In vitro cytotoxicity of anti-theta (Thy-1) antibodies combined with chlorambucil

Two methods are described for linking chlorambucil to antibodies. At low pH an association is formed which is not stable under physiological conditions and the cytotoxicity is the result of the independent action of chlorambucil and antibody. At pH 8 a more stable linkage is formed and this complex shows specific toxicity for cells carrying the appropriate antigen. Uncombined chlorambucil and antibody are more cytotoxic that chlorambucil alone, especially if the cells are exposed first to the chlorambucil.