Increased incidence of spontaneous apoptosis in the bone marrow of hyperdiploid childhood acute lymphoblastic leukemia

Abstract

Hyperdiploidy of 51-65 chromosomes is associated with a good prognosis in childhood B-lineage acute lymphoblastic leukemia (ALL). Blasts from childhood ALL patients with a hyperdiploid karyotype have a tendency to apoptosis when cultured on stromal layers in vitro. In this study, we apply a novel method to investigate the relationship between apoptosis and hyperdiploidy in lymphoblasts of childhood ALL. The DNA content of individual ALL blasts in Feulgen-stained archival bone marrow smears can be determined by static cytometry. TUNEL (TdT-mediated dUTP-biotin nick end labeling) detects the DNA degradation associated with apoptosis. We performed TUNEL in situ sequential to DNA ploidy analysis in archival bone marrow smears from 12 patients with childhood ALL. Five patients were diploid and seven were hyperdiploid (51-65 chromosomes) by conventional cytogenetic analysis. In the five diploid cases, the percentage of TUNEL-positive blasts ranged from 1.0% to 1.3%; in the seven hyperdiploid cases, the percentage of TUNEL-positive blasts ranged from 3.6% to 9.0%. Comparing TUNEL and corresponding Feulgen images, we found that apoptotic blasts were predominantly of high DNA ploidy in both diploid and hyperdiploid cases. The mean DNA value of apoptotic blasts was larger than that of the total blast population in each case. The results demonstrate an increased incidence of spontaneous apoptosis in situ of hyperdiploid blasts in ALL bone marrow and indicate that this phenomenon is not restricted to in vitro cultures. The findings provide a possible rationale for the good prognosis associated with hyperdiploid childhood ALL.