Figure 1. Synthetic defective interfering viruses.

(A) Three portions of the wild type (WT) SARS-CoV-2 genome were used to create a synthetic defective interfering genome (DI₁) and a shorter version (DI₀) comprising only parts of the two terminal portions. Numbers delimiting the portions refer to positions in the SARS-CoV-2 genome. The first position is mutated (A →C) in both DI₁ and DI₀. Open rectangles show the position of the probes and primers used. (B) To produce synthetic DI particles, DNA constructs corresponding to the RNA sequence of DI₁ or DI₀ were transcribed into RNA in vitro using T7 RNA polymerase and transfected into Vero-E6 cells that were then infected with SARS-CoV-2. The supernatant from these cell cultures was used to infect new cells.