Real time PCR for the assessment of CD8+ T cellular immune response after prophylactic vaccinia vaccination

BackgroundThe magnitude of specific CD8+ T cell reactivity responsible for vaccine-induced protection against smallpox infection has not yet been fully elucidated. Among other techniques, RT-PCR for the monitoring of cytokine release in effector T cells against tumor and viral antigens has demonstrated a novel promising method.ObjectiveTo determine the functional status of antigen specific CD8+ T cells in healthy participants before and 4 weeks after prophylactic vaccination (Lister strain) against smallpox using quantitative real-time PCR (qRT-PCR).Study designChanges of interferon-γ (IFNγ) mRNA expression levels on short term ex vivo peptide antigen stimulation were measured. The corresponding specific CD8+ T cell reactivity was then displayed as CD8-normalized IFN-γ levels (IFN-γ/CD8 ratio).ResultsWe found a 5–9 fold increase of CD8+ T cell reactivity in three out of four vaccinated individuals. The kinetics and strength determined in responders reveal a virus specific T cell effector repertoire pre-vaccination and a corresponding functional state after immunization comparable also to data obtained from tetramer- and ELISPOT analysis.ConclusionsApart from protective vaccinia-specific neutralizing antibodies, the presence of antigen-specific CD8+ T-cells has been demonstrated after vaccinia vaccination. In concordance with others, results from this PCR-based study indicate that this smallpox vaccine induces strong vaccinia virus-specific CD8+ and IFN-γ producing T cell responses.