They integrate their DNA into the host genome and you might not want to make that kind of a change in the cell.

而且也许你也并不想让逆转录病毒基因,整合进宿主的基因组

耶鲁公开课 - 生物医学工程探索课程节选

In this case, if everything goes right, you inject the DNA into the pronucleus, you implant this fertilized egg into a foster mother, the mother gives birth to offspring, it develops and when it develops this foreign DNA is in the offspring.

如此一来,如果一切顺利,DNA成功注射进原核,受精卵成功植入代孕母亲,成功的孕育了后代,后代健健康康的长大,目的基因就成功的整合进了后代的基因组

耶鲁公开课 - 生物医学工程探索课程节选