As before, cell and tissue biological products are not such modern inventions as is commonly perceived. The history of blood transfusion is beyond the scope of this chapter, but was responsible for establishing some of the fundamental concepts in this area. Organ transplantation is both routine and seriously limited in its capacity by the paucity of available organs. The implantation of cultured tissues may be a means of circumventing some of these practical limitations, and extending these therapeutic tactics.
There are various clinical conditions where administration of cultured whole cells or organ tissue may be desirable. The sources of these tissues are as diverse as the disease targets. For example, cultured fibroblasts from human prepuces are being developed as 'artificial skin' for the treatment of leg ulcers and burns (Advanced Tissue Sciences, La Jolla, CA; Organogenesis, MA). Other companies are developing an artificial pancreas from isolated pancreatic islet cells. Unlike matched transplantations, such therapies may involve treatment of large numbers of patients from a limited or sole initial human source, or may be autologous, albeit after some ex vivo manipulation and culturing of the cell mass before reimplantation.
Ex vivo therapeutic strategies may take different forms. Chronic lymphocytic leukemias have been treated for long periods of time by using cell separators to reduce the burden of lymphocytosis, and permit red cell transfusion. Laser-directed cell sorters may be used to select appropriate subpopulations of lymphocytes, which are then transfected with an appropriate gene product ex vivo and returned to the patient, where these cells will hopefully target some diseased tissue, such as widespread melanoma. Expense, availability of therapy, and the duration and specificity of effect may currently limit the widespread application of these approaches.
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