Di Lullo G, Soprana E, Panigada M, Palini A, Agresti A, Comunian C, et al. The combination of marker gene swapping and ﬂuorescence-activated cell sorting improves the ef ﬁciency of recombinant modi ﬁed vaccinia virus Ankara vaccine production for hum an use. J Virol Methods 2010;163: 195 –204.