Scurfy CD4 T cells engineered with an LNGFR.FOXP3 vector rescue scurfy mice after disease onset. Male scurfy mice (X^Sf/Y.Rag1^+/− on a CD45.2 background) were conditioned by an intraperitoneal injection of 50 mg/kg Cy on day 10 and then received either vehicle, 5 × 10⁵ congenic CD45.1 WT Tregs, CD4^LNGFR transduced scurfy cells, or 0.75 × 10⁶ CD4^LNGFR.FOXP3 transduced scurfy cells on day 14. Next, 1000 IU/g IL-2 were injected intraperitoneally once a day for 5 days and then once a week. Data from at least 2 independent experiments are shown. (A) The mean plus or minus SD scurfy disease score in mice treated with Tregs, CD4^LNGFR, and CD4^LNGFR.FOXP3, vs vehicle-treated mice (P = .01, .26, and .02 in a Mann-Whitney test, respectively) on day 42 (n ≥ 3 per group). (B) All of the mice were euthanized on day 50 for flow cytometry analysis. CD45.1 chimerism was analyzed on day 50 (gated on CD4⁺ T cells) for the lymph nodes, spleen, blood, liver, and lung in mice receiving WT Tregs or PBS. (C) ΔLNGFR chimerism was analyzed on day 50 (gated on CD4⁺ T cells) in the lymph nodes, spleen, blood, liver, and lung in mice receiving CD4^LNGFR.FOXP3 cells, CD4^LNGFR cells, or PBS. The level of chimerism was higher in CD4^LNGFR.FOXP3-treated mice than in CD4^LNGFR-treated mice (P = .001). (D) Survival of scurfy mice from 2 independent experiments. Treatment with IL-2 did not increase survival relative to treatment with Cy or CD4^LNGFR cells. Mice treated with Tregs and CD4^LNGFR.FOXP3 cells survived significantly longer than Cy-treated mice (P < .0001 and .0195, respectively; n ≥ 5 per group). Follow-up was continued up to 110 days. *P < .05; **P < .01; ***P < .001; ****P < .0001.