Control of large, established tumor xenografts with genetically retargeted human T cells containing CD28 and CD137 domains. Proc Natl Acad Sci U S A. 2009;106:3360-3365. [PMID: 19211796 DOI: 10.1073/pnas.0813101106]

Dual targeting of ErbB2 and MUC1 in breast cancer using chimeric antigen receptors engineered to provide complementary signaling

PURPOSE

Chimeric antigen receptor (CAR) engineered T-cells occupy an increasing niche in cancer immunotherapy. In this context, CAR-mediated CD3ζ signaling is sufficient to elicit cytotoxicity and interferon-γ production while the additional provision of CD28-mediated signal 2 promotes T-cell proliferation and interleukin (IL)-2 production. This compartmentalisation of signaling opens the possibility that complementary CARs could be used to focus T-cell activation within the tumor microenvironment.

METHODS

Here, we have tested this principle by co-expressing an ErbB2- and MUC1-specific CAR that signal using CD3ζ and CD28 respectively. Stoichiometric co-expression of transgenes was achieved using the SFG retroviral vector containing an intervening Thosea asigna peptide.

RESULTS

We found that "dual-targeted" T-cells kill ErbB2(+) tumor cells efficiently and proliferate in a manner that requires co-expression of MUC1 and ErbB2 by target cells. Notably, however, IL-2 production was modest when compared to control CAR-engineered T-cells in which signaling is delivered by a fused CD28 + CD3ζ endodomain.

CONCLUSIONS

These findings demonstrate the principle that dual targeting may be achieved using genetically targeted T-cells and pave the way for testing of this strategy in vivo.

Mesothelin, a novel immunotherapy target for triple negative breast cancer

Mesothelin is a cell-surface glycoprotein present on mesothelial cells and elicits T cell responses in a variety of cancers including pancreatic, biliary and ovarian cancer. Breast cancer is not known to express mesothelin. We postulated that mesothelin may be a unique tumor-associated antigen in triple negative breast cancer (TNBC), a less common breast cancer subtype which may have been under-represented in prior studies that characterized mesothelin expression. Therefore, we screened 99 primary breast cancer samples by immunohistochemistry analysis using formalin-fixed paraffin-embedded archival tumor tissues and confirmed that mesothelin was overexpressed in the majority of TNBC (67 %) but only rarely in <5 % ER(+) or Her2-neu(+) breast cancer, respectively. To determine whether mesothelin may be exploited as a novel immunotherapy target in breast cancer, an in vitro cell killing assay was performed to compare the ability of genetically modified T cells expressing a chimeric antibody receptor (CAR) specific for mesothelin (mesoCAR T cells) or non-transduced T cells to kill mesothelin-expressing primary breast cancer cells. A significantly higher anti-tumor cytotoxicity by mesoCAR T cells was observed (31.7 vs. 8.7 %, p < 0.001). Our results suggest that mesothelin has promise as a novel immunotherapy target for TNBC for which effective targeted therapy is lacking to date.

Mesothelin-targeted agents in clinical trials and in preclinical development

Mesothelin is a tumor differentiation antigen that is highly expressed in several malignant diseases in humans, including malignant mesothelioma and pancreatic, ovarian, and lung adenocarcinomas. The limited expression of mesothelin on normal human tissues and its high expression in many common cancers make it an attractive candidate for cancer therapy. Several agents, including an immunotoxin, monoclonal antibody, antibody drug conjugate, and tumor vaccine, are in various stages of development to treat patients with mesothelin-expressing tumors. This review highlights ongoing clinical trials, as well as other approaches to exploit mesothelin for cancer therapy, that are in preclinical development.

TCR-transgenic lymphocytes specific for HMMR/Rhamm limit tumor outgrowth in vivo

The hyaluronan-mediated motility receptor (HMMR/Rhamm) is overexpressed in numerous tumor types, including acute lymphoid leukemia and acute myeloid leukemia (AML). Several studies have reported the existence of T-cell responses directed against HMMR in AML patients that are linked to better clinical outcome. Therefore, we explored the use of HMMR-specific TCRs for transgenic expression in lymphocytes and their in vivo impact on HMMR(+) solid tumors and disseminated leukemia. We obtained TCRs via an in vitro priming approach in combination with CD137-mediated enrichment. Recipient lymphocytes expressing transgenic TCR revealed the specific tumor recognition pattern seen with the original T cells. Adoptive transfer experiments using a humanized xenograft mouse model resulted in significantly retarded solid tumor outgrowth, which was enhanced using IL-15-conditioned, TCR-transgenic effector memory cells. These cells also showed an increased potency to retard the outgrowth of disseminated AML, and this was further improved using CD8-enriched effector memory cells. To define a safe clinical setting for HMMR-TCR gene therapy, we analyzed transgenic T-cell recognition of hematopoietic stem cells (HSCs) and found on-target killing of HLA-A2(+) HSCs. Our findings clearly limit the use of HMMR-TCR therapy to MHC- mismatched HSC transplantation, in which HLA-A2 differences can be used to restrict recognition to patient HSCs and leukemia.

Mesothelin overexpression promotes mesothelioma cell invasion and MMP-9 secretion in an orthotopic mouse model and in epithelioid pleural mesothelioma patients

PURPOSE

Mesothelin (MSLN) is a tumor-associated antigen, being investigated as a biomarker and therapeutic target in malignant pleural mesothelioma (MPM). The biologic function of MSLN overexpression in MPM is unknown. We hypothesized that MSLN may promote tumor invasion in MPM, a tumor characterized primarily by regional aggressiveness and rare distant metastases.

EXPERIMENTAL DESIGN

Human and murine MPM cells with MSLN forced expression and short hairpin RNA knockdown were examined for proliferation, invasion, and matrix metalloproteinase (MMP) secretion. The influence of MSLN overexpression on MPM cell invasion was assessed in an orthotopic mouse model and in patient samples.

RESULTS

MSLN expression promotes MPM cell invasion and MMP secretion in both human and murine MPM cells. In an orthotopic MPM mouse model characterized by our laboratory, MPM cells with MSLN overexpression preferentially localized to the tumor invading edge, colocalized with MMP-9 expression, and promoted decreased survival without an increase in tumor burden progression. In a tissue microarray from epithelioid MPM patients (n = 139, 729 cores), MSLN overexpression correlated with higher MMP-9 expression at individual core level. Among stage III MPM patients (n = 72), high MSLN expression was observed in 26% of T2 tumors and 51% of T3 tumors.

CONCLUSIONS

Our data provide evidence elucidating a biologic role for MSLN as a factor promoting tumor invasion and MMP-9 expression in MSLN expressing MPM. As regional invasion is the characteristic feature in MSLN expressing solid cancers (MPM, pancreas, and ovarian), our observations add rationale to studies investigating MSLN as a therapeutic target.

T cells with chimeric antigen receptors have potent antitumor effects and can establish memory in patients with advanced leukemia

Tumor immunotherapy with T lymphocytes, which can recognize and destroy malignant cells, has been limited by the ability to isolate and expand T cells restricted to tumor-associated antigens. Chimeric antigen receptors (CARs) composed of antibody binding domains connected to domains that activate T cells could overcome tolerance by allowing T cells to respond to cell surface antigens; however, to date, lymphocytes engineered to express CARs have demonstrated minimal in vivo expansion and antitumor effects in clinical trials. We report that CAR T cells that target CD19 and contain a costimulatory domain from CD137 and the T cell receptor ζ chain have potent non-cross-resistant clinical activity after infusion in three of three patients treated with advanced chronic lymphocytic leukemia (CLL). The engineered T cells expanded >1000-fold in vivo, trafficked to bone marrow, and continued to express functional CARs at high levels for at least 6 months. Evidence for on-target toxicity included B cell aplasia as well as decreased numbers of plasma cells and hypogammaglobulinemia. On average, each infused CAR-expressing T cell was calculated to eradicate at least 1000 CLL cells. Furthermore, a CD19-specific immune response was demonstrated in the blood and bone marrow, accompanied by complete remission, in two of three patients. Moreover, a portion of these cells persisted as memory CAR(+) T cells and retained anti-CD19 effector functionality, indicating the potential of this major histocompatibility complex-independent approach for the effective treatment of B cell malignancies.

T cells with chimeric antigen receptors have potent antitumor effects and can establish memory in patients with advanced leukemia

Tumor immunotherapy with T lymphocytes, which can recognize and destroy malignant cells, has been limited by the ability to isolate and expand T cells restricted to tumor-associated antigens. Chimeric antigen receptors (CARs) composed of antibody binding domains connected to domains that activate T cells could overcome tolerance by allowing T cells to respond to cell surface antigens; however, to date, lymphocytes engineered to express CARs have demonstrated minimal in vivo expansion and antitumor effects in clinical trials. We report that CAR T cells that target CD19 and contain a costimulatory domain from CD137 and the T cell receptor ζ chain have potent non-cross-resistant clinical activity after infusion in three of three patients treated with advanced chronic lymphocytic leukemia (CLL). The engineered T cells expanded >1000-fold in vivo, trafficked to bone marrow, and continued to express functional CARs at high levels for at least 6 months. Evidence for on-target toxicity included B cell aplasia as well as decreased numbers of plasma cells and hypogammaglobulinemia. On average, each infused CAR-expressing T cell was calculated to eradicate at least 1000 CLL cells. Furthermore, a CD19-specific immune response was demonstrated in the blood and bone marrow, accompanied by complete remission, in two of three patients. Moreover, a portion of these cells persisted as memory CAR(+) T cells and retained anti-CD19 effector functionality, indicating the potential of this major histocompatibility complex-independent approach for the effective treatment of B cell malignancies.

CD20-specific adoptive immunotherapy for lymphoma using a chimeric antigen receptor with both CD28 and 4-1BB domains: pilot clinical trial results

Cellular immune responses have the potential to elicit dramatic and sustained clinical remissions in lymphoma patients. Recent clinical trial data demonstrate that modification of T cells with chimeric antigen receptors (CARs) is a promising strategy. T cells containing CARs with costimulatory domains exhibit improved activity against tumors. We conducted a pilot clinical trial testing a "third-generation" CD20-specific CAR with CD28 and 4-1BB costimulatory domains in patients with relapsed indolent B-cell and mantle cell lymphomas. Four patients were enrolled, and 3 received T-cell infusions after cyclophosphamide lymphodepletion. Treatment was well tolerated, although one patient developed transient infusional symptoms. Two patients without evaluable disease remained progression-free for 12 and 24 months. The third patient had an objective partial remission and relapsed at 12 months after infusions. Modified T cells were detected by quantitative PCR at tumor sites and up to 1 year in peripheral blood, albeit at low levels. No evidence of host immune responses against infused cells was detected. In conclusion, adoptive immunotherapy with CD20-specific T cells was well tolerated and was associated with antitumor activity. We will pursue alternative gene transfer technologies and culture conditions in future studies to improve CAR expression and cell production efficiency.

Muscle CARs and TcRs: turbo-charged technologies for the (T cell) masses

A central role for T cells in the control of cancer has been supported by both animal models and clinical observations. Accordingly, the development of potent anti-tumor T cell immunity has been a long-standing objective of immunotherapy. Emerging data from clinical trials that test T cell immune-modulatory agents and genetically engineered and re-targeted T cells have begun to realize the profound potential of T cell immunotherapy to target cancer. This review will focus on a description of recent conceptual and technological advances for the genetic engineering of T cells to enhance anti-tumor T cell immunity through the introduction of tumor-specific receptors, both Chimeric Antigen Receptors (CAR) and T cell receptors (TcR), as well as an overview of emerging data from ongoing clinical trials that highlight the potential of these approaches to effect dramatic and potent anti-tumor immunity.

Costimulation by chimeric antigen receptors revisited the T cell antitumor response benefits from combined CD28-OX40 signalling

The therapeutic success of adoptive therapy with chimeric antigen receptor (CAR) engineered T cells depends on the appropriate costimulation of CD3ζ to induce full T cell activation. Costimulatory endodomains of the CD28 family are therefore fused with CD3ζ in a dual signalling CAR. Serious adverse events in two most recent trials; however, highlight the need to analyse in more detail the impact of each costimulatory endodomain on individual effector functions of redirected T cells. We therefore performed a thoroughly controlled side-by-side comparison of the most frequently used endodomains with respect to their impact on CD4(+) and CD8(+) T cell effector functions. CD28 reinforced T cell proliferation and is mandatory to induce IL-2. In the absence of added IL-2, CD28 and OX40 (CD137) but not 4-1BB (CD134) enhanced specific cytolysis. While CD28, 4-1BB and OX40 similarly improved pro-inflammatory cytokine secretion, OX40 most efficiently prevented activation induced cell death of CD62L(-) effector memory T cells. CD28 was superior to initiate the T cell response, OX40 and 4-1BB sustained the response in long term with OX40 being most effective. We consequently combined the beneficial functions in a 3rd generation CD28-OX40 CAR which substantially improved the antitumor response without loosing specificity.

Gene therapy for lung neoplasms

Both advanced-stage lung cancer and malignant pleural mesothelioma are associated with a poor prognosis. Advances in treatment regimens for both diseases have had only a modest effect on their progressive course. Gene therapy for thoracic malignancies represents a novel therapeutic approach and has been evaluated in several clinical trials. Strategies have included induction of apoptosis, tumor suppressor gene replacement, suicide gene expression, cytokine-based therapy, various vaccination approaches, and adoptive transfer of modified immune cells. This review considers the clinical results, limitations, and future directions of gene therapy trials for thoracic malignancies.

GUCY2C-targeted cancer immunotherapy: past, present and future

For the last decade, we have focused on guanylyl cyclase C (GUCY2C) as a potentially ideal target antigen for colorectal cancer immunotherapy. GUCY2C is expressed only in intestinal epithelial cells and by nearly 100% of colorectal cancers. We have developed and tested a recombinant adenoviral vector possessing GUCY2C (Ad5-GUCY2C) as a candidate vaccine for colorectal cancer patients. Murine studies have revealed that this vaccine is safe and effective against GUCY2C-expressing targets, and Ad5-GUCY2C is poised for phase I clinical testing in colorectal cancer patients with minimal residual disease. Moreover, we are developing second-generation GUCY2C-targeted therapeutics, including the use of chimeric antigen receptor (CAR)-expressing T cells, for treatment of patients with advanced colorectal cancer for whom Ad5-GUCY2C immunization is not appropriate. Thus, a family of GUCY2C-targeted immunotherapeutics may bridge the gap in effective treatments for the 500,000 patients worldwide who die annually from colorectal cancer.

Emerging biomedical applications of synthetic biology

Synthetic biology aims to create functional devices, systems and organisms with novel and useful functions on the basis of catalogued and standardized biological building blocks. Although they were initially constructed to elucidate the dynamics of simple processes, designed devices now contribute to the understanding of disease mechanisms, provide novel diagnostic tools, enable economic production of therapeutics and allow the design of novel strategies for the treatment of cancer, immune diseases and metabolic disorders, such as diabetes and gout, as well as a range of infectious diseases. In this Review, we cover the impact and potential of synthetic biology for biomedical applications.

Redirected antitumor activity of primary human lymphocytes transduced with a fully human anti-mesothelin chimeric receptor

Cancer regression by gene-modified T cells bearing a chimeric antigen receptor (CAR) exodomain of mouse origin can be limited by the induction of transgene immunogenicity resulting in poor persistence and function in vivo. The development of functionally-active CAR of human origin can address this issue. Here, we constructed and evaluated fully human anti-mesothelin CARs comprised of a human mesothelin-specific single-chain antibody variable fragment (P4 scFv) coupled to T cell signaling domains. Primary human T cells expressing P4 CAR specifically produced proinflammatory cytokines, degranulated and exerted potent cytolytic functions when cultured with mesothelin-expressing tumors in vitro. P4 CAR T cells also mediated bystander killing of mesothelin-negative cancer cells during coculture. CAR reactivity was not abrogated by soluble tumor-secreted or recombinant mesothelin protein even at supraphysiological levels. Importantly, adoptive transfer of P4 CAR-expressing T cells mediated the regression of large, established tumor in the presence of soluble mesothelin in a xenogenic model of human ovarian cancer. Thus, primary human T cells expressing fully human anti-mesothelin CAR efficiently kill mesothelin-expressing tumors in vitro and in vivo and have the potential to overcome the issue of transgene immunogenicity that may limit CAR T cell trials that utilize scFvs of mouse origin.

CD27 costimulation augments the survival and antitumor activity of redirected human T cells in vivo

The costimulatory effects of CD27 on T lymphocyte effector function and memory formation has been confined to evaluations in mouse models, in vitro human cell culture systems, and clinical observations. Here, we tested whether CD27 costimulation actively enhances human T-cell function, expansion, and survival in vitro and in vivo. Human T cells transduced to express an antigen-specific chimeric antigen receptor (CAR-T) containing an intracellular CD3 zeta (CD3ζ) chain signaling module with the CD27 costimulatory motif in tandem exerted increased antigen-stimulated effector functions in vitro, including cytokine secretion and cytotoxicity, compared with CAR-T with CD3ζ alone. After antigen stimulation in vitro, CD27-bearing CAR-T cells also proliferated, up-regulated Bcl-X(L) protein expression, resisted apoptosis, and underwent increased numerical expansion. The greatest impact of CD27 was noted in vivo, where transferred CAR-T cells with CD27 demonstrated heightened persistence after infusion, facilitating improved regression of human cancer in a xenogeneic allograft model. This tumor regression was similar to that achieved with CD28- or 4-1BB-costimulated CARs, and heightened persistence was similar to 4-1BB but greater than CD28. Thus, CD27 costimulation enhances expansion, effector function, and survival of human CAR-T cells in vitro and augments human T-cell persistence and antitumor activity in vivo.

Treatment of advanced leukemia in mice with mRNA engineered T cells

Cytotoxic T lymphocytes (CTLs) modified with chimeric antigen receptors (CARs) for adoptive immunotherapy of hematologic malignancies are effective in preclinical models and are being tested in several clinical trials. Although CTLs bearing stably expressed CARs generated by integrating viral vectors are efficacious and have potential long-term persistence, this mechanism of CAR expression can potentially result in significant toxicity. T cells were electroporated with an optimized in vitro transcribed RNA encoding a CAR against CD19. These RNA CAR CTLs were then tested in vitro and in vivo for efficacy. We found that T cells expressing an anti-CD19 CAR introduced by electroporation with optimized mRNA were potent and specific killers of CD19 target cells. CD19 RNA CAR T cells given to immunodeficient mice bearing xenografted leukemia rapidly migrated to sites of disease and retained significant target-specific lytic activity. Unexpectedly, a single injection of CD19 RNA CAR T cells reduced disease burden within 1 day after administration, resulting in a significant prolongation of survival in an aggressive leukemia xenograft model. The surface expression of the RNA CARs may be titrated, giving T cells with potentially tunable levels of effector functions such as cytokine release and cytotoxicity. RNA CARs are a genetic engineering approach that should not be subject to genotoxicity, and they provide a platform for rapidly optimizing CAR design before proceeding to more costly and laborious stable expression systems.

A human memory T cell subset with stem cell-like properties

Immunological memory is thought to depend on a stem cell-like, self-renewing population of lymphocytes capable of differentiating into effector cells in response to antigen re-exposure. Here we describe a long-lived human memory T cell population that has an enhanced capacity for self-renewal and a multipotent ability to derive central memory, effector memory and effector T cells. These cells, specific to multiple viral and self-tumor antigens, were found within a CD45RO(-), CCR7(+), CD45RA(+), CD62L(+), CD27(+), CD28(+) and IL-7Rα(+) T cell compartment characteristic of naive T cells. However, they expressed large amounts of CD95, IL-2Rβ, CXCR3, and LFA-1, and showed numerous functional attributes distinctive of memory cells. Compared with known memory populations, these lymphocytes had increased proliferative capacity and more efficiently reconstituted immunodeficient hosts, and they mediated superior antitumor responses in a humanized mouse model. The identification of a human stem cell-like memory T cell population is of direct relevance to the design of vaccines and T cell therapies.

Immune responses and immunotherapeutic interventions in malignant pleural mesothelioma

Malignant pleural mesothelioma (MPM) is an aggressive, primary pleural malignancy with poor prognosis, hypothesized to originate from a chronic inflammatory state within the pleura. Similar to what has been observed in other solid tumors (melanoma, ovarian and colorectal cancer), clinical and pre-clinical MPM investigations have correlated anti-tumor immune responses with improved survival. As such, a better understanding of the complex MPM tumor microenvironment is imperative in strategizing successful immunotherapies. Herein, we review the immune responses vital to the development and progression of MPM, as well as assess the role of immunomodulatory therapies, highlighting recent pre-clinical and clinical immunotherapy investigations.

Cytotoxic activity of immunotoxin SS1P is modulated by TACE-dependent mesothelin shedding

Mesothelin is a cell-surface tumor-associated antigen expressed in several human cancers. The limited expression of mesothelin on normal tissues and its high expression in many cancers make it an attractive candidate for targeted therapies using monoclonal antibodies, immunoconjugates, and immunotoxins. Mesothelin is actively shed from the cell surface and is present in the serum of patients with malignant mesothelioma, which could negatively affect the response to these therapies. We have found that mesothelin sheddase activity is mediated by a TNF-α converting enzyme (TACE), a member of the matrix metalloproteinase/a disintegrin and metalloprotease family. We showed that EGF and TIMP-3 act through TACE as endogenous regulators of mesothelin shedding. We also found that reducing shedding significantly improved the in vitro cytotoxicity of immunotoxin SS1P, which targets mesothelin and is currently in clinical trials for the treatment of patients with mesothelioma and lung cancer. Our findings provide a mechanistic understanding of mesothelin shedding and could help improve mesothelin-based targeted therapies.

Gene therapy for mesothelioma

Mesothelioma represents an especially good target for gene therapy since few effective therapies exist, the disease remained relatively localized until late in its course, the tumor can be accessed relatively easily through the chest wall, and the thin layer of mesothelial cells offers a large surface area for efficient, rapid, and diffuse gene transfer. Gene therapy trials in mesothelioma have shown safety, and some limited evidence of efficacy. We present a review of clinical trials that have been performed in mesothelioma and describe several new approaches currently being pursued.

Chimeric antigen receptor-modified T cells in chronic lymphoid leukemia

We designed a lentiviral vector expressing a chimeric antigen receptor with specificity for the B-cell antigen CD19, coupled with CD137 (a costimulatory receptor in T cells [4-1BB]) and CD3-zeta (a signal-transduction component of the T-cell antigen receptor) signaling domains. A low dose (approximately 1.5×10(5) cells per kilogram of body weight) of autologous chimeric antigen receptor-modified T cells reinfused into a patient with refractory chronic lymphocytic leukemia (CLL) expanded to a level that was more than 1000 times as high as the initial engraftment level in vivo, with delayed development of the tumor lysis syndrome and with complete remission. Apart from the tumor lysis syndrome, the only other grade 3/4 toxic effect related to chimeric antigen receptor T cells was lymphopenia. Engineered cells persisted at high levels for 6 months in the blood and bone marrow and continued to express the chimeric antigen receptor. A specific immune response was detected in the bone marrow, accompanied by loss of normal B cells and leukemia cells that express CD19. Remission was ongoing 10 months after treatment. Hypogammaglobulinemia was an expected chronic toxic effect.

Translational advances in pleural malignancies

Pleural malignancies, including primary malignant pleural mesothelioma and secondary pleural metastasis of various tumours resulting in malignant pleural effusion, are frequent and lethal diseases that deserve devoted translational research efforts for improvements to be introduced to the clinic. This paper highlights select clinical advances that have been accomplished recently and that are based on preclinical research on pleural malignancies. Examples are the establishment of folate antimetabolites in mesothelioma treatment, the use of PET in mesothelioma management and the discovery of mesothelin as a marker of mesothelioma. In addition to established translational advances, this text focuses on recent research findings that are anticipated to impact clinical pleural oncology in the near future. Such progress has been substantial, including the development of a genetic mouse model of mesothelioma and of transplantable models of pleural malignancies in immunocompetent hosts, the deployment of stereological and imaging methods for integral assessment of pleural tumour burden, as well as the discovery of the therapeutic potential of aminobiphosphonates, histone deacetylase inhibitors and ribonucleases against malignant pleural disease. Finally, key obstacles to overcome towards a more rapid advancement of translational research in pleural malignancies are outlined. These include the dissection of cell-autonomous and paracrine pathways of pleural tumour progression, the study of mesothelioma and malignant pleural effusion separately from other tumours at both the clinical and preclinical levels, and the expansion of tissue banks and consortia of clinical research of pleural malignancies.

Potential targets for pancreatic cancer immunotherapeutics

Pancreatic adenocarcinoma is the fourth leading cause of cancer death with an overall 5-year survival of less than 5%. As there is ample evidence that pancreatic adenocarcinomas elicit antitumor immune responses, identification of pancreatic cancer-associated antigens has spurred the development of vaccination-based strategies for treatment. While promising results have been observed in animal tumor models, most clinical studies have found only limited success. As most trials were performed in patients with advanced pancreatic cancer, the contribution of immune suppressor mechanisms should be taken into account. In this article, we detail recent work in tumor antigen vaccination and the recently identified mechanisms of immune suppression in pancreatic cancer. We offer our perspective on how to increase the clinical efficacy of vaccines for pancreatic cancer.

Considerations for the clinical application of chimeric antigen receptor T cells: observations from a recombinant DNA Advisory Committee Symposium held June 15, 2010

T cells that are genetically modified to express single-chain chimeric antigen receptors (CAR) have shown promise in early cancer immunotherapy clinical trials. Unfortunately, 2 recent deaths in cancer patients treated with CAR T cells have created some uncertainty on how to best mitigate patient risk, while continuing to advance this very promising therapeutic avenue. In order to address these concerns, the Recombinant DNA Advisory Committee (RAC) held a symposium, the objectives of which were to first review the reported treatment-associated toxicities and, second, to discuss methods for improving safety and efficacy. This report highlights the issues raised as part of this discussion, with a specific focus on protocols infusing CAR T cells. Because this was not a consensus conference, the opinions described should not be construed to represent those of any individual RAC member, the RAC as a body, conference participants, the National Institutes of Health, or the U.S. Food and Drug Administration.

Engineered T cells for the adoptive therapy of B-cell chronic lymphocytic leukaemia

B-cell chronic lymphocytic leukaemia (B-CLL) remains an incurable disease due to the high risk of relapse, even after complete remission, raising the need to control and eliminate residual tumor cells in long term. Adoptive T cell therapy with genetically engineered specificity is thought to fulfil expectations, and clinical trials for the treatment of CLL are initiated. Cytolytic T cells from patients are redirected towards CLL cells by ex vivo engineering with a chimeric antigen receptor (CAR) which binds to CD19 on CLL cells through an antibody-derived domain and triggers T cell activation through CD3ζ upon tumor cell engagement. Redirected T cells thereby target CLL cells in an MHC-unrestricted fashion, secret proinflammatory cytokines, and eliminate CD19(+) leukaemia cells with high efficiency. Cytolysis of autologous CLL cells by patient's engineered T cells is effective, however, accompanied by lasting elimination of healthy CD19(+) B-cells. In this paper we discuss the potential of the strategy in the treatment of CLL, the currently ongoing trials, and the future challenges in the adoptive therapy with CAR-engineered T cells.

In vivo persistence, tumor localization, and antitumor activity of CAR-engineered T cells is enhanced by costimulatory signaling through CD137 (4-1BB)

Human T cells engineered to express a chimeric antigen receptor (CAR) specific for folate receptor-α (FRα) have shown robust antitumor activity against epithelial cancers in vitro but not in the clinic because of their inability to persist and home to tumor in vivo. In this study, CARs were constructed containing a FRα-specific scFv (MOv19) coupled to the T-cell receptor CD3ζ chain signaling module alone (MOv19-ζ) or in combination with the CD137 (4-1BB) costimulatory motif in tandem (MOv19-BBζ). Primary human T cells transduced to express conventional MOv19-ζ or costimulated MOv19-BBζ CARs secreted various proinflammatory cytokines, and exerted cytotoxic function when cocultured with FRα(+) tumor cells in vitro. However, only transfer of human T cells expressing the costimulated MOv19-BBζ CAR mediated tumor regression in immunodeficient mice bearing large, established FRα(+) human cancer. MOv19-BBζ CAR T-cell infusion mediated tumor regression in models of metastatic intraperitoneal, subcutaneous, and lung-involved human ovarian cancer. Importantly, tumor response was associated with the selective survival and tumor localization of human T cells in vivo and was only observed in mice receiving costimulated MOv19-BBζ CAR T cells. T-cell persistence and antitumor activity were primarily antigen-driven; however, antigen-independent CD137 signaling by CAR improved T-cell persistence but not antitumor activity in vivo. Our results show that anti-FRα CAR outfitted with CD137 costimulatory signaling in tandem overcome issues of T-cell persistence and tumor localization that limit the conventional FRα T-cell targeting strategy to provide potent antitumor activity in vivo.

Improving clinical outcomes using adoptively transferred immune cells from umbilical cord blood

Because of the necessary immunodepletion prior to cord blood transplantation as well as the immaturity of cord blood immune cells, recipients experience a high incidence of viral infection in addition to complications observed after hematopoietic stem cell transplantation, such as relapse and graft-versus-host disease. We describe current immunotherapeutic approaches to treating these complications, including the generation of antigen-specific T cells from cord blood, redirecting cord blood T cells using chimeric antigen receptors, and generating cord blood-derived natural killer cells and regulatory T cells.

Expression of a functional CCR2 receptor enhances tumor localization and tumor eradication by retargeted human T cells expressing a mesothelin-specific chimeric antibody receptor

PURPOSE

Adoptive T-cell immunotherapy with tumor infiltrating lymphocytes or genetically-modified T cells has yielded dramatic results in some cancers. However, T cells need to traffic properly into tumors to adequately exert therapeutic effects.

EXPERIMENTAL DESIGN

The chemokine CCL2 was highly secreted by malignant pleural mesotheliomas (MPM; a planned tumor target), but the corresponding chemokine receptor (CCR2) was minimally expressed on activated human T cells transduced with a chimeric antibody receptor (CAR) directed to the MPM tumor antigen mesothelin (mesoCAR T cells). The chemokine receptor CCR2b was thus transduced into mesoCAR T cells using a lentiviral vector, and the modified T cells were used to treat established mesothelin-expressing tumors.

RESULTS

CCR2b transduction led to CCL2-induced calcium flux and increased transmigration, as well as augmentation of in vitro T-cell killing ability. A single intravenous injection of 20 million mesoCAR + CCR2b T cells into immunodeficient mice bearing large, established tumors (without any adjunct therapy) resulted in a 12.5-fold increase in T-cell tumor infiltration by day 5 compared with mesoCAR T cells. This was associated with significantly increased antitumor activity.

CONCLUSIONS

CAR T cells bearing a functional chemokine receptor can overcome the inadequate tumor localization that limits conventional CAR targeting strategies and can significantly improve antitumor efficacy in vivo.

Targeted cytotoxic therapy: adapting a rapidly progressing anticancer paradigm for depletion of persistent HIV-infected cell reservoirs

PURPOSE OF REVIEW

HIV-infected cells persisting in the face of highly active antiretroviral therapy are arguably the greatest hurdle to eradication of the virus from the body. Complementary strategies aimed at selective killing of infected cells are described.

RECENT FINDINGS

Pioneered by research in the cancer field, various approaches are under development for selective killing of HIV-infected cells. These include targeted cytotoxic proteins, adoptive cell therapy, cytocidal virotherapy, and targeted nonbiological drug carriers.

SUMMARY

These developmental efforts may provide a critical complement to antiretroviral therapy in efforts to achieve HIV eradication, or a 'functional cure' whereby therapy can be stopped without viral rebound.

CD28 costimulation improves expansion and persistence of chimeric antigen receptor-modified T cells in lymphoma patients

Targeted T cell immunotherapies using engineered T lymphocytes expressing tumor-directed chimeric antigen receptors (CARs) are designed to benefit patients with cancer. Although incorporation of costimulatory endodomains within these CARs increases the proliferation of CAR-redirected T lymphocytes, it has proven difficult to draw definitive conclusions about the specific effects of costimulatory endodomains on the expansion, persistence, and antitumor effectiveness of CAR-redirected T cells in human subjects, owing to the lack of side-by-side comparisons with T cells bearing only a single signaling domain. We therefore designed a study that allowed us to directly measure the consequences of adding a costimulatory endodomain to CAR-redirected T cells. Patients with B cell lymphomas were simultaneously infused with 2 autologous T cell products expressing CARs with the same specificity for the CD19 antigen, present on most B cell malignancies. One CAR encoded both the costimulatory CD28 and the ζ-endodomains, while the other encoded only the ζ-endodomain. CAR+ T cells containing the CD28 endodomain showed strikingly enhanced expansion and persistence compared with CAR+ T cells lacking this endodomain. These results demonstrate the superiority of CARs with dual signal domains and confirm a method of comparing CAR-modified T cells within individual patients, thereby avoiding patient-to-patient variability and accelerating the development of optimal T cell immunotherapies.

Chimeric antigen receptor (CAR)-engineered lymphocytes for cancer therapy

INTRODUCTION

Chimeric antigen receptors (CARs) usually combine the antigen binding site of a monoclonal antibody with the signal activating machinery of a T cell, freeing antigen recognition from MHC restriction and thus breaking one of the barriers to more widespread application of cellular therapy. Similar to treatment strategies employing monoclonal antibodies, T cells expressing CARs are highly targeted, but additionally offer the potential benefits of active trafficking to tumor sites, in vivo expansion and long-term persistence. Furthermore, gene transfer allows the introduction of countermeasures to tumor immune evasion and of safety mechanisms.

AREAS COVERED

The basic structure of so-called first and later generation CARs and their potential advantages over other immune therapy systems. How these molecules can be grafted into immune cells (including retroviral and non-retroviral transduction methods) and strategies to improve the in vivo persistence and function of immune cells expressing CARs. Examples of tumor-associated antigens that have been targeted in preclinical models and clinical experience with these modified cells. Safety issues surrounding CAR gene transfer into T cells and potential solutions to them.

EXPERT OPINION

Because of recent advances in immunology, genetics and cell processing, CAR-modified T cells will likely play an increasing role in the cellular therapy of cancer, chronic infections and autoimmune disorders.

Adoptive immunotherapy of cancer: Gene transfer of T cell specificity

Adoptive transfer of tumor-reactive T cells has emerged as a promising advance in tumor immunotherapy. Specifically, infusion of tumor-infiltrating lymphocytes has led to long-term objective clinical responses for patients with metastatic melanoma. Donor lymphocyte infusion is also an effective treatment of post-transplant lymphoproliferative disease. However, adoptive T cell therapy has restrictions in the isolation and expansion of antigen-specific lymphocytes for a large group of patients. One approach to circumvent this limitation and extend adoptive immunotherapy to other cancer types is the genetic modification of T cells with antigen-specific receptors. In this article, we review strategies to redirect T cell specificity, including T cell receptor gene transfer and antibody receptor gene transfer.

The inducible costimulator (ICOS) is critical for the development of human T(H)17 cells

Human T helper 17 (T(H)17) cells regulate host defense, autoimmunity, and tumor immunity. Although cytokines that control human T(H)17 cell development have been identified, the costimulatory molecules important for T(H)17 cell generation are unknown. Here, we found that the inducible costimulator (ICOS) was critical for the differentiation and expansion of human T(H)17 cells. Human cord blood contained a subset of CD161(+)CD4(+) T cells that were recent emigrants from the thymus, expressed ICOS constitutively, and were imprinted as T(H)17 cells through ICOS signaling. ICOS stimulation induced c-MAF, RORC2, and T-bet expression in these cells, leading to increased secretion of interleukin-21 (IL-21), IL-17, and interferon-γ (IFN-γ) compared with cells stimulated with CD28. Conversely, CD28 ligation abrogated ICOS costimulation, dampening RORC2 expression while promoting the expression of the aryl hydrocarbon receptor, which led to reduced secretion of IL-17 and enhanced production of IL-22 compared with cells stimulated with ICOS. Moreover, ICOS promoted the robust expansion of IL-17(+)IFN-γ(+) human T cells, and the antitumor activity of these cells after adoptive transfer into mice bearing large human tumors was superior to that of cells expanded with CD28. The therapeutic effectiveness of ICOS-expanded cells was associated with enhanced functionality and engraftment in vivo. These findings reveal a vital role for ICOS signaling in the generation and maintenance of human T(H)17 cells and suggest that components of this pathway could be therapeutically targeted to treat cancer or chronic infection and, conversely, that interruption of this pathway may have utility in multiple sclerosis and other autoimmune syndromes. These findings have provided the rationale for designing new clinical trials for tumor immunotherapy.

T-cell engineering for cancer immunotherapy

The adoptive transfer of tumor-reactive cells is a promising approach for the treatment of melanoma and some other cancers. To remedy the difficulties associated with the isolation and expansion of tumor-reactive T cells in most cancer patients, peripheral blood T cells can be retargeted to any chosen tumor antigen by the genetic transfer of an antigen-specific receptor. The transduced receptors may be human leukocyte antigen-restricted, heterodimeric T-cell antigen receptor (TCRs), or chimeric antigen receptors (CARs), which typically recognize native cell-surface antigens. Considerable progress has been made in recent years to address the challenges posed by the transfer of either receptor type. Vector and protein modifications enable the expression of TCR chains in human T cells at functional levels and with a reduced risk of mis-pairing with endogenous TCR chains. The combinatorial inclusion of activating and costimulatory domains in CARs has dramatically enhanced the signaling properties of the chimeric receptors described over a decade ago. Based on the effective T-cell transduction and expansion procedures now available to support clinical investigation, improved designer TCRs and second generation CARs targeting an array of antigens are being evaluated in a range of hematological malignancies and solid tumors.

Targeted treatment of recurrent platinum-resistant ovarian cancer: current and emerging therapies

With advances in surgical techniques and chemotherapeutic agents, mortality rates from epithelial ovarian cancer (EOC) have slightly decreased over the last 30 years. However, EOC still ranks as the most deadly gynecologic cancer with an overall 5-year survival rate of 45%. Prognosis is especially disappointing for women with platinum-resistant disease, where 80% of patients will fail to respond to available therapies. Emerging treatment strategies have sub-sequently focused on targets which are integral to tumor growth and metastasis. In this review, we will focus on those innovative agents currently under investigation in clinical trials.

Polyfunctional T-cell responses are disrupted by the ovarian cancer ascites environment and only partially restored by clinically relevant cytokines

Background

Host T-cell responses are associated with favorable outcomes in epithelial ovarian cancer (EOC), but it remains unclear how best to promote these responses in patients. Toward this goal, we evaluated a panel of clinically relevant cytokines for the ability to enhance multiple T-cell effector functions (polyfunctionality) in the native tumor environment.

Methodology/Principal Findings

Experiments were performed with resident CD8+ and CD4+ T cells in bulk ascites cell preparations from high-grade serous EOC patients. T cells were stimulated with α-CD3 in the presence of 100% autologous ascites fluid with or without exogenous IL-2, IL-12, IL-18 or IL-21, alone or in combination. T-cell proliferation (Ki-67) and function (IFN-γ, TNF-α, IL-2, CCL4, and CD107a expression) were assessed by multi-parameter flow cytometry. In parallel, 27 cytokines were measured in culture supernatants. While ascites fluid had variable effects on CD8+ and CD4+ T-cell proliferation, it inhibited T-cell function in most patient samples, with CD107a, IFN-γ, and CCL4 showing the greatest inhibition. This was accompanied by reduced levels of IL-1β, IL-1ra, IL-9, IL-17, G-CSF, GM-CSF, Mip-1α, PDGF-bb, and bFGF in culture supernatants. T-cell proliferation was enhanced by exogenous IL-2, but other T-cell functions were largely unaffected by single cytokines. The combination of IL-2 with cytokines engaging complementary signaling pathways, in particular IL-12 and IL-18, enhanced expression of IFN-γ, TNF-α, and CCL4 in all patient samples by promoting polyfunctional T-cell responses. Despite this, other functional parameters generally remained inhibited.

Conclusions/Significance

The EOC ascites environment disrupts multiple T-cell functions, and exogenous cytokines engaging diverse signaling pathways only partially reverse these effects. Our results may explain the limited efficacy of cytokine therapies for EOC to date. Full restoration of T-cell function will require activation of signaling pathways beyond those engaged by IL-2, IL-12, IL-18, and IL-21.

Immunotherapy for ovarian cancer: what's next?

In the past decade, we have witnessed important gains in the treatment of ovarian cancer; however, additional advances are required to reduce mortality. With compelling evidence that ovarian cancers are immunogenic tumors, immunotherapy should be further pursued and optimized. The dramatic advances in laboratory and clinical procedures in cellular immunotherapy, along with the development of powerful immunomodulatory antibodies, create new opportunities in ovarian cancer therapeutics. Herein, we review current progress and future prospects in vaccine and adoptive T-cell therapy development as well as immunomodulatory therapy tools available for immediate clinical testing.

Gene therapy using genetically modified lymphocytes targeting VEGFR-2 inhibits the growth of vascularized syngenic tumors in mice

Immunotherapies based on adoptive cell transfer are highly effective in the treatment of metastatic melanoma, but the use of this approach in other cancer histologies has been hampered by the identification of appropriate target molecules. Immunologic approaches targeting tumor vasculature provide a means for the therapy of multiple solid tumor types. We developed a method to target tumor vasculature, using genetically redirected syngeneic or autologous T cells. Mouse and human T cells were engineered to express a chimeric antigen receptor (CAR) targeted against VEGFR-2, which is overexpressed in tumor vasculature and is responsible for VEGF-mediated tumor progression and metastasis. Mouse and human T cells expressing the relevant VEGFR-2 CARs mediated specific immune responses against VEGFR-2 protein as well as VEGFR-2-expressing cells in vitro. A single dose of VEGFR-2 CAR-engineered mouse T cells plus exogenous IL-2 significantly inhibited the growth of 5 different types of established, vascularized syngeneic tumors in 2 different strains of mice and prolonged the survival of mice. T cells transduced with VEGFR-2 CAR showed durable and increased tumor infiltration, correlating with their antitumor effect. This approach provides a potential method for the gene therapy of a variety of human cancers.

Multiple injections of electroporated autologous T cells expressing a chimeric antigen receptor mediate regression of human disseminated tumor

Redirecting T lymphocyte antigen specificity by gene transfer can provide large numbers of tumor-reactive T lymphocytes for adoptive immunotherapy. However, safety concerns associated with viral vector production have limited clinical application of T cells expressing chimeric antigen receptors (CAR). T lymphocytes can be gene modified by RNA electroporation without integration-associated safety concerns. To establish a safe platform for adoptive immunotherapy, we first optimized the vector backbone for RNA in vitro transcription to achieve high-level transgene expression. CAR expression and function of RNA-electroporated T cells could be detected up to a week after electroporation. Multiple injections of RNA CAR-electroporated T cells mediated regression of large vascularized flank mesothelioma tumors in NOD/scid/γc(-/-) mice. Dramatic tumor reduction also occurred when the preexisting intraperitoneal human-derived tumors, which had been growing in vivo for >50 days, were treated by multiple injections of autologous human T cells electroporated with anti-mesothelin CAR mRNA. This is the first report using matched patient tumor and lymphocytes showing that autologous T cells from cancer patients can be engineered to provide an effective therapy for a disseminated tumor in a robust preclinical model. Multiple injections of RNA-engineered T cells are a novel approach for adoptive cell transfer, providing flexible platform for the treatment of cancer that may complement the use of retroviral and lentiviral engineered T cells. This approach may increase the therapeutic index of T cells engineered to express powerful activation domains without the associated safety concerns of integrating viral vectors.

Pluripotent stem cell-derived natural killer cells for cancer therapy

Human embryonic stem cells (hESCs) and induced pluripotent stem cells (iPSCs) provide an accessible, genetically tractable, and homogenous starting cell population to efficiently study human blood cell development. These cell populations provide platforms to develop new cell-based therapies to treat both malignant and nonmalignant hematological diseases. Our group previously demonstrated the ability of hESC-derived hematopoietic precursors to produce functional natural killer (NK) cells as well as an explanation of the underlying mechanism responsible for the inefficient development of T and B cells from hESCs. hESCs and iPSCs, which can be engineered reliably in vitro, provide an important new model system to study human lymphocyte development and produce enhanced cell-based therapies with the potential to serve as a "universal" source of antitumor lymphocytes. This review will focus on the application of hESC-derived NK cells with currently used and novel therapeutics for clinical trials, barriers to translation, and future applications through genetic engineering approaches.

Epitope distance to the target cell membrane and antigen size determine the potency of T cell-mediated lysis by BiTE antibodies specific for a large melanoma surface antigen

Melanoma chondroitin sulfate proteoglycan (MCSP; also called CSPG4, NG2, HMW-MAA, MSK16, MCSPG, MEL-CSPG, or gp240) is a surface antigen frequently expressed on human melanoma cells, which is involved in cell adhesion, invasion and spreading, angiogenesis, complement inhibition, and signaling. MCSP has therefore been frequently selected as target antigen for development of antibody- and vaccine-based therapeutic approaches. We have here used a large panel of monoclonal antibodies against human MCSP for generation of single-chain MCSP/CD3-bispecific antibodies of the BiTE (for bispecific T cell engager) class. Despite similar binding affinity to MCSP, respective BiTE antibodies greatly differed in their potency of redirected lysis of CHO cells stably transfected with full-length human MCSP, or with various MCSP deletion mutants and fusion proteins. BiTE antibodies binding to the membrane proximal domain D3 of MCSP were more potent than those binding to more distal domains. This epitope distance effect was corroborated with EpCAM/CD3-bispecific BiTE antibody MT110 by testing various fusion proteins between MCSP and EpCAM as surface antigens. CHO cells expressing small surface target antigens were generally better lysed than those expressing larger target antigens, indicating that antigen size was also an important determinant for the potency of BiTE antibody. The present study for the first time relates the positioning of binding domains and size of surface antigens to the potency of target cell lysis by BiTE-redirected cytotoxic T cells. In case of the MCSP antigen, this provides the basis for selection of a maximally potent BiTE antibody candidate for development of a novel melanoma therapy.

NCI First International Workshop on The Biology, Prevention and Treatment of Relapse after Allogeneic Hematopoietic Cell Transplantation: report from the committee on prevention of relapse following allogeneic cell transplantation for hematologic malignancies

Prevention of relapse after allogeneic hematopoietic stem cell transplantation is the most likely approach to improve survival of patients treated for hematologic malignancies. Herein we review the limits of currently available transplant therapies and the innovative strategies being developed to overcome resistance to therapy or to fill therapeutic modalities not currently available. These novel strategies include nonimmunologic therapies, such as targeted preparative regimens and posttransplant drug therapy, as well as immunologic interventions, including graft engineering, donor lymphocyte infusions, T cell engineering, vaccination, and dendritic cell-based approaches. Several aspects of the biology of the malignant cells as well as the host have been identified that obviate success of even these newer strategies. To maximize the potential for success, we recommend pursuing research to develop additional targeted therapies to be used in the preparative regimen or as maintenance posttransplant, better characterize the T cell and dendritic cells subsets involved in graft-versus-host disease and the graft-versus-leukemia/tumor effect, identify strategies for timing immunologic or nonimmunologic therapies to eliminate the noncycling cancer stem cell, identify more targets for immunotherapies, develop new vaccines that will not be limited by HLA, and develop methods to identify populations at very high risk for relapse to accelerate clinical development and avoid toxicity in patients not at risk for relapse.