PDCD1 and multiple sclerosis: PD-1 normally functions by disrupting T-cell activation, thereby preventing activation of the immune response; this immune checkpoint, and others, is essential to prevent hyperactivation of the immune system, which can result in autoimmune disorders (e.g., rheumatoid arthritis and multiple sclerosis), but cancer cells can exploit this mechanism in order to evade immune-response-mediated cell death.90 Immune checkpoint inhibitors such as anti-PD-1 thus enable T cells to kill cancer cells again and further enhance the anticancer immune response induced by TTFields therapy (Fig. 3D).