Fig 1.

Signalling cascade from the interactions of tumour cells and antigen-presenting cells with naive T cells. Two signals are required for T-cell activation and proliferation. The first signal comes from T-cell receptor binding to an antigen presented on a major histocompatibility complex on the surface of a tumour cell/antigen-presenting cell. Without a costimulatory receptor, T cells remain in a quiescent state. The second signal occurs with the binding of CD28 on T cells and B7 proteins on tumour/antigen-presenting cells. These two signals initiate T-cell activation and proliferation. APC, antigen-presenting cells; MHC, major histocompatibility complex; TCR, T-cell receptor. From ‘The future of immunotherapy’, P. Sharma and J. Allison, Science, 2015; 348: 56–61 Reprinted with permission.