CD8A and influenza: Even though the split-virus influenza vaccines administered in this clinical trial contain significant amounts of M1 and NP (Co et al., 2009), re-stimulation of CD8+ T cell memory relies on antigen cross-presentation by dendritic cells, a function that declines with age (Chougnet et al., 2015) and contributes to an already weak stimulus of memory CD8+ T cells.