A phenotypically normal revertant of an adenosine deaminase-deficient lymphoblast cell line

Two lymphoblast lines from a patient with partial adenosine deaminase deficiency have been obtained. The patient has a T cell deficiency, with normal B cell function, and has been successfully treated by multiple partial exchange transfusions with normal erythrocytes. The patient's lymphocytes have about 8% of normal adenosine deaminase activity. The derived lymphoblast line that initially had low adenosine deaminase activity has undergone spontaneous reversion to normal enzyme activity. The HL-A types remain the same as the patient's. Both cell lines have the same HL-A types, and eight isoenzymes are identical. In addition, the isoenzymes of a fibroblast line derived earlier, GM-2445, are identical with those in our lymphoblast lines. The following characteristics of the enzyme in the cell lines are normal: Km, Vmax, inhibitor sensitivity, heat sensitivity, and m.w. This suggests, but does not prove, that the low adenosine deaminase activity in this patient is caused by underproduction of a normal enzyme, and the observed reversion to normal activity in one line is a correction of this regulation defect.