A novel platform for antibody library selection in mammalian cells based on a growth signalobody

Abstract

While many antibody-screening methods in vitro have been developed, these methods need repeated cycles of panning or sorting procedures to isolate antigen-specific antibodies. Here we developed a new antibody selection system based on antigen-dependent growth of mammalian cells. In this system, a growth signalobody library, which is a naïve single-chain Fv (scFv) library/cytokine receptor chimera that can transduce a growth signal in response to a specific antigen, is expressed in murine interleukin-3-dependent Ba/F3 cells. Simple culture of the cells in an antigen-containing medium results in growing cells with a high-affinity scFv gene, leading to selection of the scFv specific to the target antigen without panning/sorting procedures. To demonstrate this system, we used the SD1D2g signalobody having the signaling domain of gp130 and fluorescein-conjugated BSA as a target antigen, and investigated whether a fluorescein-specific scFv could be selected from a naïve scFv library. As a result, we successfully obtained fluorescein-binding scFv clones, and the scFv clone with the highest affinity was most abundantly selected, having the same sequence as the clone, which had been obtained through phage display. These results demonstrate the utility of our system as an affinity-based scFv selection method based on growth advantage of mammalian cells.