DETECTION OF NEOPLASTIC CLONE IN THE HYPOPLASTIC AND RECOVERY PHASES PRECEDING ACUTE LYMPHOBLASTIC-LEUKEMIA BY IN-VITRO AMPLIFICATION OF REARRANGED T-CELL RECEPTOR DELTA-CHAIN GENE

This study assessed the clonality of hypoplastic and subsequent recove ry phases before the development of overt leukemia by molecular geneti c analysis. We describe a boy who had transient granulocytopenia and a nemia before the development of acute lymphoblastic leukemia (ALL). In itially, his bone marrow was hypocellular with 23.6% of lymphoblastic cells, whereas subsequent marrow after the administration of granulocy te colony-stimulating factor (G-CSF) appeared almost normal without an y lymphoblasts. At diagnosis, we found the rearrangement of T cell rec eptor (TCR) delta gene in the leukemic cell DNA by Southern blot hybri dization. The junctional sequence of the V delta 2-D delta 3 recombina tion of leukemic cells obtained by polymerase chain reaction (PCR) was used for a clonospecific probe. Using the probe, the presence of leuk emic clone in the materials before and after diagnosis was examined. W e found that the clonespecific probe could detect one leukemic cell in 10,000 normal cells, and we demonstrated the presence of the leukemic clone at the initial hypoplastic and the subsequent recovery phase. T he PCR method is very useful to confirm the presence of leukemic clone even in a retrospective analysis using low-quality materials and may be helpful to understand the pathogenesis of a smoldering preleukemic phase.