The clonal hierachy in multiple myeloma

In this report we evaluated the number and phenotype of blood circulating B -cell subsets at different stages of differentiation in 26 patients with ne wly diagnosed multiple myeloma (MM). In all patients, plasma cells and/or p lasma blasts could be identified by flow cytometry with a mean frequency of 1.20% and 0.07%, respectively. In 76.9% of the patients these cells showed aberrant expression mainly of CD56, CD28 and CD117, none of these markers were found on the earlier B-lymphocytes. Clonal B-cells preceding the plasm a blast stage were identified by patient specific IgH RT-PCR on sorted B-ce ll subsets. The clonal cells included the less differentiated CD38(+)/CD19( +) and CD38(-)/CD19(+) subsets, illustrating that the clonal cells are part of an ongoing differentiation process. Further, the presence of CD38(-)/CD 19(+) cells with somatically mutated C gamma transcripts identical to the t umor-specific C alpha transcript, shows that the clonal hierarchy in myelom a may include memory B-cells.