Inhibition of RAR signaling in donor T cells increases Tregs in vivo. Lethally irradiated BALB/c recipients were transplanted with B6 10⁷ BM cells and 1.5 × 10⁶ dnRARα (open circles) or dnRARα-CD4^Cre (filled circles) purified T cells. (A) The frequency of CD4⁺Foxp3⁺ cells and the absolute number of CD4⁺Foxp3⁺ cells in spleen are shown. (B) Liver cells and colon lamina propria lymphocytes were isolated on day 14 and analyzed using fluorescence-activated cell sorter. The frequency of CD4⁺Foxp3⁺ cells is shown. (C) Lethally irradiated BALB/c recipients were transplanted with CD45.2⁺ TCD B6 10⁷ BM cells and 1 × 10⁶ CD45.1⁺ B6 T cells along with 1 × 10⁶ CD45.2⁺ T cells from either dnRARα (CD45.1 with dnRARα) or dnRARαCD4^Cre (CD45.1 with dnRARα-CD4^Cre) mice or were transplanted with CD45.2⁺TCD-B6 10⁷ BM cells and 2 × 10⁶ dnRARα-CD4^Cre T cells alone. The percentages of chimerism of CD4⁺ cells and frequency of CD4⁺Foxp3⁺ cells gated on CD45.2⁺ (dnRARα or dnRARαCD4^Cre) or CD45.1⁺ cells in spleens on day 14 after BMT are shown. (D) Lethally irradiated BALB/c recipients were injected with 10⁷ BM cells and 5 × 10⁶ CD25-depleted splenocytes or CD25-replete splenocytes from either dnRARα or dnRARα-CD4^Cre donors and monitored for survival. (A-D) Data were obtained from 1 experiment each with 4 (A-B), 4 to 5 (C), or 8 (D) mice per group. *P < .05; **P < .01; and ***P < .001.