Gene Expression of Terminal Deoxynucleotidyl Transferase in Neoplastic Cells of Leukemia and Lymphoma

Expression levels of terminal deoxynucleotidyl transferase (TdT) mRNA in fresh leukemia and lymphoma cells were measured by northern blotting analysis. Bands of 2.1 kb mRNA were detected in all of eight cases of TdT activity‐positive leukemias: two cases of null‐cell acute lymphoblastic leukemia (null‐ALL), two of common ALL, one of pre‐B ALL, one of T‐ALL, and two of chronic myelogenous leukemia in blastic crisis. One of the null‐ALL and one of the common ALL cases also showed large TdT mRNA (3.3 kb). Since all TdT activity‐positive samples exhibited TdT mRNA, the TdT gene might be mainly regulated at the transcription level in leukemic cells. An elevated level of 2.1 kb TdT mRNA was also detected in one lymphoma case, where neither TdT activity nor immunoreactive TdT was detected. The extensive chromosomal abnormality demonstrated in this case might be associated with the translational anomaly of TdT.