The MSC inhibitory effect is transient.

(A) Spleen cells from C6 transgenic (naive) mice were stimulated for 24 hours with HY K^kSmcy(TENSGKDI) peptide-pulsed APCs (▪). Cells were then harvested, washed, and restimulated with the same peptide for an additional 24 hours (■). (B) The same responder cells (C6 transgenic) were stimulated for 24 hours with HY K^kSmcypeptide-pulsed APCs in the presence of MSCs (MSC/R ratio = 1:10; ▪). Cells were then harvested, depleted of MSCs by CD106 antibodies and Dynabeads before restimulation with the same peptide (■). The y-axis reports the percentage of IFN-γ–producing CD8⁺ T cells. The results reported are the average of 3 experiments of identical design. The bars show the SD. * indicates statistically significant (at least P < .01) versus control cultures containing MSCs (panel A, ▪) in all experiments. The comparison between the restimulation of C6 cells with HY K^kSmcy peptide (■) previously stimulated with the same peptide in the presence (B) or absence (A) of MSCs was not statistically significant. The bars show the SD.