Early Apoptosis Largely Accounts for Functional Impairment of CD34+ Cells in Frozen-Thawed Stem Cell Grafts

Quality assessment of stem cell grafts is usually performed by flow cytometric CD34+ enumeration or assessment of clonogenic output of fresh material. Previously, we identified the occurrence of early apoptosis, not detectable with the permeability marker 7-amino actinomycin D (7-AAD), in purified frozen-thawed CD34+ cells, using the vital stain Syto16. Sytohigh/7-AAD- cells were defined as viable, Syto16low/7-AAD- cells as early apoptotic and Syto16low/7-AAD+ as dead. This was confirmed in a subsequent study using frozen-thawed transplants of lymphoma patients. In the present study on grafts from multiple myeloma and lymphoma patients, we investigated the functional consequences of the early apoptotic process. The mean Syto16-defined viability was 41 and 42%, respectively, for both graft groups, compared to 78% and 72%, respectively, using 7-AAD only. The established early apoptosis marker annexin V missed roughly 50% of the early apoptosis detected with Syto16. In contrast, viability of CD34+ cells in n...