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

A key step toward improving vaccines is understanding the molecular interac tions responsible for inducing antiviral T cell responses. An emerging them e from recent studies is that CD4(+) and CD8(+) T cell responses require di stinct costimulatory pathways for activation. In addition, these costimulat ory interactions can play a crucial role during the death phase of the T ce ll response and determine the number of effector T cells that survive to be come memory T cells.