Abstract: Loaded cells suspended in a physiological solution are prepared in a process in which their volume is expanded by osmotic pressure. Cells so prepared suspended in a physiological solution, when injected into the bloodstream of a living body are preferentially accumulated in the spleen and liver of the body, which treats them as foreign bodies, even though the original cells may have been cells of an animal of the same species. Similarly by storing the loaded cells in a solution containing substances such as glutadialdehyde, formaldehyde that react with the protein phase of membranes or which, like difluoro dinitrobenzene, react with the lipid layer thereof, the loaded cells can also be caused to be broken down by the spleen and/or liver. Premature release of the contents of the loaded cells is prevented and timely release of such contents is assured by incorporating other materials into the loaded cells during the preparation process in accordance with the related application of the same inventors, Ser. No.

Abstract: A material capable of forming hydrogen bonds or covalent bonds with loading materials incorporated in loaded cells is introduced into the cells with the loading materials to inhibit the destruction of the cell membranes by the loading material after the permeability of the membranes is brought back down to its normal value. In order to provide for the hydrogen bond formation with common loading materials, such as methotrexate, proteins such as albumin and sugars such as sucrose are effective. The time period during which these materials inhibit a destructive effect on the membranes of loaded cells is well defined.