Are mesenchymal stromal cells from children resistant to apoptosis?

Mesenchymal stromal cells (MSC) represent a novel cellular candidate in the field of transplantation and tissue regeneration. Their clinical application requires their in vitro expansion. The aim of this study was to assess the effect of conditions that would favour apoptosis, and of long-term expansion, on the characteristics of MSC from children.

Bone marrow mononuclear cells were cultured for 10 passages (P1-P10). Expression of CD105, CD146, CD95 and apoptosis by 7-amino-actinomycin D staining were evaluated. CFU-F and cell doubling time (DT) were assessed in every passage. Cell-cycle study was performed at P2 and P6.

CFU-F decreased from 38 +/- 3.7 at P2 to 9.6 +/- 3.2 per 10 MSC/cm(2) at P10 and DT increased from 1.93 +/- 0.1 (P2) to 6.1 +/- 2.45 days (P10). A low percentage of apoptotic (dead) cells was detected at P2 and this did not change until P10. Cells at P2 were at G(0)/G(1) phase, but in advanced passages more cells were in an active state. Induction of apoptosis (addition of anti-Fas agonist antibody) using standard culture conditions, showed a minor effect on MSC survival. Serum deprivation of MSC (up to 72 h) revealed no substantial apoptotic effect while cells retained their tri-lineage differentiation capacity.

We conclude that MSC from children retain their functional characteristics throughout serial passages and remain stable under conditions that usually cause apoptosis. These features render MSC, especially those of early passages, optimal candidates for use in clinical applications.