Childhood T-cell acute lymphoblastic leukemia with four distinct immunophenotypes representing different stages of T-cell development.

The authors report on a 14-year-old boy who developed T-cell acute lymphoblastic leukemia (FAB:L1) displaying 4 immunophenotypically distinct leukemic cell populations by 3-color immunofluorescence staining. Cytogenetic analysis at diagnosis showed 46,XY,add(4)(p16)[12]/46,XY[2]. A single rearrangement of the T-cell antigen receptor beta- and gamma-chain genes in these cells indicated monoclonality of the leukemic cells. These findings suggest that leukemic blast cells of monoclonal origin in this case were divided into 4 immunophenotypic populations, representing various stages of differentiation.