Peripheral blood progenitor cell mobilization: a clinical review

High-dose chemotherapy appears to confer a survival advantage on certain patients with lymphohematopoietic malignancies and may have a role in some solid tumors, notably germ cell and, possibly, breast cancer. Autologous bone marrow grafts adequately support high-dose therapy in many patients, but more-rapid engraftment is observed in those who are given mobilized peripheral blood progenitor cell grafts. The optimal method for mobilizing progenitor cells remains to be defined, but adequate numbers of cells can be obtained by apheresis after treatment with cytokines, chemotherapy, or a combination of both. The minimum number of progenitor cells that will result in rapid and durable engraftment from mobilized peripheral blood cell collections is probably between 2.5 x 10(6) and 5.0 x 10(6) CD34+ cells/kg, as determined by flow cytometry, a method not yet fully standardized among laboratories. Tumor cell contamination of peripheral blood progenitor cell grafts is less common, and there are fewer tumor cells than in matched bone marrow collections. Strategies for producing large numbers of stem cells by ex vivo expansion of small collections may be feasible in the near future. Such approaches may also reduce tumor cell contamination of the product.