CD4 predicts nonlymphocytic lineage in acute leukemia. Insights from analysis of 125 cases using two-color flow cytometry.

The classification of acute leukemia into lymphoid or nonlymphoid is of critical therapeutic importance. Two-color flow cytometric analysis has emerged as a valuable addition to morphology and cytochemistry for the distinction of acute lymphocytic leukemia (ALL) and acute nonlymphocytic leukemia (ANLL). By careful selection of monoclonal antibody (mAb) combinations, diagnostic accuracy, and cost effectiveness may be enhanced compared to flow cytometry using one-color analysis. The sensitivity and specificity of a mAb panel were assessed in the determination of nonlymphocytic lineage in acute leukemia. One hundred twenty-five consecutive cases of acute leukemia were analyzed in which Wright's-stained smears, cytochemical stains, and immunophenotyping studies had been performed. The antibody panel included the nonlymphoid markers CD13, CD33, CD14, and CD4 in combination with CD2, as well as a broad panel of lymphoid and nonlineage specific markers. Of the 125 cases of acute leukemia studied, 85 cases (68%) were nonlymphocytic and 32 cases (26%) were lymphocytic (28 cases B cell, 4 cases T cell). CD13 and CD33 were very sensitive in the detection of ANLL, being expressed on 94% and 93% of ANLL cases, respectively. Sixty-five percent of cases of ANLL were CD4+ (CD2-). However, CD4+ (CD2-) had a much higher specificity (91%) for ANLL than CD13 (75%) or CD33 (84%), which were expressed in a significant number of ALL. When leukemic cells were positive for CD4 (CD2-) and either CD13 or CD33, specificity and positive predictive value (PPV) for ANLL rose to 96% and 98%, respectively. The combination of CD4 positivity with either CD13 or CD33 has higher specificity and PPV than the traditional positivity for both CD13 and CD33 (specificity 89%, PPV 96%). Careful analysis of the sensitivity, specificity, and predictive values of mAbs using this method has also allowed us to establish a more cost-effective and diagnostically relevant mAb panel. Our studies show that CD4 is underappreciated as a very specific and moderately sensitive marker for ANLL.