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With lowering costs of sequencing and genetic profiling techniques, genetic drivers can now be detected readily in tumors but current prognostic models for Natural-killer/T cell lymphoma (NKTCL) have yet to fully leverage on them for prognosticating patients. Here, we used next-generation sequencing to sequence 260 NKTCL tumors, and trained a genomic prognostic model (GPM) with the genomic mutations and survival data from this retrospective cohort of patients using LASSO Cox regression. The GPM is defined by the mutational status of 13 prognostic genes and is weakly correlated with the risk-features in International Prognostic Index (IPI), Prognostic Index for Natural-Killer cell lymphoma (PINK), and PINK-Epstein-Barr virus (PINK-E). Cox-proportional hazard multivariate regression also showed that the new GPM is independent and significant for both progression-free survival (PFS, HR: 3.73, 95% CI 2.07-6.73; p

Although combination therapy is the standard of care for relapsed/refractory non-Hodgkin’s lymphoma (RR-NHL), combination treatment chosen for an individual patient is empirical, and response rates remain poor in individuals with chemotherapy-resistant disease. Here, we evaluate an experimental-analytic method, quadratic phenotypic optimization platform (QPOP), for prediction of patient-specific drug combination efficacy from a limited quantity of biopsied tumor samples. In this prospective study, we enrolled 71 patients with RR-NHL (39 B cell NHL and 32 NK/T cell NHL) with a median of two prior lines of treatment, at two academic hospitals in Singapore from November 2017 to August 2021. Fresh biopsies underwent ex vivo testing using a panel of 12 drugs with known efficacy against NHL to identify effective single and combination treatments. Individualized QPOP reports were generated for 67 of 75 patient samples, with a median turnaround time of 6 days from sample collection to report generation. Doublet drug combinations containing copanlisib or romidepsin were most effective against B cell NHL and NK/T cell NHL samples, respectively. Off-label QPOP-guided therapy offered at physician discretion in the absence of standard options ( n = 17) resulted in five complete responses. Among patients with more than two prior lines of therapy, the rates of progressive disease were lower with QPOP-guided treatments than with conventional chemotherapy. Overall, this study shows that the identification of patient-specific drug combinations through ex vivo analysis was achievable for RR-NHL in a clinically applicable time frame. These data provide the basis for a prospective clinical trial evaluating ex vivo–guided combination therapy in RR-NHL.

Summary Peripheral T‐cell lymphomas (PTCL) and natural killer (NK)/T‐cell lymphomas (NKTCL) are a heterogeneous group of aggressive malignancies with dismal outcomes and limited treatment options. While the phosphatidylinositol 3‐kinase (PIK3) pathway has been shown to be highly activated in many B‐cell lymphomas, its therapeutic relevance in PTCL and NKTCL remains unclear. The aim of this study is to investigate the expression of PIK3 and phosphatase and tensin homolog (PTEN) in these subtypes of lymphoma and to identify potential therapeutic targets for clinical testing. Therefore, the expression of PIK3α, PIK3β, PIK3γ, PIK3δ and PTEN was analyzed in 88 cases of PTCL and NKTCL samples by immunohistochemistry. All PTCL and NKTCL samples demonstrated high expression of PIK3 isoforms. In particular, high PIK3α expression was significantly associated with poor survival, even after adjustment for age, International Prognostic Index (IPI) score and anthracycline‐based chemotherapy in first line. Notably, copanlisib, a pan‐class I inhibitor with predominant activities towards PIK3α and PIK3δ isoforms, effectively inhibited phosphorylation of AKT, 4E‐BP‐1 and STAT3, causing G0/G1 cell cycle arrest and resulting in suppression of tumour cell growth in vitro and in vivo. This study provides evidence that targeting the PIK3 pathway, particularly simultaneous inhibition of PIK3α and δ, could be a promising approach for the treatment of PTCL and NKTCL.

Extranodal NK/T-cell lymphoma, nasal type (NKTL) is an aggressive type of non-Hodgkin lymphoma closely associated with Epstein-Barr virus and characterized by varying degrees of systemic inflammation. We aim to examine the prognostic significance of peripheral blood neutrophil-lymphocyte ratio (NLR) in patients with NKTL. Therefore, we conducted a retrospective review of 178 patients with biopsy-proven NKTL from the National Cancer Centre Singapore and Samsung Medical Center, South Korea. Using receiver operating curve analysis, an optimal cut-off for high NLR (>3.5) in predicting overall survival (OS) was derived. Survival analysis was performed using the Kaplan-Meier method and multivariable Cox proportional regression. In patients with high NLR, estimated 5-year OS was 25% compared to 53% in those with low NLR. In multivariable analysis, high NLR, in addition to age ≥60 years, presence of B-symptoms and stage III/IV at diagnosis, was independently correlated with worse OS (HR 2.08; 95% CI 1.36 to 3.18; p = 0.0008) and progression-free survival (HR 1.66; 95% CI 1.11 to 2.46; p = 0.0128). A new prognostic index (NABS score) derived from these factors stratified patients into low (0), low-intermediate (1), high-intermediate (2) and high (3–4) risk subgroups, which were associated with 5-year OS of 76.5%, 55.7%, 29.2% and 0% respectively. In conclusion, high NLR is an independent prognostic marker and the NABS model can be used to risk-stratify NKTL patients.

Key Points Whole genomic and transcriptomic analyses of MEITL revealed multiple potential therapeutic targets. Synergistic effects of pimozide and romidepsin are shown in a well-characterized MEITL PDX model.

Introduction While combination therapy is the standard of care for relapsed/ refractory non-Hodgkin lymphoma (RR-NHL), the choice of combinations for an individual patient is empirical, and response rates remain poor. Here we explore the use of a hybrid experimental/analytic method termed Quadratic Phenotypic Optimization Platform (QPOP), for prediction of optimal drug combinations from limited clinical material. This high-throughput platform identifies optimal drug-combinations on ex-vivo biopsies using an orthogonal array composite design to maximise search space. These features are potentially useful to assess personalized efficacious combinations among a set of drugs with single agent pre-clinical or clinical activity in lymphoma. Methods We performed a prospective cohort study of QPOP analysis in RR-NHL. Participants included RR-NHL patients across two tertiary oncology centres in Singapore, with disease amenable to biopsy or blood/ marrow aspiration, recruited between 1 st November 2017 and 5 th May 2021 - with a median follow up of 24.5 months. CD20, CD3 or CD56 selection was performed to enrich for B, T or NK cells respectively, depending on the specimen type. QPOP drug combination scores were derived from lymphoma samples (approximately 1,000,000 cells/ patient) using a matrix of drugs with known pre-clinical or clinical efficacy against NHL. Results were shared with the treating physician, and off-label QPOP-guided therapy was offered in the absence of standard options. The primary outcomes were feasibility and turnaround time of QPOP analysis. The secondary outcomes were identification of recurrent 2 and 3 drug-combinations, and concordance of QPOP results with clinical responses. Results In this interim analysis period, we recruited 63 patients comprising 36 B-NHL and 27 T/NK-NHL, with a median age of 57 years and median 2 prior lines of treatment. Successful QPOP analysis (Z' score >0.5) was feasible in 56/63 cases with an average turn-around time of 6 (±2.1) days. QPOP predicted frequent sensitivities to Copanlisib- and Venetoclax-based combinations in B-NHL, and Romidepsin-based combinations in T/NK-NHL. Importantly, efficacy of specific combinations was not entirely dependent on single agent dose responses. Greater variability in ex-vivo responses was seen with combinations of targeted therapy and cytotoxic therapy compared with combinations of cytotoxic agents. Clinical responses were evaluable for 29 independent treatments in 26 patients. QPOP had a positive predictive value of 60% and a negative predictive value of 78.6% with an area under the curve of 0.672 (95%CI 0.47-0.87; p=0.12) for partial response or better (n=29, p= 0.06). Complete responses were achieved with novel QPOP derived drug combinations in patients refractory to standard therapy. Examples include Palbociclib-Everolimus for diffuse large B-cell lymphoma (figure 1) and Romidepsin-copanlisib for extra nodal natural killer T-cell lymphoma. Conclusions Prediction of sensitivity to drug-combinations in a clinically applicable time-frame is feasible for RR-NHL cases through QPOP analysis. The relatively small number of patients treated with QPOP directed regimens makes a definitive conclusion on concordance with clinical outcomes difficult at this stage. QPOP was however able to identify novel clinically effective combinations in patients refractory to standard therapy. These data provide the basis for a prospective clinical trial evaluating QPOP based therapy in RR-NHL. Figure 1 Figure 1. Disclosures Chng: Amgen: Honoraria, Research Funding; Janssen: Honoraria, Research Funding; Celgene: Honoraria, Research Funding; Novartis: Honoraria; Abbvie: Honoraria. OffLabel Disclosure: everolimus palbociclib for diffuse large B cell lymphoma and rhomidepsin Bortezomib for extra nodal NK T cell lymphoma

Natural-killer/T-cell lymphoma (NKTL) is a rare subset of non-Hodgkin lymphoma that demonstrates a unique geographic distribution, with higher prevalence in Asia compared to the West1. While cure remains achievable in early-stage disease, the prognosis for advanced-stage NKTL is dismal2. Recently, some progress has been made in uncovering the molecular pathogenesis of NKTL. In a genome-wide association study, strong correlations between HLA-DPB1 single-nucleotide polymorphisms and NKTL susceptibility were discovered, implicating altered antigen processing and presentation to CD4-positive T-lymphocytes in this Epstein-Barr virus (EBV)-associated malignancy3. Next generation sequencing also revealed recurrent somatic mutations such as TP53, JAK3, STAT3 and DDX3X in NKTL4,5. In this paper, we report a pair of male siblings from a non-consanguineous Chinese family who were diagnosed with NKTL, and provide initial evidence for novel recessive germline mutations in FAM160A1 identified through next-generation sequencing. The index patient was 35 years old, when he presented with nasal blockage in March 2013. 18-FDG-PET/CT imaging revealed an 18-FDG-avid nasal mass infiltrating into the palate, as well as enlarged cervical lymph nodes. Biopsy of the mass showed abnormal lymphoid cells positive for CD56 by immunohistochemistry (IHC) as well as EBV-encoded RNA (EBER) by in-situ hybridization. He was diagnosed with stage IIA extranodal NKTL, nasal type, and treated with 4 cycles of bortezomib-GIFOX (gemcitabine, ifosfamide and oxaliplatin) as part of a clinical trial followed by radiotherapy to the nasal region. He had primary-refractory disease and was further treated with 4 cycles of SMILE (dexamethasone, methotrexate, ifosfamide, l-asparaginase, and etoposide) followed by high-dose chemotherapy and autologous stem cell transplantation. He progressed and received ruxolitinib off-label, followed by RAD001 (mTOR inhibitor) and LBH589B (histone deacetylase inhibitor) as part of another clinical trial. He then had radiotherapy to an ulcerating penile lesion before he died of progressive disease 27 months after diagnosis (Supplementary Table 1). His younger brother was 18 years old, when diagnosed with NKTL affecting the nasal floor in 1998 following a bout of epistaxis. He received 6 cycles of CHOP (cyclophosphamide, doxorubicin, vincristine, and prednisone) with high-dose methotrexate and went into complete remission. Three years later he was diagnosed with chronic myeloid leukemia, for which he received hydroxyurea. In 2004, he had a relapse of NKTL and received ESHAP (etoposide, prednisolone, cytarabine and cisplatin), total body irradiation and allogeneic bone marrow transplant. He died of transplant-related complications 6 years from diagnosis. These siblings have an older brother unaffected by any hematological malignancy. Their father died of a non-malignant condition in his fifties and their mother remains well at the age of 68 years. Among their first-degree relatives, none were known to be inflicted with hematologic malignancies (Fig. ​(Fig.11). Open in a separate window Fig. 1 Clinical characterization of brothers with familial NKTL. a 18-FDG-PET/CT image depicting a large nasal mass infiltrating into the palate, of which biopsy showed abnormal lymphoid cells positive for Epstein-Barr virus encoded RNA (EBER) by in situ hybridization. b, c Inheritance modelling identified homozygous germline mutations of FAM160A1 c.2827 C > T in both affected brothers, heterozygous carriage in their mother and paternal aunt, and homozygous wildtype in their healthy older brother. d, e The non-synonymous substitution at FAM160A1 c.2827 C > T results in an amino-acid alteration from arginine to cysteine (p.R943C). Patterns and frequencies of known mutations in other cancer types are shown

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 STAT3 and TP53 (15%), followed by JAK3 and JAK1 (6%) and SOCS1 (4%). A high prevalence of STAT3 mutation (21%) was observed specifically in NKTL. Novel STAT3 mutations (p.D427H, E616G, p.E616K, and p.E696K) were shown to increase STAT3 phosphorylation and transcriptional activity of STAT3 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 STAT3 mutations, and similar findings were observed by the overexpression of p.E616K and p.E616G in the STAT3 wild-type NKTL cell line. Conversely, STAT3 silencing and inhibition decreased PD-L1 expression in STAT3 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. ASTAR (Agency for Sci., Tech. and Research, S’pore) NMRC (Natl Medical Research Council, S’pore) MOH (Min. of Health, S’pore)

CD137 ligand (CD137L) is expressed on APCs and crosslinks CD137, a powerful costimulatory molecule on T cells during cognate interactions, and thereby greatly enhances immune responses. We report that CD137 can be transferred from activated T cells and from tumor cells that express CD137 to other cells via trogocytosis. This trogocytic transfer is independent of CD137L expression by the recipient cell. However, if CD137L is present on the recipient cell, the transferred CD137 binds to CD137L and the CD137-CD137L complex becomes internalized. The removal of CD137L from the surface of APCs lowers their ability to costimulate T cells, as evidenced by a reduced IFN-γ secretion. Removal of CD137L on APCs by trogocytic transfer of CD137 occurs within 1 h and requires cell-cell contact and the continuous presence of CD137-expressing cells. Bidirectional signaling exists for the CD137 receptor/ligand system, because CD137L also signals into APCs. We propose that the trogocytic transfer of CD137 from activated T cells to APCs and the subsequent removal of CD137L from APCs is a physiologic regulatory mechanism that limits immune activity. Furthermore, we hypothesize that the trogocytic transfer of CD137 occurs in cancers and quenches the activity of APCs, contributing to the cancer cells escaping immune surveillance. Taken together, our findings demonstrate that the trogocytic transfer of CD137 leads to an internalization of CD137L on APCs and a reduction in immune activity.

Monomorphic epitheliotropic intestinal T-cell lymphoma (MEITL) is a type of rare aggressive lymphoma accounting for 5.4% of primary intestinal peripheral T-cell lymphoma and 10-25% of all primary intestinal lymphoma. MEITL also has an extremely poor prognosis with the median overall survival of only seven months. No effective treatment or targeted therapies are currently available to manage this disease. Therefore, there is an urgent need to devise and establish an appropriate preclinical model for a better understanding of this disease and for new therapeutic strategies to be developed on it. Here, we present the first MEITL patient derived xenograft (PDX) as both orthotropic intestinal and as a subcutaneous model. The histological analysis demonstrated high similarity in the overall immunomorphologic features between the primary tumour and PDX tumours. Importantly, all the PDX tumors carried the distinctive MEITL immunophenotype; CD3+CD4-CD8+CD56+ and extensive nuclear expression of MATK. We also had Sanger sequenced 83 somatic mutations in the original tumour and rediscovered them in the 6th passage of our xenografts, which suggest that the generated MEITL PDX tumours were genetically stable. Moreover, whole exome sequencing results showed that the clonal architecture in the primary tumour was well preserved in the PDX tumours. The clonal architecture was further analysed with single cell whole genome amplification following by Sanger sequencing. We found that the most of heterozygous mutations in the primary tumour were a mixture of wild type alleles and heterozygous/homozygous mutations from separated clones, including DUPS14 heterozygous mutation (p.R300W) which was known to activate MEK pathway, and SETD2 mutations, (g.chr3:47061285_ 47061286insA and g.chr3:47127805C>A) which were the synthetic lethal partner of Wee1. Interestingly, we found that the two SETD2 mutations alone were able to differentiate three subclones. This result indicates that the tumour was highly subclonal, which could have a strong impact on the selection of drug resistant clones in the drug treatment. In order to verify this hypothesis, we proceeded to test the efficacy of MEK inhibitor, Trametinib and Wee1 inhibitor, AZD1775 both separately and combined treatment, in our PDX subcutaneous model. The results showed that both 1mg/kg/day of Trametinib and 60mg/kg/day of AZD1775 treatments significantly delayed 60-70% of tumour growth as compared with the vehicle group. The tumour growth was completely arrested in the combined treatment group. In addition, 20% and 40% of the mice exhibited Trametinib and AZD1775 resistance, respectively. From our genomic analysis, all DUPS14 and SETD2 mutations from the pretreated tumours were preserved in the treatment-resistant tumours but absent in the sensitive post-treated residual tumours. The clonality analysis from the sequencing data of the pretreated tumour supports and suggests that single-agent regimes will often not be able to induce a complete response in MEITL patients. Altogether, the current results demonstrated that our MEITL PDX model preserved the principal histological and genetic characteristics of its original tumour and is genomic stable across passages. The model also showed that MEITL could be highly subclonal and combined targeted therapy might achieve a higher efficacy for MEITL treatment. Disclosures No relevant conflicts of interest to declare.

7549 Background: Natural killer/T-cell lymphoma (NKTL) is a rare type of non-Hodgkin lymphoma that occurs more frequently in East Asia and Latin America and is associated with Epstein–Barr virus infection. Recent whole-exome sequencing studies in NKTL have reported recurrent somatic mutations in genes associated with JAK-STAT pathway, however the role of aberrant JAK-STAT signaling in tumor immune escape through PD-L1 regulation is unclear. Methods: To determine the prevalence of JAK-STAT pathway alteration in NKTL, we performed targeted sequencing of 188 genes associated with JAK-STAT pathway in 109 NKTL (22 Singapore cases, 79 China cases and 8 cell lines). Single nucleotide variants and micro-indels were called using Freebayes and candidate variants annotated using ANNOVAR. Ba/F3 model system was used to test the transformation capacity of identified variants. Cell lines were evaluated for PD-L1 expression by immunoblotting and flow cytometry. Tissue microarrays were examined for p-STAT3 and PD-L1 expression by immunohistochemistry. Results: We identified a total of 284 non-synonymous somatic mutations candidates in 114 genes, including 243 missense, 10 nonsense, 4 splice-site and 27 indel mutations. Recurrent mutations were most frequently located in STAT3 (25/109 cases, 23%) followed by TP53 (16/109 cases, 16%) and JAK3 (8/109 cases, 7%). A total of 18 STAT3 variants were identified including known hotspot mutations and novel mutations in the SH2, coiled coil and DNA-binding domains. Characterization of novel E616K mutant residing in the SH2 domain showed that E616K conferred IL3 independent growth to Ba/F3 cells, increased STAT3 phosphorylation and PD-L1 expression. Consistent with these findings, PD-L1 was over expressed in cell lines harboring STAT3 mutations. A positive correlation between PD-L1 and p-STAT3 expression was also observed in tumor tissue (R = 0.51, P = 0.02). Conclusions: We characterized a novel activating STAT3 mutant and demonstrated its ability to drive PD-L1 expression, which may promote tumor evasion from the antitumor immune response. The combination of PD-1/PD-L1 antibodies and STAT3 inhibitors might be a promising and novel therapeutic approach for NKTL in the future.

Non-Hodgkin lymphomas (NHL) are a diverse group of blood cancers on the rising trend both worldwide and in Singapore. Better understanding of the pathogenesis and biology of these tumors is urgently required to improve the diagnosis and prognostication. Moreover, the outcome using currently available therapies is poor and there is an immediate need for better treatment options. With an increasing number of genomic studies published, there is a growing demand to bring these discoveries into in vitro and in vivo models. However, the lack of publicly available cell lines and/or animal models for the majority of the NHL subtypes makes these studies difficult to proceed. With that objective, we have started collecting fresh NHL tumor samples and implanting them into NOD scid gamma (NSG) mice to generate patient-derived xenograft (PDX) models. After tumor dissemination, the cells are injected either subcutaneously or intraperitoneally into 6-10 week old mice. Each passage is thoroughly immunohistochemically characterized by a senior hematopathologist and contrasted to the primary patient specimen. Whole exome sequencing (WES) is performed and compared to the primary patient data where possible. A model is considered stable if it has not changed its phenotype for at least 3 passages. A full list of currently available stable models is listed in Table 1. Efforts are also under way to generate stable cell lines based on these models. Strategies tested are spontaneous immortalization, human telomerase reverse transcriptase (TERT), Herpesvirus saimiri (HVS) or Epstein-Barr virus (EBV) transduction and feeder culture. We have recently reported a comprehensive molecular profiling of monomorphic epitheliotropic intestinal T-cell lymphoma (MEITL; previously also known as type II enteropathy-associated T-cell lymphoma; Nairismagi et al., Leukemia, 2016). MEITL, a newly recognized WHO entity, is a rare aggressive primary intestinal disease with poor prognosis and a median overall survival of only 7 months. Frequent alterations were identified in the JAK-STAT and G-protein-coupled receptor signaling pathways and a number of epigenetic regulators. Specifically, 60-30% mutation frequencies were found in the STAT5B, JAK3, SETD2, GNAI2 and CREBBP genes. Tumor tissue was collected from a 55 year old Chinese male with relapsed MEITL. The cells have been propagated in the NSG mouse by subcutaneous or intraperitoneal injection up to 6 and 3 passages, respectively. All passages have been histologically characterized and maintained their CD3+ CD8alpha-alpha+ cytotoxic granules+ MATK+ and EBER- phenotype with aberrant expression of both TCR beta and gamma. WES was performed both in the patient primary sample and in passage 1 (P1) PDX sample. There were 83 somatic mutations present in the primary sample, all of which were also identified in the P1 PDX sample. Furthermore, Sanger sequencing was used to validate the presence of all 83 mutations in the remaining passages. There was only 1 mutation lost in the P6 subcutaneous PDX model compared to the primary patient specimen demonstrating the outstanding stability of this model. Using peritoneal fluid cells from P2 we have previously performed ex vivo studies and identified novel treatment modalities for this deadly disease (Nairismagi et al., Leukemia, 2016). Efforts are currently under way to test these regimens also in in vivo setting. In summary, we have generated a number of NHL PDX models with the objective to enhance drug testing. MEITL presents a real life situation where clinical trials are not possible due to the rarity of the disease; however, the availability of PDX models allows for efficient testing of novel therapies and can lead to improved patient outcome. Efforts are under way to further characterize the existing models and tissue collection is ongoing to establish more models. Table 1 List of available stable non-Hodgkin lymphoma models. AITL, angioimmunoblastic T-cell lymphoma; DLBCL, diffuse large B-cell lymphoma; EBV, Epstein-Barr virus; GC, germinal center; MCL, mantle cell lymphoma; MEITL, monomorphic epitheliotropic intestinal T-cell lymphoma; NK/TCL, natural killer/T-cell lymphoma and PTCL NOS, peripheral T-cell lymphoma not otherwise specified. Table 1. List of available stable non-Hodgkin lymphoma models. AITL, angioimmunoblastic T-cell lymphoma; DLBCL, diffuse large B-cell lymphoma; EBV, Epstein-Barr virus; GC, germinal center; MCL, mantle cell lymphoma; MEITL, monomorphic epitheliotropic intestinal T-cell lymphoma; NK/TCL, natural killer/T-cell lymphoma and PTCL NOS, peripheral T-cell lymphoma not otherwise specified. Disclosures No relevant conflicts of interest to declare.

CD137 is ectopically expressed on Hodgkin and Reed-Sternberg (HRS) cells, causing the removal of the immunostimulatory CD137 ligand from HRS cells as well as from surrounding antigen presenting cells. This inhibits T-cell co-stimulation and supports the immune evasion of Hodgkin’s lymphoma.

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-γ 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. ©2012 AACR.

BACKGROUND: Multiple myeloma (MM) is a malignancy of terminally-differentiated plasma cells, and the second most prevalent blood cancer. At present there is no cure for MM, and the average prognosis is only three to five years. Current treatments such as chemotherapy are able to prolong a patient's life but rarely prevent relapse of the disease. Even hematopoietic stem cell transplants and novel drug combinations are often not curative, underscoring the need for a continued search for novel therapeutics. CD137 and its ligand are members of the Tumor Necrosis Factor (TNF) receptor and TNF superfamilies, respectively. Since CD137 ligand cross-linking enhances proliferation and survival of healthy B cells we hypothesized that it would also act as a growth stimulus for B cell cancers. METHODOLOGY/PRINCIPAL FINDINGS: Proliferation and survival of B cell lymphoma cell lines were not affected or slightly enhanced by CD137 ligand agonists in vitro. But surprisingly, they had the opposite effects on MM cells, where CD137 ligand signals inhibited proliferation and induced cell death by apoptosis. Furthermore, secretion of the pro-inflammatory cytokines, IL-6 and IL-8 were also enhanced in MM but not in non-MM cell lines in response to CD137 ligand agonists. The secretion of these cytokines in response to CD137 ligand signaling was consistent with the observed activation of the classical NF-kappaB pathway. We hypothesize that the induction of this pathway results in activation-induced cell death, and that this is the underlying mechanism of CD137-induced MM cell death and growth arrest. CONCLUSIONS/SIGNIFICANCE: These data point to a hitherto unrecognized role of CD137 and CD137 ligand in MM cell biology. The selective inhibition of proliferation and induction of cell death in MM cells by CD137 ligand agonists may also warrant a closer evaluation of their therapeutic potential.