It was careful cell characterization, careful in vitro assays, and careful clonal analysis that contributed to the paper's impact, suggests Pittenger, who is now Osiris' director of discovery research. These elements together, he says, demonstrated that human mesenchymal stem cells (hMSCs) could be derived from bone marrow cells. Osiris investigators achieved differentiation into adipocytes (fat cells), chondrocytes (cartilage cells), and osteocytes (bone cells).
Initially, his group sought to generate in vitro assays that would be helpful in understanding cellular differentiation. "We went through a lot of literature, we tried a lot of different methods for differentiating the cells," he explains. "Some worked, some didn't." Then, through trial and error, they found the right combination of hormones, growth factors, vitamins, and serum and the correct methods to get the hMSCs to differentiate into each lineage. For example, to achieve adipocytic differentiation, the cells had to be confluent; whereas, too high a ...
