Agglutination microassay of hapten- or protein-modified liposomes using a multiple cell culture harvester

Coating of liposomes with subunits of monoclonal IgM antibody and targeting of the liposomes

SH-bearing subunits of IgM antibody were coupled through the Fc portion to sonicated liposomes consisting of N-(m-maleimidobenzoyl)dipalmitoylphosphatidylethanolamine, dipalmitoylphosphatidylcholine and cholesterol. Liposomes coated with subunits of monoclonal IgM antibody against a mouse mammary tumor-associated antigen selectively bound to the antigenic target cells. Assays of the liposomes for complement dependent cytotoxicity and spleen cell binding revealed inactivation of the liposome-coupled antibodies in both assays.

Antibody coating of liposomes with 1-ethyl-3-(3-dimethyl-aminopropyl)carbodiimide and the effect on target specificity

Liposome surfaces were modified with normal rabbit IgG or rabbit anti-sheep erythrocyte IgG by adsorption or by coupling with a water soluble cross-linking reagent, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDCI). Modification with normal IgG reduced the non-specific binding of the liposomes to erythrocytes. The immunological binding capacity of the immune IgG on liposomes was better for the chemically coupled preparation than for the adsorbed one. Complement dependent cytolytic activity of the immune IgG towards target erythrocytes was diminished as a consequence of liposome binding by either method, but to a lesser extent in the coupling method. Antibody coating by EDCI thus provides liposomes which can bind effectively to antigenic target cells.

Monoclonal antibody covalently coupled to liposomes: specific targeting to cells

We have evaluated optimal conditions for coupling monoclonal antibody to small unilamellar liposomes. Coupling of an IgG2 alpha monoclonal anti-beta 2-microglobulin antibody, which reacts with human cells, was examined in detail. Liposomes were composed of dipalmitoyl lecithin and cholesterol, and variable quantities of phosphatidylethanolamine substituted with the heterobifunctional cross-linking reagent N-hydroxysuccinimidyl 3-(2-pyridyldithio) propionate (SPDP). They were reacted with antibody derivatized with the same reagent at a 5- to 20-fold molar excess, and activated by mild reduction. This degree of SPDP modification had no effect on the capacity of the antibody to bind to its target antigen. More than 40% of antibody could be reproducibly bound to liposomes, resulting in the coupling of from 1 to 10 antibody molecules per liposome (mean diameter:580 A). The coupling reaction did not lead to loss of carboxyfluorescein encapsulated within liposomes. At least 80% of liposomes carried nondenatured antibody, as confirmed by precipitation of liposomes and encapsulated carboxyfluorescein by Staphylococcus aureus, strain Cowan I. The liposome-coupled antibody retained its immunological specificity: only cells expressing human beta 2-microglobulin bound liposomes in vitro, and the binding was inhibited by the free antibody in solution. Results with antibodies of different antigens specificity confirm that the technique can be generally applied.