The role of intercellular adhesion molecule-1/LFA-1 interactions in the generation of tumor-specific CD8+ T cell responses

The activation of naive CD4(+) T cells requires both TCR engagement and a second costimulatory signal mediated by the interaction of CD28 with CD80/CD86 expressed on professional APC. However, the situation for naive CD8(+) T cells is less clear. Although evidence indicates that induction of CD8(+) T cell responses is also dependent on professional APC, the ability of some tumors, which do not express CD80/CD86, to induce CTL suggests that other pathways of costimulation exist for the activation of CD8(+) T cells. We examined the ability of tumor cells expressing different levels of a tumor-specific Ag to directly prime CD8(+) T cells. We demonstrate that CD8(+) T cells are directly activated by tumor cells in a CD80/CD86-CD28 independent manner. In this system, costimulation requires ICAM-1/LFA-1 interaction. This results in the generation of CTL capable of inhibiting tumor growth in vivo, and maintaining long-term survival.