT cells, was found to be safe and immune stimulatory in cancer and hepatitis patients. We recently developed microparticle-formulated αGalCer, which is selectively presented by dendritic cells and macrophages, but not B cells, and thus can avoid the anergy of NKT cells. In this study, we have examined the immunogenicity of microparticles containing αGalCer and protein vaccine components through sublingual injection in mice. The results showed that sublingual injection of microparticles containing αGalCer and ovalbumin triggered IgG responses in serum (titer >1:100,000), which persisted for more than 3months. Microparticles containing ovalbumin alone also induced comparable level of IgG responses. However, immunoglobulin subclass analysis showed that sublingually injected microparticles containing αGalCer and ovalbumin induced 20 fold higher Th1 biased antibody (IgG2c) than microparticles containing OVA alone (1:20,000 as compared to 1:1000 titer). Sublingual injection of microparticles containing αGalCer and ovalbumin induced secretion of both IgG (titer >1:1000) and IgA (titer=1:80) in saliva secretion, while microparticles containing ovalbumin alone only induced secretion of IgG in saliva. Our results suggest that sublingual injection of microparticles and their subsequent trafficking to draining lymph nodes may induce adaptive immune responses in mucosal compartments. Ongoing studies are focused on the mechanism of antigen presentation and lymphocyte biology in the oral cavity, as well as the toxicity and efficacy of these candidate microparticles for future applications.

Natural killer T cell and TLR9 agonists as mucosal adjuvants for sublingual vaccination with clade C HIV-1 envelope protein

The vast majority of HIV-1 infections occur at mucosa during sexual contact. It may therefore be advantageous to provide mucosal barrier protection against this entry by mucosal vaccination. While a number of mucosal routes of vaccination are possible, many like enteric oral vaccines or intranasal vaccines have significant impediments that limit vaccine efficacy or pose safety risks. In contrast, immunogens applied to the sublingual region of the mouth could provide a simple route for mucosal vaccination. While sublingual immunization is appealing, this site does not always drive strong immune responses, particularly when using protein antigens. To address this issue, we have tested the ability of two mucosal adjuvants: alpha-galactosylceramide (αGalCer) that is a potent stimulator of natural killer T cells and CpG-oligodeoxynucleotide (CpG-ODN) a TLR9 agonist for their ability to amplify immune responses against clade C gp140 HIV-1 envelope protein antigen. Immunization with envelope protein alone resulted in a weak T cell and antibody responses. In contrast, CD4(+) and CD8(+) T cells responses in systemic and mucosal tissues were significantly higher in mice immunized with gp140 in the presence of either αGalCer or CpG-ODN and these responses were further augmented when the two adjuvants were used together. While both the adjuvants effectively increased gp140-specific serum IgG and vaginal IgA antibody levels, combining both significantly improved these responses. Memory T cell responses 60 days after immunization revealed αGalCer to be more potent than CpG-ODN and the combination of the αGalCer and CpG-ODN adjuvants was more effective than either alone. Serum and vaginal washes collected 60 days after immunization with gp140 with both αGalCer and CpG-ODN adjuvants had significant neutralization activity against Tier 1 and Tier 2 SHIVs. These data support the utility of the sublingual route for mucosal vaccination particularly in combination with αGalCer and CpG-ODN adjuvants.

Activation of iNKT cells by a distinct constituent of the endogenous glucosylceramide fraction

Invariant natural killer T (iNKT) cells are a specialized T-cell subset that recognizes lipids as antigens, contributing to immune responses in diverse disease processes. Experimental data suggests that iNKT cells can recognize both microbial and endogenous lipid antigens. Several candidate endogenous lipid antigens have been proposed, although the contextual role of specific antigens during immune responses remains largely unknown. We have previously reported that mammalian glucosylceramides (GlcCers) activate iNKT cells. GlcCers are found in most mammalian tissues, and exist in variable molecular forms that differ mainly in N-acyl fatty acid chain use. In this report, we purified, characterized, and tested the GlcCer fractions from multiple animal species. Although activity was broadly identified in these GlcCer fractions from mammalian sources, we also found activity properties that could not be reconciled by differences in fatty acid chain use. Enzymatic digestion of β-GlcCer and a chromatographic separation method demonstrated that the activity in the GlcCer fraction was limited to a rare component of this fraction, and was not contained within the bulk of β-GlcCer molecular species. Our data suggest that a minor lipid species that copurifies with β-GlcCer in mammals functions as a lipid self antigen for iNKT cells.

Harnessing the antibacterial and immunological properties of mucosal-associated invariant T cells in the development of novel oral vaccines against enteric infections

Enteric infections are a major cause of mortality and morbidity with significant social and economic implications worldwide and particularly in developing countries. An attractive approach to minimizing the impact of these diseases is via the development of oral vaccination strategies. However, oral vaccination is challenging due to the tolerogenic and hyporesponsive nature of antigen presenting cells resident in the gastrointestinal tract. The inclusion of adjuvants in oral vaccine formulations has the potential to overcome this challenge. To date no oral adjuvants have been licenced for human use and thus oral adjuvant discovery remains a key goal in improving the potential for oral vaccine development. Mucosal-associated invariant T (MAIT) cells are a recently discovered population of unconventional T cells characterized by an evolutionarily conserved αβ T cell receptor (TCR) that recognizes antigens presented by major histocompatibility complex (MHC) class I-related (MR1) molecule. MAIT cells are selected intra-thymically by MR1 expressing double positive thymocytes and enter the circulation with a naïve phenotype. In the circulation they develop a memory phenotype and are programmed to home to mucosal tissues and the liver. Once resident in these tissues, MAIT cells respond to bacterial and yeast infections through the production of chemokines and cytokines that aid in the induction of an adaptive immune response. Their abundance in the gastrointestinal tract and ability to promote adaptive immunity suggests that MAIT cell activators may represent attractive novel adjuvants for use in oral vaccination.

Vaccine-induced myeloid cell population dampens protective immunity to SIV

Vaccines are largely evaluated for their ability to promote adaptive immunity, with little focus on the induction of negative immune regulators. Adjuvants facilitate and enhance vaccine-induced immune responses and have been explored for mediating protection against HIV. Using a regimen of peptide priming followed by a modified vaccinia Ankara (MVA) boost in a nonhuman primate model, we found that an SIV vaccine incorporating molecular adjuvants mediated partial protection against rectal SIVmac251 challenges. Animals treated with vaccine and multiple adjuvants exhibited a reduced viral load (VL) compared with those treated with vaccine only. Surprisingly, animals treated with adjuvant alone had reduced VLs that were comparable to or better than those of the vaccine-treated group. VL reduction was greatest in animals with the MHC class I allele Mamu-A*01 that were treated with adjuvant only and was largely dependent on CD8+ T cells. Early VLs correlated with Ki67+CCR5+CD4+ T cell frequency, while set-point VL was associated with expansion of a myeloid cell population that was phenotypically similar to myeloid-derived suppressor cells (MDSCs) and that suppressed T cell responses in vitro. MDSC expansion occurred in animals receiving vaccine and was not observed in the adjuvant-only group. Collectively, these results indicate that vaccine-induced MDSCs inhibit protective cellular immunity and suggest that preventing MDSC induction may be critical for effective AIDS vaccination.

Invariant NKT cell response to dengue virus infection in human

BACKGROUND

Dengue viral infection is a global health threat without vaccine or specific treatment. The clinical outcome varies from asymptomatic, mild dengue fever (DF) to severe dengue hemorrhagic fever (DHF). While adaptive immune responses were found to be detrimental in the dengue pathogenesis, the roles of earlier innate events remain largely uninvestigated. Invariant natural killer T (iNKT) cells represent innate-like T cells that could dictate subsequent adaptive response but their role in human dengue virus infection is not known. We hypothesized that iNKT cells play a role in human dengue infection.

METHODS

Blood samples from a well-characterized cohort of children with DF, DHF, in comparison to non-dengue febrile illness (OFI) and healthy controls at various time points were studied. iNKT cells activation were analyzed by the expression of CD69 by flow cytometry. Their cytokine production was then analyzed after α-GalCer stimulation. Further, the CD1d expression on monocytes, and CD69 expression on conventional T cells were measured.

RESULTS

iNKT cells were activated during acute dengue infection. The level of iNKT cell activation associates with the disease severity. Furthermore, these iNKT cells had altered functional response to subsequent ex vivo stimulation with α-GalCer. Moreover, during acute dengue infection, monocytic CD1d expression was also upregulated and conventional T cells also became activated.

CONCLUSION

iNKT cells might play an early and critical role in the pathogenesis of severe dengue viral infection in human. Targeting iNKT cells and CD1d serve as a potential therapeutic strategy for severe dengue infection in the future.

Induction of Potent and Long-Lived Antibody and Cellular Immune Responses in the Genitorectal Mucosa Could be the Critical Determinant of HIV Vaccine Efficacy

The field of HIV prevention has indeed progressed in leaps and bounds, but with major limitations of the current prevention and treatment options, the world remains desperate for an HIV vaccine. Sadly, this continues to be elusive, because more than 30 years since its discovery there is no licensed HIV vaccine. Research aiming to define immunological biomarkers to accurately predict vaccine efficacy have focused mainly on systemic immune responses, and as such, studies defining correlates of protection in the genitorectal mucosa, the primary target site for HIV entry and seeding are sparse. Clearly, difficulties in sampling and analysis of mucosal specimens, as well as their limited size have been a major deterrent in characterizing the type (mucosal antibodies, cytokines, chemokines, or CTL), threshold (magnitude, depth, and breadth) and viral inhibitory capacity of HIV-1-specific immune responses in the genitorectal mucosa, where they are needed to immediately block HIV acquisition and arrest subsequent virus dissemination. Nevertheless, a few studies document the existence of HIV-specific immune responses in the genitorectal mucosa of HIV-infected aviremic and viremic controllers, as well as in highly exposed persistently seronegative (HEPS) individuals with natural resistance to HIV-1. Some of these responses strongly correlate with protection from HIV acquisition and/or disease progression, thus providing significant clues of the ideal components of an efficacious HIV vaccine. In this study, we provide an overview of the key features of protective immune responses found in HEPS, elite and viremic controllers, and discuss how these can be achieved through mucosal immunization. Inevitably, HIV vaccine development research will have to consider strategies that elicit potent antibody and cellular immune responses within the genitorectal mucosa or induction of systemic immune cells with an inherent potential to home and persist at mucosal sites of HIV entry.

Potent adjuvant effects of novel NKT stimulatory glycolipids on hemagglutinin based DNA vaccine for H5N1 influenza virus

H5N1 influenza virus is a highly pathogenic virus, posing a pandemic threat. Previously, we showed that phenyl analogs of α-galactosylceramide (α-GalCer) displayed greater NKT stimulation than α-GalCer. Here, we examined the adjuvant effects of one of the most potent analogs, C34, on consensus hemagglutinin based DNA vaccine (pCHA5) for H5N1 virus. Upon intramuscular electroporation of mice with pCHA5 with/without various α-GalCer analogs, C34-adjuvanted group developed the highest titer against consensus H5 and more HA-specific IFN-γ secreting CD8 cells (203±13.5) than pCHA5 alone (152.6±13.7, p<0.05). Upon lethal challenge of NIBRG-14 virus, C34-adjuvanted group (84.6%) displayed higher survival rate than pCHA5 only group (46.1%). In the presence of C34 as adjuvant, the antisera displayed broader and greater neutralizing activities against virions pseudotyped with HA of clade 1, and 2.2 than pCHA5 only group. Moreover, to simulate an emergency response to a sudden H5N1 outbreak, we injected mice intramuscularly with single dose of a new consensus H5 (pCHA5-II) based on 1192 full-length H5 sequences, with C34 as adjuvant. The latter not only enhanced the humoral immune response and protection against virus challenge, but also broadened the spectrum of neutralization against pseudotyped HA viruses. Our vaccine strategy can be easily implemented for any H5N1 virus outbreak by single IM injection of a consensus H5 DNA vaccine based on updated HA sequences using C34 as an adjuvant.

Enhancement of recombinant adenovirus vaccine-induced primary but not secondary systemic and mucosal immune responses by all-trans retinoic acid

Vaccination is an important tool for enhancing immune responses against mucosal pathogens. Intramuscularly administered adenovirus (Ad) vectors have been demonstrated to be strong inducers of both systemic and mucosal immune responses. Further enhancement of immune responses following Ad vaccination is highly desirable. All-trans retinoic acid (ATRA), a biologically active vitamin A metabolite, has been explored as an adjuvant for primary immune responses following vaccination. In this study, we investigated the effect of ATRA on a heterologous Ad prime boost regimen. ATRA co-administration during priming increased mucosal and systemic antibody responses as well as mucosal but not systemic CD8(+) T cell responses. However, this effect was no longer apparent after boosting regardless of whether ATRA was administered at the time of priming, at the time of boosting, or at both immunizations. Our findings confirm ATRA as an adjuvant for primary immune responses and suggest that the adjuvant effect does not extend to secondary immune responses.

Sublingual vaccination induces mucosal and systemic adaptive immunity for protection against lung tumor challenge

Sublingual route offers a safer and more practical approach for delivering vaccines relative to other systemic and mucosal immunization strategies. Here we present evidence demonstrating protection against ovalbumin expressing B16 (B16-OVA) metastatic melanoma lung tumor formation by sublingual vaccination with the model tumor antigen OVA plus synthetic glycolipid alpha-galactosylceramide (aGalCer) for harnessing the adjuvant potential of natural killer T (NKT) cells, which effectively bridge innate and adaptive arms of the immune system. The protective efficacy of immunization with OVA plus aGalCer was antigen-specific as immunized mice challenged with parental B16 tumors lacking OVA expression were not protected. Multiple sublingual immunizations in the presence, but not in the absence of aGalCer, resulted in repeated activation of NKT cells in the draining lymph nodes, spleens, and lungs of immunized animals concurrent with progressively increasing OVA-specific CD8+ T cell responses as well as serum IgG and vaginal IgA levels. Furthermore, sublingual administration of the antigen only in the presence of the aGalCer adjuvant effectively boosted the OVA-specific immune responses. These results support potential clinical utility of sublingual route of vaccination with aGalCer-for prevention of pulmonary metastases.

Invariant NKT cells as novel targets for immunotherapy in solid tumors

Natural killer T (NKT) cells are a small population of lymphocytes that possess characteristics of both innate and adaptive immune cells. They are uniquely poised to respond rapidly to infection and inflammation and produce cytokines that critically shape the ensuing adaptive cellular response. Therefore, they represent promising therapeutic targets. In cancer, NKT cells are attributed a role in immunosurveillance. NKT cells also act as potent activators of antitumor immunity when stimulated with a synthetic agonist in experimental models. However, in some settings, NKT cells seem to act as suppressors and regulators of antitumor immunity. Here we briefly review current data supporting these paradoxical roles of NKT cells and their regulation. Increased understanding of the signals that determine the function of NKT cells in cancer will be essential to improve current strategies for NKT-cell-based immunotherapeutic approaches.

Mucosal vaccine adjuvants update

Mucosal vaccination, capable of inducing protective immune responses both in the mucosal and systemic immune compartments, has many advantages and is regarded as a blue ocean in the vaccine industry. Mucosal vaccines can offer lower costs, better accessability, needle-free delivery, and higher capacity of mass immunizations during pandemics. However, only very limited number of mucosal vaccines was approved for human use in the market yet. Generally, induction of immune responses following mucosal immunization requires the co-administration of appropriate adjuvants that can initiate and support the effective collaboration between innate and adaptive immunity. Classically, adjuvant researches were rather empirical than keenly scientific. However, during last several years, fundamental scientific achievements in innate immunity have been translated into the development of new mucosal adjuvants. This review focuses on recent developments in the concepts of adjuvants and innate immunity, mucosal immunity with special interest of vaccine development, and basic and applied researches in mucosal adjuvant.

Natural killer T cell based Immunotherapy

Natural killer T (NKT) cells play an important immunoregulatory role and are thought to bridge the innate and adaptive immune responses. Following activation through cognate interactions with lipid antigen presented in the context of CD1d molecules, NKT cells rapidly produce a plethora of cytokines and can also mediate cytotoxicity. Due to their potent effector functions, extensive research has been performed to increase our understanding on how to effectively modulate these cells. In fact, NKT cell agonists have been used as vaccine adjuvants to enhance antigen specific T and B cell responses to infections and malignancy. In this review, we will focus on recent advances in NKT cell-based vaccination strategies. Given the role that NKT cells play in autoimmune disease, infectious diseases, cancer, transplant immunology and dermatology, it is important to understand how to effectively guide their effector functions in order to develop novel immunotherapeutic strategies.

Intranasal but not intravenous delivery of the adjuvant α-galactosylceramide permits repeated stimulation of natural killer T cells in the lung

Efficient induction of antigen-specific immunity is achieved by delivering multiple doses of vaccine formulated with appropriate adjuvants that can harness the benefits of innate immune mediators. The synthetic glycolipid α-galactosylceramide (α-GalCer) is a potent activator of NKT cells, a major innate immune mediator cell type effective in inducing maturation of DCs for efficient presentation of co-administered antigens. However, systemic administration of α-GalCer results in NKT cell anergy in which the cells are unresponsive to subsequent doses of α-GalCer. We show here that α-GalCer delivered as an adjuvant by the intranasal route, as opposed to the intravenous route, enables repeated activation of NKT cells and DCs, resulting in efficient induction of cellular immune responses to co-administered antigens. We show evidence that after intranasal delivery,α-GalCer is selectively presented by DCs for the activation of NKT cells, not B cells. Furthermore, higher levels of PD-1 expression, a potential marker for functional exhaustion of the NKT cells when α-GalCer is delivered by the intravenous route, are not observed after intranasal delivery. These results support a mucosal route of delivery for the utility of α-GalCer as an adjuvant for vaccines, which often requires repeated dosing to achieve durable protective immunity.