Immune regulation in multiple myeloma: the host-tumour conflict

Multiple myeloma (MM) remains essentially incurable by conventional anti-tu mour therapy. This has led to increased interest in the possibility that fo rms of immune therapy might be effective. The successful use of donor lymph ocyte infusions (DLI) in a few cases of Mn;I relapse following allogeneic b one marrow transplantation have added weight to this view. MM is characteri zed by several defects in the host's immune system. The influence of the ma lignant clone on the function of the immune effector cells results from bot h passive and active suppression. Despite an array of functional adhesion m olecules and HLA class I and II molecules on their surface and the secretio n of a tumour-specific peptide, they fail to express adequate levels of co- stimulatory molecules thus inducing anergy in potentially tumour-specific T cells. In addition to this passive evasion of immune regulation, MM tumour cells are capable of producing a number of immunologically active agents w hich can induce immunosuppression such as transforming growth factor-beta, Fas ligand (FasL), vascular endothelial growth factor and Muc-1. It is post ulated that these agents may be produced by the tumour cell to influence th e microenvironment to support growth and differentiation of the clone but m ay have the additional benefit of altering the function of the host immune effector cells and thus preventing tumour rejection. This duality of functi on is important if clinicians are to design immunotherapy strategies which will achieve the true potential and result in improved survival in MM. (C) 1999 Harcourt Publishers Ltd.