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Biomedical subjects

G Gregoriadis

Publications and source records attributed to G Gregoriadis.

At least 73 records · Page 4Linked to original sources
PubMed1991

Comparison of the immune response against polio peptides covalently-surface-linked to and internally-entrapped in liposomes.

The adjuvanticity of liposomes on two different modes of presentation of polio virus subunit peptides was demonstrated by incorporating the poorly immunogenic synthetic polio peptides, W1 and W2, into the internal space of and covalently-linked to the surface of dehydration-rehydration vesicles (DRV). It was found that for both peptides, liposome association in either mode boosted the primary and secondary IgG1 responses against 5 micrograms peptide as compared to controls in which free peptide was administered. Surface-linkage of peptides (both W1 and W2) exhibited an initially more rapid rise in antibody levels, as compared to internal entrapment of the peptides, but elicited no observable secondary response. However, although encapsulated W1 showed a milder primary response when compared to the surface-linked formulation, it later elicited a strong secondary response. These results suggested that it may be advantageous to administer liposomal virus subunit vaccines in both surface-linked and internally entrapped formulations to achieve adequate initial antibody levels followed by an anamnestic response.

Adjuvants, Immunologic↗
PubMed1991

A novel positively-charged lipid 1,2-bis(hexadecylcycloxy)-3-trimethyl aminopropane (BisHOP) enhances the adjuvant effect of liposomes on encapsulated tetanus toxoid.

A novel positively charged lipid, 1,2-bis(hexadecylcycloxy)-3-trimethylaminopropane-HCl (BisHOP), when incorporated into the bilayers of phosphatidylcholine (PC) and distearoyl phosphatidylcholine (DSPC) dehydration-rehydration vesicles (DRV), was shown to have a powerful effect in enhancing the IgG1 response to tetanus toxoid encapsulated within the liposomes. The adjuvant effect was significantly greater when 20% BisHOP was incorporated as compared to 10% incorporation and to control PC and DSPC DRV. Plain, uncharged DSPC DRV were found to have a greater adjuvant effect than plain PC DRV on the entrapped tetanus toxoid after a single intramuscular injection. Even though antibody levels at 8 weeks post-injection were similar for 20% BisHOP PC and DSPC DRV, the rate of rise of antibody titres was more rapid for 20% BisHOP DSPC than for 20% BisHOP PC DRV. These results suggest that faster and higher titers of antibodies may be obtained by optimal manipulation of the charged and non-charged lipid components of liposomes.

Adjuvants, Immunologic↗
PubMed1990

Immunological adjuvants: a role for liposomes.

Recent technological advances have resulted in the production of safe subunit and synthetic small peptide vaccines. These vaccines are weakly or non-immunogenic and cannot, therefore, be used effectively in the absence of immunological adjuvants (agents that can induce strong immunity to antigens). Owing to the toxicity of adjuvants, only one (aluminium salts) has hitherto been licensed for use in humans, and it is far from ideal. In this article, Gregory Gregoriadis discusses the use of liposomes as an alternative safe, versatile, universal adjuvant that can induce humoral- and cell-mediated immunity to antigens when administered parenterally or enterally.

Adjuvants, Immunologic↗
PubMed1990

A simple method for coating of liposomes with proteins.

A rapid and simple method for the coating of liposomes with proteins is described. Many proteins (e.g. bovine serum albumin, pig gammaglobulins and tetanus toxoid) could be made to adhere rapidly and efficiently to both multilamellar and small unilamellar vesicles after treatment with equimolar NaNO2 and HCl/NaCl. The reaction is complete within four hours and almost all of the protein is retained on the liposomes after storage for 2 weeks at 4 degrees C.

Hydrochloric Acid↗
PubMed1989

Vaccination against murine cutaneous leishmaniasis by using Leishmania major antigen/liposomes. Optimization and assessment of the requirement for intravenous immunization.

Efficacy of vaccination against cutaneous leishmaniasis in highly susceptible BALB/c mice was assessed comparatively by using radiation-attenuated promastigotes and colloidal Ag mixtures generated from a mixed Leishmania major (LV39) isolate (SLV39) and from a virulent cloned line (SVJ2) derived from the Jericho 2 L. major isolate. Dehydration-rehydration vesicle (DRV) liposomes were used as adjuvants. In optimization experiments phospholipid composition of DRV was varied, and the distearoyl derivative (DSPC) (liquid-crystalline phase transition temperature (Tc) 54 degrees C) of egg lecithin L-alpha-phosphatidylcholine was found to be superior to the dipalmitoyl derivative (DPPC, Tc 41.5 degrees C) and underivatized L-alpha-phosphatidylcholine (Tc -10 degrees C). The criteria studied were in vivo priming for a secondary in vitro proliferative response and the prepatency of lesion onset after L. major challenge of mice immunized once i.v. A single s.c. immunization with SLV39 either free or entrapped within DSPC liposomes primed spleen cells to produce significant levels of IL-3 when stimulated with SLV39 in vitro. In contrast, the i.v. route of immunization with the same Ag preparations led to little or no IL-3 production by the spleen cells. Despite development of significant T cell activation, both SLV39 and SVJ2 administered s.c., either free or entrapped within liposomes, were not protective. However, i.v. immunization four times with SVJ2 entrapped within DSPC liposomes induced a level of resistance comparable with that of 2 x 10(7) gamma-irradiated promastigotes in the stringent BALB/c L. major model. Although significant, protection conferred after i.v. immunization with SLV39/DSPC liposomes was less effective. These data therefore show that DSPC/DRV liposomes, although a good adjuvant for inducing protective immunity to cutaneous leishmaniasis, are not able to overcome the requirement for an i.v. route of immunization with the leishmanial Ag preparation. Additionally, they demonstrate a correlation between IL-3 secretion and non-protection. They also suggest that SVJ2 represents a better source of protective Ag than SLV39.

Adjuvants, Immunologic↗
PubMed1989

Covalent coupling of sugars to liposomes.

A procedure is described for the covalent coupling of p-aminophenyl-alpha-D-mannopyranoside, in the presence of carbodiimide, to a derivative of phosphatidylethanolamine (N-glutarylphosphatidylethanolamine) incorporated into the bilayers of multilamellar liposomes prepared by the dehydration-rehydration method. It appears that much of the phospholipid derivative exposed on the surface of the outer liposomal bilayer interacts with the aminosugar. The procedure is simple, does not destabilize liposomes and could be applied to other receptor-specific aminosugars.

Binding Sites↗
PubMed1989

Dehydration-rehydration vesicle methodology facilitates a novel approach to antibody binding to liposomes.

Mouse monoclonal IgG1 specific for hepatitis B surface antigen and ovine polyclonal antibody raised against digoxin were covalently coupled by a diazotisation method to small unilamellar vesicles (SUV) composed of equimolar phospholipid and cholesterol supplemented with 6 mol% aminophenylstearylamine (APSA). Up to 33% of the antibody used was associated with vesicles, depending on the phospholipid and the antibody type used. Antibody-coated SUV were mixed with carboxyfluorescein (CF) or beta-galactosidase to generate multilamellar dehydration-rehydration vesicles (DRV) containing CF or active enzyme. In contrast, coupling of antibodies directly to beta-galactosidase-containing DRV resulted in total inactivation of the enzyme. About 85% of the SUV-bound antibody was recovered in DRV and of this, 78-82% was exposed on the liposomal surface, possibly because of reorientation of the APSA-antibody complex during DRV formation. Antibody-coated DRV remained stable in the presence of plasma at 37 degrees C and also under storage at 4 degrees C. Further, antibody coupled to such liposomes was capable of efficient interaction with the respective antigen. The present method allows the attachment of antibodies to the liposomal surface independently of entrapment of solutes, the activity of which is thus preserved, and could be adapted to alternative coupling procedures or ligands.

Antigen-Antibody Reactions↗
PubMed1989

Immunoadjuvant action of liposomes: comparison with other adjuvants.

Dehydration-rehydration vesicles (DRV liposomes) composed of equimolar phospholipid and cholesterol and containing bovine serum albumin (BSA) were used together with free BSA to immunize Balb/C mice. Primary and secondary immune responses (IgG1) to the liposomal antigen, as measured by ELISA in mouse sera, were similar for egg phosphatidylcholine (PC) and distearoyl phosphatidylcholine (DSPC) DRV, and much greater than those elicited by free BSA. The adjuvanticity of PC DRV was compared with that of aluminium salts (alum), complete Freund's adjuvant (CFA) and N-acetyl muramyl-L-threonyl-D-isoglutamine ([Thr1]MDP), the latter used as such or in a liposome form co-entrapped with the antigen. DRV (with or without co-entrapped [Thr1]MDP), and alum were equally strong in producing primary and secondary immune responses (IgG1) to BSA. Such responses were significantly higher than those achieved with CFA and [Thr1]MDP alone. The implications of these results for the potential role of liposomes as immunological adjuvants in vaccines are discussed.

Acetylmuramyl-Alanyl-Isoglutamine↗
PubMed1989

Primary immune response to liposomal tetanus toxoid in mice: the effect of mediators.

Primary immune response (IgG1) to tetanus toxoid entrapped in liposomes composed of equimolar egg phosphatidylcholine and cholesterol, and the effect of a variety of physiological and non-physiological mediators (co-entrapped with the toxoid or entrapped in separate liposomes) on such responses, were studied in BALB/c mice. Results show that (i) primary responses, not detectable with the free antigen, were elicited with the same amount of antigen given in liposomes within a range (37.4:1-2857:1) of liposomal phospholipid to toxoid mass ratios. At a higher ratio (17,804:1) response was reduced to very low levels. Immune responses obtained with liposomal toxoid were maintained at measurable levels 24 weeks after immunization. (ii) Interleukin-2 (IL-2), interferon-gamma (IFN-gamma) and N-acetyl muramyl-L-threonyl-D-isoglutamine ([Thr1]MDP), but not its liposoluble 6-O-stearoyl derivative (6-O-S-[Thr1]MDP), co-entrapped with the toxoid at appropriate phospholipid to toxoid ratios, generally reduced primary response to levels below those achieved with liposomes containing the antigen alone. Further, responses obtained with 6-O-S[Thr1]MDP coentrapped with the toxoid or separately entrapped were higher than those seen with [Thr1]MDP in similar formulations. The significance of these findings is discussed in conjunction with the structural characteristics of liposomes.

Acetylmuramyl-Alanyl-Isoglutamine↗
PubMed1988

Kinetics and disposition of fluorescein-labelled liposomes in healthy human subjects.

The in vivo kinetics and organ uptake of multilamellar liposomes have been studied in healthy volunteers. Sodium fluorescein-containing liposomes composed of equimolar amounts of egg phosphatidylocholine and cholesterol were injected into a peripheral vein in 4 healthy subjects. Blood samples collected from the femoral artery, hepatic vein and pulmonary artery, were analysed for liposomal dye content. The results, showing involvement of the reticuloendothelial system (RES) in the removal of liposomes, confirmed those previously obtained with radiolabelled preparations. Use of an innocuous liposomal marker (sodium fluorescein) and conventional vascular catheterization techniques, as employed here, may provide a reliable and clinically acceptable approach to establishing disease-induced changes in the kinetics of uptake of drug-containing liposomes by the RES, and thus help in the design of protocols for effective treatment.

Adult↗
PubMed1988

Evaluation of the dehydration-rehydration method for production of contrast-carrying liposomes.

We measured the amounts of three types of radiographic contrast media (RCM) that could be entrapped in liposomes prepared by the dehydration-rehydration vesicle (DRV) technique. To make DRVs, one initially makes water-containing, small unilamellar vesicles, adds contrast media and lyophilizes the mixture. Upon rehydration, the DRVs re-form, passively entrapping RCM. Diatrizoate, iohexol and iotrolan proved to be entrappable in similar amounts (diatrizoate was best), but all of these amounts were less than for other small molecules, such as carboxyfluorescein (P less than 0.05). Entrapment was directly proportional to lipid concentration (r = 0.76; P less than 0.002), and inversely related to iodine concentration (r = 0.86; P less than 0.002). Under ideal conditions with neutral lipids, 19.45 +/- 9.9% of diatrizoate was entrapped, corresponding to 1.05 +/- 0.50 g I per g lipid. These values are close to those achievable for large unilamellar vesicles. Use of an automated mixing device (the Microfluidizer) in place of sonication, facilitated production of large liposome batches and improved entrapment (P less than 0.05). Computed tomography (CT) scans of rats showed 30 and 218 HU of liver and spleen enhancement, respectively, per g I/kg injected DRVs. These studies showed this method (possible augmented by the Microfluidizer) allows efficient production of contrast-carrying liposomes.

Animals↗
PubMed1988

Mannose-mediated targeted immunoadjuvant action of liposomes.

The effect of the ligand mannosylated albumin, covalently coupled to the surface of tetanus toxoid-containing dehydration-rehydration vesicles (DRV), on their adjuvanticity was investigated. Toxoid-containing DRV coated with mannosylated albumin bound in vitro to mouse (BALB/c) peritoneal macrophages selectively and to a greater extent than non-mannosylated DRV. ELISA assays of anti-toxoid IgG1 and IgG2b in the sera of BALB/c mice immunized with various toxoid-containing DRV preparations suggest that mannosylated liposomes are superior in immunoadjuvant action to conventional ones. Such targeted adjuvanticity appears to be influenced by the number of ligand molecules available on the surface of liposomes rather than the number of mannose residues on albumin.

Adjuvants, Immunologic↗