CD4 and neoplasm: For instance, the chemokine receptor CXCR6 is expressed almost selectively by CD4+ T cells, CD8+ T cells, NKT cells, NK cells, plasma cells [41], while no or only very weak CXCR6 protein expression could be detected in colon cancer cells and, of particular relevance, its increased expression and the enhanced presence of its unique ligand CXCL16 in colon tumor tissue turned out to be associated with marked T cell infiltration and improved tumor prognosis [25,32,42].