T_H17 Pathway and Associated Pro-Inflammatory Cytokines Promote Immune Dysfunction in Myeloma.

Multiple myeloma (MM) is associated with significant immune dysfunction. Although various mechanisms mediating immune dysregulation in MM have been studied, its molecular and cellular basis is ill defined. IL-6, TGF-β and IL-1β have been implicated in this process, but their mechanism of effects on immune function have not been studied in MM. Together, IL-6 and TGF-β enhance the generation of T_H17 cells, important in the development of immunity and auto-immunity. Additionally, T_H17 cells are differentiated by number of inflammatory cytokines including, IL-21, IL-22, IL-23, and IL-27. Therefore, we evaluated the immune dysfunction and the role of T_H17 cells and associated pro-inflammatory cytokines in myeloma. We have previously characterized that the production of T_H1 mediated cytokines including IFN-γ following anti-CD3-mediated activation is significantly lower in myeloma PBMC compared to normal PBMC. We hypothesize that this may be regulated via skewing the immune system towards T_H17 pathway. We observed that T_H17 cells, measured by intra-cellular flow cytometry, are significantly increased in number in myeloma (16.9%) and MGUS (6.2%) compared to normal (3.3%). Furthermore, we analysed supporting pro-inflammatory cytokine network for the generation of T_H17 cells in myeloma, which may be responsible for the observed T_H17 skewing of T cell subsets. Sera from MGUS (n=12) and myeloma (n=17) patients were evaluated for the presence of these pro-inflammatory cytokines compared with normal sera (n=6) using ELISA. We observed significant increase in serum IL-21, IL-22 and IL-23 in MGUS (373 pg/ml, 14 pg/ml and 147 pg/ml respectively; p<0.05) and myeloma (296 pg/ml, 12 pg/ml and 215 pg/ml respectively; p<0.05) compared with normal (63 pg/ml, 1.5 pg/ml and 39 pg/ml respectively). In addition, we also observed that the myeloma PBMC stimulated in the presence of IL-6 and TGF-β, both of the cytokines present at a high level in myeloma, induced significant IL-23 production compared with normal. Importantly, IL-23 levels were 10 fold higher in myeloma BM samples compared with matching blood samples. These results indicate that the cytokines from myeloma BM microenvironment may be responsible for the observed T cell subset abnormality by favouring T_H17 cells via IL-23/IL-21 production. These cytokines thus may be targets to modulate immune responses in myeloma to enhance immune function and devise effective vaccination strategies in the future.