A study showed that the transfer of higher numbers of RSV-specific CD8+ T cells results in more-severe disease although viral clearance correlates with the number of CD8+ T cells (41), consistent with another report showing that high numbers of adoptively transferred transgenic T cells induce protection following low-dose viral challenge of influenza virus but exacerbate infection after high-dose challenge (33). The gene discussed is CD8A; the disease is infection.