Detection of the CD34 antigen on the surface of leukocytes has proven to be a reliable surrogate marker for the identification of self-renewing, pluripotent Haematopoietic Progenitor Cells (HPCs) and has generally replaced the cumbersome colony forming unit assay for granulocytes and macrophages (CFU-GM). Assessment of apheresis products by measuring CD34+ cell counts by flow cytometry evaluates the most primitive HPCs along with maturing, lineage committed progenitors. Doses of >2 x 10⁶ CD34+ HPCs/kg of patient body weight have been found to be predictive of both short-term and long-term hematopoietic recovery after high-dose chemotherapy. 

Our laboratory at the Centre for Blood Cell Therapies (CBCT) at Peter MacCallum Cancer Centre performs CD34+ cell counts on 4 different sample types:

1) Peripheral Blood (PB) pre-apheresis to determine patient suitability for HPC-A collection;

2) HPC-A Product to determine the total CD34+ cell dose collected in the apheresis product;

3) Apheresis bulb samples at the end of apheresis to determine the total CD34+ dose collected prior to HPC-A processing; and

4) Reference vial samples to determine the viability and CD34+ dose recovered post cryopreservation and thawing.

The role of PB CD34+ cell counts in predicting the optimal timing of HPC-A collection is well established, as is its contribution to achieving an adequate CD34 dose. This presentation will focus on the role that CD34+ cell counts play in optimising HPC-A transplantation, using the range of CD34+ cell counts available.