Comparison of purine degradative enzymes and terminal deoxynucleotidyl transferase in T cell leukaemias and in normal thymic and post‐thymic T cells

Abstract

Summary. Adenosine deaminase (ADA), ecto 5’ nucleotidase (5′NT), purine nucleoside phosphorylase (PNP) and terminal deoxynucleotidyl transferase (TdT) were measured in the cells of patients with acute or chronic T cell leukaemia and compared with normal putative prothymocytes (large, blast‐like cortical thymocytes), cortical and medullary thymocytes and peripheral blood T lymphocytes. Distinct patterns of enzyme activities were found in the individual types of T cell leukaemia. Mean ADA, TdT and 5′NT activities in thymic acute lymphoblastic leukaemia (Thy‐ALL) were 41·9 u/108 cells, 31·1 u/108 cells and 4·7 u/106 cells respectively; in chronic T cell leukaemia they were 7·1 u/108 cells, 0·6 u/108 cells and 18·1 u/106 cells respectively. Mean PNP activity was similar between these two groups of leukaemia (68·6 u/106 cells in Thy‐ALL and 77·9 u/106 cells in chronic T cell leukaemia). The activities of these four enzymes in OKT4+ chronic T cell leukaemia did not differ significantly from those in the OKT8+ chronic T cell leukaemia cases. The activities of TdT, ADA, PNP and 5′NT in Thy‐ALL closely resembled those in normal immature thymocytes, and in the chronic T cell leukaemias showed a similar pattern of enzyme activities to that of mature T lymphocytes. These findings are consistent with surface phenotypic studies of T cell malignancies which suggest that different T cell leukaemias represent malignant proliferation of T cell clones arrested at different stages of T cell differentiation. They also demonstrate the value of biochemical markers in defining the different subtypes of acute and chronic leukaemia.