These limitations were overcome by the rescue of infectious LCMV progeny entirely from cloned cDNAs using either a T7 RNA polymerase (RP) (Sanchez and de la Torre, 2006) or pol-I RP (Flatz et al., 2006) system to launch intracellular synthesis of S and L genome, or antigenome, RNA species that were subsequently replicated and transcribed by the virus polymerase complex reconstituted intracellularly via plasmid-supplied L and NP (Fig.