Overexpression of PD-L1 Correlates with JAK2-V617F Mutational Burden and Is Associated with Chromosome 9p Uniparental Disomy in MPN

Myeloproliferative neoplasms (MPN) are characterized by clonal hematopoiesis, hyperproliferation of myeloid cells, hyperinflammation and immune deregulation. The three classical BCR-ABL1-negative MPN are essential thrombocythemia (ET), polycythemia vera (PV) and primary myelofibrosis (PMF). The disease is driven by JAK2, CALR or MPL somatic mutations in most patients. Drug resistance is a major problem in MPN. Recent data suggest that MPN cells display certain immune checkpoint molecules that may contribute to resistance, including PD-L1. Antibodies targeting the PD1/PD-L1 axis are highly promising anti-cancer drugs. Their potential use in MPN is being explored but it is unclear which MPN subtypes are most suitable for testing in clinical trials. The aim of our project was to assess PD-L1 expression in disease-initiating neoplastic stem cells (SC) and differentiated cells of MPN patients and to develop therapeutic approaches capable of blocking PD-L1 expression in MPN SC. In a first step, PD-L1 expression was assessed by RNA-sequencing of granulocytes of 106 MPN patients and 15 healthy donors (HD). The cohort included 56 PMF, 33 ET and 17 PV patients. For 102 patients data from Human Genome-wide Affymetrix 6.0 SNP arrays were available. We observed a ~5-fold higher expression of PD-L1 mRNA in patients with PV compared to other MPN (P Download : Download high-res image (174KB) Download : Download full-size image Disclosures Gisslinger: Celgene: Honoraria; MyeloPro Diagnostics and Research: Honoraria; AOP Orphan Pharmaceuticals AG: Honoraria, Research Funding; Novartis: Honoraria, Research Funding; PharmaEssentia: Honoraria; Janssen-Cilag: Honoraria; Roche: Honoraria. Kralovics: AOP Orphan Pharmaceuticals AG: Honoraria; PharmaEssentia: Honoraria; Qiagen: Honoraria; Novartis: Honoraria; MyeloPro Diagnostics and Research: Current equity holder in private company. Valent: Allcyte GmbH: Research Funding; Pfizer: Honoraria; Cellgene: Honoraria, Research Funding.