MO3-1-1JAK2 (V617F) positively regulates PD-L1 mRNA expression via STAT3/5 activation in MNP (PV and ET) patients

Abstract Background Escalated PD-L1 expression is reported in many cancer types initiating an immune escape mechanism. This led to the development of checkpoint inhibitors against PD-1/PD-L1. However, the mechanisms underlying escalated production of PD-L1 in many cancers is not clear yet. Methods In this study, we studied PD-L1 mRNA expression levels in concert to JAK2 (V617F) mutation in a group of 72 MPN patients (38 PV and 33 of ET). Clinical and demographical characters were noted carefully. Results Confirmed MPN patients were screened for JAK2 (V617F) mutation by tetra-primer ARMS-PCR. We next quantified JAK2 (V617F) with ASO-PCR. The patients were also screened for BCR/ABL1 fusion gene transcripts to clarify Ph negative MPN status. The mRNA expression levels of PD-L1, STAT3/5 in all MPN patients were evaluated and it was identified that PD-L1, STAT3 but not STAT5 mRNA levels were significantly high in JAK2 (V617F) patients compared to JAK2 (WT) ones. It was also identified that PD-L1, STAT3/5 mRNA expression was upregulated in MPN patients with more JAK2 (V617F) percentage/allele burden than those MPN patients with less JAK2 (V617F) percentage/allele burden. Finally, we evaluated correlation of JAK2 (V617F) percentage with PD-L1, STAT3/5 mRNA expression levels and discovered that PD-L1 and STAT3 are in strong and direct correlation with JAK2 (V617F) burden while STAT5 was found to be moderately correlated. In addition, we identified strong coexpression of PD-L1 and STAT3 and as expected STAT5 moderately coexisted with PD-L1. Conclusion In summary,this study shows that increased PD-L1 expression accompanies JAK2 (V617F) mutation. The increased expression of PD-L1 may be caused by excessive activation of STAT3/5 which are regulators of PD-L1. The study finds that PD-L1 expression is mainly mediated by JAK2 (V617F) via STAT3 and thatSTAT5 only plays a minor role.The study supports the concept of using PD-L1/STAT3/5 axes as targets for developing checkpoint inhibitors.