The VEGAS platform is not suitable for mammalian directed evolution. VEGAS Replicability

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

定向进化（directed evolution）通过多轮基因多样化与筛选循环，制备具备全新特性的蛋白质。尽管传统定向进化多在原核生物系统中开展，但近期已有研究报道了一种哺乳动物定向进化系统——基因调控序列病毒进化（viral evolution of genetically actuating sequences，简称"VEGAS"）。本研究发现该系统存在多项重大技术缺陷，导致其无法应用于定向进化实验。这些缺陷具体包括：VEGAS系统完整性快速丧失、无法在多轮转导（transduction）过程中传代扩增VEGAS辛德毕斯（Sindbis）病毒颗粒、回路"cheaters"广泛存在，以及突变率降低。该结论已在多家独立实验室中得到重复验证。未来或可借助辛德毕斯病毒开展哺乳动物定向进化研究，但就当前已报道的构建形式而言，VEGAS系统并不适合作为哺乳动物定向进化的实验平台。