In summary, our in vitro studies demonstrate that the tumour cells of Myeloma are capable of inducing T-cells with the phenotypic and functional characteristics of TReg cells, associated with the production of IL-10 and IFNγ The induction of TReg cells is mediated by cell-to-cell contact with the ICOS/ICOS-L system demonstrating a central role in the induction. Here, ICOSLG is linked to plasma cell myeloma.