While LDNs in cancer suppress T cells via the PD-L1:PD-1 axis [37,38], arginase I in β-thalassemia LDNs might hydrolyze L-arginine, which is an essential amino acid for T cell receptors [39,40], as observed by an increase in plasma arginase I (Figure 3L) similar to other hemoglobinopathies [41]. This evidence concerns the gene CD274 and hemoglobinopathy.