Number of viable CD34+ cells reinfused predicts engraftment in autologous hematopoietic stem cell transplantation

Reduced CD34+ cell viability due to cryopreservation has unknown effects on subsequent hematopoietic engraftment in autologous transplantation. Thirty-six consecutive autologous peripheral stem cell collections were analyzed for absolute viable CD34+ cell numbers at the time of stem cell collection and prior to re-infusion. Viable CD34+ cells were enumerated using single platform flow cytometry and the molecular exclusion dye 7-amino actinomycin D. The median number of viable CD34+ cells was 3.6 × 106/kg at the time of harvest and 2.0 × 106/kg after thawing. When viable CD34+cells enumerated after thawing were <2.0, 2.0–5.0, or >5.0 × 106/kg, the median time to platelet engraftment was 17, 12 and 10 days, respectively (P < 0.05 for comparison of the group with <2.0 × 106/kg and the other two groups), and the median time to neutrophil engraftment was 13, 14 and 12 days, respectively (P = NS). A minimum of 2.0 × 106 CD34+ cells/kg was harvested in 33 of 36 patients (92%) but only 19 of 36 (52%) patients met this threshold at the time of reinfusion. The reduced numbers of viable CD34+ cells measured prior to re-infusion is associated with time to platelet engraftment and may be useful in monitoring stem cell loss during processing and identifying patients at risk of graft failure.