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 β ) and gamma (T ± ) chain genes, and a germline immunoglobulin heavy chain (J H ) gene. These findings support the concept that pre‐T cell leukemias may demonstrate germline T β and T ± 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 β and T ± gene rearrangements, and TdT expression.