Use of photosensitive, antibody directed liposomes to destroy target populations of cells in bone marrow: a potential purging method for autologous bone marrow transplantation.

Liposomes containing the photosensitive dye sulphonated aluminium phthalocyanine (AlSPc) were coupled to polyclonal sheep anti-mouse-Ig antibody and bound to cells coated with specific mouse monoclonal antibody. When illuminated with red light, the AlSPc in the liposomes was activated to produce singlet oxygen and the antibody and liposome targeted cells were destroyed. DW-BCL cells (an Epstein Barr virus immortalised B-cell line) were targeted with an anti-B-cell antibody (8A) and killed specifically, both alone and in the presence of bone marrow mononuclear cells (BM-cells), without phototoxic effects on the untargeted bone marrow CFU-GM progenitor cells. The presence of an excess of non-target cells did not interfere with antibody and liposome binding, or light access to target cells. Similar results were obtained with T-lymphocytes as target cells using anti-CD3 antibody. Specific targeting to the B-cells was demonstrated in the cell mixtures by use of fluorescent microscopy combined with a sensitive technique to detect low levels of AlSPc fluorescence, a cooled charge couple device (CCD) camera. This was also able to show low levels of non-specific background binding of AlSPc to BM-cells and a small population of cells that took up AlSPc in the absence of antibody. The latter were shown to be monocytes by flow cytometry.