A
leukemia-associated CD9
glycoprotein antigen released into the extracellular milieu from
acute lymphoblastic leukemia cells has been detected using a unique
lectin-
monoclonal antibody immunoassay. It has been demonstrated that the release of
CD9 antigen is an active process and is associated with active cell growth. In addition, the difference of
carbohydrate moiety, and hence glycosylation, in the
CD9 antigen derived from lymphoblasts and neuroblasts was verified using
lectin affinity chromatography. The
lectin affinity of the
carbohydrate moiety of lymphoblast
CD9 antigen would indicate the presence of N-linked
oligosaccharide chains having groups of
N-acetyl glucosamine residues, a
mannose core and a terminal
D-galactose. The soluble
CD9 antigen is specifically detected in plasma from ALL patients at the time of diagnosis, in cerebrospinal fluid from patients with central nervous system involvement, and spent medium from CD9-positive leukemic blasts obtained at the time of diagnosis. Interestingly when bone marrow cells taken from patients
in complete remission were studied, a distinct amount of
CD9 antigen was released into spent medium in some of the cases. All of these patients have subsequently developed hematological relapse. The present data suggest that shedding of
CD9 antigen by leukemic cells may enable the clinical monitoring of residual leukemic cell burden.