Table 1.

Mutant frequency of HIV-1 among selected cell lines^a

Cell line	Mutant frequency
CEM-GFP	0.11 ± 0.04
U373-MAGI	0.12 ± 0.03
293T	0.11 ± 0.04
SupT1	0.11 ± 0.01

^aTwo million 293T cells were transfected with 10 μg of pHIG and 1 μg of pVSV-G using the calcium phosphate method as previously described (17). The viral supernatants were collected 48 h posttransfection, filtered, and used to infect permissive target cells (1.4 × 10⁶). Twenty-four hours postinfection, the cells were harvested and prepared for flow cytometry as described previously (8). Infected cells, typically 20 to 40% of the total for each target cell line, were analyzed by flow cytometry for expression of two marker genes, coding for HSA and GFP. Mutant frequencies were calculated from the cell population phenotypes identified by flow cytometry using the formula (HSA⁻ GFP⁺)/[(HSA⁻ GFP⁺) + (HSA⁺ GFP⁺)]. For each target cell line, ∼7 × 10⁵ to 9 × 10⁵ cells were identified as infected cells (i.e., HSA⁻ GFP⁺ and HSA⁺ GFP⁺ cell populations) and ∼8 × 10⁴ cells were identified as infected cells with a mutation in the reporter gene (i.e., HSA⁻ GFP⁺).