PERIPHERAL-BLOOD PROGENITOR-CELL TRANSPLANTATION - WHERE DO WE STAND - CHAIRMANS SUMMARY OF THE EUROPEAN-SCHOOL-OF-ONCOLOGY TASK-FORCE MEETING PERIPHERAL-BLOOD PROGENITOR CELLS HELD SEPTEMBER 29-30, 1995 - INTRODUCTION

Whether or not peripheral stem cells have an unlimited capacity for se lf renewal is debated. However, everyday haematopoietic requirements a re met by progenitors; and it seems that few 'real' stem cells are nee ded. 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 p rogenitor cell (PBPC) transplantation is largely confined to non-ablat ive regimens. It is therefore difficult to determine the number of PBP Cs needed to effect long-term reconstitution. The number of tumour cel ls present among mobilised PBPCs can be reduced using the CD34 affinit y column and by positive purging methods. The ex vivo expansion of CD3 4 cells also has the effect of diluting tumour cell concentration. In clinical use, PBPC transplantation has a proven role in support of hig h dose chemotherapy in certain haematological and oncological malignan cies but the concept of dose intensification is not universally accept ed. With the exception of leukaemia, lymphoma, myeloma or relapsed tes ticular cancer and possibly some subgroups of breast cancer; high dose chemotherapy does not demonstrate a survival benefit. For patients wi th CML, autografting with Ph(-) cells appears to become a useful alter native to allogeneic BMT Allogeneic PBPC transplantation may have pote ntial, though work is preliminary. Cord blood transplantation between matched siblings is viable, but it is not yet clear whether this sourc e will increase the donor pool for adults needing allogeneic transplan tation. For gene therapy using haematopoietic cells to be effective, a greatly increased rate of transduction will be needed. Meeting in Par is in September 1995, a European School of Oncology Task Force conside red a number of important questions relating to peripheral blood proge nitor cell(PBPC) physiology and transplantation. This review is a brie f account of their conclusions.