T lymphocytes targeting native receptors

Targeted cellular therapy for treatment of relapsed or refractory leukemia

While the mainstay of treatment for high-risk or relapsed, refractory leukemia has historically revolved around allogeneic hematopoietic stem cell transplant (allo-HSCT), targeted immunotherapies have emerged as a promising therapeutic option, especially given the poor prognosis of patients who relapse after allo-HSCT. Novel cellular immunotherapies that harness the cytotoxic abilities of the immune system in a targeted manner (often called "adoptive" cell therapy), have changed the way we treat r/r hematologic malignancies and continue to change the treatment landscape given the rapid evolution of these powerful, yet sophisticated precision therapies that often offer a less toxic alternative to conventional salvage therapies. Importantly, adoptive cell therapy can be allo-HSCT-enabling or a therapeutic option for patients in whom transplantation has failed or is contraindicated. A solid understanding of the core concepts of adoptive cell therapy is necessary for stem cell transplant physicians, nurses and ancillary staff given its proximity to the transplant field as well as its inherent complexities that require specific expertise in compliant manufacturing, clinical application, and risk mitigation. Here we will review use of targeted cellular therapy for the treatment of r/r leukemia, focusing on chimeric antigen receptor T-cells (CAR T-cells) given the remarkable sustained clinical responses leading to commercial approval for several hematologic indications including leukemia, with brief discussion of other promising investigational cellular immunotherapies and special considerations for sustainability and scalability.

Feasibility of using CT radiomic signatures for predicting CD8-T cell infiltration and PD-L1 expression in renal cell carcinoma

Objectives

To identify computed tomography (CT)-based radiomic signatures of cluster of differentiation 8 (CD8)-T cell infiltration and programmed cell death ligand 1 (PD-L1) expression levels in patients with clear-cell renal cell carcinoma (ccRCC).

Methods

Seventy-eight patients with pathologically confirmed localized ccRCC, preoperative multiphase CT and tumor resection specimens were enrolled in this retrospective study. Regions of interest (ROI) of the ccRCC volume were manually segmented from the CT images and processed using a radiomics panel comprising of 1708 metrics. The extracted metrics were used as inputs to three machine learning classifiers: Random Forest, AdaBoost, and ElasticNet to create radiomic signatures for CD8-T cell infiltration and PD-L1 expression, respectively.

Results

Using a cut-off of 80 lymphocytes per high power field, 59 % were classified to CD8 highly infiltrated tumors and 41 % were CD8 non highly infiltrated tumors, respectively. An ElasticNet classifier discriminated between these two groups of CD8-T cells with an AUC of 0.68 (95 % CI, 0.55-0.80). In addition, based on tumor proportion score with a cut-off of > 1 % tumor cells expressing PD-L1, 76 % were PD-L1 positive and 24 % were PD-L1 negative. An Adaboost classifier discriminated between PD-L1 positive and PD-L1 negative tumors with an AUC of 0.8 95 % CI: (0.66, 0.95). 3D radiomics metrics of graylevel co-occurrence matrix (GLCM) and graylevel run-length matrix (GLRLM) metrics drove the performance for CD8-Tcell and PD-L1 classification, respectively.

Conclusions

CT-radiomic signatures can differentiate tumors with high CD8-T cell infiltration with moderate accuracy and positive PD-L1 expression with good accuracy in ccRCC.

Dual-antigen targeted iPSC-derived chimeric antigen receptor-T cell therapy for refractory lymphoma

We generated dual-antigen receptor (DR) T cells from induced pluripotent stem cells (iPSCs) to mitigate tumor antigen escape. These cells were engineered to express a chimeric antigen receptor (CAR) for the antigen cell surface latent membrane protein 1 (LMP1; LMP1-CAR) and a T cell receptor directed to cell surface latent membrane protein 2 (LMP2), in association with human leucocyte antigen A24, to treat therapy-refractory Epstein-Barr virus-associated lymphomas. We introduced LMP1-CAR into iPSCs derived from LMP2-specific cytotoxic T lymphocytes (CTLs) to generate rejuvenated CTLs (rejTs) active against LMP1 and LMP2, or DRrejTs. All DRrejT-treated mice survived >100 days. Furthermore, DRrejTs rejected follow-up inocula of lymphoma cells, demonstrating that DRrejTs persisted long-term. We also demonstrated that DRrejTs targeting CD19 and LMP2 antigens exhibited a robust tumor suppressive effect and conferred a clear survival advantage. Co-operative antitumor effect and in vivo persistence, with unlimited availability of DRrejT therapy, will provide powerful and sustainable T cell immunotherapy.

iPSC-Derived Neoantigen-Specific CTL Therapy for Ewing Sarcoma

The prognosis of Ewing sarcoma caused by EWS/FLI1 fusion is poor, especially after metastasis. Although therapy with CTLs targeted against altered EWS/FLI1 sequences at the gene break/fusion site may be effective, CTLs generated from peripheral blood are often exhausted because of continuous exposure to tumor antigens. We addressed this by generating induced pluripotent stem cell (iPSC)-derived functionally rejuvenated CTLs (rejT) directed against the neoantigen encoded by the EWS/FLI1 fusion gene. In this study, we examined the antitumor effects of EWS/FLI1-rejTs against Ewing sarcoma. The altered amino acid sequence at the break/fusion point of EWS/FLI1, when presented as a neoantigen, evokes an immune response that targets EWS/FLI1 ⁺ sarcoma. Although the frequency of generated EWS/FLI1-specific CTLs was only 0.003%, we successfully established CTL clones from a healthy donor. We established iPSCs from a EWS/FLI1-specific CTL clone and redifferentiated them into EWS/FLI1-specific rejTs. To evaluate cytotoxicity, we cocultured EWS/FLI1-rejTs with Ewing sarcoma cell lines. EWS/FLI1-rejTs rapidly and continuously suppressed the proliferation of Ewing sarcoma for >40 hours. Using a Ewing sarcoma xenograft mouse model, we verified the antitumor effect of EWS/FLI1-rejTs via imaging, and EWS/FLI1-rejTs conferred a statistically significant survival advantage. "Off-the-shelf" therapy is less destructive and disruptive than chemotherapy, and radiation is always desirable, particularly in adolescents, whom Ewing sarcoma most often affects. Thus, EWS/FLI1-rejTs targeting a Ewing sarcoma neoantigen could be a promising new therapeutic tool.

Lymphocyte expansion in bioreactors: upgrading adoptive cell therapy

Bioreactors are essential tools for the development of efficient and high-quality cell therapy products. However, their application is far from full potential, holding several challenges when reconciling the complex biology of the cells to be expanded with the need for a manufacturing process that is able to control cell growth and functionality towards therapy affordability and opportunity. In this review, we discuss and compare current bioreactor technologies by performing a systematic analysis of the published data on automated lymphocyte expansion for adoptive cell therapy. We propose a set of requirements for bioreactor design and identify trends on the applicability of these technologies, highlighting the specific challenges and major advancements for each one of the current approaches of expansion along with the opportunities that lie in process intensification. We conclude on the necessity to develop targeted solutions specially tailored for the specific stimulation, supplementation and micro-environmental needs of lymphocytes’ cultures, and the benefit of applying knowledge-based tools for process control and predictability.

Virus-specific T cells for malignancies - then, now and where to?

Purpose of Review

Virus-associated malignancies are a global health burden, constituting 10-12% of cancers worldwide. As these tumors express foreign viral antigens that can elicit specific T cell responses, virus-directed immunotherapies are a promising treatment strategy. Specifically, adoptive cell transfer of virus-specific T cells (VSTs) has demonstrated the potential to eradicate cancers associated with certain viruses.

Recent Findings

Initial studies in 1990s first showed that VSTs specific for the Epstein-Barr virus (EBVSTs) can induce complete remissions in patients with post-transplant lymphoproliferative disease. Since then, studies have validated the specificity and safety of VSTs in multiple lymphomas and solid malignancies. However, challenges remain to optimize this platform for widespread use, including enhancing potency and persistence, overcoming the immunosuppressive tumor microenvironment, and streamlining manufacturing processes that comply with regulatory requirements.

Summary

This review focuses on data from clinical trials evaluating VSTs directed against three viruses (EBV, HPV and MCPyV), as well as recent preclinical and clinical advances, and potential future directions.

How I treat CMV reactivation after allogeneic hematopoietic stem cell transplantation

Cytomegalovirus (CMV) reactivation remains one of the most common and life-threatening infectious complications following allogeneic hematopoietic stem cell transplantation, despite novel diagnostic technologies, several novel prophylactic agents, and further improvements in preemptive therapy and treatment of established CMV disease. Treatment decisions for CMV reactivation are becoming increasingly difficult and must take into account whether the patient has received antiviral prophylaxis, the patient's individual risk profile for CMV disease, CMV-specific T-cell reconstitution, CMV viral load, and the potential drug resistance detected at the time of initiation of antiviral therapy. Thus, we increasingly use personalized treatment strategies for the recipient of an allograft with CMV reactivation based on prior use of anti-CMV prophylaxis, viral load, the assessment of CMV-specific T-cell immunity, and the molecular assessment of resistance to antiviral drugs.

Sustainable Tumor-Suppressive Effect of iPSC-Derived Rejuvenated T Cells Targeting Cervical Cancers

Immunotherapy utilizing induced pluripotent stem cell (iPSC) technology has great potential. Functionally rejuvenated cytotoxic T lymphocytes (CTLs) can survive long-term as young memory T cells in vivo, with continuous tumor eradication. Banking of iPSCs as an unlimited “off-the-shelf” source of therapeutic T cells may be feasible. To generate safer iPSCs, we reprogrammed human papilloma virus type 16 (HPV16) E6-specific CTLs by Sendai virus vector without cotransduction of SV40 large T antigen. The iPSCs efficiently differentiated into HPV16-specific rejuvenated CTLs that demonstrated robust cytotoxicity against cervical cancer. The tumor-suppressive effect of rejuvenated CTLs was stronger and more persistent than that of original peripheral blood CTLs. These rejuvenated HPV16-specific CTLs provide a sustained tumor-suppressive effect even for epithelial cancers and constitute promising immunotherapy for cervical cancer.

Adoptive Immunotherapy with Antigen-Specific T Cells Expressing a Native TCR

Although T cells genetically modified with chimeric antigen receptors became the first immune effector product to obtain FDA approval, T-cell products that recognize their antigenic targets through their native receptors have also produced encouraging responses. For instance, T cells recognizing immunogenic viral antigens are effective when infused in immunosuppressed patients. A large number of tumor antigens are also expressed on nonviral tumors, but these antigens are less immunogenic. Many tumors can evade a transferred immune response by producing variants, which have lost the targeted antigens, or inhibitory molecules that recruit suppressive cells, impeding persistence and function of immune effectors. Nevertheless, infusion of antigen-specific T cells has been well-tolerated, and clinical responses have been consistently associated with immune activity against tumor antigens and epitope spreading. To overcome some of the obstacles mentioned above, current research is focused on defining ex vivo culture conditions that promote in vivo persistence and activity of infused antigen-specific T cells. Combinations with immune checkpoint inhibitors or epigenetic modifiers to improve T-cell activity are also being evaluated in the clinic. Antigen-specific T cells may also be manufactured to overcome tumor evasion mechanisms by targeting multiple antigens and engineered to be resistant to inhibitory factors, such as TGFβ, or to produce the cytokines that are essential for T-cell expansion and sustained antitumor activity. Here, we discuss the use of T cells specific to tumor antigens through their native receptors and strategies under investigation to improve antitumor responses.

TGF-β in T Cell Biology: Implications for Cancer Immunotherapy

Transforming Growth Factor beta (TGF-β) is a pleiotropic cytokine produced in large amounts within cancer microenvironments that will ultimately promote neoplastic progression, notably by suppressing the host’s T-cell immunosurveillance. This effect is mostly due to the well-known inhibitory effect of TGF-β on T cell proliferation, activation, and effector functions. Moreover, TGF-β subverts T cell immunity by favoring regulatory T-cell differentiation, further reinforcing immunosuppression within tumor microenvironments. These findings stimulated the development of many strategies to block TGF-β or its signaling pathways, either as monotherapy or in combination with other therapies, to restore anti-cancer immunity. Paradoxically, recent studies provided evidence that TGF-β can also promote differentiation of certain inflammatory populations of T cells, such as Th17, Th9, and resident-memory T cells (Trm), which have been associated with improved tumor control in several models. Here, we review current advances in our understanding of the many roles of TGF-β in T cell biology in the context of tumor immunity and discuss the possibility to manipulate TGF-β signaling to improve cancer immunotherapy.

TGF-β in T Cell Biology: Implications for Cancer Immunotherapy

Transforming Growth Factor beta (TGF-β) is a pleiotropic cytokine produced in large amounts within cancer microenvironments that will ultimately promote neoplastic progression, notably by suppressing the host’s T-cell immunosurveillance. This effect is mostly due to the well-known inhibitory effect of TGF-β on T cell proliferation, activation, and effector functions. Moreover, TGF-β subverts T cell immunity by favoring regulatory T-cell differentiation, further reinforcing immunosuppression within tumor microenvironments. These findings stimulated the development of many strategies to block TGF-β or its signaling pathways, either as monotherapy or in combination with other therapies, to restore anti-cancer immunity. Paradoxically, recent studies provided evidence that TGF-β can also promote differentiation of certain inflammatory populations of T cells, such as Th17, Th9, and resident-memory T cells (Trm), which have been associated with improved tumor control in several models. Here, we review current advances in our understanding of the many roles of TGF-β in T cell biology in the context of tumor immunity and discuss the possibility to manipulate TGF-β signaling to improve cancer immunotherapy.

Comprehensive review of post-organ transplant hematologic cancers

A higher risk for a variety of cancers is among the major complications of posttransplantation immunosuppression. In this part of a continuing series on cancers posttransplantation, this review focuses on the hematologic cancers after solid organ transplantation. Posttransplantation lymphoproliferative disorders (PTLDs), which comprise the great majority of hematologic cancers, represent a spectrum of conditions that include, but are not limited to, the Hodgkin and non-Hodgkin lymphomas. The oncogenic Epstein-Barr virus is a key pathogenic driver in many PTLD cases, through known and unknown mechanisms. The other hematologic cancers include leukemias and plasma cell neoplasms (multiple myeloma and plasmacytoma). Clinical features vary across malignancies and location. Preventive screening strategies have been attempted mainly for PTLDs. Treatments include the chemotherapy regimens for the specific cancers, but also include reduction of immunosuppression, rituximab, and other therapies.

Opportunities and challenges for the cellular immunotherapy sector: a global landscape of clinical trials

Global investments in cellular immunotherapies reflect their curative potential. Our landscape of clinical trials will aid developers, investors, adopters and payers in planning for adoption and implementation along realistic time horizons. Trend data enable stakeholders to adapt their business models and capacity to bring immunotherapies to the clinic. For cancer, trends suggest a shift from cancer vaccines to adoptive cellular transfer, alongside a focus on solid tumors. Academic centers, mainly in the USA, lead in early-phase clinical trials and target identification; but industry involvement has increased fourfold over the past two decades. Trends indicate an increasingly personalized approach to onco-immunology, which raises challenges for cost-effective manufacturing and delivery models. Overcoming these challenges provides opportunities for innovative biotechnology firms.

Checkpoint inhibition and cellular immunotherapy in lymphoma

Hodgkin and non-Hodgkin lymphoma are both good targets for immunotherapy, as they are accessible to antibodies and cell-based immunotherapy, express costimulatory molecules, and express lineage-restricted, viral, and unique tumor antigens. Blockade of the programmed-death 1 (PD-1) immune checkpoint has produced very encouraging response rates in patients with Hodgkin lymphoma, whereas adoptive transfer of Epstein-Barr Virus (EBV)-specific T cells has shown clinical activity in patients with posttransplant lymphoma and other EBV-associated lymphomas. T cells can also be genetically modified with chimeric antigen receptors (CARs) to confer specificity for surface antigens, and studies of CD19 CARs in lymphoma also have had encouraging response rates. Future directions include combination of checkpoint blockade and adoptive T-cell studies.

Recent advances in T-cell immunotherapy for haematological malignancies

In vitro discoveries have paved the way for bench-to-bedside translation in adoptive T cell immunotherapy, resulting in remarkable clinical responses in a variety of haematological malignancies. Adoptively transferred T cells genetically modified to express CD19 CARs have shown great promise, although many unanswered questions regarding how to optimize T-cell therapies for both safety and efficacy remain. Similarly, T cells that recognize viral or tumour antigens though their native receptors have produced encouraging clinical responses. Honing manufacturing processes will increase the availability of T-cell products, while combining T-cell therapies has the ability to increase complete response rates. Lastly, innovative mechanisms to control these therapies may improve safety profiles while genome editing offers the prospect of modulating T-cell function. This review will focus on recent advances in T-cell immunotherapy, highlighting both clinical and pre-clinical advances, as well as exploring what the future holds.

Genome-wide analysis of Epstein-Barr virus (EBV) isolated from EBV-associated gastric carcinoma (EBVaGC)

Epstein-Barr virus (EBV) is linked to the development of a variety of malignancies, including EBV-associated gastric carcinoma (EBVaGC). In this study, EBVaGC was detected in 15 (7.3%) of 206 GC cases. To identify the EBV genomic variation, EBV genomic sequences isolated from 9 EBVaGC biopsy specimens were successfully retrieved, designated EBVaGC1 to EBVaGC9. By comparative analysis of these strains with another 6 completely sequenced EBV strains, EBV-wild type, B95–8, AG876, GD1, GD2, and HKNPC1, it was demonstrated that EBVaGC1 to 9 were most closely related to the GD1 strain. Phylogenetic analysis of the GC biopsy specimen-derived EBV (GC-EBV) genomes was subsequently performed to assess their genomic diversity and it exhibited the greatest divergence from the type 2 strain, AG876. Compared with the reference EBV strain GD1, they harbored 961 variations in total, including 919 substitutions, 23 insertions, and 19 deletions. Single nucleotide polymorphism (SNP) density varied substantially across all known open reading frames and was highest in latency-associated genes. Moreover, we identified 2 interstrain recombinants at the EBNA1 locus, which provided a further mechanism for the generation of diversity. Some T-cell epitope sequences in EBNA1 and LMP2A genes showed extensive variation across strains, which implied their importance in the development of vaccines and T-cell therapy. In conclusion, we reported the first genome-wide view of sequence variation of EBV isolated from primary EBVaGC biopsy specimens, which might serve as an effective method for further understanding the genomic variations contribute to EBVaGC carcinogenesis and treatment.

Epstein-Barr Virus: Diseases Linked to Infection and Transformation

Epstein–Barr virus (EBV) was first discovered in 1964, and was the first known human tumor virus now shown to be associated with a vast number of human diseases. Numerous studies have been conducted to understand infection, propagation, and transformation in various cell types linked to human diseases. However, a comprehensive lens through which virus infection, reactivation and transformation of infected host cells can be visualized is yet to be formally established and will need much further investigation. Several human cell types infected by EBV have been linked to associated diseases. However, whether these are a direct result of EBV infection or indirectly due to contributions by additional infectious agents will need to be fully investigated. Therefore, a thorough examination of infection, reactivation, and cell transformation induced by EBV will provide a more detailed view of its contributions that drive pathogenesis. This undoubtedly expand our knowledge of the biology of EBV infection and the signaling activities of targeted cellular factors dysregulated on infection. Furthermore, these insights may lead to identification of therapeutic targets and agents for clinical interventions. Here, we review the spectrum of EBV-associated diseases, the role of the encoded latent antigens, and the switch to latency or lytic replication which occurs in EBV infected cells. Furthermore, we describe the cellular processes and critical factors which contribute to cell transformation. We also describe the fate of B-cells and epithelial cells after EBV infection and the expected consequences which contribute to establishment of viral-associated pathologies.

T-cell and natural killer cell therapies for hematologic malignancies after hematopoietic stem cell transplantation: enhancing the graft-versus-leukemia effect

Hematopoietic stem cell transplantation has revolutionized the treatment of hematologic malignancies, but infection, graft-versus-host disease and relapse are still important problems. Calcineurin inhibitors, T-cell depletion strategies, and immunomodulators have helped to prevent graft-versus-host disease, but have a negative impact on the graft-versus-leukemia effect. T cells and natural killer cells are both thought to be important in the graft-versus-leukemia effect, and both cell types are amenable to ex vivo manipulation and clinical manufacture, making them versatile immunotherapeutics. We provide an overview of these immunotherapeutic strategies following hematopoietic stem cell transplantation, with discussions centered on natural killer and T-cell biology. We discuss the contributions of each cell type to graft-versus-leukemia effects, as well as the current research directions in the field as related to adoptive cell therapy after hematopoietic stem cell transplantation.

Post-transplant lymphoproliferative disorders

Post-transplant lymphoproliferative disorders (PTLDs) are a group of conditions that involve uncontrolled proliferation of lymphoid cells as a consequence of extrinsic immunosuppression after organ or haematopoietic stem cell transplant. PTLDs show some similarities to classic lymphomas in the non-immunosuppressed general population. The oncogenic Epstein-Barr virus (EBV) is a key pathogenic driver in many early-onset cases, through multiple mechanisms. The incidence of PTLD varies with the type of transplant; a clear distinction should therefore be made between the conditions after solid organ transplant and after haematopoietic stem cell transplant. Recipient EBV seronegativity and the intensity of immunosuppression are among key risk factors. Symptoms and signs depend on the localization of the lymphoid masses. Diagnosis requires histopathology, although imaging techniques can provide additional supportive evidence. Pre-emptive intervention based on monitoring EBV levels in blood has emerged as the preferred strategy for PTLD prevention. Treatment of established disease includes reduction of immunosuppression and/or administration of rituximab (a B cell-specific antibody against CD20), chemotherapy and EBV-specific cytotoxic T cells. Despite these strategies, the mortality and morbidity remains considerable. Patient outcome is influenced by the severity of presentation, treatment-related complications and risk of allograft loss. New innovative treatment options hold promise for changing the outlook in the future.

Selection of adenovirus-specific and Epstein-Barr virus-specific T cells with major histocompatibility class I streptamers under Good Manufacturing Practice (GMP)-compliant conditions

BACKGROUND AIMS

Despite antiviral drug therapies, human adenovirus (HAdV), cytomegalovirus (CMV) and Epstein-Barr virus (EBV) infections still contribute substantially to transplant-related death of patients after hematopoietic stem cell transplantation. Earlier clinical studies demonstrated successful adoptive transfer of magnetically selected CMV-specific T cells via removable, and thus Good Manufacturing Practice-compliant, major histocompatibility class I streptamers. Thus, the primary focus of the present study was the selection of HAdV-streptamer+ T cells, although in three experiments, EBV-streptamer+ T cells were also selected.

METHODS

Cells from leukaphereses of healthy donors were prepared in large (1-6 × 10(9)) and small (25 × 10(6)) cell batches. Whereas the larger batch was directly labeled with streptamers to select HAdV- and/or EBV-specific T cells (large-scale), the smaller batch was used to generate in vitro virus-specific T-cell lines before streptamer labeling for streptamer selection (small-scale). Isolation of HAdV- and/or EBV-specific T cells was performed with the use of the CliniMACS device.

RESULTS

The purity of HAdV- and EBV-streptamer+ T cells among CD3+ cells, obtained from large-scale selection, was up to 6.7% and 44%, respectively. If HAdV- and EBV-streptamers were applied simultaneously, the purity of antigen-specific T cells reached up to 50.7%. A further increase in purity reaching up to 98% was achieved by small-scale selection of HAdV-specific T cells. All final products fulfilled the microbiological and chemical release criteria. Interferon-γ-response indicating functional activity was seen in 6 of 9 HAdV and 2 of 3 EBV large-scale selections and in 2 of 3 HAdV small-scale selections.

CONCLUSIONS

HAdV-streptamers were shown to be clinically feasible for few patients after the large-scale approach but for larger patient numbers if combined with EBV-streptamers or after the small-scale approach.

The immunology of Epstein-Barr virus-induced disease

Epstein-Barr virus (EBV) is usually acquired silently early in life and carried thereafter as an asymptomatic infection of the B lymphoid system. However, many circumstances disturb the delicate EBV-host balance and cause the virus to display its pathogenic potential. Thus, primary infection in adolescence can manifest as infectious mononucleosis (IM), as a fatal illness that magnifies the immunopathology of IM in boys with the X-linked lymphoproliferative disease trait, and as a chronic active disease leading to life-threatening hemophagocytosis in rare cases of T or natural killer (NK) cell infection. Patients with primary immunodeficiencies affecting the NK and/or T cell systems, as well as immunosuppressed transplant recipients, handle EBV infections poorly, and many are at increased risk of virus-driven B-lymphoproliferative disease. By contrast, a range of other EBV-positive malignancies of lymphoid or epithelial origin arise in individuals with seemingly intact immune systems through mechanisms that remain to be understood.

Pan-viral-microRNA screening identifies interferon inhibition as a common function of diverse viruses

Diverse viruses encode regulatory RNAs called microRNAs (miRNAs). Despite much progress, the functions of the majority of viral miRNAs remain unknown. Most previous studies have used biochemical methods to uncover targets of viral miRNAs, but it is unclear what fraction of these targets is functionally important. Here, we apply an alternative strategy based on the premise that assorted viral miRNAs will share functionality. Screening a library of >70 human viral miRNAs showed that three unrelated miRNAs from distantly related herpesviruses significantly inhibited IFN signaling. Strikingly, each of these miRNAs directly reduced expression of the cyclic AMP-responsive element-binding protein (CBP), which as part of the p300-CBP complex, mediates IFN signaling. We show that both 5' and 3' derivatives from Epstein-Barr virus (EBV) encoded miR-BART-18 precursor miRNA (pre-miRNA) and the orthologous pre-miRNA from Rhesus lymphocryptovirus contribute to reducing IFN signaling. Thus, through both convergent and divergent evolutionary mechanisms, varied herpesviral miRNAs share the ability to decrease IFN signaling. Restoring miR-BART-18 to cells infected with an EBV miRNA mutant conveyed a cellular growth advantage upon IFN treatment, and relevant miRNAs from other herpesviruses were able to complement this activity. Blocking miR-BART-18 function in an EBV(+) tumor cell line renders cells more susceptible to IFN-mediated effects. These findings provide a mechanism that can at least partially explain the resistance of some EBV-associated tumors to IFN therapy. Our work suggests that similar pan-viral-miRNA functional-based screening strategies are warranted for determining relevant activities of other viral miRNAs.