The VEGAS platform is not suitable for mammalian directed evolution

Directed evolution uses cycles of gene diversification and selection to generate proteins with novel properties. While traditionally directed evolution is performed in prokaryotic systems, recently a mammalian directed evolution system (viral evolution of genetically actuating sequences, or “VEGAS”) has been described. Here we report this system has major technical issues precluding its use for directed evolution. These issues include a rapid loss of VEGAS system integrity, an inability to propagate VEGAS Sindbis particles across rounds of transduction, widespread prevalence of circuit “cheaters”, and a reduced mutation rate. Similar results have been obtained in independent labs. It may be possible to use Sindbis virus for mammalian directed evolution in the future, however in its reported form, the VEGAS system is not suitable for use as a mammalian directed evolution platform