Primary cells are mammalian cells that are harvested directly from living human or animal tissues. They differ from stem cells in that non-stem primary cells are typically terminally differentiated and are therefore considered closely representative of the tissues from which they are isolated, particularly where characteristics of cancer biology may make cancer cell lines less predictive models of normal systems or noncancer pathologies. Common primary cell phenotypes include epithelial, endothelial, keratinocytes, melanocytes, fibroblasts, osteoblasts, myocytes, and hepatocytes.
Like cell lines derived from tumors or immortalized by other methods, primary cells from human or animal sources provide a method for modeling biological systems. Because they are typically viable for fewer doublings, primary cells are less susceptible to the loss of tissue-specific traits that can characterize cells cultured over long periods of time and repeated passages in vitro. Primary cells may be documented with donor characteristics, including age, gender, and disease state where applicable, and may therefore prove useful models for the development of personalized medicine approaches.
Research institutions associated with hospitals may have access to primary tissues and cells. Primary cell suppliers offer cell lots from individual donors or cells pooled from multiple donors. Reputable suppliers or patient collection protocols should include documentation demonstrating ethical oversight for the isolation of cells from human donors, as well as validation of cell type. Primary cells differ from mammalian cell lines in that they are generally more fastidious, requiring extra nutrients, particularly when cultured in media that is low in serum or serum-free. These additional, defined nutrients include cytokines and growth factors.