Bone Marrow-Derived Clonal Mesenchymal Stromal Cells with Smaller Size Have Higher Proliferation Capacity

Objective: Production of clonal mesenchymal stromal cells (cMSCs) from a single colony-forming unit is among the best prosperous methods to obtain a homogenous population of MSCs with the endeavor of high passage number. To find the best passageable clones we have to passage tens of clones for more than two months, which is so time and cost consuming. Therefore, we put emphasis to find a factor that can predict the high-proliferative clones.Materials and Methods: In this study, ۹۳ clones were isolated from the bone marrow aspirations of three healthy donors with signed consent. After screening, the best-selected clones were assessed by immunophenotype, differentiation potential, karyo-type, and tumorgenicity. We profiled the cell size of different clones at passage number two using an automated cell counter(TC۲۰). The histograms drawn by this machine were carefully analyzed.Results: Based on our data, clones with the cell size in the range of ۱۰-۱۴, ۱۴-۱۸, ۱۸-۲۲, ۲۲-۲۶, and ۲۶-۳۰ micrometer could reach to passage number ۱۲-۱۵, ۹-۱۲, ۶-۹, ۳-۶ and ۲-۴, respectively. The data shows that there is a significant reverse relationship between the size of cMSCs in passage number two and the passage ability of the clones. Here, four clones could reach passage number ۱۵ which all of them were at the range of ۱۰-۱۴ micrometers. Morphology, expression of standard MSC markers, and differentiation potential of these cMSCs at passage number ۱۵ were normal. Moreover, their karyotype has shown no abnormality and no tumors were made in three months after injection to nude mice.Conclusion: Accordingly, cell size can be used as a novel ro-bust criterion to predict the best proliferative cMSCs in the cell manufacturing units.