Cytotoxic T-cell memory without antigen

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Abstract
MEMORY is a hallmark of the immune system and ever since its recognition there has been considerable interest in understanding how immunity is maintained1–5. The current model is that long-term memory is dependent on persistent antigenic stimulation6–11. We report here results that challenge this view and provide evidence that antigen is not essential for the maintenance of CD8+ T-cell memory. We show that memory CD8+ cytotoxic T lymphocytes persist indefinitely in the absence of priming antigen, retain the memory phenotype (CD44hi), and provide protection against virus challenge. These findings suggest a re-evaluation of our current thinking on mechanisms involved in maintaining immunity and have implications towards designing effective vaccination strategies.