Functional and molecular characteristics of acute lymphoblastic leukemia cells with a mature T-cell phenotype from a patient with ataxia telangiectasia.

A 12-year-old male patient with ataxia telangiectasia developed an acute lymphoblastic leukemia of T-cell phenotype. The lymphoblasts showed uniform surface expression of CD3, CD7, CD8, and T-cell receptor (TCR) alpha/beta chains, positive immunofluorescent staining of terminal deoxynucleotidyl transferase, complex cytogenetic aberrations including t(14;14) (q11;q32) and unique rearrangements of TCR beta and gamma chain genes, indicating the clonal expansion of leukemic cells. CD25 expression could be readily induced on the leukemic cells by mitogenic stimulation, followed by CD71 expression, but interleukin-2 production and subsequent proliferation in response to mitogens were subnormal.