Detection of NTP expression by FACS analysis in retrovirally transduced human primary T lymphocytes. On the X-axis, staining of the mutated LNGFR; on the Y-axis, staining of CD3 in (A), (B) and (E) through (H); CD4 in (C); and CD8 in (D). The PBMC were infected 10 days earlier with PG13 supernatant in (A) and with PG13/NTP6 supernatant in (B) through (D). In (E) through (H), the PBMC were infected with a 1:300, 1:3,000, 1:30,000, and 1:300,000 dilution of the concentrated 293gpg/NTP7 stock, respectively, and stained 10 days thereafter. The percentage indicated in the upper right quadrant is the percentage of NTP⁺ cells among the CD3⁺, CD4⁺, or CD8⁺ cells.