An update on peripheral blood progenitor cell transplantation.

High-dose therapy with stem cell rescue is increasingly being used as a salvage or consolidation therapy for patients with poor-risk malignant disease. The availability of peripheral blood progenitor cells (PBPC) has opened new therapeutic perspectives to alleviate the severe toxicity related to prolonged myelo-suppression. The preferred method of collection is still a matter of much debate. PBPC can be collected in steady state and after chemotherapeutic conditioning, growth factor priming, or both. Usually a heterogeneous population containing both committed progenitors and pluripotent stem cells can be harvested. Studies comparing engraftment after mobilized PBPC with recovery after autologous bone marrow transplantation confirm the beneficial effect on neutrophil and platelet engraftment. The accelerated hematological recovery can be associated with a number of clinical benefits including a reduction of platelet transfusions and shorter hospital stay. Only a few randomized studies are currently available on the long-term outcome after PBPC transplantation. Recent findings on tumor cell mobilization stimulated the development of techniques for tumor cell reduction, based on negative selection ("purging") of tumor cells or positive selection of CD34-positive progenitor cells. Positive CD34 selection is also imperative for successful ex vivo expansion of progenitor cells and gene transfer experiments. The value of PBPC in the field of allogeneic transplantation is currently being examined.