CD4 and infection: Moreover, viruses produced by the NLENG1-IRES vector are fully infectious and express all viral genes, unlike previously described HIV-1 reporter constructs that are deficient in nef, vpr and/or env. Following exposure of the isolated cell population highly enriched in CD4+ T cells to the viral input used (i.e. 10 ng of p24 per 1 × 105 cells), we found that on average less than 10% of cells are expressing the virus-encoded reporter protein at 5 days post-infection when infection was allowed to proceed with viruses lacking host-derived ICAM-1 (i.e. NL4-3 wt) (Fig. 1B).