Costimulation in antiviral immunity: differential requirements for CD4(+) and CD8(+) T cell responses

A key step toward improving vaccines is understanding the molecular interactions responsible for inducing antiviral T cell responses. An emerging theme from recent studies is that CD4(+) and CD8(+) T cell responses require distinct costimulatory pathways for activation. In addition, these costimulatory interactions can play a crucial role during the death phase of the T cell response and determine the number of effector T cells that survive to become memory T cells.