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

Abstract

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.