The cytotoxic T-lymphocyte-associated antigen 4 (CTLA-4), the key immune checkpoint and target gene of miR-155, plays a key regulatory role in mediating self-tolerance, preventing autoimmunity, and protecting tissues from immune attack (Zhang & Zheng, 2020; Chikuma, 2017; Chao et al., 2019). The gene discussed is CTLA4; the disease is Autoimmunity.