The reduced toxicity is consistent with the distinct phenotypes of PD1 genetic knockout mice, which develop delayed-onset organ-specific inflammation as opposed to the uncontrolled global T cell proliferation seen in CTLA-4 knockouts [3], and might hint at the benefits of specifically targeting the properties of cancer that inhibit the immune response rather than non-specific activation of the immune system [11]. Here, CTLA4 is linked to cancer.