|Extreme cellular stress can trigger senescence, a mechanism protecting|
against malignant cell transformation.
Adapted from: Kovacic J C et al. Circulation. 2011;123:1650-1660
Given MSCs definition as the plastic-adherent fraction of the bone marrow, and their need to be expanded ex vivo prior to therapeutic administration, age has often been associated with and reported as a function of passage level, or the number of times these cells have been plated onto and harvested from tissue culture plastic. True MSC age, however, is actually related to when these cells will senesce (i.e. stop growing), and this is a function of how many times the cells have divided, or their population doubling level (PDL).