Enforced expression of cyclin D2 enhances the proliferative potential of myeloid progenitors, accelerates in vivo myeloid reconstitution, and promotes rescue of mice from lethal myeloablation

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Abstract
Severe and prolonged cytopenias represent a considerable problem in clinical stem cell transplantations. Cytokine-induced ex vivo expansion of hematopoietic stem and progenitor cells has been intensively explored as a means of accelerating hematopoietic recovery following transplantation but have so far had limited success. Herein, overexpression of D-type cyclins, promoting G0/G1 to S transition, was investigated as an alternative approach to accelerate myeloid reconstitution following stem cell transplantation. With the use of retroviral-mediated gene transfer, cyclin D2 was overexpressed in murine bone marrow progenitor cells, which at limited doses showed enhanced ability to rescue lethally ablated recipients. Competitive repopulation studies demonstrated that overexpression of cyclin D2 accelerated myeloid reconstitution following transplantation, and, in agreement with this, cyclin D2–transduced myeloid progenitors showed an enhanced proliferative response to cytokines in vitro. Furthermore, cyclin D2–overexpressing myeloid progenitors and their progeny were sustained for longer periods in culture, resulting in enhanced and prolonged granulocyte production in vitro. Thus, overexpression of cyclin D2 confers myeloid progenitors with an enhanced proliferative and granulocyte potential, facilitating rapid myeloid engraftment and rescue of lethally ablated recipients.