Titers of MLV and HIV-1 vectors bearing XMRV Env and truncation mutants.

The MLV titers were determined as described in Table 1 except HTX cells were used for infection. For HIV-1 lentiviral vectors, 293T cells were transfected with a plasmid encoding HIV-1 Gag-Pol, an HIV-1 vector expressing GFP and a plasmid expressing XMRV Env or truncation mutant. Virions were harvested 48–72 h post-transfection, and used to infect HTX cells. Titers were determined by detecting GFP+ cells 48 h post-infection. Results of a typical representative experiment are shown. Experiments were repeated three times, with similar titers obtained.