Expression pattern of hybrid phenotype in adult acute lymphoblastic leukemia.

We examined the expression of hybrid phenotype in 236 adults with acute lymphoblastic leukemia (ALL; 188 B-lineage ALL and 48 T-lineage ALL). In B-lineage ALL, myeloid antigen (mAg) CD15 was concentrated in CD10-CD20- cases (49%); CD13 (42%); and CD33 (43%) in CD10+CD20- cases. This trend had no correlation with the presence of Ph1 or t(4;11) chromosomal abnormality. T-cell antigen CD2, CD4, and CD7 was seen in four, four, and two cases, respectively, and CD4+ and CD7+ cases commonly expressed CD13 and/or CD33 (CD13/CD33). In T-lineage ALL, expression of mAg, CD11b (47%), CD13 (38%), CD15 (28%), and CD33 (51%) was restricted to CD3- cases. B-cell antigen CD19 was found in two cases with CD7 solely as T-cell antigen, and these cases possessed CD13/CD33. CD21 was detected in three cases with CD3. In whole ALL, CD13/CD33 was associated closely with the presence of stem-cell antigen CD34, and in T-lineage ALL, CD13/CD33 had a significant correlation with additional stem-cell features, such as HLA-DR, multidrug resistance 1 (MDR1) and c-kit gene expression. Our results suggest that immature ALL cells frequently express B+M+, T+M+, and occasionally B+T+M+ phenotype; that B+T+M- phenotype is extremely rare; and that mAg expression in B-lineage ALL is complicated as compared to T-lineage ALL.