Rapid discovery and optimization of therapeutic antibodies against emerging infectious diseases

Rogers, J.; Schoepp, R.J.; Schröder, O.; Clements, T.L.; Holland, T.F.; Li, J.Q.; Li, J.; Lewis, L.M.; Dirmeier, R.P.; Frey, G.J.; Tan, X.; Wong, K.; Woodnutt, G.; Keller, M.; Reed, D.S.; Kimmel, B.E.; Tozer, E.C.

While there are significant benefits from screening an immunized library (e.g. higher affinity antibodies due to in vivo maturation, smaller library diversity required), antibodies of mouse origin often result in a human anti-murine antibody response (Schroff et al., 1985) . To reduce undesired immunogenicity, it is now relatively common to exchange the mouse FRs with corresponding regions of human antibodies, in essence 'humanizing' the antibody (Clark, 2000) . Several strategies for humanizing have been developed and implemented. In an approach called 'CDR grafting' the nonhuman CDRs are grafted onto a given human sequence. The human sequence is selected either by the similarity of its framework sequences with the mouse frameworks or by the similarity of its CDRs with the mouse's (Hwang et al., 2005) . Unfortunately, both approaches do not guarantee that the CDRs are presented in the same conformation as in the WT antibody. As a consequence, a significant drop in affinity is often observed (Hwang et al., 2005) . The necessity to identify and back-mutate crucial parental framework residues in the humanized antibody by computer modeling is difficult and often empirical.