Reversion of a polymerase-defective integrated HIV-1 genome

The 8E5 clonal cell line, derived from HIV-1-infected CEM cells, carries a single, reverse transcriptase (RT)-defective copy of an integrated HIV genome. The absence of RT production is a consequence of a frame shift in the pol gene, due to the addition of a single base at position 3241. We report here that 8E5 cells produce an infectious virus that can be serially passaged on CD4+ lymphoid cells. This virus (8E5R) is RT positive, but displays a slow replication profile, together with a reduced cytopathic effect. The nucleotide sequence of a segment of the pol region produced by PCR amplification of DNA from 8E5R-infected cells shows that the single nucleotide insertion characteristic of the 8E5 genome had been corrected. The same reversion event was also found to occur in most single-cell clones derived from the 8E5 cell line. Because this cell line is used in many laboratories, notably as a standard for PCR quantitation, and is generally considered as unable to produce infectious virus, our findings should prompt investigators to use particular care in the handling of these cells.