New immune checkpoint inhibitors that mediate T cell inhibitory signaling such as lymphocyte-activation gene 3 (LAG-3), T-cell immunoglobulin and mucin domain-3 (TIM-3), V-domain Ig suppressor of T cell activation (VISTA), T-cell immunoreceptor with Ig and ITIM domains (TIGIT), inducible T-cell co-stimulatory receptor (ICOS), Nuclear receptor subfamily 2, group F, member 6 (NR2F6), sialic acid-binding immunoglobulin-like lectins-8 (SIGLEC8) and B and T lymphocyte attenuator (BTLA) are developed to overcome resistance to cancer immunotherapy and improve the outcome for cancer patients (8–10). Here, ICOS is linked to cancer.