CD4+ T cell responses to interleukin-2 administration in HIV-infected patients are directly related to the baseline level of immune activation.

Background: Intermittent interleukin (IL)-2 administration to human immunodeficiency virus (HIV)-infected patients leads to CD4(+) T cell expansions. The factors potentially affecting these expansions were investigated in the present study.

Methods: A matched (for baseline CD4(+) T cell count) case-control study was designed. Nonresponders (NRs) were defined as patients with a or=50% increase in CD4(+) T cell count at week 24. Immunophenotype, Ki67 and forkhead box protein P3 (FoxP3) expression, and T cell receptor excision circle (TREC) measurements in T cells were evaluated at weeks 0 and 24 in both groups.

Results: Control subjects and NRs did not differ significantly at baseline in age, viral load, CD4(+) T cell count, nadir CD4(+) T cell count, or CD8(+) T cell count. At week 0, NRs had lower TREC levels per 1x106 T cells and higher levels of T cell proliferation and activation than did control subjects. At week 24, both groups experienced decreases in T cell proliferation and increases in CD25 and FoxP3 expression on CD4(+) T cells, with TREC levels per 1x106 CD4(+) T cells decreasing significantly only in control subjects.

Conclusions: Increased immune activation can adversely affect CD4(+) T cell expansions after IL-2 administration. Despite the lack of expansion, other evidence of IL-2-induced biological activity was observed.