Increased Apoptosis in Aplastic Anemia Bone Marrow Progenitor Cells: Possible Pathophysiologic Significance

We have quantitated apoptotic cells by flow cytometry in human bone marrow (BM) and peripheral blood (PB) from normal donors and aplastic anemia (AA) patients, using the fluorescent DNA-binding dye 7-amino actinomycin D (7AAD). No significant difference was found in baseline percent apoptosis between normal and AA samples. Serum deprivation induced cell death to a greater degree in AA samples than in normal samples, but this was not significant. Using dual staining with anti CD34 antibody and 7AAD, we have shown that CD34+ progenitors in normal PB are significantly more apoptotic than those in normal BM. AA BM CD34+ cells contain a significantly greater proportion of apoptotic cells than normal BM CD34+ cells. Those AA patients with the lowest absolute number of CD34+ cells showed the highest proportion of apoptotic CD34+ cells. This appears to be related to clinical severity (transfusion dependence) at the time of study. We conclude that apoptosis is accelerated in AA BM progenitors and that this may contribute to the stem cell deficiency characteristic of this disorder.