The JAK2 46/1 haplotype influences PD-L1 expression.

Although described more than a decade ago, the mechanism by which the JAK2 46/1 haplotype increases the risk of developing JAK2-mutated myeloproliferative neoplasms (MPN) remains unexplained. Inflammation and immunity are linked to MPN development and thus could be relevant to the mechanism by which 46/1 mediates its effect. Here, we show that PD-L1 expression is elevated in 46/1 haplotype both in healthy carriers and CD34+ cells from MPN patients. Using circular chromosome conformation capture (4C-seq) we observed that PD-L1 and the neighboring PD-L2 loci physically interact with JAK2 in a manner that differs between 46/1 and non-risk haplotypes. CRISPR/Cas9 genome editing identified a region within JAK2 intron 2 that influences both JAK2 and PD-L1 expression. We suggest that increased PD-L1 expression may be relevant to the mechanism by which 46/1 leads to an increased inherited risk of developing MPN.