Therapeutic antibody fragments with prolonged in vivo half-lives

Antibody fragments can be isolated rapidly using techniques such as phage d isplay and can be expressed to high levels in microbial systems. However, t o date such antibody fragments have been of limited use for many therapeuti c applications because they are rapidly cleared from the body. We present a strategy for the site-specific chemical modification of antibody fragments with polyethylene glycol, which results in the production of antibody frag ments with long in vivo half-lives and full retention of antigen-binding pr operties. This technology should allow more rapid and economical production of therapeutic antibodies for chronic disease therapy.