Differential expression of adenosine deaminase isozymes in acute leukemia

Total adenosine deaminase (ADA) and purine nucleoside phosphorylase (PNP) activities were measured in cell samples from 13 cases of de novo acute leukemia and from three cases of chronic myeloid leukemia in blast crisis (CMLBC). These cases could be separated into lymphoid and nonlymphoid types on the basis of enzyme activity, with two misclassifications. However, PNP activity added little or no discriminatory information. Analysis for expression of the various molecular weight (mol wt) ADA isozymes, ADA₁ (40 Kd) and ADA₂ (110 Kd), revealed that ADA₂ was expressed exclusively in nonlymphoid cells whereas ADA₁ was found in both lymphoid and nonlymphoid cell types. Identification of ADA₂ divided these leukemia cases into lymphoid and nonlymphoid types with no misclassification (P = .0002; Fisher's exact test). Acute nonlymphoblastic leukemia (ANLL) with a monocytic component tended to have a greater percentage of ADA₂ than ANLL without a monocytic component. These studies suggest that ADA₂ may be a novel biochemical marker for an immature nonlymphoid cell.