CXCR4 and plasma cell myeloma: It is important to note, however, that anti-IL-6 therapy has not proven to be an efficacious agent in MM thus far, suggesting that targeting this signalling axis alone is likely to be insufficient to achieve clinical benefit.43 PADI2 may therefore represent a novel upstream target, as our data suggest that its activity increases expression of other central signalling networks between BMMSCs and myeloma cells, such as HGF-cMET and CXCL12-CXCR4 (Figure 4b).