Tetraspanin CD37 protects against the development of B cell lymphoma

CD20 expression regulates CD37 levels in B-cell lymphoma - implications for immunotherapies

Rituximab (RTX) plus chemotherapy (R-CHOP) applied as a first-line therapy for lymphoma leads to a relapse in approximately 40% of the patients. Therefore, novel approaches to treat aggressive lymphomas are being intensively investigated. Several RTX-resistant (RR) cell lines have been established as surrogate models to study resistance to R-CHOP. Our study reveals that RR cells are characterized by a major downregulation of CD37, a molecule currently explored as a target for immunotherapy. Using CD20 knockout (KO) cell lines, we demonstrate that CD20 and CD37 form a complex, and hypothesize that the presence of CD20 stabilizes CD37 in the cell membrane. Consequently, we observe a diminished cytotoxicity of anti-CD37 monoclonal antibody (mAb) in complement-dependent cytotoxicity in both RR and CD20 KO cells that can be partially restored upon lysosome inhibition. On the other hand, the internalization rate of anti-CD37 mAb in CD20 KO cells is increased when compared to controls, suggesting unhampered efficacy of antibody drug conjugates (ADCs). Importantly, even a major downregulation in CD37 levels does not hamper the efficacy of CD37-directed chimeric antigen receptor (CAR) T cells. In summary, we present here a novel mechanism of CD37 regulation with further implications for the use of anti-CD37 immunotherapies.

Membrane organization by tetraspanins and galectins shapes lymphocyte function

Immune receptors are not randomly distributed at the plasma membrane of lymphocytes but are segregated into specialized domains that function as platforms to initiate signalling, as exemplified by the B cell or T cell receptor complex and the immunological synapse. 'Membrane-organizing proteins' and, in particular, tetraspanins and galectins, are crucial for controlling the spatiotemporal organization of immune receptors and other signalling proteins. Deficiencies in specific tetraspanins and galectins result in impaired immune synapse formation, lymphocyte proliferation, antibody production and migration, which can lead to impaired immunity, tumour development and autoimmunity. In contrast to conventional ligand-receptor interactions, membrane organizers interact in cis (on the same cell) and modulate receptor clustering, receptor dynamics and intracellular signalling. New findings have uncovered their complex and dynamic nature, revealing shared binding partners and collaborative activity in determining the composition of membrane domains. Therefore, immune receptors should not be envisaged as independent entities and instead should be studied in the context of their spatial organization in the lymphocyte membrane. We advocate for a novel approach to study lymphocyte function by globally analysing the role of membrane organizers in the assembly of different membrane complexes and discuss opportunities to develop therapeutic approaches that act via the modulation of membrane organization.

Rice tetraspanins express in specific domains of diverse tissues and regulate plant architecture and root growth

Tetraspanins (TETs) are small transmembrane scaffold proteins that distribute proteins into highly organized microdomains, consisting of adaptors and signaling proteins, which play important roles in various biological events. In plants, understanding of tetraspanin is limited to the Arabidopsis TET genes' expression pattern and their function in leaf and root growth. Here, we comprehensively analyzed all rice tetraspanin (OsTET) family members, including their gene expression pattern, protein topology, and subcellular localization. We found that the core domain of OsTETs is conserved and shares a similar topology of four membrane-spanning domains with animal and plant TETs. OsTET genes are partially overlapping expressed in diverse tissue domains in vegetative and reproductive organs. OsTET proteins preferentially targeted the endoplasmic reticulum. Mutation analysis showed that OsTET5, OsTET6, OsTET9, and OsTET10 regulated plant height and tillering, and that OsTET13 controlled root growth in association with the jasmonic acid pathway. In summary, our work provides systematic new insights into the function of OsTETs in rice growth and development, and the data provides valuable resources for future research.

Functionalized Parylene Films for Enhancement of Antibody Production by Hybridoma Cells

In this study, the influence of microenvironments on antibody production of hybridoma cells was analyzed using six types of functionalized parylene films, parylene-N and parylene-C (before and after UV radiation), parylene-AM, and parylene-H, and using polystyrene as a negative control. Hybridoma cells were cultured on modified parylene films that produced a monoclonal antibody against the well-known fungal toxin ochratoxin-A. Surface properties were analyzed for each parylene film, such as roughness, chemical functional groups, and hydrophilicity. The proliferation rate of the hybridoma cells was observed for each parylene film by counting the number of adherent cells, and the total amount of produced antibodies from different parylene films was estimated using indirect ELISA. In comparison with the polystyrene, the antibody-production by parylene-H and parylene-AM was estimated to be observed to be as high as 210-244% after the culture of 24 h. These results indicate that the chemical functional groups of the culture plate could influence antibody production. To analyze the influence of the microenvironments of the modified parylene films, we performed cell cycle analysis to estimate the ratio of the G0/G1, S, and G2/M phases of the hybridoma cells on each parylene film. From the normalized proportion of phases of the cell cycle, the difference in antibody production from different surfaces was considered to result from the difference in the proliferation rate of hybridoma cells, which occurred from the different physical and chemical properties of the parylene films. Finally, protein expression was analyzed using an mRNA array to determine the effect of parylene films on protein expression in hybridoma cells. The expression of three antibody production-related genes (CD40, Sox4, and RelB) was analyzed in hybridoma cells cultured on modified parylene films.

[Recent Progress of Tertiary Lymphoid Structure in Prognosis and Immunotherapy of Non-small Cell Lung Cancer]

Lung cancer is the leading cause of cancer death, and non-small cell lung cancer (NSCLC) accounts for 85%. Immunotherapy has significantly improved the clinical prognosis of patients with NSCLC. However, because of the complexity and heterogeneousness of the tumor microenvironment, only a subset of individuals can benefit from immunotherapy. Therefore, it is necessary to explore effective predictive biomarkers for immunotherapy of NSCLC. Tertiary lymphoid structure (TLS) is an ectopic lymphoid organ that is highly similar to secondary lymphoid organs (SLO), and the presence of TLS has been found to be closely associated with a good prognosis in immunotherapy for a variety of solid tumors, including NSCLC. This article provides a review of the prognostic role of tertiary lymphoid structures in immunotherapy of NSCLC, in order to offer references for screening suitable candidates for immunotherapy of NSCLC and develop personalized and precise treatment plans.
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Prognostic and immunological significance of an M1 macrophage-related gene signature in osteosarcoma

As the most abundant infiltrating immune cells in the tumor microenvironment (TME), tumor-associated macrophages (TAMs) are pivotal in tumor development and treatment. The present investigation endeavors to explore the potential of M1 macrophage-related genes (MRGs) as biomarkers for assessing risk in individuals with osteosarcoma. RNA-sequence data and clinical data were derived from TCGA and GEO databases. The CIBERSORT method was utilized to discern subtypes of tumor-infiltrating immune cells. Identification of MRGs was achieved through Pearson correlation analysis. A prognostic risk model for MRGs was developed using Cox and LASSO regression analyses. A tripartite gene signature comprising CD37, GABRD, and ARHGAP25 was an independent prognostic indicator and was employed to develop a risk score model. The internal and external validation cohort confirmed the results. The area under the ROC curve (AUC) was determined for survival periods of 1 year, three years, and five years, yielding values of 0.746, 0.839, and 0.850, respectively. The C-index of the risk score was found to be superior to clinicopathological factors. GO/KEGG enrichment showed that the differences between high- and low-risk groups were predominantly associated with immune response pathways. Immune-related analysis related to proportions of immune cells, immune function, and expression levels of immune checkpoint genes all showed differences between the high- and low-risk groups. The qRT-PCR and Western blotting results indicate that CD37 expression was markedly higher in MG63 and U2OS cell lines when compared to normal osteoblast hFOB1.19. In U2OS cell line, GABRD expression levels were significantly upregulated. ARHGAP25 expression levels were elevated in both 143B and U2OS cell lines. In summary, utilizing a macrophage genes signature demonstrates efficacy in predicting both the prognosis and therapy response of OS. Additionally, immune analysis confirms a correlation between the risk score and the tumor microenvironment. Our findings, therefore, provide a cogent account for the disparate prognoses observed among patients and furnish a justification for further inquiry into biomarkers and anti-tumor treatment strategies.

The versatile roles of testrapanins in cancer from intracellular signaling to cell-cell communication: cell membrane proteins without ligands

The tetraspanins (TSPANs) are a family of four-transmembrane proteins with 33 members in mammals. They are variably expressed on the cell surface, various intracellular organelles and vesicles in nearly all cell types. Different from the majority of cell membrane proteins, TSPANs do not have natural ligands. TSPANs typically organize laterally with other membrane proteins to form tetraspanin-enriched microdomains (TEMs) to influence cell adhesion, migration, invasion, survival and induce downstream signaling. Emerging evidence shows that TSPANs can regulate not only cancer cell growth, metastasis, stemness, drug resistance, but also biogenesis of extracellular vesicles (exosomes and migrasomes), and immunomicroenvironment. This review summarizes recent studies that have shown the versatile function of TSPANs in cancer development and progression, or the molecular mechanism of TSPANs. These findings support the potential of TSPANs as novel therapeutic targets against cancer.

The meningeal transcriptional response to traumatic brain injury and aging

Emerging evidence suggests that the meningeal compartment plays instrumental roles in various neurological disorders, however, we still lack fundamental knowledge about meningeal biology. Here, we utilized high-throughput RNA sequencing (RNA-seq) techniques to investigate the transcriptional response of the meninges to traumatic brain injury (TBI) and aging in the sub-acute and chronic time frames. Using single-cell RNA sequencing (scRNA-seq), we first explored how mild TBI affects the cellular and transcriptional landscape in the meninges in young mice at one-week post-injury. Then, using bulk RNA-seq, we assessed the differential long-term outcomes between young and aged mice following TBI. In our scRNA-seq studies, we highlight injury-related changes in differential gene expression seen in major meningeal cell populations including macrophages, fibroblasts, and adaptive immune cells. We found that TBI leads to an upregulation of type I interferon (IFN) signature genes in macrophages and a controlled upregulation of inflammatory-related genes in the fibroblast and adaptive immune cell populations. For reasons that remain poorly understood, even mild injuries in the elderly can lead to cognitive decline and devastating neuropathology. To better understand the differential outcomes between the young and the elderly following brain injury, we performed bulk RNA-seq on young and aged meninges 1.5 months after TBI. Notably, we found that aging alone induced upregulation of meningeal genes involved in antibody production by B cells and type I IFN signaling. Following injury, the meningeal transcriptome had largely returned to its pre-injury signature in young mice. In stark contrast, aged TBI mice still exhibited upregulation of immune-related genes and downregulation of genes involved in extracellular matrix remodeling. Overall, these findings illustrate the dynamic transcriptional response of the meninges to mild head trauma in youth and aging.

Antibody-drug conjugates for lymphoma patients: preclinical and clinical evidences

Antibody-drug conjugates (ADCs) are a recent, revolutionary approach for malignancies treatment, designed to provide superior efficacy and specific targeting of tumor cells, compared to systemic cytotoxic chemotherapy. Their structure combines highly potent anti-cancer drugs (payloads or warheads) and monoclonal antibodies (Abs), specific for a tumor-associated antigen, via a chemical linker. Because the sensitive targeting capabilities of monoclonal Abs allow the direct delivery of cytotoxic payloads to tumor cells, these agents leave healthy cells unharmed, reducing toxicity. Different ADCs have been approved by the US Food and Drug Administration (FDA) and the European Medicines Agency (EMA) for the treatment of a wide range of malignant conditions, both as monotherapy and in combination with chemotherapy, including for lymphoma patients. Over 100 ADCs are under preclinical and clinical investigation worldwide. This paper it provides an overview of approved and promising ADCs in clinical development for the treatment of lymphoma. Each component of the ADC design, their mechanism of action, and the highlights of their clinical development progress are discussed.

Fatty acid metabolism in aggressive B-cell lymphoma is inhibited by tetraspanin CD37

The importance of fatty acid (FA) metabolism in cancer is well-established, yet the mechanisms underlying metabolic reprogramming remain elusive. Here, we identify tetraspanin CD37, a prognostic marker for aggressive B-cell lymphoma, as essential membrane-localized inhibitor of FA metabolism. Deletion of CD37 on lymphoma cells results in increased FA oxidation shown by functional assays and metabolomics. Furthermore, CD37-negative lymphomas selectively deplete palmitate from serum in mouse studies. Mechanistically, CD37 inhibits the FA transporter FATP1 through molecular interaction. Consequently, deletion of CD37 induces uptake and processing of exogenous palmitate into energy and essential building blocks for proliferation, and inhibition of FATP1 reverses this phenotype. Large lipid deposits and intracellular lipid droplets are observed in CD37-negative lymphoma tissues of patients. Moreover, inhibition of carnitine palmitoyl transferase 1 A significantly compromises viability and proliferation of CD37-deficient lymphomas. Collectively, our results identify CD37 as a direct gatekeeper of the FA metabolic switch in aggressive B-cell lymphoma.

Tetraspanin CD37 deficiency has been reported as a prognostic marker for aggressive B-cell lymphoma. Here, the authors show that CD37 interacts with the fatty acid transporter 1 to inhibit palmitate uptake and its deficiency leads to increased fatty acid metabolism which promotes tumorigenesis in B-cell lymphoma.

CD37 expression in follicular lymphoma

CD37 is a tetraspanin protein expressed in various B-cell lymphomas that mediates tumor survival signaling. Follicular lymphoma (FL) is a representative B-cell neoplasm composed of germinal center B cells. In recent years, CD37 has been focused on as a therapeutic target for B-cell lymphoma. The purpose of this study was to characterize CD37 expression in FL patients to identify risk factors associated with various prognostic factors. We retrospectively reviewed 167 cases of FL and evaluated the immunohistochemical expression of CD37 and its statistical association with clinicopathological features. Immunohistochemically, CD37 was observed in the cytoplasm and/or membrane of neoplastic cells, mainly in neoplastic follicles to various extents. One hundred cases (100/167, 60.0%) were categorized as CD37-positive, and 67 cases were CD37-negative. In cases with high Follicular Lymphoma International Prognostic Index (FLIPI), CD37-negative cases had a poor overall survival compared with CD37-positive cases (P = 0.047), although no significant differences were observed in other clinicopathologic factors, including histological grade, BCL2-IGH translocation, and immunohistochemical phenotype. Therefore, CD37 protein may play a role in tumor progression and may serve as a therapeutic target. However, further studies are needed to explore its significance.

IRF8 is a transcriptional activator of CD37 expression in diffuse large B-cell lymphoma

IRF8 is a transcriptional regulator of CD37 expression in DLBCL, which may have implications for anti-CD37 therapies.

Patients with poor prognostic CD37-negative DLBCL show significantly lower IRF8 expression compared with patients with CD37-positive DLBCL.

Diffuse large B-cell lymphoma (DLBCL) represents the most common form of non-Hodgkin lymphoma (NHL) that is still incurable in a large fraction of patients. Tetraspanin CD37 is highly expressed on mature B lymphocytes, and multiple CD37-targeting therapies are under clinical development for NHL. However, CD37 expression is nondetectable in ∼50% of DLBCL patients, which correlates with inferior treatment outcome, but the underlying mechanisms for differential CD37 expression in DLBCL are still unknown. Here, we investigated the regulation of the CD37 gene in human DLBCL at the (epi-)genetic and transcriptional level. No differences were observed in DNA methylation within the CD37 promoter region between CD37-positive and CD37-negative primary DLBCL patient samples. On the contrary, CD37-negative DLBCL cells specifically lacked CD37 promoter activity, suggesting differential regulation of CD37 gene expression. Using an unbiased quantitative proteomic approach, we identified transcription factor IRF8 to be significantly higher expressed in nuclear extracts of CD37-positive as compared with CD37-negative DLBCL. Direct binding of IRF8 to the CD37 promoter region was confirmed by DNA pulldown assay combined with mass spectrometry and targeted chromatin immunoprecipitation (ChIP). Functional analysis indicated that IRF8 overexpression enhanced CD37 protein expression, while CRISPR/Cas9 knockout of IRF8 decreased CD37 levels in DLBCL cell lines. Immunohistochemical analysis in a large cohort of primary DLBCL (n = 206) revealed a significant correlation of IRF8 expression with detectable CD37 levels. Together, this study provides new insight into the molecular mechanisms underlying differential CD37 expression in human DLBCL and reveals IRF8 as a transcriptional regulator of CD37 in B-cell lymphoma.

The clinical features, prognostic significance, and immune heterogeneity of CD37 in diffuse gliomas

Diffuse glioma is the most prevalent and malignant brain tumor. The function and significance of CD37 in diffuse gliomas remain largely unknown. Here, we showed CD37 was abnormally expressed in diverse cancers, especially glioma by pan-cancer differential expression analysis. In addition, we found CD37 was upregulated in higher grade and IDH or IDH1-wildtype gliomas, which was further validated by qPCR and IHC. Survival analysis revealed CD37 served as an independent indicator for unfavorable prognosis of patients with diffuse gliomas. Functional enrichment analysis revealed CD37 was associated with immunological processes. Moreover, immune infiltration analyses suggested gliomas with high-expression CD37 had greater infiltration of M2 macrophages and neutrophils, and lower NK cell abundance. CD37 was closely correlated to immune checkpoint molecules, including CD276, CD80, CD86, and PD-L2. Our results indicated CD37 is an independent prognostic factor and plays an immunosuppressive role in diffuse gliomas. Targeting CD37 could be a promising immunotherapeutic strategy for diffuse gliomas.

A Deep Insight Into CAR-T Cell Therapy in Non-Hodgkin Lymphoma: Application, Opportunities, and Future Directions

Non-Hodgkin's lymphoma (NHL) is a cancer that starts in the lymphatic system. In NHL, the important part of the immune system, a type of white blood cells called lymphocytes become cancerous. NHL subtypes include marginal zone lymphoma, small lymphocytic lymphoma, follicular lymphoma (FL), and lymphoplasmacytic lymphoma. The disease can emerge in either aggressive or indolent form. 5-year survival duration after diagnosis is poor among patients with aggressive/relapsing form of NHL. Therefore, it is necessary to understand the molecular mechanisms of pathogenesis involved in NHL establishment and progression. In the next step, we can develop innovative therapies for NHL based on our knowledge in signaling pathways, surface antigens, and tumor milieu of NHL. In the recent few decades, several treatment solutions of NHL mainly based on targeted/directed therapies have been evaluated. These approaches include B-cell receptor (BCR) signaling inhibitors, immunomodulatory agents, monoclonal antibodies (mAbs), epigenetic modulators, Bcl-2 inhibitors, checkpoint inhibitors, and T-cell therapy. In recent years, methods based on T cell immunotherapy have been considered as a novel promising anti-cancer strategy in the treatment of various types of cancers, and particularly in blood cancers. These methods could significantly increase the capacity of the immune system to induce durable anti-cancer responses in patients with chemotherapy-resistant lymphoma. One of the promising therapy methods involved in the triumph of immunotherapy is the chimeric antigen receptor (CAR) T cells with dramatically improved killing activity against tumor cells. The CAR-T cell-based anti-cancer therapy targeting a pan-B-cell marker, CD19 is recently approved by the US Food and Drug Administration (FDA) for the treatment of chemotherapy-resistant B-cell NHL. In this review, we will discuss the structure, molecular mechanisms, results of clinical trials, and the toxicity of CAR-T cell-based therapies. Also, we will criticize the clinical aspects, the treatment considerations, and the challenges and possible drawbacks of the application of CAR-T cells in the treatment of NHL.

CD37 high expression as a potential biomarker and association with poor outcome in acute myeloid leukemia

BACKGROUND

CD37, a member of the transmembrane 4 superfamilies (TM4SF), has been proved to be abnormally expressed in a range of malignancies. Herein, we investigate the effects of CD37 expression and analyze its clinical outcome in acute myeloid leukemia (AML) patients.

METHODS

The RNA-seq and clinical data of AML patients were obtained from cBioPortal database. CD37 correlated genes, the expression prolife and survival curve of eight key genes were acquired from Gene Expression Profiling Interactive Analysis (GEPIA) and UALCAN. Pathway enrichment and protein-protein interaction (PPI) network analysis were performed based on metascape databases.

RESULTS

Our results showed that CD37 mRNA expression level was significantly up-regulated in patients with AML compared with healthy persons. Patients with high CD37 expression had shorter overall survival (OS) and disease-free survival (DFS). Pathway analysis data showed that CD37 is involved in DNA replication, RNA transport, Salmonella infection, ribonucleoprotein complex biogenesis, cell cycle phase transition and so on. Furthermore, we found eight genes correlated with CD37 are all highly expressed in AML patients, and high expression is associated with poor prognosis.

CONCLUSION

Our study described systematical expression profiles and the prognostic values of CD37 in AML; our data suggested CD37 might be novel therapeutic target and promising prognostic biomarker in the patients.

CD37 in B Cell Derived Tumors-More than Just a Docking Point for Monoclonal Antibodies

CD37 is a tetraspanin expressed prominently on the surface of B cells. It is an attractive molecular target exploited in the immunotherapy of B cell-derived lymphomas and leukemia. Currently, several monoclonal antibodies targeting CD37 as well as chimeric antigen receptor-based immunotherapies are being developed and investigated in clinical trials. Given the unique role of CD37 in the biology of B cells, it seems that CD37 constitutes more than a docking point for monoclonal antibodies, and targeting this molecule may provide additional benefit to relapsed or refractory patients. In this review, we aimed to provide an extensive overview of the function of CD37 in B cell malignancies, providing a comprehensive view of recent therapeutic advances targeting CD37 and delineating future perspectives.

Dynamic Plasma Membrane Organization: A Complex Symphony

Membrane protein organization is essential for proper cellular functioning and the result of a dynamic exchange between protein monomers, nanoscale protein clusters, and microscale higher-order structures. This exchange is affected by both lipid bilayer intrinsic factors, such as lipid rafts and tetraspanins, and extrinsic factors, such as cortical actin and galectins. Because membrane organizers act jointly like instruments in a symphony, it is challenging to define the 'key' organizers. Here, we posit, for the first time, definitions of key intrinsic and extrinsic membrane organizers. Tetraspanin nanodomains are key organizers that are often overlooked. We discuss how different key organizers can collaborate, which is important to get a full grasp of plasma membrane biology.

Tetraspanins: useful multifunction proteins for the possible design and development of small-molecule therapeutic tools

Tetraspanins constitute a well-conserved superfamily of four-span small membrane proteins (TM4SF), with >30 members in humans, with important roles in numerous mechanisms of cell biology. Moreover, tetraspanins associate with either specific partner proteins or another tetraspanin, generating a network of interactions involved in cell and membrane compartmentalization and having a role in cellular development, proliferation, activation, motility, and membrane fusions. Therefore, tetraspanins are considered regulators of cellular signaling and are often depicted as 'molecular facilitators'. In view of these many physiological functions, it is likely that these molecules are important actors in pathological processes. In this review, we present the main characteristics of this superfamily, providing a more detailed description of some significant representatives and discuss their relevance as potential targets for the design and development of small-molecule therapeutics in different pathologies.

Tetraspanin CD53: an overlooked regulator of immune cell function

Tetraspanins are membrane organizing proteins that play a role in organizing the cell surface through the formation of subcellular domains consisting of tetraspanins and their partner proteins. These complexes are referred to as tetraspanin enriched microdomains (TEMs) or the tetraspanin web. The formation of TEMs allows for the regulation of a variety of cellular processes such as adhesion, migration, signaling, and cell fusion. Tetraspanin CD53 is a member of the tetraspanin superfamily expressed exclusively within the immune compartment. Amongst others, B cells, CD4+ T cells, CD8+ T cells, dendritic cells, macrophages, and natural killer cells have all been found to express high levels of this protein on their surface. Almost three decades ago it was reported that patients who lacked CD53 suffered from an increased susceptibility to pathogens resulting in the clinical manifestation of recurrent viral, bacterial, and fungal infections. This clearly suggests a vital and non-redundant role for CD53 in immune function. Yet, despite this striking finding, the specific functional roles of CD53 within the immune system have remained elusive. This review aims to provide a concise overview of the published literature concerning CD53 and reflect on the underappreciated role of this protein in immune cell regulation and function.

Preclinical development of CD37CAR T-cell therapy for treatment of B-cell lymphoma

T cells modified to express chimeric antigen receptor (CAR) targeting CD19 (CD19CAR) have produced remarkable clinical responses in patients with relapsed/refractory B-cell acute lymphoblastic leukemia. CD19CAR T-cell therapy has also demonstrated prominent effects in B-cell non-Hodgkin lymphoma (B-NHL) patients. However, a subset of patients who relapse after CD19CAR T-cell therapy have outgrowth of CD19^- tumor cells. Hence, development of alternative CARs targeting other B-cell markers represents an unmet medical need for B-cell acute lymphoblastic leukemia and B-NHL. Here, we confirmed previous data by showing that, overall, B-NHL has high expression of CD37. A second-generation CD37CAR was designed, and its efficacy in T cells was compared with that of CD19CAR. In vitro assessment of cytotoxicity and T-cell function upon coculture of the CAR T cells with different target B-cell lymphoma cell lines demonstrated comparable efficacy between the 2 CARs. In an aggressive B-cell lymphoma xenograft model, CD37CAR T cells were as potent as CD19CAR T cells in controlling tumor growth. In a second xenograft model, using U2932 lymphoma cells containing a CD19^- subpopulation, CD37CAR T cells efficiently controlled tumor growth and prolonged survival, whereas CD19CAR T cells had limited effect. We further show that, unlike CD19CAR, CD37CAR was not sensitive to antigen masking. Finally, CD37CAR reactivity was restricted to B-lineage cells. Collectively, our results demonstrated that CD37CAR T cells also can effectively eradicate B-cell lymphoma tumors when CD19 antigen expression is lost and support further clinical testing for patients with relapsed/refractory B-NHL.

DuoHexaBody-CD37®, a novel biparatopic CD37 antibody with enhanced Fc-mediated hexamerization as a potential therapy for B-cell malignancies

Tetraspanin CD37 has recently received renewed interest as a therapeutic target for B-cell malignancies. Although complement-dependent cytotoxicity (CDC) is a powerful Fc-mediated effector function for killing hematological cancer cells, CD37-specific antibodies are generally poor inducers of CDC. To enhance CDC, the E430G mutation was introduced into humanized CD37 monoclonal IgG1 antibodies to drive more efficient IgG hexamer formation through intermolecular Fc-Fc interactions after cell surface antigen binding. DuoHexaBody-CD37, a bispecific CD37 antibody with the E430G hexamerization-enhancing mutation targeting two non-overlapping epitopes on CD37 (biparatopic), demonstrated potent and superior CDC activity compared to other CD37 antibody variants evaluated, in particular ex vivo in patient-derived chronic lymphocytic leukemia cells. The superior CDC potency was attributed to enhanced IgG hexamerization mediated by the E430G mutation in combination with dual epitope targeting. The mechanism of action of DuoHexaBody-CD37 was shown to be multifaceted, as it was additionally capable of inducing efficient antibody-dependent cellular cytotoxicity and antibody-dependent cellular phagocytosis in vitro. Finally, potent anti-tumor activity in vivo was observed in cell line- and patient-derived xenograft models from different B-cell malignancy subtypes. These encouraging preclinical results suggest that DuoHexaBody-CD37 (GEN3009) may serve as a potential therapeutic antibody for the treatment of human B-cell malignancies.

High frequency of inactivating tetraspanin C D37 mutations in diffuse large B-cell lymphoma at immune-privileged sites

Tetraspanin CD37 is predominantly expressed on the cell surface of mature B lymphocytes and is currently being studied as novel therapeutic target for B-cell lymphoma. Recently, we demonstrated that loss of CD37 induces spontaneous B-cell lymphoma in Cd37-knockout mice and correlates with inferior survival in patients with diffuse large B-cell lymphoma (DLBCL). Here, CD37 mutation analysis was performed in a cohort of 137 primary DLBCL samples, including 44 primary immune-privileged site-associated DLBCL (IP-DLBCL) samples originating in the testis or central nervous system. CD37 mutations were exclusively identified in IP-DLBCL cases (10/44, 23%) but absent in non-IP-DLBCL cases. The aberrations included 10 missense mutations, 1 deletion, and 3 splice-site CD37 mutations. Modeling and functional analysis of CD37 missense mutations revealed loss of function by impaired CD37 protein expression at the plasma membrane of human lymphoma B cells. This study provides novel insight into the molecular pathogenesis of IP-DLBCL and indicates that anti-CD37 therapies will be more beneficial for DLBCL patients without CD37 mutations.

Identification of CD37, cystatin A, and IL-23A gene expression in association with brain metastasis: analysis of a prospective trial

PURPOSE/OBJECTIVES

We aimed to assess the predictive value of a lung cancer gene panel for the development of brain metastases.

MATERIALS/METHODS

Between 2011 and 2015, 102 patients with lung cancer were prospectively enrolled in a clinical trial in which a diagnostic fine-needle aspirate was obtained. Gene expression was conducted on all samples that rendered a diagnosis of non-small cell lung cancer (NSCLC). Subsequent retrospective analysis of brain metastases-related outcomes was performed by reviewing patient electronic medical records. A competing risk multivariable regression was performed to estimate the adjusted hazard ratio for the development of brain metastases and non-brain metastases from NSCLC.

RESULTS

A total of 49 of 102 patients had died by the last follow-up. Median time of follow-up was 13 months (range 0.23-67 months). A total of 17 patients developed brain metastases. Median survival time after diagnosis of brain metastases was 3.58 months (95% confidence interval (CI) 2.17, not available). A total of 30 patients developed metastases without any evidence of brain metastases until the time of death or last follow-up. Competing risk analysis identified three genes that were downregulated differentially in the patients with brain metastases versus non-brain metastatic disease: CD37 (0.017), cystatin A (0.022), and IL-23A (0.027). Other factors associated with brain metastases include: stage T ( P ⩽ 8.3e-6) and stage N ( P= 6.8e-4).

CONCLUSIONS

We have identified three genes, CD37, cystatin A, and IL-23A, for which downregulation of gene expression was associated with a greater propensity for developing brain metastases. Validation of these biomarkers could have implications on surveillance patterns in patients with brain metastases from NSCLC.

Targeting the Tetraspanins with Monoclonal Antibodies in Oncology: Focus on Tspan8/Co-029

Tetraspanins are exposed at the surface of cellular membranes, which allows for the fixation of cognate antibodies. Developing specific antibodies in conjunction with genetic data would largely contribute to deciphering their biological behavior. In this short review, we summarize the main functions of Tspan8/Co-029 and its role in the biology of tumor cells. Based on data collected from recently reported studies, the possibilities of using antibodies to target Tspan8 in immunotherapy or radioimmunotherapy approaches are also discussed.

Anti-CD37 chimeric antigen receptor T cells are active against B- and T-cell lymphomas

Chimeric antigen receptor (CAR) T cells have emerged as a novel form of treatment of patients with B-cell malignancies. In particular, anti-CD19 CAR T-cell therapy has effected impressive clinical responses in B-cell acute lymphoblastic leukemia and diffuse large B-cell lymphoma. However, not all patients respond, and relapse with antigen loss has been observed in all patient subsets. Here, we report on the design and optimization of a novel CAR directed to the surface antigen CD37, which is expressed in B-cell non-Hodgkin lymphomas, in chronic lymphocytic leukemia, and in some cases of cutaneous and peripheral T-cell lymphomas. We found that CAR-37 T cells demonstrated antigen-specific activation, cytokine production, and cytotoxic activity in models of B- and T-cell lymphomas in vitro and in vivo, including patient-derived xenografts. Taken together, these results are the first showing that T cells expressing anti-CD37 CAR have substantial activity against 2 different lymphoid lineages, without evidence of significant T-cell fratricide. Furthermore, anti-CD37 CARs were readily combined with anti-CD19 CARs to generate dual-specific CAR T cells capable of recognizing CD19 and CD37 alone or in combination. Our findings indicate that CD37-CAR T cells represent a novel therapeutic agent for the treatment of patients with CD37-expressing lymphoid malignancies.

C-type lectin-like receptor 2 (CLEC-2)-dependent dendritic cell migration is controlled by tetraspanin CD37

Cell migration is central to evoking a potent immune response. Dendritic cell (DC) migration to lymph nodes is dependent on the interaction of C-type lectin-like receptor 2 (CLEC-2; encoded by the gene Clec1b), expressed by DCs, with podoplanin, expressed by lymph node stromal cells, although the underlying molecular mechanisms remain elusive. Here, we show that CLEC-2-dependent DC migration is controlled by tetraspanin CD37, a membrane-organizing protein. We identified a specific interaction between CLEC-2 and CD37, and myeloid cells lacking CD37 (Cd37-/-) expressed reduced surface CLEC-2. CLEC-2-expressing Cd37-/- DCs showed impaired adhesion, migration velocity and displacement on lymph node stromal cells. Moreover, Cd37-/- DCs failed to form actin protrusions in a 3D collagen matrix upon podoplanin-induced CLEC-2 stimulation, phenocopying CLEC-2-deficient DCs. Microcontact printing experiments revealed that CD37 is required for CLEC-2 recruitment in the membrane to its ligand podoplanin. Finally, Cd37-/- DCs failed to inhibit actomyosin contractility in lymph node stromal cells, thus phenocopying CLEC-2-deficient DCs. This study demonstrates that tetraspanin CD37 controls CLEC-2 membrane organization and provides new molecular insights into the mechanisms underlying CLEC-2-dependent DC migration.This article has an associated First Person interview with the first author of the paper.

Expression and Function of Tetraspanins and Their Interacting Partners in B Cells

Tetraspanins are transmembrane proteins that modulate multiple diverse biological processes, including signal transduction, cell–cell communication, immunoregulation, tumorigenesis, cell adhesion, migration, and growth and differentiation. Here, we provide a systematic review of the involvement of tetraspanins and their partners in the regulation and function of B cells, including mechanisms associated with antigen presentation, antibody production, cytokine secretion, co-stimulator expression, and immunosuppression. Finally, we direct our focus to the signaling mechanisms, evolutionary conservation aspects, expression, and potential therapeutic strategies that could be based on tetraspanins and their interacting partners.

Immune Targeting of Tetraspanins Involved in Cell Invasion and Metastasis

Metastasis is the ultimate consequence of cancer progression and the cause of patients’ death across different cancer types. Patients with initial diagnosis of distant disease have a worst 5-year survival compared to patients with localized disease. Therapies that target primary tumors fail to eradicate distant dissemination of cancer. Recently, immunotherapies have improved the survival of patients with metastatic disease, such as melanoma and lung cancer. However, only a fraction of patients responds to immunotherapy modalities that target the host immune system. The need to identify new druggable targets that inhibit or prevent metastasis is, therefore, much needed. Tetraspanins have emerged as key players in regulating cell migration, invasion, and metastasis. By serving as molecular adaptors that cluster adhesion receptors, signaling molecules, and cell surface receptors; tetraspanins are involved in all steps of the metastatic cascade. They regulate cell proliferation, participate in EMT transition, modulate integrin-mediated cell adhesion, and participate in angiogenesis and invasion processes. Tetraspanins have also been shown to modulate metastasis indirectly through exosomes and by regulating cellular interactions in the immune system. Importantly, targeting individual tetraspanin with antibodies has impacted tumor progression. This review will focus on the contribution of tetraspanins to the metastatic process and their potential as therapeutic tumor targets.

Antitumor Immunity Is Controlled by Tetraspanin Proteins

Antitumor immunity is shaped by the different types of immune cells that are present in the tumor microenvironment (TME). In particular, environmental signals (for instance, soluble factors or cell–cell contact) transmitted through the plasma membrane determine whether immune cells are activated or inhibited. Tetraspanin proteins are emerging as central building blocks of the plasma membrane by their capacity to cluster immune receptors, enzymes, and signaling molecules into the tetraspanin web. Whereas some tetraspanins (CD81, CD151, CD9) are widely and broadly expressed, others (CD53, CD37, Tssc6) have an expression pattern restricted to hematopoietic cells. Studies using genetic mouse models have identified important immunological functions of these tetraspanins on different leukocyte subsets, and as such, may be involved in the immune response against tumors. While multiple studies have been performed with regards to deciphering the function of tetraspanins on cancer cells, the effect of tetraspanins on immune cells in the antitumor response remains understudied. In this review, we will focus on tetraspanins expressed by immune cells and discuss their potential role in antitumor immunity. New insights in tetraspanin function in the TME and possible prognostic and therapeutic roles of tetraspanins will be discussed.

Prognostication of diffuse large B-cell lymphoma in the molecular era: moving beyond the IPI

Diffuse large B-cell lymphoma (DLBCL) is a heterogeneous disease with variable outcomes. Despite the majority of patients being cured with combination chemoimmunotherapy, up to 30% eventually succumb to the disease. Until recently, baseline prognostic assessment has centred on the International Prognostic Index (IPI), although this index is yet to impact strongly on treatment choice. Molecular features such as cell of origin, MYC and BCL-2 genetic alterations and protein overexpression were identified over a decade ago, yet their prognostic value is still not fully elucidated. Adding complexity are the plethora of new clinical, biological and molecular prognostic markers described in the recent literature, most of which lack independent validation, likely act as surrogate markers for those already in common use and have yet to substantially impact on therapeutic decision making. This review comprehensively assesses the value of individual prognostic markers in the clinical setting and their potential to predict response to novel agents, and ways to optimise their use in future research.

Interleukin-6 is essential for glomerular immunoglobulin A deposition and the development of renal pathology in Cd37-deficient mice

Immunoglobulin A (IgA) nephropathy (IgAN), the most common glomerulonephritis worldwide, is characterized by IgA depositions in the kidney. Deficiency of CD37, a leukocyte-specific tetraspanin, leads to spontaneous development of renal pathology resembling IgAN. However, the underlying molecular mechanism has not been resolved. Here we found that CD37 expression on B cells of patients with IgAN was significantly decreased compared to B cells of healthy donors. Circulating interleukin (IL)-6 levels, but not tumor necrosis factor-α or IL-10, were elevated in Cd37^-/- mice compared to wild-type mice after lipopolysaccharide treatment. Cd37^-/- mice displayed increased glomerular neutrophil influx, immune complex deposition, and worse renal function. To evaluate the role of IL-6 in the pathogenesis of accelerated renal pathology in Cd37^-/-mice, we generated Cd37xIl6 double-knockout mice. These double-knockout and Il6^-/- mice displayed no glomerular IgA deposition and were protected from exacerbated renal failure following lipopolysaccharide treatment. Moreover, kidneys of Cd37^-/- mice showed more mesangial proliferation, endothelial cell activation, podocyte activation, and segmental podocyte foot process effacement compared to the double-knockout mice, emphasizing that IL-6 mediates renal pathology in Cd37^-/- mice. Thus, our study indicates that CD37 may protect against IgA nephropathy by inhibition of the IL-6 pathway.

Staining the target: CD37 expression in lymphomas

In this issue of Blood, Xu-Monette et al show that CD37 protein expression is a strong prognostic marker in diffuse large B-cell lymphoma (DLBCL) treated with R-CHOP.1 CD37 negativity is associated with poor outcome and a high prevalence of adverse genetic and biologic features.1

Tetraspanin 8 (TSPAN 8) as a potential target for radio-immunotherapy of colorectal cancer

Tetraspanin 8 (TSPAN8) overexpression is correlated with poor prognosis in human colorectal cancer (CRC). A murine mAb Ts29.2 specific for human TSPAN8 provided significant efficiency for immunotherapy in CRC pre-clinical models. We therefore evaluate the feasability of targeting TSPAN8 in CRC with radiolabeled Ts29.2. Staining of tissue micro-arrays with Ts29.2 revealed that TSPAN8 espression was restricted to a few human healthy tissues. DOTA-Ts29.2 was radiolabeled with 111In or 177Lu with radiochemical purities >95%, specific activity ranging from 300 to 600 MBq/mg, and radioimmunoreactive fractions >80%. The biodistribution of [111In]DOTA-Ts29.2 in nude mice bearing HT29 or SW480 CRC xenografts showed a high specificity of tumor localization with high tumor/blood ratios (HT29: 4.3; SW480-TSPAN8: 3.9 at 72h and 120h post injection respectively). Tumor-specific absorbed dose calculations for [177Lu]DOTA-Ts29.2 was 1.89 Gy/MBq, establishing the feasibility of using radioimmunotherapy of CRC with this radiolabeled antibody. A significant inhibition of tumor growth in HT29 tumor-bearing mice treated with [177Lu]DOTA-Ts29.2 was observed compared to control groups. Ex vivo experiments revealed specific DNA double strand breaks associated with cell apoptosis in [177Lu]DOTA-Ts29.2 treated tumors compared to controls. Overall, we provide a proof-of-concept for the use of [111In/177Lu]DOTA-Ts29.2 that specifically target in vivo aggressive TSPAN8-positive cells in CRC.

DCZ3301, a novel cytotoxic agent, inhibits proliferation in diffuse large B-cell lymphoma via the STAT3 pathway

Diffuse large B-cell lymphoma (DLBCL) is the most common type of lymphoma in adults, characterized by a rapidly increasing painless mass. A novel compound, DCZ3301, was synthesized that exerted direct cytotoxicity against DLBCL cell lines. The effects of DCZ3301 on DLBCL cells in vitro and in vivo and the associated mechanisms were investigated. DCZ3301 inhibited the viability of DLBCL cell lines, even in the presence of protumorigenesis cytokines. Additionally, the compound induced apoptosis and cell cycle arrest at the G2/M phase by reducing mitochondrial membrane potential. DCZ3301 exerted an antitumor effect through modulation of Akt, extracellular signal-regulated kinases 1/2 (ERK1/2) and janus kinase 2 (JAK2)/signal transducer and activator of transcription 3 (STAT3) signaling pathways. Furthermore, DCZ3301 downregulates STAT3 phosphorylation by inhibiting Lck/Yes-related novel protein tyrosine kinase (Lyn) activation in DLBCL. A synergistic cytotoxic effect on DLBCL cells was observed upon combination of DCZ3301 with panobinostat. In vivo, intraperitoneal injection of xenograft mice with DCZ3301 resulted in reduced tumor volume. Our preliminary results collectively support the utility of the small-molecule inhibitor DCZ3301 as an effective novel therapeutic option for DLBCL that requires further clinical evaluation.

Identification of key genes and pathways associated with classical Hodgkin lymphoma by bioinformatics analysis

The current study aimed to explore the mechanisms associated with classic Hodgkin lymphoma (cHL) to identify novel diagnostic and therapeutic targets. The GES12453 microarray dataset was downloaded from the Gene Expression Omnibus database; the differentially expressed genes (DEGs) between cHL samples and normal B cell samples by were identified using the limma package. Gene ontology (GO) and pathway enrichment analysis of DEGs gene were performed. Furthermore, construction and analysis of protein-protein interaction (PPI) network was performed, and co-expression modules of DEGs were produced. A total of 450 DEGs were identified, comprising 216 upregulated and 234 downregulated genes in cHL compared with normal B cell samples. The DEGs were enriched in biological processes associated with immune response. The upregulated genes were mainly associated with the pathway of transcriptional misregulation in cancer, while downregulated genes were associated with B cell receptor signaling. PPI network analysis demonstrated that IL6 had the highest connectivity degree. Interleukin-6 (IL6) and signal transducer and activator of transcription 1 (STAT1) were demonstrated to be involved with the response to cytokine GO term in co-expression module 1. Spleen tyrosine kinase (SYK), B-cell linker protein (BLNK), CD79B, phospholipase C γ2 (PLCG2) were enriched in the B cell receptor signaling pathway in module 2. Matrix metallopeptidase 9 (MMP9), protein tyrosine phosphatase receptor type C had the highest connectivity degrees in module 3 and module 4, respectively. The results suggested that DEGs, including IL6, STAT1, MMP9, SYK, BLNK, PLCG2 and CD79B, and the pathways of B cell receptor signaling, Epstein-Barr virus infection and transcriptional misregulation in cancer have strong potential to be useful as targets for diagnosis or treatment of cHL.

Mismatch Repair Proteins Initiate Epigenetic Alterations during Inflammation-Driven Tumorigenesis

Aberrant silencing of genes by DNA methylation contributes to cancer, yet how this process is initiated remains unclear. Using a murine model of inflammation-induced tumorigenesis, we tested the hypothesis that inflammation promotes recruitment of epigenetic proteins to chromatin, initiating methylation and gene silencing in tumors. Compared with normal epithelium and noninflammation-induced tumors, inflammation-induced tumors gained DNA methylation at CpG islands, some of which are associated with putative tumor suppressor genes. Hypermethylated genes exhibited enrichment of repressive chromatin marks and reduced expression prior to tumorigenesis, at a time point coinciding with peak levels of inflammation-associated DNA damage. Loss of MutS homolog 2 (MSH2), a mismatch repair (MMR) protein, abrogated early inflammation-induced epigenetic alterations and DNA hypermethylation alterations observed in inflammation-induced tumors. These results indicate that early epigenetic alterations initiated by inflammation and MMR proteins lead to gene silencing during tumorigenesis, revealing a novel mechanism of epigenetic alterations in inflammation-driven cancer. Understanding such mechanisms will inform development of pharmacotherapies to reduce carcinogenesis. Cancer Res; 77(13); 3467-78. ©2017 AACR.

Crystal Structure of a Full-Length Human Tetraspanin Reveals a Cholesterol-Binding Pocket

Tetraspanins comprise a diverse family of four-pass transmembrane proteins that play critical roles in the immune, reproductive, genitourinary, and auditory systems. Despite their pervasive roles in human physiology, little is known about the structure of tetraspanins or the molecular mechanisms underlying their various functions. Here, we report the crystal structure of human CD81, a full-length tetraspanin. The transmembrane segments of CD81 pack as two largely separated pairs of helices, capped by the large extracellular loop (EC2) at the outer membrane leaflet. The two pairs of helices converge at the inner leaflet to create an intramembrane pocket with additional electron density corresponding to a bound cholesterol molecule within the cavity. Molecular dynamics simulations identify an additional conformation in which EC2 separates substantially from the transmembrane domain. Cholesterol binding appears to modulate CD81 activity in cells, suggesting a potential mechanism for regulation of tetraspanin function.

Assessment of CD37 B-cell antigen and cell of origin significantly improves risk prediction in diffuse large B-cell lymphoma

CD37 (tetraspanin TSPAN26) is a B-cell surface antigen widely expressed on mature B cells. CD37 is involved in immune regulation and tumor suppression but its function has not been fully elucidated. We assessed CD37 expression in de novo diffuse large B-cell lymphoma (DLBCL), and investigated its clinical and biologic significance in 773 patients treated with rituximab plus cyclophosphamide, doxorubicin, vincristine, and prednisone (R-CHOP) and 231 patients treated with CHOP. We found that CD37 loss (CD37^-) in ∼60% of DLBCL patients showed significantly decreased survival after R-CHOP treatment, independent of the International Prognostic Index (IPI), germinal center B-cell-like (GCB)/activated B-cell-like (ABC) cell of origin, nodal/extranodal primary origin, and the prognostic factors associated with CD37^-, including TP53 mutation, NF-κB^high, Myc^high, phosphorylated STAT3^high, survivin^high, p63^-, and BCL6 translocation. CD37 positivity predicted superior survival, abolishing the prognostic impact of high IPI and above biomarkers in GCB-DLBCL but not in ABC-DLBCL. Combining risk scores for CD37^- status and ABC cell of origin with the IPI, defined as molecularly adjusted IPI for R-CHOP (M-IPI-R), or IPI plus immunohistochemistry (IHC; IPI+IHC) for CD37, Myc, and Bcl-2, significantly improved risk prediction over IPI alone. Gene expression profiling suggested that decreased CD20 and increased PD-1 levels in CD37^- DLBCL, ICOSLG upregulation in CD37⁺ GCB-DLBCL, and CD37 functions during R-CHOP treatment underlie the pivotal role of CD37 status in clinical outcomes. In conclusion, CD37 is a critical determinant of R-CHOP outcome in DLBCL especially in GCB-DLBCL, representing its importance for optimal rituximab action and sustained immune responses. The combined molecular and clinical prognostic indices, M-IPI-R and IPI+IHC, have remarkable predictive values in R-CHOP-treated DLBCL.