MSCs abrogate T-cell proliferation in response to antigen stimulation. C6 splenocytes (5 × 10⁶) were stained with 1.7 μM CFSE and were stimulated with K^k-restricted HY peptide (HY K^kSmcy)–pulsed syngeneic APCs (5 × 10⁶) in the presence or absence of MSCs (1 × 10⁵). After 24, 48, and 72 hours, cells were harvested and T-cell proliferation was assessed using cytofluorometry with anti-CD8 mAb and CFSE intensity. FACS profiles are gated on CD8 T cells in the absence (A) or presence (B) of MSCs. FACS plot is representative of 1 of 3 experiments of identical design.