Fc‐Receptor‐mediated Targeting of Antibody‐bearing Liposomes Containing Dideoxycytidine Triphosphate to Human Monocyte/Macrophages

Abstract— Liposomes bearing surface‐attached antibody (L‐Ab) molecules can be used for various purposes including the immunospecific delivery of drugs or other materials to antigenic target cells. In this study, L‐Ab were prepared to deliver an anti‐human immunodeficiency virus (HIV) drug, dideoxycytidine triphosphate (ddCTP) to human monocyte/macrophages. Cells of the monocyte/macrophage lineage are an important reservoir of HIV‐1. A mouse monoclonal antibody IgG_2a was labelled with ¹²⁵I and modified using N succinimidyl‐3‐(2‐pyridyldithio)propionate (SPDP) as a heterobifunctional reagent in order to conjugate with liposomes to produce a covalent bond (thioether). SPDP‐modified antibody was incubated with liposomes containing 5 mol% of maleimido phenyl butyrate phosphatidylethanolamine (MPB‐PE) at room temperature (21°C) for 24 h. L‐Ab were separated from free and aggregated antibodies by centrifugation. L‐Ab were characterized by measuring particle size and binding to anti‐mouse IgG‐sepharose. Ninety five per cent of the liposomal (L‐Ab) lipid label was bound to anti‐mouse IgG‐sepharose, whereas only 7% of plain liposomes were bound, indicating non‐specific binding. Uptake of L‐Ab was measured in human monocyte/macrophages as a function of time and compared with that of plain liposomes. The uptake increased with time and it was 4–6 times greater than that of plain liposomes although part of that effect may have been due to unreacted MPB groups. 1993 Royal Pharmaceutical Society of Great Britain