KLRC1 and post-transplant lymphoproliferative disease: Compared to cytomegalovirus (CMV)-seropositive and -negative IM patients, PTLD patients co-infected with CMV and EBV had significantly higher levels of a CMV-associated CD56dimNKG2ChiCD57+NKG2A−KIR+ NK cell subset accumulating at the expense of NKG2A+KIR− NK cells.