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The use of cytokines to improve gene transfer to human hematopoietic stem cells.

The introduction of a new gene into the DNA of a hematopoietic stem cell (HSC) offers the potential for permanent repopulation of a host with functionally modified stem cells and their progeny. At present, retroviral vectors are the only integrating agents available for clinical use. Because these vectors function only in dividing cells, cycling of the target cell is a current requirement for permanent gene transfer. Few HSC are in cycle, so until clinical-grade vectors are developed that integrate in resting cells, stimulation with cytokine combinations will likely be an important component of successful gene therapy protocols. The relationship between cytokines and gene transfer may be of benefit in another way. Marker genes can be used to analyze the effects of cytokines on HSC growth and differentiation. Since two or more distinctive markers can be added to separately treated portions of the HSC, it is possible to compare simultaneously in a single individual the effects of multiple ex vivo cytokine treatments on subsequent HSC engraftment. This approach should greatly simplify the development of optimal ex vivo expansion regimens for accelerated and permanent engraftment in patients receiving infusions of HSC.