Immunogenicity of liposomal model membranes

The immunological adjuvant and vaccine carrier properties of liposomes

Animal immunization studies by numerous laboratories have shown that liposomes promote humoural and cell-mediated immunity to a wide spectrum of bacterial, protozoan and viral antigens as well as tumour cell antigens, venoms and allergens. Adjuvanticity depends on liposomal structural characteristics which determine vesicle fate in vivo and, thus, the mode of antigen interaction with antigen-presenting cells. Adjuvanticity is further promoted by receptor mediated targeting of liposomes to macrophages, or the presence of other adjuvants including cytokines. The immunoadjuvant function of liposomes is supplemented by their ability to act as a carrier for co-entrapped B and T-cell epitopes, thus eliminating the need for a carrier protein. Recently, a technique has been developed for the entrapment of live or attenuated microbial vaccines into giant liposomes under conditions which retain their viability. Liposomes containing microbial vaccines (together with other soluble antigens or cytokines) could be used as carriers of vaccines in cases where there is a need to prevent interaction of vaccines with maternal antibodies or preformed antibodies to vaccine impurities.

The intestinal and serum humoral immune response of mice to systemically and orally administered antigens in liposomes: I. The response to liposome-entrapped soluble proteins

The development of oral vaccines is of great importance in veterinary medicine and new adjuvants and carriers are essential to this aim. Liposomes are effective systemic adjuvants but the relatively little data on their potential as oral adjuvants is inconclusive. Liposomes containing ovalbumin (OA) were effective adjuvants when administered intraperitoneally to mice. Feeding mice with OA or keyhole limpet haemocyanin in liposomes in a series of priming and boosting regimes failed to elicit any significant increase in serum or intestinal antibody response compared with feeding the free antigen. Oral tolerance induction to systemic challenge was also unaffected by OA entrapment in liposomes. In vitro liposome stability assays at 37 degrees C demonstrated a substantial resistance to disruption in the presence of acidic stomach contents. However, the addition of bile caused a rapid and profound release of protein marker from the liposomes. The rate and degree of disruption was influenced by the type of phospholipid used. These results suggest that liposomes may be useful as carriers for orally administered compounds but they are ineffective as adjuvants for the non-particulate, naturally weak immunogens used in this study.

Liposomes enhance the immunogenicity of reconstituted influenza virus A/PR/8 envelopes and the formation of protective antibody by influenza virus A/Sichuan/87 (H3N2) surface antigen

Reconstituted influenza virus (A/PR/8 strain) envelopes (RIVE) and influenza virus (A/Sichuan/87 (H3N2) strain) surface antigens were entrapped in dehydration-rehydration vesicles (DRV liposomes) composed of egg phosphatidylcholine (PC) or distearoyl phosphatidylcholine (DSPC DRV) and equimolar (32 mumol) cholesterol. Entrapment values for RIVE were 31.2 (PC) and 29.4% (DSPC DRV) of the material used. Corresponding entrapment values for the A/Sichuan/87 strain antigens were 40.7 and 39.3%. Balb/c mice injected intramuscularly with PC or DSPC DRV liposomes containing 0.1 and 1.0 microgram RIVE exhibited primary (higher dose only) and secondary responses (IgG1) which were significantly higher than those obtained in mice injected with identical amounts of non-entrapped RIVE. Significantly higher secondary responses were also observed for the IgG2a and IgG2b subclasses. In experiments designed to assess the effectiveness of DRV liposomes as a carrier of influenza virus antigens in a potential vaccine, hamsters were immunized intramuscularly with 0.1, 0.5 and 5.0 micrograms of free or liposome-entrapped influenza A/Sichuan/87 surface antigens. Results showed increased haemagglutination inhibition (HI) antibody levels in terms of both primary (0.5 and 5.0 micrograms doses) and secondary (all doses) responses in the sera of animals treated with the liposomal formulations. DSPC compared with PC DRV exhibited greater adjuvanticity when the lower doses of antigens were used.

Lung cytochrome P450-dependent benzyloxyphenoxazone debenzylase and ethoxyphenoxazone deethylase activities in total microsomal and isolated alveolar type II cells: responses to changes in assay conditions with special reference to non-linear dependence at low enzyme concentration

1. Responses of cytochrome P450-dependent ethoxyphenoxazone deethylase (EtOPx'ase) and benzyloxyphenoxazone debenzylase (BzOPx'ase) activities to changes in assay conditions were measured in total microsomal and isolated alveolar type II (tII) cells from rats pretreated with beta-naphthoflavone. 2. Whereas microsomal EtOPx'ase activity was unaffected by storage at -80 degrees C for up to 4 months, BzOPx'ase activity began to decline after only 1 month. 3. The microsomal and type II activities were unaffected by changes in pH (7.2-8.0) or salt content. 4. The type II activities increased after sonication 2.3-2.7-fold or in the presence of 10 microM dicumarol 1.7-1.9-fold. 5. Type II BzOPx'ase was sensitive to metyrapone (MP) whereas EtOPx'ase was sensitive to alpha-naphthoflavone (ANF). I50 values for the tII activities were calculated as: 0.63 microM--MP (BzOPx'ase), 80 microM--MP (EtOPx'ase), 0.024 microM--ANF (EtOPx'ase). At the highest concentration of ANF (10 microM), 50% inhibition tII BzOPx'ase was not observed. The results were similar to those obtained with the total lung microsomal fraction. 6. Microsomal and tII BzOPx'ase activities exhibited non-linear dependence at low enzyme concentration. Linearity was restored by 0.5 mM dimyristoylphosphatidylcholine.

Production of oligosaccharide-binding monoclonal antibodies of diverse specificities by immunization with purified tumor-associated glycolipids inserted into liposomes with lipid A

Two species of neutral glycosphingolipids purified from rat colon carcinoma tissue, isoglobotetraosylceramide [GalNAc(beta 1----3)Gal(alpha 1----3)Gal(beta 1----3)Glc(beta 1----1)Cer] and a related 6-sugar "analogue" were inserted into liposomes together with lipid A (from bacterial lipopolysaccharide) and used for immunization of mice and monoclonal antibody production. The yield of hybridomas producing glycolipid-specific antibody was 5-10% using a high-dose booster schedule with liposome-inserted glycolipid. In contrast the frequency was below 0.1% (no glycolipid-binding antibodies were found) when using the previously described method of immunizing with glycolipid coated on the surface of acid-treated S. minnesota. Monoclonal antibodies were screened on the purified glycolipids used for immunization and selected for differential reactivity to the two glycolipids. A diversity of specificities was demonstrated by binding to the purified antigens, in a thin-layer chromatogram binding assay and in binding tests to tumor and normal target cells.

Serological specificity of the liposome lysis test for measurement of anti-ganglioside antibodies. A comparison with hemagglutination inhibition

A simple and reliable complement-dependent liposome lysis test for the detection of anti-ganglioside antibodies is described. For sera raised in rabbits against the monosialoganglioside NG-GM3, the sensitivity and specificity of antibody detection was compared with that of the HRBC hemagglutination-inhibition test: the liposome lysis test appears more sensitive. A difference in antigen presentation was also demonstrated.

Effects of structural variations in synthetic glycolipids upon mitogenicity for spleen lymphocytes, adjuvancy for humoral immune response and on anti-tumour potential

Synthetic glycolipids prepared by esterification of various sugars and sorbitol, and containing various numbers of saturated or unsaturated fatty acid residues as well as bacterial lipid A and lipopolysaccharide, were tested for mitogenicity of splenic cells of Fischer rats and Swiss mice and for the augmentation of humoral immune response against sheep red blood cells in these species. Subsequently a few of the humoral immune-response-enhancing glycolipids were compared with non-enhancers in their anti-tumour activity against 13762 rat mammary carcinoma in inbred Fischer 344 rats and Ehrlich tumour in Swiss mice. They were given systemically after tumour inoculation and intratumourally in squalene and Tween emulsion after intradermal MAC tumour development. It was observed that certain structural characteristics in glycolipids with respect to the type of sugar, the type and number of fatty-acid residues were needed for their adjuvant action of the humoral arm of the immune response. Although humoral immune-response enhancers were somewhat superior to non-enhancers in their anti-tumour activity, the correlation coefficient demonstrated a lack of significant concordance. It is concluded that glycolipids selected for their ability to augment humoral immune responses against standard antigens need not be suspect as tumour-enhancers on the grounds that they would elicit blocking antibodies in vivo against tumour-associated antigens.

Liposomes as carrier for production of sugar specific antibodies: preparation of antigalactosyl antiserum

Negatively charged multilamellar liposomes, covalently coupled with p-aminophenylated derivative of D-galactose, have been used to raise galactose specific antibodies in rabbits. The specificity of the antiserum has been characterized by immunodiffusion, quantitative precipitation and hapten inhibition studies. In addition to its specificity against the sugar moiety the antibody population also recognizes the aromatic aglycone portion of the introduced hapten. This offers a new method of raising sugar specific antibodies using liposomes as immunological carriers.

Pseudosarcoid granulomas in Hodgkin's disease

The sarcoid-like granulomas encountered in lymph nodes, spleens, and hepatic biopsy specimens removed from patients being "staged" in the course of Hodgkin's disease and, in lower incidence, in non-Hodgkin's lymphomas may, at least in part, be due to reactions to the oily radiographic contrast medium used in lymphangiography. They are seen more often following lymphangiography than when no contrast medium is used. The granulomas in patients who have not undergone lymphangiographic procedures are attributed to the many agents inciting pseudosarcoid lesions. It is speculated that the granulomas seen in Hodgkin's disease after lymphangiography may be the result of a combination of lipogranulomatous reaction and the effects of an immune adjuvant.

Liposomal enhancement of the immunogenicity of adenovirus type 5 hexon and fiber vaccines

Immunogenicity of adenovirus capsid proteins carried in liposomes was comparable to that with equivalent doses administered in Freund adjuvant, and both forms were more potent than aqueous vaccines.