Peripheral blood progenitor cell transplantation: Where do we stand? Chairman's summary of the European School of Oncology Task Force Meeting ‘Peripheral Blood Progenitor Cells’ held September 29–30, 1996

Whether or not peripheral stem cells have an unlimited capacity for self renewal is debated. However, everyday haematopoietic requirements are met by progenitors ; and it seems that few 'real' stem cells are needed. Although we may not yet have identified these 'true' stem cells, for practical purposes the long term culture-initiating cells (LTC-ICs) are a close approximation. To date, experience in peripheral blood progenitor cell (PBPC) transplantation is largely confined to non-ablative regimens. It is therefore difficult to determine the number of PBPCs needed to effect long-term reconstitution. The number of tumour cells present among mobilised PBPCs can be reduced using the CD34 affinity column and by positive purging methods. The ex vivo expansion of CD34 cells also has the effect of diluting tumour cell concentration. In clinical use, PBPC transplantation has a proven role in support of high dose chemotherapy in certain haematological and oncological malignancies but the concept of dose intensification is not universally accepted. With the exception of leukaemia, lymphoma, myeloma or relapsed testicular cancer and possibly some subgroups of breast cancer ; high dose chemotherapy does not demonstrate a survival benefit. For patients with CML, autografting with Ph - cells appears to become a useful alternative to allogeneic BMT. Allogeneic PBPC transplantation may have potential, though work is preliminary. Cord blood transplantation between matched siblings is viable, but it is not yet clear whether this source will increase the donor pool for adults needing allogeneic transplantation. For gene therapy using haematopoietic cells to be effective, a greatly increased rate of transduction will be needed. Meeting in Paris in September 1995, a European School of Oncology Task Force considered a number of important questions relating to peripheral blood progenitor cell (PBPC) physiology and transplantation. This review is a brief account of their conclusions.