The OX40⁺ cells are negative for RT7.1 and are therefore of donor allotype. The OX40⁺ cells (solid histogram) are negative for RT7.1, which indicates they possess the donor allele. The control F1 lymphocytes (open histogram) were positive for RT7.1, indicative of Lewis or (Lewis × Buffalo)F1 cells. The cell lines were stained on day 3 (spleen), day 10 (skin), day 14 (lymph node), and day 14 (liver) postsorting.