However, cell-mediated immunity is more important than humoral immunity in controlling CMV infection.3 Cellular immune responses measured as the in vitro production of IFN-γ by CD8+ T lymphocytes in response to CMV peptides has recently been defined as a biomarker associated with the risk of CMV infection and disease post-transplant.4–7 As these cellular immune responses are restricted by HLA Class I alleles for peptide recognition, in addition to determining the CMV seroprevalence rate in Ireland, the association of CMV seropositivity with HLA Class I alleles was also examined. This evidence concerns the gene IFNG and cytomegalovirus infection.