Mouse T-cell lines of different genetic background allow VSV-G-mediated HIV-1 entry, but restrict CMV-driven gene expression. Results for (A) virion fusion and (B) CMV-driven GFP gene expression for MT-4 (human), TIMI.4, R1.1 and S1A.TB (mouse) T-cell lines from the experiment shown in Fig. 1. Values are the arithmetic mean ± S.D. of triplicates. Panel C depicts the Relative-Post-Entry-Efficiency calculated as the ratio of the percentage of GFP-expressing cells (panel B) divided by the percentage of cleaved-CCF2-positive cells (virion fusion; panel A) × 1000 in arbitrary units. Data are representative for 3–4 independent experiments.