Monoclonal antibodies to leukaemic cell surface antigens

Abstract

Kohier and Milstein’s method for producing monospecific antibodies by fusing antibody-producing spleen cells and myeloma cells to derive cell lines secreting monoclonal antibodies considerably facilitates the analysis of the cell surface. In particular it will be possible to produce monoclonal antibodies to a large number of human cell surface antigens. We have applied the above approach to an analysis of the cell surface of cells from patients with chronic lymphatic leukaemia (CLL) and acute myeloid leukaemia (AML). Balb/c mice were immunized with membrane from leukaemic cells and screened for antibody activity against the immunizing cell using a radioimmune binding assay. The spleen cells of mice with the highest antibody titre were fused with the parental myeloma line P3-NSI/I-Ag 4-1. The production of antibody from hybrids was screened with a similar radioimmune binding assay. Hybrid supernatants were also screened for mouse immunoglobulin by a surface binding assay using an I125 labelled affinity purified rabbit anti-mouse immunoglobulin. Mice were immunized with a cell membrane extract of cells prepared by detergent (Tween 40) treatment from patients with CLL and AML. Hybrids grew in 85 144 wells and 57 of the hybrids secreted mouse immunoglobulins (67%). However, only 39 of the clones were positive when tested against the original cells in the binding assay (45%). One of the antibodies undetected by surface binding assays recognizes a cytoplasmic antigen and one represents an antigen only found on a minority of the immunizing cells. The specificity of the nine antibodies fully characterized shows that they recognize antigens of wide tissue distribution, but a number of leucocyte associated lines and a putative B cell antibody producing line have been established. The latter line showed activity against CLL cells and Daudi cells but was negative against HSB2. AML. HELA and red blood cells. Neither leukaemia-specific nor myeloid differentiation antigens were detected. Antibodies directed against HLA or β2 microglobulin were also not present. It seems that immunizing techniques will have to be varied to produce antibodies directed against antigens of greater interest.