Injection of R-sIL-7gly rapidly induces major circulating T-cell loss in healthy rhesus macaques. Total lymphocyte (A), CD4⁺ T-cell (B), CD8⁺ T-cell (C), and CD20⁺ B-cell counts (D) were measured over 1 to 7 days in 5 R-sIL-7gly–injected healthy rhesus macaques (no. 14424, ; no. 14694, ; no. 26007-2 and no. 41127-2, ; no. 40885-2, ▲; left panels), in 2 untreated control animals (no. 21045 and no. 26007, ○ and □; right panels), and in an animal previously immunized against simian IL-7 and presenting high levels of neutralizing antibodies that also received R-sIL-7 at day 0 (no. 17021, ♦; right panels). Three monkeys were killed at day 1 (no. 26007-2 and no. 41127-2) or at day 7 (no. 40885-2). Compared with baseline, lymphocyte counts drop reached statistical significance at H24 (P < .05), whereas both CD4⁺ and CD8⁺ counts were significantly reduced at H6, H12 (P < .01), H24, and H48 (P < .05). (E) Evolution of naive, central memory, and effector memory CD4⁺ and CD8⁺ T-cell counts in R-sIL-7gly–injected rhesus macaques (no. 14424 and no. 14694, and ) and untreated controls (no. 21045 and no. 26007, ○ and □).