Modern research indicates that IFN-γ secretion, the upregulation of NKG2D ligands (such as MICA and ULBP3/6), and the increased expression of MHC I and MHC II molecules and chemokines (such as IL-15, IL-2, and CXCLs) in HFs, all contribute to the failure of HF immune privilege (Paus and Bertolini, 2013). This evidence concerns the gene KLRK1 and Hand-foot syndrome.