Work by Kochupurakkal et al. in NOD mice demonstrated that specific strains are protected from developing T1D after PD-1 blockade by having functional alleles for Il2 and Ctla4. It was speculated that the functional Ctla4 allele with the help of IL-2 was sufficient to maintain self-tolerance and prevent T1D [25]. Here, CTLA4 is linked to type 1 diabetes mellitus.