Association with an IgG Fc improves in vivo mitogenic effect of IL-7 on CD8⁺ T cells. (A) B6.CD45.2 hosts received intravenous injections of 4.5 × 10⁶ CTV-labeled B6.CD45.1⁺ LN cells on day 0 and intraperitoneal injections on days 1, 3, and 5 of rhIL-7 (1.5 μg), rhIL-7/M25 (1.5 μg/7.5 μg), or IL-7-Fc (in vitro activity equal to 1.5 μg rhIL-7). Shown here are CTV histograms of CD45.1⁺ TCRβ⁺CD8⁺ cells from host LNs analyzed at day 7 representative of at least 3 experiments with 2 separately analyzed mice per treatment group. (B) CD8⁺ cells were purified from LN of B6.CD45.1⁺ donors, CFSE-labeled, and adoptively transferred (1.8 × 10⁶ per host) by intravenous injection to CD45.2⁺ hosts, either wild-type or FcRn^−/−, at day 0. Hosts received intraperitoneal injections on days 1, 3, and 5 of PBS alone, rhIL-7/M25 (3 μg/15 μg), or IL-7-Fc (equivalent of 3 μg rhIL-7). The number of CD45.1⁺ TCRβ⁺CD8⁺ cells recovered from host LNs and spleen at day 7 is shown (2 mice per group ± SEM). Results are representative of 2 experiments with 2 to 3 separately analyzed mice per group. *P < .05; **P < .005; ns, not significant.