Antimetastatic Effect of Immunization with Liposome-Encapsulated Tumor Cell-Membrane Proteins Obtained from Experimental Tumors

Immunization of C57BL/6 mice with tumor-derived membrane-proteins encapsulated in sized liposomes (0.2 microgram/mouse) and composed by phosphatidylcholine or sphingomyelin, significantly reduced the mean values of spontaneous lung metastasis from both B16 (0.7 +/- 0.5 and 1.2 +/- 0.6, respectively) and 3LL (4.8 +/- 2.5 and 7.2 +/- 4.1, respectively) tumors, with respect to control (HEPES) groups (4.8 +/- 1.1 and 19.0 +/- 4.4, respectively). However, no significant antimetastatic effect was observed using free tumor-derived proteins (2 micrograms/mouse) or liposome vehicle alone. Specific humoral immune response after the vaccination was studied by flow cytometry of tumor cells incubated wi…