In vivo treatment with IL-7 induces α4β7 in humans. (A) Expression of α4β7, CXCR4, CD127, CD95, and CD25 as analyzed by flow cytometry in circulating T cells derived from HIV-1–infected individuals under antiretroviral therapy before and after in vivo injection of the indicated doses of IL-7 or placebo. Naive and memory CD4⁺ and CD8⁺ T-cell populations were separately analyzed by multicolor staining and individual gating. For all markers except CD25, each dot represents the percentage increase in expression (MFI) from baseline after the indicated treatment for each of the subjects studied; for CD25 (for which MFI values could be misleading because of a marked shift in fluorescence intensity restricted to a minor subpopulation of cells), the percentage of positive cells is presented. Posttreatment samples were obtained on days 4, 7, or 14 after IL-7 administration (supplemental Table 1), except for the single patient treated with 30 μg/kg of IL-7 from whom the sample (indicated by the asterisk) was obtained at 24 hours. (B) Expression of α4β7 in naive and memory CD4⁺ T cells from 2 representative individuals before and after treatment with a low (Patient 4; 3 μg/kg) or high (Patient 11; 60 μg/kg) dose of IL-7. The shaded histograms denote the staining in posttreatment samples; the empty profiles denote the staining in pretreatment samples.