Isolation and Characterization of Early Lineage Adult Stem Cells from the Synovial Fluid of Osteoarthritis Patients

Adult stem cells (ASCs), which possess the ability to self-renew and regenerate tissue, are of significant value for the development of cellular therapies, tissue engineering tools, and drug screening models. Conventional protocols for ASC enrichment generate a small number of cells that do not represent the total ASC population of tissues. We avoided these conventional methodologies and used a different approach to identify early lineage adult (ELA) stem cells, a subpopulation of ASCs 4-6 µm in diameter, in the synovial fluid of osteoarthritic patients. These cells lack cell surface markers expressed by other ASC (e.g. CD34, CD73, CD105, SSEA-1, CXCR4). However, RT-PCR studies demonstrated expression of pluripotency genes such as NANOG, OCT4, REX1, KLF4, STELLA, and SOX. When cultured in adipogenic, chondrogenic, or osteogenic differentiation media, ELA cells differentiated into fat, cartilage, and bone tissue, respectively. Quantitative PCR analysis revealed unique molecular signatures consisting of tissue-specific and non-tissue specific mRNA in the differentiated tissues, suggesting a continuum of mRNA expression. Furthermore, the ELA cell population shared unique gene sets with embryonic stem cells, mesenchymal stem cells, and induced pluripotent stem cells. Some of these genes are unique to neuronal, cardiac, pancreatic, and hepatic progenitor cells, while others, such as mucins, ICAM, and tetraspans, have tissue-specific cell functions. ELA cells also demonstrated strong in vitro immunomodulatory properties by inhibiting T cell proliferation, inducing CD4+/ CD25+ regulatory T cells, and inhibiting natural killer cell activity. Collectively, these observations suggest that ELA cells might be useful for cell-based regenerative therapies and the treatment of systemic diseases with immunological etiologies.