Method of producing catalytic antibodies in a human

A method for producing catalytic antibodies to a specific antigen in a non-human subject. The method comprises administering to the non-human subject a growth factor precursor comprising an antigen capable of interacting with a B cell bound catalytic antibody. The antigen is fused to at least one B cell surface molecule binding portion which is flanked by one or more blocking groups that prevent the binding portion from interacting with a surface molecule until the blocking groups are cleaved by a target catalytic antibody. The administration is conducted for a time and under conditions for the antigen to be cleaved and for the remainder of the molecule to induce B cell mitogenesis.