Residual low-level viral replication could explain discrepancies between viral load and CD4+ cell response in human immunodeficiency virus-infected patients receiving antiretroviral therapy.

We report the evolution of chronic infection with human immunodeficiency virus type 1 (HIV-1) in a patient treated with stavudine plus didanosine, whose CD4+ lymphocyte count progressively decreased, despite a sustained plasma viral load <20 copies/mL. After 12 months of therapy, treatment was switched to zidovudine plus lamivudine plus nelfinavir. CD4+ T cell count decreased from 559 x 10(6)/L at month 0 to 259 x 10(6)/L at month 12. Plasma viral load decreased from 21,665 HIV-1 RNA copies/mL at baseline (month 0) to <20 copies/mL after 1 month of therapy with stavudine plus didanosine, and remained below 20 copies/mL until month 12, but always >5 copies/mL. Viral load in tonsilar tissue at month 12 was 125,000 copies/mg of tissue. After the change to triple-drug therapy, the plasma viral load decreased to 5 copies/mL, the CD4+ T cell count increased to 705 x 10(6)/L, and the viral load in tonsilar tissue decreased to <40 copies/mg of tissue at month 24. A low level of HIV-1 replication could explain the lack of immunologic response in patients with apparent virological response.