Enzyme therapy. X. Immune response induced by enzyme- and buffer-loaded liposomes in C3H/HeJ Gus(h) mice

The immune response to negatively charged liposomes loaded with protein (predominantly bovine β-glucuronidase) or buffer was evaluated in C3H/HeJ mice. After repeated intravenous and subcutaneous sensitizations (2-7 injections) with enzyme loaded liposomes, antibodies to the enzyme preparation were detected by a double antibody technique; no antibodies to the liposome vesicle itself were detected by complement dependent lysis. In time course experiments monitoring the tissue recovery of liposome-entrapped β-glucuronidase activity, striking decreases were demonstrated in mice repeatedly sensitized with enzyme-loaded liposomes, compared to the recovery in unsensitized mice. In addition, a similarly decreased tissue recovery of liposome-entrapped activity was observed in mice with circulating anti-β-glucuronidase antibody (produced by subcutaneous sensitizations with unentrapped enzyme), suggesting that liposomes did not protect the entrapped protein from immunologic surveillance and that the rapid tissue clearance and degradation of the entrapped enzyme was in part due to the processing of antigen-antibody complexes. Notably, an altered fate of liposome- (as well as erythrocyte-) entrapped activity was observed in mice up to 24 days after the repeated, or even a single, intravenous sensitization with buffer-loaded liposomes. These results indicate that a cellular response was elicited to the liposome vesicle itself by phagocytic cells of the reticuloendothelial system. This was supported by the appearance of activated peritoneal macrophages after intraperitoneal sensitization with buffer-loaded liposomes. These data suggest that caution should be exercised in the administration of enzymes or drugs in liposomes since these lipid carriers may induce adverse host responses in the recipient.