PD‐L1 overexpression correlates with JAK2‐V617F mutational burden and is associated with 9p uniparental disomy in myeloproliferative neoplasms

Abstract

Myeloproliferative neoplasms (MPN) are chronic stem cell disorders characterized by enhanced proliferation of myeloid cells, immune deregulation, and drug resistance. JAK2 somatic mutations drive the disease in 50–60% and CALR mutations in 25–30% of cases. Published data suggest that JAK2‐V617F‐mutated MPN cells express the resistance‐related checkpoint PD‐L1. By applying RNA‐sequencing on granulocytes of 113 MPN patients, we demonstrate that PD‐L1 expression is highest among polycythemia vera patients and that PD‐L1 expression correlates with JAK2‐V617F mutational burden (R = 0.52; p < .0001). Single nucleotide polymorphism (SNP) arrays showed that chromosome 9p uniparental disomy (UPD) covers both PD‐L1 and JAK2 in all MPN patients examined. MPN cells in JAK2‐V617F‐positive patients expressed higher levels of PD‐L1 if 9p UPD was present compared to when it was absent (p < .0001). Moreover, haplotype‐based association analyses provided evidence for germline genetic factors at PD‐L1 locus contributing to MPN susceptibility independently of the previously described GGCC risk haplotype. We also found that PD‐L1 is highly expressed on putative CD34+CD38− disease‐initiating neoplastic stem cells (NSC) in both JAK2 and CALR‐mutated MPN. PD‐L1 overexpression decreased upon exposure to JAK2 blockers and BRD4‐targeting agents, suggesting a role for JAK2‐STAT5‐signaling and BRD4 in PD‐L1 expression. Whether targeting of PD‐L1 can overcome NSC resistance in MPN remains to be elucidated in forthcoming studies.

Phenotypic characterization of disease‐initiating stem cells in JAK2‐ or CALR‐mutated myeloproliferative neoplasms

“…Some of these antigens, such as CD99, CD117, CD123, CD184, and CD274 were found to be expressed at higher levels on MPN NSC compared to HSC in most donors, confirming the neoplastic nature of cells. With regard to CD274 (PD‐L1) these data confirm our previous observations 52 . Whether this excess in target expression would provide a therapeutic window remains unknown.…”

“…So far, little is known about the phenotype of NSC in patients with MPN 51,52 . In the present study, we found that CD34 + /CD38 − MPN NSC display numerous 'therapeutic' targets, including CD33, CD44, CD47, CD97, CD99, CD117, CD123, CD133, CD184, and CD274 (PD‐L1) independent of the type of MPN or molecular driver lesion.…”

“…Although MPN are considered to be stem cell‐derived neoplasms, little is known about phenotypic and functional properties of MPN NSC 46,51,52 . In this study, we show that MPN‐initiating NSC reside in a CD34 + /CD38 − fraction of neoplastic cells and that these MPN NSC exhibit several cytokine receptors and various clinically relevant target antigens and checkpoint molecules, including CD33 and PD‐L1.…”

“…Although MPN are considered to be stem cell-derived neoplasms, little is known about phenotypic and functional properties of MPN NSC. 46,51,52 In this study, we show that MPN-initiating NSC reside in a CD34 + /CD38 À fraction of neoplastic cells and that these MPN NSC A number of different mouse models have been examined for their ability to serve as a tool for studying engraftment of MPN NSC. [41][42][43]47,48,53 In earlier studies, NSG mice were employed, but in these mice, only little if any engraftment was found.…”

“…With regard to CD274 (PD-L1) these data confirm our previous observations. 52 Whether this excess in target expression would provide a therapeutic window remains unknown. Some of these markers were variably expressed on NSC among patients depending on the MPN variant.…”