Tissue culture: unlocking the mysteries of viruses and cancer

An old dream is realised

Although short term survival outside the body of the beating heart and twitching muscle was known to the ancients, serious attempts to achieve lengthy tissue survival in vitro were possible only in the second half of the 19th century. Among the pioneers were embryologists, who studied the early development of amphibian and avian eggs and began to experiment on “organisers,” soluble messengers that directed organ development. With the advent of cell culture the nature of these growth factors could be elucidated. Modern stem cell research is the most exciting and controversial descendent of this work.

Surgeons had dreamt of organ transplantation since the Middle Ages. In the 1920s and 1930s Alexis Carrel, a French surgeon working at the Rockefeller Institute in New York, collaborated with the aviator Charles Lindberg to overcome the technical challenges of organ perfusion. Their tissue survival studies attracted enormous public interest, fuelled by newspaper reports such as “birthday” notices for one culture of chick embryo cardiac muscle cells. Carrel's earlier Nobel prize for work on surgical anastomoses and his philosophical writings added to the mystique of cell culture, which was reinforced by the extreme precautions needed against contamination.

Only the most determined groups succeeded. Before the second world war Thomas Strangeways and Honor Fell in Cambridge used cell culture as part of their multidisciplinary approach to bone and joint disease, paving the way for the recognition of tissue specific markers, which are now so widely used in diagnostic pathology.

After the second world war the serial subculture of cells was achieved through the use of trypsin to produce single cell suspensions, antibiotics to control contamination, and better growth media, such as the famous “199” with its 64 ingredients. The finite number of divisions achievable in the culture of normal cells contrasted with the “immortality” of cancer cell lines. HeLa, the most famous of these, was derived from the cervical cancer that killed Henrietta Lacks in 1951. Continuous lines were used to develop convenient in vitro methods for testing the efficacy of potential anticancer drugs and the carcinogenic effects of drugs and chemicals. The demonstration of integrated viral genes in many tumours and of similar homologues in normal cells revolutionised concepts of growth regulation. The discovery of mutations in these homologues—the cellular “oncogenes”—in cancer tissues and in the normal cells of family members with an inherited risk of cancer had applications in cancer diagnosis and screening.

By the 1960s, cell culture technology was well established in virology and cancer research. The time was right for the interaction between cell biology and genetics that gave birth to molecular biology. Study of the chromosomes of dividing cultured cells spawned the new discipline of cytogenetics, while work on gene expression began to explain the mechanisms involved in differentiation, which could now be observed in vitro. This ultimately produced skin cultures that could be used for grafting, but its more profound consequences resulted from elucidating the functions of T cells as they proliferated in vitro after stimulation with antigens.

Exquisitely specific antibodies

Fusing cultured benign and malignant cells provided important insight into the control of cell division, and the technique was spectacularly exploited to generate “hybridomas” between myeloma cells and B cells to produce monoclonal antibodies. Immortalised cell lines now provided a potentially unlimited source of antibodies of exquisite specificity for enzyme linked immunosorbent assay and radioimmunoassay, and monoclonal antibodies are now being used in treatment, for instance to treat haematological malignancies.

The ability to transfect cultured cells with DNA gene sequences has allowed us to assign functions to different genes and understand the mechanisms that activate or redress their function. Gene therapy has yet to fulfil its promise, but it may ultimately overtake the many other medical applications of cell culture.

Without cell culture we would lack vaccines against measles, mumps, and rubella and would still be dependent on much more expensive and reactogenic vaccines for polio, rabies, and yellow fever. We would be unable to karyotype patients with suspected genetic disorders or to perform in vitro fertilisation. Antibodies for diagnostic or therapeutic use would be derived from immunisation of whole animals—with much greater variation in titre and specificity than products derived from cells. Our concepts of growth, differentiation, biological ageing, and malignant transformation would be simplistic; and gene therapy and the use of stem cells to repopulate damaged organs or clone individuals would be beyond imagination.