KLRK1 and neoplasm: It is noteworthy that the delivery of IL-21 by human UC-MSCs altered the expression of TNF-α and IFN-γ in the murine serum, increased the expression of major histocompatibility (MHC) class I polypeptide-related sequence A (MICA) and NK group 2D (NKG2D) molecules in tumour tissues, and finally reduced the expression of cyclin-D1 and β-catenin in the tumour, resulting in hampered tumour growth post-transplantation (53).