In vivo testing of RQR8. C57BL/6 splenocytes were retrovirally transduced to express RQR8 and selected to >90% purity with Miltenyi CD34 beads. Approximately 1.5 million of these cells were injected IV into 5-Gy radiograph preconditioned C57BL/6 × BALB/c cross (F1) recipients. Seven days posttransfer, engraftment was assessed by peripheral blood. ritux-mIgG2a therapy commenced with 150-μg doses at days 7, 10, and 12 by IV injection or phosphate-buffered saline carrier for the control cohort. Each cohort had 5 mice. An additional 2 mice were irradiated but given neither T cells nor ritux-mIgG2a. Animals were sacrificed at day 14, and engraftment was assessed by considering the proportion of QBEnd10-positive T cells as a proportion of the T-cell population. (A) Peripheral blood marking levels in control and in treated mice. (B) Flow cytometry of the T-cell population in spleen showing RQR8 vs CD8 in mice not receiving transgenic T cells and control and rituximab-treated mice. (C) Percentage marking in lymph nodes, bone marrow, blood, and spleen.