Natural killer T cell ligand alpha-galactosylceramide enhances protective immunity induced by malaria vaccines

Application prospect of polysaccharide in the development of vaccine adjuvants

Vaccination is an effective strategy for preventing infectious diseases. Subunit vaccines offer more precise targeting and safer protection compared with traditional inactivated virus vaccines. However, due to their poor immunogenicity, subunit vaccines necessitate the use of adjuvants to stimulate the immune system. Adjuvants have long been incorporated into vaccines to enhance the body's immune response, allowing for reduced dosage and lower production costs. Despite the development of numerous vaccine adjuvants, few exhibit the necessary potency and low toxicity for clinical use, often due to limited efficacy or adverse side effects. This underscores the urgent need for novel human vaccine adjuvants that are safe, effective, and cost-efficient. Recent studies have identified certain natural polysaccharides as promising human vaccine adjuvants due to their immunostimulatory properties, low toxicity, and high safety profiles, which enhance both humoral and cellular immunity. These natural polysaccharides are primarily derived from traditional Chinese medicine (TCM) plants, bacteria, and yeast. This review comprehensively analyzes several promising polysaccharide adjuvants, discussing their clinical applications, market potential, and immunoregulatory activities. In summary, the future prospects of polysaccharides provide valuable insights for the application and development of vaccine adjuvants.

Targeting T-Cell Activation for Malaria Immunotherapy: Scoping Review

Malaria remains a critical global health issue due to high mortality rates, drug resistance, and low treatment efficacy. The genetic variability of Plasmodium proteins complicates the development of long-lasting immunity, as it impedes the human immune system's ability to sustain effective responses. T cells play a crucial role in combating malaria, but the parasite's complex life cycle-spanning liver and blood stages-presents significant challenges in effectively activating and targeting these cells. Immunotherapy, which enhances the immune response and promotes durable T cell activity, offers a promising avenue for more effective and lasting malaria treatments. This review systematically analyzed 63 studies published in the last decade, focusing on the role of T cells in malaria. Among the studies, 87.2% targeted T cells as immunotherapy candidates, with CD4+ and CD8+ T cells each accounting for 47.6% of the studies. γδ T cells were the focus in 7.9% of cases, while 12.7% explored non-T cell contributions to enhancing T cell-mediated responses. The findings underscore the potential of T cells, particularly CD8+ T cells, in liver-stage defense and advocate for the exploration of advanced vaccine platforms and novel therapies, such as mRNA-based vectors and monoclonal antibodies.

Developing a potent vaccine against Helicobacter pylori: critical considerations and challenges

Helicobacter pylori (H. pylori) is closely associated with gastric cancer and peptic ulcers. The effectiveness of antibiotic treatment against H. pylori is diminished by the emergence of drug-resistant strains, side effects, high cost and reinfections. Given the circumstances, it is imperative to develop a potent vaccination targeting H. pylori. Understanding H. pylori's pathogenicity and the host's immune response is essential to developing a vaccine. Furthermore, vaccine evaluation necessitates the careful selection of design formulation. This review article aims to provide a concise overview of the considerations involved in selecting the optimal antigen, adjuvant, vaccine delivery system and laboratory animal model for vaccine formulation. Furthermore, we will discuss some significant obstacles in the realm of developing a potent vaccination against H. pylori.

Glycolipid antigen recognition by invariant natural killer T cells and its role in homeostasis and antimicrobial responses

Due to the COVID-19 pandemic, the importance of developing effective vaccines has received more attention than ever before. To maximize the effects of vaccines, it is important to select adjuvants that induce strong and rapid innate and acquired immune responses. Invariant natural killer T (iNKT) cells, which constitute a small population among lymphocytes, bypass the innate and acquired immune systems through the rapid production of cytokines after glycolipid recognition; hence, their activation could be used as a vaccine strategy against emerging infectious diseases. Additionally, the diverse functions of iNKT cells, including enhancing antibody production, are becoming more understood in recent years. In this review, we briefly describe the functional subset of iNKT cells and introduce the glycolipid antigens recognized by them. Furthermore, we also introduce novel vaccine development taking advantages of iNKT cell activation against infectious diseases.

Innate immune cell activation after HIV-1 vaccine administration is associated with increased antibody production

The RV144 Thai phase III clinical trial's canarypox-protein HIV vaccine regimen showed modest efficacy in reducing infection. We therefore sought to determine the effects of vaccine administration on innate cell activation and subsequent associations with vaccine-induced immune responses. RV306 was a randomized, double-blind clinical trial in HIV-uninfected Thai adults that tested delayed boosting following the RV144 regimen. PBMC collected from RV306 participants prior to and 3 days after the last boost were used to investigate innate immune cell activation. Our analysis showed an increase in CD38+ mucosal associated invariant T (MAIT) cells, CD38+ invariant natural killer T (iNKT) cells, CD38+ γδ T cells, CD38+, CD69+ and HLA-DR+ NK cells 3 days after vaccine administration. An increase in CD14-CD16+ non-classical monocytes and CD14+CD16+ intermediate monocytes accompanied by a decrease in CD14+CD16- classical monocytes was also associated with vaccine administration. Inclusion of ALVAC-HIV in the boost did not further increase MAIT, iNKT, γδ T, and NK cell activation or increase the proportion of non-classical monocytes. Additionally, NK cell activation 3 days after vaccination was positively associated with antibody titers of HIV Env-specific total IgG and IgG1. Vδ1 T cell activation 3 days after vaccine administration was associated with HIV Env-specific IgG3 titers. Finally, we observed trending associations between MAIT cell activation and Env-specific IgG3 titers and between NK cell activation and TH023 pseudovirus neutralization titers. Our study identifies a potential role for innate cells, specifically NK, MAIT, and γδ T cells, in promoting antibody responses following HIV-1 vaccine administration.

Recruiting Natural Killer T Cells to Improve Vaccination: Lessons from Preclinical and Clinical Studies

The capacity of type I natural killer T (NKT) cells to provide stimulatory signals to antigen-presenting cells has prompted preclinical research into the use of agonists as immune adjuvants, with much of this work focussed on stimulating T cell responses to cancer. In attempting to evaluate this approach in the clinic, our recent dendritic-cell based study failed to show an advantage to adding an agonist to the vaccine. Here we present potential limitations of the study, and suggest why other simpler strategies may be more effective. These include strategies to target antigen-presenting cells in the host, either through promoting efficient transfer from injected cell lines, facilitating uptake of antigen and agonist as injected conjugates, or encapsulating the components into injected nanovectors. While the vaccine landscape has changed with the rapid uptake of mRNA vaccines, we suggest that there is still a role for recruiting NKT cells in altering T cell differentiation programmes, notably the induction of resident memory T cells.

Natural Killer T Cell Diversity and Immunotherapy

Invariant natural killer T cells (iNKTs), a type of unconventional T cells, share features with NK cells and have an invariant T cell receptor (TCR), which recognizes lipid antigens loaded on CD1d molecules, a major histocompatibility complex class I (MHC-I)-like protein. This interaction produces the secretion of a wide array of cytokines by these cells, including interferon gamma (IFN-γ) and interleukin 4 (IL-4), allowing iNKTs to link innate with adaptive responses. Interestingly, molecules that bind CD1d have been identified that enable the modulation of these cells, highlighting their potential pro-inflammatory and immunosuppressive capacities, as required in different clinical settings. In this review, we summarize key features of iNKTs and current understandings of modulatory α-galactosylceramide (α-GalCer) variants, a model iNKT cell activator that can shift the outcome of adaptive immune responses. Furthermore, we discuss advances in the development of strategies that modulate these cells to target pathologies that are considerable healthcare burdens. Finally, we recapitulate findings supporting a role for iNKTs in infectious diseases and tumor immunotherapy.

Chemically augmented malaria sporozoites display an altered immunogenic profile

Despite promising results in malaria-naïve individuals, whole sporozoite (SPZ) vaccine efficacy in malaria-endemic settings has been suboptimal. Vaccine hypo-responsiveness due to previous malaria exposure has been posited as responsible, indicating the need for SPZ vaccines of increased immunogenicity. To this end, we here demonstrate a proof-of-concept for altering SPZ immunogenicity, where supramolecular chemistry enables chemical augmentation of the parasite surface with a TLR7 agonist-based adjuvant (SPZ-SAS(CL307)). In vitro, SPZ-SAS(CL307) remained well recognized by immune cells and induced a 35-fold increase in the production of pro-inflammatory IL-6 (p < 0.001). More promisingly, immunization of mice with SPZ-SAS(CL307) yielded improved SPZ-specific IFN-γ production in liver-derived NK cells (percentage IFN-γ+ cells 11.1 ± 1.8 vs. 9.4 ± 1.5%, p < 0.05), CD4+ T cells (4.7 ± 4.3 vs. 1.8 ± 0.7%, p < 0.05) and CD8+ T cells (3.6 ± 1.4 vs. 2.5 ± 0.9%, p < 0.05). These findings demonstrate the potential of using chemical augmentation strategies to enhance the immunogenicity of SPZ-based malaria vaccines.

A randomised controlled trial of long NY-ESO-1 peptide-pulsed autologous dendritic cells with or without alpha-galactosylceramide in high-risk melanoma

AIM

We have previously reported that polyfunctional T cell responses can be induced to the cancer testis antigen NY-ESO-1 in melanoma patients injected with mature autologous monocyte-derived dendritic cells (DCs) loaded with long NY-ESO-1-derived peptides together with α-galactosylceramide (α-GalCer), an agonist for type 1 Natural Killer T (NKT) cells.

OBJECTIVE

To assess whether inclusion of α-GalCer in autologous NY-ESO-1 long peptide-pulsed DC vaccines (DCV + α-GalCer) improves T cell responses when compared to peptide-pulsed DC vaccines without α-GalCer (DCV).

DESIGN, SETTING AND PARTICIPANTS

Single-centre blinded randomised controlled trial in patients ≥ 18 years old with histologically confirmed, fully resected stage II-IV malignant cutaneous melanoma, conducted between July 2015 and June 2018 at the Wellington Blood and Cancer Centre of the Capital and Coast District Health Board.

INTERVENTIONS

Stage I. Patients were randomised to two cycles of DCV or DCV + α-GalCer (intravenous dose of 10 × 106 cells, interval of 28 days). Stage II. Patients assigned to DCV + α-GalCer were randomised to two further cycles of DCV + α-GalCer or observation, while patients initially assigned to DCV crossed over to two cycles of DCV + α-GalCer.

OUTCOME MEASURES

Primary: Area under the curve (AUC) of mean NY-ESO-1-specific T cell count detected by ex vivo IFN-γ ELISpot in pre- and post-treatment blood samples, compared between treatment arms at Stage I. Secondary: Proportion of responders in each arm at Stage I; NKT cell count in each arm at Stage I; serum cytokine levels at Stage I; adverse events Stage I; T cell count for DCV + α-GalCer versus observation at Stage II, T cell count before versus after cross-over.

RESULTS

Thirty-eight patients gave written informed consent; 5 were excluded before randomisation due to progressive disease or incomplete leukapheresis, 17 were assigned to DCV, and 16 to DCV + α-GalCer. The vaccines were well tolerated and associated with increases in mean total T cell count, predominantly CD4+ T cells, but the difference between the treatment arms was not statistically significant (difference - 6.85, 95% confidence interval, - 21.65 to 7.92; P = 0.36). No significant improvements in T cell response were associated with DCV + α-GalCer with increased dosing, or in the cross-over. However, the NKT cell response to α-GalCer-loaded vaccines was limited compared to previous studies, with mean circulating NKT cell levels not significantly increased in the DCV + α-GalCer arm and no significant differences in cytokine response between the treatment arms.

CONCLUSIONS

A high population coverage of NY-ESO-1-specific T cell responses was achieved with a good safety profile, but we failed to demonstrate that loading with α-GalCer provided an additional advantage to the T cell response with this cellular vaccine design.

CLINICAL TRIAL REGISTRATION

ACTRN12612001101875. Funded by the Health Research Council of New Zealand.

How Long Will It Take to Launch an Effective Helicobacter pylori Vaccine for Humans?

Helicobacter pylori infection often occurs in early childhood, and can last a lifetime if not treated with medication. H. pylori infection can also cause a variety of stomach diseases, which can only be treated with a combination of antibiotics. Combinations of antibiotics can cure H. pylori infection, but it is easy to relapse and develop drug resistance. Therefore, a vaccine is a promising strategy for prevention and therapy for the infection of H. pylori. After decades of research and development, there has been no appearance of any H. pylori vaccine reaching the market, unfortunately. This review summarizes the aspects of candidate antigens, immunoadjuvants, and delivery systems in the long journey of H. pylori vaccine research, and also introduces some clinical trials that have displayed encouraging or depressing results. Possible reasons for the inability of an H. pylori vaccine to be available over the counter are cautiously discussed and some propositions for the future of H. pylori vaccines are outlined.

Alpha-galactosylceramide as adjuvant induces protective cell-mediated immunity against Leishmania mexicana infection in vaccinated BALB/c mice

Adjuvants represent a promising strategy to improve vaccine effectiveness against infectious diseases such as leishmaniasis. Vaccination with the invariant natural killer T cell ligand α-galactosylceramide (αGalCer) has been used successfully as adjuvant, generating a Th1-biased immunomodulation. This glycolipid enhances experimental vaccination platforms against intracellular parasites including Plasmodium yoelii and Mycobacterium tuberculosis. In the present study, we assessed the protective immunity induced by a single-dose intraperitoneal injection of αGalCer (2 μg) co-administrated with a lysate antigen of amastigotes (100 μg) against Leishmania mexicana infection in BALB/c mice. The prophylactic vaccination led to 5.0-fold reduction of parasite load at the infection site, compared to non-vaccinated mice. A predominant pro-inflammatory response was observed in challenged vaccinated mice, represented by a 1.9 and 2.8-fold-increase of IL-1β and IFN-γ producing cells, respectively, in the lesions, and by 23.7-fold-increase of IFN-γ production in supernatants of restimulated splenocytes, all compared to control groups. The co-administration of αGalCer also stimulated the maturation of splenic dendritic cells and modulated a Th1-skewed immune response, with high amounts of IFN-γ production in serum. Furthermore, peritoneal cells of αGalCer-immunized mice exhibited an elevated expression of Ly6G and MHCII. These findings indicate that αGalCer improves protection against cutaneous leishmaniasis, supporting evidence for its potential use as adjuvant in Leishmania-vaccines.

Glycolipid-peptide conjugate vaccines elicit CD8+ T-cell responses and prevent breast cancer metastasis

Objectives

Metastasis is the principal cause of breast cancer mortality. Vaccines targeting breast cancer antigens have yet to demonstrate clinical efficacy, and there remains an unmet need for safe and effective treatment to reduce the risk of metastasis, particularly for people with triple-negative breast cancer (TNBC). Certain glycolipids can act as vaccine adjuvants by specifically stimulating natural killer T (NKT) cells to provide a universal form of T-cell help.

Methods

We designed and made a series of conjugate vaccines comprising a prodrug of the NKT cell-activating glycolipid α-galactosylceramide covalently linked to tumor-expressed peptides, and assessed these using E0771- and 4T1-based breast cancer models in vivo. We employed peptides from the model antigen ovalbumin and from clinically relevant breast cancer antigens HER2 and NY-ESO-1.

Results

Glycolipid-peptide conjugate vaccines that activate NKT cells led to antigen-presenting cell activation, induced inflammatory cytokines, and, compared with peptide alone or admixed peptide and α-galactosylceramide, specifically enhanced CD8⁺ T-cell responses against tumor-associated peptides. Primary tumor growth was delayed by vaccination in all tumor models. Using 4T1-based cell lines expressing HER2 or NY-ESO-1, a single administration of the relevant conjugate vaccine prevented tumor colonisation of the lung following intravenous inoculation of tumor cells or spontaneous metastasis from breast, respectively.

Conclusion

Glycolipid-peptide conjugate vaccines that activate NKT cells prevent lung metastasis in breast cancer models and warrant investigation as adjuvant therapies for high-risk breast cancer.

Encapsulation of MERS antigen into α-GalCer-bearing-liposomes elicits stronger effector and memory immune responses in immunocompetent and leukopenic mice

OBJECTIVES

Here, we prepared a liposome-based vaccine formulation containing Middle East Respiratory Syndrome Coronavirus papain-like protease (MERS-CoV-PLpro).

METHODS

A persistent leukopenic condition was induced in mice by injecting cyclophosphamide (CYP) three days before each dose of immunization. Mice were immunized on days 0, 14 and 21 with α-GalCer-bearing MERS-CoV PLpro-encapsulated DPPC-liposomes (α-GalCer-MERS-PLpro-liposomes or MERS-CoV PLpo-encapsulated DPPC-liposomes (MERS-PLpro-liposomes), whereas the antigen emulsified in Alum (MERS-PLpro-Alum) was taken as a control. On day 26, the blood was taken from the immunized mice to analyze IgG titer, whereas the splenocytes were used to analyze the lymphocyte proliferation and the level of cytokines. In order to assess the memory immune response, mice were given a booster dose after 150 days of the last immunization.

RESULTS

The higher levels of MERS-CoV-PLpro-specific antibody titer, IgG2a and lymphocyte proliferation were noticed in mice immunized with α-GalCer-MERS-PLpro-liposomes. Besides, the splenocytes from mice immunized with α-GalCer-MERS-PLpro-liposomes produced larger amounts of IFN-γ as compared to the splenocytes from MERS-PLpro-liposomes or MERS- PLpro-Alum immunized mice. Importantly, an efficient antigen-specific memory immune response was observed in α-GalCer-MERS-PLpro-liposomes immunized mice.

CONCLUSIONS

These findings suggest that α-GalCer-MERS-PLpro-liposomes may substantiate to be a successful vaccine formulation against MERS-CoV infection, particularly in immunocompromised individuals.

Intratumoural administration of an NKT cell agonist with CpG promotes NKT cell infiltration associated with an enhanced antitumour response and abscopal effect

Intratumoural administration of unmethylated cytosine-phosphate-guanine motifs (CpG) to stimulate toll-like receptor (TLR)-9 has been shown to induce tumour regression in preclinical studies and some efficacy in the clinic. Because activated natural killer T (NKT) cells can cooperate with pattern-recognition via TLRs to improve adaptive immune responses, we assessed the impact of combining a repeated dosing regimen of intratumoural CpG with a single intratumoural dose of the NKT cell agonist α-galactosylceramide (α-GalCer). The combination was superior to CpG alone at inducing regression of established tumours in several murine tumour models, primarily mediated by CD8⁺ T cells. An antitumour effect on distant untreated tumours (abscopal effect) was reliant on sustained activity of NKT cells and was associated with infiltration of KLRG1⁺ NKT cells in tumours and draining lymph nodes at both injected and untreated distant sites. Cytometric analysis pointed to increased exposure to type I interferon (IFN) affecting many immune cell types in the tumour and lymphoid organs. Accordingly, antitumour activity was lost in animals in which dendritic cells (DCs) were incapable of signaling through the type I IFN receptor. Studies in conditional ablation models showed that conventional type 1 DCs and plasmacytoid DCs were required for the response. In tumour models where the combined treatment was less effective, the addition of tumour-antigen derived peptide, preferably conjugated to α-GalCer, significantly enhanced the antitumour response. The combination of TLR ligation, NKT cell agonism, and peptide delivery could therefore be adapted to induce responses to both known and unknown antigens.

Immunomodulatory potential of in vivo natural killer T (NKT) activation by NKTT320 in Mauritian-origin cynomolgus macaques

Invariant natural killer T-lymphocytes (iNKT) are unique immunomodulatory innate T cells with an invariant TCRα recognizing glycolipids presented on MHC class-I-like CD1d molecules. Activated iNKT rapidly secrete pro-and anti-inflammatory cytokines, potentiate immunity, and modulate inflammation. Here, we report the effects of in vivo iNKT activation in Mauritian-origin cynomolgus macaques by a humanized monoclonal antibody, NKTT320, that binds to the invariant region of the iNKT TCR. NKTT320 led to rapid iNKT activation, increased polyfunctionality, and elevation of multiple plasma analytes within 24 hours. Flow cytometry and RNA-Seq confirmed downstream activation of multiple immune subsets, enrichment of JAK/STAT and PI3K/AKT pathway genes, and upregulation of inflammation-modulating genes. NKTT320 also increased iNKT frequency in adipose tissue and did not cause iNKT anergy. Our data indicate that NKTT320 has a sustained effect on in vivo iNKT activation, potentiation of innate and adaptive immunity, and resolution of inflammation, which supports its future use as an immunotherapeutic.

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NKTT320 rapidly activates iNKT in vivo, modulating downstream immune function

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In vivo NKTT320 treatment modulates pro- and anti-inflammatory genes

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NKTT320 treatment results in activation of innate and adaptive immune subsets

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NKTT320 has promise as an immunotherapeutic with translational potential

Harnessing NKT cells for vaccination

Natural killer T (NKT) cells are innate-like T cells capable of enhancing both innate and adaptive immune responses. When NKT cells are stimulated in close temporal association with co-administered antigens, strong antigen-specific immune responses can be induced, prompting the study of NKT cell agonists as novel immune adjuvants. This activity has been attributed to the capacity of activated NKT cells to act as universal helper cells, with the ability to provide molecular signals to dendritic cells and B cells that facilitate T cell and antibody responses, respectively. These signals can override the requirement for conventional CD4⁺ T cell help, so that vaccines can be designed without need to consider CD4⁺ T cell repertoire and major histocompatibility complex Class II diversity. Animal studies have highlighted some drawbacks of the approach, namely, concerns around induction of NKT cell hyporesponsiveness, which may limit vaccine boosting, and potential for toxicity. Here we highlight studies that suggest these obstacles can be overcome by targeted delivery in vivo. We also feature new studies that suggest activating NKT cells can help encourage differentiation of T cells into tissue-resident memory cells that play an important role in prophylaxis against infection, and may be required in cancer therapy.

Systems analysis and controlled malaria infection in Europeans and Africans elucidate naturally acquired immunity

Controlled human infections provide opportunities to study the interaction between the immune system and malaria parasites, which is essential for vaccine development. Here, we compared immune signatures of malaria-naive Europeans and of Africans with lifelong malaria exposure using mass cytometry, RNA sequencing and data integration, before and 5 and 11 days after venous inoculation with Plasmodium falciparum sporozoites. We observed differences in immune cell populations, antigen-specific responses and gene expression profiles between Europeans and Africans and among Africans with differing degrees of immunity. Before inoculation, an activated/differentiated state of both innate and adaptive cells, including elevated CD161⁺CD4⁺ T cells and interferon-γ production, predicted Africans capable of controlling parasitemia. After inoculation, the rapidity of the transcriptional response and clusters of CD4⁺ T cells, plasmacytoid dendritic cells and innate T cells were among the features distinguishing Africans capable of controlling parasitemia from susceptible individuals. These findings can guide the development of a vaccine effective in malaria-endemic regions.

Discovery of Semi- and Fully-Synthetic Carbohydrate Vaccines Against Bacterial Infections Using a Medicinal Chemistry Approach

The glycocalyx, a thick layer of carbohydrates, surrounds the cell wall of most bacterial and parasitic pathogens. Recognition of these unique glycans by the human immune system results in destruction of the invaders. To elicit a protective immune response, polysaccharides either isolated from the bacterial cell surface or conjugated with a carrier protein, for T-cell help, are administered. Conjugate vaccines based on isolated carbohydrates currently protect millions of people against Streptococcus pneumoniae, Haemophilus influenzae type b, and Neisseria meningitides infections. Active pharmaceutical ingredients (APIs) are increasingly discovered by medicinal chemistry and synthetic in origin, rather than isolated from natural sources. Converting vaccines from biologicals to pharmaceuticals requires a fundamental understanding of how the human immune system recognizes carbohydrates and could now be realized. To illustrate the chemistry-based approach to vaccine discovery, I summarize efforts focusing on synthetic glycan-based medicinal chemistry to understand the mammalian antiglycan immune response and define glycan epitopes for novel synthetic glycoconjugate vaccines against Streptococcus pneumoniae, Clostridium difficile, Klebsiella pneumoniae, and other bacteria. The chemical tools described here help us gain fundamental insights into how the human system recognizes carbohydrates and drive the discovery of carbohydrate vaccines.

Type I Natural Killer T Cells as Key Regulators of the Immune Response to Infectious Diseases

The immune system must work in an orchestrated way to achieve an optimal response upon detection of antigens. The cells comprising the immune response are traditionally divided into two major subsets, innate and adaptive, with particular characteristics for each type. Type I natural killer T (iNKT) cells are defined as innate-like T cells sharing features with both traditional adaptive and innate cells, such as the expression of an invariant T cell receptor (TCR) and several NK receptors. The invariant TCR in iNKT cells interacts with CD1d, a major histocompatibility complex class I (MHC-I)-like molecule. CD1d can bind and present antigens of lipid nature and induce the activation of iNKT cells, leading to the secretion of various cytokines, such as gamma interferon (IFN-γ) and interleukin 4 (IL-4). These cytokines will aid in the activation of other immune cells following stimulation of iNKT cells. Several molecules with the capacity to bind to CD1d have been discovered, including α-galactosylceramide. Likewise, several molecules have been synthesized that are capable of polarizing iNKT cells into different profiles, either pro- or anti-inflammatory. This versatility allows NKT cells to either aid or impair the clearance of pathogens or to even control or increase the symptoms associated with pathogenic infections. Such diverse contributions of NKT cells to infectious diseases are supported by several publications showing either a beneficial or detrimental role of these cells during diseases. In this article, we discuss current data relative to iNKT cells and their features, with an emphasis on their driving role in diseases produced by pathogenic agents in an organ-oriented fashion.

Development of Plasmodium-specific liver-resident memory CD8+ T cells after heat-killed sporozoite immunization in mice

Malaria remains a major cause of mortality in the world and an efficient vaccine is the best chance of reducing the disease burden. Vaccination strategies for the liver stage of disease that utilise injection of live radiation-attenuated sporozoites (RAS) confer sterile immunity, which is mediated by CD8⁺ memory T cells, with liver-resident memory T cells (T_RM ) being particularly important. We have previously described a TCR transgenic mouse, termed PbT-I, where all CD8⁺ T cells recognize a specific peptide from Plasmodium. PbT-I form liver T_RM cells upon RAS injection and are capable of protecting mice against challenge infection. Here, we utilize this transgenic system to examine whether nonliving sporozoites, killed by heat treatment (HKS), could trigger the development of Plasmodium-specific liver T_RM cells. We found that HKS vaccination induced the formation of memory CD8⁺ T cells in the spleen and liver, and importantly, liver T_RM cells were fewer in number than that induced by RAS. Crucially, we showed the number of T_RM cells was significantly higher when HKS were combined with the glycolipid α-galactosylceramide as an adjuvant. In the future, this work could lead to development of an antimalaria vaccination strategy that does not require live sporozoites, providing greater utility.

Glycolipid-peptide vaccination induces liver-resident memory CD8+ T cells that protect against rodent malaria

Liver resident-memory CD8⁺ T cells (T_RM cells) can kill liver-stage Plasmodium-infected cells and prevent malaria, but simple vaccines for generating this important immune population are lacking. Here, we report the development of a fully synthetic self-adjuvanting glycolipid-peptide conjugate vaccine designed to efficiently induce liver T_RM cells. Upon cleavage in vivo, the glycolipid-peptide conjugate vaccine releases an MHC I-restricted peptide epitope (to stimulate Plasmodium-specific CD8⁺ T cells) and an adjuvant component, the NKT cell agonist α-galactosylceramide (α-GalCer). A single dose of this vaccine in mice induced substantial numbers of intrahepatic malaria-specific CD8⁺ T cells expressing canonical markers of liver T_RM cells (CD69, CXCR6, and CD101), and these cells could be further increased in number upon vaccine boosting. We show that modifications to the peptide, such as addition of proteasomal-cleavage sequences or epitope-flanking sequences, or the use of alternative conjugation methods to link the peptide to the glycolipid improved liver T_RM cell generation and led to the development of a vaccine able to induce sterile protection in C57BL/6 mice against Plasmodium berghei sporozoite challenge after a single dose. Furthermore, this vaccine induced endogenous liver T_RM cells that were long-lived (half-life of ~425 days) and were able to maintain >90% sterile protection to day 200. Our findings describe an ideal synthetic vaccine platform for generating large numbers of liver T_RM cells for effective control of liver-stage malaria and, potentially, a variety of other hepatotropic infections.

Harnessing liver-resident memory T cells for protection against malaria

INTRODUCTION

Tissue-resident memory T cells (T_RM cells) are powerful mediators of protracted adaptive immunity to infection in peripheral organs. Harnessing T_RM cells through vaccination hence promises unprecedented potential for protection against infection. A paramount example of this is malaria, a major infectious disease for which immunity through traditional vaccination strategies remains challenging. Liver T_RM cells appear to be highly protective against malaria, and recent developments in our knowledge of the biology of these cells have defined promising, novel strategies for their induction.

AREAS COVERED

Here, we describe the path that led to the discovery of T_RM cells and discuss the importance of liver T_RM cells in immunity against Plasmodium spp. infection; we summarize current knowledge on T_RM cell biology and discuss the current state and potential of T_RM-based vaccination against malaria.

EXPERT OPINION

T_RM based vaccination has emerged as a promising means to achieve efficient protection against malaria. Recent advances provide a solid basis for continuing the development of this area of research. Deeper understanding of the mechanisms that mediate T_RM formation and maintenance and identification of immunogenic and protective target epitopes suitable for human vaccination remain the main challenges for translation of these discoveries.

Invariant natural killer T cells balance B cell immunity

Invariant natural killer T (iNKT) cells mediate rapid immune responses which bridge the gap between innate and adaptive responses to pathogens while also providing key regulation to maintain immune homeostasis. Both types of important iNKT immune responses are mediated through interactions with innate and adaptive B cells. As such, iNKT cells sit at the decision-making fulcrum between regulating inflammatory or autoreactive B cells and supporting protective or regulatory B cell populations. iNKT cells interpret the signals in their environment to set the tone for subsequent adaptive responses, with outcomes ranging from getting licensed to maintain homeostasis as an iNKT regulatory cell (iNKT_reg ) or being activated to become an iNKT follicular helper (iNKT_FH ) cell supporting pathogen-specific effector B cells. Here we review iNKT and B cell cooperation across the spectrum of immune outcomes, including during allergy and autoimmune disease, tumor surveillance and immunotherapy, or pathogen defense and vaccine responses. Because of their key role as influencers, iNKT cells provide a valuable target for therapeutic interventions. Understanding the nature of the interactions between iNKT and B cells will enable the development of clinical interventions to strategically target regulatory iNKT and B cell populations or inflammatory ones, depending on the circumstance.

Using agonists for iNKT cells in cancer therapy

The capacity of α-galactosylceramide (α-GalCer) to act as an anti-cancer agent in mice through the specific stimulation of type I NKT (iNKT) cells has prompted extensive investigation to translate this finding to the clinic. However, low frequencies of iNKT cells in cancer patients and their hypo-responsiveness to repeated stimulation have been seen as barriers to its efficacy. Currently the most promising clinical application of α-GalCer, or its derivatives, is as stimuli for ex vivo expansion of iNKT cells for adoptive therapy, although some encouraging clinical results have recently been reported using α-GalCer pulsed onto large numbers of antigen presenting cells (APCs). In on-going preclinical studies, attempts to improve efficacy of injected iNKT cell agonists have focussed on optimising presentation in vivo, through encapsulation in particulate vectors, making structural changes that help binding to the presenting molecule CD1d, or injecting agonists covalently attached to recombinant CD1d. Variations on these same approaches are being used to enhance the APC-licencing function of iNKT cells in vivo to induce adaptive immune responses to associated tumour antigens. Looking ahead, a unique capacity of in vivo-activated iNKT cells to facilitate formation of resident memory CD8⁺ T cells is a new observation that could find a role in cancer therapy.

Targeted Co-delivery of Tumor Antigen and α-Galactosylceramide to CD141+ Dendritic Cells Induces a Potent Tumor Antigen-Specific Human CD8+ T Cell Response in Human Immune System Mice

Active co-delivery of tumor antigens (Ag) and α-galactosylceramide (α-GalCer), a potent agonist for invariant Natural Killer T (iNKT) cells, to cross-priming CD8α⁺ dendritic cells (DCs) was previously shown to promote strong anti-tumor responses in mice. Here, we designed a nanoparticle-based vaccine able to target human CD141⁺ (BDCA3⁺) DCs - the equivalent of murine CD8α⁺ DCs – and deliver both tumor Ag (Melan A) and α-GalCer. This nanovaccine was inoculated into humanized mice that mimic the human immune system (HIS) and possess functional iNKT cells and CD8⁺ T cells, called HIS-CD8/NKT mice. We found that multiple immunizations of HIS-CD8/NKT mice with the nanovaccine resulted in the activation and/or expansion of human CD141⁺ DCs and iNKT cells and ultimately elicited a potent Melan-A-specific CD8⁺ T cell response, as determined by tetramer staining and ELISpot assay. Single-cell proteomics further detailed the highly polyfunctional CD8⁺ T cells induced by the nanovaccine and revealed their predictive potential for vaccine potency. This finding demonstrates for the first time the unique ability of human iNKT cells to license cross-priming DCs in vivo and adds a new dimension to the current strategy of cancer vaccine development.

A Peptide-Based PD1 Antagonist Enhances T-Cell Priming and Efficacy of a Prophylactic Malaria Vaccine and Promotes Survival in a Lethal Malaria Model

The blockade of programmed cell death-1 (PD1) and its ligand PDL1 has been proven to be a successful immunotherapy against several cancers. Similar to cancer, PD1 contributes to the establishment of several chronic infectious diseases, including malaria. While monoclonal antibodies (mAbs) targeting checkpoint receptors are revolutionary in cancer treatment, the immune-related adverse events (irAEs) may prevent their utilization in prophylactic and therapeutic treatments of infectious diseases. The irAEs are, in part, due to the prolonged half-life of mAbs resulting in prolonged activation of the immune system. As an alternative modality to mAbs, peptides represent a viable option because they possess a shorter pharmacokinetic half-life and offer more formulation and delivery options. Here, we report on a 22-amino acid immunomodulatory peptide, LD01, derived from a Bacillus bacteria. When combined prophylactically with an adenovirus-based or irradiated sporozoite-based malaria vaccine, LD01 significantly enhanced antigen-specific CD8⁺ T cell expansion. Therapeutically, LD01 treatment of mice infected with a lethal malaria strain resulted in survival that was associated with lower numbers of FOXP3⁺Tbet⁺CD4⁺ regulatory T cells. Taken together, our results demonstrate that LD01 is a potent immunomodulator that acts upon the adaptive immune system to stimulate T cell responses both prophylactically and therapeutically.

Lipo-Based Vaccines as an Approach to Target Dendritic Cells for Induction of T- and iNKT Cell Responses

In this study we developed a liposome-based vaccine containing palmitoylated synthetic long peptides (SLP) and alpha galactosylceramide (αGC) to specifically target dendritic cells (DC) for activation of both innate (invariant natural killer T-cells [iNKT]) and adaptive (CD8⁺ T-cells) players of the immune system. Combination of model tumor specific antigens (gp100/MART-1) formulated as a SLP and αGC in one liposome results in strong activation of CD8⁺ and iNKT, as measured by IFNγ secretion. Moreover, addition of lipo-Lewis Y (Le^Y) to the liposomes for C-type lectin targeting increased not only uptake by monocyte-derived dendritic cells (moDC), dermal dendritic cells and Langerhans cells but also enhanced gp100-specific CD8⁺ T- and iNKT cell activation by human skin-emigrated antigen presenting cells in an ex vivo explant model. Loading of moDC with liposomes containing Le^Y also showed priming of MART-1_26−35L specific CD8⁺ T-cells. In conclusion, chemically linking a lipid tail to a glycan-based targeting moiety and SLP combined with αGC in one liposome allows for easy generation of vaccine formulations that target multiple skin DC subsets and induce tumor antigen specific CD8⁺ T- and iNKT cells. These liposomes present a new vaccination strategy against tumors.

Vaccines adjuvanted with an NKT cell agonist induce effective T-cell responses in models of CNS lymphoma

Aim: The efficacy of anti-lymphoma vaccines that exploit the cellular adjuvant properties of activated natural killer T (NKT) cells were examined in mouse models of CNS lymphoma. Materials & methods: Vaccines were prepared by either loading the NKT cell agonist, α-galactosylceramide onto irradiated and heat-shocked B- and T-lymphoma cells, or chemically conjugating α-galactosylceramide to MHC-binding peptides from a lymphoma-associated antigen. Vaccine efficacy was analyzed in mice bearing intracranial tumors. Results: Both forms of vaccine proved to be effective in preventing lymphoma engraftment through activity of T cells that accessed the CNS. Established lymphoma was harder to treat with responses constrained by Tregs, but this could be overcome by depleting Tregs prior to vaccination. Conclusion: Simply designed NKT cell-activating vaccines enhance T-cell responses and have the potential to protect against CNS lymphoma development or prevent CNS relapse. To be effective against established CNS lymphoma, vaccines need to be combined with Treg suppression.

Novel Peptide-Based PD1 Immunomodulators Demonstrate Efficacy in Infectious Disease Vaccines and Therapeutics

Many pathogens use the same immune evasion mechanisms as cancer cells. Patients with chronic infections have elevated levels of checkpoint receptors (e.g., programed cell death 1, PD1) on T cells. Monoclonal antibody (mAb)-based inhibitors to checkpoint receptors have also been shown to enhance T-cell responses in models of chronic infection. Therefore, inhibitors have the potential to act as a vaccine “adjuvant” by facilitating the expansion of vaccine antigen-specific T-cell repertoires. Here, we report the discovery and characterization of a peptide-based class of PD1 checkpoint inhibitors, which have a potent adaptive immunity adjuvant capability for vaccines against infectious diseases. Briefly, after identifying peptides that bind to the recombinant human PD1, we screened for in vitro efficacy in reporter assays and human peripheral blood mononuclear cells (PBMC) readouts. We first found the baseline in vivo performance of the peptides in a standard mouse oncology model that demonstrated equivalent efficacy compared to mAbs against the PD1 checkpoint. Subsequently, two strategies were used to demonstrate the utility of our peptides in infectious disease indications: (1) as a therapeutic in a bacteria-induced lethal sepsis model in which our peptides were found to increase survival with enhanced bacterial clearance and increased macrophage function; and (2) as an adjuvant in combination with a prophylactic malaria vaccine in which our peptides increased T-cell immunogenicity and the protective efficacy of the vaccine. Therefore, our peptides are promising as both a therapeutic agent and a vaccine adjuvant for infectious disease with a potentially safer and more cost-effective target product profile compared to mAbs. These findings are essential for deploying a new immunomodulatory regimen in infectious disease primary and clinical care settings.

Synthesis and biological activities of amino acids functionalized α-GalCer analogues

Invariant natural killer T-cells (iNKT-cells) are promising targets for manipulating the immune system, which can rapidly release a large amount of Th1 and Th2 cytokines upon the engagement of their T cell receptor with glycolipid antigens presented by CD1d. In this paper, we wish to report a novel series of α-GalCer analogues which were synthesized by incorporation of l-amino acid methyl esters in the C-6' position of glycolipid. The evaluation of these synthetic analogues for their capacities to stimulate iNKT-cells into producing Th1 and Th2 cytokines both in vitro and in vivo indicated that they were potent CD1d ligands and could stimulate murine spleen cells into a higher release of the Th1 cytokine IFN-γ in vitro. In vivo, Gly-α-GalCer (1) and Lys-α-GalCer (3) showed more Th1-biased responses than α-GalCer, especially analogue 3 showed the highest selectivity for IFN-γ production (IFN-γ/IL-4 = 5.32) compared with α-GalCer (IFN-γ/IL-4 = 2.5) in vivo. These novel α-GalCer analogues might be used as efficient X-ray crystallographic probes to reveal the relationship between glycolipids and CD1d proteins in α-GalCer/CD1d complexes and pave the way for developing new potent immunostimulating agents.

Emerging Marine Immunomodulatory Small-molecules (2010- Present)

Background:

Immunomodulation-based therapy has achieved a breakthrough in the last decade, which stimulates the passion of searching for potential immunomodulatory substances in recent years.

Objective:

Marine natural products are a unique source of immunomodulatory substances. This paper summarized the emerging marine natural small-molecules and related synthesized derivatives with immunomodulatory activities to provide readers an overview of these bioactive molecules and their potential in immunomodulation therapy.

Conclusion:

An increasing number of immunomodulatory marine small-molecules with diverse intriguing structure-skeletons were discovered. They may serve as a basis for further studies of marine natural products for their chemistry, related mechanism of action and structure- activity relationships.

A Glycolipid Adjuvant, 7DW8-5, Enhances the Protective Immune Response to the Current Split Influenza Vaccine in Mice

Vaccination is an effective strategy to control influenza disease. Adjuvants enhance the efficacy of vaccines, but few adjuvants are approved for human use, so novel, safe, and effective adjuvants are urgently needed. The glycolipid adjuvant 7DW8-5 has shown adjuvanticity to malaria vaccine; however, its adjuvant effect for seasonal influenza vaccine remains unknown. Here, we evaluated the adjuvanticity of 7DW8-5 to a quadrivalent split influenza vaccine in a mouse model. 7DW8-5 significantly enhanced virus-specific antibody production when administrated with influenza vaccine compared with that of vaccine alone; 10 μg of 7DW8-5 induced similar antibody levels to those induced by alum. Mouse body weight loss was reduced and, notably, the survival rate was increased in the vaccine plus 7DW8-5 group compared with that in the vaccine plus alum group. Our results indicate that the glycolipid 7DW8-5 is a promising adjuvant for influenza vaccine.

Immunometabolism regulates TCR recycling and iNKT cell functions

Invariant natural killer T (iNKT) cells are innate-like T lymphocytes that express an invariant T cell receptor (TCR), which recognizes glycolipid antigens presented on CD1d molecules. These cells are phenotypically and functionally distinct from conventional T cells. When we characterized the metabolic activity of iNKT cells, consistent with their activated phenotype, we found that they had much less mitochondrial respiratory capacity but increased glycolytic activity in comparison to naïve conventional CD4⁺ T cells. After TCR engagement, iNKT cells further increased aerobic glycolysis, which was important for the expression of interferon-γ (IFN-γ). Glycolytic metabolism promoted the translocation of hexokinase-II to mitochondria and the activation of mammalian target of rapamycin complex 2 (mTORC2). Inhibiting glycolysis reduced the activity of Akt and PKCθ, which inhibited TCR recycling and accumulation within the immune synapse. Diminished TCR accumulation in the immune synapse reduced the activation of proximal and distal TCR signaling pathways and IFN-γ production in activated iNKT cells. Our studies demonstrate that glycolytic metabolism augments TCR signaling duration and IFN-γ production in iNKT cells by increasing TCR recycling.

OX40 Stimulation Enhances Protective Immune Responses Induced After Vaccination With Attenuated Malaria Parasites

Protection against a malaria infection can be achieved by immunization with live-attenuated Plasmodium sporozoites and while the precise mechanisms of protection remain unknown, T cell responses are thought to be critical in the elimination of infected liver cells. In cancer immunotherapies, agonistic antibodies that target T cell surface proteins, such as CD27, OX40 (CD134), and 4-1BB (CD137), have been used to enhance T cell function by increasing co-stimulation. In this study, we have analyzed the effect of agonistic OX40 monoclonal antibody treatment on protective immunity induced in mice immunized with genetically attenuated parasites (GAPs). OX40 stimulation enhanced protective immunity after vaccination as shown by an increase in the number of protected mice and delay to blood-stage infection after challenge with wild-type sporozoites. Consistent with the enhanced protective immunity enforced OX40 stimulation resulted in an increased expansion of antigen-experienced effector (CD11a^hiCD44^hi) CD8⁺ and CD4⁺ T cells in the liver and spleen and also increased IFN-γ and TNF producing CD4⁺ T cells in the liver and spleen. In addition, GAP immunization plus α-OX40 treatment significantly increased sporozoite-specific IgG responses. Thus, we demonstrate that targeting T cell costimulatory receptors can improve sporozoite-based vaccine efficacy.

Development of a novel mechanism-based glycolipid adjuvant for vaccination

The inability to elicit strong and durable cellular responses is a major obstacle in the development of successful vaccines, in particular those against malaria. In this regard, the generation of novel adjuvants that will potently boost cell-mediated immunity induced by candidate vaccines is helpful. We and others have found a glycolipid, called α-galactosylceramide (α-GalCer), which could be presented on CD1d expressed by antigen-presenting cells (APCs) and stimulate natural killer T (NKT) cells. This triggers the activation/maturation of APCs, particularly dendritic cells (DCs). By activating NKT cells and subsequently DCs, α-GalCer has been shown to enhance adaptive immune responses, particularly of CD8 ⁺ T cells, induced by the vaccines. More recently, we identified an analogue of α-GalCer, which can display a potent adjuvant activity in conjunction with malaria vaccines in mice and non-human primates. It is anticipated that CD1d-binding, NKT cell-stimulating glycolipids will be tested as adjuvants in humans in the near future.

Functions of CD1d-Restricted Invariant Natural Killer T Cells in Antimicrobial Immunity and Potential Applications for Infection Control

CD1d-restricted invariant natural killer T (iNKT) cells are innate-type lymphocytes that express a T-cell receptor (TCR) containing an invariant α chain encoded by the Vα14 gene in mice and Vα24 gene in humans. These iNKT cells recognize endogenous, microbial, and synthetic glycolipid antigens presented by the major histocompatibility complex (MHC) class I-like molecule CD1d. Upon TCR stimulation by glycolipid antigens, iNKT cells rapidly produce large amounts of cytokines, including interferon-γ (IFNγ) and interleukin-4 (IL-4). Activated iNKT cells contribute to host protection against a broad spectrum of microbial pathogens, and glycolipid-mediated stimulation of iNKT cells ameliorates many microbial infections by augmenting innate and acquired immunity. In some cases, however, antigen-activated iNKT cells exacerbate microbial infections by promoting pathogenic inflammation. Therefore, it is important to identify appropriate microbial targets for the application of iNKT cell activation as a treatment or vaccine adjuvant. Many studies have found that iNKT cell activation induces potent adjuvant activities promoting protective vaccine effects. In this review, we summarize the functions of CD1d-restricted iNKT cells in immune responses against microbial pathogens and describe the potential applications of glycolipid-mediated iNKT cell activation for preventing and controlling microbial infections.

CD1d-Restricted Type II NKT Cells Reactive With Endogenous Hydrophobic Peptides

NKT cells belong to a distinct subset of T cells that recognize hydrophobic antigens presented by major histocompatibility complex class I-like molecules, such as CD1d. Because NKT cells stimulated by antigens can activate or suppress other immunocompetent cells through an immediate production of a large amount of cytokines, they are regarded as immunological modulators. CD1d-restricted NKT cells are classified into two subsets, namely, type I and type II. CD1d-restricted type I NKT cells express invariant T cell receptors (TCRs) and react with lipid antigens, including the marine sponge-derived glycolipid α-galactosylceramide. On the contrary, CD1d-restricted type II NKT cells recognize a wide variety of antigens, including glycolipids, phospholipids, and hydrophobic peptides, by their diverse TCRs. In this review, we focus particularly on CD1d-restricted type II NKT cells that recognize endogenous hydrophobic peptides presented by CD1d. Previous studies have demonstrated that CD1d-restricted type I NKT cells usually act as pro-inflammatory cells but sometimes behave as anti-inflammatory cells. It has been also demonstrated that CD1d-restricted type II NKT cells play opposite roles to CD1d-restricted type I NKT cells; thus, they function as anti-inflammatory or pro-inflammatory cells depending on the situation. In line with this, CD1d-restricted type II NKT cells that recognize type II collagen peptide have been demonstrated to act as anti-inflammatory cells in diverse inflammation-induction models in mice, whereas pro-inflammatory CD1d-restricted type II NKT cells reactive with sterol carrier protein 2 peptide have been demonstrated to be involved in the development of small vessel vasculitis in rats.

CD8+ T-cell mediated anti-malaria protection induced by malaria vaccines; assessment of hepatic CD8+ T cells by SCBC assay

Malaria is a severe infectious disease with relatively high mortality, thus having been a scourge of humanity. There are a few candidate malaria vaccines that have shown a protective efficacy in humans against malaria. One of the candidate human malaria vaccines, which is based on human malaria sporozoites and called PfSPZ Vaccine, has been shown to protect a significant proportion of vaccine recipients from getting malaria. PfSPZ Vaccine elicits a potent response of hepatic CD8+ T cells that are specific for malaria antigens in non-human primates. To further characterize hepatic CD8+ T cells induced by the sporozoite-based malaria vaccine in a mouse model, we have used a cutting-edge Single-cell Barcode (SCBC) assay, a recently emerged approach/method for investigating the nature of T-cells responses during infection or cancer. Using the SCBC technology, we have identified a population of hepatic CD8+ T cells that are polyfunctional at a single cell level only in a group of vaccinated mice upon malaria challenge. The cytokines/chemokines secreted by these polyfunctional CD8+ T-cell subsets include MIP-1α, RANTES, IFN-γ, and/or IL-17A, which have shown to be associated with protective T-cell responses against certain pathogens. Therefore, a successful induction of such polyfunctional hepatic CD8+ T cells may be a key to the development of effective human malaria vaccine. In addition, the SCBC technology could provide a new level of diagnostic that will allow for a more accurate determination of vaccine efficacy.

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.

A simple, clinically relevant therapeutic vaccine shows long-term protection in an aggressive, delayed-treatment B lymphoma model

Despite initial remission after successful treatments, B lymphoma patients often encounter relapses and resistance causing high mortality. Thus, there is a need to develop therapies that prevent relapse by providing long-term protection and, ultimately, lead to functional cure. In this study, our goal was to develop a simple, clinically relevant, and easily translatable therapeutic vaccine that provides durable immune protection against aggressive B cell lymphoma and identify critical immune biomarkers that are predictive of long-term survival. In a delayed-treatment, aggressive, murine model of A20 B lymphoma that mimics human diffuse large B cell lymphoma, we show that therapeutic A20 lysate vaccine adjuvanted with an NKT cell agonist, α-galactosylceramide (α-GalCer), provides long-term immune protection against lethal tumor challenges and the antitumor immunity is primarily CD8 T cell dependent. Using experimental and computational methods, we demonstrate that the initial strength of germinal center reaction and the magnitude of class-switching into a Th1 type humoral response are the best predictors for the long-term immunity of B lymphoma lysate vaccine. Our results not only provide fundamentally insights for successful immunotherapy and long-term protection against B lymphomas, but also present a simple, therapeutic vaccine that can be translated easily due to the facile and inexpensive method of preparation.

DNA Vaccines Encoding Toxoplasma gondii Cathepsin C 1 Induce Protection against Toxoplasmosis in Mice

Toxoplasma gondii cathepsin C proteases (TgCPC1, 2, and 3) are important for the growth and survival of T. gondii. In the present study, B-cell and T-cell epitopes of TgCPC1 were predicted using DNAstar and the Immune Epitope Database. A TgCPC1 DNA vaccine was constructed, and its ability to induce protective immune responses against toxoplasmosis in BALB/c mice was evaluated in the presence or absence of the adjuvant α-GalCer. As results, TgCPC1 DNA vaccine with or without adjuvant α-GalCer showed higher levels of IgG and IgG2a in the serum, as well as IL-2 and IFN-γ in the spleen compared to controls (PBS, pEGFP-C1, and α-Galcer). Upon challenge infection with tachyzoites of T. gondii (RH), pCPC1/α-Galcer immunized mice showed the longest survival among all the groups. Mice vaccinated with DNA vaccine without adjuvant (pCPC1) showed better protective immunity compared to other controls (PBS, pEGFP-C1, and α-Galcer). These results indicate that a DNA vaccine encoding TgCPC1 is a potential vaccine candidate against toxoplasmosis.

Development of a Novel CD4+ TCR Transgenic Line That Reveals a Dominant Role for CD8+ Dendritic Cells and CD40 Signaling in the Generation of Helper and CTL Responses to Blood-Stage Malaria

We describe an MHC class II (I-A^b)-restricted TCR transgenic mouse line that produces CD4⁺ T cells specific for Plasmodium species. This line, termed PbT-II, was derived from a CD4⁺ T cell hybridoma generated to blood-stage Plasmodium berghei ANKA (PbA). PbT-II cells responded to all Plasmodium species and stages tested so far, including rodent (PbA, P. berghei NK65, Plasmodium chabaudi AS, and Plasmodium yoelii 17XNL) and human (Plasmodium falciparum) blood-stage parasites as well as irradiated PbA sporozoites. PbT-II cells can provide help for generation of Ab to P. chabaudi infection and can control this otherwise lethal infection in CD40L-deficient mice. PbT-II cells can also provide help for development of CD8⁺ T cell-mediated experimental cerebral malaria (ECM) during PbA infection. Using PbT-II CD4⁺ T cells and the previously described PbT-I CD8⁺ T cells, we determined the dendritic cell (DC) subsets responsible for immunity to PbA blood-stage infection. CD8⁺ DC (a subset of XCR1⁺ DC) were the major APC responsible for activation of both T cell subsets, although other DC also contributed to CD4⁺ T cell responses. Depletion of CD8⁺ DC at the beginning of infection prevented ECM development and impaired both Th1 and follicular Th cell responses; in contrast, late depletion did not affect ECM. This study describes a novel and versatile tool for examining CD4⁺ T cell immunity during malaria and provides evidence that CD4⁺ T cell help, acting via CD40L signaling, can promote immunity or pathology to blood-stage malaria largely through Ag presentation by CD8⁺ DC.

GLP-1 receptor agonist, liraglutide, ameliorates hepatosteatosis induced by anti-CD3 antibody in female mice

AIMS

Hepatosteatosis is mainly induced by obesity and metabolic disorders, but various medications also induce hepatosteatosis. The administration of anti-CD3 antibody was shown to induce hepatosteatosis, but changes in lipid and glucose metabolism remain unclear. We investigated the mechanism of hepatosteatosis induced by anti-CD3 antibody and the effects of glucagon-like peptide-1 (GLP-1) receptor agonist that was recently shown to affect immune function in metabolic disorders.

METHODS

Anti-CD3 antibody was administered to female BALB/c and C.B-17-scid mice with or without reconstitution by naïve CD4-positive splenocytes. Hepatic lipid content, serum lipid profile and glucose tolerance were evaluated. Splenic CD4-positive T lymphocytes were stimulated with the GLP-1R agonist, liraglutide, and cytokine production was measured. The effect of liraglutide on metabolic parameters in vivo was investigated in a T-cell activation-induced hepatosteatosis model.

RESULTS

The administration of anti-CD3 antibody induced hepatosteatosis, hyperlipidemia, and glucose intolerance. C.B-17-scid mice reconstituted with CD4-positive T lymphocytes developed hepatosteatosis induced by anti-CD3 antibody. Liraglutide suppressed CD4-positive T lymphocyte cytokine expression in vitro and in vivo, and improved hepatosteatosis, glucose tolerance, and insulin sensitivity.

CONCLUSIONS

Liraglutide suppressed the activation of CD4-positive T lymphocytes, and improved hepatosteatosis and metabolic disorders induced by T-cell activation in female mice.

A brief review of clinical trials involving manipulation of invariant NKT cells as a promising approach in future cancer therapies

In the recent years researchers have put a lot of emphasis on the possible immunotherapeutic strategies able to target tumors. Many studies have proven that the key role in recognition and eradication of cancer cells, both for mice and humans, is being conducted by the invariant natural killer T-cells (NKT). This small subpopulation of lymphocytes can kill other cells, either directly or indirectly, through the natural killer cells’ (NK) activation. They can also swiftly release cytokines, causing the involvement of elements of the innate and acquired immune system. With the discovery of α-galactosylceramide (α-GalCer) – the first known agonist for iNKT cells – and its later subsequent analogs, it became possible to effectively stimulate iNKT cells, hence to keep control over the tumor progression. This article refers to the current knowledge concerning iNKT cells and the most important aspects of their antitumor activity. It also highlights the clinical trials that aim at increasing the amount of iNKT cells in general and in the microenvironment of the tumor. For sure, the iNKT-based immunotherapeutic approach holds a great potential and is highly probable to become a part of the cancer immunotherapy in the future.

Exploiting Antitumor Immunotherapeutic Novel Strategies by Deciphering the Cross Talk between Invariant NKT Cells and Dendritic Cells

Immune checkpoint blockade therapy has prevailed for several types of cancer; however, its effectiveness as a single therapy is still limited. In principle, dendritic cells (DCs) should be able to control the post-therapy immune response, in particular since they can link the two major arms of the immune system: innate and adaptive immunity. Therefore, DCs would be a logical and ideal target for the development of immunotherapies. Since DCs are not activated in the steady state, an adjuvant to convert their function from tolerogenic to immunogenic would be desirable. Upon ligand activation, invariant natural killer T (iNKT) cells simultaneously activate NK cells and also energize the DCs, resulting in their full maturation. To utilize such iNKT-licensed "fully" matured DCs as adjuvants, mechanisms of both intercellular communication between DC subsets and iNKT cells and intracellular molecular signaling in DCs have to be clarified and optimized. To generate both innate and adaptive immunity against cancer, a variety of strategies with the potential to target iNKT-licensed DCs in situ have been studied. The benchmark of success in these studies, each with distinct approaches, will be the development of functional NK cells and cytotoxic T cells (CTLs) as well as generation of long-term, memory CTL. In this review, we provide a framework for NKT-mediated immunotherapy through selective DC targeting in situ, describe progress in the design of licensed therapies for iNKT cell targeting of DCs, and highlight the challenge to provide maximal benefit to patients.

An Overview of Novel Adjuvants Designed for Improving Vaccine Efficacy

Adjuvants incorporated in prophylactic and/or therapeutic vaccine formulations impact vaccine efficacy by enhancing, modulating, and/or prolonging the immune response. In addition, they reduce antigen concentration and the number of immunizations required for protective efficacy, therefore contributing to making vaccines more cost effective. Our better understanding of the molecular mechanisms of immune recognition and protection has led research efforts to develop new adjuvants that are currently at various stages of development or clinical evaluation. In this review, we focus mainly on several of these promising adjuvants, and summarize recent work conducted in various laboratories to develop novel lipid-containing adjuvants.