Expression Systems ATCC Expression Systems match reliable, authenticated cells with their ideal media and reagents to create optimized, easy to use systems for protein expression and virus propagation. Serum-Free HEK Cell Systems The HEKPlus Expression System is an all-in-one system that combines HEK 293T/17 SF suspension cells, with xeno-free, serum-free culture medium, the GeneXPlus transfection reagent, and the HEKPlus boost reagent. Serum-Free VERO Cell System The new Vero-SF-ACF is adapted to grow in serum-free, animal component-free media, such as VeroPlus SFM and provide the ideal host for the in vitro propagation of viruses.