Oligomannose-coated liposomes as an adjuvant for the induction of cell-mediated immunity

Antiviral nanopharmaceuticals: Engineered surface interactions and virus-selective activity

The COVID-19 pandemic has inspired large research investments from the global scientific community in the study of viral properties and antiviral technologies (e.g., self-cleaning surfaces, virucides, antiviral drugs, and vaccines). Emerging viruses are a constant threat due to the substantial variation in viral structures, limiting the potential for expanded broad-spectrum antiviral agent development, and the complexity of targeting multiple and diverse viral species with unique characteristics involving their virulence. Multiple, more infectious variants of SARS-CoV2 (e.g., Delta, Omicron) have already appeared, necessitating research into versatile, robust control strategies in response to the looming threat of future viruses. Nanotechnology and nanomaterials have played a vital role in addressing current viral threats, from mRNA-based vaccines to nanoparticle-based drugs and nanotechnology enhanced disinfection methods. Rapid progress in the field has prompted a review of the current literature primarily focused on nanotechnology-based virucides and antivirals. In this review, a brief description of antiviral drugs is provided first as background with most of the discussion focused on key design considerations for high-efficacy antiviral nanomaterials (e.g., nanopharmaceuticals) as determined from published studies as well as related modes of biological activity. Insights into potential future research directions are also provided with a section devoted specifically to the SARS-CoV2 virus. This article is categorized under: Toxicology and Regulatory Issues in Nanomediciney > Toxicology of Nanomaterials Therapeutic Approaches and Drug Discovery > Nanomedicine for Infectious Disease Therapeutic Approaches and Drug Discovery > Nanomedicine for Respiratory Disease.

Oligomannose-coated liposome-entrapped dense granule protein 7 induces protective immune response to Neospora caninum in cattle

Neospora caninum is an intracellular protozoan parasite that causes abortion in cows. Vaccination is an important strategy for control of neosporosis, and a safe and effective vaccine suitable for cattle is required. Dense granule protein 7 of N. caninum (NcGRA7) is a secretory protein with high antigenicity in hosts. We demonstrated previously that NcGRA7 entrapped in liposomes coated with mannotriose (M3-NcGRA7) could induce a parasite-specific T-helper type 1 immune response and produce humoral antibodies that resulted in increased offspring survival and decreased infection in the brains of mice dams. In the present study, the efficacy of M3-NcGRA7 as a vaccine candidate against N. caninum has been evaluated in cattle (n=12). Cattle were immunized with M3-NcGRA7 containing 50 μg (n=4) or 200 μg NcGRA7 (n=4) subcutaneously twice with a 4-week interval and all cattle including the non-immunized controls (n=4) were inoculated with 10(7) tachyzoites of Nc-1 strain 27 days after the second immunization and euthanized at 85-87 days post infection (dpi). In immunized cattle, NcGRA7-specific antibody production and IFN-γ production in PBMC was induced before challenge. At 3 dpi, body temperature and concentration of serum IFN-γ tended to be higher in control cattle than in the immunized cattle. Furthermore, the parasite load in the brain significantly decreased in cattle immunized with 50 μg M3-NcGRA7 compared with controls. These results suggest that M3-NcGRA7 can induce protective immune responses to N. caninum tachyzoites in cattle, which could lead to practical application of safe and effective subunit vaccines.

Liposomes and nanotechnology in drug development: focus on oncotargets

Nanotechnology is the development of an engineered device at the atomic, molecular, and macromolecular level in the nanometer range. Advances in nanotechnology have proven beneficial in therapeutic fields such as drug-delivery and gene/protein delivery. Antigen delivery systems are important for inducing and modifying immune responses. In cellular immunity, cytotoxic T lymphocytes (CTLs) are important in the host defense against tumors. Key to the development of CTL-inducible vaccines is the ability to deliver antigens to antigen-presenting cells efficiently and to induce the subsequent activation of T cell-mediated immunity without adjuvants, as they can induce excessive inflammation leading to systemic febrile disease. Since expression and cloning methods for tumor-associated antigens have been reported, cancer vaccines that induce effective cell immunity may be promising therapeutic candidates, but Th2 cells are undesirable for use in cancer immunotherapy. Peptide vaccines have immunological and economic advantages as cancer vaccines because CTL epitope peptides from tumor-associated antigens have high antigen-specificity. However, cancer vaccines have had limited effectiveness in clinical responses due to the ability of cancer cells to “escape” from cancer immunity and a low efficiency of antigen-specific CTL induction due to immunogenic-free synthetic peptides. In contrast, carbohydrate-decorated particles such as carbohydrate-coated liposomes with encapsulated antigens might be more suitable as antigen delivery vehicles to antigen-presenting cells. Oligomannose-coated liposomes (OML) can eliminate established tumors in mouse cancer models. In addition, OMLs with an encased antigen can induce antigen-specific CTLs from peripheral blood mononuclear cells obtained from patients. Feasibility studies of OML-based vaccines have revealed their potential for clinical use as vaccines for diseases where CTLs act as effector cells. Furthermore, use of the hepatitis B core particle, in which tumor-antigen epitopes are set, has consistently been shown to induce strong CTL responses without the use of an adjuvant. Thus, nanoparticles may provide a new prophylactic strategy for infectious disease and therapeutic approaches for cancer via the induction of T-cell immunity.

[New treatment strategy for adult T-cell leukemia targeting for anti-tumor immunity and a longevity gene-encoded protein]

Adult T-cell leukemia-lymphoma (ATL) is an aggressive peripheral T-cell neoplasm with a poor prognosis, developing after long-term infection with human T-cell leukemia virus-1 (HTLV-1). Multiple factors (e.g., virus, host cells, epigenetic aberrations, and immune factors) have been implicated in the development of ATL, although the underlying mechanisms of leukemogenesis have not been fully elucidated. Despite recent progress in both chemotherapy and supportive care for hematological malignancies, the prognosis of ATL is still poor; overall survival at 3 years is only 24%. New strategies for the therapy and prophylaxis of ATL (e.g., vaccines and novel molecular target agents) are still required. This article reviews new strategy of ATL treatment targeted for HTLV-1-specific cytotoxic T-lymphocytes (CTLs) and SIRT1, a longevity gene-encoded protein. HTLV-1-specific CTLs play a critical role in the host immune response against HTLV-1. We have described here the decreased frequency and function of HTLV-1-specific CD8+ T cells in ATL patients and the efficient induction of the HTLV-1-specific CTLs response in human leukocyte antigen-A* 0201-transgenic mice by the HTLV-1/hepatitis B core chimeric particle and oligomannose-coated liposomes encapsulating HTLV-1 epitope without adjuvant, suggesting that the efficient antigen delivery system and CTL induction can be exploited to develop a prophylactic vaccine model against tumors and infectious diseases. Furthermore, our studies suggest that SIRT1, a longevity gene-encoded protein, is a crucial anti-apoptotic molecule in ATL cells, and that SIRT1 inhibitors may be useful therapeutic agents for leukemia, especially in patients with ATL. These studies targeted for anti-tumor immunity such as vaccine and SIRT1 may support the new prophylactic and therapeutic approach for ATL.

Oligomannose-coated liposomes efficiently induce human T-cell leukemia virus-1-specific cytotoxic T lymphocytes without adjuvant

Human T-cell leukemia virus-1 (HTLV-1) causes adult T-cell leukemia/lymphoma, which is an aggressive peripheral T-cell neoplasm. Insufficient T-cell response to HTLV-1 is a potential risk factor in adult T-cell leukemia/lymphoma. Efficient induction of antigen-specific cytotoxic T lymphocytes is important for immunological suppression of virus-infected cell proliferation and oncogenesis, but efficient induction of antigen-specific cytotoxic T lymphocytes has evaded strategies utilizing poorly immunogenic free synthetic peptides. Here, we examined the efficient induction of an HTLV-1-specific CD8+ T-cell response by oligomannose-coated liposomes (OMLs) encapsulating the human leukocyte antigen (HLA)-A*0201-restricted HTLV-1 Tax-epitope (OML/Tax). Immunization of HLA-A*0201 transgenic mice with OML/Tax induced an HTLV-1-specific gamma-interferon reaction, whereas immunization with epitope peptide alone induced no reaction. Upon exposure of dendritic cells to OML/Tax, the levels of CD86, major histocompatibility complex class I, HLA-A02 and major histocompatibility complex class II expression were increased. In addition, our results showed that HTLV-1-specific CD8+ T cells can be efficiently induced by OML/Tax from HTLV-1 carriers compared with epitope peptide alone, and these HTLV-1-specific CD8+ T cells were able to lyse cells presenting the peptide. These results suggest that OML/Tax is capable of inducing antigen-specific cellular immune responses without adjuvants and may be useful as an effective vaccine carrier for prophylaxis in tumors and infectious diseases by substituting the epitope peptide.

Mannosylated liposomes as antigen delivery vehicles for targeting to dendritic cells

The immune stimulating ability of mannosylated liposomes containing FITC-ovalbumin as a model antigen and displaying either a branched tri-mannose or a mono-mannose ligand on the liposome surface was investigated in human monocyte-derived dendritic cells (MoDCs) and murine bone-marrow-derived dendritic cells (BMDCs). Uptake of liposomes, dendritic cell activation and proliferation of CD8+ T cells from OT-I transgenic mice were determined by flow cytometry. Uptake of liposomes displaying the tri-mannose ligand was enhanced in human MoDCs compared with both non-mannosylated liposomes and liposomes displaying mono-mannose ligands. However, this increased uptake did not result in an increase in expression of CD80 or CD86 on the surface of the MoDCs. In contrast, neither tri-mannose- nor mono-mannose-containing liposomes were taken up by murine BMDCs to a greater extent than non-mannose-containing liposomes. The expression of CD86 and CD40 on the surface of BMDCs was not increased after exposure to mannosylated lipo-somes and BMDCs incubated with mannosylated liposomes were not able to stimulate proliferation of CD8+ T cells to any greater extent than BMDCs incubated with non-mannosylated liposomes. These findings suggest that while mannose-containing ligands can enhance the uptake of antigen-containing liposomes by some dendritic cells, important differences in the affinity of carbohydrate-binding receptors for mannose-containing ligands do exist between species. In addition, the increase in uptake of antigen by dendritic cells using mannosylated liposomes does not necessarily result in enhanced dendritic cell activation.

Mannosylated Niosomes as Adjuvant-Carrier System for Oral Mucosal Immunization

The aim of the present study was to develop mannosylated niosomes as oral vaccine delivery carrier and adjuvant for the induction of humoral, cellular, and mucosal immunity. Tetanus toxoid (TT) loaded niosomes composed of sorbiton monostearate (Span 60), cholesterol, and stearylamine were prepared by the reverse-phase evaporation method. They were coated with a modified polysaccharide o-palmitoyl mannan (OPM) to protect them from bile salts caused dissolution and enzymatic degradation in the gastrointestinal tract and to enhance their affinity toward the antigen presenting cells of Peyer's patches. Prepared niosomes were characterized in vitro for their size, shape, entrapment efficiency, ligand binding specificity, and stability in simulated gastric fluid and simulated intestinal fluid. OPM-coated niosomes were found to more stable in simulated gastrointestinal conditions. The immune stimulating activity was studied by measuring serum IgG titer, IgG2a/IgG1 ratio in serum, and sIgA levels in intestinal and salivary secretions following oral administration of niosomal formulations in albino rats. The results were compared with alum-adsorbed TT following oral and intramuscular administration, and it was observed that OPM-coated niosomes produced better IgG levels as compared to plain uncoated niosomes and alum-adsorbed TT upon oral administration. Oral niosomes also elicited a significant mucosal immune response (sIgA levels in mucosal secretions). The developed formulations also elicited a combined serum IgG2a/IgG1 response, suggesting that they were capable of eliciting both humoral and cellular response. The study signifies the potential of OPM-coated niosomes as an oral vaccine delivery carrier and adjuvant. The proposed system is simple, stable, and cost-effective and may be clinically acceptable.

Preparation and Characterization of Nickel Nanoparticles for Binding to His-tag Proteins and Antigens

PURPOSE

The purpose of these studies was to prepare nanoparticles (NPs) with a small amount of surface-chelated nickel for obtaining enhanced binding of histidine-tagged (his-tag) proteins compared to non-histidine-tagged protein binding to charged nanoparticles.

MATERIALS AND METHODS

NPs were prepared from oil-in-water microemulsion precursors using emulsifying wax, 3 mM Brij 78 and 0.1 mM DOGS-NTA-Ni lipid (referred to as Ni-NPs). The amount of lipid entrapped in the NPs was quantitated by atomic emission spectroscopy (AES). The Ni-NPs were investigated for binding to two his-tag proteins, green fluorescent protein (GFP) and his-tag HIV-1 Gag p24. In vivo studies in mice were carried out to evaluate the immune responses obtained to his-tag Gag p24 bound to Ni-NPs.

RESULTS

AES studies demonstrated that approximately 5% of the DOGS-NTA-Ni lipid used was entrapped in the NPs. The optimal binding ratio his-tag GFP and his-tag Gag p24 to Ni-NPs was found to be 1:33.7 and 1:35.4 w/w, respectively. This interaction was stable at 37 degrees C in PBS, pH 7.4 over 4 h and the interaction of his-tag GFP with the Ni-NPs was enhanced compared to control NPs prepared with no Ni on the surface (NTA-NPs). The in vivo studies demonstrated enhanced serum IgG and IgG2a responses to his-tag Gag p24 bound to Ni-NPs compared to protein adjuvanted with Alum or adsorbed on the surface of control NTA-NPs.

CONCLUSIONS

Ni-NPs can be used to bind strongly to his-tag proteins. This system was demonstrated to have potential applications in vaccine delivery for enhancing immune responses to protein-based vaccines.

EFFICACY OF DIPALMITOYLPHOSPHATIDYLCHOLINE LIPOSOME AGAINST AFRICAN TRYPANOSOMES

We demonstrate here that dipalmitoylphosphatidylcholine (DPPC) liposome has an antitrypanosomal effect, especially against the bloodstream forms (BSFs) of African trypanosomes (Trypanosoma congolense, T. brucei rhodesiense, and T. brucei brucei). The DPPC liposome significantly decreased the in vitro percentage of viable and motile BSF African trypanosomes but only marginally reduced the percentage of viable and motile procyclic form (PCF) of trypanosomes. The DPPC liposome absorption was much more pronounced to BSF than to PCF trypanosomes. Administration of the DPPC liposome showed a slight but significant reduction in the early development of parasitemia in T. congolense-infected mice. These results suggest that parasites were killed by specific binding of the DPPC liposome to the trypanosomes. This work demonstrates for the first time that a liposome has antitrypanosomal activity.

Mannosylated niosomes as carrier adjuvant system for topical immunization

The aim of this study was to develop mannosylated niosomes as a topical vaccine delivery carrier and adjuvant for the induction of both humoral and cellular immunity. Bovine serum albumin (BSA)-loaded niosomes composed of sorbitan monostearate/sorbitan trioleate (Span 60/Span 85), cholesterol and stearylamine as constitutive lipids were prepared by the reverse-phase evaporation method. The niosomes were coated with a modified polysaccharide O-palmitoyl mannan (OPM) to target them to Langerhan's cells, the major antigen presenting cells found in abundance beneath the stratum corneum. Prepared niosomes were characterized in-vitro for their size, shape, entrapment efficiency and ligand binding specificity. The immune stimulating activity was studied by measuring serum IgG titre and its subclasses (IgG2a/IgG1 ratio) following topical application of various niosomal formulations in albino rats. The results were compared with alum-adsorbed BSA following topical application and intramuscular injection. It was observed that niosomal formulations elicited a significantly higher serum IgG titre upon topical application as compared with topically applied alum adsorbed BSA (P<0.05). The serum IgG levels were significantly higher for the mannosylated niosomes as compared with plain uncoated niosomes (P<0.05). All formulations displayed a combined serum IgG2a/IgG1 response, which suggested that the formulations were capable of eliciting both humoral and cellular responses. The study signified the potential of OPM-coated niosomes as a topical vaccine delivery carrier and adjuvant. The proposed system would be simple, stable, and cost effective and might be clinically acceptable.

A Model Vaccine Exploiting Fungal Mannosylation to Increase Antigen Immunogenicity

Ag mannosylation represents a promising strategy to augment vaccine immunogenicity by targeting Ag to mannose receptors (MRs) on dendritic cells. Because fungi naturally mannosylate proteins, we hypothesized that Ags engineered in fungi would have an enhanced capacity to stimulate T cell responses. Using the model Ag OVA, we generated proteins that differentially expressed N- and O-linked mannosylation in the yeast Pichia pastoris and compared them to their unglycosylated counterparts produced in Escherichia coli. We found that yeast-derived OVA proteins containing N-linkages, extensive O-linkages, or both were more potent than the unmannosylated Ags at inducing OVA-specific CD4+ T cell proliferation. This elevated response to fungal Ags was inhibited by mannan, suggesting involvement of MRs. However, the macrophage MR (CD206) was not essential, because macrophage MR-deficient dendritic cells were fully competent in presenting yeast-derived OVA Ags. Thus, the use of fungal glycosylation to provide N-linked and/or extensive O-linked mannosylation increased the capacity of the model Ag OVA to stimulate Ag-specific T cell responses in an MR-dependent manner. These data have implications for vaccine design by providing proof of principle that yeast-derived mannosylation can enhance immunogenicity.

Protection against experimental Aeromonas salmonicida infection in carp by oral immunisation with bacterial antigen entrapped liposomes

Liposome-entrapped atypical Aeromonas salmonicida antigen was prepared to investigate the potential protective efficacy for A. salmonicida infection. Carp (Cyprinus carpio) were immunised orally with liposome-entrapped A. salmonicida antigen. After immunisation, significantly higher antigen-specific antibodies were detected in serum, intestinal mucus and bile than non-immunised control group. Furthermore, immunised carp were challenged by immersion with 1 x 10(6) cfu ml(-1) of A. salmonicida for 60 min. Of the eight non-immunised carp, three carp died (62.5% survival), whereas five out of six (83.5%) immunised survived. Furthermore, the development of skin ulcers was significantly inhibited in carp immunised with liposomes containing A. salmonicida antigen. These results suggest that liposomes containing A. salmonicida antigen have the potential for the induction of a protective immune response against atypical A. salmonicida infection and also suggest the possibility of developing a vaccine that may ultimately be used for the prevention of fish diseases.

Synthesis and preliminary physical applications of a rhodamin-biotin phosphatidylethanolamine, an easy attainable lipid double probe

In route to a physical study aimed at understanding lipids and proteins sorting in cells, we designed a rhodamin-labelled biotinylated phosphatidylethanolamine (PE), as a useful and easy-attainable lipid double probe. The target compound was successfully engaged in preliminary physical experiments.

Protection against Leishmania major infection by oligomannose-coated liposomes

Liposomes coated with neoglycolipids constructed with mannopentaose and dipalmitoylphosphatidylethanolamine (Man5-DPPE) have been shown to induce cellular immunity against antigens encapsulated in the liposomes. To assess whether these neoglycolipid-coated liposomes can elicit protective immune response against challenge infection, effects of immunization with soluble leishmanial antigens encapsulated in the liposomes were evaluated using Leishmania major infection in susceptible BALB/c mice. Intraperitoneal immunization of mice with leishmanial antigens in the Man5-DPPE-coated liposomes significantly suppressed footpad swelling in comparison to the control, non-immunized mice, while progression of the disease was observed in mice administered antigens in uncoated liposomes and those administered soluble antigens alone, as seen with control mice. Similarly, the number of parasites decreased substantially in local lymph nodes of mice immunized with the antigen in the Man5-DPPE-coated liposomes. Protection against L. major infection in the immunized mice also coincided with an elevated ratio of antigen-specific IgG2a/IgG1 antibodies, which is a profile of T helper-type 1-like immune response. Taken together, these results indicate the possibility that Man5-DPPE-coated liposome-encapsulated antigens could serve as a vaccine that triggers protection against infectious disease.

Delayed-type hypersensitivity in sheep induced by synthetic peptides of bovine leukemia virus encapsulated in mannan-coated liposome

Four sheep were immunized with synthesized peptides, derived from bovine leukemia virus (BLV) envelope glycoprotein, encapsulated in mannan coated liposomes as adjuvant. On the seventh day after the immunization, the sheep were intradermally challenged with BLV antigen, or synthesized peptides. The areas challenged with antigen were increased skin thickness and biopsied sequentially for immunohistological examinations. Strong delayed-type hypersensitivity was induced in sheep immunized and challenged with peptides encapsulated in mannan-coated liposomes. The major phenotype of the infiltrating lymphocytes was CD5(+). The ratio of CD4(+) to CD8(+) cells was about 1:1.

Use of the mannan receptor to selectively target vaccine antigens for processing and antigen presentation through the MHC class I and class II pathways

Extensive studies have shown that synthetic and recombinant vaccines developed against hemoparasites have not been as effective as whole parasites or crude membrane fractions in eliciting protective immunity. A possible reason is that synthetic vaccines are not being presented in a form that induces the appropriate immune response. We have developed a bovine model system to evaluate the ability of adjuvant compounds to induce an immune response to peptide antigens dominated by a cytokine profile with a Type 1 (cell-mediated) or Type 2 (humoral) bias. In the initial testing of this system, we found that mRNA expression of certain cytokines (interleukin [IL]-1beta, IL-6, IL-12, IL-15, GM-CSF, iNOS, and tumor necrosis factor [TNF]-alpha) is enhanced when monocyte-derived macrophages are stimulated with peptide antigen conjugated with mannan under oxidizing conditions compared to peptide conjugated with reduced mannan. The data suggest this model will be useful in identifying adjuvant systems that selectively modulate the cytokine profile of antigen presenting cells at the time of antigen presentation and the consequent downstream maturation of naive T cells to effector cells with Type 1 or Type 2 cytokine bias.

Protection against influenza virus challenge by topical application of influenza DNA vaccine

We studied the use of a DNA vaccine expressing the matrix (M) gene of the influenza virus A/PR/8/34. Mice were immunized by painting the DNA vaccine three times on the skin after removal of its keratinocytic layers. Immunization by this method produced M-specific antibodies and cytotoxic T lymphocyte (CTL) response, and acquired resistance against influenza virus challenge. This protection was abrogated by the in vivo injection of anti-CD8 or anti-CD4 monoclonal antibody. We further found that simultaneous topical application (t.a.) of GM-CSF expression plasmid (pGM-CSF) or liposomes plus mannan produced stronger immune response competence and enhanced the protective effect against influenza virus challenge. The present study revealed that administering DNA vaccine by topical application can elicit both humoral and cell-mediated immunity (CMI).

Epitope-Mapping of antigen-specific T lymphocyte in cattle immunized with recombinant major piroplasm surface protein of Theileria sergenti

The cellular immune responses against major piroplasm surface protein (MPSP) of Theileria sergenti were characterized. Three cattle were immunized with recombinant MPSP (C type) encapsulated by mannan-coated liposome. The proliferative responses of peripheral blood mononuclear cells (PBMC) against MPSP were detected in all immunized animals. Reverse transcriptase polymerase chain reaction (RT-PCR) analysis revealed that T cell lines derived from each animal expressed relatively high levels of interferon (IFN)-gamma mRNA, low levels of interleukin (IL)-2, IL-10, and tumor necrosis factor (TNF)-alpha mRNAs, but no detectable level of IL-4 mRNA. From the results of T cell epitope-mapping, T-cell lines from two animals responded to DTSKFTPTVAHRLKHAEDLF (residues 61 to 80), while other animal responded to GTGKVYDFVGNFKVTKVKFE (residues 141 to 160). The MPSP-type specific response of a T-cell line was observed in the latter region of MPSP. These data suggest that immunization with cocktail vaccine consisting of different types of MPSP may be necessary in the field trial.

Simultaneous quantification of components of neoglycolipid-coated liposomes using high-performance liquid chromatography with evaporative light scattering detection

Liposomes composed of dipalmitoylphosphatidylcholine (DPPC), cholesterol and a neoglycolipid, mannopentaose-conjugated dipalmitoylphosphatidylethanolamine (Man5-DPPE), have been shown to have a strong adjuvant effect in inducing the antigen-specific cellular immunity. In this study, a rapid and simple analytical method using a HPLC system with an evaporative light scattering detector was developed for simultaneous quantification of the liposome components Man5-DPPE, cholesterol and DPPC. The chromatographic separation of these components was performed using a trimethylsilane column with an isocratic mobile phase of chloroform-methanol-water (1:33:6, v/v) after disrupting the liposomes with chloroform-methanol-water (10:10:3, v/v). This HPLC method provided sufficient reproducibility and linearity of calibration curves for the quantification of the liposome constituents. In addition, this method can be used for the quantification of various neoglycolipids with different carbohydrate structures.

Biodistribution characteristics of mannosylated, fucosylated, and galactosylated liposomes in mice

The in vivo disposition behavior and pharmacokinetic characteristics of galactosylated (Gal), mannosylated (Man) and fucosylated (Fuc) liposomes were compared in this study. For the preparation of the glycosylated liposomes, cholesten-5-yloxy-N-(4-((1-imino-2-beta-D-thiogalactosyle thyl)amino)a lkyl)formamide (Gal-C4-Chol) (Kawakami et al., Biochem. Biophys. Res. Commun. 252 (1998) 78-83) and its mannosylated and fucosylated derivatives (Man-C4-Chol and Fuc-C4-Chol, respectively) were synthesized. The glycosylated liposomes are composed of distearoylphosphatidylcholine (DSPC), cholesterol (Chol), and Gal-C4-Chol (or Man-C4-Chol or Fuc-C4-Chol) with the molar ratio of 60:35:5. After intravenous injection in mice, these three types of [(3)H]cholesteryl hexadecyl ether-labeled glycosylated liposomes were rapidly eliminated from the circulating blood and preferentially recovered in the liver. In contrast, DSPC/Chol (60:40) liposomes without glycosylation were retained for a long time in the circulating blood. The uptake ratios by parenchymal cells (PC) and nonparenchymal cells (NPC) (PC/NPC ratios) for 0.5% Gal, Man and Fuc liposomes were found to be 15.1, 0.6 and 0.2, respectively. The effect of predosing glycosylated proteins and liposomes on the hepatic uptake of 0.5% (3)H-labeled Gal, Man, and Fuc liposomes was investigated and the results support the conclusion that Gal, Man, and Fuc liposomes are taken up by the liver via asialoglycoprotein receptors in PC, mannose receptors in NPC, and fucose receptors in NPC, respectively. Interestingly, Gal liposomes were taken up by NPC rather than by PC at a high dose (5%). Together with the finding that 5% Gal liposomes inhibit the hepatic uptake of (3)H-labeled Fuc liposomes, this suggests that Gal-liposomes administered at a high dose will also be taken up by fucose receptors in NPC, that are considered to act as galactose particle receptors.

Liposomes coated with chemically modified dextran interact with human endothelial cells

Some liposomal formulations are now in clinical use. New applications in biology and medicine using targeted liposomes remain an intensive research area. In this context, liposomes constituted of phosphatidylcholine (PC), phosphatidylethanolamine (PE), and cholesterol (70/10/20 mol %) were prepared by detergent dialysis and coated with dextran (Dx) or functionalized dextran (FDx), both hydrophobized by a cholesterol anchor which penetrates the lipid bilayer during the vesicle formation. The coating of liposomes with these polysaccharides was performed because chemically modified dextran but not native Dx interacted with vascular cells. The liposome uptake by human endothelial cells was followed using uncoated and coated liposomes radiolabeled with a neutral lipid (3H-cholesterol) and a polar phospholipid (14C-PC). The results indicated for both radiolabels a preferential uptake by endothelial cells of FDx-coated liposomes compared to uncoated or Dx-coated liposomes. Addition to the culture medium of calcium up to 10 mM further enhanced the level and rate of incorporation of FDx-coated liposomes, whereas interaction of endothelial cells with uncoated liposomes or liposomes coated with Dx was poorly affected. Liposome membranes were then labeled with N-(lissamine rhodamine B sulfonyl)diacyl-PE and liposome uptake by endothelial cells was observed by fluorescence microscopy. The punctate intracellular fluorescence of cells incubated at 37 degrees C with fluorolabeled liposomes is indicative of the liposome localization within the endocytotic pathway of the cells. Altogether, these data demonstrate that coating of liposomes with FDx enable specific interactions with human endothelial cells in culture. Consequently, these liposomes coated with bioactive polymers represent an attractive approach as materials for use as drug delivery vehicles targeting vascular cells.

Liposomes, a potential immunoadjuvant and carrier for a cryptococcal vaccine

Mice immunized with a cryptococcal culture filtrate antigen (CneF) emulsified in complete Freund's adjuvant (CFA) develop an anticryptococcal cell-mediated immune response (CMI). CMI is detected by delayed-type hypersensitivity (DTH) reactions and by enhanced clearance of Cryptococcus neoformans from infected tissues. The objective of this research was to evaluate anticryptococcal DTH reactivity and clearance of cryptococci from groups of mice immunized with CneF encapsulated into liposomes (CneF-liposome) and compare the results to results from mice immunized with CneF-CFA. CBA/J mice were injected subcutaneously with vaccines or control formulations (saline-liposome or saline-CFA). Six days later the mice were footpad tested to assess their DTH response to CneF or the animals were challenged intravenously with 10(5) viable C. neoformans to determine clearance of infection. Clearance was evaluated 7 days later by enumeration of cryptococcal colony forming units (CFU) in lungs, spleens, livers, and brains of the infected mice. The CneF-liposome formulation induced a positive anticryptococcal DTH response and elicited increased clearance of C. neoformans from tissues as compared to mice treated with saline-liposome. Even though the CneF-liposome preparation did not induce as strong of a DTH response or as much protection as did CneF-CFA, our results indicate that liposomes are promising carriers for immunization with cryptococcal antigen and that such immunization can provide some protection to subsequent infection with C. neoformans.

Human immunodeficiency virus type-1-specific immune responses induced by DNA vaccination are greatly enhanced by mannan-coated diC14-amidine

Use of mannan-coated N-t-butyl-N'-tetradecyl-3-tetradecylamino-propionamidine (diC14-amidine) as an adjuvant for a DNA vaccine encoding glycoprotein 160 of human immunodeficiency virus type-1 (HIV-1) enhanced the antigen-specific immune responses. The role of interferon-gamma (IFN-gamma) and interleukin-12 in the mechanism of adjuvant action was also evaluated. Coating of diC14-amidine with mannan significantly augmented the HIV-specific delayed-type hypersensitivity reaction induced by the immunogenic DNA. HIV-1-specific cytotoxic T lymphocyte activity was also markedly enhanced by the mannan-diC14-amidine cocktail. An immunomodulatory effect of this cocktail was inhibited by treatment with anti-IFN-gamma monoclonal antibody in vivo, which suggests that IFN-gamma plays an important role in inducing cell-mediated immunity by the DNA vaccine containing this adjuvant. The results of both antigen-specific immunoglobulin isotype analysis and cytokine measurement showed that the immunogenic DNA incorporated into mannan-coated diC14-amidine elicits Th1-biased immune responses.

Strength in numbers: non-natural polyvalent carbohydrate derivatives

Many processes mediated by protein-carbohydrate interactions involve multivalent low-affinity binding, which is inherently difficult to study. New structural templates for the generation of multivalent carbohydrate displays have recently been developed, and tailored multivalent saccharide derivatives can now be used to study and modulate a wide variety of biological recognition events.