Do autologous peripheral blood cell transplants provide more than hematopoietic recovery?

Bone marrow damage caused by myeloablative radiation therapy and/or chemotherapy can be repaired by intravenously infusing viable stem/progenitor cells collected from either blood or bone marrow. The hematopoietic graft product contains both stem/progenitor cells and populations of hematopoietic and nonhematopoietic (accessory) cells. The frequency of accessory cell types varies with the source of the graft product; marrow or blood. Reinfusion of these accessory cells causes effects other than the hematopoietic restoration provided by the stem/progenitor cells such as graft versus host disease and graft versus leukemia effect after allogeneic transplants. Effects of infused accessory cells in the autologous setting are less well studied and could provide ancillary advantages and/or disadvantages to the patient. Do these additional effects actually occur, and, if they do, are they more likely to appear following peripheral blood cell transplants (PBCT) or after autologous bone marrow transplants (AMBT)? Preliminary data are beginning to accumulate which suggest that reinfusion of occult tumor cells is less likely with PBCT, that immune reconstitution is different depending on the source of the autograft and that, for certain diseases, patient event-free survival following PBCT rather than ABMT may be better. However, infusion of occult tumor cells may result in re-establishment of the malignancy. If the accessory cells (including potential occult tumor cells) are eliminated from the product before transplant, will the patient have a better clinical outcome, or would benefits provided by infused accessory cells outweigh the risks of infused occult tumor cells? These controversial issues are in the very early stages of investigation.