Engineering Antibody Heavy Chain CDR3 to Create a Phage Display Fab Library Rich in Antibodies That Bind Charged Carbohydrates

A number of small charged carbohydrate moieties have been associated with inflammation and cancer. However, the development of therapeutic Abs targeting these moieties has been hampered by their low immunogenicity and their structural relationship to self-Ag. We report the design of an Ab repertoire enriched in Abs binding to small charged carbohydrates and the construction of a human Fab phagemid library, "FAB-CCHO." This library combines L chain Ig sequences from human donors and H chain synthetic diversity constructed in key Ag contact sites in CDRs 1, 2, and 3 of the human framework V(H)3-23. The H chain CDR3 has been engineered to enrich the library in Abs that bind charged carbohydrates by the introduction of basic residues at specific amino acid locations. These residues were selected on the basis of anti-carbohydrate Ab sequence alignment. The success of this design is demonstrated by the isolation of phage Abs against charged carbohydrate therapeutic target Ags such as sulfated sialyl-Lewis X glycan and heparan sulfate.