Consistently, treatment with a STAT3 inhibitor, Stattic, in NKYS and SNK6 reduced pSTAT3 and PD-L1 expression levels (Figure 4D-F), which was also observed in p

Consistently, treatment with a STAT3 inhibitor, Stattic, in NKYS and SNK6 reduced pSTAT3 and PD-L1 expression levels (Figure 4D-F), which was also observed in p.E616K-expressing Ba/F3 cells (supplemental Figure 5). activated STAT3 to the PD-L1 gene promoter. Consistent with these findings, PD-L1 was overexpressed in NKTL cell lines harboring hotspot mutations, and similar findings were observed by the overexpression of p.E616K and p.E616G in the wild-type NKTL cell line. Conversely, STAT3 silencing and inhibition decreased PD-L1 expression in mutant NKTL cell lines. In NKTL tumors, STAT3 activation correlated significantly with PD-L1 expression. We demonstrated that STAT3 activation confers high PD-L1 expression, which may promote tumor immune evasion. The combination of PD-1/PD-L1 antibodies and STAT3 inhibitors might be a promising therapeutic approach for NKTL, and possibly PTCL. Visual Abstract Open in a separate window Introduction Mature T-cell MG-262 lymphomas, including peripheral T-cell lymphoma (PTCL) and NK/T-cell lymphoma (NKTL), appear to have a geographical predilection for Asia.1-3 The World Health Organization classification recognizes a number of distinctive subtypes of PTCL and NKTL, including angioimmunoblastic T-cell lymphoma, anaplastic MG-262 lymphoma kinase-positive (ALK+) and anaplastic lymphoma kinase-negative (ALK?) anaplastic large cell lymphoma (ALCL), cutaneous T-cell lymphoma (CTCL), and PTCL not otherwise specified (PTCL-NOS).4 With the exception of ALK+ ALCL, patients with PTCL and NKTL generally have a poor prognosis, with 5-year overall survival rates less than 40%.4 Multiple studies have suggested that the JAK/STAT pathway plays a significant role in the pathogenesis of PTCL and NKTL. We previously identified activating mutations in about one-third of NKTL cases.5 Activating mutations of and/or were found in 18% of ALK? ALCL, while being absent either in ALK+ ALCL or in PTCL-NOS.6 In contrast, and mutations were recently reported in 2 of 4 patients with PTCL-NOS.7 Collectively, the mutation frequencies varied greatly among the PTCL and NKTL subtypes and between studies. In NKTL, was constitutively activated in 87% of cases; however, only 21% of these could be explained by mutations. This suggests the presence of key activating and/or cooperating mutations other than the JAKs and STATs.8 Programmed cell death-ligand 1 (PD-L1) and programmed cell death-1 (PD-1) are important immune checkpoint molecules involved in immune evasion.9 PD-1/PD-L1 blockade by monoclonal antibodies has achieved great efficacy and is approved by the US Food and Drug Administration for a number of malignancies ZCYTOR7 such as gastric carcinoma,10 urothelial carcinoma,11 melanoma,12 and classical Hodgkin lymphoma (cHL).13 Recently, PD-1 blockade demonstrated a promising clinical response in patients with relapsed or refractory NKTL, and a strong PD-L1 expression level was found to correlate with better outcome.14,15 The genetic and molecular basis of PD-L1 overexpression has been investigated in multiple hematological malignancies.16-18 In cHL, copy gains of MG-262 9p24.1 locus resulted in PD-L1 overexpression,16 and in diffuse large B-cell lymphoma and adult T-cell lymphoma, the structural variants disrupting the 3 region of the gene led to aberrant transcripts with elevated expression.19 In ALK+ ALCL, the oncogenic fusion induced the expression of PD-L1 through STATWeb site. Cell lines and cell culture conditions are described in supplemental Methods. This study was approved by the SingHealth Centralized Institutional Review Board (study number 2004/407/F). Primary natural killer cell isolation for western blot Primary human natural killer (NK) cells were isolated from peripheral blood mononuclear cells by depletion of non-NK cells using a human NK cell isolation kit (Miltenyi Biotec). Purity of NK cells was evaluated by CD56-PE staining, and samples with more than 90% CD56+ cells were used. Cells were cultured in X-VIVO 15 medium (Lonza) supplemented with 5% human serum (Innova Biosciences) with 200 U/mL interleukin 2 (IL-2; Proleukin). Genomic DNA extraction Genomic DNA from formalin-fixed, paraffin-embedded, snap-frozen tumor tissues and whole blood was extracted as previously described.21 For buccal swab samples, DNA was extracted using EZNA Tissue DNA kit (Omega Bio-tek). Genomic DNA yield and quality were assessed as previously described.21 Deep-targeted capture sequencing Targeted capture sequencing was performed with a customized capture probe set that targeted exons of 188 JAK/STAT pathway-related genes (supplemental Table 2). One hundred seventy-one PTCL and NKTL gDNA samples were sequenced on the HiSeq2000 platform (Illumina) to a mean depth of 726-fold (supplemental Table 3). GATK was used to call single-nucleotide substitutions and insertion/deletions (indels), and candidate variants were MG-262 annotated using wAnnovar. A subset of mutations was randomly selected and verified by Sanger sequencing, as described previously,5.