Development of in vitro resistance to macrophage-tropic- and T-cell-line-adapted HIV-1 strains among HIV-positive volunteers treated with highly active antiretroviral therapy.

We have described a peripheral blood mononuclear cell (PBMC) culture system in which control of endogenous virus and resistance to exogenous HIV-1 correlates with low viremia among HIV-1-positive people. Nineteen patients remained consistently resistant or susceptible for more than 5 years of follow-up. On the fifth year, 5 consistently susceptible volunteers with high viral loads began receiving highly active anti-retroviral therapy (HAART). After >6 months on HAART, 5 of 5 became completely or predominantly resistant on four visits over the next 6 months. Among HIV-1-positive donors, we had never observed reversal of PBMC phenotype from consistently susceptible to consistently resistant. Resistance correlated with suppression of plasma viremia and rebound in CD4 + T-cell counts and percentages. When resistant PBMCs were challenged after CD8 + T-cell depletion, 38 of 41 and 40 of 59 cultures became susceptible to HIV-1 MN and HIV-1 BaL , respectively. After combined CD8 + T-cell depletion and antibody neutralization of β-chemokines, 16 of 18 cultures became susceptible to HIV-1 BaL . Overall, the finding that >90% of these cultures depleted of relevant antiviral effector arms could become infected indicates resistance was not due to residual antiretroviral drug metabolites in vitro. For 2 volunteers who discontinued therapy because of side effects, pretreatment viral load correlated with loss of in vitro resistance and viral rebound. In addition to resistance to laboratory strains of HIV-1, all patients developed resistance to at least one of two CCR5-tropic, clade B primary isolates: HIV-1 P15 and HIV-1 P27 .