1. antibody affinity maturation services Affinity maturation is the process to improve antibody affinity for an antigen. In vivo, natural affinity maturation by the immune system takes place by somatic hypermutation and clonal selection. In vitro, in the laboratory affinity maturation, can be obtained by mutation and selection.

2. Creative Biolabs has gained extensive experience in antibody affinity maturation. We usually take scFv as the antibody format in affinity maturation. Also, a monovalent display phagemid system is used to reduce the avidity effects during antigen-binding screening. We also provide affinity maturation services for single domain antibodies. Two methods, untargeted mutagenesis and oligonucleotide-directed mutagenesis, are employed to construct random or defined sub-libraries to introduce a large number of mutants of the original antibody. Antibody binders of higher affinity are then selected by increasing the screening stringency. By constructing a series of sub-libraries of a scFv/Fab antibody, our proprietary protocol allows increase of the affinity of the scFv antibodies from 10 -9 to 10 -10. We have successfully obtained a scFv antibody that has an extremely high affinity of 10 -12, whose binding to the antigen is essentially irreversible.

3. If the structure of the antibody/antigen complex is available or modeling the structure of the antibody/antigen is possible, certain positions can be randomized at a defined diversity (such as full randomization with all 20 amino acids or biased randomization with selected amino acids at fixed percentages) to improve the affinity. We are able to create any sub-libraries to incorporate the defined mutations using trimer codon technology. Most of the time, we need study the AA sequences of the antibody to find out the conserved sequences (in comparison with the germ-line and antibody subfamily sequences). We may then introduce mutations to the positions in the frame work regions that are not conserved. Supposedly, these regions will be antigen-specific and change in these regions may not increase immunogenicity.

4. Subsequent library screening will fish out the antibody mutants that have high affinity. Two library screening strategies are available. In the first "surface-panning" strategy, decreasing concentrations of antigen is surface immobilized. In the second "solution-sorting" strategy, in which a labeled antigen in solution is used, we have two approaches, selection based on the equilibrium constant (Kd) and selection based on binding kinetics. In the first approach, sub-library phage is incubated with biotinylated antigen at controlled concentrations and bound phages are captured by immobilized NeutrAvidin. Selection based on binding kinetics is also termed off-rate (Koff) selection, in which phage population is allowed to saturate the labeled antigen before a large molar excess of unlabeled antigen is added to the mix for controlled periods of time. This allows the selection of mutant antibodies that have slower off-rates. Since a reduction in Koff usually results in a higher affinity, this selection approach singles out antibody variants with improved Kd.