Adenosine deaminase activity of normal lymphocytes and leukemic cells

Adenosine deaminase (ADA) activity was determined in peripheral blood T cells, thymocytes and blasts of 42 acute leukemia patients. Thymocytes had higher ADA activity than mature peripheral blood T cells. B ALL (acute lymphoblastic leukemia) cells had significantly lower activity compared with T ALL and non-B, non-T cells. The latter had a wide range of enzymatic activities but mostly in the T cell range. Based on these results, as well as on assays of B and T cell lines, it seems that thymus-derived cells--and especially prethymic and immature T cells--have high ADA activity. This finding could be useful in subtyping the heterogeneous group of non-B, non-T ALL.