T-cell therapy in the treatment of post-transplant lymphoproliferative disease

Prophylactic and therapeutic adenoviral vector-based multivirus-specific T-cell immunotherapy for transplant patients

Viral infections including cytomegalovirus, Epstein-Barr virus, adenovirus, and BK virus are a common and predictable problem in transplant recipients. While cellular immune therapies have been successfully used to tackle infectious complications in transplant recipients, manufacturing immunotherapies to address the multitude of possible pathogens can be technically challenging and labor-intensive. Here we describe a novel adenoviral antigen presentation platform (Ad-MvP) as a tool for rapid generation of multivirus-specific T-cells in a single step. Ad-MvP encodes 32 CD8+ T-cell epitopes from cytomegalovirus, Epstein-Barr virus, adenovirus, and BK virus as a contiguous polyepitope. We demonstrate that Ad-MvP vector can be successfully used for rapid in vitro expansion of multivirus-specific T-cells from transplant recipients and in vivo priming of antiviral T-cell immunity. Most importantly, using an in vivo murine model of Epstein-Barr virus-induced lymphoma, we also show that adoptive immunotherapy with Ad-MvP expanded autologous and allogeneic multivirus-specific T-cells is highly effective in controlling Epstein-Barr virus tumor outgrowth and improving overall survival. We propose that Ad-MvP has wide ranging therapeutic applications in greatly facilitating in vivo priming of antiviral T-cells, the generation of third-party T-cell banks as “off-the-shelf” therapeutics as well as autologous T-cell therapies for transplant patients.

T-cell-based Immunotherapy: Adoptive Cell Transfer and Checkpoint Inhibition

Tumor immunotherapy has had demonstrable efficacy in patients with cancer. The most promising results have been with T-cell-based therapies. These include adoptive cell transfer of tumor-infiltrating lymphocytes, genetically engineered T cells, and immune checkpoint inhibitor antibodies. In this review, we describe the different T-cell-based strategies currently in clinical trials and put their applications, present and future, into perspective.

Virus-specific T-cell banks for 'off the shelf' adoptive therapy of refractory infections

Adoptive immunotherapy with transplant donor-derived virus-specific T cells has emerged as a potentially curative approach for the treatment of drug-refractory EBV+lymphomas as well as CMV and adenovirus infections complicating allogeneic hematopoietic cell transplants. Adoptive transfer of HLA partially matched virus-specific T cells from healthy third party donors has also shown promise in the treatment of these conditions, with disease response rates of 50-76% and strikingly low incidences of toxicity or GVHD recorded in initial trials. In this review, we examine the reported experience with transplant donor and third party donor-derived virus-specific T cells, identifying characteristics of the viral pathogen, the T cells administered and the diseased host that contribute to treatment response or failure. We also describe the characteristics of virus-specific T-cell lines in our center's bank and the frequency with which in vitro culture promotes expansion of immunodominant T cells specific for epitopes that are presented by a limited array of prevalent HLA alleles, which facilitates their broad applicability for treatment.

T cells specific for different latent and lytic viral proteins efficiently control Epstein-Barr virus-transformed B cells

BACKGROUND AIMS

Epstein-Barr virus (EBV)-associated post-transplant lymphoproliferative disorders (PTLD) belong to the most dreaded complications of immunosuppression. The efficacy of EBV-specific T-cell transfer for PTLD has been previously shown, yet the optimal choice of EBV-derived antigens inducing polyclonal CD4(+) and CD8(+) T cells that cover a wide range of human leukocyte antigen types and efficiently control PTLD remains unclear.

METHODS

A pool of 125 T-cell epitopes from seven latent and nine lytic EBV-derived proteins (EBVmix) and peptide pools of EBNA1, EBNA3c, LMP2a and BZLF1 were used to determine T-cell frequencies and to isolate T cells through the use of the interferon (IFN)-γ cytokine capture system. We further evaluated the phenotype and functionality of the generated T-cell lines in vitro.

RESULTS

EBVmix induced significantly higher T-cell frequencies and allowed selecting more CD4(+)IFN-γ(+) and CD8(+)IFN-γ(+) cells than single peptide pools. T cells of all specificities expanded similarly in vitro, recognized cognate antigen, and, to a lower extent, EBV-infected cells, exerted moderate cytotoxicity and showed reduced alloreactivity. However, EBVmix-specific cells most efficiently controlled EBV-infected lymphoblastoid cell lines (LCLs). This control was mainly mediated by EBV-specific CD8(+) cells with an oligoclonal epitope signature covering both latent and lytic viral proteins. Notably, EBV-specific CD4(+) cells unable to control LCLs produced significantly less perforin and granzyme B, probably because of limited LCL epitope presentation.

CONCLUSIONS

EBVmix induces a broader T-cell response, probably because of its coverage of latent and lytic EBV-derived proteins that may be important to control EBV-transformed B cells and might offer an improvement of T-cell therapies.

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.

Memory T cell-driven differentiation of naive cells impairs adoptive immunotherapy

Adoptive cell transfer (ACT) of purified naive, stem cell memory, and central memory T cell subsets results in superior persistence and antitumor immunity compared with ACT of populations containing more-differentiated effector memory and effector T cells. Despite a clear advantage of the less-differentiated populations, the majority of ACT trials utilize unfractionated T cell subsets. Here, we have challenged the notion that the mere presence of less-differentiated T cells in starting populations used to generate therapeutic T cells is sufficient to convey their desirable attributes. Using both mouse and human cells, we identified a T cell-T cell interaction whereby antigen-experienced subsets directly promote the phenotypic, functional, and metabolic differentiation of naive T cells. This process led to the loss of less-differentiated T cell subsets and resulted in impaired cellular persistence and tumor regression in mouse models following ACT. The T memory-induced conversion of naive T cells was mediated by a nonapoptotic Fas signal, resulting in Akt-driven cellular differentiation. Thus, induction of Fas signaling enhanced T cell differentiation and impaired antitumor immunity, while Fas signaling blockade preserved the antitumor efficacy of naive cells within mixed populations. These findings reveal that T cell subsets can synchronize their differentiation state in a process similar to quorum sensing in unicellular organisms and suggest that disruption of this quorum-like behavior among T cells has potential to enhance T cell-based immunotherapies.

Recent advances in the risk factors, diagnosis and management of Epstein-Barr virus post-transplant lymphoproliferative disease

Fifty years after the first reports of Epstein-Barr virus (EBV)-associated endemic Burkitt's lymphoma, EBV has emerged as the third most prevalent oncogenic virus worldwide. EBV infection is associated with various malignancies including Hodgkin and non-Hodgkin lymphoma, NK/T-cell lymphoma and nasopharyngeal carcinoma. Despite the highly specific immunologic control in the immunocompetent host, EBV can cause severe complications in the immunocompromised host (namely, post-transplant lymphoproliferative disease). This is particularly a problem in patients with delayed immune reconstitution post-hematopoietic stem cell transplant or solid organ transplant. Despite advances in diagnostic techniques and treatment algorithms allowing earlier identification and treatment of patients at highest risk, mortality rates remain as high as 90% if not treated early. The cornerstones of treatment include reduction in immunosuppression and in vivo B cell depletion with an anti-CD20 monoclonal antibody. However, these treatment modalities are not always feasible due to graft rejection, emergence of graft vs. host disease, and toxicity. Newer treatment modalities include the use of adoptive T cell therapy, which has shown promising results in various EBV-related malignancies. In this article we will review recent advances in risk factors, diagnosis and management of EBV-associated malignancies, particularly post-transplant lymphoproliferative disease. We will also discuss new and innovative treatment options including adoptive T cell therapy as well as management of special situations such as chronic active EBV and EBV-associated hemophagocytic lymphohistiocytosis.

Primary immunodeficiencies and the control of Epstein-Barr virus infection

Human primary immunodeficiency (PID) states, where mutations in single immune system genes predispose individuals to certain infectious agents and not others, are experiments of nature that hold important lessons for the immunologist. The number of genetically defined PIDs is rising rapidly, as is the opportunity to learn from them. Epstein-Barr virus (EBV), a human herpesvirus, has long been of interest because of its complex interaction with the immune system. Thus, it causes both infectious mononucleosis (IM), an immunopathologic disease associated with exaggerated host responses, and at least one malignancy, EBV-positive lymphoproliferative disease, when those responses are impaired. Here, we describe the full range of PIDs currently linked with an increased risk of EBV-associated disease. These provide examples where IM-like immunopathology is fatally exaggerated, and others where responses impaired at the stage of induction, expansion, or effector function predispose to malignancy. Current evidence from this rapidly moving field supports the view that lesions in both natural killer cell and T cell function can lead to EBV pathology.

Epstein-Barr virus-related post-transplant lymphoproliferative disorder in solid organ transplant recipients

Epstein-Barr virus (EBV) contributes to the pathogenesis of post-transplant lymphoproliferative disease (PTLD) in more than 70% of cases. EBV DNAemia surveillance has been reported to assist in the prevention and treatment of PTLD in hematopoietic stem-cell transplantation (HSCT) recipients. Derived from experience in HSCT and taking into account that PCR-based EBV monitoring techniques are currently available in most solid organ transplant (SOT) centres, there is a great interest in EBV surveillance and prevention of PTLD in SOT recipients. In the present document we have tried to address from a practical perspective different important topics regarding the prevention and management of EBV-related PTLD in SOT. To this end, available information on SOT was analysed and combined with potentially useful data from HSCT and expert observations. The document is therefore structured according to different specific questions, each of them culminating in a consensus opinion of the panel of European experts, grading the answers according to internationally recognized levels of evidence. The addressed issues were grouped under the following topics. (i) Timing and epidemiological data of PTLD. Prophylaxis guided by clinical risk factors of early and late PTLD in SOT. (ii) Relationship of EBV DNAemia load monitoring and the development of PTLD in solid organ transplant recipients. (iii) Monitoring of EBV DNAemia after SOT. Which population should be monitored? What is the optimal timing of the monitoring? (iv) Management of SOT recipients with persistent and/or increasing EBV DNAemia.

The Impact of EBV Status on Characteristics and Outcomes of Posttransplantation Lymphoproliferative Disorder

We examined the associations of Epstein-Barr virus (EBV) status with characteristics and outcomes of posttransplantation lymphoproliferative disorder (PTLD) by studying 176 adult solid organ transplant recipients diagnosed with PTLD between 1990 and 2013 (58 [33%] EBV-negative; 118 [67%] EBV-positive). The proportion of EBV-negative cases increased over time from 10% (1990-1995) to 48% (2008-2013) (p < 0.001). EBV-negative PTLD had distinct characteristics (monomorphic histology, longer latency) though high-risk features (advanced stage, older age, high lactate dehydrogenase, central nervous system involvement) were not more common compared to EBV-positive PTLD. In multivariable analysis, EBV negativity was not significantly associated with worse response to initial therapy (adjusted odds ratio, 0.84; p = 0.75). The likelihood of achieving a complete remission (CR) was not significantly different for EBV-negative versus EBV-positive PTLD including when therapy was reduction of immunosuppression alone (35% vs. 43%, respectively, p = 0.60) or rituximab (43% vs. 47%, p = 1.0). EBV negativity was also not associated with worse overall survival (adjusted hazard ratio, 0.91; p = 0.71). Our findings indicate that EBV status is not prognostic or predictive of treatment response in adults with PTLD. The high proportion of EBV-negative disease diagnosed in recent years highlights the need for new strategies for prevention and management of EBV-negative PTLD.

Epstein-Barr virus lymphoproliferative disease after hematopoietic stem cell transplant

PURPOSE OF REVIEW

Epstein-Barr virus (EBV) reactivation can cause significant morbidity and mortality after allogeneic hematopoietic stem cell transplant. Delays in reconstitution of EBV-specific T lymphocyte activity can lead to life-threatening EBV lymphoproliferative disease (EBV-PTLD). This review highlights recent advances in the understanding of pathophysiology, risk factors, diagnosis, and management of EBV viremia and PTLD.

RECENT FINDINGS

During the past decade, early detection strategies, such as serial measurement of EBV-DNA load, have helped identify high-risk patients and diagnose early lymphoproliferation. The most significant advances have come in the form of innovative treatment options, including manipulation of the balance between outgrowing EBV-infected B cells and the EBV cytotoxic T lymphocyte response, and targeting infected B cells with monoclonal antibodies, chemotherapy, unmanipulated donor lymphocytes, and donor or more recently third-party EBV cytotoxic T lymphocytes. Defining criteria for preemptive therapy remains a challenge.

SUMMARY

EBV reactivation is a significant complication after stem cell transplant. Continued improvements in risk stratification and treatment options are required to improve the morbidity and mortality caused by EBV-associated diseases. Current approaches use rituximab to deplete B cells or adoptive transfer of EBV cytotoxic T lymphocyte to reconstitute immunity. The availability of rapid EBV-specific T cell products offers the possibility of improved outcomes.

Post-transplant lymphoproliferative disorders: from epidemiology to pathogenesis-driven treatment

Post-transplant lymphoproliferative disorders (PTLDs) represent the most severe complication of both solid organ and hematopoietic stem cell transplantation. The Epstein-Barr Virus (EBV) is the main driver of PTLD, particularly those occurring early after transplantation. EBV-driven malignancies are associated with selective expression of latent viral proteins, but uncontrolled lytic replication may favor early phases of cell transformation. Besides immunodepression, persistent immune activation and chronic inflammation play an important role in both virus reactivation and expansion of EBV-infected B cells. EBV-induced immortalization requires the expression of telomerase. TERT, the rate-limiting component of the telomerase complex, is central in the switch from the lytic to the latent viral program, and TERT inhibition induces the EBV lytic cycle and cell death. Immunotherapy and combination of EBV lytic cycle inducers with antiviral drugs are promising strategies to improve the treatment of PTLD patients. This review is aimed at providing an update on the intriguing association between EBV and PTLD, mainly focusing on cases arising after kidney and liver transplantation, which account for the vast majority of transplants.

Directed T-cell therapies for leukemia and lymphoma after hematopoietic stem cell transplant: beyond chimeric antigen receptors

This review focuses on the recent advances utilizing adoptive T-cell immunotherapies for patients after hematopoietic stem cell transplant using T cells after autologous transplant to treat the highest risk patients. The particular emphasis is the use of T cells to treat leukemias and lymphomas with gene transfer and nongene transfer approaches to direct specificity to tumor associated antigens. In this review, we will highlight how these novel therapeutics can be successfully used to prevent or treat high-risk patients who relapse after hematopoietic stem cell transplant.

Approaches for monitoring of non virus-specific and virus-specific T-cell response in solid organ transplantation and their clinical applications

Opportunistic viral infections are still a major complication following solid organ transplantation. Immune monitoring may allow the identification of patients at risk of infection and, eventually, the modulation of immunosuppressive strategies. Immune monitoring can be performed using virus-specific and non virus-specific assays. This article describes and summarizes the pros and cons of the different technical approaches. Among the assays based on non virus-specific antigens, the enumeration of T-cell subsets, the quantification of cytokines and chemokines and the quantification of intracellular adenosine triphosphate following mitogen stimulation are described and their clinical applications to determine the risk for viral infection are discussed. In addition, current specific methods available for monitoring viral-specific T-cell responses are summarized, such as peptide-MHC multimer staining, intracellular cytokine staining, enzyme-linked immunospot and virus-specific IFN-γ ELISA assays, and their clinical applications to determine the individual risk for opportunistic viral infections with human cytomegalovirus, Epstein-Barr virus and polyoma BK virus are discussed. The standardization of the procedure, the choice of the antigen(s) and the criteria to define cut-off values for positive responses are needed for some of these approaches before their implementation in the clinic. Nevertheless, immune monitoring combined with virological monitoring in transplant recipients is increasingly regarded as a helpful tool to identify patients at risk of infection as well as to assess treatment efficacy.

Antigen-specific T cell therapies for cancer

Adoptively transferred antigen-specific T cells that recognize tumor antigens through their native receptors have many potential benefits as treatment for virus-associated diseases and malignancies, due to their ability to selectively recognize tumor antigens, expand and persist to provide long-term protection. Infusions of T cells targeting Epstein-Barr virus (EBV) antigens have shown encouraging response rates in patients with post-transplant lymphoproliferative disease as well as EBV-positive lymphomas and nasopharyngeal cancer, although a recent study also showed that human papilloma virus-reactive T cells can induce complete regression of metastatic cervical cancer. This strategy is also being evaluated to target non-viral tumor-associated antigens. Targeting these less immunogenic antigens is more challenging, as tumor antigens are generally weak, and high avidity T cells specific for self-antigens are deleted in the thymus, but tumor responses have been reported. Current research focusses on defining factors that promote in vivo persistence of transferred cells and ameliorate the immunosuppressive microenvironment. To this end, investigators are evaluating the effects of combining adoptive transfer of antigen-specific T cells with other immunotherapy moieties such as checkpoint inhibitors. Genetic modification of infused T cells may also be used to overcome tumor evasion mechanisms, and vaccines may be used to promote in vivo proliferation.

The DNA damage response and immune signaling alliance: Is it good or bad? Nature decides when and where

The characteristic feature of healthy living organisms is the preservation of homeostasis. Compelling evidence highlight that the DNA damage response and repair (DDR/R) and immune response (ImmR) signaling networks work together favoring the harmonized function of (multi)cellular organisms. DNA and RNA viruses activate the DDR/R machinery in the host cells both directly and indirectly. Activation of DDR/R in turn favors the immunogenicity of the incipient cell. Hence, stimulation of DDR/R by exogenous or endogenous insults triggers innate and adaptive ImmR. The immunogenic properties of ionizing radiation, a prototypic DDR/R inducer, serve as suitable examples of how DDR/R stimulation alerts host immunity. Thus, critical cellular danger signals stimulate defense at the systemic level and vice versa. Disruption of DDR/R-ImmR cross talk compromises (multi)cellular integrity, leading to cell-cycle-related and immune defects. The emerging DDR/R-ImmR concept opens up a new avenue of therapeutic options, recalling the Hippocrates quote "everything in excess is opposed by nature."

Impaired T-Cell Function in B-Cell Lymphoma: A Direct Consequence of Events at the Immunological Synapse?

Tumors can escape immune destruction through the development of antigen loss variants and loss of antigen processing/presentation pathways, thereby rendering them invisible to T cells. Alternatively, mechanisms of peripheral T-cell tolerance that would normally be important for protection from the development of autoimmunity may also be co-opted to (i) generate an immuno-inhibitory tumor environment, (ii) promote development of regulatory cell populations, or (iii) cell-intrinsically inactivate tumor-specific T cells. Emerging evidence suggests that T-cell function is impaired in hematological malignancies, which may manifest from cognate interactions between T cells and the tumor. The immunological synapse forms the cognate T-cell and antigen-presenting cell interaction and is the site where key signalling events, including those delivered by co-inhibitory receptors, that determine the fate of T cells occur. Here, we review evidence that events at the immune synapse between T cells and malignant B cells and alterations in immune synapse function may contribute to loss of T-cell function in B-cell malignancies.

Identification of novel CD8+ T cell epitopes in human herpesvirus 6B U11 and U90

Human herpesvirus 6B (HHV6B) infects over 90% of the population, and normally establishes a latent infection, where episodes of reactivation are asymptomatic. However, in immunocompromised patients HHV6B reactivation is associated with high morbidity and mortality. Cellular immunotherapy has been utilised against other herpesvirus in immunocompromised settings. However, limited information on the immune response against HHV6B has hampered the development of immunotherapy for HHV6B-driven disease. In this study, we have analysed the cellular immune response against four HHV6B antigens in a panel of 30 healthy donors. We show that the base-line level of T cell reactivity in peripheral blood is very low to undetectable. A short-term reactivation step enabled expansion of T cell responses, and all donors responded to at least 1 antigen, but more commonly 3 or 4. A hierarchy of immunogenicity was determined with antigens U90 and U54 being co-dominant, followed by U11 and U39. Putative CD8+ T cell epitopes were mapped to U90 and U11, predicted to be presented in the context of HLA-A1, A29, B39 and C6. T cells reactive against these novel epitopes were able to recognise virus-infected cells. Our data is supportive of the application and on-going development of T cell immunotherapy against HHVB-driven disease in the immunocompromised host.

Peripheral blood-derived virus-specific memory stem T cells mature to functional effector memory subsets with self-renewal potency

Memory T cells expressing stem cell-like properties have been described recently. The capacity of self-renewal and differentiation into various memory/effector subsets make them attractive for adoptive T cell therapy to combat severe virus infections and tumors. The very few reports on human memory stem T cells (T(SCM)) are restricted to analyses on polyclonal T cells, but extensive data on Ag-specific T(SCM )are missing. This might be due to their very low frequency limiting their enrichment and characterization. In this article, we provide functional and phenotypic data on human viral-specific T(SCM), defined as CD8(+)CD45RA(+)CCR7(+)CD127(+)CD95(+). Whereas <1% of total T cells express the T(SCM) phenotype, human CMV-specific T(SCM) can be detected at frequencies similar to those seen in other subsets, resulting in ∼ 1 /10,000 human CMV-specific T(SCM). A new virus-specific expansion protocol of sort-purified T(SCM) reveals both upregulation of various T cell subset markers and preservation of their stem cell phenotype in a significant proportion, indicating both self-renewal and differentiation potency of virus-specific T cells sharing their TCR repertoire. Furthermore, we describe a simplified culture protocol that allows fast expansion of virus-specific T(SCM) starting from a mixed naive T/T(SCM) pool of PBLs. Due to the clinical-grade compatibility, this might be the basis for novel cell therapeutic options in life-threatening courses of viral and tumor disease.

The Epstein-Barr virus and the pathogenesis of lymphoma

Since the discovery in 1964 of the Epstein-Barr virus (EBV) in African Burkitt lymphoma, this virus has been associated with a remarkably diverse range of cancer types. Because EBV persists in the B cells of the asymptomatic host, it can easily be envisaged how it contributes to the development of B-cell lymphomas. However, EBV is also found in other cancers, including T-cell/natural killer cell lymphomas and several epithelial malignancies. Explaining the aetiological role of EBV is challenging, partly because the virus probably contributes differently to each tumour and partly because the available disease models cannot adequately recapitulate the subtle variations in the virus-host balance that exist between the different EBV-associated cancers. A further challenge is to identify the co-factors involved; because most persistently infected individuals will never develop an EBV-associated cancer, the virus cannot be working alone. This article will review what is known about the contribution of EBV to lymphoma development.

Early exposure to interleukin-21 limits rapidly generated anti-Epstein-Barr virus T-cell line differentiation

BACKGROUND AIMS

The adoptive transfer of ex vivo-expanded Epstein-Barr virus (EBV)-specific T-cell lines is an attractive strategy to treat EBV-related neoplasms. Current evidence suggests that for adoptive immunotherapy in general, clinical responses are superior if the transferred cells have not reached a late or terminal effector differentiation phenotype before infusion. The cytokine interleukin (IL)-21 has shown great promise at limiting late T-cell differentiation in vitro, but this remains to be demonstrated in anti-viral T-cell lines.

METHODS

We adapted a clinically validated protocol to rapidly generate EBV-specific T-cell lines in 12 to 14 days and tested whether the addition of IL-21 at the initiation of the culture would affect T-cell expansion and differentiation.

RESULTS

We generated clinical-scale EBV-restricted T-cell line expansion with balanced T-cell subset ratios. The addition of IL-21 at the beginning of the culture decreased both T-cell expansion and effector memory T-cell accumulation, with a relative increase in less-differentiated T cells. Within CD4 T-cell subsets, exogenous IL-21 was notably associated with the cell surface expression of CD27 and high KLF2 transcript levels, further arguing for a role of IL-21 in the control of late T-cell differentiation.

CONCLUSIONS

Our results show that IL-21 has profound effects on T-cell differentiation in a rapid T-cell line generation protocol and as such should be further explored as a novel approach to program anti-viral T cells with features associated with early differentiation and optimal therapeutic efficacy.

Epstein Barr virus-associated lymphoproliferative diseases: the virus as a therapeutic target

Epstein Barr virus (EBV)-associated lymphoproliferative diseases (LPDs) express all EBV latent antigens (type III latency) in immunodeficient patients and limited antigens (type I and II latencies) in immunocompetent patients. Post-transplantation lymphoproliferative disease (PTLD) is the prototype exhibiting type III EBV latency. Although EBV antigens are highly immunogenic, PTLD cell proliferation remains unchecked because of the underlying immunosuppression. The restoration of anti-EBV immunity by EBV-specific T cells of either autologous or allogeneic origin has been shown to be safe and effective in PTLDs. Cellular therapy can be improved by establishing a bank of human leukocyte antigen-characterized allogeneic EBV-specific T cells. In EBV+ LPDs exhibiting type I and II latencies, the use of EBV-specific T cells is more limited, although the safety and efficacy of this therapy have also been demonstrated. The therapeutic role of EBV-specific T cells in EBV+ LPDs needs to be critically reappraised with the advent of monoclonal antibodies and other targeted therapy. Another strategy involves the use of epigenetic approaches to induce EBV to undergo lytic proliferation when expression of the viral thymidine kinase renders host tumor cells susceptible to the cytotoxic effects of ganciclovir. Finally, the prophylactic use of antiviral drugs to prevent EBV reactivation may decrease the occurrence of EBV+ LPDs.

Epstein-Barr virus-positive T/NK-cell lymphoproliferative disorders

Epstein–Barr virus, a ubiquitous human herpesvirus, can induce both lytic and latent infections that result in a variety of human diseases, including lymphoproliferative disorders. The oncogenic potential of Epstein–Barr virus is related to its ability to infect and transform B lymphocytes into continuously proliferating lymphoblastoid cells. However, Epstein–Barr virus has also been implicated in the development of T/natural killer cell lymphoproliferative diseases. Epstein–Barr virus encodes a series of products that mimic several growth, transcription and anti-apoptotic factors, thus usurping control of pathways that regulate diverse homeostatic cellular functions and the microenvironment. However, the exact mechanism by which Epstein–Barr virus promotes oncogenesis and inflammatory lesion development remains unclear. Epstein–Barr virus-associated T/natural killer cell lymphoproliferative diseases often have overlapping clinical symptoms as well as histologic and immunophenotypic features because both lymphoid cell types derive from a common precursor. Accurate classification of Epstein–Barr virus-associated T/natural killer cell lymphoproliferative diseases is a prerequisite for appropriate clinical management. Currently, the treatment of most T/natural killer cell lymphoproliferative diseases is less than satisfactory. Novel and targeted therapies are strongly required to satisfy clinical demands. This review describes our current knowledge of the genetics, oncogenesis, biology, diagnosis and treatment of Epstein–Barr virus-associated T/natural killer cell lymphoproliferative diseases.

Adoptive T-cell therapy with hexon-specific Th1 cells as a treatment of refractory adenovirus infection after HSCT

Hematopoietic stem cell transplantation (HSCT) has improved over the last few decades. However, viral infections are often refractory to pharmacologic treatment and require alternative treatment strategies such as immunotherapy. Adenovirus (AdV) is th predominant disease-causing pathogen in pediatric HSCT. In a clinical trial, we analyzed safety and efficacy of ex vivo adoptive T-cell transfer (ACT) with hexon-specific T cells, predominantly of the T-helper cell 1 (Th1) phenotype, in 30 patients with AdV disease or viremia. ACT was feasible with no acute toxicities or significant onset of graft-versus-host disease. ACT led to in vivo antiviral immunity for up to 6 months with viral control, resulting in complete clearance of viremia in 86% of patients with antigen-specific T-cell responses. After ACT and a follow-up of 6 months, overall survival was markedly increased in responders (mean, 122 days; 15 survivors) compared with nonresponders who all died shortly after ACT (mean, 24 days; no survivors). AdV-related mortality was 100% in nonresponders compared with 9.5% in responders (≥1 log reduction of DNA copies per milliliter after ACT). In summary, ex vivo ACT of AdV-specific Th1 cells was well tolerated and led to successful and sustained restoration of T-cell immunity correlated with virologic response and protection from virus-related mortality. This cellular immunotherapy is a short-term available and broadly applicable treatment. The study is registered at European Union Clinical Trials Register as 2005-001092-35.

Ex vivo expansion of human T cells for adoptive immunotherapy using the novel Xeno-free CTS Immune Cell Serum Replacement

The manufacture of clinical grade cellular products for adoptive immunotherapy requires ex vivo culture and expansion of human T cells. One of the key components in manufacturing of T cell therapies is human serum (HS) or fetal bovine serum (FBS), which can potentially expose immunotherapy recipient to adventitious infectious pathogens and are thus considered as non-cGMP compliant for adoptive therapy. Here we describe a novel xeno-free serum replacement (SR) with defined components that can be reproducibly used for the production of clinical grade T-cell therapies in combination with several different cell culture media. Dynabeads CD3/CD28 Cell Therapy System (CTS)-activated or antigen-specific T cells expanded using the xeno-free SR, CTS Immune Cell SR, showed comparable growth kinetics observed with cell culture media supplemented with HS or FBS. Importantly the xeno-free SR supplemented medium supported the optimal expansion of T cells specific for subdominant tumour-associated antigens and promoted expansion of T cells with central memory T-cell phenotype, which is favourable for in vivo survival and persistence following adoptive transfer. Furthermore, T cells expanded using xeno-free SR medium were highly amenable to lentivirus-mediated gene transduction for potential application for gene-modified T cells. Taken together, the CTS Immune Cell SR provides a novel platform strategy for the manufacture of clinical grade adoptive cellular therapies.

The Development of Prophylactic and Therapeutic EBV Vaccines

Over the last century, the development of effective vaccine approaches to treat a number of viral infections has provided the impetus for the continual development of vaccine platforms for other viral infections, including Epstein-Barr virus (EBV). The clinical manifestations associated with EBV infection occur either following primary infection, such as infectious mononucleosis, or following an extended period of latency, primarily the EBV-associated malignancies and potentially including a number of autoimmune disorders, such as multiple sclerosis. As a consequence, two independent vaccine approaches are under development to prevent or control EBV-associated diseases. The first approach, which has been widely successful against other viral infections, is aimed at inducing a viral neutralisation antibody response to prevent primary infection. The second approach focuses upon the induction of cell-mediated immunity to control latent infected cells in persistently infected individuals. Early clinical studies have offered some insight into the potential efficacy of both of these approaches.

Management of patients with non-Hodgkin's lymphoma: focus on adoptive T-cell therapy

Non-Hodgkin’s lymphoma (NHL) represents a heterogeneous group of malignancies with high diversity in terms of biology, clinical responses, and prognosis. Standard therapy regimens produce a 5-year relative survival rate of only 69%, with the critical need to increase the treatment-success rate of this patient population presenting at diagnosis with a median age of 66 years and many comorbidities. The evidence that an impaired immune system favors the development of NHL has opened the stage for new therapeutics, and specifically for the adoptive transfer of ex vivo-expanded antigen-specific T-cells. In this review, we discuss how T-cells specific for viral-associated antigens, nonviral-associated antigens expressed by the tumor, T-cells redirected through the expression of chimeric antigen receptors, and transgenic T-cell receptors against tumor cells have been developed and used in clinical trials for the treatment of patients with NHLs.

Molecular signature of Epstein Barr virus-positive Burkitt lymphoma and post-transplant lymphoproliferative disorder suggest different roles for Epstein Barr virus

Epstein Barr virus (EBV) infection is commonly associated with human cancer and, in particular, with lymphoid malignancies. Although the precise role of the virus in the pathogenesis of different lymphomas is largely unknown, it is well recognized that the expression of viral latent proteins and miRNA can contribute to its pathogenetic role. In this study, we compared the gene and miRNA expression profile of two EBV-associated aggressive B non-Hodgkin lymphomas known to be characterized by differential expression of the viral latent proteins aiming to dissect the possible different contribution of such proteins and EBV-encoded miRNAs. By applying extensive bioinformatic inferring and an experimental model, we found that EBV+ Burkitt lymphoma presented with significant over-expression of EBV-encoded miRNAs that were likely to contribute to its global molecular profile. On the other hand, EBV+ post-transplant diffuse large B-cell lymphomas presented a significant enrichment in genes regulated by the viral latent proteins. Based on these different viral and cellular gene expression patterns, a clear distinction between EBV+ Burkitt lymphoma and post-transplant diffuse large B-cell lymphomas was made. In this regard, the different viral and cellular expression patterns seemed to depend on each other, at least partially, and the latency type most probably played a significant role in their regulation. In conclusion, our data indicate that EBV influence over B-cell malignant clones may act through different mechanisms of transcriptional regulation and suggest that potentially different pathogenetic mechanisms may depend upon the conditions of the interaction between EBV and the host that finally determine the latency pattern.

Cytotoxic T lymphocytes for leukemia and lymphoma

This chapter focuses on the recent advances in adoptive T-cell immunotherapies, not only for patients after hematopoietic stem cell transplantation, but also in the autologous setting using T cells early in the disease process for the treatment of the highest-risk patients with leukemias and lymphomas. The particular emphasis is to highlight the role of T-cell therapies for hematologic malignancies using a non-gene-transfer approach to direct specificity, including the clinical use of T-cell therapies for EBV-associated lymphomas and strategies for targeting nonviral lymphoma- and leukemia-associated antigens.

Immunotherapy: opportunities, risks and future perspectives

This review is intended to reflect upon the current status and perspectives of cell-based immunotherapy at a time when the promise of extensive pre-clinical research has been translated into encouraging clinical responses. However, some of these have also been complicated by significant adverse reactions. As the field moves towards definitive late stage trials, with a growing interest from pharmaceutical companies, we realize that novel cell therapy strategies pose questions that are familiar to traditional drug development, along with new considerations due to the potential of T cells to persist long term and to expand after adoptive transfer. These questions address the safety of the product, the efficacy, the mode of action, and the anticipation of risks. From different perspectives, we intend to address exciting opportunities and safety concerns in current concepts of cellular immunotherapy.

Type I interferon signaling enhances CD8+ T cell effector function and differentiation during murine gammaherpesvirus 68 infection

CD8(+) T cell responses are critical to the control of replication and reactivation associated with gammaherpesvirus infection. Type I interferons (IFNs) have been shown to have direct and indirect roles in supporting CD8(+) T cell development and function during viral infection; however, the role of type I interferons during latent viral infection has not been examined. Mice deficient in type I IFN signaling (IFNAR1(-/-) mice) have high levels of reactivation during infection with murine gammaherpesvirus 68 (MHV68), a murine gammaherpesvirus model for Epstein-Barr virus. We hypothesized that type I IFNs function to enhance the anti-gammaherpesvirus CD8(+) T cell response. To test this, IFNAR1(-/-) mice were infected with MHV68 and the CD8(+) T cell response was analyzed. In the absence of type I IFN signaling, there was a marked increase in short-lived effector CD8(+) T cells, and MHV68-specific CD8(+) T cells had upregulated expression of PD-1 and reduced tumor necrosis factor alpha (TNF-α), gamma IFN (IFN-γ), and interleukin-2 (IL-2) production. Suppressing MHV68 replication early in infection using the antiviral cidofovir rescued CD8(+) T cell cytokine production and reduced PD-1 expression. However, suppressing high levels of reactivation in IFNAR1(-/-) mice failed to improve CD8(+) T cell cytokine production during latency. T cell-specific abrogation of type I IFN signaling showed that the effects of type I IFNs on the CD8(+) T cell response during MHV68 infection are independent of direct type I IFN signaling on T cells. Our findings support a model in which type I IFNs likely suppress MHV68 replication, thus limiting viral antigen and facilitating an effective gammaherpesvirus-directed CD8(+) T cell response.

IMPORTANCE

The murine gammaherpesvirus MHV68 has both genetic and biologic homology to the human gammaherpesvirus Epstein-Barr virus (EBV), which infects over 90% of humans. Latent EBV infection and reactivation are associated with various life-threatening diseases and malignancies. Host suppression of gammaherpesvirus latency and reactivation requires both CD8(+) T cells as well as type I interferon signaling. Type I IFNs have been shown to critically support the antiviral CD8(+) T cell response in other virus models. Here, we identify an indirect role for type I IFN signaling in enhancing gammaherpesvirus-specific CD8(+) T cell cytokine production. Further, this function of type I IFN signaling can be partially rescued by suppressing viral replication during early MHV68 infection. Our data suggest that type I IFN signaling on non-T cells can enhance CD8(+) T cell function during gammaherpesvirus infection, potentially through suppression of MHV68 replication.

Towards gene therapy for EBV-associated posttransplant lymphoma with genetically modified EBV-specific cytotoxic T cells

Epstein-Barr virus (EBV)-associated posttransplant lymphoma (PTLD) is a major cause of morbidity/mortality after hematopoietic stem cell (SCT) or solid organ (SOT) transplant. Adoptive immunotherapy with EBV-specific cytotoxic lymphocytes (CTLs), although effective in SCT, is less successful after SOT where lifelong immunosuppression therapy is necessary. We have genetically engineered EBV-CTLs to render them resistant to calcineurin (CN) inhibitor FK506 through retroviral transfer of a calcineurin A mutant (CNA12). Here we examined whether or not FK506-resistant EBV-CTLs control EBV-driven tumor progression in the presence of immunosuppression in a xenogeneic mouse model. NOD/SCID/IL2rγ(null) mice bearing human B-cell lymphoma were injected with autologous CTLs transduced with either CNA12 or eGFP in the presence/absence of FK506. Adoptive transfer of autologous CNA12-CTLs induced dramatic lymphoma regression despite the presence of FK506, whereas eGFP-CTLs did not. CNA12-CTLs persisted longer, homed to the tumor, and expanded more than eGFP-CTLs in mice treated with FK506. Mice receiving CNA12-CTLs and treated with FK506 survived significantly longer than control-treated animals. Our results demonstrate that CNA12-CTL induce regression of EBV-associated tumors in vivo despite ongoing immunosuppression. Clinical application of this novel approach may enhance the efficacy of adoptive transfer of EBV-CTL in SOT patients developing PTLD without the need for reduction in immunosuppressive therapy.

Malignancies after pediatric kidney transplantation: more than PTLD?

Post-transplant lymphoproliferative disease (PTLD) is the most frequent malignant complication of transplantation in childhood. Even with modern post-transplant immunosuppressive strategies, 1-2% of all kidney transplant recipients will develop PTLD within the first 5 years after transplantation, and the risk remains high even thereafter as long as immunosuppression is required. In addition to PTLD, adult kidney transplant recipients have an increased incidence of other immunosuppression-related malignancies, such as non-melanoma skin cancer or Kaposi's sarcoma. It is foreseeable that pediatric transplant recipients will face similar complications during their adult life. Not only immunosuppression but also other risk factors have been identified for some of these malignancies. Strategies addressing these risk factors during childhood may contribute to life-long cancer prevention. Furthermore, early recognition and regular screening may facilitate early diagnosis and treatment, thereby reducing transplant-related morbidity. In this review we focus on malignant complications after renal transplantation and discuss known risk factors. We also review current screening strategies for malignancies during post-transplant follow-up.

Exploiting the curative potential of adoptive T-cell therapy for cancer

Adoptive T-cell therapy (ACT) is a potent and flexible cancer treatment modality that can induce complete, durable regression of certain human malignancies. Long-term follow-up of patients receiving tumor-infiltrating lymphocytes (TILs) for metastatic melanoma reveals a substantial subset that experienced complete, lasting tumor regression - and may be cured. Increasing evidence points to mutated gene products as the primary immunological targets of TILs from melanomas. Recent technological advances permit rapid identification of the neoepitopes resulting from these somatic gene mutations and of T cells with reactivity against these targets. Isolation and adoptive transfer of these T cells may improve TIL therapy for melanoma and permit its broader application to non-melanoma tumors. Extension of ACT to other malignancies may also be possible through antigen receptor gene engineering. Tumor regression has been observed following transfer of T cells engineered to express chimeric antigen receptors against CD19 in B-cell malignancies or a T-cell receptor against NY-ESO-1 in synovial cell sarcoma and melanoma. Herein, we review recent clinical trials of TILs and antigen receptor gene therapy for advanced cancers. We discuss lessons from this experience and consider how they might be applied to realize the full curative potential of ACT.

T lymphocytes targeting native receptors

The adoptive transfer of T cells specific for native tumor antigens (TAs) is an increasingly popular cancer treatment option because of the ability of these cells to discriminate between normal and tumor tissues and the corresponding lack of short or long-term toxicities. Infusions of antigen-specific CD4(+) and CD8(+) T cells targeting viral antigens derived from Epstein-Barr virus (EBV) induce sustained complete tumor remissions in patients with highly immunogenic tumors such as post-transplant lymphoproliferative disease, although resistance occurred when the infused T-cell population had restricted antigen specificity. T cells specific for EBV antigens have also produced complete remissions of EBV-positive nasopharyngeal carcinomas and lymphomas developing in immunocompetent individuals, even though in these patients tumor survival is dependent on their ability to evade T-cell immunity. Adapting this strategy to non-viral tumors is more challenging, as the target antigens expressed are less immunogenic and the tumors lack the potent danger signals that are characteristic of viruses. The goals of current studies are to define conditions that promote expansion of antigen-specific T cells ex vivo and to ensure their in vivo persistence and survival by combining with maneuvers such as lymphodepletion, checkpoint inhibition, cytokine infusions, or genetic manipulations. More pragmatic goals are to streamline manufacturing to facilitate the transition of these therapies to late phase trials and to evaluate closely histocompatibility antigen (HLA)-matched banked antigen-specific T cells so that T-cell therapies can be made more broadly available.

Establishment and operation of a Good Manufacturing Practice-compliant allogeneic Epstein-Barr virus (EBV)-specific cytotoxic cell bank for the treatment of EBV-associated lymphoproliferative disease

Epstein-Barr virus (EBV) is associated with several malignancies, including post-transplant lymphoproliferative disorder (PTLD). Conventional treatments for PTLD are often successful, but risk organ rejection and cause significant side effects. EBV-specific cytotoxic T lymphocytes (CTLs) generated in vitro from peripheral blood lymphocytes provide an alternative treatment modality with few side effects, but autologous CTLs are difficult to use in clinical practice. Here we report the establishment and operation of a bank of EBV-specific CTLs derived from 25 blood donors with human leucocyte antigen (HLA) types found at high frequency in European populations. Since licensure, there have been enquiries about 37 patients, who shared a median of three class I and two class II HLA types with these donors. Cells have been infused into ten patients with lymphoproliferative disease, eight of whom achieved complete remission. Neither patient with refractory disease was matched for HLA class II. Both cases of EBV-associated non-haematopoietic sarcoma receiving cells failed to achieve complete remission. Thirteen patients died before any cells could be issued, emphasizing that the bank should be contacted before patients become pre-terminal. Thus, this third party donor-derived EBV-specific CTL cell bank can supply most patients with appropriately matched cells and most recipients have good outcomes.

Calcineurin inhibitor-free graft-versus-host disease prophylaxis with sirolimus and mycophenolate mofetil in a second allogeneic stem cell transplantation for engraftment failure and rituximab-refractory Epstein-Barr virus-induced posttransplant lymphoproliferative disease

Posttransplant lymphoproliferative disease (PTLD) is a life-threatening complication after allogeneic hematopoietic stem cell transplantation. We describe here the case of a boy with history of induction failure of a T-cell acute lymphoblastic leukemia, who presented a life-threatening situation of nonengraftment and rituximab-refractory PTLD after the first hematopoietic stem cell transplantation. We decided to use an unusual strategy of combining a nonmyeloablative conditioning (fludarabine and cyclophosphamide) with a calcineurin inhibitor-free GvHD prophylaxis (sirolimus and mycophenolate mofetil). This strategy had permitted the control of an Epstein-Barr virus PLTD in umbilical cord blood transplantation without further reactivation.

Defining immune engagement thresholds for in vivo control of virus-driven lymphoproliferation

Persistent infections are subject to constant surveillance by CD8⁺ cytotoxic T cells (CTL). Their control should therefore depend on MHC class I-restricted epitope presentation. Many epitopes are described for γ-herpesviruses and form a basis for prospective immunotherapies and vaccines. However the quantitative requirements of in vivo immune control for epitope presentation and recognition remain poorly defined. We used Murid Herpesvirus-4 (MuHV-4) to determine for a latently expressed viral epitope how MHC class-I binding and CTL functional avidity impact on host colonization. Tracking MuHV-4 recombinants that differed only in epitope presentation, we found little latitude for sub-optimal MHC class I binding before immune control failed. By contrast, control remained effective across a wide range of T cell functional avidities. Thus, we could define critical engagement thresholds for the in vivo immune control of virus-driven B cell proliferation.

Chronic viral infections cause huge morbidity and mortality worldwide. γ-herpesviruses provide an example relevant to all human demographics, causing, inter alia, Hodgkin's disease, Burkitt's lymphoma, Kaposi's Sarcoma, and nasopharyngeal carcinoma. The proliferation of latently infected B cells and their control by CD8⁺ T cells are central to pathogenesis. Although many viral T cell targets have been identified in vitro, the functional impact of their engagement in vivo remains ill-defined. With the well-established Murid Herpesvirus-4 infection model, we used a range of recombinant viruses to define functional thresholds for the engagement of a latently expressed viral epitope. These data advance significantly our understanding of how the immune system must function to control γ-herpesvirus infection, with implications for vaccination and anti-cancer immunotherapy.

Comparison of different rabbit ATG preparation effects on early lymphocyte subset recovery after allogeneic HSCT and its association with EBV-mediated PTLD

PURPOSE

Rabbit antithymocyte globulin (ATG) is commonly used before allogeneic hematopoietic stem cell transplantation (allo-HSCT) to prevent graft-versus-host disease. Studies comparing the effect of different ATG preparations and dosages on immune reconstitution and risk for Epstein-Barr virus (EBV)-mediated post-transplant lymphoproliferative disorder (PTLD) are rare.

METHODS

In this retrospective study, we determined T and B cell subsets by flow cytometry after allo-HSCT in children, who received ATG-Genzyme (ATG-G, n = 15), ATG-Fresenius (ATG-F, n = 25) or no-ATG treatment (n = 19). Additionally, PCR-quantified EBV-genome copy counts were correlated with incidence of PTLD.

RESULTS

We could confirm a dose-dependent impairment of CD8(+) and CD4(+) T cell regeneration by ATG-G, including naïve and memory CD4(+) T cells. No differences were seen between the currently applied dosages of 5-10 mg/kg ATG-G and 20-60 mg/kg ATG-F. Significantly delayed T cell subset reconstitution was determined only at high dosages of 20-60 mg/kg ATG-G compared to ATG-F. B cell reconstitution was comparably impaired in ATG-G- and ATG-F-treated patients. Although the incidence of EBV reactivation was similar in both ATG groups, EBV copy counts of >10(4) copies/10(5) peripheral blood mononuclear cells and the occurrence of PTLD were only found in ATG-G-treated patients.

CONCLUSIONS

We conclude that high, but importantly not currently applied low dosages of ATG-G, impair thymic T cell regeneration and memory T cell immunity to a greater extent than ATG-F in pediatric patients. In addition, our results suggest an increased risk for EBV-PTLD when treated with ATG-G. Prospective studies are warranted to compare different ATG preparations with regard to the immune reconstitution and EBV-PTLD.

Determination of EBV serostatus prior to kidney transplantation: comparison of VIDAS®, LIAISON® and immunofluorescence assays

Immunosuppression following solid organ transplantation reduces T cell-mediated immune control of Epstein-Barr Virus (EBV), which may then drive development of post-transplant lymphoproliferative disease. Serology plays a key role in determination of risk of outgrowth of such lesions following transplantation. The study compared the VIDAS(®) (bioMérieux) and LIAISON(®) (DiaSorin) enzyme immunoassays (EIAs) and immunofluorescence assays (IFA; MBL-Bion) in the kidney transplantation setting. Sera from 100 live kidney donors [51 males; age range 20-82 years (mean 51.2 years)] and 100 cadaveric kidney recipients [70 males; age range 17-77 years (mean 51.0 years)] were tested. Overall proportional agreement ranged from 96% to 100% for VIDAS(®) and LIAISON(®). Sensitivity ranged from 91% to 100% and 92% to 100% for VIDAS(®)/IFA and LIAISON(®)/IFA, respectively. The VIDAS(®) and LIAISON(®) approaches gave similar results. Such automated random access EIAs are well suited to busy clinical virology laboratories and rapid determination of donor and recipient EBV serostatus prior to transplantation.

Possible alternatives to antimicrobial therapies

The care of immunosuppressed patients has constantly improved over the years, and pharmacologic developments contributed significantly to this success. However, despite these advances, current anti-infectious agents are limited in their efficacy by either weak specificity or side effects, including suppression of bone marrow function. Control of infection will ultimately depend on reconstitution of specific immunity. Thus, adoptive cellular immunotherapy represents an attractive, low-toxicity strategy to restore specific immune surveillance, and prevent/treat potentially life-threatening disease due to pathogens relevant to the immunosuppressed host. Evidence derived from trials conducted in recipients of hematopoietic stem cell transplantation indicate that adoptive transfer of antigen-specific T cells is a feasible and safe strategy to restore protective immunity and prevent or reverse virus-associated disease. Despite the great potential, immunotherapy for viral and fungal disease still has a marginal role in the management of immunosuppressed patients. This is due to limitations inherent to the technologies and products employed, and, more importantly, to the financial and structural requirements that are associated with GMP production. However, cell therapy offers a unique opportunity to restore antipathogen immune surveillance, and it is therefore conceivable that application of this strategy will increase in the next few years.

Enhanced response of T cells from murine gammaherpesvirus 68-infected mice lacking the suppressor of T cell receptor signaling molecules Sts-1 and Sts-2

The human gammaherpesviruses establish life-long infections that are associated with the development of lymphomas and neoplasms, especially in immunocompromised individuals. T cells play a crucial role in the control of gammaherpesvirus infection through multiple functions, including the direct killing of infected cells, production of cytokines such as interferon-γ (IFN-γ), and costimulation of B cells. Impaired T cell function in mice infected with murine gammaherpesvirus 68 (MHV68) leads to increased reactivation and pathologies, including a higher incidence of lymphoid hyperplasia. Here we report that the absence of Suppressor of TCR signaling −1 and −2 (Sts-1^-/-/2^-/-) during MHV68 infection leads to the generation of T cells with significantly heightened responses. Transient differences in the T and B cell response of infected Sts-1^-/-/2^-/- (Sts dKO) mice were also observed when compared to WT mice. However, these alterations in the immune response and the overall absence of Sts-1 and Sts-2 did not impact viral pathogenesis or lead to pathology. Acute lytic replication in the lungs, establishment of latency in the spleen and reactivation from latency in the spleen in the Sts dKO mice were comparable to WT mice. Our studies indicate that Sts-1 and Sts-2 are not required for the immune control of MHV68 in a normal course of gammaherpesvirus infection, but suggest that interference with negative regulators of T cell responses might be further explored as a safe and efficacious strategy to improve adoptive T cell therapy.

EBV-related lymphomas: new approaches to treatment

In the treatment of Epstein-Barr virus (EBV)-related lymphomas, there are few therapies specifically targeted against the latent virus within these tumors; in most cases the treatment approach is not different than the approach to EBV-negative lymphomas. Nonetheless, current and emerging therapies focused on exploiting aspects of EBV biology may offer more targeted strategies for EBV-positive lymphomas in the future. Conceptually, EBV-specific approaches include bolstering the antiviral/antitumor immune response with vaccines or EBV-specific cytotoxic T-lymphocytes, activating lytic viral genes to render the tumor cells susceptible to antiviral therapies, and inhibiting the downstream prosurvival or antiapoptotic pathways that may be activated by latent EBV proteins. EBV-specific cytotoxic T-cell infusions have proven effective in EBV-related posttransplantation lymphoproliferative disorder (EBV-PTLD) and expanding such adoptive immunotherapies to other EBV-related malignancies is an area of active research. However, other EBV-related lymphomas typically have more restricted, less immunogenic arrays of viral antigens to therapeutically target with adoptive immunotherapy compared with EBV-PTLD. Furthermore, the malignant EBV-positive tumor cells of Hodgkin lymphoma are scattered amid a dense infiltrate of regulatory T-cells, macrophages, and other cells that may dampen the antitumor efficacy of adoptive immunotherapy. Strategies to overcome these obstacles are areas of ongoing preclinical and clinical investigations. Some emerging approaches to EBV-related lymphomas include the coupling of agents that induce lytic viral replication with antiherpesvirus agents, or the use of small molecule inhibitors that block signaling pathways that are constitutively activated by EBV. EBV vaccines seem most promising for the treatment or prevention of EBV-related malignancies, rather than the prevention of primary EBV infection. EBV vaccine trials in patients with residual or low-bulk EBV-related malignancies or for the prevention of EBV-PTLD in EBV-seronegative patients awaiting solid organ transplantation are ongoing.

Immunologic special forces: anti-pathogen cytotoxic T-lymphocyte immunotherapy following hematopoietic stem cell transplantation

Anti-pathogen adoptive T-cell immunotherapy has been proven to be highly effective in preventing or controlling viral infections following hematopoietic stem cell transplantation. Recent advances in manufacturing protocols allow an increased number of targeted pathogens, eliminate the need for viral transduction, broaden the potential donor pool to include pathogen-naïve sources, and reduce the time requirement for production. Early studies suggest that anti-fungal immunotherapy may also have clinical benefit. Future advances include further broadening of the pathogens that can be targeted and development of T-cells with resistance to pharmacologic immunosuppression.