Analysis of Human Haemopoietic Precursor Cell Antigens Using Astatine Labelled Monoclonal Antibodies

In this study we describe a new approach to producing extremely cytotoxic monoclonal antibodies. A non-cytotoxic antibody BK19.45 was rendered cytotoxic by coupling the antibody to the radioisotope astatine 211. BK19.45 was chosen for this study since this antibody recognises an antigen which is uniformly distributed on human bone marrow leukocytes. Hence the ability of astatine labelled antibodies to specifically kill myeloid precursor cells (CFU-C) can be documented precisely. Bone marrow cells and the cell line HL60 were treated in suspension with increasing amounts of labelled BK19.45 or concanavalin A. Astatine has a short half life (7.2hr) and produces short range a particles. Therefore the radiation dose to the cells is limited to only those cells binding the antibody. The cytotoxicity of astatine labelled reagents was determined by growing colonies in semi-solid agar. D 37 values in the range 5-12 atoms/cell were obtained. In conclusion (1) the extreme toxicity (2) short half-life of the radioisotope and (3) consequentially the lack of residual long-term toxic effects of astatine labelled reagents provide a system which can be used to eliminate in vitro subpopulations of cells from bone marrow in analysing precursor cell antigens.