Cytokine enhancement of peripheral blood stem cells

The use of cytokines to improve peripheral blood stem cell enhancement and recruitment has recently received close attention. Three main cytokines have been, or are still being, investigated in this way in human clinical trials so far: recombinant human granulocyte-macrophage colony stimulating factor (rhGM-CSF), granulocyte CSF (rhG-CSF) and interleukin 3 (IL-3). While cytokines used alone appear undoubtedly capable of a marked peripheral blood stem cell (PBSC) enhancement, their combination with a chemotherapy priming often increases this phenomenon. This is particularly evident with rhIL-3, which is an earlier acting cytokine than rhGM-CSF and rhG-CSF. rhIL-3 priming alone leads to only a minor elevation of circulating progenitor cells, while its combination with chemotherapy and/or a late acting cytokine may allow enhancement and recruitment of large amounts of PBSC. The effect of cytokines on PBSC enhancement may also be at least partially thwarted by various factors. Additionally, their adequate dosage often remains uncertain. So it is presently too early to determine what is actually the most appropriate cytokine or cytokine combination to improve PBSC enhancement. Also the risk of stimulation of tumor clonogenic cells in some malignant diseases remains, and the experimenters should be as cautious as possible to not jeopardize the patients' safety.