Antibody producing human-human hybridomas. II. Derivation and characterization of an antibody specific for human leukemia cells

Human-human hybridoma technology was used to immortalize human B lymphocytes from patients with acute myeloid leukemia (AML) to study the antigenic repertoire of the humoral immune response against the patients' own leukemia cells and against leukemic cells from other patients. Nine fusions were done with lymphocytes from seven AML patients, and all with the human RH-L4 B lymphoma line as malignant fusion partner. A total of 305 Ig-producing hybrids were obtained. 26 reacted with cell surface components on AML cells, but 21 were found not to be specific for leukemia cells, when screened for reactivity against a panel of normal and malignant cells of both human and murine origin. Five hybridomas secreted Ig with high specificity for human leukemia cells, but only one hybridoma culture, aml-18, was stable in respect to Ig-production and growth upon repeated clonings and expansion in liquid cultures. A method was developed to grow human hybridomas as ascites tumors in nude mice, but the ascites fluid did not contain increased amount of antibody. The reactivity of the aml-18 antibody (gamma, kappa) was analyzed against samples of mononuclear cells from peripheral blood of 63 patients with leukemia and with cytologically verified leukemia cells in the blood. 22 of 54 AML samples reacted with aml-18. The reactivity pattern was not correlated to any categories of the French-American-British (FAB) classification; two of four ALL were positive. Moreover, a pronounced intratumoral antigenic heterogeneity in regard to aml-18 reactivity was seen and indicates a high degree of diversity in the immunological phenotype within individual AML cell populations. The study demonstrates that some patients with AML generate an immune response against their autologous malignant cells, and that the antigenic determinant in the case of aml-18 is also expressed specifically on leukemic cells from other patients.