FIG 4.
Exposition of murine MDTF cells expressing the receptor for GALV (PiT1) or the receptor for KoRV-B (THTR1) to vectors bearing different GALV/KoRV-B envelopes. The structure of a gammaretroviral envelope protein with the surface unit (SU) and the transmembrane subunit (TM) is schematically depicted at the top of the figure underneath which is a depiction of the receptor-binding domain (RBD) located within the surface unit gene. In the schematic representation of the chimeric envelopes, sequences from KoRV-B envelope are in red, and those from GALV-SEATO are in blue. The GALV chimeric envelope within which the VRA of GALV-SEATO was replaced by the corresponding region of KoRV-B is designated GALV-VRAKoRV-B, whereas the GALV-SEATO chimeric envelope containing both KoRV-B VRA and VRB is designated GALV-VRA/VRBKoRV-B. Murine MDTF cells expressing PiT1 or THTR1 were exposed to vectors bearing GALV, KoRV-B, GALV-VRAKoRV-B, or GALV-VRA/VRBKoRV-B envelopes and assessed for susceptibility to these vectors using a conventional β-galactosidase assay. The titers of the viral vectors were averaged from at least three independent experiments and are expressed as mean numbers of β-galactosidase-expressing cells ± the SD of the mean. Panel B demonstrates the ability of GALV (black line), GALV-VRAKoRV-B (green line) and GALV-VRA/VRBKoRV-B (pink line) envelopes, each with a V5 epitope tag, to bind to MDTF cells expressing either PiT1 or THTR1. The binding ability of the vectors was assessed using flow cytometry.