A sandwich CD7-ELISA for detection of solubilized CD7 from normal and leukemic T cells.

CD7 is a T differentiation antigen which is useful in the identification of precursor T cells as well as an important marker for the identification of leukemic T cells. It has proved to be useful as a target for immunotherapy by immunotoxins in several clinical settings. Most monoclonal antibodies to this antigen bind to the same or similar epitope. We have produced a monoclonal antibody, 69, which identifies a different epitope as that of the prototypic mAb to CD7, 3A1. Using mAB 69, we have devised a sandwich CD7-ELISA to detect solubilized CD7 antigen, with mAb 69 in the solid phase as the capturing mAb. This assay is sensitive and is able to detect antigen present on 2-5 x 10(4) activated T cells. This assay has been used to study the fate of CD7 on the membrane and in the cytosol of T cells during the process of mitogenesis. We have also utilized this assay to demonstrate the presence of free CD7 antigen in culture supernatant of activated T cells. This method will be useful to analyze antigen recovery from bulk cell cultures or from molecularly engineered microbial organisms. In addition, the sandwich CD7-ELISA may prove useful in monitoring the effects of immunotherapy in patients with leukemia.