B-LYMPHOMA CELLS ARE ACTIVATED BY PEPTIDE LIGANDS OF THE ANTIGEN-BINDING RECEPTOR OR BY ANTIIDIOTYPIC ANTIBODY TO INDUCE EXTRACELLULAR ACIDIFICATION

Synthetic peptide ligands specific for the surface immunoglobulin rece ptor of the human Burkitt's lymphoma cell line SUP-B8, previously iden tified using phage display libraries, induced apoptosis of the SUP-B8 cells in vitro when administered as dimers or tetramers, The use of sy nthetic peptide ligands is being explored for immunotherapy of B-cell lymphoma. It will be critical to identify which of the peptide ligands identified are the most active functionally. Using the Cytosensor mic rophysiometer, SUP-B8 cells and B-lymphoma cells obtained from patient s were found to acidify their extracellular environment within minutes of specific activation by surrogate peptide ligands or by anti-idioty pe antibodies. This signal was blocked by pretreatnent of the lymphoma cells with the tyrosine kinase inhibitor genistein, Treatment of SUP- B8 cells with dimeric and tetrameric specific peptide ligands caused a rapid increase in extracellular acidification rate, which peaked afte r 10 min at approximately 15 and 20% above basal rates, respectively. These responses were blocked by excess monomeric peptide. To evaluate the ability of different peptide ligands to induce a signal directly o n lymphoma cells, thereby establishing their relative affinity to the surface immunoglobulin receptor, acidification rate changes were measu red at varying peptide concentrations. The microphysiometer signal cor related with the known relative affinities and antiproliferative poten cies of the peptides. This approach is particularly useful for primary tumor cells that cannot be cultured. The signal may be predictive of the efficacy of treatment with synthetic peptide ligands and may be us eful in the evaluation of ligands for other cell surface receptors wit h biological effects on B-lymphoma cells.