Virus-free survival and down-regulation of CD4 in C8166 cells infected with human immunodeficiency virus type 1 at low density

Compared with other T cell lines, C8166 lymphocytes are particularly susceptible to human immunodeficiency virus (HIV) infection and the outcome is invariably cell death. The results reported in this study demonstrate that the virus-induced cytolysis is strongly dependent on the initial cell density of C8166 cultures. Cultures diluted to 50 to 500 cells/ml almost completely maintained their cell duplication rate and released infectious virus into the medium. HIV infection of diluted C8166 cells is a simple and easily reproducible procedure for obtaining persistently infected cultures. These cultures contained genomic and extragenomic HIV DNA, the latter being assayed by PCR for two-long terminal repeat circular forms. The status of persistent infection disappeared within 2 months. The recovery is due to the replacement of CD4 down-regulated infected cells by overgrowing uninfected cell variants, which are transcriptionally inactive for CD4. The mechanisms underlying the emergence of these variants in persistently infected cultures are considered.