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While mutations that arise from insertion are a concern with viral systems, lentiviral mutagenesis occurs at a much lower frequency making them a common choice. Most retroviruses insert randomly into the host genome, with a high incidence of insertion into the promoter/repressor regions of a gene causing disruption in the host and possible activation of oncogenes. However, several studies have indicated that this is not a big problem when using Lentivirus, a subset of retroviruses which has led to their utilization in clinical applications such as gene therapy.
If potential insertional mutagenesis is a concern for your experimental set up, consider using an mRNA transfection approach, which has been shown to be effective in hard to transfect cell lines, and usually why lentiviral expression systems are used. While expression will be transient, Lipofectamine MessengerMax reagent may provide you with an alternative to lentiviral infection.