Zinc finger, X-linked, duplicated family member C (ZXDC) is a human CIITA-binding protein involved in the activation of major histocompatibility complex (MHC) class I and II. For binding to occur, ZXDC must form an oligomeric complex with another copy of itself or with ZXDA, a related protein. ZXDC is activated by sumoylation, a post-translational modification. ZXDC plays a role in controlling immunological responses, cancer formation and progression, and cell proliferation, differentiation, and survival.