The application of adenine deaminase in antibody affinity maturation.

Previously, we established a platform for antibody/protein affinity maturation based on CHO cell display. The gene of interest was mutated by activation-induced cytidine deaminase (AID), and then, a mutation library mainly containing G/C to A/T conversion was obtained by simply proliferating cells. However, the AID-induced G/C to A/T conversion limits the diversity space of the mutation library. In contrast to AID, adenine deaminase (ADA) can convert A/T to G/C. In this study, we demonstrated that ADA could efficiently induce random A/T to G/C mutations on the target gene in the CHO cell display and could be applied in affinity maturation. Our data also showed that more mutant types were obtained through the combined use of AID and ADA, thus offering an opportunity to acquire new mutants offering higher affinities than those obtained by only using AID. Examples presented in this study showed that ADA contributed to the improvement of antibody affinity either with or without AID in CHO display. KEY POINTS: • ADA is able to induce random mutations on antibody gene in mammalian cells. • ADA induces mutations on A/T bases to compensate AID which can induce mutation on G/C. • Combination of AID and ADA can increase mutation types and maturation efficiencies.