MSCs equally inhibit CD8⁺, CD4⁺, and B cells. (A) C57BL/6 (5 × 10⁶) splenocytes were stained with 1.7 μM of CFSE and were stimulated by anti-CD3/CD28–coated Dynal beads (5 × 10⁵/mL) in the presence or absence of MSCs (1 × 10⁵). After 3 days, T-cell proliferation was assessed by CFSE intensity gated within CD8⁺ or CD4⁺ T cells. FACS plots are representative of 1 of 3 experiments of identical design. Percentages refer to the proportion of cells that have undergone at least 1 cycle. (B) B-cell splenocytes (1 × 10⁵), obtained by removing T cells using antimouse Thy1.2 Dynal beads, were stimulated with anti-CD40 mAb (2 μg/mL) and IL-4 (10 μg/mL) in the absence (▪) or presence (□) of MSCs (1 × 10⁴) (right). As a comparison, unfractionated C57BL/6 splenocytes (1 × 10⁵) were stimulated with 10 μg/mL ConA in the presence or absence of (1 × 10⁴) MSCs (left). ³H-Tdr was added to cultures on day 2, and cell proliferation was assessed on day 3. Results are the average of 3 experiments of identical design; bars show the SD. ^*Statistically significant (P < .01)