Expression of CD10 by B-chronic lymphocytic leukemia cells undergoing apoptosis in vivo and in vitro

B-cell chronic lymphocytic leukemia (B-CLL) is an accumulating disease of slowly proliferating cells. CD10 is not normally expressed on the surface of B-CLL cells. The aim of this study was to ascertain whether B-CLL cells, induced into apoptosis, expressed surface CD10, since a correlation between apoptosis and CD10 expression has been demonstrated.

Peripheral blood cells from 31 untreated B-CLL patients were induced into apoptosis by etoposide, fludarabine or Ga(mu)-Ab treatment and tested for CD10 expression by flow cytometry. Normal CD5+ B cells were also induced into apoptosis and tested for CD10 expression.

CD10 positive cells were absent in B-CLL cell suspensions, but were detected following in vitro culture, and their appearance paralleled that of apoptotic cells. Treatment with etoposide, fludarabine or Ga(mu)-Ab enhanced both apoptosis and CD10 expression. Inhibition of apoptosis by VAD-fmk or Ga(delta)-Ab prevented CD10 expression. Cell separation tests following induction of apoptosis demonstrated that CD10+ cells were apoptotic. CD10+ cells were observed in the peripheral blood of two patients within a few hours following fludarabine infusion. In another patient, who failed to respond, no CD10+ cells were seen. Expression of CD10 was observed also in normal CD5+ B cells when these were induced into apoptosis.

This study demonstrates that B-CLL cells, as well as normal CD5+ B cells, become CD10+ following apoptosis induction in vitro. Some of the data obtained also suggest a use for CD10 to monitor apoptosis of B-CLL in a clinical setting.