- At least 5 percent of each patient's peripheral blood, lymph node, pulmonary or dermal malignant cells must react with the anti-Tac mAb as determined by immunofluorescent staining or, alternatively, the serum-soluble interleukin 2 (IL-2) receptor levels must be greater than 1,000 units/ml (normal geometric mean, 235; with a 95% confidence interval of 112 to 502 units/mL).