PDCD1 and type 1 diabetes mellitus: Considering the above characteristics, what follows in the passage reviews the possible therapeutic implications in T1D via regulating immune checkpoint molecules (Figure 3), including co-inhibitory molecules (Table 1) and co-stimulatory molecules (Table 2), especially CTLA-4, PD-1, LAG3, and TIGIT, which seems to be considered as pivotal regulatory molecules with excellent clinical application value.