Is there a threshold dose of CD34-positive cells for posttransplant bone marrow recovery?

Using diverse data we show CD34-positive cells are not an accurate estimator of numbers of haematopoietic stem cells in humans. We also show in the context of umbilical cord transplants for leukaemia there is likely no threshold of CD34-positive cells needed to restore bone marrow function after high-dose pretransplant therapy. Lastly, we show that, when CD34-positive cells are used as a surrogate marker for human haematopoietic stem cells, the dose should be expressed as numbers per blood volume and not body weight. These conclusions, if validated, may have important clinical implications.