when the lyophilized product is rehydrated usually with a small amount of distilled water the small unilamellar liposomes to be used in this process are produced by dispersing the lipids in an aqueous medium followed by a mechanical means of dispersion such as sonication use of a high pressure device or a solvent injection method large and intermediate sized unilamellar liposomes can also be produced by conventional techniques including detergent dialysis extrusion through small pore size membranes under high pressure freeze thawing followed by slow swelling dehydration followed by rehydration and dilution or dialysis of lipids in the presence of chaotropic ions the size of the liposomes can be made more uniform by fractionation procedures such as centrifugation or size exclusion chromatography homogenization or capillary pore membrane extrusion the target within the host and major site of uptake of liposomes is the reticuloendothelial system mainly in the liver spleen and lung of the host factors affecting uptake of liposomes by the host include liposome size stability and surface charge the apparent optimal size for targeting the reticuloendothelial system is gt 1 0 u03bcm particularly for targeting liver lung and spleen according to the subject invention antitumor vaccine compositions are formed by encapsulating tumor associated antigens or taas with intermediate sized liposomes water soluble taas which may partition into either the lipid bilayer or the aqueous component are added to the aqueous phase before formation of liposomes in order to entrap the agent with the liposomes during formation alternatively lipid soluble taas are added to the lipid mixture before formation of the liposomes wherein the taa partitions into the lipid bilayer lipophilic taas may require detergent dialysis in.