Although there is only a very small chance of creating replication competent virus, steps should still be taken to avoid added risk. The virus is expanded in two rounds of amplification, and all secondary expansions should be performed from an initial expansion stock. Secondary amplifications in HEK293 cells should not be performed from the stock of another secondary expansion, as this could increase the chance of making replication competent virus. See the product manual for more detail and guidelines for screening.
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