Pre infusion, post thaw CD34⁺ peripheral blood stem cell enumeration as a predictor of haematopoietic engraftment in autologous haematopoietic cell transplantation

Introduction: By convention, peripheral blood stem cell products for autologous transplantation are evaluated for quality by CD34⁺ cell dose at the time of harvesting. A CD34⁺ cell dose in excess of 2.0×10⁶/kg of recipient body weight is considered adequate for haematopoietic engraftment. Viable CD34⁺ cell numbers are enumerated in most laboratories using the ISHAGE single platform flow cytometric method which utilizes monoclonal antibodies to CD45, CD34 and 7 amino actinomycin D (7AAD) dye exclusion. Methods: One hundred and six consecutive autologous transplantation procedures underwent viable CD34⁺ cell enumeration at the time of harvesting and post thaw prior to re-infusion. Neutrophil and platelet engraftment and markers of haematopoietic support were analyzed. Results: Mean pre-cryopreservation viable CD34⁺ numbers were 4.882×10⁶/kg. Mean post thaw viable CD34⁺ numbers were 3.234×10⁶/kg. Mean loss of viable CD34⁺ cells with processing and cryo-preservation was 1.648×10⁶/kg (33%). For neutrophil engraftment, there was no significant difference between high (≥3.0×10⁶/kg) and low (<1.5×10⁶/kg) post thaw viable CD34⁺ cell counts (p=0.545). For platelet engraftment, there was however a significant difference observed between the high and low pre infusion viable CD34⁺ groups (p<0.001). Additionally, significant differences were seen between the post thaw viable CD34⁺ cell count and the associated length of hospital admission, days of use of G-CSF post transplantation, use of antibiotics in the post transplantation period and transfusion support in the post transplantation period. Conclusion: A significant loss of viable CD34⁺ cells occurs during processing, cryopreservation and thawing. Low numbers of viable CD34⁺ cells infused post thaw will still result in adequate neutrophil engraftment however may delay platelet engraftment. Low viable CD34⁺ cell numbers have significant effects on admission duration and use of haematopoietic supportive measures with consequent effects on healthcare resources.