PDCD1 and type 1 diabetes mellitus: The clinical and cellular phenotypes of the PD-1-deficient proband—including T1D, thyroiditis, pneumonitis, hepatosplenomegaly, and high levels of CD4−CD8− double-negative αβ T cells—resembled those of patients heterozygous for STAT3 GOF variants (Fabre et al., 2019).