Clinical development of a novel CD1d-binding NKT cell ligand as a vaccine adjuvant

Chemoenzymatic synthesis and immunological evaluation of sialyl-Thomsen-Friedenreich (sTF) antigen conjugate to CRM197

sTF (sialyl-Thomsen-Friedenreich) is a type of tumor-associated carbohydrate antigens (TACAs) and is highly expressed in various human malignancies. To validate if sTF could be a valuable molecular target for future cancer vaccine development, in this work the sTF antigen was prepared by adopting a strategy combining chemical and enzymatic methods, and then was covalently conjugated to a carrier protein, CRM197. The preliminary immunological evaluation, performed on BALB/c mice, revealed that the sTF-CRM197 conjugate elicited high titers of specific IgG antibodies. FACS experiments showed that the antisera induced by sTF-CRM197 conjugate could specifically recognize and bind to sTF-positive cancer cells T-47D. Furthermore, the conjugate mediated effective and specific antibody-mediated complement-dependent cytotoxicity (CDC).

Diversification of a Novel α-Galactosyl Ceramide Hotspot Boosts the Adjuvant Properties in Parenteral and Mucosal Vaccines

The development of potent adjuvants is an important step for improving the performance of subunit vaccines. CD1d agonists, such as the prototypical α-galactosyl ceramide (α-GalCer), are of special interest due to their ability to activate iNKT cells and trigger rapid dendritic cell maturation and B-cell activation. Herein, we introduce a novel derivatization hotspot at the α-GalCer skeleton, namely the N-substituent at the amide bond. The multicomponent diversification of this previously unexplored glycolipid chemotype space permitted the introduction of a variety of extra functionalities that can either potentiate the adjuvant properties or serve as handles for further conjugation to antigens toward the development of self-adjuvanting vaccines. This strategy led to the discovery of compounds eliciting enhanced antigen-specific T cell stimulation and a higher antibody response when delivered by either the parenteral or the mucosal route, as compared to a known potent CD1d agonist. Notably, various functionalized α-GalCer analogues showed a more potent adjuvant effect after intranasal immunization than a PEGylated α-GalCer analogue previously optimized for this purpose. Ultimately, this work could open multiple avenues of opportunity for the use of mucosal vaccines against microbial infections.

Sex-Specific Differences in Cytokine Induction by the Glycolipid Adjuvant 7DW8-5 in Mice

7DW8-5 is a potent glycolipid adjuvant that improves malaria vaccine efficacy in mice by inducing IFN-γ and increasing protective CD8⁺ T cell responses. The addition of 7DW8-5 was previously shown to improve the efficacy of a CD8⁺ T cell-mediated heterologous 'prime-and-trap' malaria vaccine against Plasmodium yoelii sporozoite challenge in inbred female mice. Here, we report significant differential sex-specific responses to 7DW8-5 in inbred and outbred mice. Male mice express significantly less IFN-γ and IL-4 compared to females following intravenous 7DW8-5 administration. Additionally, unlike in female mice, 7DW8-5 did not improve the vaccine efficacy against sporozoite challenge in prime-and-trap vaccinated male mice. Our findings highlight the importance of including both female and male sexes in experimental adjuvant studies.

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.

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.

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.

A practical and scalable synthesis of KRN7000 using glycosyl iodide as the glycosyl donor

KRN7000 is particularly useful because it is a powerful and specific CD1d agonist and has prompted intense interest in the context of immunology in the past 25 years. Its limited commercial availability and high price has led to the publication of many different syntheses. However, almost all of them focused on the methodology development rather than a scalable synthesis. Herein, we have described a practical and scalable procedure for the synthesis of KRN7000 basing on the glycosyl iodide method. This procedure involves total of eight steps to obtain the highly pure product KNR7000 on gram scale from the commercially available starting materials (d-galactose and the phytosphingosine) with only three column chromatographic purifications.

A glycolipid adjuvant, 7DW8-5, provides a protective effect against colonic inflammation in mice by the recruitment of CD1d-restricted natural killer T cells

Background/Aims

The modulation of CD1d-restricted natural killer T (NKT) cells by glycolipids has been considered as a potential therapy against immunologic diseases, including inflammatory bowel disease. A recently identified a glycolipid analog, 7DW8-5, which is derived from α-galactosylceramide (α-GalCer), is as much as 100-fold more active at stimulating both human and mice NKT cells when compared to α-GalCer. We explored the effects of 7DW8-5 in mouse models of acute and chronic colitis.

Methods

We investigated the effects of 7DW8-5 on intestinal inflammation by assessing the effects of 7dW8-5 on a murine dextran sulfate sodium (DSS)-induced acute colitis model and a chronic colitis-associated tumor model.

Results

The acute DSS-induced colitis model showed a dose-dependent response to 7DW8-5, as mice administered 7DW8-5 showed a significant improvement in DSS-induced colitis based on their disease activity index, histologic analysis, and serum C-reactive protein levels, when compared to mice administered vehicle alone. However, DSS-induced colitis in CD1d-KO mice showed no response to 7DW8-5. A fluorescence-activating cell sorting analysis revealed an increase in NKT cells in colonic tissues of 7DW8-5-treated mice. RNA-seq and real-time quantitative polymerase chain reaction showed a significant increase in the expression of interleukin (IL)-4, IL-13, and interferon-gamma in 7DW8-5-treated mice. In addition, 7DW8-5 treatment reduced colitis-associated tumor development in an azoxymethane/DSS mouse model.

Conclusions

7DW8-5 activates NKT cells through CD1d and provides a protective effect against intestinal inflammation in mice. Therefore, 7DW8-5 may be a promising therapeutic agent for treatment of inflammatory bowel disease.

A molecular switch in mouse CD1d modulates natural killer T cell activation by α-galactosylsphingamides

Type I natural killer T (NKT) cells are a population of innate like T lymphocytes that rapidly respond to α-GalCer presented by CD1d via the production of both pro- and anti-inflammatory cytokines. While developing novel α-GalCer analogs that were meant to be utilized as potential adjuvants because of their production of pro-inflammatory cytokines (Th1 skewers), we generated α-galactosylsphingamides (αGSA). Surprisingly, αGSAs are not potent antigens in vivo despite their strong T-cell receptor (TCR)-binding affinities. Here, using surface plasmon resonance (SPR), antigen presentation assays, and X-ray crystallography (yielding crystal structures of 19 different binary (CD1d-glycolipid) or ternary (CD1d-glycolipid-TCR) complexes at resolutions between 1.67 and 2.85 Å), we characterized the biochemical and structural details of αGSA recognition by murine NKT cells. We identified a molecular switch within murine (m)CD1d that modulates NKT cell activation by αGSAs. We found that the molecular switch involves a hydrogen bond interaction between Tyr-73 of mCD1d and the amide group oxygen of αGSAs. We further established that the length of the acyl chain controls the positioning of the amide group with respect to the molecular switch and works synergistically with Tyr-73 to control NKT cell activity. In conclusion, our findings reveal important mechanistic insights into the presentation and recognition of glycolipids with polar moieties in an otherwise apolar milieu. These observations may inform the development αGSAs as specific NKT cell antagonists to modulate immune responses.

3,4-Dideoxy-3,3,4,4-tetrafluoro- and 4-OH epimeric 3-deoxy-3,3-difluoro-α-GalCer analogues: Synthesis and biological evaluation on human iNKT cells stimulation

iNKT cells recognize CD1d/α-galactosylceramide (α-GalCer) complexes via their invariant TCR receptor and stimulate the immune response. Many α-GalCer analogues have been investigated to interrogate this interaction. Following our previous work related to the modification of the hydrogen bond network between α-GalCer and CD1d, we have now focused our attention on the synthesis of 3-deoxy-3,3-difluoro- and 3,4-dideoxy-3,3,4,4-tetrafluoro-α-GalCer analogues, and studied their ability to stimulate human iNKT cells. In each case, deoxygenation at the indicated positions was accompanied by difluoro introduction in order to evaluate the resulting electronic effect on the stability of the ternary CD1d/Galcer/TCR complex which has been rationalized by modeling study. With deoxy-difluorination at the 3-position, the two epimeric 4-OH analogues were investigated to establish their capacity to compensate for the lack of the hydrogen bond donating group at the 3-position. The 3,4-dideoxytetrafluoro analogue was of interest to highlight the amide NH-bond hydrogen bond properties.

Vaccine Designs Utilizing Invariant NKT-Licensed Antigen-Presenting Cells Provide NKT or T Cell Help for B Cell Responses

Vaccines against a variety of infectious diseases have been developed and tested. Although there have been some notable successes, most are less than optimal or have failed outright. There has been discussion about whether either B cells or dendritic cells (DCs) could be useful for the development of antimicrobial vaccines with the production of high titers of antibodies. Invariant (i)NKT cells have direct antimicrobial effects as well as adjuvant activity, and iNKT-stimulated antigen-presenting cells (APCs) can determine the form of the ensuing humoral and cellular immune responses. In fact, upon activation by ligand, iNKT cells can stimulate both B cells and DCs as via either cognate or non-cognate help. iNKT-licensed DCs generate antigen-specific follicular helper CD4⁺ T cells, which in turn stimulate B cells, thus leading to long-term antigen-specific antibody production. Follicular helper iNKT cell-licensed B cells generally produce rapid, but short-term antibody. However, under some conditions in the presence of Th cells, the antibody production can be prolonged. With regards to humoral immunity, the quality and quantity of Ab produced depends on the APC type and the form of the vaccine. In terms of cellular immunity and, in particular, the induction of cytotoxic CD8⁺ T cells, iNKT-licensed DCs show prominent activity. In this review, we discuss differences in iNKT-stimulated APC types and the quality of the ensuing immune response, and also discuss their application in vaccine models to develop successful preventive immunotherapy against infectious diseases.

Modeling the effect of boost timing in murine irradiated sporozoite prime-boost vaccines

Vaccination with radiation-attenuated sporozoites has been shown to induce CD8+ T cell-mediated protection against pre-erythrocytic stages of malaria. Empirical evidence suggests that successive inoculations often improve the efficacy of this type of vaccines. An initial dose (prime) triggers a specific cellular response, and subsequent inoculations (boost) amplify this response to create a robust CD8+ T cell memory. In this work we propose a model to analyze the effect of T cell dynamics on the performance of prime-boost vaccines. This model suggests that boost doses and timings should be selected according to the T cell response elicited by priming. Specifically, boosting during late stages of clonal contraction would maximize T cell memory production for vaccines using lower doses of irradiated sporozoites. In contrast, single-dose inoculations would be indicated for higher vaccine doses. Experimental data have been obtained that support theoretical predictions of the model.

Innate immune cells for immunotherapy of autoimmune and cancer disorders

Modulation of the immune system has been widely targeted for the treatment of several immune-related diseases, such as autoimmune disorders and cancer, due to its crucial role in these pathologies. Current available therapies focus mainly on symptomatic treatment and are often associated with undesirable secondary effects. For several years, remission of disease and subsequently recovery of immune homeostasis has been a major goal for immunotherapy. Most current immunotherapeutic strategies are aimed to inhibit or potentiate directly the adaptive immune response by modulating antibody production and B cell memory, as well as the effector potential and memory of T cells. Although these immunomodulatory approaches have shown some success in the clinic with promising therapeutic potential, they have some limitations related to their effectiveness in disease models and clinical trials, as well as elevated costs. In the recent years, a renewed interest has emerged on targeting innate immune cells for immunotherapy, due to their high plasticity and ability to exert a potent and extremely rapid response, which can influence the outcome of the adaptive immune response. In this review, we discuss the immunomodulatory potential of several innate immune cells, as well as they use for immunotherapy, especially in autoimmunity and cancer.

Co-localization of a CD1d-binding glycolipid with an adenovirus-based malaria vaccine for a potent adjuvant effect

A CD1d-binding, invariant (i) natural killer T (NKT)-cell stimulatory glycolipid, α-Galactosylceramide (αGalCer), has been shown to act as an adjuvant. We previously identified a fluorinated phenyl ring-modified αGalCer analog, 7DW8-5, displaying a higher binding affinity for CD1d molecule and more potent adjuvant activity than αGalCer. In the present study, 7DW8-5 co-administered intramuscularly (i.m.) with a recombinant adenovirus expressing a Plasmodium yoelii circumsporozoite protein (PyCSP), AdPyCS, has led to a co-localization of 7DW8-5 and a PyCSP in draining lymph nodes (dLNs), particularly in dendritic cells (DCs). This occurrence initiates a cascade of events, such as the recruitment of DCs to dLNs and their activation and maturation, and the enhancement of the ability of DCs to prime CD8+ T cells induced by AdPyCS and ultimately leading to a potent adjuvant effect and protection against malaria.

A potent adjuvant effect of a CD1d-binding NKT cell ligand in human immune system mice

OBJECTIVES

A CD1d-binding invariant natural killer T (iNKT)-cell stimulatory glycolipid, namely 7DW8-5, is shown to enhance the efficacy of radiation-attenuated sporozoites (RAS)-based malaria vaccine in mice. In the current study, we aim to determine whether 7DW8-5 can display a potent adjuvant effect in human immune system (HIS) mice.

METHODS

HIS-A2/hCD1d mice, which possess both functional human iNKT cells and CD8+ T cells, were generated by the transduction of NSG mice with adeno-associated virus serotype 9 expressing genes that encode human CD1d molecules and HLA-A*0201, followed by the engraftment of human hematopoietic stem cells. The magnitudes of human iNKT-cell response against 7DW8-5 and HLA-A*0201-restricted human CD8+ T-cell response against a human malaria antigen in HIS-A2/hCD1d mice were determined by using human CD1d tetramer and human HLA-A*0201 tetramer, respectively.

RESULTS

We found that 7DW8-5 stimulates human iNKT cells in HIS-A2/hCD1d mice, as well as those derived from HIS-A2/hCD1d mice in vitro. We also found that 7DW8-5 significantly increases the level of a human malarial antigen-specific HLA-A*0201-restricted human CD8+ T-cell response in HIS-A2/hCD1d mice.

CONCLUSIONS

Our study indicates that 7DW8-5 can display a potent adjuvant effect on RAS vaccine-induced anti-malarial immunity by augmenting malaria-specific human CD8+ T-cell response.

Glycolipid activators of invariant NKT cells as vaccine adjuvants

Natural Killer T cells (NKT cells) are a subpopulation of T lymphocytes with unique phenotypic properties and a remarkably broad range of immune effector and regulatory functions. One subset of these cells, known as invariant NKT cells (iNKT cells), has become a significant focus in the search for new and better ways to enhance immunotherapies and vaccination. These unconventional T cells are characterized by their ability to be specifically activated by a range of foreign and self-derived glycolipid antigens presented by CD1d, an MHC class I-related antigen presenting molecule that has evolved to bind and present lipid antigens. The development of synthetic α-galactosylceramides as a family of powerful glycolipid agonists for iNKT cells has led to approaches for augmenting a wide variety of immune responses, including those involved in vaccination against infections and cancers. Here we review the basic background biology of iNKT cells that is relevant to their potential for improving immune responses, and summarize recent work supporting the further development of glycolipid activators of iNKT cells as a new class of vaccine adjuvants.

Co-administration of α-GalCer analog and TLR4 agonist induces robust CD8(+) T-cell responses to PyCS protein and WT-1 antigen and activates memory-like effector NKT cells

In the present study, the combined adjuvant effect of 7DW8-5, a potent α-GalCer-analog, and monophosphoryl lipid A (MPLA), a TLR4 agonist, on the induction of vaccine-induced CD8(+) T-cell responses and protective immunity was evaluated. Mice were immunized with peptides corresponding to the CD8(+) T-cell epitopes of a malaria antigen, a circumsporozoite protein of Plasmodium yoelii, and a tumor antigen, a Wilms Tumor antigen-1 (WT-1), together with 7DW8-5 and MPLA, as an adjuvant. These immunization regimens were able to induce higher levels of CD8(+) T-cell responses and, ultimately, enhanced levels of protection against malaria and tumor challenges compared to the levels induced by immunization with peptides mixed with 7DW8-5 or MPLA alone. Co-administration of 7DW8-5 and MPLA induces activation of memory-like effector natural killer T (NKT) cells, i.e. CD44(+)CD62L(-)NKT cells. Our study indicates that 7DW8-5 greatly enhances important synergistic pathways associated to memory immune responses when co-administered with MPLA, thus rendering this combination of adjuvants a novel vaccine adjuvant formulation.

Synthetic glycolipid activators of natural killer T cells as immunotherapeutic agents

Certain types of glycolipids have been found to have remarkable immunomodulatory properties as a result of their ability to activate specific T lymphocyte populations with an extremely wide range of immune effector properties. The most extensively studied glycolipid reactive T cells are known as invariant natural killer T (iNKT) cells. The antigen receptors of these cells specifically recognize certain glycolipids, most notably glycosphingolipids with α-anomeric monosaccharides, presented by the major histocompatibility complex class I-like molecule CD1d. Once activated, iNKT cells can secrete a very diverse array of pro- and anti-inflammatory cytokines to modulate innate and adaptive immune responses. Thus, glycolipid-mediated activation of iNKT cells has been explored for immunotherapy in a variety of disease states, including cancer and a range of infections. In this review, we discuss the design of synthetic glycolipid activators for iNKT cells, their impact on adaptive immune responses and their use to modulate iNKT cell responses to improve immunity against infections and cancer. Current challenges in translating results from preclinical animal studies to humans are also discussed.

Design, Synthesis, and Immunological Evaluation of Benzyloxyalkyl-Substituted 1,2,3-Triazolyl α-GalCer Analogues

Replacement of the amide moiety in the structure of α-GalCer with a 1,2,3-triazole linker is known to elicit a response skewed toward Th2 immunity, and glycolipids containing an aromatic ring in the terminus of their acyl or phytosphingosine structural component exhibit an enhanced Th1 immune response. In the current study, synthesis and immunological screening of a focused library of benzyloxyalkyl-substituted 1,2,3-triazolyl α-GalCer analogues are reported. The novel α-GalCer analogues activate invariant natural killer T (iNKT) cells via CD1d mediated presentation, which was confirmed by in vitro tests performed on iNKT hybridomas incubated with CD1d proteins. When tested on isolated murine splenocytes, the T1204B and T1206B compounds stimulated higher levels of both IFN-γ and IL-4 cytokine expression in vitro compared to that of α-GalCer.

Colocalization of a CD1d-Binding Glycolipid with a Radiation-Attenuated Sporozoite Vaccine in Lymph Node-Resident Dendritic Cells for a Robust Adjuvant Effect

A CD1d-binding glycolipid, α-Galactosylceramide (αGalCer), activates invariant NK T cells and acts as an adjuvant. We previously identified a fluorinated phenyl ring-modified αGalCer analog, 7DW8-5, displaying nearly 100-fold stronger CD1d binding affinity. In the current study, 7DW8-5 was found to exert a more potent adjuvant effect than αGalCer for a vaccine based on radiation-attenuated sporozoites of a rodent malaria parasite, Plasmodium yoelii, also referred to as irradiated P. yoelii sporozoites (IrPySpz). 7DW8-5 had a superb adjuvant effect only when the glycolipid and IrPySpz were conjointly administered i.m. Therefore, we evaluated the effect of distinctly different biodistribution patterns of αGalCer and 7DW8-5 on their respective adjuvant activities. Although both glycolipids induce a similar cytokine response in sera of mice injected i.v., after i.m. injection, αGalCer induces a systemic cytokine response, whereas 7DW8-5 is locally trapped by CD1d expressed by dendritic cells (DCs) in draining lymph nodes (dLNs). Moreover, the i.m. coadministration of 7DW8-5 with IrPySpz results in the recruitment of DCs to dLNs and the activation and maturation of DCs. These events cause the potent adjuvant effect of 7DW8-5, resulting in the enhancement of the CD8(+) T cell response induced by IrPySpz and, ultimately, improved protection against malaria. Our study is the first to show that the colocalization of a CD1d-binding invariant NK T cell-stimulatory glycolipid and a vaccine, like radiation-attenuated sporozoites, in dLN-resident DCs upon i.m. conjoint administration governs the potency of the adjuvant effect of the glycolipid.

The Role of Invariant Natural Killer T Cells in Dendritic Cell Licensing, Cross-Priming, and Memory CD8(+) T Cell Generation

New vaccination strategies focus on achieving CD8⁺ T cell (CTL) immunity rather than on induction of protective antibody responses. While the requirement of CD4⁺ T (Th) cell help in dendritic cell (DC) activation and licensing, and in CTL memory induction has been described in several disease models, CTL responses may occur in a Th cell help-independent manner. Invariant natural killer T cells (iNKT cells) can substitute for Th cell help and license DC as well. iNKT cells produce a broad spectrum of Th1 and Th2 cytokines, thereby inducing a similar set of costimulatory molecules and cytokines in DC. This form of licensing differs from Th cell help by inducing other chemokines, while Th cell-licensed DCs produce CCR5 ligands, iNKT cell-licensed DCs produce CCL17, which attracts CCR4⁺ CD8⁺ T cells for subsequent activation. It has recently been shown that iNKT cells do not only enhance immune responses against bacterial pathogens or parasites but also play a role in viral infections. The inclusion of iNKT cell ligands in influenza virus vaccines enhanced memory CTL generation and protective immunity in a mouse model. This review will focus on the role of iNKT cells in the cross-talk with cross-priming DC and memory CD8⁺ T cell formation.

Lipid and Carbohydrate Modifications of α-Galactosylceramide Differently Influence Mouse and Human Type I Natural Killer T Cell Activation

The ability of different glycosphingolipids (GSLs) to activate type I natural killer T cells (NKT cells) has been known for 2 decades. The possible therapeutic use of these GSLs has been studied in many ways; however, studies are needed in which the efficacy of promising GSLs is compared under identical conditions. Here, we compare five unique GSLs structurally derived from α-galactosylceramide. We employed biophysical and biological assays, as well as x-ray crystallography to study the impact of the chemical modifications of the antigen on type I NKT cell activation. Although all glycolipids are bound by the T cell receptor of type I NKT cells in real time binding assays with high affinity, only a few activate type I NKT cells in in vivo or in vitro experiments. The differences in biological responses are likely a result of different pharmacokinetic properties of each lipid, which carry modifications at different parts of the molecule. Our results indicate a need to perform a variety of assays to ascertain the therapeutic potential of type I NKT cell GSL activators.

Optimizing NKT cell ligands as vaccine adjuvants

NKT cells are a subpopulation of T lymphocytes with phenotypic properties of both T and NK cells and a wide range of immune effector properties. In particular, one subset of these cells, known as invariant NKT cells (iNKT cells), has attracted substantial attention because of their ability to be specifically activated by glycolipid antigens presented by a cell surface protein called CD1d. The development of synthetic α-galactosylceramides as a family of powerful glycolipid agonists for iNKT cells has led to approaches for augmenting a wide variety of immune responses, including those involved in vaccination against infections and cancers. Here, we review basic, preclinical and clinical observations supporting approaches to improving immune responses through the use of iNKT cell-activating glycolipids. Results from preclinical animal studies and preliminary clinical studies in humans identify many promising applications for this approach in the development of vaccines and novel immunotherapies.

iNKT/CD1d-antitumor immunotherapy significantly increases the efficacy of therapeutic CpG/peptide-based cancer vaccine

Background

Therapeutic cancer vaccines aim to boost the natural immunity against transformed cancer cells, and a series of adjuvants and co-stimulatory molecules have been proposed to enhance the immune response against weak self-antigens expressed on cancer cells. For instance, a peptide/CpG-based cancer vaccine has been evaluated in several clinical trials and was shown in pre-clinical studies to favor the expansion of effector T versus Tregs cells, resulting in a potent antitumor activity, as compared to other TLR ligands. Alternatively, the adjuvant activity of CD1d-restricted invariant NKT cells (iNKT) on the innate and adaptive immunity is well demonstrated, and several CD1d glycolipid ligands are under pre-clinical and clinical evaluation. Importantly, additive or even synergistic effects have been shown upon combined CD1d/NKT agonists and TLR ligands. The aim of the present study is to combine the activation and tumor targeting of activated iNKT, NK and T cells.

Methods

Activation and tumor targeting of iNKT cells via recombinant α-galactosylceramide (αGC)-loaded CD1d-anti-HER2 fusion protein (CD1d-antitumor) is combined or not with OVA peptide/CpG vaccine. Circulating and intratumoral NK and H-2Kb/OVA-specific CD8 responses are monitored, as well as the state of activation of dendritic cells (DC) with regard to activation markers and IL-12 secretion. The resulting antitumor therapy is tested against established tumor grafts of B16 melanoma cells expressing human HER2 and ovalbumin.

Results

The combined CD1d/iNKT antitumor therapy and CpG/peptide-based immunization leads to optimized expansion of NK and OVA-specific CD8 T cells (CTLs), likely resulting from the maturation of highly pro-inflammatory DCs as seen by a synergistic increase in serum IL-12. The enhanced innate and adaptive immune responses result in higher tumor inhibition that correlates with increased numbers of OVA-specific CTLs at the tumor site. Antibody-mediated depletion experiments further demonstrate that in this context, CTLs rather than NK cells are essential for the enhanced tumor inhibition.

Conclusions

Altogether, our study in mice demonstrates that αGC/CD1d-antitumor fusion protein greatly increases the efficacy of a therapeutic CpG-based cancer vaccine, first as an adjuvant during T cell priming and second, as a therapeutic agent to redirect immune responses to the tumor site.

Electronic supplementary material

The online version of this article (doi:10.1186/s40425-014-0039-8) contains supplementary material, which is available to authorized users.

Improving Mycobacterium bovis bacillus Calmette-Guèrin as a vaccine delivery vector for viral antigens by incorporation of glycolipid activators of NKT cells

Recombinant Mycobacterium bovis bacillus Calmette-Guèrin (rBCG) has been explored as a vector for vaccines against HIV because of its ability to induce long lasting humoral and cell mediated immune responses. To maximize the potential for rBCG vaccines to induce effective immunity against HIV, various strategies are being employed to improve its ability to prime CD8+ T cells, which play an important role in the control of HIV infections. In this study we adopted a previously described approach of incorporating glycolipids that activate CD1d-restricted natural killer T (NKT) cells to enhance priming of CD8+ T cells by rBCG strains expressing an SIV Gag antigen (rBCG-SIV gag). We found that the incorporation of the synthetic NKT activating glycolipid α-galactosylceramide (α-GC) into rBCG-SIV gag significantly enhanced CD8+ T cell responses against an immunodominant Gag epitope, compared to responses primed by unmodified rBCG-SIV gag. The abilities of structural analogues of α-GC to enhance CD8+ T cell responses to rBCG were compared in both wild type and partially humanized mice that express human CD1d molecules in place of mouse CD1d. These studies identified an α-GC analogue known as 7DW8-5, which has previously been used successfully as an adjuvant in non-human primates, as a promising compound for enhancing immunogenicity of antigens delivered by rBCG.vectors. Our findings support the incorporation of synthetic glycolipid activators of NKT cells as a novel approach to enhance the immunogenicity of rBCG-vectored antigens for induction of CD8+ T cell responses. The glycolipid adjuvant 7DW8-5 may be a promising candidate for advancing to non-human primate and human clinical studies for the development of HIV vaccines based on rBCG vectors.

Effective cancer vaccine platform based on attenuated salmonella and a type III secretion system

Vaccines explored for cancer therapy have been based generally on injectable vector systems used to control foreign infectious pathogens, to which the immune system evolved to respond naturally. However, these vectors may not be effective at presenting tumor-associated antigens (TAA) to the immune system in a manner that is sufficient to engender antitumor responses. We addressed this issue with a novel orally administered Salmonella-based vector that exploits a type III secretion system to deliver selected TAA in the cytosol of professional antigen-presenting cells in situ. A systematic comparison of candidate genes from the Salmonella Pathogenicity Island 2 (SPI2) locus was conducted in the vaccine design, using model antigens and a codon-optimized form of the human TAA survivin (coSVN), an oncoprotein that is overexpressed in most human cancers. In a screen of 20 SPI2 promoter:effector combinations, a PsifB::sseJ combination exhibited maximal potency for antigen translocation into the APC cytosol, presentation to CD8 T cells, and murine immunogenicity. In the CT26 mouse model of colon carcinoma, therapeutic vaccination with a lead PsifB::sseJ-coSVN construct (p8032) produced CXCR3-dependent infiltration of tumors by CD8 T cells, reversed the CD8:Treg ratio at the tumor site, and triggered potent antitumor activity. Vaccine immunogenicity and antitumor potency were enhanced by coadministration of the natural killer T-cell ligand 7DW8-5, which heightened the production of IL12 and IFNγ. Furthermore, combined treatment with p8032 and 7DW8-5 resulted in complete tumor regression in A20 lymphoma-bearing mice, where protective memory was demonstrated. Taken together, our results demonstrate how antigen delivery using an oral Salmonella vector can provide an effective platform for the development of cancer vaccines.

Adjuvants in the Driver's Seat: How Magnitude, Type, Fine Specificity and Longevity of Immune Responses Are Driven by Distinct Classes of Immune Potentiators

The mechanism by which vaccine adjuvants enhance immune responses has historically been considered to be the creation of an antigen depot. From here, the antigen is slowly released and provided to immune cells over an extended period of time. This "depot" was formed by associating the antigen with substances able to persist at the injection site, such as aluminum salts or emulsions. The identification of Pathogen-Associated Molecular Patterns (PAMPs) has greatly advanced our understanding of how adjuvants work beyond the simple concept of extended antigen release and has accelerated the development of novel adjuvants. This review focuses on the mode of action of different adjuvant classes in regards to the stimulation of specific immune cell subsets, the biasing of immune responses towards cellular or humoral immune response, the ability to mediate epitope spreading and the induction of persistent immunological memory. A better understanding of how particular adjuvants mediate their biological effects will eventually allow them to be selected for specific vaccines in a targeted and rational manner.

Biology of CD1- and MR1-restricted T cells

Over the past 15 years, investigators have shown that T lymphocytes can recognize not only peptides in the context of MHC class I and class II molecules but also foreign and self-lipids in association with the nonclassical MHC class I-like molecules, CD1 proteins. In this review, we describe the most recent events in the field, with particular emphasis on (a) structural and functional aspects of lipid presentation by CD1 molecules, (b) the development of CD1d-restricted invariant natural killer T (iNKT) cells and transcription factors required for their differentiation, (c) the ability of iNKT cells to modulate innate and adaptive immune responses through their cross talk with lymphoid and myeloid cells, and (d) MR1-restricted and group I (CD1a, CD1b, and CD1c)-restricted T cells.

A glycolipid adjuvant, 7DW8-5, enhances CD8+ T cell responses induced by an adenovirus-vectored malaria vaccine in non-human primates

A key strategy to a successful vaccine against malaria is to identify and develop new adjuvants that can enhance T-cell responses and improve protective immunity. Upon co-administration with a rodent malaria vaccine in mice, 7DW8-5, a recently identified novel analog of α-galactosylceramide (α-GalCer), enhances the level of malaria-specific protective immune responses more strongly than the parent compound. In this study, we sought to determine whether 7DW8-5 could provide a similar potent adjuvant effect on a candidate human malaria vaccine in the more relevant non-human primate (NHP) model, prior to committing to clinical development. The candidate human malaria vaccine, AdPfCA (NMRC-M3V-Ad-PfCA), consists of two non-replicating recombinant adenoviral (Ad) vectors, one expressing the circumsporozoite protein (CSP) and another expressing the apical membrane antigen-1 (AMA1) of Plasmodium falciparum. In several phase 1 clinical trials, AdPfCA was well tolerated and demonstrated immunogenicity for both humoral and cell-mediated responses. In the study described herein, 25 rhesus macaques received prime and boost intramuscular (IM) immunizations of AdPfCA alone or with an ascending dose of 7DW8-5. Our results indicate that 7DW8-5 is safe and well-tolerated and provides a significant enhancement (up to 9-fold) in malaria-specific CD8+ T-cell responses after both priming and boosting phases, supporting further clinical development.

Carbohydrates and T cells: a sweet twosome

Carbohydrates as T cell-activating antigens have been generating significant interest. For many years, carbohydrates were thought of as T-independent antigens, however, more recent research had demonstrated that mono- or oligosaccharides glycosidically linked to peptides can be recognized by T cells. T cell recognition of these glycopeptides depends on the structure of both peptide and glycan portions of the antigen. Subsequently, it was discovered that natural killer T cells recognized glycolipids when presented by the antigen presenting molecule CD1d. A transformative insight into glycan-recognition by T cells occurred when zwitterionic polysaccharides were discovered to bind to and be presented by MHCII to CD4+ T cells. Based on this latter observation, the role that carbohydrate epitopes generated from glycoconjugate vaccines had in activating helper T cells was explored and it was found that these epitopes are presented to specific carbohydrate recognizing T cells through a unique mechanism. Here we review the key interactions between carbohydrate antigens and the adaptive immune system at the molecular, cellular and systems levels exploring the significant biological implications in health and disease.

Malaria vaccine adjuvants: latest update and challenges in preclinical and clinical research

There is no malaria vaccine currently available, and the most advanced candidate has recently reported a modest 30% efficacy against clinical malaria. Although many efforts have been dedicated to achieve this goal, the research was mainly directed to identify antigenic targets. Nevertheless, the latest progresses on understanding how immune system works and the data recovered from vaccination studies have conferred to the vaccine formulation its deserved relevance. Additionally to the antigen nature, the manner in which it is presented (delivery adjuvants) as well as the immunostimulatory effect of the formulation components (immunostimulants) modulates the immune response elicited. Protective immunity against malaria requires the induction of humoral, antibody-dependent cellular inhibition (ADCI) and effector and memory cell responses. This review summarizes the status of adjuvants that have been or are being employed in the malaria vaccine development, focusing on the pharmaceutical and immunological aspects, as well as on their immunization outcomings at clinical and preclinical stages.

Molecular basis of lipid antigen presentation by CD1d and recognition by natural killer T cells

Together with peptides, T lymphocytes respond to hydrophobic molecules, mostly lipids, presented by the non-classical CD1 family (CD1a-e). These molecules have evolved complex and diverse binding grooves in order to survey different cellular compartments for self and exogenous antigens, which are then presented for recognition to T-cell receptors (TCRs) on the surface of T cells. In particular, most CD1d-presented antigens are recognized by a population of lymphocytes denominated natural killer T (NKT) cells, characterized by a strong immunomodulatory potential. Among NKT cells, two major subsets (type I and type II NKT cells) have been described, based on their TCR repertoire and antigen specificity. Here we review recent structural and biochemical studies that have shed light on the molecular details of CD1d-mediated antigen recognition by type I and II NKT cells, which are in many aspects distinct from what has been observed for peptide major histocompatibility complex-reactive TCRs.

Controlling the HIV/AIDS epidemic: current status and global challenges

This review provides an overview of the current status of the global HIV pandemic and strategies to bring it under control. It updates numerous preventive approaches including behavioral interventions, male circumcision (MC), pre- and post-exposure prophylaxis (PREP and PEP), vaccines, and microbicides. The manuscript summarizes current anti-retroviral treatment options, their impact in the western world, and difficulties faced by emerging and resource-limited nations in providing and maintaining appropriate treatment regimens. Current clinical and pre-clinical approaches toward a cure for HIV are described, including new drug compounds that target viral reservoirs and gene therapy approaches aimed at altering susceptibility to HIV infection. Recent progress in vaccine development is summarized, including novel approaches and new discoveries.

Developing understanding of the roles of CD1d-restricted T cell subsets in cancer: reversing tumor-induced defects

Invariant natural killer T-cells ('iNKT') are the best-known CD1d-restricted T-cells, with recently-defined roles in controlling adaptive immunity. CD1d-restricted T-cells can rapidly produce large amounts of Th1 and/or Th2//Treg/Th17-type cytokines, thereby regulating immunity. iNKT can stimulate potent anti-tumor immune responses via production of Th1 cytokines, direct cytotoxicity, and activation of effectors. However, Th2//Treg-type iNKT can inhibit anti-tumor activity. Furthermore, iNKT are decreased and/or reversibly functionally impaired in many advanced cancers. In some cases, CD1d-restricted T-cell cancer defects can be traced to CD1d(+) tumor interactions, since hematopoietic, prostate, and some other tumors can express CD1d. Ligand and IL-12 can reverse iNKT defects and therapeutic opportunities exist in correcting such defects alone and in combination. Early stage clinical trials have shown potential for reconstitution of iNKT IFN-gamma responses and evidence of activity in a subset of patients, with rational new approaches to capitalize on this progress ongoing, as will be discussed here.