Construction of a human Ig combinatorial library from genomic V segments and synthetic CDR3 fragments

A naive combinatorial Ig library was constructed from semi-synthetic V genes consisting of human genomic V segments and synthetic CDR3 fragments. VH and V kappa segments were amplified from human genomic DNA by polymerase chain reaction using V subgroup-specific primers. The amplified VH and V kappa segments were combined with synthetic oligonucleotides containing a J region and CDR3 with amino acid sequence variations, resulting in complete V genes. These V genes were cloned into a phagemid expression vector in a single-chain form fused to the carboxyl-terminus of the M13 minor coat protein III. Phagemid particles displaying the single chain hybrid proteins on their surface were screened with Con A as Ag. Several clones showing specific binding to Con A were obtained after four rounds of selection and were further analyzed for their binding properties and DNA sequences. This method provides a novel way to create a naive combinatorial library without using mRNA from B lymphocytes as template. The method should be useful to isolate human antibodies that react with self-Ag.