In vitro induction of primary and secondary xenoimmune responses by liposomes containing human colon tumor cell antigens

Abstract

Liposomes prepared with human LS174T colon tumor cell membranes induce specific primary and secondary xenogeneic immune responses in BALB/c splenocytes in vitro. The multilamellar vesicular liposomes were prepared by adding sonicated membrane fragments in 8 m M CaCl 2 to a dried lipid film. Cytotoxic splenocytes generated in vivo exhibited specificity for the LS174T cell; liposomes elicited higher levels of cytotoxicity than did membranes ( P < 0.01). Secondary blastogenic responses elicited in in vivo-primed spleen cells by liposome-antigens also produced a significantly greater ( P < 0.005) response than membranes. Subsequently, in vitro induction of primary blastogenic and cytotoxic responses by liposome-antigens were accomplished and revealed similar kinetics to that of whole LS174T cell immunogens. Specificity of the in vitro-primed spleen cells was clearly demonstrated ( P < 0.01) on a variety of human tumor cells using both the primed lymphocyte and cell-mediated cytotoxicity assays. The results of competitive inhibition tests with autologous lymphoblasts demonstrated that 30% of the cytotoxic activity was directed against lymphocyte antigens. Incorporation of tumor antigens into liposomes has thus enabled primary immunization in vitro to human colon cancer antigens and may afford an adaptable means to evaluate and to select desired immune responses, as well as to identify colon tumor-specific determinants.