IRF4 and plasma cell myeloma: To further determine if activation of STAT3 is involved in resistance to IMiDs in this cell line, a selective STAT3 inhibitor (PB-1-102) was then employed which re-sensitized XG1LenRes to lenalidomide and induced a synergistic anti-myeloma activity and downregulation of IRF4 (both full length and short form) and MYC expression (Fig. 5f, g).