Induction of in vitro and in vivo anti‐tumor responses by sensitization of mice with liposomes containing a crude butanol extract of leukemia cells and transferred inter‐membranously with cell‐surface proteins

Generation of cytotoxic T lymphocytes (CTL) in vitro and tumor‐rejection responses by sensitization of semi‐syngeneic mice with tumor‐antigen‐reconstituted liposomes were investigated. Liposomes were prepared from a crude' butanol extract (CBE) of BALBRVD leukemia cells and egg phosphatidylcholine (PC): 1,2‐dimyristoylamido‐1,2‐deoxyphosphatidylcholine (DDPC) (3:2) or dimyristoylphosphatidylcholine (DMPC) : DDPC (1:4). Inter‐membrane protein transfer (IMPT) liposomes were prepared by incubating BALBRVD cells with DMPC : DDPC (1:4) liposomes. Sensitization of male CB6F, mice with CBE or IMPT liposomes induced a level of cytotoxicity similar to that on sensitization with mitomycin‐C(MMC)‐treated BALBRVD against BALBRVD target cells after In vitro sensitization with the tumor cells. Sensitization with CBE alone resulted in only marginal cytotoxicity. The cytotoxic effector cells induced by either mode of sensitization were CD8⁺ T‐cells whose recognition was K^d‐restricted. No difference in specificity was observed with the different modes of sensitization. Two in vivo immunizations with CBE or with CBE liposomes at a dose of 25 μg of protein (equivalent to 2.5 × 10⁷ cells) cause moderate inhibition of BALBRVD tumor growth in male CB6F₁ mice and immunization with IMPT liposomes at a dose of 1 μg of protein result in efficient protection.