Phosphatidylserine Receptor-Mediated Recognition of Archaeosome Adjuvant Promotes Endocytosis and MHC Class I Cross-Presentation of the Entrapped Antigen by Phagosome-to-Cytosol Transport and Classical Processing

Ether lipids from archaeas in nano-drug delivery and vaccination

Archaea are microorganisms more closely related to eukaryotes than bacteria. Almost 50 years after being defined as a new domain of life on earth, new species continue to be discovered and their phylogeny organized. The study of the relationship between their genetics and metabolism and some of their extreme habitats has even positioned them as a model of extraterrestrial life forms. Archaea, however, are deeply connected to the life of our planet: they can be found in arid, acidic, warm areas; on most of the earth's surface, which is cold (below 5 °C), playing a prominent role in the cycles of organic materials on a global scale and they are even part of our microbiota. The constituent materials of these microorganisms differ radically from those produced by eukaryotes and bacteria, and the nanoparticles that can be manufactured using their ether lipids as building blocks exhibit unique properties that are of interest in nanomedicine. Here, we present for the first time a complete overview of the pre-clinical applications of nanomedicines based on ether archaea lipids, focused on drug delivery and adjuvancy over the last 25 years, along with a discussion on their pros, cons and their future industrial implementation.

A Potent Micron Neoantigen Tumor Vaccine GP-Neoantigen Induces Robust Antitumor Activity in Multiple Tumor Models

Therapeutic tumor neoantigen vaccines have been widely studied given their good safety profile and ability to avoid central thymic tolerance. However, targeting antigen-presenting cells (APCs) and inducing robust neoantigen-specific cellular immunity remain challenges. Here, a safe and broad-spectrum neoantigen vaccine delivery system is proposed (GP-Neoantigen) based on β-1,3-glucan particles (GPs) derived from Saccharomyces cerevisiae and coupling peptide antigens with GPs through convenient click chemistry. The prepared system has a highly uniform particle size and high APC targeting specificity. In mice, the vaccine system induced a robust specific CD8⁺ T cell immune response and humoral immune response against various conjugated peptide antigens and showed strong tumor growth inhibitory activity in EG7·OVA lymphoma, B16F10 melanoma, 4T1 breast cancer, and CT26 colon cancer models. The combination of the toll-like receptors (TLRs) agonist PolyI:C and CpG 2395 further enhanced the antitumor response of the particle system, achieving complete tumor clearance in multiple mouse models and inducing long-term rejection of reinoculated tumors. These results provide the broad possibility for its further clinical promotion and personalized vaccine treatment.

Adjuvants: Engineering Protective Immune Responses in Human and Veterinary Vaccines

Adjuvants are key components of many vaccines, used to enhance the level and breadth of the immune response to a target antigen, thereby enhancing protection from the associated disease. In recent years, advances in our understanding of the innate and adaptive immune systems have allowed for the development of a number of novel adjuvants with differing mechanisms of action. Herein, we review adjuvants currently approved for human and veterinary use, describing their use and proposed mechanisms of action. In addition, we will discuss additional promising adjuvants currently undergoing preclinical and/or clinical testing.

Development of Extracellular Vesicle Therapeutics: Challenges, Considerations, and Opportunities

Extracellular vesicles (EVs) hold great promise as therapeutic modalities due to their endogenous characteristics, however, further bioengineering refinement is required to address clinical and commercial limitations. Clinical applications of EV-based therapeutics are being trialed in immunomodulation, tissue regeneration and recovery, and as delivery vectors for combination therapies. Native/biological EVs possess diverse endogenous properties that offer stability and facilitate crossing of biological barriers for delivery of molecular cargo to cells, acting as a form of intercellular communication to regulate function and phenotype. Moreover, EVs are important components of paracrine signaling in stem/progenitor cell-based therapies, are employed as standalone therapies, and can be used as a drug delivery system. Despite remarkable utility of native/biological EVs, they can be improved using bio/engineering approaches to further therapeutic potential. EVs can be engineered to harbor specific pharmaceutical content, enhance their stability, and modify surface epitopes for improved tropism and targeting to cells and tissues in vivo. Limitations currently challenging the full realization of their therapeutic utility include scalability and standardization of generation, molecular characterization for design and regulation, therapeutic potency assessment, and targeted delivery. The fields' utilization of advanced technologies (imaging, quantitative analyses, multi-omics, labeling/live-cell reporters), and utility of biocompatible natural sources for producing EVs (plants, bacteria, milk) will play an important role in overcoming these limitations. Advancements in EV engineering methodologies and design will facilitate the development of EV-based therapeutics, revolutionizing the current pharmaceutical landscape.

Mechanistic insight into the induction of cellular immune responses by encapsulated and admixed archaeosome-based vaccine formulations

Archaeosomes are liposomes formulated using total polar lipids (TPLs) or semi-synthetic glycolipids derived from archaea. Conventional archaeosomes with entrapped antigen exhibit robust adjuvant activity as demonstrated by increased antigen-specific humoral and cell-mediated responses and enhanced protective immunity in various murine infection and cancer models. However, antigen entrapment efficiency can vary greatly resulting in antigen loss during formulation and variable antigen:lipid ratios. In order to circumvent this, we recently developed an admixed archaeosome formulation composed of a single semi-synthetic archaeal lipid (SLA, sulfated lactosylarchaeol) which can induce similarly robust adjuvant activity as an encapsulated formulation. Herein, we evaluate and compare the mechanisms involved in the induction of early innate and antigen-specific responses by both admixed (Adm) and encapsulated (Enc) SLA archaeosomes. We demonstrate that both archaeosome formulations result in increased immune cell infiltration, enhanced antigen retention at injection site and increased antigen uptake by antigen-presenting cells and other immune cell types, including neutrophils and monocytes following intramuscular injection to mice using ovalbumin as a model antigen. In vitro studies demonstrate SLA in either formulation is preferentially taken up by macrophages. Although the encapsulated formulation was better able to induce antigen-specific CD8⁺ T cell activation by dendritic cells in vitro, both encapsulated and admixed formulations gave equivalently enhanced protection from tumor challenge when tested in vivo using a B16-OVA melanoma model. Despite some differences in the immunostimulatory profile relative to the SLA (Enc) formulation, SLA (Adm) induces strong in vivo immunogenicity and efficacy, while offering an ease of formulation.

Effect of Different Adjuvants on the Longevity and Strength of Humoral and Cellular Immune Responses to the HCV Envelope Glycoproteins

Infection by Hepatitis C virus (HCV) can lead to liver cirrhosis/hepatocellular carcinoma and remains a major cause of serious disease morbidity and mortality worldwide. However, current treatment regimens remain inaccessible to most patients, particularly in developing countries, and, therefore, the development of a novel vaccine capable of protecting subjects from chronic infection by HCV could greatly reduce the rates of HCV infection, subsequent liver pathogenesis, and in some cases death. Herein, we evaluated two different semi-synthetic archaeosome formulations as an adjuvant to the E1/E2 HCV envelope protein in a murine model and compared antigen-specific humoral (levels of anti-E1/E2 IgG and HCV pseudoparticle neutralization) and cellular responses (numbers of antigen-specific cytokine-producing T cells) to those generated with adjuvant formulations composed of mimetics of commercial adjuvants including a squalene oil-in-water emulsion, aluminum hydroxide/monophosphoryl lipid A (MPLA) and liposome/MPLA/QS-21. In addition, we measured the longevity of these responses, tracking humoral, and cellular responses up to 6 months following vaccination. Overall, we show that the strength and longevity of anti-HCV responses can be influenced by adjuvant selection. In particular, a simple admixed sulfated S-lactosylarchaeol (SLA) archaeosome formulation generated strong levels of HCV neutralizing antibodies and polyfunctional antigen-specific CD4 T cells producing multiple cytokines such as IFN-γ, TNF-α, and IL-2. While liposome/MPLA/QS-21 as adjuvant generated superior cellular responses, the SLA E1/E2 admixed formulation was superior or equivalent to the other tested formulations in all immune parameters tested.

RNA is taking its Toll: Impact of RNA-specific Toll-like receptors on health and disease

RNA-sensing Toll-like receptors (TLRs) are often described as antiviral receptors of the innate immune system. However, the past decade has shown that the function and relevance of these receptors are far more complex. They were found to be essential for the detection of various bacterial, archaeal, and eukaryotic microorganisms and facilitate the discrimination between dead and living microbes. The cytokine and interferon response profile that is triggered has the potential to improve the efficacy of next-generation vaccines and may prevent the development of asthma and allergy. Nevertheless, the ability to recognize foreign RNA comes with a cost as also damaged host cells can release nucleic acids that might induce an inappropriate immune response. Thus, it is not surprising that RNA-sensing TLRs play a key role in various autoimmune diseases. However, promising new inhibitors and antagonists are on the horizon to improve their treatment.

Sulfated archaeol glycolipids: Comparison with other immunological adjuvants in mice

Archaeosomes are liposomes traditionally comprised of total polar lipids (TPL) or semi-synthetic glycerolipids of ether-linked isoprenoid phytanyl cores with varied glyco- and amino-head groups. As adjuvants, they induce robust, long-lasting humoral and cell-mediated immune responses and enhance protection in murine models of infectious disease and cancer. Traditional total polar lipid (TPL) archaeosome formulations are relatively complex and first generation semi-synthetic archaeosomes involve many synthetic steps to arrive at the final desired glycolipid composition. We have developed a novel archaeosome formulation comprising a sulfated disaccharide group covalently linked to the free sn-1 hydroxyl backbone of an archaeal core lipid (sulfated S-lactosylarchaeol, SLA) that can be more readily synthesized yet retains strong immunostimulatory activity for induction of cell-mediated immunity following systemic immunization. Herein, we have evaluated the immunostimulatory effects of SLA archaeosomes when used as adjuvant with ovalbumin (OVA) and hepatitis B surface antigen (HBsAg) and compared this to various other adjuvants including TLR3/4/9 agonists, oil-in-water and water-in-oil emulsions and aluminum hydroxide. Overall, we found that semi-synthetic sulfated glycolipid archaeosomes induce strong Ag-specific IgG titers and CD8 T cells to both antigens. In addition, they induce the expression of a number of cytokines/chemokines including IL-6, G-CSF, KC & MIP-2. SLA archaeosome formulations demonstrated strong adjuvant activity, superior to many of the other tested adjuvants.

Recent advances in applying nanotechnologies for cancer immunotherapy

Cancer immunotherapy aimed at boosting cancer-specific immunoresponses to eradicate tumor cells has evolved as a new treatment modality. Nanoparticles incorporating antigens and immunomodulatory agents can activate immune cells and modulate the tumor microenvironment to enhance anti-tumor immunity. The nanotechnology approach has been demonstrated to be superior to standard formulations in in-vivo settings. In this article, we focus on recent advances made within the last 5 years in nanoparticle-based cancer immunotherapy, including peptide- and nucleic acid-based nanovaccines, nanomedicines containing an immunoadjuvant to activate anti-tumor immunity, nanoparticle delivery of immune checkpoint inhibitors and the combination of the above approaches. Encouraging results and new emerging nanotechnologies in drug delivery promise the continuous growth of this field and ultimately clinical translation of enhanced immunotherapy of cancer.

Safety and biodistribution of sulfated archaeal glycolipid archaeosomes as vaccine adjuvants

Archaeosomes are liposomes comprised of ether lipids derived from various archaea. Unlike conventional ester-linked liposomes, archaeosomes exhibit high pH and thermal stability. As adjuvants, archaeosomes can induce robust, long-lasting humoral and cell-mediated immune responses and enhance protection in murine models of infectious disease and cancer. Archaeosomes constituted with total polar lipids (TPL) of various archaea are relatively complex, comprising >10 different lipid compounds. Archaeosomes can be constituted with semi-synthetic glycerolipids built on ether-linked isoprenoid phytanyl cores with varied synthetic glycol- and amino-head groups. However, such semi-synthetic archaeosomes involve many synthetic steps to arrive at the final desired glycolipid composition. We have developed a novel archaeosome formulation comprising a sulfated saccharide group covalently linked to the free sn-1 hydroxyl backbone of an archaeal core lipid (sulfated S-lactosylarchaeol, SLA) mixed with uncharged glycolipid (lactosylarchaeol, LA). This new class of adjuvants can be easily synthesized and retains strong immunostimulatory activity for induction of cell-mediated immunity following systemic immunization. Herein, we demonstrate the safety of SLA/LA archaeosomes following intramuscular injection to mice and evaluate the immunogenicity, in vivo distribution and cellular uptake of antigen (ovalbumin) encapsulated into SLA/LA archaeosomes. Overall, we have found that semi-synthetic sulfated glycolipid archaeosomes are a safe and effective novel class of adjuvants capable of inducing strong antigen-specific immune responses in mice and protection against subsequent B16 melanoma tumor challenge. A key step in their mechanism of action appears to be the recruitment of immune cells to the injection site and the subsequent trafficking of antigen to local draining lymph nodes.

Homologous Prime-Boost Vaccination with OVA Entrapped in Self-Adjuvanting Archaeosomes Induces High Numbers of OVA-Specific CD8⁺ T Cells that Protect Against Subcutaneous B16-OVA Melanoma

Homologous prime-boost vaccinations with live vectors typically fail to induce repeated strong CD8⁺ T cell responses due to the induction of anti-vector immunity, highlighting the need for alternative delivery vehicles. The unique ether lipids of archaea may be constituted into liposomes, archaeosomes, which do not induce anti-carrier responses, making them an ideal candidate for use in repeat vaccination systems. Herein, we evaluated in mice the maximum threshold of antigen-specific CD8⁺ T cell responses that may be induced by multiple homologous immunizations with ovalbumin (OVA) entrapped in archaeosomes derived from the ether glycerolipids of the archaeon Methanobrevibacter smithii (MS-OVA). Up to three immunizations with MS-OVA administered in optimized intervals (to allow for sufficient resting of the primed cells prior to boosting), induced a potent anti-OVA CD8⁺ T cell response of up to 45% of all circulating CD8⁺ T cells. Additional MS-OVA injections did not add any further benefit in increasing the memory of CD8⁺ T cell frequency. In contrast, OVA expressed by Listeria monocytogenes (LM-OVA), an intracellular bacterial vector failed to evoke a boosting effect after the second injection, resulting in significantly reduced antigen-specific CD8⁺ T cell frequencies. Furthermore, repeated vaccination with MS-OVA skewed the response increasingly towards an effector memory (CD62_low) phenotype. Vaccinated animals were challenged with B16-OVA at late time points after vaccination (+7 months) and were afforded protection compared to control. Therefore, archaeosomes constituted a robust particulate delivery system to unravel the kinetics of CD8⁺ T cell response induction and memory maintenance and constitute an efficient vaccination regimen optimized for tumor protection.

Cytotoxicity and uptake of archaeosomes prepared from Aeropyrum pernix lipids

Archaeon Aeropyrum pernix K1 is an obligate aerobic hyperthermophilic organism with C25,25-archeol membrane lipids with head groups containing inositol. Interactions of archaeosomes, liposomes prepared from lipids of A. pernix, with mammalian cells in vitro were studied. In vitro cytotoxicity was tested on five different cell lines: rodent mouse melanoma cells (B16-F1) and Chinese hamster ovary (CHO) cells, and three human cell lines—epithelial colorectal adenocarcinoma cells (CACO-2), liver hepatocellular carcinoma cell line (Hep G2) and endothelial umbilical vein cell line (EA.hy926). Archaeosomes were nontoxic to human Hep G2, CACO-2 and mildly toxic to rodent CHO and B16-F1 cells but showed strong cytotoxic effect on EA.hy926 cells. Confocal microscopy revealed that archaeosomes are taken up by endocytosis. The uptake of archaeosomes and the release of loaded calcein are more prominent in EA.hy926 cells, which is in line with high toxicity toward these cells. The mechanisms of uptake, release and action in these cells as well as in vivo functioning have to be further studied for possible targeted drug delivery.

Synthetic archaeosome vaccines containing triglycosylarchaeols can provide additive and long-lasting immune responses that are enhanced by archaetidylserine

The relation between archaeal lipid structures and their activity as adjuvants may be defined and explored by synthesizing novel head groups covalently linked to archaeol (2,3-diphytanyl-sn-glycerol). Saturated archaeol, that is suitably stable as a precursor for chemical synthesis, was obtained in high yield from Halobacterium salinarum. Archaeosomes consisting of the various combinations of synthesized lipids, with antigen entrapped, were used to immunize mice and subsequently determine CD8⁺ and CD4⁺-T cell immune responses. Addition of 45 mol% of the glycolipids gentiotriosylarchaeol, mannotriosylarchaeol or maltotriosylarchaeol to an archaetidylglycerophosphate-O-methyl archaeosome, significantly enhanced the CD8⁺ T cell response to antigen, but diminished the antibody titres in peripheral blood. Archaeosomes consisting of all three triglycosyl archaeols combined with archaetidylglycerophosphate-O-methyl (15/15/15/55 mol%) resulted in approximately additive CD8⁺ T cell responses and also an antibody response not significantly different from the archaetidylglycerophosphate-O-methyl alone. Synthetic archaetidylserine played a role to further enhance the CD8⁺ T cell response where the optimum content was 20–30 mol%. Vaccines giving best protection against solid tumor growth corresponded to the archaeosome adjuvant composition that gave highest immune activity in immunized mice.

Lipoidal soft hybrid biocarriers of supramolecular construction for drug delivery

Lipid-based innovations have achieved new heights during the last few years as an essential component of drug development. The current challenge of drug delivery is liberation of drug agents at the right time in a safe and reproducible manner to a specific target site. A number of novel drug delivery systems has emerged encompassing various routes of administration, to achieve controlled and targeted drug delivery. Microparticulate lipoidal vesicular system represents a unique technology platform suitable for the oral and systemic administration of a wide variety of molecules with important therapeutic biological activities, including drugs, genes, and vaccine antigens. The success of liposomes as drug carriers has been reflected in a number of liposome-based formulations, which are commercially available or are currently undergoing clinical trials. Also, novel lipid carrier-mediated vesicular systems are originated. This paper has focused on the lipid-based supramolecular vesicular carriers that are used in various drug delivery and drug targeting systems.

Lipoidal soft hybrid biocarriers of supramolecular construction for drug delivery

Lipid-based innovations have achieved new heights during the last few years as an essential component of drug development. The current challenge of drug delivery is liberation of drug agents at the right time in a safe and reproducible manner to a specific target site. A number of novel drug delivery systems has emerged encompassing various routes of administration, to achieve controlled and targeted drug delivery. Microparticulate lipoidal vesicular system represents a unique technology platform suitable for the oral and systemic administration of a wide variety of molecules with important therapeutic biological activities, including drugs, genes, and vaccine antigens. The success of liposomes as drug carriers has been reflected in a number of liposome-based formulations, which are commercially available or are currently undergoing clinical trials. Also, novel lipid carrier-mediated vesicular systems are originated. This paper has focused on the lipid-based supramolecular vesicular carriers that are used in various drug delivery and drug targeting systems.

License to kill: Formulation requirements for optimal priming of CD8(+) CTL responses with particulate vaccine delivery systems

Induction of CD8(+) T-cell responses is critical for the immunological control of a variety of diseases upon vaccination. Modern subunit vaccines are based on highly purified recombinant proteins. The high purity represents a major advancement in terms of vaccine safety compared to previous vaccination strategies with live attenuated or whole killed pathogens, but typically renders vaccine antigens poorly immunogenic and insufficient in mobilizing protective immunity. Adjuvants are therefore needed in vaccine formulations to enhance, direct and maintain the immune response to vaccine antigens. However, a weakness of many adjuvants is the lack of induction of CD8(+) T-cell responses against protein antigens, which are required for protection against challenging and difficult infectious diseases such as AIDS and for therapeutic cancer vaccination. Within the last decade, adjuvant systems that can induce CD8(+) T-cell responses have been developed and the first clinical trials demonstrating the clinical relevance of such formulations have been performed. This paper reviews the current status of lipid- and polymer-based particulate antigen delivery systems capable of stimulating CD8(+) T-cell immunity with special focus on mechanisms of priming and pharmaceutical requirements for optimal activation of cytotoxic T-lymphocytes that can kill virus-infected or abnormal (cancer) cells.

Liposome-coupled antigens are internalized by antigen-presenting cells via pinocytosis and cross-presented to CD8 T cells

We have previously demonstrated that antigens chemically coupled to the surface of liposomes consisting of unsaturated fatty acids were cross-presented by antigen-presenting cells (APCs) to CD8⁺ T cells, and that this process resulted in the induction of antigen-specific cytotoxic T lymphocytes. In the present study, the mechanism by which the liposome-coupled antigens were cross-presented to CD8⁺ T cells by APCs was investigated. Confocal laser scanning microscopic analysis demonstrated that antigens coupled to the surface of unsaturated-fatty-acid-based liposomes received processing at both MHC class I and class II compartments, while most of the antigens coupled to the surface of saturated-fatty-acid-based liposomes received processing at the class II compartment. In addition, flow cytometric analysis demonstrated that antigens coupled to the surface of unsaturated-fatty-acid-liposomes were taken up by APCs even in a 4°C environment; this was not true of saturated-fatty-acid-liposomes. When two kinds of inhibitors, dimethylamiloride (DMA) and cytochalasin B, which inhibit pinocytosis and phagocytosis by APCs, respectively, were added to the culture of APCs prior to the antigen pulse, DMA but not cytochalasin B significantly reduced uptake of liposome-coupled antigens. Further analysis of intracellular trafficking of liposomal antigens using confocal laser scanning microscopy revealed that a portion of liposome-coupled antigens taken up by APCs were delivered to the lysosome compartment. In agreement with the reduction of antigen uptake by APCs, antigen presentation by APCs was significantly inhibited by DMA, and resulted in the reduction of IFN-γ production by antigen-specific CD8⁺ T cells. These results suggest that antigens coupled to the surface of liposomes consisting of unsaturated fatty acids might be pinocytosed by APCs, loaded onto the class I MHC processing pathway, and presented to CD8⁺ T cells. Thus, these liposome-coupled antigens are expected to be applicable for the development of vaccines that induce cellular immunity.

Delivery of Exogenous Antigens to Induce Cytotoxic CD8+ T Lymphocyte Responses

Vaccines intended to induce a cytotoxic CD8+ T-cell response are highly sought after. However, some of these vaccines can be problematic if they replicate in the host. An alternative strategy is to exploit cross-presentation of exogenous antigens to express peptides on major histocompatibility complex (MHC) class I molecules. During cross-presentation, the delivered exogenous antigen can be taken up and processed through diverse mechanisms. Here, we will discuss the recent advances regarding the complex nature of the cross-priming process and the models that reflect its relevance in vivo. Moreover, we summarize current data that explore potential adjuvants and vaccine vectors that deliver antigens to activate CD8+ T cells relying on cross-presentation.

Isopranoid- and dipalmitoyl-aminophospholipid adjuvants impact differently on longevity of CTL immune responses

The success of lipid membranes as cytotoxic T-cell (CTL) adjuvants requires targeted uptake by antigen-presenting cells (APCs) and delivery of the antigen cargo to the cytosol for processing. To target the phosphatidylserine (PS) receptor of APCs, we prepared antigen-loaded liposomes containing dipalmitoylphosphatidylserine and archaeal lipid liposomes (archaeosomes), containing an equivalent amount of archaetidylserine, and compared their ability to promote short and long-term CTL activity in animals. CTL responses were enhanced by the incorporation of PS into phosphatidylcholine/cholesterol liposomes and, to a lesser extent, into phosphatidylglycerol/cholesterol liposomes, that correlated to the amount of surface amino groups reactive with trinitrobenzoyl sulfonate. Archaeosomes contrasted to the liposome adjuvants by exhibiting higher amounts of surface amino groups and inducing superior shorter and, especially, longer-term CTL responses. The incorporation of dipalmitoyl lipids into archaeosomes induced instability and prevented long-term, but not short-term, CTL responses in mice. The importance of glycero-lipid cores (isopranoid versus dipalmitoyl) to the longevity of the CTL response achieved was shown further by incorporating dipalmitoyl phosphatidylethanolamine (DPPE) or equivalent amounts of synthetic archaetidylethanolamine (AE) into archaeosome adjuvants. Both DPPE and AE at equivalent (5 mol%) concentrations enhanced the rapidity of CTL responses in mice, indicating the importance of the head group in the short term. In the longer term, 5% of DPPE (but not 5% of AE) was detrimental. In addition to head-group effects critical to the potency of short-term CTL responses, the longer term CTL adjuvant properties of archaeosomes may be ascribed to stability imparted by the archaeal isopranoid core lipids.

Galactosylated LDL nanoparticles: a novel targeting delivery system to deliver antigen to macrophages and enhance antigen specific T cell responses

We aim to define the role of Kupffer cells in intrahepatic antigen presentation, using the selective delivery of antigen to Kupffer cells rather than other populations of liver antigen-presenting cells. To achieve this we developed a novel antigen delivery system that can target antigens to macrophages, based on a galactosylated low-density lipoprotein nanoscale platform. Antigen was delivered via the galactose particle receptor (GPr), internalized, degraded and presented to T cells. The conjugation of fluoresceinated ovalbumin (FLUO-OVA) and lactobionic acid with LDL resulted in a substantially increased uptake of FLUO-OVA by murine macrophage-like ANA1 cells in preference to NIH3T3 cells, and by primary peritoneal macrophages in preference to primary hepatic stellate cells. Such preferential uptake led to enhanced proliferation of OVA specific T cells, showing that the galactosylated LDL nanoscale platform is a successful antigen carrier, targeting antigen to macrophages but not to all categories of antigen presenting cells. This system will allow targeted delivery of antigen to macrophages in the liver and elsewhere, addressing the question of the role of Kupffer cells in liver immunology. It may also be an effective way of delivering drugs or vaccines directly at macrophages.

Tumor cell lysate-pulsed dendritic cells induce a T cell response against colon cancer in vitro and in vivo

To investigate whether tumor cell lysate-pulsed (TP) dendritic cells (DCs) induce cytotoxic T lymphocyte (CTL) activity against colon cancer in vitro and in vivo. Hematopoietic progenitor cells were magnetically isolated from BALB/c mice bone marrow cells. These cells were cultured with cytokines GM-CSF, IL-4, and TNFalpha to induce their maturation. They were analyzed by morphological observation and phenotype analysis. DCs were pulsed with tumor cell lysate obtained by rapid freezing and thawing at a 1:3 DC:tumor cell ratio. CTL activity and interferon gamma (IFNgamma) secretion was evaluated ex vivo. In order to determine whether or not vaccination with CT26 TP DCs induce the therapeutic potential in the established colon tumor model, CT26 colon tumor cells were implanted subcutaneously (s.c.) in the midflank of naïve BALB/c mice. Tumor-bearing mice were injected with vaccination with CT26 TP DCs on days 3 and 10. Tumor growth was assessed every 2-3 days. Finally, CTL activity and IFNgamma secretion were evaluated in immunized mice. Hematopoietic progenitor cells from mice bone marrow cells cultured with cytokines for 8 days showed the character of typical mature DCs. Morphologically, these cells were large with oval or irregularly shaped nuclei and with many small dendrites. Phenotypically, FACS analysis showed that they expressed high levels of MHC II, CD11b, CD80, and CD86 antigen, and were negative for CD8alpha. However, immature DCs cultured with cytokines for 5 days did not have typical DCs phenotypic markers. Ex vivo primed T cells with CT26 TP DCs were able to induce effective CTL activity against CT26 tumor cells, but not B16 tumor cells (E:T = 100:1, 60.36 +/- 7.11% specific lysis in CT26 group vs. 17.36 +/- 4.10% specific lysis in B16 group), and produced higher levels of IFNgamma when stimulated with CT26 tumor cells but not when stimulated with B16 tumor cells (1210.33 +/- 72.15 pg/ml in CT26 group vs. 182.25 +/- 25.51 pg/ml in B16 group, P < 0.01). Vaccination with CT26 TP DCs could induce anti-tumor immunity against CT26 colon tumor in murine therapeutic models (tumor volume on day 19: CT26 TP DCs 342 +/- 55 mm(3) vs. the other control groups, P < 0.05). In addition, all splenic CD3(+) T cells obtained from mice vaccinated with CT26 TP DCs produced high levels of IFNgamma and shown specific cytotoxic activity against CT26 tumor cells, but no cytotoxic activity when stimulated with B16 tumor cells. Tumor cell lysate-pulsed DCs can induce tumor-specific CTL activity against colon cancer in vitro and in vivo.

Alteration of lipid composition of rat thymus during thymic atrophy by whole-body X-irradiation

PURPOSE

Thymic atrophy induced by irradiation is well known, but in vivo lipid metabolism during the atrophy has not been studied in detail. We determined the lipid composition of rat thymus during the progress of thymic atrophy induced by whole-body X-irradiation.

MATERIALS AND METHODS

The lipid analysis of total lipid of rat thymus after 5 Gy whole-body X-irradiation was performed by high performance liquid chromatography and gas chromatography equipped with mass spectrometry.

RESULTS

Major changes observed were a 16.2-fold elevation of cholesterol ester (CE) during a 48-h post-irradiation period and a 6.1-fold increase of alkyldiacylglycerol (ADG) at 24 h. Other significant changes detected were an increase in lysophosphatidylcholine and a transient increase in ceramide and phosphatidic acid. Acyl chain analysis revealed a substantial elevation of arachidonate composition of CE and an unusually high content of polyunsaturated fatty acids (71.5%, mol/mol) in ADG.

CONCLUSION

Lipid analysis shows that the thymic atrophy by X-irradiation was accompanied by a significant change in thymic lipids. This in vivo result opens up new vistas of the role of lipids in apoptosis and phagocytosis during thymic atrophy.

Glycosidase-induced fusion of isoprenoid gentiobiosyl lipid membranes at acidic pH

A difficulty in explaining the mechanism whereby archaeal lipid membrane vesicles (archaeosomes) deliver entrapped protein antigens to the MHC class I cytosolic pathway from phagolysosomes of antigen-presenting cells has been the observation that they tend not to fuse. Here, we determine that archaeosomes, composed of archaeal isoprenoid mixtures of glyco and phospholipids, can be highly fusogenic when exposed to the pH and enzymes found in late phagolysosomes. Fusions were strictly dependent on acidic pH and the presence of alpha- or beta-glucosidase. Resonance energy transfer (RET) assays demonstrated that fusion conditions induced lipid mixing of archaeosome lipids with self-unlabeled archaeosomes. Because PC/PG/cholesterol liposomes by themselves did not fuse, it was possible to unequivocally show a fusion of rhodamine-labeled liposomes with archaeosomes by fluorescence microscopy and to demonstrate lipid mixing between labeled liposomes and archaeosomes by the RET assay. Radiotracer and (1)H NMR studies revealed that glycolipids in fused archaeosomes were not degraded significantly by glucosidase treatment during fusion. Rather, the glucosidases dramatically induced small archaeosomes to rapidly and visually aggregate at pH 4.8, but not 6.8, thus bringing membranes together appropriately as a first step in the fusion process. (1)H NMR was used to demonstrate that conditions causing aggregation correlated with binding of glucosidase to the archaeosomes. Binding at acidic pH occurred by the electrostatic interaction of positively charged glucosidase with the anionic phospholipids, although the interaction also occurred with the gentiobiosyl lipids. The data indicate a mechanism of membrane-membrane fusion for archaeal glycolipid membranes induced by glycosidase and illustrate the importance for inclusion of glycolipids in compositions of vesicles designed to deliver protein antigens to the cytosol for MHC class I presentation.

Distribution of Archaea in Japanese patients with periodontitis and humoral immune response to the components

There is controversy regarding the existence of archaeal pathogens. Periodontitis is one of the human diseases in which Archaea have been suggested to have roles as pathogens. This study was performed to investigate the distribution of Archaea in Japanese patients with periodontitis and to examine the serum IgG responses to archaeal components. Subgingival plaque samples were collected from 111 periodontal pockets of 49 patients (17 with aggressive periodontitis and 32 with chronic periodontitis), and 30 subgingival plaque samples were collected from 17 healthy subjects. By PCR targeting the 16S rRNA gene, Archaea were detected in 15 plaque samples (13.5% of total samples) from 11 patients (29.4% of patients with aggressive periodontitis and 18.8% of patients with chronic periodontitis). Archaea were detected mostly (14/15) in severe diseased sites (pocket depth > or =6 mm), while no amplicons were observed in any samples from healthy controls. Sequence analysis of the PCR products revealed that the majority of Archaea in periodontal pockets were a Methanobrevibacter oralis-like phylotype. Western immunoblotting detected IgG antibodies against M. oralis in eight of the 11 sera from patients. These results suggest the potential of Archaea (M. oralis) as an antigenic pathogen of periodontitis.

Archaeosome adjuvants: immunological capabilities and mechanism(s) of action

Archaeosomes (liposomes comprised of glycerolipids of Archaea) constitute potent adjuvants for the induction of Th1, Th2 and CD8(+) T cell responses to the entrapped soluble antigen. Archaeal lipids are uniquely constituted of ether-linked isoprenoid phytanyl cores conferring stability to the membranes. Additionally, varied head groups displayed on the glycerol-lipid cores facilitate unique immunostimulating interactions with mammalian antigen-presenting cells (APCs). The polar lipid from the archaeon, Methanobrevibacter smithii has been well characterized for its adjuvant potential, and is abundant in archaetidyl serine, promoting interaction with a phosphatidylserine receptor on APCs. These archaeosomes mediate MHC class I cross-priming via the phagosome-to-cytosol TAP-dependent classical processing pathway, and also upregulate costimulation by APCs without overt inflammatory cytokine production. Furthermore, they facilitate potent CD8(+) T cell memory to co-delivered antigen, comparable in magnitude and quality to live bacterial vaccine vectors. Archaeosome vaccines provide profound protection in murine models of infection and cancer. This technology is being developed for clinical application and offers a novel prospect for rational design and development of safe and potent subunit vaccines capable of eliciting T cell immunity against intracellular infections and cancers.

Recombinant gas vesicles from Halobacterium sp. displaying SIV peptides demonstrate biotechnology potential as a pathogen peptide delivery vehicle

Background

Previous studies indicated that recombinant gas vesicles (r-GV) from a mutant strain of Halobacterium sp. NRC-1 could express a cassette containing test sequences of SIVmac gag derived DNA, and function as an antigen display/delivery system. Tests using mice indicated that the humoral immune response to the gag encoded sequences evoked immunologic memory in the absence of an exogenous adjuvant.

Results

The goal of this research was to extend this demonstration to diverse gene sequences by testing recombinant gas vesicles displaying peptides encoded by different SIV genes (SIV^{tat, rev or nef}). Verification that different peptides can be successfully incorporated into the GvpC surface protein of gas vesicle would support a more general biotechnology application of this potential display/delivery system. Selected SIVsm-GvpC fusion peptides were generated by creating and expressing fusion genes, then assessing the resulting recombinant gas vesicles for SIV peptide specific antigenic and immunogenic capabilities. Results from these analyses support three conclusions: (i) Different recombinant gvpC-SIV genes will support the biosynthesis of chimeric, GvpC fusion proteins which are incorporated into the gas vesicles and generate functional organelles. (ii) Monkey antibody elicited by in vivo infection with SHIV recognizes these expressed SIV sequences in the fusion proteins encoded by the gvpC-SIV fusion genes as SIV peptides. (iii) Test of antiserum elicited by immunizing mice with recombinant gas vesicles demonstrated notable and long term antibody titers. The observed level of humoral responses, and the maintenance of elevated responses to, Tat, Rev and Nef1 encoded peptides carried by the respective r-GV, are consistent with the suggestion that in vivo there may be a natural and slow release of epitope over time.

Conclusion

The findings therefore suggest that in addition to providing information about these specific inserts, r-GV displaying peptide inserts from other relevant pathogens could have significant biotechnological potential for display and delivery, or serve as a cost effective initial screen of pathogen derived peptides naturally expressed during infections in vivo.

Sulfated glycosphingolipid as mediator of phagocytosis: SM4s enhances apoptotic cell clearance and modulates macrophage activity

Sulfoglycolipids are present on the surface of a variety of cells. The sulfatide SM4s is increased in lung, renal, and colon cancer and is associated with an adverse prognosis, possibly due to a low immunoreactivity of the tumor. As macrophages significantly contribute to the inflammatory infiltrate in malignancies, we postulated that SM4s may modulate macrophage function. We have investigated the effect of SM4s on the uptake of apoptotic tumor cells, macrophage cytokine profile, and receptor expression. Using flow cytometry and microscopic analyses, we found that coating apoptotic murine carcinoma cells from the colon and kidney with SM4s promoted their phagocytosis by murine macrophages up to 3-fold ex vivo and in vivo. This increased capacity was specifically inhibited by preincubation of macrophages with oxidized or acetylated low density lipoprotein and maleylated albumin, indicating involvement of scavenger receptors in this interaction. The uptake of SM4s-coated apoptotic cells significantly enhanced macrophage production of TGF-beta1, expression of P-selectin, and secretion of IL-6. These data suggest that SM4s within tumors may promote apoptotic cell removal and alter the phenotype of tumor-associated macrophages.

Traffic of proteins and peptides across membranes for immunosurveillance by CD8(+) T lymphocytes: a topological challenge

Cytotoxic CD8(+) T lymphocytes kill infected cells that display major histocompatibility complex (MHC) class I molecules presenting peptides processed from pathogen proteins. In general, the peptides are proteolytically processed from newly made endogenous antigens in the cytosol and require translocation to the endoplasmic reticulum (ER) for MHC class I loading. This last task is performed by the transporters associated with antigen processing (TAP). Sampling of suspicious pathogen-derived proteins reaches beyond the cytosol, and MHC class I loading can occur in other secretory or endosomal compartments besides the ER. Peptides processed from exogenous antigens can also be presented by MHC class I molecules to CD8(+) T lymphocytes, in this case requiring delivery from the extracellular medium to the processing and MHC class I loading compartments. The endogenous or exogenous antigen can be processed before or after its transport to the site of MHC class I loading. Therefore, mechanisms that allow the full-length protein or processed peptides to cross several subcellular membranes are essential. This review deals with the different intracellular pathways that allow the traffic of antigens to compartments proficient in processing and loading of MHC class I molecules for presentation to CD8(+) T lymphocytes and highlights the need to molecularly identify the transporters involved.

Rapid clonal expansion and prolonged maintenance of memory CD8+ T cells of the effector (CD44highCD62Llow) and central (CD44highCD62Lhigh) phenotype by an archaeosome adjuvant independent of TLR2

Vaccines capable of eliciting long-term T cell immunity are required for combating many diseases. Live vectors can be unsafe whereas subunit vaccines often lack potency. We previously reported induction of CD8(+) T cells to Ag entrapped in archaeal glycerolipid vesicles (archaeosomes). In this study, we evaluated the priming, phenotype, and functionality of the CD8(+) T cells induced after immunization of mice with OVA-Methanobrevibacter smithii archaeosomes (MS-OVA). A single injection of MS-OVA evoked a profound primary response but the numbers of H-2K(b)OVA(257-264)-specific CD8(+) T cells declined by 14-21 days, and <1% of primarily central phenotype (CD44(high)CD62L(high)) cells persisted. A booster injection of MS-OVA at 3-11 wk promoted massive clonal expansion and a peak effector response of approximately 20% splenic/blood OVA(257-264)-specific CD8(+) T cells. Furthermore, contraction was protracted and the memory pool (IL-7Ralpha(high)) of approximately 5% included effector (CD44(high)CD62L(low)) and central (CD44(high)CD62L(high)) phenotype cells. Recall response was observed even at >300 days. CFSE-labeled naive OT-1 (OVA(257-264) TCR transgenic) cells transferred into MS-OVA-immunized recipients cycled profoundly (>90%) within the first week of immunization indicating potent Ag presentation. Moreover, approximately 25% cycling of Ag-specific cells was seen for >50 days, suggesting an Ag depot. In vivo, CD8(+) T cells evoked by MS-OVA killed >80% of specific targets, even at day 180. MS-OVA induced responses similar in magnitude to Listeria monocytogenes-OVA, a potent live vector. Furthermore, protective CD8(+) T cells were induced in TLR2-deficient mice, suggesting nonengagement of TLR2 by archaeal lipids. Thus, an archaeosome adjuvant vaccine represents an alternative to live vectors for inducing CD8(+) T cell memory.

Murine polyomavirus-like particles induce maturation of bone marrow-derived dendritic cells and proliferation of T cells

We analysed the effects of murine polyomavirus-like particles (PLPs) on bone marrow-derived dendritic cells (BMDCs) and T cells in vitro. BMDCs activated with PLPs up-regulated CD40, CD80, CD86 and major histocompatibility complex (MHC) class II surface markers and produced proinflammatory cytokines. Chimeric PLPs [expressing the ovalbumin (OVA)-peptides OVA(257-264) or OVA(323-339)], but not wildtype PLPs, activated OVA-specific CD8 T cells and OVA-specific CD4 T cells, respectively, indicating both MHC class I and II presentation of the peptides by antigen-presenting cells. Our results suggest that PLPs may be used as vaccine adjuvants priming dendritic cells to induce potent T cell responses.