Increased levels of circulating HLA-DR antigen in sera of patients with acute lymphoblastoid leukemia.

Monoclonal antibodies that define HLA-DR antigen bind to a variety of human tumors, such as Burkitt lymphoma and melanoma cells grown in vitro and with the spent medium of these cultures. Two radioimmunoassays have been developed to detect HLA-DR antigen circulating in human sera. The inhibition assay is based on the inhibition of binding of monoclonal antibodies against HLA-DR to the target preparation; the double-determinant assay traces antigen bound by a solid-phase monoclonal antibody by the use of a second 125I-labeled antibody. Twenty-six of 39 sera from patients with acute lymphoblastoid leukemia, 2 of 29 sera from patients with acute myeloid leukemia, and 5 of 31 sera from patients with advanced metastatic melanoma showed increased levels of HLA-DR antigen, whereas none of 28 sera from patients with other malignancies had increased levels of HLA-DR antigen, and only 2 of 155 sera from healthy donors bound monoclonal antibodies to HLA-DR at detectable levels. The detection of circulating HLA-DR antigen in sera of cancer patients may be useful in monitoring patients with certain malignancies.