Suppression of Myeloma Growth In Vitro by Anti-idiotypic Antibodies: Inhibition of DNA Synthesis and Colony Formation 2

Abstract

Antibodies reactive with the unique (i.e., idiotypic) determinants of the S107 myeloma protein were raised in rabbits. Such anti-idiotypic antibodies inhibited DNA synthesis and colony formation of S107 myeloma cells in soft agar. Variant subclones of the S107 myeloma were isolated. They differed in the density of surface immunoglobulin (Ig) and in the amounts of Ig secreted. Clear differences were found in the sensitivity of the different sublines to the anti-idiotypic antibody and complement. Colony formation of myeloma cells with a high density of surface idiotype was strongly inhibited, whereas the antibody only moderately suppressed the growth of myeloma cells with a reduced density of cell-surface idiotype. The effect of anti-idiotypic antibodies depended on the presence of complement or normal spleen cells. Developing colonies of the myeloma cells became increasingly protected from the effects of the antibodies at a rate that was a function of the amount of myeloma protein secreted. Furthermore, preincubation of the tumor cells with anti-idiotypic antibodies in the absence of complement made myeloma cells resistant to subsequently added antibody and complement. Anti-idiotypic antisera were not cytotoxic as measured by a⁵¹Cr-release or dye-exclusion assay. Thus assays measuring inhibition of DNA synthesis and colony formation of the myeloma cells proved to be highly sensitive and effective methods to detect specific cell-surface-bound Ig markers and to demonstrate the susceptibility of tumor cells to specific immune effector mechanisms. Furthermore, the cloning procedure permitted isolation of tumor cell variants that differed in susceptibility to idiotype-specific immunity.