Assay of cell surface-bound immunoliposomes using monoclonal antibody reactive with a cross-linking reagent.

A monoclonal antibody (mAb) reactive with a crosslinking reagent, N-(m-maleimidobenzoyl)dipalmitoylphosphatidylethanolamine (mMBPE), in liposomes was produced from a hybridoma clone established by a fusion between P3X63Ag8.653 mouse myeloma cells and spleen cells from a BALB/c mouse hyperimmunized with the antibody-coated liposomes containing mMBPE. Using this mAb (termed AL-6), the quantity of immunoliposomes bound on target tumor cells was assessed by flow cytofluorometry. The results obtained using fluorescein isothiocyanate-coupled AL-6 allowed the enumeration not only of the immunoliposomes bound on all tumor cells but also those on individual target tumor cells. The relevance of this assay method was confirmed by a comparison with another assay method of cell-bound liposomes using immunoliposomes containing carboxyfluorescein in the vesicles.