T cells transduced with CD200R_-9aas-CD28_cysenhance adoptive immunotherapy of disseminated leukemia. (A-B) CD200R-CD28 IFP-transduced TCR_gag T cells were generated as described in Figure 2. B6 mice were injected with 4 × 10⁶ CD200⁺ FBL cells. Five days later, CD200R_-9aas-CD28_cys or empty vector control TCR_gag T cells were injected into Cy-treated FBL-bearing B6 mice. The expression of surface markers on splenic CD200R_-9aas-CD28_cys TCR_gag T cells (blue lines), control TCR_gag T cells (red lines), and endogenous T cells (shaded) was assessed by flow cytometry at days 8 (A) and 15 (B) post–T-cell transfer; representative of 2 independent experiments. (C-D) Survival of mice treated with T-cell immunotherapy in the presence (C) or absence (D) of IL-2 injections. B6 mice were injected with 4 × 10⁶ CD200⁺ FBL cells. Five days later, CD200R_-9aas-CD28_cys or empty vector control TCR_gag T cells were injected i.p. into Cy-treated FBL-bearing mice at 10⁵ cells/mouse (indicated by arrow). IL-2 was administered every 2 days for a total of 10 days (2 × 10⁴ U/dose) in a cohort of mice. (C) Data from 1 experiment are shown (n = 3-4 mice/group). (D) Pooled data from 3 independent experiments are shown (No therapy [tx], n = 6; Cytoxan [Cy] only, or Cy plus T-cell treated: n = 9-10 mice/group). Statistical analyses are shown: Cy + CD200R_-9aas-CD28_cys T cells (red) vs Cy + empty vector T cells (blue), *P < .05; Cy + CD200R_-9aas-CD28_cys T cells (red) vs Cy only (black dashed line), ***P < .001); Cy + empty vector T cells (blue) vs Cy only (blacked dashed line), *P < .05).; and Cy only (blacked dashed line) vs No treatment (tx; black), ****P < .001; log-rank Mantel-Cox test.