To date, there have been 6 immune checkpoint inhibitor antibodies (ipilimumab [17], nivolumab [18], pembrolizumab [19], avelumab [20], atezolizumab [21], and durvalumab [22]) against CTLA4 or PD-1 approved by the U.S. Food and Drug Administration (FDA) for the treatment of a few cancer types. Here, CTLA4 is linked to cancer.