As a first step, we measured the frequencies of HCMV-specific CD4+ and CD8+ T-cells in the naïve repertoire of six HCMV-seronegative healthy donors, and in the memory compartment of six patients with primary HCMV infection and seven HCMV-seropositive healthy donors with remote (i.e. occurring >5 years before) infection (Fig 1). Here, CD4 is linked to infection.