Ellis James
Developmental Biology Program, Hospital for Sick Children, Toronto, ON, Canada M5G 1L7.
Hum Gene Ther. 2005 Nov;16(11):1241-6. doi: 10.1089/hum.2005.16.1241.
Retrovirus vectors integrate into the genome, providing stable gene transfer, but integration contributes in part to transcriptional silencing that compromises long-term expression. In the case of gammaretrovirus vectors based on murine leukemia virus, many integration events are completely silenced in undifferentiated stem cells and in transgenic mice. Gammaretrovirus vectors are also subject to variegation in which sister cells bearing the same provirus differentially express, and cell differentiation can lead to extinction of vector expression. In contrast, lentivirus vectors based on human immunodeficiency virus type 1 appear to express more efficiently, although other reports indicate that lentivirus vectors can be silenced. This review summarizes the key features of gammaretrovirus vector silencing. The evidence for and against gene silencing of lentivirus vectors is described with special emphasis on the potential effects of vector design, provirus copy number, and integration site preferences on silencing. This analysis suggests that the difference between selfinactivating (SIN) lentivirus vectors and their modified SIN gammaretrovirus counterparts may be less dramatic than previously thought. It will therefore be important to further characterize the mechanisms of silencing, in order to create better gammaretrovirus and lentivirus vectors that consistently express at single copy for gene therapy.
逆转录病毒载体整合到基因组中，可实现稳定的基因转移，但整合在一定程度上会导致转录沉默，从而影响长期表达。对于基于小鼠白血病病毒的γ逆转录病毒载体而言，许多整合事件在未分化的干细胞和转基因小鼠中会完全沉默。γ逆转录病毒载体还会出现斑驳现象，即携带相同原病毒的姐妹细胞会有差异地表达，并且细胞分化会导致载体表达消失。相比之下，基于1型人类免疫缺陷病毒的慢病毒载体似乎表达效率更高，不过其他报告表明慢病毒载体也可能被沉默。本综述总结了γ逆转录病毒载体沉默的关键特征。阐述了支持和反对慢病毒载体基因沉默的证据，特别强调了载体设计、原病毒拷贝数和整合位点偏好对沉默的潜在影响。该分析表明，自我失活（SIN）慢病毒载体与其修饰的SINγ逆转录病毒对应物之间的差异可能没有先前认为的那么显著。因此，进一步阐明沉默机制很重要，以便创建出能在基因治疗中以单拷贝持续表达的更好的γ逆转录病毒和慢病毒载体。
