An Epstein-Barr virus deletion mutant associated with fatal lymphoproliferative disease unresponsive to therapy with virus-specific CTLs

T-cell depleted allogeneic hematopoietic cell transplants as a platform for adoptive therapy with leukemia selective or virus-specific T-cells

Allogeneic hematopoietic cell transplants adequately depleted of T-cells can reduce or prevent acute and chronic GVHD in both HLA-matched and haplotype-disparate hosts, without post-transplant prophylaxis with immunosuppressive drugs. Recent trials indicate that high doses of CD34+ progenitors from G-CSF mobilized peripheral blood leukocytes isolated and T-cell depleted by immunoadsorption to paramagnetic beads, when administered after myeloablative conditioning with TBI and chemotherapy or chemotherapy alone can secure consistent engraftment and abrogate GVHD in patients with acute leukemia without incurring an increased risk of a recurrent leukemia. Early clinical trials also indicate that high doses of in vitro generated leukemia-reactive donor T-cells can be adoptively transferred and can induce remissions of leukemia relapse without GVHD. Similarly, virus-specific T-cells generated from the transplant donor or an HLA partially matched third party, have induced remissions of Rituxan-refractory EBV lymphomas and can clear CMV disease or viremia persisting despite antiviral therapy in a high proportion of cases. Analyses of treatment responses and failures illustrate both the advantages and limitations of donor or banked, third party-derived T-cells, but underscore the potential of adoptive T-cell therapy in the absence of ongoing immunosuppression.

Genome diversity of Epstein-Barr virus from multiple tumor types and normal infection

Epstein-Barr virus (EBV) infects most of the world's population and is causally associated with several human cancers, but little is known about how EBV genetic variation might influence infection or EBV-associated disease. There are currently no published wild-type EBV genome sequences from a healthy individual and very few genomes from EBV-associated diseases. We have sequenced 71 geographically distinct EBV strains from cell lines, multiple types of primary tumor, and blood samples and the first EBV genome from the saliva of a healthy carrier. We show that the established genome map of EBV accurately represents all strains sequenced, but novel deletions are present in a few isolates. We have increased the number of type 2 EBV genomes sequenced from one to 12 and establish that the type 1/type 2 classification is a major feature of EBV genome variation, defined almost exclusively by variation of EBNA2 and EBNA3 genes, but geographic variation is also present. Single nucleotide polymorphism (SNP) density varies substantially across all known open reading frames and is highest in latency-associated genes. Some T-cell epitope sequences in EBNA3 genes show extensive variation across strains, and we identify codons under positive selection, both important considerations for the development of vaccines and T-cell therapy. We also provide new evidence for recombination between strains, which provides a further mechanism for the generation of diversity. Our results provide the first global view of EBV sequence variation and demonstrate an effective method for sequencing large numbers of genomes to further understand the genetics of EBV infection.

IMPORTANCE

Most people in the world are infected by Epstein-Barr virus (EBV), and it causes several human diseases, which occur at very different rates in different parts of the world and are linked to host immune system variation. Natural variation in EBV DNA sequence may be important for normal infection and for causing disease. Here we used rapid, cost-effective sequencing to determine 71 new EBV sequences from different sample types and locations worldwide. We showed geographic variation in EBV genomes and identified the most variable parts of the genome. We identified protein sequences that seem to have been selected by the host immune system and detected variability in known immune epitopes. This gives the first overview of EBV genome variation, important for designing vaccines and immune therapy for EBV, and provides techniques to investigate relationships between viral sequence variation and EBV-associated diseases.

The Epstein-Barr Virus Lytic Protein BZLF1 as a Candidate Target Antigen for Vaccine Development

The Epstein-Barr virus (EBV) is an oncogenic, γ-herpesvirus associated with a broad spectrum of disease. Although most immune-competent individuals can effectivley develop efficient adaptive immune responses to EBV, immunocompromised individuals are at serious risk for developing life-threatening diseases, such as Hodgkin lymphoma and posttransplant lymphoproliferative disorder (PTLD). Given the significant morbidity associated with EBV infection in high-risk populations, there is a need to develop vaccine strategies that restore or enhance EBV-specific immune responses. Here, we identify the EBV immediate-early protein BZLF1 as a potential target antigen for vaccine development. Primary tumors from patients with PTLD and a chimeric human-murine model of EBV-driven lymphoproliferative disorder (EBV-LPD) express BZLF1 protein. Pulsing human dendritic cells (DC) with recombinant BZLF1 followed by incubation with autologous mononuclear cells led to expansion of BZLF1-specific CD8(+) T cells in vitro and primed BZLF1-specific T-cell responses in vivo. In addition, vaccination of hu-PBL-SCID mice with BZLF1-transduced DCs induced specific cellular immunity and significantly prolonged survival from fatal EBV-LPD. These findings identify BZLF1 as a candidate target protein in the immunosurveillance of EBV and provide a rationale for considering BZLF1 in vaccine strategies to enhance primary and recall immune responses and potentially prevent EBV-associated diseases.

Antiviral T-cell therapy

Serious viral infections are a common cause of morbidity and mortality after allogeneic stem cell transplantation. They occur in the majority of allograft recipients and are fatal in 17–20%. These severe infections may be prolonged or recurrent and add substantially to the cost, both human and financial, of the procedure. Many features of allogeneic stem cell transplantation contribute to this high rate of viral disease. The cytotoxic and immunosuppressive drugs administered pretransplant to eliminate the host hematopoietic/immune system and any associated malignancy, the delay in recapitulating immune ontogeny post‐transplant, the immunosuppressive drugs given to prevent graft versus host disease (GvHD), and the effects of GvHD itself, all serve to make stem cell transplant recipients vulnerable to disease from endogenous (latent) and exogenous (community) viruses, and to be incapable of controlling them as quickly and effectively as most normal individuals.

The EBNA3 Family: Two Oncoproteins and a Tumour Suppressor that Are Central to the Biology of EBV in B Cells

Epstein-Barr virus nuclear antigens EBNA3A , EBNA3B and EBNA3C are a family of three large latency-associated proteins expressed in B cells induced to proliferate by the virus. Together with the other nuclear antigens (EBNA-LP, EBNA2 and EBNA1), they are expressed from a polycistronic transcription unit that is probably unique to B cells. However, compared with the other EBNAs, hitherto the EBNA3 proteins were relatively neglected and their roles in EBV biology rather poorly understood. In recent years, powerful new technologies have been used to show that these proteins are central to the latency of EBV in B cells, playing major roles in reprogramming the expression of host genes affecting cell proliferation, survival, differentiation and immune surveillance. This indicates that the EBNA3s are critical in EBV persistence in the B cell system and in modulating B cell lymphomagenesis. EBNA3A and EBNA3C are necessary for the efficient proliferation of EBV-infected B cells because they target important tumour suppressor pathways--so operationally they are considered oncoproteins. In contrast, it is emerging that EBNA3B restrains the oncogenic capacity of EBV, so it can be considered a tumour suppressor--to our knowledge the first to be described in a tumour virus. Here, we provide a general overview of the EBNA3 genes and proteins. In particular, we describe recent research that has highlighted the complexity of their functional interactions with each other, with specific sites on the human genome and with the molecular machinery that controls transcription and epigenetic states of diverse host genes.

Epstein-Barr Virus: From the Detection of Sequence Polymorphisms to the Recognition of Viral Types

The Epstein-Barr virus is etiologically linked with the development of benign and malignant diseases, characterized by their diversity and a heterogeneous geographic distribution across the world. The virus possesses a 170-kb-large genome that encodes for multiple proteins and non-coding RNAs. Early on there have been numerous attempts to link particular diseases with particular EBV strains, or at least with viral genetic polymorphisms. This has given rise to a wealth of information whose value has been difficult to evaluate for at least four reasons. First, most studies have looked only at one particular gene and missed the global picture. Second, they usually have not studied sufficient numbers of diseased and control cases to reach robust statistical significance. Third, the functional significance of most polymorphisms has remained unclear, although there are exceptions such as the 30-bp deletion in LMP1. Fourth, different biological properties of the virus do not necessarily equate with a different pathogenicity. This was best illustrated by the type 1 and type 2 viruses that markedly differ in terms of their transformation abilities, yet do not seem to cause different diseases. Reciprocally, environmental and genetic factors in the host are likely to influence the outcome of infections with the same virus type. However, with recent developments in recombinant virus technology and in the availability of high throughput sequencing, the tide is now turning. The availability of 23 complete or nearly complete genomes has led to the recognition of viral subtypes, some of which possess nearly identical genotypes. Furthermore, there is growing evidence that some genetic polymorphisms among EBV strains markedly influence the biological and clinical behavior of the virus. Some virus strains are endowed with biological properties that explain crucial clinical features of patients with EBV-associated diseases. Although we now have a better overview of the genetic diversity within EBV genomes, it has also become clear that defining phenotypic traits evinced by cells infected by different viruses usually result from the combination of multiple polymorphisms that will be difficult to identify in their entirety. However, the steadily increasing number of sequenced EBV genomes and cloned EBV BACS from diseased and healthy patients will facilitate the identification of the key polymorphisms that condition the biological and clinical behavior of the viruses. This will allow the development of preventative and therapeutic approaches against highly pathogenic viral strains.

Betting on improved cancer immunotherapy by doubling down on CD134 and CD137 co-stimulation

The ability of T cells to recognize a vast array of antigens enables them to destroy tumor cells while inflicting minimal collateral damage. Nevertheless, tumor antigens often are a form of self-antigen, and thus tumor immunity can be dampened by tolerance mechanisms that evolved to prevent autoimmunity. Since tolerance can be induced by steady-state antigen-presenting cells that provide insufficient co-stimulation, the exogenous administration of co-stimulatory agonists can favor the expansion and tumoricidal functions of tumor-specific T cells. Agonists of the co-stimulatory tumor necrosis factor receptor (TNFR) family members CD134 and CD137 exert antitumor activity in mice, and as monotherapies have exhibited encouraging results in clinical trials. This review focuses on how the dual administration of CD134 and CD137 agonists synergistically boosts T-cell priming and elaborates a multi-pronged antitumor immune response, as well as how such dual co-stimulation might be translated into effective anticancer therapies.

The time is now: moving toward virus-specific T cells after allogeneic hematopoietic stem cell transplantation as the standard of care

Adoptive immunotherapy-in particular, T-cell therapy-has recently emerged as a useful strategy with the potential to overcome many of the limitations of antiviral drugs for the treatment of viral complications after hematopietic stem cell transplantation. In this review, we briefly summarize the current methods for virus-specific T-cell isolation or selection and we report results from clinical trials that have used these techniques, focusing specifically on the strategies aimed to broaden the application of this technology.

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.

Design and development of therapies using chimeric antigen receptor-expressing T cells

Investigators developed chimeric antigen receptors (CARs) for expression on T cells more than 25 years ago. When the CAR is derived from an antibody, the resultant cell should combine the desirable targeting features of an antibody (e.g. lack of requirement for major histocompatibility complex recognition, ability to recognize non-protein antigens) with the persistence, trafficking, and effector functions of a T cell. This article describes how the past two decades have seen a crescendo of research which has now begun to translate these potential benefits into effective treatments for patients with cancer. We describe the basic design of CARs, describe how antigenic targets are selected, and the initial clinical experience with CAR-T cells. Our review then describes our own and other investigators' work aimed at improving the function of CARs and reviews the clinical studies in hematological and solid malignancies that are beginning to exploit these approaches. Finally, we show the value of adding additional engineering features to CAR-T cells, irrespective of their target, to render them better suited to function in the tumor environment, and discuss how the safety of these heavily modified cells may be maintained.

Sustained complete responses in patients with lymphoma receiving autologous cytotoxic T lymphocytes targeting Epstein-Barr virus latent membrane proteins

PURPOSE

Tumor cells from approximately 40% of patients with Hodgkin or non-Hodgkin lymphoma express the type II latency Epstein-Barr virus (EBV) antigens latent membrane protein 1 (LMP1) and LMP2, which represent attractive targets for immunotherapy. Because T cells specific for these antigens are present with low frequency and may be rendered anergic by the tumors that express them, we expanded LMP-cytotoxic T lymphocytes (CTLs) from patients with lymphoma using autologous dendritic cells and EBV-transformed B-lymphoblastoid cell lines transduced with an adenoviral vector expressing either LMP2 alone (n = 17) or both LMP2 and ΔLMP1 (n = 33).

PATIENTS AND METHODS

These genetically modified antigen-presenting cells expanded CTLs that were enriched for specificity against type II latency LMP antigens. When infused into 50 patients with EBV-associated lymphoma, the expanded CTLs did not produce infusional toxicities.

RESULTS

Twenty-eight of 29 high-risk or multiple-relapse patients receiving LMP-CTLs as adjuvant therapy remained in remission at a median of 3.1 years after CTL infusion. None subsequently died as a result of lymphoma, but nine succumbed to complications associated with extensive prior chemoradiotherapy, including myocardial infarction and secondary malignancies. Of 21 patients with relapsed or resistant disease at the time of CTL infusion, 13 had clinical responses, including 11 complete responses. T cells specific for LMP as well as nonviral tumor-associated antigens (epitope spreading) could be detected in the peripheral blood within 2 months after CTL infusion, but this evidence for epitope spreading was seen only in patients achieving clinical responses.

CONCLUSION

Autologous T cells directed to the LMP2 or LMP1 and LMP2 antigens can induce durable complete responses without significant toxicity. Their earlier use in the disease course may reduce delayed treatment-related mortality.

Accelerating immune reconstitution after hematopoietic stem cell transplantation

Viral infections remain a significant cause of morbidity and mortality after hematopoietic stem cell transplantation. Pharmacologic agents are effective against some pathogens, but they are costly and can be associated with significant toxicities. Thus, many groups have investigated adoptive T-cell transfer as a means of hastening immune reconstitution and preventing and treating viral infections. This review discusses the immunotherapeutic strategies that have been explored.

Genetically modified T cells to target glioblastoma

Despite advances in surgical procedures, radiation, and chemotherapy the outcome for patients with glioblastoma (GBM) remains poor. While GBM cells express antigens that are potentially recognized by T cells, GBMs prevent the induction of GBM-specific immune responses by creating an immunosuppressive microenvironment. The advent of gene transfer has allowed the rapid generation of antigen-specific T cells as well as T cells with enhanced effector function. Here we review recent advances in the field of cell therapy with genetically modified T cells and how these advances might improve outcomes for patients with GBM in the future.

A vaccine that co-targets tumor cells and cancer associated fibroblasts results in enhanced antitumor activity by inducing antigen spreading

Dendritic cell (DC) vaccines targeting only cancer cells have produced limited antitumor activity in most clinical studies. Targeting cancer-associated fibroblasts (CAFs) in addition to cancer cells may enhance antitumor effects, since CAFs, the central component of the tumor stroma, directly support tumor growth and contribute to the immunosuppressive tumor microenvironment. To co-target CAFs and tumor cells we developed a new compound DC vaccine that encodes an A20-specific shRNA to enhance DC function, and targets fibroblast activation protein (FAP) expressed in CAFs and the tumor antigen tyrosine-related protein (TRP)2 (DC-shA20-FAP-TRP2). DC-shA20-FAP-TRP2 vaccination induced robust FAP- and TRP2-specific T-cell responses, resulting in greater antitumor activity in the B16 melanoma model in comparison to monovalent vaccines or a vaccine encoding antigens and a control shRNA. DC-shA20-FAP-TRP2 vaccination enhanced tumor infiltration of CD8-positive T cells, and induced antigen-spreading resulting in potent antitumor activity. Thus, co-targeting of tumor cells and CAFs results in the induction of broad-based tumor-specific T-cell responses and has the potential to improve current vaccine approaches for cancer.

T-cell therapy for viral infections

Viral infections remain a major cause of morbidity in patients with immunodeficiency, such as recipients of hemopoietic stem cell transplantation. Adoptive transfer of donor-derived virus-specific cytotoxic T lymphocytes is a strategy to restore virus-specific immunity to prevent or treat viral diseases and has been tested in the clinical setting for more than 20 years. Several different groups have used expanded virus-specific T-cell products specific for one or multiple viruses to both reconstitute antiviral immunity after transplantation and to treat active viral infections. Response rates are encouraging, although resistance has been seen when the infused cell population has had restricted specificity or has targeted antigens expressed in donor-infected but not virally infected recipient cells. The goal of current trials is to make this approach more broadly applicable using more rapidly available products from the donor, such as directly selected or briefly expanded cells or closely matched banked cells.

Molecular monitoring and stepwise preemptive therapy for Epstein-Barr virus viremia after allogeneic stem cell transplantation

The optimal preemptive therapy for Epstein-Barr virus (EBV)-associated diseases remains under discussion. We developed a stepwise preemptive therapy (antiviral agents and reduction of immunosuppressants [RI] followed by rituximab) for EBV viremia, based on duration of EBV viremia and changes of viral loads. The blood EBV-DNA loads were regularly monitored by quantitative real-time polymerase chain reaction in 251 recipients undergoing allogeneic stem cell transplantation. The 3-year cumulative incidence of EBV viremia and EBV-associated diseases were 31.1% ± 3.1% and 15.6% ± 2.5%, which rose steeply with greater numbers of major risk factors. Of the 64 patients undergoing first-step preemption, 24 achieved complete response (CR) and 40 showed no response, including 25 progressing to EBV-associated diseases. The effective rates of antiviral agents and RI plus antiviral agents were 2/16 and 22/48 (P = 0.017). Fourteen achieved CR and one progressed to lymphoproliferative disease in the 15 patients undergoing rituximab preemption. Of the 26 patients progressing to EBV-associated diseases during preemptive therapy, 20 obtained CR in the 23 cases with rituximab-based treatments. The preemptive efficacy of RI plus antiviral agents was correlated with the numbers of major risk factors (rs  = -0.298; P = 0.04). B-cell reconstitution was significantly delayed for at least 6 months in patients with rituximab preemption. The risk of herpesvirus infection was similar in patients who showed effective progress to first-step and rituximab preemption (P = 0.094). RI plus antiviral agents could be given priority to low-risk patients, whereas more frequent monitoring of blood EBV-DNA and earlier preemptive rituximab should be advocated in high-risk patients.

Safety and clinical efficacy of rapidly-generated trivirus-directed T cells as treatment for adenovirus, EBV, and CMV infections after allogeneic hematopoietic stem cell transplant

Adoptive transfer of virus-specific T cells can prevent and treat serious infections with Epstein-Barr virus (EBV), cytomegalovirus (CMV), and adenovirus (Adv) after allogeneic hematopoietic stem cell transplant. It has, however, proved difficult to make this approach widely available since infectious virus and viral vectors are required for T cell activation, followed by an intensive and prolonged culture period extending over several months. We now show that T cells targeting a range of viral antigens derived from EBV, CMV, and Adv can be reproducibly generated in a single culture over a 2-3-week period, using methods that exclude all viral components and employ a much-simplified culture technology. When administered to recipients of haploidentical (n = 5), matched unrelated (n = 3), mismatched unrelated (n = 1) or matched related (n = 1) transplants with active CMV (n = 3), Adv (n = 1), EBV (n = 2), EBV+Adv (n = 2) or CMV+Adv (n = 2) infections, the cells produced complete virological responses in 80%, including all patients with dual infections. In each case, a decrease in viral load correlated with an increase in the frequency of T cells directed against the infecting virus(es); both immediate and delayed toxicities were absent. This approach should increase both the feasibility and applicability of T cell therapy. The trial was registered at www.clinicaltrials.gov as NCT01070797.

Generation of multi-leukemia antigen-specific T cells to enhance the graft-versus-leukemia effect after allogeneic stem cell transplant

Adoptive immunotherapy with ex vivo expanded T cells is a promising approach to prevent or treat leukemia. Myeloid leukemias express tumor-associated antigens (TAA) that induce antigen-specific cytotoxic T lymphocyte (CTL) responses in healthy individuals. We explored the feasibility of generating TAA-specific CTLs from stem cell donors of patients with myeloid leukemia to enhance the graft-versus-leukemia effect after stem cell transplantation. CTL lines were manufactured from peripheral blood of 10 healthy donors by stimulation with 15mer peptide libraries of five TAA (proteinase 3 (Pr3), preferentially expressed antigen in melanoma, Wilms tumor gene 1 (WT1), human neutrophil elastase (NE) and melanoma-associated antigen A3) known to be expressed in myeloid leukemias. All CTL lines responded to the mix of five TAA and were multi-specific as assessed by interferon-γ enzyme-linked immunospot. Although donors showed individual patterns of antigen recognition, all responded comparably to the TAAmix. Immunogenic peptides of WT1, Pr3 or NE could be identified by epitope mapping in all donor CTL lines. In vitro experiments showed recognition of partially human leukocyte antigen (HLA)-matched myeloid leukemia blasts. These findings support the development of a single clinical grade multi-tumor antigen-specific T-cell product from the stem cell source, capable of broad reactivity against myeloid malignancies for use in donor-recipient pairs without limitation to a certain HLA-type.

Immunotherapies in CLL

Chronic lymphocytic leukemia (CLL) is the most frequently diagnosed leukemia in the Western world, yet remains essentially incurable. Although initial chemotherapy response rates are high, patients invariably relapse and subsequently develop resistance to chemotherapy. For the moment, allogeneic hematopoietic stem cell transplant (allo-HSCT) remains the only potentially curative treatment for patients with CLL, but it is associated with high rates of treatment-related mortality. Immune-based treatment strategies to augment the cytotoxic potential of T cells offer exciting new treatment options for patients with CLL, and provide a unique and powerful spectrum of tools distinct from traditional chemotherapy. Among the most novel and promising of these approaches are chimeric antigen receptor (CAR)-based cell therapies that combine advances in genetic engineering and adoptive immunotherapy.

Immunotherapeutic strategies to prevent and treat human herpesvirus 6 reactivation after allogeneic stem cell transplantation

Human herpesvirus (HHV) 6 causes substantial morbidity and mortality in the immunocompromised host and has no approved therapy. Adoptive transfer of virus specific T cells has proven safe and apparently effective as prophylaxis and treatment of other virus infections in immunocompromised patients; however, extension to subjects with HHV6 has been hindered by the paucity of information on targets of cellular immunity. We now characterize the cellular immune response from 20 donors against 5 major HHV6B antigens predicted to be immunogenic and define a hierarchy of immunodominance of antigens based on the frequency of responding donors and the magnitude of the T-cell response. We identified specific epitopes within these antigens and expanded the HHV6 reactive T cells using a GMP-compliant protocol. The expanded population comprised both CD4(+) and CD8(+) T cells that were able to produce multiple effector cytokines and kill both peptide-loaded and HHV6B wild-type virus-infected target cells. Thus, we conclude that adoptive T-cell immunotherapy for HHV6 is a practical objective and that the peptide and epitope tools we describe will allow such cells to be prepared, administered, and monitored in human subjects.

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

Post-transplant lymphoproliferative diseases (PTLD) associated with Epstein-Barr virus (EBV) infection often develop after organ and haematopoietic stem-cell transplantation. These lymphoproliferative diseases are tumours that usually express all latent EBV viral proteins, and are therefore amenable to T-cell-based immune therapies, such as donor lymphocyte infusions and the adoptive transfer of EBV-specific cytotoxic T lymphocytes. In this Review, we describe current approaches of T-cell-based therapies to treat PTLD, and describe strategies that improve the feasibility of such treatment.

Cellular therapies in acute lymphoblastic leukemia

ALL remains a difficult disease to treat. In the adult setting, most patients will ultimately die of their disease, whereas in the pediatric setting, relapsed and refractory disease remains a therapeutic challenge. Cellular therapy through allo-HSCT remains an option for these patients, and recent advances in alternative forms of allo-HSCT, including unrelated donor transplants, UCB transplants, and haploidentical transplants, have expanded the numbers of patients eligible for allo-HSCT but have not improved outcomes when compared with HLA-matched related allo-HSCTs. In light of this persistent failure, several novel adoptive cellular approaches are being investigated to treat patients with ALL. The use of enriched WT-1–specific donor T cells to treat patients with ALL is currently under investigation in phase I trials at several centers. Treatment of ALL with genetically modified T cells targeted to the CD19 antigen through the expression of a CD19-specific CAR also have entered phase I clinical trials at several centers. Similarly, a clinical trial treating patients with ALL with genetically modified NK cells targeted to the CD19 antigen has recently opened for accrual. Collectively, these ongoing and anticipated trials provide a promising role for adoptive cellular therapies in the treatment of ALL. What remains to be seen is whether this promise will either translate into improved outcomes for these patients or provide significant insights on which to design second-generation adoptive cell therapeutic clinical trials for ALL in the future.

EBNA3B-deficient EBV promotes B cell lymphomagenesis in humanized mice and is found in human tumors

Epstein-Barr virus (EBV) persistently infects more than 90% of the human population and is etiologically linked to several B cell malignancies, including Burkitt lymphoma (BL), Hodgkin lymphoma (HL), and diffuse large B cell lymphoma (DLBCL). Despite its growth transforming properties, most immune-competent individuals control EBV infection throughout their lives. EBV encodes various oncogenes, and of the 6 latency-associated EBV-encoded nuclear antigens, only EBNA3B is completely dispensable for B cell transformation in vitro. Here, we report that infection with EBV lacking EBNA3B leads to aggressive, immune-evading monomorphic DLBCL-like tumors in NOD/SCID/γc-/- mice with reconstituted human immune system components. Infection with EBNA3B-knockout EBV (EBNA3BKO) induced expansion of EBV-specific T cells that failed to infiltrate the tumors. EBNA3BKO-infected B cells expanded more rapidly and secreted less T cell-chemoattractant CXCL10, reducing T cell recruitment in vitro and T cell-mediated killing in vivo. B cell lines from 2 EBV-positive human lymphomas encoding truncated EBNA3B exhibited gene expression profiles and phenotypic characteristics similar to those of tumor-derived lines from the humanized mice, including reduced CXCL10 secretion. Screening EBV-positive DLBCL, HL, and BL human samples identified additional EBNA3B mutations. Thus, EBNA3B is a virus-encoded tumor suppressor whose inactivation promotes immune evasion and virus-driven lymphomagenesis.

Natural and adoptive T-cell immunity against herpes family viruses after allogeneic hematopoietic stem cell transplantation

Reactivated infections with herpes family-related cytomegalovirus, Epstein-Barr virus and varicella zoster virus are serious and sometimes life-threatening complications for patients undergoing allogeneic hematopoietic stem cell transplantation. The pathogenesis of these infections critically involves the slow and inefficient recovery of antiviral T-cell immunity after transplantation. Although efficient drugs to decrease viral load during this vulnerable period have been developed, long-term control of herpes viruses and protection from associated diseases require the sufficient reconstitution of virus-specific memory T cells. To heal the deficiency by immunotherapeutic means, numerous research groups have developed antiviral vaccines and strategies based on the adoptive transfer of virus-specific T cells. This article summarizes the substantial progress made in this field during the past two decades and gives future perspectives about challenges that need to be addressed before antigen-specific immunotherapy against herpes family viruses can be implemented in general clinical practice.

Specific mutation of a gammaherpesvirus-expressed antigen in response to CD8 T cell selection in vivo

Herpesviruses are thought to be highly genetically stable, and their use as vaccine vectors has been proposed. However, studies of the human gammaherpesvirus, Epstein-Barr virus, have found viral isolates containing mutations in HLA class I-restricted epitopes. Using murine gammaherpesvirus 68 expressing ovalbumin (OVA), we examined the stability of a gammaherpesvirus antigenic locus under strong CD8 T cell selection in vivo. OVA-specific CD8 T cells selected viral isolates containing mutations in the OVA locus but minimal alterations in other genomic regions. Thus, a CD8 T cell response to a gammaherpesvirus-expressed antigen that is not essential for replication or pathogenesis can result in selective mutation of that antigen in vivo. This finding may have relevance for the use of herpesvirus vectors for chronic antigen expression in vivo.

Adoptive immunotherapy with unselected or EBV-specific T cells for biopsy-proven EBV+ lymphomas after allogeneic hematopoietic cell transplantation

We evaluated HLA-compatible donor leukocyte infusions (DLIs) and HLA-compatible or HLA-disparate EBV-specific T cells (EBV-CTLs) in 49 hematopoietic cell transplantation recipients with biopsy-proven EBV-lymphoproliferative disease (EBV-LPD). DLIs and EBV-CTLs each induced durable complete or partial remissions in 73% and 68% of treated patients including 74% and 72% of patients surviving ≥ 8 days after infusion, respectively. Reversible acute GVHD occurred in recipients of DLIs (17%) but not EBV-CTLs. The probability of complete response was significantly lower among patients with multiorgan involvement. In responders, DLIs and EBV-CTLs regularly induced exponential increases in EBV-specific CTL precursor (EBV-CTLp) frequencies within 7-14 days, with subsequent clearance of EBV viremia and resolution of disease. In nonresponders, EBV-CTLps did not increase and EBV viremia persisted. Treatment failures were correlated with impaired T-cell recognition of tumor targets. Either donor-derived EBV-CTLs that had been sensitized with autologous BLCLs transformed by EBV strain B95.8 could not lyse spontaneous donor-derived EBV-transformed BLCLs expanded from the patient's blood or biopsied tumor or they failed to lyse their targets because they were selectively restricted by HLA alleles not shared by the EBV-LPD. Therefore, either unselected DLIs or EBV-specific CTLs can eradicate both untreated and Rituxan-resistant lymphomatous EBV-LPD, with failures ascribable to impaired T-cell recognition of tumor-associated viral antigens or their presenting HLA alleles.

Soluble rhesus lymphocryptovirus gp350 protects against infection and reduces viral loads in animals that become infected with virus after challenge

Epstein-Barr virus (EBV) is a human lymphocryptovirus that is associated with several malignancies. Elevated EBV DNA in the blood is observed in transplant recipients prior to, and at the time of post-transplant lymphoproliferative disease; thus, a vaccine that either prevents EBV infection or lowers the viral load might reduce certain EBV malignancies. Two major approaches have been suggested for an EBV vaccine- immunization with either EBV glycoprotein 350 (gp350) or EBV latency proteins (e.g. EBV nuclear antigens [EBNAs]). No comparative trials, however, have been performed. Rhesus lymphocryptovirus (LCV) encodes a homolog for each gene in EBV and infection of monkeys reproduces the clinical, immunologic, and virologic features of both acute and latent EBV infection. We vaccinated rhesus monkeys at 0, 4 and 12 weeks with (a) soluble rhesus LCV gp350, (b) virus-like replicon particles (VRPs) expressing rhesus LCV gp350, (c) VRPs expressing rhesus LCV gp350, EBNA-3A, and EBNA-3B, or (d) PBS. Animals vaccinated with soluble gp350 produced higher levels of antibody to the glycoprotein than those vaccinated with VRPs expressing gp350. Animals vaccinated with VRPs expressing EBNA-3A and EBNA-3B developed LCV-specific CD4 and CD8 T cell immunity to these proteins, while VRPs expressing gp350 did not induce detectable T cell immunity to gp350. After challenge with rhesus LCV, animals vaccinated with soluble rhesus LCV gp350 had the best level of protection against infection based on seroconversion, viral DNA, and viral RNA in the blood after challenge. Surprisingly, animals vaccinated with gp350 that became infected had the lowest LCV DNA loads in the blood at 23 months after challenge. These studies indicate that gp350 is critical for both protection against infection with rhesus LCV and for reducing the viral load in animals that become infected after challenge. Our results suggest that additional trials with soluble EBV gp350 alone, or in combination with other EBV proteins, should be considered to reduce EBV infection or virus-associated malignancies in humans.

Epstein-Barr virus (EBV) is the primary cause of infectious mononucleosis and is associated with several cancers. Presently there is no licensed vaccine to prevent EBV diseases. Two types of candidate vaccines are under development; one involves immunization with the major glycoprotein (gp350) on the outside of the virus, while the other involves vaccination with EBV proteins expressed during latency. We compared these two types of candidate vaccines in a rhesus monkey model of EBV and found that the gp350 vaccine induced better protection from infection. In addition, animals that received the rhesus EBV glycoprotein and became infected had a lower level of rhesus EBV DNA in the blood at 23 months after challenge than animals that received the rhesus EBV latency protein vaccine that subsequently were infected. Since levels of EBV DNA in the blood have been predictive for EBV lymphomas in transplant patients, the ability of rhesus EBV gp350 to reduce levels of rhesus EBV in the blood after infection suggests the EBV gp350 could have a role in reducing certain EBV-associated cancers. This is the first test of candidate vaccines in the rhesus monkey model of EBV and shows that this model should be useful in further evaluation of EBV vaccines.

Cytotoxic T lymphocytes simultaneously targeting multiple tumor-associated antigens to treat EBV negative lymphoma

Although immunotherapy with Epstein-Barr virus (EBV)-specific cytotoxic T lymphocytes (CTLs) can treat EBV-associated Hodgkin and non-Hodgkin lymphoma (HL/NHL), more than 50% of such tumors are EBV negative. We now describe an approach that allows us to consistently generate, in a single line, CTLs that recognize a wide spectrum of nonviral tumor-associated antigens (TAAs) expressed by human HL/NHL, including Survivin, MAGE-A4, Synovial sarcoma X (SSX2), preferentially expressed antigen in melanoma (PRAME) and NY-ESO-1. We could generate these CTLs from nine of nine healthy donors and five of eight lymphoma patients, irrespective of human leukocyte antigen (HLA) type. We reactivated TAA-directed T cells ex vivo, by stimulation with dendritic cells (DCs) pulsed with overlapping peptide libraries spanning the chosen antigens in the presence of an optimized Th1-polarizing, prosurvival/proliferative and Treg inhibitory cytokine combination. The resultant lines of CD4(+) and CD8(+), polycytokine-producing T cells are directed against a multiplicity of epitopes expressed on the selected TAAs, with cytolytic activity against autologous tumor cells. Infusion of such multispecific monocultures may extend the benefits of CTL therapy to treatment even of EBV negative HL and NHL.

Expansion of T cells targeting multiple antigens of cytomegalovirus, Epstein-Barr virus and adenovirus to provide broad antiviral specificity after stem cell transplantation

BACKGROUND AIMS

Hematopoietic stem cell transplant (HSCT) is the treatment of choice for a proportion of patients with hematologic malignancies as well as for non-malignant diseases. However, viral infections, particularly Epstein-Barr virus (EBV), cytomegalovirus (CMV) and adenovirus (Ad), remain problematic after transplant despite the use of antiviral drugs. We have shown that cytotoxic T lymphocytes (CTL) generated against CMV-pp65, EBV and Ad antigens in a single culture are capable of controlling infections with all three viruses after HSCT. Although pp65-specific CTL have proved efficacious for the control of CMV infection, several reports highlight the importance of targeting additional CMV antigens.

METHODS

To expand multivirus-specific T cells with activity against both CMV-pp65 and CMV-IE-1, peripheral blood mononuclear cells (PBMC) were transduced with the adenoviral vector (Ad5f35-IE-1-I-pp65). After 9-12 days the CTL were restimulated with autologous EBV-transformed B cells transduced with the same Ad vector.

RESULTS

After 18 days in culture nine CTL lines expanded from less than 1.5 × 10(7) PBMC to a mean of 6.1 × 10(7) T cells that recognized CMV antigens pp65 [median 273 spot-forming cells (SFC), range 47-995] and IE-1 (median 154 SFC, range 11-505), the Ad antigens hexon (median 153 SFC, range 26-465) and penton (median 37 SFC, range 1-353), as well as EBV lymphoblastoid cell lines (median 55 SFC, range 9-301). Importantly, the T cells recognized at least two antigens per virus and lysed virus peptide-pulsed targets.

CONCLUSIONS

CTL that target at least two antigens each of CMV, EBV and Ad should have clinical benefit with broad coverage of all three viruses and enhanced control of CMV infections compared with current protocols.

T cell therapy for nasopharyngeal carcinoma

Among the novel biologic therapeutics that will increase our ability to cure human cancer in the years to come, T cell therapy is one of the most promising approaches. However, with the possible exception of tumor-infiltrating lymphocytes therapy for melanoma, clinical trials of adoptive T-cell therapy for solid tumors have so far provided only clear proofs-of-principle to build on with further development. Epstein-Barr virus (EBV)-associated malignancies offer a unique model to develop T cell-based immune therapies, targeting viral antigens expressed on tumor cells. In the last two decades, EBV-specific cytotoxic T-lymphocytes (CTL) have been successfully employed for the prophylaxis and treatment of EBV-related lymphoproliferative disorders in immunocompromised hosts. More recently, this therapeutic approach has been applied to the setting of EBV-related solid tumors, such as nasopharyngeal carcinoma. The results are encouraging, although further improvements to the clinical protocols are clearly necessary to increase anti-tumor activity. Promising implementations are underway, including harnessing the therapeutic potential of CTLs specific for subdominant EBV latent cycle epitopes, and delineating strategies aimed at targeting immune evasion mechanisms exerted by tumor cells.

Virus-specific T cells for therapy--approaches, problems, solutions

Adoptive T cell therapy is the transfer of T cells to a patient in order to combat disease. This procedure is mainly being used but not limited to the treatment of viral infections and malignancies including virus-associated tumors. Depending on the clinical context, the T cell donor may be the same patient or another donor, usually a healthy person. Recent research is centered on the use of antigen-specific T cells, but T cells of uncharacterized specificity can be successfully used in some clinical conditions where target antigens are not known. Depending on underlying scientific hypotheses and preferred technologies, the therapeutic T cells may be anything from monoclonal to highly polyclonal; they may be specific for one epitope, several epitopes from one antigen, or various antigens; they may have been selected during the preparation process for their specificity, their functional capacity, their survival and proliferation in vitro, or the expression of surface markers associated with desirable functional properties. In this minireview, we give a brief overview on selected approaches, problems and solutions in adoptive T cell therapy. We focus on an area where T cell therapy has been particularly successful but is still calling for improvement: herpesviral disease in patients after transplantation.

Adoptive transfer of EBV-specific T cells results in sustained clinical responses in patients with locoregional nasopharyngeal carcinoma

Patients with recurrent or refractory Epstein Barr Virus (EBV)-positive nasopharyngeal carcinoma (NPC) continue to have poor outcomes. Our earlier Phase I dose escalation clinical study of 10 NPC patients showed that infusion of EBV-specific cytotoxic T cells (EBV-CTLs) was safe and had antitumor activity. To better define the overall response rate and discover whether disease status, EBV-antigen specificity, and/or in vivo expansion of infused EBV-CTLs predicted outcome, we treated 13 additional NPC patients with EBV-CTLs in a fixed-dose, Phase II component of the study. We assessed toxicity, efficacy, specificity, and expansion of infused CTLs for all 23 recurrent/refractory NPC patients treated on this Phase I/II clinical study. At the time of CTL infusion, 8 relapsed NPC patients were in remission and 15 had active disease. No significant toxicity was observed. Of the relapsed patients treated in their second or subsequent remission, 62% (5/8) remain disease free (at 17 to 75 mo), whereas 48.7% (7/15) of those with active disease had a CR/CRu (33.3%) or PR (15.4%). In contrast to locoregional disease, metastatic disease was associated with an increased risk of disease progression (HR: 3.91, P=0.015) and decreased overall survival (HR: 5.55, P=0.022). Neither the specificity of the infused CTLs for particular EBV antigens nor their measurable in vivo expansion discernibly influenced outcome. In conclusion, treatment of patients with relapsed/refractory EBV-positive NPC with EBV-CTLs is safe and can be associated with significant, long-term clinical benefit, particularly for patients with locoregional disease.

Immunotherapy for EBV-associated malignancies

Since 1995 to date, more than 250 patients with EBV-related diseases received virus-specific CTL. Cell therapy proved to be safe and effective, and achieved some complete remissions also in patients who failed all previous standard treatments. The first clinical results with EBV-specific CTL were obtained for both prophylaxis and treatment of post-transplant lymphoproliferative disease arising in stem cell transplant or solid organ transplant recipients. Based on such encouraging results, the same approach was then extended to other EBV-related diseases, namely Hodgkin's lymphoma, nasopharyngeal carcinoma, and chronic active infection. Nowadays, the modification of the CTL generation protocols and the introduction of new specificities into EBV-specific CTL lines by chimeric antigen receptor transfer allow targeting other viral infections and also non-EBV related malignancies. Aim of this review is to summarize clinical results obtained thus far in adoptive cell therapy approaches with EBV-specific CTL. Moreover, by analyzing ongoing clinical trials, we also provide some insights on the potential future of a successful and paradigmatic history.

Cytolytic T lymphocytes from HLA-B8+ donors frequently recognize the Hodgkin's lymphoma associated latent membrane protein 2 of Epstein Barr virus

Epstein Barr virus (EBV) is a lymphotrophic γ-herpesvirus that infects more than 90% of the adult human population. It transforms B cells in vitro and is associated with lymphomas in vivo. In most EBV carriers the emergence of these malignancies, however, is prevented by T cell mediated immune control. Part of this control is mediated by CD8+ T cells, which mainly target a subset of viral nuclear antigens, EBNA3A, B and C, in healthy EBV carriers. In HLA-B8 positive individuals, the dominant CTL response is biased towards recognition of EBNA3A. However, spontaneously arising EBV-associated malignancies, such as Hodgkin's lymphoma and nasopharyngeal carcinoma do not express EBNA3s and instead express latent membrane protein 2 (LMP2) as well as LMP1 and EBNA1. Here we describe the new HLA-B8 restricted, LMP2 derived CD8+ T cell epitope, LMP2345-352. Although the frequency of LMP2345-352 specific CD8+ T cells is usually lower than immunodominant EBNA3A specific CD8+ T cells in fresh blood, the former can be expanded in the majority of HLA-B8+ EBV carriers after 1 week co-culture with peptide pulsed dendritic cells. We demonstrate that LMP2345-352 specific CD8+ T cells secrete IFN-γ and kill both peptide pulsed targets as well as HLA-B8 matched LCL and LMP2 expressing Hodgkin's lymphoma cells. We suggest that cytotoxic CD8+ T cell responses against LMP2 coexist with the immunodominant EBNA3 specific responses in healthy EBV carriers and help to resist EBV associated malignancies.

Successful medical treatment of EBV smooth muscle tumor in a renal transplant recipient

EBV is associated with various malignancies in patients with acquired or induced immune impairment. EBV-SMT is very uncommon in immunocompromised patients, and a kidney localization has been described only anecdotally. We report the case of a 17-yr-old kidney transplant recipient diagnosed as having an EBV-SMT inside the renal graft, which was successfully managed by minimizing isolated immunosuppression.

Immunotherapeutic options for Epstein-Barr virus-associated lymphoproliferative disease following transplantation

Epstein-Barr virus-associated lymphoproliferative diseases (EBV-LPD) after hematopoietic stem cell transplantation or solid-organ transplantation remain a serious and potentially life-threatening complication. In the last decade, outcomes for EBV-LPD have significantly improved. Key to this success was the development of early detection methods, such as serial measurements of EBV-DNA load in the peripheral blood of transplant recipients. Immunotherapeutic interventions for EBV-LPD include reduction of immunosuppression, CD20 monoclonal antibodies (rituximab) as monotherapy or in conjunction with chemotherapy, and adoptive immunotherapy with EBV-specific T cells. Pre-emptive immunotherapeutic interventions can prevent the development of EBV-LPD. As monotherapy, immunotherapy is effective in inducing remissions of EBV-LPD with low-risk features. For high-risk disease, combining immunotherapy with conventional therapies has led to superior outcomes. Current challenges consist of risk stratifying patients so that patients receive the most efficacious therapy without suffering from unwanted side effects.

Trends in cancer immunotherapy

Modulation of the immune system for therapeutic ends has a long history, stretching back to Edward Jenner's use of cowpox to induce immunity to smallpox in 1796. Since then, immunotherapy, in the form of prophylactic and therapeutic vaccines, has enabled doctors to treat and prevent a variety of infectious diseases, including cholera, poliomyelitis, diphtheria, measles and mumps. Immunotherapy is now increasingly being applied to oncology. Cancer immunotherapy attempts to harness the power and specificity of the immune system for the treatment of malignancy. Although cancer cells are less immunogenic than pathogens, the immune system is capable of recognizing and eliminating tumor cells. However, tumors frequently interfere with the development and function of immune responses. Thus, the challenge for cancer immunotherapy is to apply advances in cellular and molecular immunology and develop strategies that effectively and safely augment antitumor responses.

Expansion of EBNA1-specific effector T cells in posttransplantation lymphoproliferative disorders

Immunosuppression resulting in impaired Epstein-Barr virus (EBV)-specific T-cell immunity is involved in the pathogenesis of EBV-positive post-transplantation lymphoproliferative disorder (EBV(+) PTLD). Restoration of EBV-specific T-cell immunity by adoptive immunotherapy can induce remission. EBV-nuclear antigen-1 (EBNA1) is unique in being expressed in all cases of EBV(+) PTLD. Recent data demonstrate that EBNA1 is not immunologically silent and can be exploited as a T-cell target. There are no data on EBNA1-specific T cells in PTLD. EBNA1-specific T cells capable of proliferation, interferon-γ release, and CD107a/b degranulation were assayed in 14 EBV(+) PTLD diagnostic blood samples and 19 healthy controls. EBNA1-specific CD4(+) T cells predominated and were expanded in 10 of 14 patients and 19 of 19 controls. Although human leukocyte antigen class I alleles influenced the magnitude of the response, EBNA1-specific CD8(+) effector T cells were successfully generated in 9 of 14 EBV(+) PTLD patients and 16 of 19 controls. The majority of PTLD patients had a polymorphism in an EBNA1 epitope, and T-cell recognition was greatly enhanced when EBNA1 peptides derived from the polymorphic epitope were used. These results indicate that EBNA1-specific T cells should be included in adoptive immunotherapy for PTLD. Furthermore, expansion protocols should use antigenic sequences from relevant EBV strains.

Antigen-specific cytotoxic T lymphocytes can target chemoresistant side-population tumor cells in Hodgkin lymphoma

Side-population (SP) analysis has been used to identify progenitor cells from normal and malignant tissues as well as revealing tumor cells with increased resistance to radiation and chemotherapy. Despite enhanced chemoresistance, tumor SP cells may still express tumor-associated antigens (TAAs), which may render them susceptible to elimination by the immune system. In this study, we show that both Hodgkin lymphoma (HL) cell lines and primary HL tumor samples contain a distinct SP phenotype. Importantly, while these cells showed increased resistance to gemcitabine, a commonly used drug for the treatment of refractory HL, HL SP cells also expressed higher levels of the TAAs MAGEA4, SSX2, survivin, and NY-ESO-1, which allowed them to be specifically recognized and killed by TAA-specific cytotoxic T lymphocytes. This study suggests that chemoresistant HL SP cells can be targeted by the immune system, providing a rationale for combined chemotherapy and immunotherapy for the treatment of HL.

Challenges of T cell therapies for virus-associated diseases after hematopoietic stem cell transplantation

IMPORTANCE OF THE FIELD

Hematopoietic stem cell transplantation (HSCT) is the treatment of choice for many hematological malignancies and genetic disorders. The majority of patients do not have a human leukocyte antigen (HLA) identical sibling donor, and alternative stem cell sources include HLA-matched or mismatched unrelated donors and haploidentical related donors. However, alternative donor HSCT are associated with three major complications i) graft rejection; ii) graft-versus-host disease (GvHD); and iii) delayed immune reconstitution leading to viral infections and relapse.

AREAS COVERED IN THIS REVIEW

Graft rejection and the risk of GvHD can be significantly reduced by using intensive conditioning regimens, including in vivo T cell depletion as well as ex vivo T cell depletion of the graft. However, the benefits of removing alloreactive T cells from the graft are offset by the concomitant removal of T cells with anti-viral or anti-tumor activity as well as the profound delay in endogenous T cell recovery post-transplant. Thus, opportunistic infections, many of which are not amenable to conventional small-molecule therapeutics, are frequent in these patients and are associated with significant morbidity and high mortality rates. This review discusses current cell therapies to prevent or treat viral infections/reactivations post-transplant.

WHAT THE READER WILL GAIN

The reader will gain an understanding of the current state of cell therapy to prevent and treat viral infections post-HSCT, and will be introduced to preclinical studies designed to develop and validate new manufacturing procedures intended to improve therapeutic efficacy and reduce associated toxicities.

TAKE HOME MESSAGE

Reconstitution of HSCT recipients with antigen-specific T cells, produced either by allodepletion or in vitro reactivation, can offer an effective strategy to provide both immediate and long-term protection without harmful alloreactivity.

The interplay between Epstein-Barr virus and the immune system: a rationale for adoptive cell therapy of EBV-related disorders

The Epstein-Barr virus has evolved a plethora of strategies to evade immune system recognition and to establish latent infection in memory B cells, where the virus resides lifelong without any consequence in the majority of individuals. However, some imbalances in the equilibrium between the inherent virus transforming properties and the host immune system can lead to the development of different tumors, such as lymphoproliferative disorders, Hodgkin's lymphoma, Burkitt's lymphoma, and nasopharyngeal carcinoma. The expression of viral antigens in malignant cells makes them suitable targets for immunotherapeutic approaches, which are mainly based on the ex vivo expansion of EBV-specific T cells. Indeed, the infusion of virus-specific cytotoxic T lymphocytes has proved not only to be safe and effective, but also capable of restoring or inducing a protective anti-virus immunity, which is lacking, albeit to a different extent, in every EBV-driven malignancy. The purpose of this review is to summarize the results of adoptive immunotherapy approaches for EBV-related malignancies, with particular emphasis on the immunological and virological aspects linked to the clinical responses obtained. Data collected confirm the clinical relevance of the use of EBV-specific cytotoxic T lymphocytes in the field of adoptive immunotherapy and suggest the increasing importance of this approach also against other tumors, concurrent with the increasing knowledge of the intimate and continuous interplay between the virus and the host immune system.

HER2-specific T cells target primary glioblastoma stem cells and induce regression of autologous experimental tumors

PURPOSE

Glioblastoma multiforme (GBM) is the most aggressive human primary brain tumor and is currently incurable. Immunotherapies have the potential to target GBM stem cells, which are resistant to conventional therapies. Human epidermal growth factor receptor 2 (HER2) is a validated immunotherapy target, and we determined if HER2-specific T cells can be generated from GBM patients that will target autologous HER2-positive GBMs and their CD133-positive stem cell compartment.

EXPERIMENTAL DESIGN

HER2-specific T cells from 10 consecutive GBM patients were generated by transduction with a retroviral vector encoding a HER2-specific chimeric antigen receptor. The effector function of HER2-specific T cells against autologous GBM cells, including CD133-positive stem cells, was evaluated in vitro and in an orthotopic murine xenograft model.

RESULTS

Stimulation of HER2-specific T cells with HER2-positive autologous GBM cells resulted in T-cell proliferation and secretion of IFN-gamma and interleukin-2 in a HER2-dependent manner. Patients' HER2-specific T cells killed CD133-positive and CD133-negative cells derived from primary HER2-positive GBMs, whereas HER2-negative tumor cells were not killed. Injection of HER2-specific T cells induced sustained regression of autologous GBM xenografts established in the brain of severe combined immunodeficient mice.

CONCLUSIONS

Gene transfer allows the reliable generation of HER2-specific T cells from GBM patients, which have potent antitumor activity against autologous HER2-positive tumors including their putative stem cells. Hence, the adoptive transfer of HER2-redirected T cells may be a promising immunotherapeutic approach for GBM.

Cellular immunotherapy of cancer

Standard therapies for many common cancers remain toxic and are often ineffective. Cellular immunotherapy has the potential to be a highly targeted alternative, with low toxicity to normal tissues but a high capacity to eradicate tumor. In this chapter we describe approaches that generate cellular therapies using active immunization with cells, proteins, peptides, or nucleic acids, as well as efforts that use adoptive transfer of effector cells that directly target antigens on malignant cells. Many of these approaches are proving successful in hematologic malignancy and in melanoma. In this chapter we discuss the advantages and limitations of each and how over the next decade investigators will attempt to broaden their reach, increase their efficacy, and simplify their application.

Treatment of lymphoma with adoptively transferred T cells

BACKGROUND

Chemotherapy-resistant lymphomas can be cured with allogeneic hematopoietic cell transplantation, demonstrating the susceptibility of these tumors to T cell mediated immune responses. However, high rates of transplant-related morbidity and mortality limit this approach. Efforts have, therefore, been made to develop alternative T cell based therapies, and there is growing evidence that adoptive therapy with T cells targeted to lymphoma-associated antigens may be a safe and effective new method for treating this group of diseases.

OBJECTIVE/METHODS

We review publications on adoptive therapy with ex vivo expanded T cells targeting viral antigens, as well as genetically modified autologous T cells, as strategies for the treatment of lymphoma, with the goal of providing an overview of these approaches.

RESULTS/CONCLUSIONS

Epstein-Barr virus specific T cell therapy is an effective and safe method of treating Epstein-Barr virus associated lymphomas; however, most lymphoma subtypes do not express EBV antigens. For these diseases, adoptive immunotherapy with genetically modified T cells expressing chimeric T cell receptors targeting lymphoma-associated antigens such as CD19 and CD20 appears to be a promising alternative. Recent innovations including enhanced co-stimulation, exogenous cytokine administration and use of memory T cells promise to overcome many of the limitations and pitfalls initially encountered with this approach.

Long-term outcome of EBV-specific T-cell infusions to prevent or treat EBV-related lymphoproliferative disease in transplant recipients

T-cell immunotherapy that takes advantage of Epstein-Barr virus (EBV)-stimulated immunity has the potential to fill an important niche in targeted therapy for EBV-related cancers. To address questions of long-term efficacy, safety, and practicality, we studied 114 patients who had received infusions of EBV-specific cytotoxic T lymphocytes (CTLs) at 3 different centers to prevent or treat EBV(+) lymphoproliferative disease (LPD) arising after hematopoietic stem cell transplantation. Toxicity was minimal, consisting mainly of localized swelling at sites of responsive disease. None of the 101 patients who received CTL prophylaxis developed EBV(+) LPD, whereas 11 of 13 patients treated with CTLs for biopsy-proven or probable LPD achieved sustained complete remissions. The gene-marking component of this study enabled us to demonstrate the persistence of functional CTLs for up to 9 years. A preliminary analysis indicated that a patient-specific CTL line can be manufactured, tested, and infused for $6095, a cost that compares favorably with other modalities used in the treatment of LPD. We conclude that the CTL lines described here provide safe and effective prophylaxis or treatment for lymphoproliferative disease in transplantation recipients, and the manufacturing methodology is robust and can be transferred readily from one institution to another without loss of reproducibility.

CD4+ T-cell clones recognizing human lymphoma-associated antigens: generation by in vitro stimulation with autologous Epstein-Barr virus-transformed B cells

Epstein-Barr virus (EBV)-specific T-cell preparations, generated by stimulating immune donor lymphocytes with the autologous virus-transformed B-lymphoblastoid cell line (LCL) in vitro, can be used to target EBV-positive malignancies. Although these preparations are enriched for EBV antigen-specific CD8(+) T cells, most also contain a CD4(+) T-cell population whose specificity is unknown. Here, we show that, although CD4(+) T-cell clones derived from such cultures recognize HLA class II-matched LCLs but not mitogen-activated B lymphoblasts, many (1) do not map to any known EBV antigen, (2) can be raised from EBV-naive as well as EBV-immune persons, and (3) can recognize a broad range of human B lymphoma-derived cell lines irrespective of EBV genome status, providing those lines to express the relevant HLA class II-restricting allele. Importantly, such CD4(+) clones not only produce IFNgamma but are also cytotoxic and can control the outgrowth of HLA-matched lymphoma cells in cocultivation assays. We infer that such CD4(+) T cells recognize cellular antigens that are preferentially up-regulated in EBV-transformed but not mitogen-activated B lymphoblasts and that are also expressed in a range of B-cell malignancies. Such antigens are therefore of potential value as targets for CD4(+) T cell-based immunotherapy.