Gene transfer in primary T lymphocytes infected with VSV-G–coated virions. (Upper panel) One million lymphocytes were infected with VSV-G virions at a multiplicity of infection of 100 as described in Fig 2. Cells were analyzed for NTP expression 3 days after infection (left panel) and 10 days after infection (right panel). (Middle panel) CD3⁺ cells were sorted on day 4 in three groups: NTP⁻ cells (N), NTP^lo cells (L), and NTP^hi cells (H). (Lower panel) Southern blot analysis of the three sorted fractions. See Figs 1 and 3 for assay conditions and copy number controls. The N fraction shows virtually no vector signal. The L fraction shows a faint band, indicating that a majority of the cells in this fraction do not have integrated viral sequences. The H fraction shows a strong signal, corresponding to about 1 vector copy per cell.