CD28 and neoplasm: Mechanistically, in the presence of T-cell receptor signalling, tumour antigen-targeted 4-1BB agonists induce 4-1BB stimulation in response to crosslinking with tumour antigen-expressing cells without relying on FcγR-mediated crosslinking.52 As well as 4-1BB, other co-stimulatory molecules such as CD28 have been shown to improve anti-tumour immune responses to CD3+ T-cell-redirecting antibodies.