The effect of extended first passage culture on the proliferation and differentiation of human marrow-derived mesenchymal stem cells.

Human marrow-derived mesenchymal stem cells (hMSCs) have been investigated for more than 20 years. They have been shown to be therapeutic in a number of animal models and are currently in use in more than 200 clinical trials, thus documenting their importance in the field of translational medicine. Standard protocols for the passage and collection of hMSCs involve trypsinization of preconfluent cultures. This practice is based, at least in part, on concerns that the multipotency of these cells would be diminished if the cultures became confluent. To test this concern, hMSCs were isolated and maintained in standard culture conditions in primary culture and were then subcultured after 2 weeks. The resulting first passage cultures were divided into two groups: those that were subcultured at the normal frequency, usually at 7 days for each passage (referred to as standard conditions [SC]), and those that were maintained for up to 53 days without being further subcultured (extended first passage [EFP]). At the end of the second passage and each of five subsequent subcultures for cells in SC (i.e., through passage 7), complementary EFP cultures were also trypsinized. Cells from each group were counted, resuspended in serum-free medium, and assayed to determine the ability of the cells to differentiate along osteogenic, chondrogenic, and adipogenic lineages. Cells in SC experienced an average of 27 population doublings through seven passages, whereas hMSCs in EFP achieved approximately 16 population doublings after 34 days but demonstrated very little increase in cell number after that time. The ability of hMSCs in EFP to produce bone in ceramic cubes implanted subcutaneously in immunocompromised mice and to differentiate into cartilage in pellet or aggregate culture was at least equivalent to that of the cells in SC through seven passages, whereas the capacity of the EFP hMSCs to produce lipid droplets in adipogenic conditions was maintained but was diminished relative to that of SC cells.