Quantitative Analysis of Adenovirus-Specific CD4 + T-Cell Responses from Healthy Adults

Although nearly all adults are seropositive for adenoviruses, little is known about the cellular immune responses to these ubiquitous pathogens. We have previously identified adenovirus-specific proliferative T-cell responses in peripheral blood mononuclear cells (PBMC) from healthy adults. In this study, memory T-cell responses to adenovirus were further evaluated in healthy adult donors using a short term, quantitative enzyme-linked immunospot assay (ELISPOT) assay. Adenovirus antigen induced specific secretion of interferon-γ (IFN-γ) from PBMC within 12 hours of incubation. PBMC from 20 of 22 healthy donors (90.9%) expressed IFN-γ in response to adenovirus. Responder cells were identified as CD4⁺ T cells by immunomagnetic depletion methods. Interleukin-4(IL-4) secretion was not detected, consistent with a TH1 response. There was a 10-fold variation in the frequencies of adenovirus-specific CD4⁺ T cells between donors (range, 34 to 294; median, 122 per million PBMC). Adenovirus-specific T cell frequencies remained stable over periods up to 2 years among individual donors, but there was an inverse correlation between frequency and donor age. These quantitative data suggest that most adults retain adenovirus-specific cellular memory after childhood exposure. This assay may be useful for the evaluation of adenovirus-specific CD4⁺ T-cell responses in patients treated with adenovirus gene therapy vectors and the identification of major T-cell epitopes.