The interaction of Sendai virus glycoprotein-bearing recombinant vesicles with cell surfaces

The characterization of cationic fusogenic liposomes mediated antisense oligonucleotides into HeLa cells

Antisense oligonucleotides (ODNs) are potential therapeutic agents, but their development is still limited due to poor cellular uptake and high degradation rate in biological media. To resolve these problems, we propose to attach the Sendai virus to cationic liposomes. Cationic-fusogenic liposomes (CFLs) were prepared by reverse-phase evaporation and fused with the Sendai virus. The mean diameter was about 186 nm, determined by photon correlation laser light scattering method. The cytotoxicity of CFLs and the ODN loading efficiency depended on the +/- charge ratio. The fluorescence intensity in cytoplasm was enhanced with the increasing of DC-Chol content and +/- charge ratio. We also investigated the mechanism of cellular uptake using temperature shifts and lysosomotropic agent. The results indicated that the vector was introduced into the cells, not via endocytosis but membrane fusion. The preliminary experiment showed that CFLs are a promising formulation for ODN delivery with high levels of transfection and minimal cytotoxicity.

Effects of temperature on viral glycoprotein mobility and a possible role of internal "viroskeleton" proteins in Sendai virus fusion

The effect of temperature on fusion of Sendai virus with target membranes and mobility of the viral glycoproteins was studied with fluorescence methods. When intact virus was used, the fusion threshold temperature (20-22 degrees C) was not altered regardless of the different types of target membranes. Viral glycoprotein mobility in the intact virus increased with temperature, particularly sharply at the fusion threshold temperature. This effect was suppressed by the presence of erythrocyte ghosts and/or dextran sulfate in the virus suspension. In these cases also, no change in the fusion threshold temperature was observed. On the other hand, reconstituted viral envelopes (virosomes) bearing viral glycoproteins but lacking matrix proteins were capable of fusing with erythrocyte ghosts even at temperatures lower than the fusion threshold temperature and no fusion threshold temperature was observed over the range of 10-40 degrees C. The mobility of viral glycoproteins on virosomes was much greater and virtually temperature-independent. The intact virus treated with an actin-affector, jasplakinolide, reduced the extent of fusion with erythrocyte ghosts and the mobility of viral glycoproteins, while the treatment of virosomes with the same drug did not affect the extent of fusion of virosomes with erythrocyte ghosts and the mobility of the glycoproteins. These results suggest that viral matrix proteins including actins affect viral glycoprotein mobility and may be responsible for the temperature threshold phenomenon observed in Sendai virus fusion.

Effect of lipid compositions on gene transfer into 293 cells using Sendai F/HN-virosomes

Fusogenic liposomes that incorporate Sendai virus envelope proteins, so-called Sendai virosomes, have been developed for in vitro and in vivo genetic modification of animal cells. In this study, several different virosomes of varying lipid compositions were formulated and their in vitro gene-transfer efficiencies compared. The virosomes were prepared by quantitative reconstitution of the Sendai envelope, fusion (F) and hemagglutinin-neuraminidase (HN) proteins into liposomal vesicles. Virosomes that contained luciferase reporter genes were tested in 293 transformed human kidney cells. F/HN-virosomes that were prepared with an artificial Sendai viral envelope (ASVE-virosomes) or phosphatidylserine (PS-virosomes) exhibited an 8- or 6-fold higher gene-transfer efficiency than cationic liposomes that were made with 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP). F/HNvirosomes that were prepared with phosphatidic acid (PA-virosomes) instead of PS were less efficient in gene transfer than either ASVE- or PS-virosomes. In addition, the gene-transfer capability of ASVE- and PS-virosomes was maximal at a Ca2+ concentration of 510 mM. These results suggest that the incorporated lipid components significantly affect the in vitro gene transfer that is mediated by Sendai F/HN-virosomes.

Novel strategy for the selection of human recombinant Fab fragments to membrane proteins from a phage-display library

Traditionally, the selection of phage-display libraries is performed on purified antigens (Ags), immobilized to a solid substrate. However, this approach may not be applicable for some Ags, such as membrane proteins, which for structural integrity strongly rely on their native environment. Here we describe an approach for the selection of phage-libraries against membrane proteins. The envelope glycoproteins (Env) of the Human Immunodeficiency Virus type-1 (HIV-1) were used as a model for a type-1 integral membrane protein. HIV-1IHI Env, expressed on the surface of Rabbit Kidney cells (RK13) with a recombinant vaccinia virus (rVV), was solubilized using the non-ionic detergent n-Octyl beta-D-glucopyranoside (OG). Membrane associated Env was reconstituted into vesicles by the simultaneous removal of detergent and free monomeric Env subunits by gel-filtration. The resulting antigen preparation, termed OG-P1IHI, was captured on microtiter plates coated with Galanthus nivalis agglutinin (GNA) and used for rounds of selection (panning) of a well-characterized phage-display library derived from an HIV-1 seropositive donor. Simultaneously, an identical experiment was performed with OG-P1IHI vesicles disrupted by Nonidet P-40 (NP-P1IHI). Both membrane-associated and soluble Ags were selected for vaccinia-specific clones (OG-P1IHI: 59/75 and NP-P1IHI: 1/75) and HIV-1-specific clones (OG-P1IHI: 11/75 and NP-P1IHI: 65/75) using our approach. Hence, the novel panning strategy described here may be applicable for selection of phage-libraries against membrane proteins.

Gene transfection by quantitatively reconstituted Sendai envelope proteins into liposomes

Fusogenic liposomes (virosomes) consisting of Sendai virus envelope proteins have been utilized for in vitro and in vivo genetic modification of animal cells. In this study, the virosomes containing DNA were prepared by quantitative reconstitution of Sendai envelope proteins, fusion protein and hemagglutinin-neuramindase in liposomal vesicles. The Sendai virosomes more efficiently transferred genes into cultured 293 transformed kidney cells than 1,2-dioleoyl-3-(trimethylammonium) propane-based cationic liposomes. At 200:1 weight ratio of envelope protein and lipid, the virosomes exhibited the best efficiency of gene transfection into the cells. The Sendai virosomes required relatively a short period of incubation time and much less cytotoxic, compared to the cationic liposome/DNA complex. The transfection efficiency of the Sendai virosomes containing DNA was maintained 70% after a month. This type of Sendai virosomes is relatively convenient for preparation and storage, compared to fusogenic liposomes prepared by liposome-virus fusion. First of all, because the constituents are quantitatively formulated, this type of virosome formulation can provide further consistent transfection for gene therapy.

Effects of anionic and nonionic polymers on fusion and binding of Sendai virus to human erythrocyte ghosts

Effects of various polymers (dextran sulfate, dextran and polyethylene glycol) on binding and fusion of Sendai virus to target cells were studied by use of fluorescence spectroscopy. Direct binding of dextran sulfate but not dextran to Sendai virus was detected. Anionic and nonionic polymers showed definite effects on segmental motions of the viral envelope proteins. Sendai virus binding to human erythrocyte ghost membranes (HEG) was reduced by dextran sulfate and dextran while the fusion temperature dependence remained unaltered at approximately 20 degrees C. Nonionic polymer, polyethylene glycol, caused an increase in extent of fusion of Sendai virus with HEG. Segmental motion of viral envelope proteins, determined in terms of anisotropy of fluorescent probes attached to viral surface proteins, exhibited a temperature dependent transition at 20 degrees C by a sharp change from restricted to less restricted motion. In the presence of each of the polymers, this transition was no longer apparent. Since fusion did occur in the presence of all polymers, the temperature dependent characteristic of Sendai virus target cell fusion can be said not to depend on viral surface protein segmental motion. A reasonable and coherent explanation was given for the apparent disparity between the effects of inhibiting and enhancing polymers on fusion and motion of viral proteins.

The surface properties of phospholipid liposome systems and their characterisation

The field of liposome (vesicle) research has expanded considerably over the last 30 years. In physical chemical terms liposomes have many of the characteristics of colloidal particles and their stability is determined in part by the classical surface forces. It is now possible to engineer a wide range of liposomes varying in size, phospholipid composition and surface characteristics. The surfaces of liposomes can be modified by the choice of bilayer lipid as well as by the incorporation and covalent linkage of proteins (e.g. antibodies and sugar binding proteins [lectins]), glycoproteins and synthetic polymers. Much of the impetus for liposome design has come from their potential value as drug delivery systems. The development of technologies for the production of such a range of liposome systems has presented interesting problems in the characterisation of their properties. The review addresses the progress that has been made in characterising the surfaces of different types of liposomes with specific reference to their electrophoretic properties and their interpretation and the physical interactions between liposomal bilayers.

B lymphocytes respond specifically to phytohaemagglutinin after liposome-dependent transfer of purified phytohaemagglutinin receptors

Phytohaemagglutinin (PHA) receptor glycoproteins purified by affinity chromatography from porcine splenic lymphocytes, were reconstituted into vesicles made of phosphatidylcholine and phosphatidylserine, concomitantly with Sendai virus fusogenic proteins HN and F. The vesicles were used as a vehicle to insert the PHA receptor glycoproteins into a highly enriched population of porcine B lymphocytes. Fluorescence analyses showed that 52 +/- 2% of the reconstituted B cells had incorporated the lectin receptors. The modified B lymphocytes were assayed for their response (tritiated thymidine incorporation into nucleic acids) to PHA, concanavalin A (Con A), or to lipopolysaccharide (LPS). The results showed that porcine B cells fused with vesicles containing only viral fusogenic proteins failed to respond to either PHA or Con A. Tritiated thymidine incorporation was similar to background values. The cells did, however, respond to LPS with values of label incorporation similar to those observed in the case of pre-fused B lymphocytes. When purified B lymphocytes were fused with vesicles containing PHA receptors and viral fusogenic proteins, assays of thymidine incorporation showed a statistically significant (P less than 0.001) and specific response of the modified cells to PHA stimulation. Reconstituted cells cultured in the presence of PHA incorporated approximately nine times more radioactive label than pre-fused cells or cells fused with vesicles containing only fusogenic viral proteins. In marked contrast, reconstituted B lymphocytes did not show any significant label incorporation above background level in response to Con A, but they retained their ability to respond to LPS. Our findings suggest that B lymphocytes can be made to respond specifically to PHA by insertion of appropriate lymphocyte-derived receptors.

Induction of H-2-specific antibodies by injections of syngeneic Sendai virus-coated cells

The capacity of the B cell immunoglobulin receptor to recognize complexes of Sendai viral and H-2b antigens was investigated by studying the antibody response to injections of syngeneic Sendai virus-coated (SV+) spleen cells in C57BL/6 (B6) mice. Almost all mice produced alloreactive anti-H2 lymphocytotoxic antibodies. In contrast, such antibodies were found very exceptionally in mice injected with normal (SV-) cells or with Sendai virus (SV) only. The reaction pattern of the cytotoxic antibodies induced was variable and ranged from almost anti-private to widely cross-reactive serotypes. The results of reactions on H-2-congenic, -recombinant and -mutant mouse strains, and of capping and immunoprecipitation experiments showed that the cytotoxic antibodies were directed against H-2 class I molecules. The anti-H-2 antibodies exhibited enhanced binding for SV+ target cells, but absorption experiments showed that this was not the result of cross-reactions with cell surface Sendai viral determinants or with a molecular complex of H-2 plus SV. This conclusion was supported by the observation that syngeneic SV+ cells were not the predominant targets for the induced lymphocytotoxic antibodies. Our results do not support the existence of MHC-restricted antiviral antibodies, but show the induction of anti-class I H-2 alloantibodies by injections with syngeneic SV-coated cells. We present a model for regular induction of anti-H-2 antibodies without intentional alloimmunization.

Model membranes bearing glycolipids and glycoproteins

The forces that hold cell membrane components together are non-covalent and thermodynamically favoured in aqueous media. Hence virtually any glycolipid or membrane glycoprotein might be expected to be incorporable into lipid bilayer membranes and this expectation has been borne out. In addition methods have been developed for linking lipid fragments to species that would not otherwise be expected to associate with bilayers. Techniques that have been successfully used to generate bilayer structures bearing glycolipids and glycoproteins include hydration of films dried down from non-aqueous solutions of the components, detergent removal from aqueous component solutions, exogenous addition to preformed membranes, and various organic solvent injection or reverse phase approaches. Bilayer association of glycolipids and membrane glycoproteins, with preservation of specific receptor function, seem easy to achieve--in fact difficult not to achieve. Optimization of receptor function to accurately mimic that of cell membranes and efficient preservation of functions such as transport or second messenger activation, are typically more demanding, although still feasible. A systematic approach can give considerable insight into the processes involved via identification of minimal necessary factors. Unfortunately, the actual relative arrangement of components, so critical to subtleties of glycolipid and glycoprotein function, remains almost totally unknown for lack of morphological information in the size range of individual macromolecules. The latter problem has come to be the most critical limitation to many studies.