Individuals with inherited chromosomally integrated human herpes virus 6 (ciHHV-6) have functionally active HHV-6 specific T-cell immunity

To evaluate the human herpes virus 6 (HHV-6) -specific immune response in individuals with chromosomally integrated HHV-6 (ciHHV-6), we measured HHV-6-antigen-specific cytokine responses (interferon-γ, interleukin-2, tumour necrosis factor-α) in T cells by flow cytometry in 12 and 16 individuals with and without ciHHV-6, respectively. All individuals with ciHHV-6 showed HHV-6-specific T cells with higher frequencies of HHV-6-specific CD8+ cells (0.03–14.93, median 2.15% of CD8+ cells) compared with non-ciHHV-6 (0.0–10.67, median 0.36%, p 0.026). The observed increased HHV-6-specific functionally active responses in individuals with ciHHV-6 clearly disprove speculations on immune tolerance in ciHHV-6 and indicate clinical and immunological implications of ciHHV-6.