JAK2 haplotype regulates PD-L1 expression as shown by CRISPR/Cas9 deletion. (A) Genomic locus of JAK2, indicating the region of intron 2 that was deleted to test its regulatory activity (hg19 chr9:5006961-5018796) based on the location of strongly linked 46/1 SNPs (see the supplemental Methods; supplemental Table 3). (B) Expression of JAK2 (left), PD-L1 (middle), and RIC1 (right) in control (green), heterozygous (red), and homozygous (blue) intron 2 element (E_i2) deleted K562 clones. (C) Expression of JAK2 (left), PD-L1 (middle), and RIC1 (right) in control (green), heterozygous (red), and homozygous (blue) intron 2 element (E_i2) deleted K562 clones treated overnight with 10 ng/mL of interferon gamma. In panels B-C, mRNA levels were normalized using GAPDH as an endogenous control, and data were analyzed by 1-way analysis of variance followed by Tukey multiple comparison test; ∗P < .05; ∗∗P < .01; ∗∗∗P < .005; ∗∗∗∗P < .001. Het, hetrorozygous; Hom, homozygous; IFN-γ, interferon gamma; mRNA, messenger RNA.