Possible mechanism of toxicity of zidovudine by induction of apoptosis of CD4+ and CD8+ T-cells in vivo.

Some HIV-infected patients have a discordant response to highly active antiretroviral therapy with a low virus load and an incomplete restoration of CD4+ T-cell counts. Zidovudine may limit CD4+ restoration by a hematotoxic mechanism. Apoptosis and T-cell counts were assessed in two patients before and after they switched from zidovudine to stavudine. Whereas CD4+ T-cell apoptosis fell from 52% and 66% before the zidovudine switch to 7% and 12%, respectively, after the switch, the patients' CD4+ counts rose gradually to +183 and +150 cells, respectively. It was therefore hypothesized that zidovudine directly induced apoptosis. Zidovudine withdrawal could be tested before immunological interventions such as interleukin-2 therapy are considered.