Virus-free continuous directed evolution in human cells using somatic hypermutation
The B cells of the human immune system have evolved somatic hypermutation (SHM) mechanisms that introduce mutations at the immunoglobulin genomic loci at a significantly higher frequency than the rest of the genome thereby allowing them to evolve antibody sequences without compromising fitness due to genome-wide mutations. Inspired by these observations, here we developed a continuous directed evolution platform in human B cell lines (CODE-HB) that repurposes the SHM mechanisms to a stable, non-immunoglobulin genomic locus of the human B cell lines to continuously evolve cytosolic and surface displayed proteins with a broad mutational spectrum comprising of substitutions, deletions and insertions. We developed a human B cell surface display platform and used CODE-HB to evolve neutralizing antibodies targeting avian influenza and escape variants of influenza. Given the modularity and simplicity of CODE-HB, we anticipate that this platform can be used for rapidly evolving biotechnologically relevant biomolecules directly in human cells.