POTENTIATION OF ANTIPROLIFERATIVE EFFECTS OF MONOCLONAL-ANTIBODY LYM-1 AND IMMUNOCONJUGATE LYM-1-GELONIN ON HUMAN BURKITTS-LYMPHOMA CELLS WITH GAMMA-INTERFERON AND TUMOR-NECROSIS-FACTOR

A type I ribosome inactivating protein, gelonin, was linked to Lym-1, a murine monoclonal antibody reactive with a polymorphic determinant o f class II HLA-DR histocompatibility leukocyte antigen (HLA) on human lymphoma cells, via a disulfide linkage using the heterobifunctional c ross-linking agent, N-succinimidyl-3-(2-pyridyldithio) propionate. Thi s immunotoxin was purified from unreacted gelonin and unconjugated Lym -1 by fast protein liquid chromatography using sephacryl S-300 gel fil tration and blue sepharose affinity gradient separation. Binding of Ly m-1-gelonin immunoconjugate to human Raji Burkitt's lymphoma cells was demonstrated by indirect immunofluorescence using flow cytometry. Lym -1-gelonin was very active in 3-(4,5-dimethylthiazol-2-yl)-2,5-dipheny l tetrazolium salt and sulforhodamine B in vitro cytotoxicity assays a gainst the Raji lymphoma cell line and confirmed the fact that monoclo nal antibody Lym-1 internalizes into human lymphoma cells. A weaker cy tostatic antiproliferative effect was also noted for unconjugated Lym- 1. gamma-interferon augmented the antiproliferative effects of Lym-1-g elonin conjugate and unconjugated Lym-1, by having a direct cytotoxic effect on the Raji cells. Tumor necrosis factor-alpha also enhanced th e antiproliferative effect of unconjugated Lym-1, but did not signific antly augment the cytotoxic activity of the Lym-1-gelonin conjugate. T hese results suggest that anti-HLA class II monoclonal antibodies may be useful in constructing immunotoxins for the treatment of human lymp homas and leukemias expressing HLA class II antigens, and that unconju gated anti-HLA class II monoclonal antibodies may be therapeutically u seful in conjunction with recombinant cytokines, especially gamma-inte rferon.