The infective antibody library platform developed by the Lerner team approximately 2 years ago, in which lentiviral infection of a mammalian cell host by an antibody library effectively links antibody genotype and cell phenotype, has been used in several successful screens, delivering antibodies with unique properties such as those having the ability to transdifferentiate cells without the need for transitional induced pluripotency (see commentaries: Assay Drug Dev Technol 2013;11:347 and Assay Drug Dev Technol 2013;11:516). Here* the team uses the platform to find antibody tools to dissect a fundamental process of cell death brought about by an acute viral infection.
An iterative selection was devised in which antibody genes recovered from surviving cells were used for each new round. A 108-member naive antibody lentivirus library was used to induce cytoplasmic expression of antibodies in HeLa cells prior to infecting them with rhinovirus. Cells expressing functional antibodies were expected to be protected from death while other cells were killed. The antibody-coding information from the surviving cells was fed into a secondary lentiviral library that served as the starting point for the next round of selection (see Figure). After five rounds of such selection, the team obtained antibodies that when expressed in the cytoplasm as distinct agents were shown to offer protection to mammalian cells from rhinovirus-induced death. Mechanism of action studies implicated the viral 3C protease, responsible for virus maturation, as the target to which the antibodies bound and whose blockage rescued the mammalian host cell from virus-induced cell death.
The present work is a fine example of a selection strategy that carries an additional kinetic-based component, as if the virus infection and host cell replication enter a race of sorts during the initial stages of which any rare rescue antibody clones remain invisible and are only revealed if they are truly effective and after several successive rounds of enrichment. It is anticipated that future uses of this approach will incorporate earlier markers for cell death, such as onset of apoptosis, autophagy, or cell cycle arrest. In turn, knowing the factors that preferentially protect cells from death should inform the efforts directed at finding ways to selectively kill unwanted cells, such as rapidly proliferating cancers.