CD7-positive acute leukemia lacking T cell receptor gene rearrangements and terminal deoxynucleotidyl transferase expression suggesting pre-T cell origin

In this report, we describe a case of acute leukemia possessing a unique immunophenotype. Leukemic cells isolated from peripheral blood were analyzed by automated fluorescence-activated flow cytometry. They demonstrated the following antigen pattern: CD7+, CD38+, transferrin receptor+, HLA-DR+, common ALL antigen (CALLA)-, and terminal deoxynucleotidyl transferase (TdT)-. No expression of B cell or myeloid antigens was observed. The observed antigen pattern suggests a pre-T cell origin. In addition, the tumor cells contained germline T cell receptor beta (T beta) and gamma (T gamma) chain genes, and a germline immunoglobulin heavy chain (JH) gene. These findings support the concept that pre-T cell leukemias may demonstrate germline T beta and T gamma genes as well as lack TdT expression. In addition, our results suggest that CD7 expression may be one of the earliest events in T cell differentiation, occurring prior to both T beta an T gamma gene rearrangements, and TdT expression.