Diminished lymphocyte and granulocyte γ‐glutamyltranspeptidase activity in acute lymphocytic leukemia and response to chemotherapy

γ‐Glutamyltranspeptidase (GGT) acitivity (per mg protein) in blood lymphoid cells of 27 children with acute lymphoblastic leukemia (ALL) (1.05 ± 0.15) was significantly below that of controls (2.25 ± 0.30), became normalized during chemotherapy‐induced remission (2.47 ± 0.26), and was low again (1.59 ± 0.62) in relapsed subjects. Individual variations in the GGT activity of the blood lymphoid cell fraction (per mg protein) bore a significant inverse correlation to the number of white blood cells (WBC) as well as of blasts per ml blood. Blasts had minimal GGT activity; however, partial GGT deficiency was also exhibited by the microscopically normal circulatory lymphocytes of several patients prior to treatment and in relapsed subjects whose blood was still devoid of blasts. Significantly diminished GGT activity (per mg protein) was found in the blood granulocytes of ALL subjects. This deficit, restored during remission and present again at relapse, varied in magnitude but showed no statistically significant correlation to the different patients' degree of neutropenia. In about one‐third of the newly diagnosed or relapsed pre‐B ALL children, the circulatory granulocytes' GGT activity was only 10–20% of normal. The results suggest that 1) the presence or absence of this sign of functional maldifferentiation in granulocytes is a factor in the heterogeneity of disease manifestation among subjects with apparently the same type of ALL and that 2) measurement of GGT in the circulatory granulocytes, as well lymphocytes, may be useful for monitoring the efficacy of chemotherapy.