Ex vivo expansion of haemopoietic progenitor cells.

Over the last few years, techniques have become available that allow the extensive proliferation of haemopoietic progenitor cells in ex vivo culture systems. The most commonly used method involves a simple liquid suspension culture system supplemented with a range of cytokines. Alternatively, more complex systems have been devised in which the formation of a stromal layer is required. Large increases in total cell numbers and committed progenitor cells can be readily obtained and, with some techniques, significant expansion of primitive haemopoietic cells has been demonstrated. Although these strategies have several potential applications, few clinical studies have been performed. It has been shown that infusion of ex vivo cultured cells is well tolerated with no associated toxicity. However, it is still unclear whether these culture systems sustain sufficient numbers of long-term repopulating cells to secure durable engraftment following myeloablative therapy. In gene therapy studies, ex vivo expansion of stem cells should improve the efficiency of gene transduction to enable the production of genetically modified cells that are capable of expressing the gene of interest for extended periods of time.