Mature T-cell lymphomas, including peripheral T-cell lymphoma (PTCL) and extranodal NK/T-cell lymphoma (NKTL), represent a heterogeneous group of non-Hodgkin lymphomas with dismal outcomes and limited treatment options. To determine the extent of involvement of the JAK/STAT pathway in this malignancy, we performed targeted capture sequencing of 188 genes in this pathway in 171 PTCL and NKTL cases. A total of 272 nonsynonymous somatic mutations in 101 genes were identified in 73% of the samples, including 258 single-nucleotide variants and 14 insertions or deletions. Recurrent mutations were most frequently located in and (15%), followed by and (6%) and (4%). A high prevalence of mutation (21%) was observed specifically in NKTL. Novel mutations (p.D427H, E616G, p.E616K, and p.E696K) were shown to increase STAT3 phosphorylation and transcriptional activity of in the absence of cytokine, in which p.E616K induced programmed cell death-ligand 1 (PD-L1) expression by robust binding of 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.

Epitheliotropic intestinal T-cell lymphoma (EITL, also known as type II enteropathy-associated T-cell lymphoma) is an aggressive intestinal disease with poor prognosis and its molecular alterations have not been comprehensively characterized. We aimed to identify actionable easy-to-screen alterations that would allow better diagnostics and/or treatment of this deadly disease. By performing whole-exome sequencing of four EITL tumor-normal pairs, followed by amplicon deep sequencing of 42 tumor samples, frequent alterations of the JAK-STAT and G-protein-coupled receptor (GPCR) signaling pathways were discovered in a large portion of samples. Specifically, STAT5B was mutated in a remarkable 63% of cases, JAK3 in 35% and GNAI2 in 24%, with the majority occurring at known activating hotspots in key functional domains. Moreover, STAT5B locus carried copy-neutral loss of heterozygosity resulting in the duplication of the mutant copy, suggesting the importance of mutant STAT5B dosage for the development of EITL. Dysregulation of the JAK-STAT and GPCR pathways was also supported by gene expression profiling and further verified in patient tumor samples. In vitro overexpression of GNAI2 mutants led to the upregulation of pERK1/2, a member of MEK-ERK pathway. Notably, inhibitors of both JAK-STAT and MEK-ERK pathways effectively reduced viability of patient-derived primary EITL cells, indicating potential therapeutic strategies for this neoplasm with no effective treatment currently available.

Hodgkin lymphoma is caused by a minority population of malignant Hodgkin and Reed-Sternberg (HRS) cells that recruit an abundance of inflammatory cells. The long-term survival of HRS cells among the vast majority of immune cells indicates that they have developed potent immune escape mechanisms. We report that the TNF receptor family member CD137 (TNFRSF9) is expressed on HRS cells, while normal B cells, from which HRS cells are most often derived, do not express CD137. In 48 of 53 cases of classical Hodgkin lymphoma, CD137 was detected on HRS cells. Ectopically expressed CD137 transferred by trogocytosis from HRS cells to neighboring HRS and antigen-presenting cells, which constitutively express the CD137 ligand (CD137L and TNFSF9), became associated with CD137L and the CD137-CD137L complex was internalized. Disappearance of CD137L from the surface of HRS and antigen-presenting cells led to reduced costimulation of T cells through CD137, reducing IFN-g release and proliferation. Our results reveal a new regulatory mechanism for CD137L expression that mediates immune escape by HRS cells, and they identify CD137 as a candidate target for immunotherapy of Hodgkin lymphoma. Cancer Res; 73(2); 652-61. Ó2012 AACR.

Aberrant activation of the JAK3-STAT signaling pathway is a characteristic feature of many hematological malignancies. In particular, hyperactivity of this cascade has been observed in natural killer/T-cell lymphoma (NKTL) cases. Although the first-in-class JAK3 inhibitor tofacitinib blocks JAK3 activity in NKTL both in vitro and in vivo, its clinical utilization in cancer therapy has been limited by the pan-JAK inhibition activity. To improve the therapeutic efficacy of JAK3 inhibition in NKTL, we have developed a highly selective and durable JAK3 inhibitor PRN371 that potently inhibits JAK3 activity over the other JAK family members JAK1, JAK2, and TYK2. PRN371 effectively suppresses NKTL cell proliferation and induces apoptosis through abrogation of the JAK3-STAT signaling. Moreover, the activity of PRN371 has a more durable inhibition on JAK3 compared to tofacitinib in vitro, leading to significant tumor growth inhibition in a NKTL xenograft model harboring JAK3 activating mutation. These findings provide a novel therapeutic approach for the treatment of NKTL.