IL-7/M25 requires FcRn, but not FcγR, to induce proliferation of CD8⁺ T cells in vivo. (A) On day 0, 8 × 10⁶ CFSE-labeled CD8⁺ T cells purified from LNs of B6.CD90.1⁺ IL-7tg⁺ mice were adoptively transferred to the indicated B6.CD90.2⁺ hosts. Host mice received 3 intraperitoneal injections (inj.) of rhIL-7 and M25 (1.5 μg and 7.5 μg per injection) or PBS (data not shown) every other day. CFSE profiles of CD90.1⁺ CD8⁺CD44^hi cells from day 7 host LNs are shown and are representative of 2 to 3 independent experiments with 2 separately analyzed mice per treatment. (B) CFSE-labeled CD8⁺ T cells (1.3 × 10⁶) purified from B6.CD45.1⁺ LNs were adoptively transferred to B6.CD45.2⁺ hosts that were either wild-type (WT) or FcRn^−/− (knockout [KO]). Host mice received intraperitoneal injections 3 times (days 1, 3, and 5) of either PBS or 1.5 µg rhIL-7 with or without 7.5 µg M25 or 6 injections (days 1 to 6) of 10 μg rhIL-7. Hosts were euthanized on day 7 and analyzed separately by flow cytometry. Shown here are CFSE histograms (LNs) and numbers of CD45.1⁺CD8⁺ T cells recovered from each host LN and spleen, with horizontal bars indicating the mean of each group. Data are representative of 2 experiments with 2 to 3 mice per treatment. *P < .05; **P < .005.