Highly efficient immunoliposomes prepared with a method which is compatible with various lipid compositions

Monoclonal antibody was conjugated to N-glutaryl-phosphatidylethanolamine in the presence of octylglucoside by using N-hydroxysulfosuccinimide as a carboxyl-activation reagent. The conjugated antibody was then incorporated into liposomes by a simple dialysis method. The method is mild and is compatible with various lipid compositions of the liposomes. We have prepared immunoliposomes containing a lung endothelium-specific monoclonal antibody and showed excellent target binding (approximately 75% injected dose) of the immunoliposomes in mouse. Immunoliposomes can be prepared to contain other acidic lipids such as phosphatidylserine and various amounts of cholesterol. The presence of 20% or more cholesterol in liposomes resulted in high level of target binding. We have used in these experiments a new radioactive lipid-phase marker, 111In-DTPA-SA, which was very stable in vivo. The halflife of clearance in mouse exceeded 3 weeks.