XCL1 and cancer: Enhancement of NK cells in DC-based vaccines is important because activated NK cells can help T cells to eradicate cancer cells that lose expression of MHC class I. Additionally, in vivo tumor-infiltrating NK cells can recruit more DCs through the secretion of CCL5 and XC-chemokine ligand 1 (XCL1), along with enhanced DC development and proliferation through secretion of FMS-related tyrosine kinase 3 ligand (FLT3L) [7].