When T cells are activated, there are both stimulatory and inhibitory pathways that are activated. CD28 is the activating cytokine. It binds to CD80 and CD86 receptors on antigen-presenting cells. CTLA-4 is homologous to CD28. In fact, it binds CD80 and CD86 receptors with much greater avidity than CD28. Therefore, after some time, the T cell response will be inhibited. In immunotherapy, it has been shown by James P. Allison that blocking the CTLA-4 inhibitory mechanism leads to improved cancer treatment. James Allison won the 2018 Nobel Prize in Physiology and Medicine for this discovery.
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