Chimeric recipients of allogeneic BM and syngeneic MSCs do not respond to donor and host antigens. (A) Splenocytes from chimeric BALB/c recipients of B6 BM and BALB/c MSCs (n = 5; left) and BALB/c recipients of B6 BM only who rejected allogeneic BM (n = 5; right) were isolated 4 months after transplantation. Recipient splenocytes were stimulated with D1 cells, B6 splenocytes, or BALB/c splenocytes for 4 days. Results are expressed as the mean (± SD) obtained from triplicate cultures. (B) CTL responses were generated by incubation of recipient splenocytes (3 × 10⁶) with D1 cells (10⁴) for 6 days. CTL activity was measured in a cytotoxicity assay using targets of H-2K^b haplotype (RMA). Values represent means (± SD) of triplicates.