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 pnenotype. The lymphoblasts showed uniform surface expression of CD3, CD7, CD8, and T-cell receptor (TCR) α/β chains, positive immunofluorescent staining of terminal deoxynucleotidyl transferase, complex cytogenetic aberrations including t(14;14) (q11;q32) and unique rearrangements of TCR β and γ 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.