Stem cells
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Granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-3 (IL-3) are functionally related hematopoietins with overlapping but distinct hematopoietic effects. GM-CSF supports more myeloid progenitor cells, whereas IL-3 promotes more erythroid, megakaryocytic and multipotential progenitor cells. Their complementary in vivo biological effects and cross competition for receptor binding prompted the development of PIXY321, a synthetic hybrid protein of GM-CSF and IL-3. ⋯ Based on these preclinical observations, clinical trials have been initiated examining the therapeutic potential of this agent in ameliorating treatment- or disease-related hematopoietic suppression. The early results indicate that PIXY321 can stimulate multilineage hematopoiesis in vivo and enhance neutrophil and platelet recovery following chemotherapy and bone marrow transplantation (BMT). These results suggest that PIXY321 elicits the biological effects of both its component cytokines and represents a novel means of delivering two independent but interactive cytokines in combination.