Some factors determining the minimum number of cells required for successful clinical engraftment

Theoretically, a single pluripotent haemopoietic stem cell should be able to reconstitute haemopoiesis following transplantation. However, clinical and experimental observations demonstrate that it is necessary to transplant numerous stem cells to obtain engraftment. Here we discuss some of the reasons for this apparent discrepancy and provide some quantitative estimates of the influence of kinetic factors in determining the number of stem cells required for clinical engraftment.