Donor T cells show decreased velocity, low displacement ratios, and early engagement with DCs in LNs 2 hours after transplant. Intravital imaging of donor T cells (labeled with CMTPX) and host DCs in the popliteal LNs of irradiated or naïve CD11c-DTR-EGFP mice (BALB/c background). (A) Still images from the movies of 2, 8, 19, and 24 hours (hrs) posttransplant. Red cells are donor T cells and green cells are DCs. (B) Instantaneous velocity of donor T cells at 2 and 8 hrs after transplant. Median values are indicated by arrows. Allogeneic (filled bar): donor T cells and BM cells from C57BL/6 mice. Syngeneic (open bar): donor T cells and BM cells from BALB/c mice. Syngeneic–no conditioning (dashed bar): donor T cells from BALB/c mice transferred into naïve nonirradiated CD11c-DTR-EGFP mice. (C) Time course of mean velocity of donor T cells from 2 to 26 hrs after transplant. (D) Displacement ratio (displacement/total track length of 30 minutes) of donor T-cell movement from 2 to 26 hrs after transplant. (E) Contact time between allogeneic donor T cells and host DCs at various time points posttransplant compared with syngeneic T-cell controls. The red bars in all graphs represent median values. Asterisks indicate statistically significant differences between 2 time points or conditions (*P < .05). Data are representative of 3 separate experiments, with 1 or 2 mice imaged per condition per experiment.