Safety of archaeosome adjuvants evaluated in a mouse model

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.

Vesicular and Planar Membranes of Archaea Lipids: Unusual Physical Properties and Biomedical Applications

Liposomes and planar membranes made of archaea or archaea-like lipids exhibit many unusual physical properties compared to model membranes composed of conventional diester lipids. Here, we review several recent findings in this research area, which include (1) thermosensitive archaeosomes with the capability to drastically change the membrane surface charge, (2) MthK channel's capability to insert into tightly packed tetraether black lipid membranes and exhibit channel activity with surprisingly high calcium sensitivity, and (3) the intercalation of apolar squalane into the midplane space of diether bilayers to impede proton permeation. We also review the usage of tetraether archaeosomes as nanocarriers of therapeutics and vaccine adjuvants, as well as the biomedical applications of planar archaea lipid membranes. The discussion on archaeosomal therapeutics is focused on partially purified tetraether lipid fractions such as the polar lipid fraction E (PLFE) and glyceryl caldityl tetraether (GCTE), which are the main components of PLFE with the sugar and phosphate removed.

Lipid-Based Nanocarriers for Lymphatic Transportation

The effectiveness of any drug is dependent on to various factors like drug solubility, bioavailability, selection of appropriate delivery system, and proper route of administration. The oral route for the delivery of drugs is undoubtedly the most convenient, safest and has been widely used from past few decades for the effective delivery of drugs. However, despite of the numerous advantages that oral route offers, it often suffers certain limitations like low bioavailability due to poor water solubility as well as poor permeability of drugs, degradation of the drug in the physiological pH of the stomach, hepatic first-pass metabolism, etc. The researchers have been continuously working extensively to surmount and address appropriately the inherent drawbacks of the oral drug delivery. The constant and continuous efforts have led to the development of lipid-based nano drug delivery system to overcome the aforesaid associated challenges of the oral delivery through lymphatic transportation. The use of lymphatic route has demonstrated its critical and crucial role in overcoming the problem associated and related to low bioavailability of poorly water-soluble and poorly permeable drugs by bypassing intestinal absorption and possible first-pass metabolism. The current review summarizes the bonafide perks of using the lipid-based nanocarriers for the delivery of drugs using the lymphatic route. The lipid-based nanocarriers seem to be a promising delivery system which can be optimized and further explored as an alternative to the conventional dosage forms for the enhancement of oral bioavailability of drugs, with better patient compliance, minimum side effect, and improved the overall quality of life.

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.

Reality of a Vaccine in the Prevention and Treatment of Atherosclerosis

Atherosclerosis together with multiple sclerosis, psoriasis and rheumatoid arthritis can be used as examples of chronic inflammatory diseases associated with multifactorial components that evolve over the years. Nevertheless, an important difference between these diseases relies on the fact that atherosclerosis develops from early ages where inflammation dominates the very beginning of the disease. This review highlights the inflammatory nature of atherosclerosis and the role the immune system plays in the process of atherogenesis. Although treatment of atherosclerosis has been for years based on lipid-lowering therapies reducing a series of risk factors, the degree of success has been only limited because cardiovascular complications related to the evolution of atherosclerotic lesions continue to appear in the population worldwide. In this sense, alternative treatments for atherosclerosis have come into play where both innate and adaptive immunity have been proposed to modulate atherosclerosis-associated inflammatory phenomena. When tested for their atheroprotective properties, several immunogens have been studied through passive and active immunization with good results and, therefore, the strategy through vaccination to control the disease has been made possible. Many experimental pre-clinical studies demonstrating proof of concept that vaccination using DNA and protein with an effective use of adjuvants and the optimal route of administration now provide a tangible new therapeutic approach that sets the stage for several of these vaccines to be tested in large, randomized, long-term clinical studies. A vaccine ready for human use will only be accomplished through the close association between academia, regulatory government organizations and private industry, allowing the reality of a simple and successful therapy to reduce atherosclerosis and its severe clinical complications.

Vaccines against Francisella tularensis – past, present and future

Francisella tularensis is a facultative intracellular bacterial pathogen capable of causing a spectrum of human diseases collectively called tularemia. The pathogen is highly infectious and some strains can cause rapidly lethal infection especially when inhaled. The latter were developed as biological weapons in the past and nowadays cause concern as potential bioterrorism agents. A live attenuated strain of the pathogen was developed more that 40 years ago and remains the sole prophylactic measure against the pathogen. Research to develop better live and subunit vaccines is under way. The former will require an understanding of the virulence factors of F. tularensis and a facile means of mutating them and the latter will require identification of the protective antigens of the pathogen. The current vaccine and its potential replacements are the focus of this review.

Ether lipid vesicle-based antigens impart protection against experimental listeriosis

Background

Incidence of food-borne infections from Listeria monocytogenes, a parasite that has adapted intracellular residence to avoid antibody onslaught, has increased dramatically in the past few years. The apparent lack of an effective vaccine that is capable of evoking the desired cytotoxic T cell response to obliterate this intracellular pathogen has encouraged the investigation of alternate prophylactic strategies. It should also be noted that Archaebacteria (Archae) lipid-based adjuvants enhance the efficacy of subunit vaccines. In the present study, the adjuvant properties of archaeosomes (liposomes prepared from total polar lipids of archaebacteria, Halobacterium salinarum) combined with immunogenic culture supernatant antigens of L. monocytogenes have been exploited in designing a vaccine candidate against experimental listeriosis in murine model.

Methods

Archaeosome-entrapped secretory protein antigens (SAgs) of L. monocytogenes were evaluated for their immunological responses and tendency to deplete bacterial burden in BALB/c mice challenged with sublethal listerial infection. Various immunological studies involving cytokine profiling, lymphocyte proliferation assay, detection of various surface markers (by flowcytometric analysis), and antibody isotypes (by enzyme-linked immunosorbent assay) were used for establishing the vaccine potential of archaeosome-entrapped secretory proteins.

Results

Immunization schedule involving archaeosome-encapsulated SAgs resulted in upregulation of Th1 cytokine production along with boosted memory in BALB/c mice. It also showed protective effect by reducing listerial burden in various vital organs (liver and spleen) of the infected mice. However, the soluble form of the antigens (SAgs) and their physical mixture with sham (empty) archaeosomes, besides showing feeble Th1 response, were unable to protect the animals against virulent listerial infection.

Conclusion

On the basis of the evidence provided by the current data, it is inferred that archaeosome-entrapped SAgs formulation not only enhances cytotoxic T cell response but also helps in the clearance of pathogens and thereby increases the survival of the immunized animals.

Nanoparticle delivery systems in cancer vaccines

Therapeutic strategies that involve the manipulation of the host's immune system are gaining momentum in cancer research. Antigen-loaded nanocarriers are capable of being actively taken up by antigen-presenting cells (APCs) and have shown promising potential in cancer immunotherapy by initiating a strong immunostimulatory cascade that results in potent antigen-specific immune responses against the cancer. Such carrier systems offer versatility in that they can simultaneously co-deliver adjuvants with the antigens to enhance APC activation and maturation. Furthermore, modifying the surface properties of these nanocarriers affords active targeting properties to APCs and/or enhanced accumulation in solid tumors. Here, we review some recent advances in these colloidal and particulate nanoscale systems designed for cancer immunotherapy and the potential for these systems to translate into clinical cancer vaccines.

Archaeosomes made of Halorubrum tebenquichense total polar lipids: a new source of adjuvancy

Background

Archaeosomes (ARC), vesicles prepared from total polar lipids (TPL) extracted from selected genera and species from the Archaea domain, elicit both antibody and cell-mediated immunity to the entrapped antigen, as well as efficient cross priming of exogenous antigens, evoking a profound memory response. Screening for unexplored Archaea genus as new sources of adjuvancy, here we report the presence of two new Halorubrum tebenquichense strains isolated from grey crystals (GC) and black mood (BM) strata from a littoral Argentinean Patagonia salt flat. Cytotoxicity, intracellular transit and immune response induced by two subcutaneous (sc) administrations (days 0 and 21) with BSA entrapped in ARC made of TPL either form BM (ARC-BM) and from GC (ARC-GC) at 2% w/w (BSA/lipids), to C3H/HeN mice (25 μg BSA, 1.3 mg of archaeal lipids per mouse) and boosted on day 180 with 25 μg of bare BSA, were determined.

Results

DNA G+C content (59.5 and 61.7% mol BM and GC, respectively), 16S rDNA sequentiation, DNA-DNA hybridization, arbitrarily primed fingerprint assay and biochemical data confirmed that BM and GC isolates were two non-previously described strains of H. tebenquichense. Both multilamellar ARC mean size were 564 ± 22 nm, with -50 mV zeta-potential, and were not cytotoxic on Vero cells up to 1 mg/ml and up to 0.1 mg/ml of lipids on J-774 macrophages (XTT method). ARC inner aqueous content remained inside the phago-lysosomal system of J-774 cells beyond the first incubation hour at 37°C, as revealed by pyranine loaded in ARC. Upon subcutaneous immunization of C3H/HeN mice, BSA entrapped in ARC-BM or ARC-GC elicited a strong and sustained primary antibody response, as well as improved specific humoral immunity after boosting with the bare antigen. Both IgG1 and IgG2a enhanced antibody titers could be demonstrated in long-term (200 days) recall suggesting induction of a mixed Th1/Th2 response.

Conclusion

We herein report the finding of new H. tebenquichense non alkaliphilic strains in Argentinean Patagonia together with the adjuvant properties of ARC after sc administration in mice. Our results indicate that archaeosomes prepared with TPL from these two strains could be successfully used as vaccine delivery vehicles.

Safety of Intranasally Administered Archaeal Lipid Mucosal Vaccine Adjuvant and Delivery (AMVAD) Vaccine in Mice

The safety profile of a recently described novel archaeal lipid mucosal vaccine adjuvant and delivery (AMVAD) system capable of eliciting robust antigen-specific mucosal and systemic immune responses was evaluated in female Balb/c mice (10/group) using ovalbumin (OVA) antigen. Mice were intranasally immunized (0, 7, and 21 days) with a vaccine comprising 1 μg OVA (0.05 mg/kg body weight) formulated in 0.04 mg total polar lipids extract (2.17 mg/kg body weight) of Methanobrevibacter smithii constituting the AMVAD system. Control groups were similarly immunized with 10-fold higher AMVAD vaccine dose (0.54 mg OVA and 21.7 mg lipid per kg), saline, 10 μg OVA in saline, or 0.04 or 0.4 mg lipid constituting empty AMVAD (no OVA) in saline, or were naïve mice. Clinical signs, rectal temperature, and body weight were monitored once daily or as appropriate. Half the mice in each group were euthanized at 2 days after the first immunization. Blood was collected for clinical chemistry analyses. Major organs (heart, lungs, kidneys, liver, spleen, thymus, and brain) were examined macroscopically and histologically. The remaining mice were euthanized at 29 days and blood and organs collected for analyses as done at 2 days. Feces collected at 27 days, and sera, bile, and nasal lavage at 29 days, were assayed for antibody responses. Based on clinical symptoms, temperature, body weight changes, serum clinical chemistry, and tissue histopathology, there were no overt toxicities associated with OVA/AMVAD or empty AMVAD vaccines. There were no antibodies elicited against the lipids comprising the AMVAD system. These results demonstrate that at 10-fold excess dose of that required for vaccine efficacy, intranasally administered AMVAD vaccine appears to be relatively safe.

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.

Mucosal and systemic immune responses by intranasal immunization using archaeal lipid-adjuvanted vaccines

The utility of archaeal polar lipids as an adjuvant/delivery system for elicitation of antigen-specific mucosal immune responses in intranasally administered vaccines was investigated. Although unilamellar archaeosomes (liposomes made from archaeal polar lipids) with encapsulated ovalbumin (OVA/archaeosomes) induced anti-OVA IgG antibody responses in sera, they failed to induce anti-OVA IgA antibody responses at mucosal sites. However, the addition of CaCl2 to convert OVA/archaeosomes into an archaeal lipid mucosal vaccine adjuvant and delivery (AMVAD) vaccine (OVA/AMVAD) consisting of larger, particulate, aggregated structures resulted in an efficacious intranasal (i.n.) vaccine. Intranasal immunization of mice with OVA/AMVAD vaccines prepared from various archaeal polar lipid compositions elicited anti-OVA IgA antibody responses in sera, feces, bile, vaginal and nasal wash samples. The i.n. immunization also induced anti-OVA IgG, IgG1 and IgG2a antibody responses in sera, as well as cytotoxic T lymphocyte responses. The mucosal and systemic immune responses induced by OVA/AMVAD immunization were generally sustained over several months, and were subject to memory boost responses. Thus, polar archaeal lipids appear to be promising for developing a non-replicating mucosal adjuvant and vaccine delivery system.

Immunization without needles

Most current immunization procedures make use of needles and syringes for vaccine administration. With the increase in the number of immunizations that children around the world routinely receive, health organizations are beginning to look for safer alternatives that reduce the risk of cross-contamination that arises from needle reuse. This article focuses on contemporary developments in needle-free methods of immunization, such as liquid-jet injectors, topical application to the skin, oral pills and nasal sprays.

Archaeosomes as adjuvants for combination vaccines

The present study evaluated the potential of archaesomes, prepared from the total polar lipids extracted from Methanobrevibacter smithii, as adjuvants for combination (multivalent) vaccines. Groups of Balb/c mice were immunized subcutaneously at day 0 and 21 with one of the following vaccines: trivalent vaccine formulated by the simultaneous co-encapsulation of bovine serum albumine (BSA), ovalbumin (OVA) and hen egg lysozyme (HEL) into archaeosomes (CEC vaccine); an univalent archaeosome vaccine (UVE vaccine) containing either BSA, OVA or HEL; or an admixture vaccine (AMC vaccine) consisting of the three UVE vaccines. Serum specific antibody (IgG + M) responses were determined at day 32, 112 and 203, and specific IgG1 and IgG2a responses were determined at day 112. Mice immunized with the CEC of AMC vaccine developed strong and sustained specific antibody responses to all three antigens at a magnitude similar to those seen in control mice immunized with UVE vaccines. Moreover, the serum BSA-, OVA-, and HEL-specific IgG1 and IgG2a levels in the CEC and AMC immunized mice were overall comparable to those of the UVE immunized control mice. Boosting CEC and AMC vaccinated mice with antigens alone at day 203 elicited strong antibody memory responses, comparable to those in the UVE vaccinated groups. These results show that archaeosomes could be used as adjuvants in developing combination vaccines.

Short Synthesis of Polyoxygenated Macrocyclic Rings Using Acetal Linkages. Application to the Preparation of a New Lipidic Polyamine

A short preparation of polyoxygenated macrocycles can be carried out by combining the formation of an acetal linkage, to introduce long alkyl chains, with a ring closure metathesis. As an example, this methodology was used to synthesize a new polyamino lipid.

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

Archaeal isopranoid glycerolipid vesicles (archaeosomes) serve as strong adjuvants for cell-mediated responses to entrapped Ag. We analyzed the processing pathway of OVA entrapped in archaeosomes composed of Methanobrevibacter smithii lipids, high in archaetidylserine (OVA-archaeosomes). In vitro, OVA-archaeosomes stimulated spleen cells from OVA-TCR-transgenic mice, D011.10 (CD4(+) cells expressing OVA(323-339) TCR) or OT1 (>90% CD8(+) OVA(257-264) cells), indicating both MHC class I and II presentations. In vivo, when naive (Thy1.2(+)) CFSE-labeled OT1 cells were transferred into OVA-archaeosome-immunized Thy 1.1(+) recipient mice, there was profound accumulation and cycling of donor-specific cells, and differentiation of H-2K(b)Ova(257-264) CD8(+) T cells into CD44(high)CD62L(low) effectors. Both macrophages and dendritic cells (DCs) efficiently cross-presented OVA-archaeosomes on MHC class I. Blocking phagocytosis by phosphatidylserine-specific receptor agonists strongly inhibited MHC class I presentation of OVA-archaeosomes, whereas blocking mannose receptors or FcRs lacked effect, indicating specific recognition of the archaetidylserine head group of M. smithii lipids by APCs. In addition, inhibitors of endosomal acidification blocked MHC class I processing of OVA-archaeosomes, whereas endosomal protease inhibitors lacked effect, suggesting acidification-dependent phagosome-to-cytosol diversion. Proteasomal inhibitors blocked OVA-archaeosome MHC class I presentation, confirming cytosolic processing. Both in vitro and in vivo, OVA-archaeosome MHC class I presentation required TAP. Ag-free archaeosomes also activated DC costimulation and cytokine production, without overt inflammation. Phosphatidylserine-specific receptor-mediated endocytosis is a mechanism of apoptotic cell clearance and DCs cross-present Ags sampled from apoptotic cells. Our results reveal the novel ability of archaeosomes to exploit this mechanism for cytosolic MHC class I Ag processing, and provide an effective particulate vaccination strategy.