Background: The number of peripheral blood (PB) CD34+ cells has been widely used to monitor the timing of leukapheresis for autologous transplantation. However, no cutoff value for CD34+ cells in PB has been defined as a guideline for the identification of patients in whom the harvest would be effective and those in whom there was a high probability of failure.
Study design and methods: The present study investigated the best threshold of CD34+ cells in PB for successful harvesting and engraftment, using 263 PB samples with their corresponding leukapheresis components. In addition, that measure has been compared to other commonly used criteria such as the white cell count, the number of mononuclear cells, and the number of colony-forming units-granulocyte macrophage in PB.
Results: Time to engraftment of both granulocytes and platelets was significantly influenced by the number of CD34+ cells transfused, but all patients receiving > or = 0.75 x 10(6) CD34+ cells per kg achieved engraftment within a reasonable number of days (> 0.5 x 10(9)/L granulocytes by Day 11 and > 20 x 10(9)/L platelets by Day 13). A clear correlation between the number of CD34+ cells per microL in PB and of CD34+ cells per kg collected was found at each apheresis (r = 0.9, p < 0.0001). Moreover, the number of CD34+ cells per microL measured in PB the day the first leukapheresis was initiated displayed an excellent correlation with the total amount of CD34+ cells per kg finally collected (r = 0.81, p < 0.0001). On the basis of the regression curve obtained and the clinical engraftment results, it was found that the presence of > 5 CD34+ cells per microL in PB ensured a good yield from the harvest in 95 percent of patients and would avoid an unsuccessful harvest in 81 percent of cases.
Conclusion: A dose of only 0.75 x 10(6) CD34+ cells per kg guarantees hematopoietic recovery within a reasonable number of days. To initiate a leukapheresis from which enough progenitor cells may confidently be obtained, a minimum of 5 CD34+ cells per microL in PB is required.