The ability of an alpha-emitter conjugated to a chimaeric anti-CD20 monoclonal antibody to kill selectively human B-lymphoma cells in vitro is reported. Two B-lymphoma cell lines RAEL and K422, and normal haematopoietic progenitor cells from human bone marrow aspirates were incubated with(211)At-rituximab (Rituxan(R) or MabTheratrade mark) and plated in clonogenic assays for survival analyses. Following 1 h incubation with(211)At-rituximab, in concentrations which gave an initial activity of 50 kBq ml(-1), a high tumour cell to normal bone marrow cell toxicity ratio was obtained; 4.1 to 1.0 log cell kill. Biodistribution studies of(211)At-rituximab in Balb/c mice showed similar stability as that of the iodinated analogue. The data indicate that testing of(211)At-rituximab in human patients is warranted.
