Peripheral blood stem cell transplantations: past, present and future.

Since the first successful attempt in 1985, peripheral blood stem cell transplants are increasingly performed worldwide and should now be considered as an essential therapeutic weapon against onco-hematological diseases. Their development has benefited greatly from a rapid concomitant advance of experimental knowledge regarding the nature of hematopoietic progenitor cells. For this reason and also for technical ones, until now these transplants generally have been autotransplants. Although one of the main reasons to use blood rather than bone marrow-derived stem cells was that they might carry less risk of relapse than autologous bone marrow cells, the lack of clinical randomized trials and/or the short follow-up make conclusions difficult so far in terms of disease-free and overall survival. Probably the risk of relapse also depends on the type of disease, on prior chemotherapies, on the type of peripheral stem cell mobilization regimen and on the number of blood-derived cells transplanted. Nevertheless, there are several major clinical indications for autologous blood stem cell transplant: acute nonlymphoblastic leukemias (ANLL), low-grade non-Hodgkin's lymphomas, multiple myeloma, some solid tumors, and even chronic myeloid leukemia. Now well-demonstrated advantages add a socioeconomic interest to this technique. The speed of post-transplant hematopoietic recovery induces a briefer hospitalization and a lower cost of the procedure, which represents "per se" important progress. Furthermore, the increasing use of hematopoietic growth factor(s) at time of blood-derived cell mobilization should increase the safety of the procedure. Also new trends are currently being developed: autotransplants with purified peripheral CD34+ cells; addition of adjuvant immunotherapy to induce graft-versus-tumor effect, which is lacking in autotransplant; and transplants using allogenic umbilical cord blood progenitors. Allogenic blood cell transplants might also be developed, provided that blood cells would be less likely to cause graft-versus-host disease (GVHD) than bone marrow, which is still not verified. Finally, the use of blood-derived cells as a vehicle for gene therapy should develop greatly in the near future.