Subsets of CD34⁺ cells and rapid hematopoietic recovery after peripheral-blood stem-cell transplantation

Purpose; To study whether there is a relationship between transplanted cell dose and rate of hematopoietic recovery after peripheral-blood stem-cell (PBSC) transplantation, and to obtain an indication whether specific subsets of CD34⁺ cell populations contribute to rapid recovery of neutrophils or platelets. Patients and Methods: Based on data from 59 patients, we calculated for each day after PBSC transplantation the dose of CD34⁺ cells that resulted in rapid recov-ery of either neutrophils or platelets in the majority (> 70%) of patients. Using dual-color flow cytometry, subsets of peripheral-blood CD34⁺ cells were quantified and the numbers of CD34⁺ cells belonging to each of the reinfused subsets correlated with hematopoietic recovery following high-dose chemotherapy. Results: The calculated threshold values with a high probability of engraftment showed a steep dose-effect relationship between CD34⁺ cell dose and time to recovery of both neutrophils or platelets. Predominantly CD34⁺ cells with the phenotype of myeloid precursors were mobilized. A minority of CD34⁺ cells expressed the erythroid and megakaryocytic lineage-associated antigens and a low but distinct population of CD34⁺ cells expressed antigens associated with multipotent stem cells. Analysis showed that the number of CD34⁺CD33^- cells (r = -.74, P < .05), as well as the number of CD34⁺CD41⁺ cells (r = -.81, P < .005), correlated significantly better with time to neutrophil and platelet recovery, respectively, than with the total number of CD34⁺ cells (r = -.55 and r = -.56, respectively). Conclusion: The numbers of CD34⁺CD33^- cells and CD34⁺CD41⁺ cells may help to predict short-term repopulation capacity of PBSCs, especially when relatively low numbers of CD34⁺ cells per kilogram are reinfused.