Complex sentence: An important variant of this cell line is the 293T cell line that contains the SV40 Large T-antigen, that allows for episomal replication of transfected plasmids containing the SV40 origin of replication.
Split into simpler sentences: An important variant of this cell line is the 293T cell line. It contains the SV40 Large T-antigen that allows for episomal replication of transfected plasmids containing the SV40 origin of replication.