Cutting edge: 4-1BB is a bona fide CD8 T cell survival signal

After recognition of Ag/MHC and ligation of a costimulatory molecule, resti ng T cells will clonally expand and then delete to very low levels. Previou sly, it was shown that deletion can be prevented by coinjection of cytokine s or proinflammatory agents such as adjuvants, Here, we demonstrate that li gation of 4-1BB blocks deletion of superantigen-activated T cells in the ab sence of adjuvant or additional cytokine treatment. Nearly 10 times as many staphylococcal enterotoxin A-specific T cells were detected in the spleens of mice injected 21 days previously with staphylococcal enterotoxin A and an agonist anti-4-1BB Ab compared with mice given staphylococcal enterotoxi n A and a control IgG, Even though both CD4- and CDS-activated T cells expr essed 4-1BB, a higher proportion of CD8 T cells were rescued compared CD4 T cells, These data suggest that although 4-1BB provides costimulation, it m ay also promote long-term T cell survival.