Evaluation of the efficiency of GALV cell-cell transmission in co-culture experiments with MDTFPiT1 cells productively infected with GALV expressing GFP (GALV-GFP). MDTFPiT1 cells were exposed to GALV-GFP and then maintained and cultured for one week before being analyzed by FACS for GFP expression (A). Next GALV-GFP producer cells were co-cultured with MDTF cells expressing an HA epitope tagged PiT1 and analyzed by FACS for GFP and HA expression (B) or MDTF cells expressing the HA epitope tagged mutant receptor PiT2K522E and analyzed by FACS for GFP and HA expression (C). Approximately 24 hours after co-culture, cells were harvested for FACS analysis. The MFI of HA expression is indicated on the y-axis and the MFI of GFP expression is on the x-axis. Three independent experiments were performed and representative images presented.