Relevance of 3A1 monoclonal antibody in the diagnosis of T-cell acute lymphoblastic leukemia.

: Two childhood and three adult patients with acute lymphoblastic leukemia (ALL) are described. The identification of the T-cell nature of their ALL-cells was based on the positivity of their blasts with 3A1 monoclonal antibody which recognizes immature and mature T-cells. Four tested cases showed a terminal deoxynucleotidyl transferase (TdT) positivity, and four out of five were acid phosphatase (AcP)-positive. Cells from all cases were characterized with a panel of 15 monoclonal antibodies: 3A1 was constantly positive; J5, BA-1, OKT6, Leu-7, and other monoclonal antibodies reactive with T-cells (OKT3, OKT4, OKT8, OKT11, Leu-1, T65) were negative; only two cases had weak positivity with OKT11 and Leu-1, respectively; cells from all cases were surface immunoglobulin (SIg)-negative; three out of the five cases were OKT10-positive and three OKT9-positive; none of the cases reacted with OKM1 and anti-HLA-DR. Our findings indicate that the use of 3A1 monoclonal antibody was helpful in the recognition of individual cases of T-ALL otherwise considered as unclassified-ALL (U-ALL). 3A1 and an anti-common ALL Antigen (CALLA) reagent may represent the essential monoclonal antibodies to be used for screening ALL cells.