CD2 and cytomegalovirus infection: Tumour-primed NK cells show expansion of metacluster “3”, which is characterized by high expression of CD2, further confirming the importance of the CD2-CD15 interaction in tumour-priming [77]; thus, it appears that memory induced by tumour-priming share a dependence on CD2 ligation with memory generated during CMV infection [58,77,78,79,80].