The primary reason for these difficulties has been that the steps of affinity selection and maturation have often been separated from the screening for biological function, the latter requiring the use of biology-specific mammalian model system. Zhang and colleagues* present an elegant solution to the bottleneck by designing a combinatorial antibody library in lentivirus (Figure): after infection, multiple antibodies are expressed within each mammalian cell and are also secreted, allowing for multidimensional assessment of interactions and biological effects.
Because more than one virus can infect a single cell, the initial diversity of the antibody population attained at the phage display level is retained and even enhanced upon the step of lenti infection and functional selection because of the possibility for further combinatorial associations of heavy and light chains derived from different antibody clones. In the example presented, the authors select directly for antibodies that operate as phenocopies of erythropoietin working through its receptor (EpoR). Phage displaying the initial combinatorial antibody library were enriched for EpoR binding through solution panning. The enriched pool was used to isolate the antibody genes and transfer them to lentivirus, which in turn were used to infect TF-1 cells overexpressing wild-type EpoR. The team was able to select directly high-quality agonist antibodies from cells expressing more than one antibody, with several distinct clones possessing high efficiency and acting through slightly different epitopes.
The overall methodology presented in this work should be easy to adopt by others because it derives from readily available phage libraries and lentiviral vectors.