In vitro evaluation of B-CLL cells apoptotic responses to irradiation

Defective apoptosis is a mechanism which could possibly explain B chronic l ymphocytic leukemia (B-CLL) cell accumulation. Differences in evolution and prognosis of B-CLL patients may be due to heterogeneity in apoptotic cell death. We studied the apoptotic response to in vitro gamma radiation of blo od mononuclear cells from 18 untreated B-CLL patients. In cells irradiated with 2, 4 or 8 Gy and then cultured for 20 hours, the percentage of trypan blue excluding (viable) cells was not modified (>92%). An apoptotic respons e to irradiation was detected in the majority of the patients, but the indi vidual percentage of apoptotic cells varied widely (8 to 81% after 8 Gy irr adiation) in individual cases. The flow cytometric analysis of nick-end DNA labeling demonstrated a dose effect of irradiation, particularly in patien ts with an apoptotic response of over 20%. In the future, a valuable clue t o the selection of irradiation regimens for B-CLL patients may be the inves tigation of correlations between in vitro radiation-induced apoptosis and t he in vivo response to radiation therapy.