Antibody therapies for the prevention and treatment of viral infections

Salazar, Georgina; Zhang, Ningyan; Fu, Tong-Ming; An, Zhiqiang

Phage displayed antibody libraries. mAbs can be isolated from immunized or infected humans or animals using a library of displayed antibodies (Fig. 1) . Genes encoding the antibody heavy and light chains from B cells of immunized or infected humans or animals are cloned as Fab or scFv fragments and displayed, for instance on filamentous phage. Virus-specific antibodies are isolated by panning the libraries against antigens. This approach has been used to isolate potent neutralizing antibodies from the B cells of rhesus macaques immunized with recombinant adenoviruses carrying a synthetic gene encoding hemagglutinin (HA) of the influenza virus 6 and from human IgM + memory B cells of recent seasonal influenza vaccines. 5 In addition to panning libraries constructed from antibody repertoires following infection, panning of native antibody libraries has yielded potent neutralizing antibodies against viral infections. For example, a broadly neutralizing HIV antibody (D5) was isolated from panning a native antibody library. 21 It might be difficult to identify highly neutralizing antibodies when panning against native phage libraries, because of the lack of antibody somatic hypermutation process. This disadvantage may be overcome by an in vitro affinity maturation step or by panning of libraries constructed from immunized or infected human or animal donors in which antibody somatic hypermutations took place against a given virus. While phage display is an efficient way to generate viral neutralizing antibodies from immunized, or infected, or non-immune humans or animals, the resulting antibodies do not necessarily represent the natural antibody repertoire, since the antibody fragments are generated from the random paring of IgG heavy and light variable regions. 22 Further, since a predefined and well-characterized antigen is required to pan the library, the approach is not suitable to identify new neutralizing epitopes of viral pathogens. 22 Single-memory B cells. The ability to clone antibody encoding genes from single B cells of naturally infected or immunized individuals is a significant advance in isolating anti-viral mAbs. Three different approaches have been developed for the isolation of mAbs from single-memory B cells (Fig. 2) . One approach involves isolating memory B cells specific for viral antigens by flow cytometry, followed by direct cloning of the antibody-encoding genes without culturing of the B cells. This approach has been applied to isolate neutralizing antibodies from naturally infected and immunized human donors for Zika, 23 respiratory syncytial virus (RSV), 24 HIV, 12 and HPV. 25 Antibodies were also isolated through this method from antigen-specific individual memory B cells of rhesus macaques immunized with gp140-F trimers based on the HIV-1 YU2 isolate. 26 Fig. 1 Schematic representation of generation of mAbs using phage display. This method has the advantage of being relatively easy with the potential to generate VH and VL combinations not found in nature. The diagram was generated based on a combination of publications 6, 21 Fig. 2 Schematic of isolation of mAbs from memory B cells. When these cells producing antibodies with desired characteristics can be found, a supply of these antibodies can be maintained by culture and cloning, immortalization, or direct cloning. The diagram was generated by summarizing multiple published papers. The diagram was generated based on a combination of publications [10] [11] [12]