THE MYELOMA CELL ANTIGEN SYNDECAN-1 IS LOST BY APOPTOTIC MYELOMA CELLS

Syndecan-1 is a cell membrane proteoglycan that binds extracellular ma trix components and various growth factors, It is ex-pressed only on m alignant plasma cells in bone marrow samples from patients with multip le myeloma (MM). Several reports have suggested that syndecan-1 was pr esent only on a part of the myeloma cells, By using either IL-6-depend ent myeloma cell lines or primary myeloma cells stained by annexin V, rye report here that syndecan-1 was rapidly lost by myeloma cells unde rgoing apoptosis. In the same experimental conditions, expression of o ther cell membrane antigens such as CD38, HLA class-I or CD49d on apop totic myeloma cells was not affected. In addition, we show that syndec an-1 loss was independent of activation of the gp130 IL-6 transducer. Dexamethasone induced a strong apoptosis of myeloma cells associated w ith the loss of syndecan-1. Finally by using freshly-explanted tumoura l samples, we show that syndecan-1 rapidly disappeared from myeloma ce lls in association with induction of apoptosis. In conclusion we showe d that syndecan-1 is a marker for viable myeloma cells which is rapidl y lost by apoptotic cells. These results emphasize the usefulness of a nti-syndecan-1 antibodies to purge tumoural cells from haemopoietic gr afts or to purify these cells for further manipulations for immune or gene therapies.