Human adenovirus (HAdV) is a cause of significant morbidity and mortality in immunocompromised patients, especially after stem cell transplantation (SCT). Viral clearance has been attributed to CD4(+) T-cell responses against the Hexon-protein, but the frequency of specific T(HELPER) cells is extremely low or not detectable ex vivo and preference for different CD4(+) T-cell epitopes is variable among individuals. We therefore analyzed 44 healthy donors and 6 SCT-recipients for Hexon-specific CD4(+)-responses ex vivo, to identify epitopes which would be broadly applicable. We selected 19 candidate epitopes with predicted restriction to HLA-DR1/DR3/DR4/DR7; 16 were located within the highly conserved regions, indicating cross-reactivity of T cells among HAdV-subspecies. Ten epitopes induced CD4(+)-proliferation in >50% of individuals, confirmed by intracellular IFN-gamma detection. Three SCT recipients who recovered from an infection with HAdV displayed reactivity towards only a single hexon epitope, whereas healthy individuals were responsive to two to eight epitopes (median 3). The ex vivo detection of Hexon-specific CD4(+) T-cells, without any long-term culture in vitro, enables the detection and generation of HAdV-specific CD4(+) T cells for adoptive T-cell transfer against HAdV-infection post SCT.
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