Selective RNase cytotoxic reagents

The present invention relates to a selective cytotoxic RNase reagent. The reagent comprises a toxic moiety that is an RNase linked to a recognition moiety that binds a specific cell surface marker. Binding of the recognition moiety to a surface marker on a cell allows the toxic moiety to selectively kill the cell. To reduce immunogenicity, preferably the toxic moiety and the recognition moiety of the conjugate are endogenous to the species in which the reagent is intended for use. Cytotoxic reagents intended for use in humans preferably have as the toxic moiety a human ribonuclease, such as angiogenin, and as the recognition moiety as humanized chimeric antibody. The human ribonuclease and chimeric antibody preferably form a fused protein. The present invention also relates to pharmaceutical compositions including the cytotoxic reagent as well as treatment methods involving the use of the cytotoxic reagent.