Human MSCs are the single most used cell source for tissue engineering and regenerative medicine applications, and clinical trials involving hMSCs have outpaced all other cell types in recent years (see here and here). However, despite indications of clinical effectiveness (see here and here), there is repeated news of the failure of high-profile MSC trials to demonstrate efficacy in a number of therapeutic applications (see here, here, here, here and here). It has been suggested that the large amount of intra- and inter-donor variability in the MSC populations used in these trials may be responsible for their falling short of expectations despite highly encouraging in vitro and in vivo pre-clinical data.
A team led by Steve Bauer at the US FDA has reported that large variations in proliferation, morphology, differentiation capacity, and cell surface marker expression profiles exist within any population of MSCs and that these intra-population heterogeneities may arise as a result of long-term in vitro culture and the in vivo microenvironment (Free article available here.) In addition, their work has demonstrated that there are inherent differences in MSCs from donors of similar age, and they have noted the “potential for other donor-related factors in MSC biological variability, which may play a role in their clinical usefulness or performance in various model systems.” Other research groups have also corroborated donor-related differences in MSC function, including in response to stimuli, such as challenge with inflammatory cytokines (see here and here). A review article on developing cell therapy manufacturing processes reinforces that several donors should be tested prior to implementing; 1) changes in media composition (such as serum reduction/elimination or addition of growth supplements), 2) extensions of the product dose population doubling level (PDL), or 3) changes in lot size during scale-up.