Molecular nature of a cell membrane antigen specific for human T-cell acute lymphoblastic leukemia.

In the present work, we characterized the molecular nature of a T-cell acute lymphoblastic leukemia (T ALL) specific antigen, termed TALLA, which is defined by monoclonal antibody SN1. SN1 shows an extremely high specificity for T ALL. In the present study, SN1 was further shown not to react significantly with various normal solid tissues. TALLA was determined to be a glycoprotein with an approximate molecular weight of 150,000. However, the molecular nature of TALLA is peculiar in that heating at 100 degrees C for 2 min renders TALLA undetectable in sodium dodecyl sulfate-polyacrylamide gel electrophoresis. It should be noted that such heating is a common practice before analysis of proteins and glycoproteins by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. No significant antigenic modulation of TALLA was observed when T ALL cells were reacted with SN1. Two new monoclonal antibodies, SN1a and SN1b, which show the same cell binding specificity as SN1 were also generated in the present work and compared to SN1. Competitive binding experiments showed that the epitopes on TALLA recognized by SN1, SN1a, and SN1b are sufficiently close to one another to allow complete reciprocal inhibition of antibody binding. These epitopes apparently became more exposed to antibody when T ALL cells were treated with neuraminidase; neuraminidase-treated T ALL cells bind 29-35% more SN1, SN1a, and SN1b as compared to the original T ALL cells.