Problem: Choosing an in vitro model system that faithfully represents the natural physiology of the cell being studied is fundamental to understanding its in vivo function. Cultures of primary cell isolates retain their physiology and karyotype after isolation, but cultures may be difficult to prepare and are susceptible to contamination. More importantly, primary cells, with few exceptions, do not express telomerase. Without telomerase to maintain them, the telomere ends of the chromosomes shorten with each cell division, leading to telomere-induced replicative senescence. Thus, although primary cells are good models of cellular physiology, they become senescent in vitro before they can be expanded to provide the number of cells needed for biochemical or genetic assays.

Continuous cell lines, on the other hand, are not encumbered by telomere-induced replicative senescence and can be expanded indefinitely, making them ideal for performing biochemical and genetic assays.  Continuous cell lines, however, are often derived from malignant tissue. As a result, they contain numerous genetic mutations, exhibit an unstable karyotype, and have protein expression patterns that may not represent the normal parent cell. Moreover, continuous cell lines representing normal, healthy tissue or non-malignant, genetic diseases like Cystic Fibrosis or Parkinson’s disease are difficult to obtain. Consequently, continuous cell lines represent a narrow range of in vivo cellular function. Therefore, the ideal in vitro model must combine the physiology and stable karyotype of primary cell isolates and the indefinite propagation properties of continuous cell lines, while avoiding the replicative senescence of the former and the spurious genetics and limited reach of the latter.

hTERT Immortalized Retinal Pigmented Epithelial Cells ATCC® No. CRL-4000™stained with a monoclonal pancytokeratin antibody (green) and Hoechst dye (blue)Solution: ATCC offers a wide variety of primary cells that have been immortalized through the forced expression of the hTERT component of the Telomerase gene. Expression of hTERT allows human primary cells to maintain the telomere ends of chromosomes and repress replicative senescence. Analysis of numerous hTERT-immortalized cell lines indicates these cells have a stable karyotype and retain many of the physiological characteristics of the primary cell, including normal phenotypic marker expression. Further, they exhibit normal p53 cell cycle checkpoint control, are non-malignant, contact inhibited, and anchorage dependent. Furthermore, they retain normal growth responses to serum and mitogens, require growth factors for proliferation, and do not show changes associated with transformation, such as tumorigenicity or growth in soft agar.

hTERT Immortalized Hepatocyte Epithelial Cells ATCC® No. CRL-4020™ stained with a monoclonal pan-cytokeratin antibody (green) and Hoechst dye (blue)Importantly, hTERT technology allows for the straightforward development of matched cell lines from normal and diseased tissue. For example, ATCC offers hTERT-immortalized lines with non-malignant, genetic disease origins, such as those derived from the lung epithelium of Cystic Fibrosis patients (ATCC® CRL-4013™, -4015™, -4016™, -4017™). Additionally, these lines may be used experimentally with hTERT-immortalized lung epithelium from normal, healthy control subjects (ATCC® CRL-4011™). Thus, investigators no longer need to settle for primary cell isolates or continuous cell lines and their respective flaws. They now have the option of using hTERT-immortalized primary cell lines to provide a physiologically relevant, continuous cell culture model to build powerful experiments and advance their research.

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