Production of new T cells by thymus in children: effect of HIV infection and antiretroviral therapy.

The decrease in the number of CD4(+) T cells during HIV infection is the result of both peripheral destruction of cells by the virus and inadequate replacement of these cells. Aging and HIV infection lead to lower production of new T cells by the thymus, and, therefore, a complete restoration of the immune system is not generally achieved in infected adults after antiretroviral therapy. Because children have a completely functional thymus, we addressed the effects of HIV-1 infection on the production of new T cells in vertically infected children and whether the decrease of viral load after therapy results in a restoration of thymic function. To analyze the thymic function, T-cell receptor rearrangement excision circles were measured by quantitative PCR. Our results indicate that HIV-infected children have lower T-cell receptor rearrangement excision circle levels than age-matched uninfected children, likely due to an inhibitory effect of HIV on thymic function. Additionally, in some patients, the decrease in viral load after retroviral therapy allows the generation of new T cells by the thymus, thus recovering the normal number of CD4 cells.