CRITICAL FACTORS FOR LIPOSOME-INCORPORATED TUMOR-ASSOCIATED ANTIGENS TO INDUCE PROTECTIVE TUMOR-IMMUNITY TO SL2 LYMPHOMA-CELLS IN MICE

Physical and immunogenic properties of reconstituted membranes designe d for the presentation of tumour-associated antigens (TAA) to the immu ne system are described. Proteins and lipids of crude membranes of SL2 murine lymphosarcoma cells were partially solubilized with octylgluco side. Reconstituted membranes, consisting mainly of unilamellar vesicl es with a diameter of 0.03-0.15 mum, were formed by detergent removal and were purified by floatation in a discontinuous sucrose gradient to remove non-lipid-bound protein. Subcutaneous immunization of syngenei c mice with reconstituted membranes or with purified reconstituted mem branes induced protection against an intraperitoneal challenge with 10 (3) viable SL2 cells. Reconstituted membranes were more immunogenic th an crude membranes in immunoprotection experiments when compared on th e basis of protein dose. Detergent removal was required to obtain an i mmunogenic presentation form of SL2 membrane antigens and to avoid tox icity associated with the detergent. Reconstitution of SL2 membranes i n the presence of exogenous phospholipid slightly increased the fracti on of protein that associated with the reconstituted membranes. Howeve r, the immunogenicity of the solubilized membrane TAA was not signific antly affected by the presence of exogenous phospholipid. The reconsti tution procedure described may be useful in identifying membrane facto rs required for the induction of immune responses against TAA. The ver satility of the system may be employed to develop safe alternatives fo r whole-cell vaccines.