The goal of this proposal is the development of an alternative method for the preparation of immunogenic liposomal model membranes which circumvents the need to synthesize the N-(hapten)-substituted derivatives of phosphatidylethanolamine that were previously employed for this purpose. Preformed liposomes, in which appropriate N-hydroxysuccinimide (NHS) esters are anchored in the lipid bilayers, should (can) covalently bind materials that possess a free, substitutable, amino group. As a consequence of this covalent attachment, the liposomes should be able to induce antibody formation against these determinants (e.g., in mice); furthermore, the response should be enhanced by incorporation of lipid A (a B cell mitogen) into the same bilayers to which the determinant has been bound. If successful, these experiments would suggest inter alia that liposomes might be employed for """"""""vaccination"""""""" considering the likelihood that lipid bilayers act as nonimmunogenic carriers and as a nontoxic adjuvant. Besides such applications, several laboratories have also advocated the in vivo use of liopsomes as vehicles for the delivery of cytotoxic agents to specific cells (e.g., cancer cells). To this end, methods have been devised for attaching antibodies to the liposomal surface so that the liposomes are selectively targeted to cells that bear the corresponding antigen in their membrane. Experiments in this proposal are designed to test the possibility that antibodies, which are covalently bound to liposomes via the NHS derivatives, may induce formation of anti-antibodies. These experiments are relevant to """"""""liposomal therapy"""""""" since the presence of anti-antibodies in the serum may not only interfere with selective targeting, but also render the recipient susceptible to allergic reactions upon subsequent readministration of liposomes with attached antibodies. A related project concerns the covalent attachment of liposomes, containing the NHS derivatives, to cells in vitro. Experiments will be performed to investigate the fate of such liposomes, i.e., whether they remain stably absorbed onto the cell surface, undergo fusion with the cell membrane, or are endocytosed by the cell. The results should indicate whether covalent linkage between liposomes and cells may facilitate the transfer of foreign material (e.g., DNA) from within the liposomes to the cytoplasm, and thereby serve as a method for establishing cells that possess new biological properties.
