Effect of CD34+ peripheral blood progenitor cell dose on hematopoietic recovery

The CD34+ cell surface antigen is expressed on progenitor cells required for blood stem cell transplantation. The number of cells expressing CD34+ can be used to assess the peripheral blood progenitor cell (PBPC) graft quality and predict hematopoietic recovery after engraftment. Because there is considerable variability among centers in the determination of CD34+ cell counts, standardizing flow cytometry methodology is essential. It is necessary to define a minimum safety threshold CD34+ cell dose for hematopoietic cell transplantation. This minimum dose would define a cell number in the graft, below which a proportion of patients would be expected to have delayed hematopoietic recovery or failure to engraft. We reviewed data from numerous studies. Although 1-2 x 10(6) CD34+ cells/kg can be considered an adequate graft, available data suggested that doses >5 x 10(6) CD34+ cells/kg were associated with more rapid engraftment and a lower probability of graft failure. The risk of delayed recovery was inversely related to CD34+ cell dose. Delayed recovery may result in greater transfusion requirements, longer hospitalization, increased antibiotic use and growth factor support, and higher health care costs. The extent of prior chemotherapy and radiation treatment are major risk factors for poor PBPC collection. To achieve an optimal CD34+ cell yield, PBPC collection should be initiated early during therapy. PBPC collection should be coordinated with the anticipated number of chemotherapy cycles, duration of chemotherapy, interval between chemotherapy and apheresis, need for radiotherapy, and exposure to the more progenitor cell-toxic drugs such as carmustine or busulfan.