Expression of hCD2 surrogate marker in bone marrow of mice. Doubly transgenic animals were killed, and cells were flushed from the long bones of the hind legs. Flow cytometry was performed as described using either an IgG_k1 isotype control (A-B) or an anti-hCD2 antibody (C-D). Jurkat cells were used as a positive control for anti-hCD2 in all experiments (data not shown). Mice from both founder lines 6468 (A,C) and 6543 (B,D) were included in the analysis. The percentage of positive cells is indicated in each panel.