Clinical Grade Manufacture of CYAD-101, a NKG2D-based, First in Class, Non-Gene-edited Allogeneic CAR T-Cell Therapy

Allogeneic chimeric antigen receptor (CAR) T holds the promise of taking this therapeutic approach to broader patient populations while avoiding the intensive manufacturing demands of autologous cell products. One limitation to delivering an allogeneic CAR T is T-cell receptor (TCR) driven toxicity. In this work, the expression of a peptide to interfere with TCR signaling was assessed for the generation of allogeneic CAR T cells. The expression of a truncated CD3ζ peptide was shown to incorporate into the TCR complex and to result in blunted TCR responses. When coexpressed with a natural killer group 2D (NKG2D) CAR, the allogeneic T cells (called CYAD-101) failed to induce graft-versus-host disease in mouse models while maintaining antitumor activity driven by the CAR in vitro and in vivo. Two clinical grade discrete batches of CYAD-101 cells were produced of single donor apheresis resulting in 48 billion CAR T cells sufficient for the entire dose-escalation phase of the proposed clinical trial. The 2 batches showed high consistency producing a predominantly CD4+ T-cell population that displayed an effector/central memory phenotype with no evidence of exhaustion markers expression. These clinical grade CYAD-101 cells secreted cytokines and chemokines in response to ligands expressing target cells in vitro, demonstrating effector function through the CAR. Moreover, CYAD-101 cells failed to respond to TCR stimulation, indicating a lack of allogeneic potential. This bank of clinical grade, non-gene-edited, allogeneic CYAD-101 cells are used in the alloSHRINK clinical trial (NCT03692429).

Chimeric Antigen Receptor-T Cells for Targeting Solid Tumors: Current Challenges and Existing Strategies

Chimeric antigen receptor-T cells (CAR-Ts) are an exciting new cancer treatment modality exemplified by the recent regulatory approval of two CD19-targeted CAR-T therapies for certain B cell malignancies. However, this success in the hematological setting has yet to translate to a significant level of objective clinical responses in the solid tumor setting. The reason for this lack of translation undoubtedly lies in the substantial challenges raised by solid tumors to all therapies, including CAR-T, that differ from B cell malignancies. For instance, intravenously infused CAR-Ts are likely to make rapid contact with cancerous B cells since both tend to reside in the same vascular compartments within the body. By contrast, solid cancers tend to form discrete tumor masses with an immune-suppressive tumor microenvironment composed of tumor cells and non-tumor stromal cells served by abnormal vasculature that restricts lymphocyte infiltration and suppresses immune function, expansion, and persistence. Moreover, the paucity of uniquely and homogeneously expressed tumor antigens and inherent plasticity of cancer cells provide major challenges to the specificity, potency, and overall effectiveness of CAR-T therapies. This review focuses on the major preclinical and clinical strategies currently being pursued to tackle these challenges in order to drive the success of CAR-T therapy against solid tumors.

Overcoming Target Driven Fratricide for T Cell Therapy

Chimeric Antigen Receptor (CAR) T cells expressing the fusion of the NKG2D protein with CD3ζ (NKG2D-CAR T Cells) acquire a specificity for stress-induced ligands expressed on hematological and solid cancers. However, these stress ligands are also transiently expressed by activated T cells implying that NKG2D-based T cells may undergo self-killing (fratricide) during cell manufacturing or during the freeze thaw cycle prior to infusion in patients. To avoid target-driven fratricide and enable the production of NKG2D-CAR T cells for clinical application, two distinct approaches were investigated. The first focused upon the inclusion of a Phosphoinositol-3-Kinase inhibitor (LY294002) into the production process. A second strategy involved the inclusion of antibody blockade of NKG2D itself. Both processes impacted T cell fratricide, albeit at different levels with the antibody process being the most effective in terms of cell yield. While both approaches generated comparable NKG2D-CAR T cells, there were subtle differences, for example in differentiation status, that were fine-tuned through the phasing of the inhibitor and antibody during culture in order to generate a highly potent NKG2D-CAR T cell product. By means of targeted inhibition of NKG2D expression or generic inhibition of enzyme function, target-driven CAR T fratricide can be overcome. These strategies have been incorporated into on-going clinical trials to enable a highly efficient and reproducible manufacturing process for NKG2D-CAR T cells.

Phase I Trial of Autologous CAR T Cells Targeting NKG2D Ligands in Patients with AML/MDS and Multiple Myeloma

NKG2D ligands are widely expressed in solid and hematologic malignancies but absent or poorly expressed on healthy tissues. We conducted a phase I dose-escalation study to evaluate the safety and feasibility of a single infusion of NKG2D-chimeric antigen receptor (CAR) T cells, without lymphodepleting conditioning in subjects with acute myeloid leukemia/myelodysplastic syndrome or relapsed/refractory multiple myeloma. Autologous T cells were transfected with a γ-retroviral vector encoding a CAR fusing human NKG2D with the CD3ζ signaling domain. Four dose levels (1 × 10⁶-3 × 10⁷ total viable T cells) were evaluated. Twelve subjects were infused [7 acute myeloid leukemia (AML) and 5 multiple myeloma]. NKG2D-CAR products demonstrated a median 75% vector-driven NKG2D expression on CD3⁺ T cells. No dose-limiting toxicities, cytokine release syndrome, or CAR T cell-related neurotoxicity was observed. No significant autoimmune reactions were noted, and none of the ≥ grade 3 adverse events were attributable to NKG2D-CAR T cells. At the single injection of low cell doses used in this trial, no objective tumor responses were observed. However, hematologic parameters transiently improved in one subject with AML at the highest dose, and cases of disease stability without further therapy or on subsequent treatments were noted. At 24 hours, the cytokine RANTES increased a median of 1.9-fold among all subjects and 5.8-fold among six AML patients. Consistent with preclinical studies, NKG2D-CAR T cell-expansion and persistence were limited. Manufactured NKG2D-CAR T cells exhibited functional activity against autologous tumor cells in vitro, but modifications to enhance CAR T-cell expansion and target density may be needed to boost clinical activity.

A Syngeneic Mouse B-Cell Lymphoma Model for Pre-Clinical Evaluation of CD19 CAR T Cells

The astonishing clinical success of CD19 chimeric antigen receptor (CAR) T-cell therapy has led to the approval of two second generation chimeric antigen receptors (CARs) for acute lymphoblastic leukemia (ALL) andnon-Hodgkin lymphoma (NHL). The focus of the field is now on emulating these successes in other hematological malignancies where less impressive complete response rates are observed. Further engineering of CAR T cells or co-administration of other treatment modalities may successfully overcome obstacles to successful therapy in other cancer settings.

We therefore present a model in which others can conduct pre-clinical testing of CD19 CAR T cells. Results in this well tested B-cell lymphoma model are likely to be informative CAR T-cell therapy in general.

This protocol allows the reproducible production of mouse CAR T cells through calcium phosphate transfection of Plat-E producer cells with MP71 retroviral constructs and pCL-Eco packaging plasmid followed by collection of secreted retroviral particles and transduction using recombinant human fibronectin fragment and centrifugation. Validation of retroviral transduction, and confirmation of the ability of CAR T cells to kill target lymphoma cells ex vivo, through the use of flow cytometry, luminometry and enzyme-linked immunosorbent assay (ELISA), is also described.

Protocols for testing CAR T cells in vivo in lymphoreplete and lymphodepleted syngeneic mice, bearing established, systemic lymphoma are described. Anti-cancer activity is monitored by in vivo bioluminescence and disease progression. We show typical results of eradication of established B-cell lymphoma when utilizing 1^st or 2^nd generation CARs in combination with lymphodepleting pre-conditioning and a minority of mice achieving long term remissions when utilizing CAR T cells expressing IL-12 in lymphoreplete mice.

These protocols can be used to evaluate CD19 CAR T cells with different additional modification, combinations of CAR T cells and other therapeutic agents or adapted for the use of CAR T cells against different target antigens.

Ex vivo expanded tumour-infiltrating lymphocytes from ovarian cancer patients release anti-tumour cytokines in response to autologous primary ovarian cancer cells

Epithelial ovarian cancer (EOC) is the leading cause of gynaecological cancer-related death in Europe. Although most patients achieve an initial complete response with first-line treatment, recurrence occurs in more than 80% of cases. Thus, there is a clear unmet need for novel second-line treatments. EOC is frequently infiltrated with T lymphocytes, the presence of which has been shown to be associated with improved clinical outcomes. Adoptive T-cell therapy (ACT) using ex vivo-expanded tumour-infiltrating lymphocytes (TILs) has shown remarkable efficacy in other immunogenic tumours, and may represent a promising therapeutic strategy for EOC. In this preclinical study, we investigated the efficacy of using anti-CD3/anti-CD28 magnetic beads and IL-2 to expand TILs from freshly resected ovarian tumours. TILs were expanded for up to 3 weeks, and then subjected to a rapid-expansion protocol (REP) using irradiated feeder cells. Tumours were collected from 45 patients with EOC and TILs were successfully expanded from 89.7% of biopsies. Expanded CD4⁺ and CD8⁺ subsets demonstrated features associated with memory phenotypes, and had significantly higher expression of key activation and functional markers than unexpanded TILs. Expanded TILs produced anti-tumour cytokines when co-cultured with autologous tumour cells, inferring tumour cytotoxicity. Our findings demonstrate that it is possible to re-activate and expand tumour-reactive T cells from ovarian tumours. This presents a promising immunotherapy that could be used sequentially or in combination with current therapeutic strategies.

Abstract CT123: A phase I study assessing the safety and clinical activity of multiple doses of a NKG2D-based CAR-T therapy, CYAD-01, administered concurrently with the neoadjuvant FOLFOX treatment in patients with potentially resectable liver metastases from colorectal cancer

We recently developed a novel chimeric antigen receptor (CAR) T-cell therapy, called CYAD-01 (a.k.a. NKR-2), incorporating the full-length human natural killer receptor NKG2D fused with the human CD3 zeta signaling domain, which associates with the adaptor molecule DAP10 to provide co-stimulatory signal upon ligand binding. CYAD-01 is currently evaluated in the ongoing THINK study (NCT03018405) without preconditioning therapy in both hematological and solid indications. Classical CAR-Ts has yet to demonstrate positive results in the context of solid tumors. Underlying reasons for this reduced clinical activity include the need to extravasate from the peripheral circulation, infiltrate into the tumor and overcome the hostile immune suppressive tumor microenvironment (TME) to deliver anti-tumor effector responses. To address the challenge related to the immunosuppressive TME, the SHRINK trial (Standard cHemotherapy Regimen and Immunotherapy with NKR-2) has been developed to assess the safety and clinical activity of multiple infusion CYAD-01 treatment (every 2 weeks x 3 infusions) in patients undergoing standard-of-care FOLFOX (Folinic acid, Fluorouracil (5-FU) and Oxaliplatin) chemotherapy, as neoadjuvant treatment, for the treatment of colorectal metastatic disease with potentially resectable metastases (NCT03310008). The FOLFOX treatment is given every two weeks for six cycles and CYAD-01 cells are infused shortly after chemotherapy on cycles 3, 4 and 5. This concurrent administration of chemotherapy and CYAD-01 treatments would not only (i) favor infiltration into the immunosuppressive TME due to the effect of chemotherapy on TME and cancer cells but also (ii) provide an opportunity for the CYAD-01 cells to better engraft due to the lymphodepletion induced by the standard chemotherapy administration, and likely (iii) increase the NKG2D ligand expression in tumor tissues targeted by CYAD-01, even in patients presenting heterogeneity and/or low ligand expression. The study contains two consecutive segments. The dose escalation segment will enroll 9 patients and will evaluate 3 dose levels of CYAD-01 (1x108, 3x108 and 1x109 CYAD-01 per injection) following a 3+3 design. The expansion segment will then enroll 21 additional patients to further evaluate the safety and potential signs of activity of the CYAD-01 therapy when administered concurrently with chemotherapy. Peripheral blood samples, as well as tumor biopsies from patients at baseline and at resection, will be collected to determine, among others, CYAD-01 persistence, NKG2D ligand expression and systemic cytokine levels in peripheral blood post-infusion.

Citation Format: Caroline Lonez, Alain Hendlisz, Leila Shaza, Philippe Aftimos, Ahmad Awada, Jean-Pascal H. Machiels, Marc Van Den Eynde, Jean-Luc Canon, Javier Carrasco, Bikash Verma, David E. Gilham, Frédéric F. Lehmann. A phase I study assessing the safety and clinical activity of multiple doses of a NKG2D-based CAR-T therapy, CYAD-01, administered concurrently with the neoadjuvant FOLFOX treatment in patients with potentially resectable liver metastases from colorectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr CT123.

Abstract CT134: A phase I study assessing the safety and clinical activity of multiple hepatic transarterial administrations of a NKG2D-based CAR-T therapy CYAD-01, in patients with unresectable liver metastases from colorectal cancer

We recently developed a novel chimeric antigen receptor (CAR) T-cell therapy, called CYAD-01 (a.k.a. NKR-2), incorporating the full-length human natural killer receptor NKG2D fused with the human CD3 zeta signaling domain, which associates with the adaptor molecule DAP10 to provide co-stimulatory signal upon ligand binding. CYAD-01 is currently evaluated in multiple intravenous administrations in the ongoing THINK study (NCT03018405) in both hematological and solid indications. Classical CAR-Ts has yet to demonstrate positive results in the context of solid tumors. Underlying reasons for this reduced clinical activity include the need to extravasate from the peripheral circulation, infiltrate into the tumor and overcome the hostile immune suppressive tumor microenvironment (TME) to deliver anti-tumor effector responses. To address the challenge related to the difficulty of CAR-T cells to access the site of metastasis, the LINK trial (Locoregional Immunotherapy with NKR-2) has been developed to assess the safety and clinical activity of multiple hepatic transarterial administrations of CYAD-01 treatment (every 2 weeks x 3 infusions) in colorectal cancer patients with unresectable liver metastases (NCT03370198). The hepatic transarterial administration (HTAA) cell therapy may offer the advantage of lower systemic toxicity and higher and more persistent concentration of the infused cells on the TME compared with systemic administration. The difference in blood supply between uninvolved liver parenchyma and metastases may favor CYAD-01 tumor homing. Moreover, based on the potential impact of the CYAD-01 treatment on the host immune system, combined with the tumor antigens spreading induced by its direct anti-cancer cells activity, the CYAD-01 HTAA may boost the adaptive immune response and therefore may control any distant lesion (aboscopal effect). This dose escalation study will use a 3+3 design including 3 dose levels of CYAD-01 (3x108, 1x109 and 3x109 cells per injection) to evaluate the maximum tolerated dose of the CYAD-01 hepatic transarterial administration. Peripheral blood samples, as well as tumor biopsies will be collected to determine systemic CYAD-01 kinetics and within the liver tumor tissues, NKG2D ligand expression and systemic cytokine levels in peripheral blood post-infusion. This study will enroll 12 patients in case of no DLT and is open for recruitment.

Citation Format: Nathalie Braun, Alain Hendlisz, Leila Shaza, Michaël Vouche, Vincent Donckier, Philippe Aftimos, Ahmad Awada, Caroline Lonez, Bikash Verma, David E. Gilham, Frédéric F. Lehmann. A phase I study assessing the safety and clinical activity of multiple hepatic transarterial administrations of a NKG2D-based CAR-T therapy CYAD-01, in patients with unresectable liver metastases from colorectal cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr CT134.

Study protocol for THINK: a multinational open-label phase I study to assess the safety and clinical activity of multiple administrations of NKR-2 in patients with different metastatic tumour types

INTRODUCTION

NKR-2 are autologous T cells genetically modified to express a chimeric antigen receptor (CAR) comprising a fusion of the natural killer group 2D (NKG2D) receptor with the CD3ζ signalling domain, which associates with the adaptor molecule DNAX-activating protein of 10 kDa (DAP10) to provide co-stimulatory signal upon ligand binding. NKG2D binds eight different ligands expressed on the cell surface of many tumour cells and which are normally absent on non-neoplastic cells. In preclinical studies, NKR-2 demonstrated long-term antitumour activity towards a breadth of tumour indications, with maximum efficacy observed after multiple NKR-2 administrations. Importantly, NKR-2 targeted tumour cells and tumour neovasculature and the local tumour immunosuppressive microenvironment and this mechanism of action of NKR-2 was established in the absence of preconditioning.

METHODS AND ANALYSIS

This open-label phase I study will assess the safety and clinical activity of NKR-2 treatment administered three times, with a 2-week interval between each administration in different tumour types. The study will contain two consecutive segments: a dose escalation phase followed by an expansion phase. The dose escalation study involves two arms, one in solid tumours (five specific indications) and one in haematological tumours (two specific indications) and will include three dose levels in each arm: 3×10⁸, 1×10⁹ and 3×10⁹ NKR-2 per injection. On the identification of the recommended dose in the first segment, based on dose-limiting toxicity occurrences, the study will expand to seven different cohorts examining the seven different tumour types separately. Clinical responses will be determined according to standard Response Evaluation Criteria In Solid Tumors (RECIST) criteria for solid tumours or international working group response criteria in haematological tumours.

ETHICS APPROVAL AND DISSEMINATION

Ethical approval has been obtained at all sites. Written informed consent will be taken from all participants. The results of this study will be disseminated through presentation at international scientific conferences and reported in peer-reviewed scientific journals.

TRIAL REGISTRATION NUMBER

NCT03018405, EudraCT 2016-003312-12; Pre-result.

'Atypical' CAR T cells: NKG2D and Erb-B as examples of natural receptor/ligands to target recalcitrant solid tumors

Chimeric antigen receptor (CAR) T-cell therapy has recently been recommended for approval for certain B-cell malignancies bringing the approach closer to mainstream cancer treatment. This rapid rise to prominence has been driven by impressive clinical results and the means to successfully commercialize the approach now being actively pursued. The current success of CAR T cells in B-cell malignancies relies upon the absolute lineage specificity of the CD19 antigen. CARs can also be targeted using non-antibody approaches, including the use of receptors and ligands to provide target specificity that have different specificities and binding kinetics. The specific examples of NKG2D and Erb-B are used that provide different characteristics and target profiles for CAR T-cell therapy of cancer.

Exploiting natural killer group 2D receptors for CAR T-cell therapy

Chimeric antigen receptors (CARs) are genetically engineered proteins that combine an extracellular antigen-specific recognition domain with one or several intracellular T-cell signaling domains. When expressed in T cells, these CARs specifically trigger T-cell activation upon antigen recognition. While the clinical proof of principle of CAR T-cell therapy has been established in hematological cancers, CAR T cells are only at the early stages of being explored to tackle solid cancers. This special report discusses the concept of exploiting natural killer cell receptors as an approach that could broaden the specificity of CAR T cells and potentially enhance the efficacy of this therapy against solid tumors. New data demonstrating feasibility of this approach in humans and supporting the ongoing clinical trial are also presented.

CD3ζ-based chimeric antigen receptors mediate T cell activation via cis- and trans-signalling mechanisms: implications for optimization of receptor structure for adoptive cell therapy

Chimeric antigen receptors (CARs) can mediate redirected lysis of tumour cells in a major histocompatibility complex (MHC)-independent manner, thereby enabling autologous adoptive T cell therapy for a variety of malignant neoplasms. Currently, most CARs incorporate the T cell receptor (TCR) CD3ζ signalling chain; however, the precise mechanisms responsible for CAR-mediated T cell activation are unclear. In this study, we used a series of immunoreceptor tyrosine-based activation motif (ITAM)-mutant and transmembrane-modified receptors to demonstrate that CARs activate T cells both directly via the antigen-ligated signalling chain and indirectly via associated chains within the TCR complex. These observations allowed us to generate new receptors capable of eliciting polyfunctional responses in primary human T cells. This work increases our understanding of CAR function and identifies new avenues for the optimization of CAR-based therapeutic interventions.

Differential role of Th1 and Th2 cytokines in autotoxicity driven by CD19-specific second-generation chimeric antigen receptor T cells in a mouse model

T cells engrafted with chimeric AgRs (CAR) are showing exciting potential for targeting B cell malignancies in early-phase clinical trials. To determine whether the second-generation CAR was essential for optimal antitumor activity, two CD28-based CAR constructs targeting CD19 were tested for their ability to redirect mouse T cell function against established B cell lymphoma in a BALB/c syngeneic model system. T cells armed with either CAR eliminated A20 B cell lymphoma in vivo; however, one construct induced a T cell dose-dependent acute toxicity associated with a raised serum Th1 type cytokine profile on transfer into preconditioned mice. Moreover, a chronic toxicity manifested as granuloma-like formation in spleen, liver, and lymph nodes was observed in animals receiving T cells bearing either CD28 CAR, albeit with different kinetics dependent upon the specific receptor used. This phenotype was associated with an expansion of CD4+ CAR+ T cells and CD11b+ Gr-1(+) myeloid cells and increased serum Th2-type cytokines, including IL-10 and IL-13. Mouse T cells engrafted with a first-generation CAR failed to develop such autotoxicity, whereas toxicity was not apparent when T cells bearing the same receptors were transferred into C57BL/6 or C3H animals. In summary, the adoptive transfer of second-generation CD19-specific CAR T cells can result in a cell dose-dependent acute toxicity, whereas the prolonged secretion of high levels of Th2 cytokines from these CAR T cells in vivo drives a granulomatous reaction resulting in chronic toxicity. Strategies that prevent a prolonged Th2-cytokine biased CAR T cell response are clearly warranted.

Definition and application of good manufacturing process-compliant production of CEA-specific chimeric antigen receptor expressing T-cells for phase I/II clinical trial

Adoptive cell therapy employing gene-modified T-cells expressing chimeric antigen receptors (CARs) has shown promising preclinical activity in a range of model systems and is now being tested in the clinical setting. The manufacture of CAR T-cells requires compliance with national and European regulations for the production of medicinal products. We established such a compliant process to produce T-cells armed with a first-generation CAR specific for carcinoembryonic antigen (CEA). CAR T-cells were successfully generated for 14 patients with advanced CEA(+) malignancy. Of note, in the majority of patients, the defined procedure generated predominantly CD4(+) CAR T-cells with the general T-cell population bearing an effector-memory phenotype and high in vitro effector function. Thus, improving the process to generate less-differentiated T-cells would be more desirable in the future for effective adoptive gene-modified T-cell therapy. However, these results confirm that CAR T-cells can be generated in a manner compliant with regulations governing medicinal products in the European Union.

Genetic modification of mouse effector and helper T lymphocytes expressing a chimeric antigen receptor

Genetic modification of primary mouse T cells with chimeric antigen receptors (CAR) has emerged as an important tool for optimizing adoptive T cell immunotherapy strategies. However, limitations in current protocols for generating highly pure and sufficient numbers of enriched effector and helper CAR(+) T cell subsets remain problematic. Here, we describe a new retroviral transduction protocol for successfully generating transduced CD8(+) and CD4(+) T lymphocytes for in vitro and in vivo characterization.

Targeting T cells to tumor: exploiting the chimeric antibody receptor

Adoptive therapy using gene-modified T cells to express chimeric antigen receptors (CARs) is gaining pace in the clinic, particularly in hematological malignancies. Translation into treatment of solid tumors has been slower, not least because of the lack of truly tumor-specific target antigens. Alonso-Camino et al. describe experiments that further develop the concept of using the therapeutic entity (in this case, the CAR T cell) to screen for functional binding of tumor target cells. This article highlights the potential for the approach, but also underlies some of the key hurdles that remain to be overcome in order to produce a functional antibody-based screening approach that is able to identify novel tumor antigens that can be recognized by CAR T cells.

Potential limitations of the NSG humanized mouse as a model system to optimize engineered human T cell therapy for cancer

The genetic modification of peripheral blood lymphocytes using retroviral vectors to redirect T cells against tumor cells has been recently used as a means to generate large numbers of antigen-specific T cells for adoptive cell therapy protocols. However, commonly used retroviral vector-based genetic modification requires T cells to be driven into cell division; this potent mitogenic stimulus is associated with the development of an effector phenotype that may adversely impact upon the long-term engraftment potential and subsequent antitumor effects of T cells. To investigate whether the cytokines used during culture impact upon the engraftment potential of gene-modified T cells, a humanized model employing T cells engrafted with a MART-1-specific T cell receptor adoptively transferred into NOD/Shi-scid IL-2rγ(-/-) (NSG) immune-deficient mice bearing established melanoma tumors was used to compare the effects of the common γ chain cytokines IL-2, IL-7, and IL-15 upon gene-modified T cell activity. MART-1-specific T cells cultured in IL-7 and IL-15 demonstrated greater relative in vitro proliferation and viability of T cells compared with the extensively used IL-2. Moreover, the IL-15 culture prolonged the survival of animals bearing melanoma tumors after adoptive transfer. However, the combination of IL-7 and IL-15 produced T cells with improved engraftment potential compared with IL-15 alone; however, a high rate of xenogeneic graft-versus-host disease prevented the identification of a clear improvement in antitumor effect of these T cells. These results clearly demonstrate modulation of gene-modified T cell engraftment in the NSG mouse, which supports the future testing of the combination of IL-7 and IL-15 in adoptive cell therapy protocols; however, this improved engraftment is also associated with the long-term maintenance of xenoreactive T cells, which limits the ultimate usefulness of the NSG mouse model in this situation.

Targeted immunotherapy of cancer with CAR T cells: achievements and challenges

The adoptive transfer of chimeric antigen receptor (CAR)-expressing T cells is a relatively new but promising approach in the field of cancer immunotherapy. This therapeutic strategy is based on the genetic reprogramming of T cells with an artificial immune receptor that redirects them against targets on malignant cells and enables their destruction by exerting T cell effector functions. There has been an explosion of interest in the use of CAR T cells as an immunotherapy for cancer. In the pre-clinical setting, there has been a considerable focus upon optimizing the structural and signaling potency of the CAR while advances in bio-processing technology now mean that the clinical testing of these gene-modified T cells has become a reality. This review will summarize the concept of CAR-based immunotherapy and recent clinical trial activity and will further discuss some of the likely future challenges facing CAR-modified T cell therapies.

Regulation of autologous immunity to the mouse 5T4 oncofoetal antigen: implications for immunotherapy

Effective vaccination against tumour-associated antigens (TAA) such as the 5T4 oncofoetal glycoprotein may be limited by the nature of the T cell repertoire and the influence of immunomodulatory factors in particular T regulatory cells (Treg). Here, we identified mouse 5T4-specific T cell epitopes using a 5T4 knock out (5T4KO) mouse and evaluated corresponding wild-type (WT) responses as a model to refine and improve immunogenicity. We have shown that 5T4KO mice vaccinated by replication defective adenovirus encoding mouse 5T4 (Adm5T4) generate potent 5T4-specific IFN-γ CD8 and CD4 T cell responses which mediate significant protection against 5T4 positive tumour challenge. 5T4KO CD8 but not CD4 primed T cells also produced IL-17. By contrast, Adm5T4-immunized WT mice showed no tumour protection consistent with only low avidity CD8 IFN-γ, no IL-17 T cell responses and no detectable CD4 T cell effectors producing IFN-γ or IL-17. Treatment with anti-folate receptor 4 (FR4) antibody significantly reduced the frequency of Tregs in WT mice and enhanced 5T4-specific IFN-γ but reduced IL-10 T cell responses but did not reveal IL-17-producing effectors. This altered balance of effectors by treatment with FR4 antibody after Adm5T4 vaccination provided modest protection against autologous B16m5T4 melanoma challenge. The efficacy of 5T4 and some other TAA vaccines may be limited by the combination of TAA-specific T regs, the deletion and/or alternative differentiation of CD4 T cells as well as the absence of distinct subsets of CD8 T cells.

Targeting breast cancer vaccines to dendritic cells: improved immunological responses with less protein?

The central goal of cancer immunotherapy is to control tumors through the mobilization of the patient's immune system. Vaccines targeting the Her2/neu proto-oncogene have been tested with some early encouraging responses in breast cancer. However, a more effective set of vaccines targeting specific immune cell subtypes may provide a more potent means to stimulate anti-tumor immunity. Dendritic cell-specific antibodies fused with the Her2/neu protein proved effective at generating immune responses in preclinical models. Importantly, only low amounts of protein vaccine were required to generate this response, which has potentially significant implications for the future clinical development of Her2/neu-targeted vaccines and other vaccine targets.

CAR-T cells and solid tumors: tuning T cells to challenge an inveterate foe

Recent reports on the impressive efficacy of adoptively transferred T cells to challenge cancer in early phase clinical trials have significantly raised the profile of T cell therapy. Concomitantly, general expectations are also raised by these reports, with the natural aspiration to deliver this therapy over a wide range of tumor indications. Chimeric antigen receptors (CARs) endow T cell populations with defined antigen specificities that function independently of the natural T cell receptor and permit targeting of T cells towards virtually any tumor. Here, we review the current clinical application of CAR-T cells and relate clinical efficacy and safety of CAR-T cell trials to parameters considered critical for CAR engineering, classified as the three T's of CAR-T cell manipulation.

Immunology in the clinic review series; focus on cancer: double trouble for tumours: bi-functional and redirected T cells as effective cancer immunotherapies

Cancer is one of the most important pathological conditions facing mankind in the 21st century, and is likely to become the most important cause of death as improvements continue in health, diet and life expectancy. The immune response is responsible for controlling nascent cancer through immunosurveillance. If tumours escape this control, they can develop into clinical cancer. Although surgery and chemo- or radiotherapy have improved survival rates significantly, there is a drive to reharness immune responses to treat disease. As T cells are one of the key immune cells in controlling cancer, research is under way to enhance their function and improve tumour targeting. This can be achieved by transduction with tumour-specific T cell receptor (TCR) or chimaeric antigen receptors (CAR) to generate redirected T cells. Virus-specific cells can also be transduced with TCR or CAR to create bi-functional T cells with specificity for both virus and tumour. In this review we outline the development and optimization of redirected and bi-functional T cells, and outline the results from current clinical trials using these cells. From this we discuss the challenges involved in generating effective anti-tumour responses while avoiding concomitant damage to normal tissues and organs.

Functional expression of secreted proteins from a bicistronic retroviral cassette based on foot-and-mouth disease virus 2A can be position dependent

The expression of two or more genes from a single viral vector has been widely used to label or select for cells containing the transgenic element. Identification of the foot-and-mouth disease virus (FMDV) 2A cleavage peptide as a polycistronic linker capable of producing equivalent levels of transgene expression has greatly improved this approach in the field of gene therapy. However, as a consequence of 2A posttranslational cleavage the upstream protein is left with a residual 19 amino acids from the 2A sequence on its carboxy terminus, and the downstream protein is left with an additional 2 to 5 amino acids on its amino terminus. Here we have assessed the functional consequences of the FMDV 2A cleavage motif on two secreted proteins (interleukin [IL]-2 and transforming growth factor [TGF]-β) when expressed from a retroviral bicistronic vector. Whereas IL-2 expression and function were found to be unaffected by the 2A motif in either orientation, functional expression of secreted TGF-β was significantly abrogated when the transgene was expressed upstream of the 2A sequence. We believe this is a consequence of aberrant cleavage and intracellular trafficking of the TGF-β polyprotein. These results highlight that to achieve functional expression of secreted proteins consideration must be taken of the transgenic protein's posttranslational modification and trafficking when using 2A-based bicistronic cassettes.

Effective adoptive T-cell therapy for cancer in the absence of host lymphodepletion

Evaluation of: Ly LV, Sluijter M, Versluis M et al.: Peptide vaccination after T-cell transfer causes massive clonal expansion, tumor eradication and manageable cytokine storm. Cancer Res. 70(21), 8339–8346 (2010). Adoptive T-cell transfer (ACT) to treat cancer, autoimmunity and infectious disease holds great promise. In the cancer field, current dogma suggests that achieving a high frequency of circulating, transferred T cells is critical for therapeutic success. Achieving this high level of T-cell engraftment currently requires preconditioning of the patient. In effect, this means the eradication of the patient’s own immune system, thereby creating ‘space’ for the adoptively transferred T cells to populate in the absence of host-cell competition. While different forms of preconditioning are employed, each carries a significant level of toxicity itself. In the paper being evaluated, Ly et al. demonstrate that the combination of ACT with vaccination using long peptides, a Toll-like receptor-7 ligand and cytokine support in the form of IL-2 can drive the expansion of adoptively transferred antigen-specific T cells in the absence of preconditioning regimens. This paper infers that reduced intensity regimens may be suitable for ACT clinical protocols.

Gene delivery of a mutant TGFβ3 reduces markers of scar tissue formation after cutaneous wounding

The transforming growth factor-β (TGFβ) family plays a critical regulatory role in repair and coordination of remodeling after cutaneous wounding. TGFβ1-mediated chemotaxis promotes the recruitment of fibroblasts to the wound site and their resultant myofibroblastic transdifferentiation that is responsible for elastic fiber deposition and wound closure. TGFβ3 has been implicated in an antagonistic role regulating overt wound closure and promoting ordered dermal remodeling. We generated a mutant form of TGFβ3 (mutTGFβ3) by ablating its binding site for the latency-associated TGFβ binding protein (LTBP-1) in order to improve bioavailability and activity. The mutated cytokine is secreted as the stable latency-associated peptide (LAP)-associated form and is activated by normal intracellular and extracellular mechanisms including integrin-mediated activation but is not sequestered. We show localized intradermal transduction using a lentiviral vector expressing the mutTGFβ3 in a mouse skin wounding model reduced re-epithelialization density and fibroblast/myofibroblast transdifferentiation within the wound area, both indicative of reduced scar tissue formation.

Building better chimeric antigen receptors for adoptive T cell therapy

The last few years have seen the transfer of two decades of research into Chimeric Antigen Receptors (CARs) into clinical trials. Despite this extensive research, there is still a great deal of debate into the optimal design strategy for these, primarily, anti-cancer entities. The archetypal CAR consists of a single-chain antibody fragment, specific to a tumour-associated antigen, fused to a component of the T-cell receptor complex (typically CD3zeta) which on antigen binding primes the engrafted T-cell for anti-tumour activity. The modular nature of these artificial receptors has enabled researchers to modify aspects of their structure, including the extracellular spacer, transmembrane and cytoplasmic domain, to achieve laboratory defined optimal activity. Despite this there is no consensus on the optimal structure, a problem exacerbated by conflicting results using identical receptors. In this review, we provide a structural overview of CAR development and highlight areas that require further refinement. We also attempt to identify possible reasons for conflicting results in the hope that this information will inspire future rational design strategies for optimal tumour targeting using CARs.

Cytokine stimulation and the choice of promoter are critical factors for the efficient transduction of mouse T cells with HIV-1 vectors

BACKGROUND

HIV-1 fails to successfully infect mouse T cells as a result of several blocks in the viral replication cycle. We investigated whether this also impacted on the use of HIV-1 derived lentiviral vectors for stable gene transfer into mouse T cells.

METHODS

Freshly isolated primary mouse T cells were immediately mixed with lentiviral vectors encoding an enhanced green fluorescent protein marker gene and transduction frequency was determined after 5 days of culture.

RESULTS

Optimal transduction required both mouse T cell activation and cytokine support. Furthermore, transduction was also dependent upon the promoter chosen, with the rank order of potency being PGK > EF1 > SFFV > CMV. HIV-1 lentiviral vectors also efficiently transduced cytokine-stimulated T cells (in the absence of antibody driven T cell activation), albeit with a lower level of transgene expression compared to fully-activated T cells.

CONCLUSIONS

The present study demonstrates that primary mouse T cells can be efficiently transduced with HIV-1 lentiviral vectors, opening up prospects for their use in mouse models of gene-modified adoptive cellular therapy.

The optimal antigen response of chimeric antigen receptors harboring the CD3zeta transmembrane domain is dependent upon incorporation of the receptor into the endogenous TCR/CD3 complex

Chimeric Ag receptors (CARs) expressed in T cells permit the redirected lysis of tumor cells in an MHC-unrestricted manner. In the Jurkat T cell model system, expression of a carcinoembryonic Ag-specific CD3zeta CAR (MFEzeta) resulted in an increased sensitivity of the transduced Jurkat cell to generate cytokines when stimulated through the endogenous TCR complex. This effect was driven through two key characteristics of the MFEzeta CAR: 1) receptor dimerization and 2) the interaction of the CAR with the endogenous TCR complex. Mutations of the CAR transmembrane domain that abrogated these interactions resulted in a reduced functional capacity of the MFEzeta CAR to respond to carcinoembryonic Ag protein Ag. Taken together, these results indicate that CARs containing the CD3zeta transmembrane domain can form a complex with the endogenous TCR that may be beneficial for optimal T cell activation. This observation has potential implications for the future design of CARs for cancer therapy.

Natural expression of the CD19 antigen impacts the long-term engraftment but not antitumor activity of CD19-specific engineered T cells

T cells gene-modified to express chimeric Ag receptors (CARs) have shown potent antitumor activity in vivo and are in clinical trials at locations worldwide. However, CAR activity has been investigated in mouse models in which Ag expression is restricted to the tumor. To explore the impact of normal tissue expression of the target Ag, we developed a mouse CD19-specific CAR to investigate antitumor efficacy against a syngeneic B cell lymphoma cell line within a background of normal CD19(+) host B cells. Mouse T cells engrafted with the amCD19CD3zeta CAR specifically lysed A20 lymphoma targets and B cells in vitro. These T cells also eradicated a 12-d established disseminated A20 lymphoma in mice preconditioned with 6 Gy total body irradiation. In the short-term (7 d after adoptive transfer), amCD19z T cells underwent Ag-dependent proliferation in vivo with a concomitant depletion in host B cell levels. However, the levels of amCD19z CAR(+) T cells decreased significantly at later time points, at which point host B cells returned, eventually reaching normal levels. In contrast, CAR(+) T cells lacking a signaling domain or specificity for mCD19 persisted over extended periods in blood and spleen. Importantly, no overt clinical signs of autotoxicity were observed in tumor-free or tumor-bearing mice treated with amCD19z T cells over an extended period of time. These observations highlight the importance of studying the activity of CAR(+) T cells in autologous models that have the normal range of tissue expression of Ag.

Rapid high-performance liquid chromatographic analysis of adenovirus type 5 particles with a prototype anion-exchange analytical monolith column

To support effective process development there is a requirement for rapid analytical methods that can identify and quantitate adenoviral particles throughout the manufacturing process, from cellular lysate through to purified adenovirus. An anion-exchange high-performance liquid chromatography method for the analysis of adenovirus type 5 (Ad5) particles has been developed using a novel quaternary amine monolithic column (Bio-Monolith QA, Agilent). The developed method separates intact Ad5 from contaminating proteins and DNA, thus allowing analysis of non-purified samples during process development. Regeneration conditions were incorporated to extend the functional life of the column. Once developed, the method was qualified according to performance criteria of repeatability, intermediate precision and linearity. The linear working range of analysis was established between 7.5 x 10(8) to at least 2.4 x 10(10) viral particles (3 x 10(10) to 9.6 x 10(11) viral particles/mL), with a correlation coefficient of 0.9992. Relative standard deviations (RSDs) for intra- and inter-day repeatability and precision for retention time and peak area were less than 1 and 2.5%, respectively.

The combination of cyclophosphamide and human T cells genetically engineered to target CD19 can eradicate established B-cell lymphoma

T cells genetically engineered to express tumour-targeting receptors are attractive anti-cancer therapeutic agents. Human T cells engrafted with a chimeric receptor specific for the B-cell lymphoma antigen CD19 fused to the CD3zeta receptor (aCD19z) are functional in vitro. Current successful clinical protocols targeting melanoma use pre-conditioning chemotherapy in combination with T cells. This study demonstrated that interleukin-2 expanded aCD19z T cells combined with cyclophosphamide effectively treated five-day established Raji B-cell lymphoma in an immunocompromised model system with 50% of mice surviving >100 days. This observation strongly supports the combination of antibody targeted T cells with chemotherapy as a novel approach for the therapy of CD19(+) B-cell malignancies.

Adoptive transfer of T(reg) depleted autologous T cells in advanced renal cell carcinoma

PURPOSE

CD4(+)CD25(+) regulatory T (T(reg)) cells are present in increased numbers in patients with advanced cancer and CD25(+) T cell depletion potentiates tumour immunity in animal models. The aim of this study was to assess the feasibility and safety of adoptive transfer of CD25(+) depleted autologous T cells in patients with advanced renal cell carcinoma and to examine resulting changes in lymphocyte subsets.

PATIENTS AND METHODS

Six patients with advanced renal cell carcinoma underwent leukapheresis followed by conditioning chemotherapy with cyclophosphamide and fludarabine. The autologous leukapheresis product was depleted of CD25(+) cells using CliniMACS System then re-infused into the patient.

RESULTS

Efficient CD25(+) depletion from all leukapheresis products was achieved and 0.55-5.87 x 10(7)/kg CD3(+) cells were re-infused. Chemotherapy related haematological toxicity was observed, but blood counts recovered in all patients allowing discharge after a mean inpatient stay of 21 days. One patient subsequently developed a rapidly progressive neurological syndrome. A transient reduction in CD25(+) subset was noted in the peripheral blood of 5 out of 6 patients with evidence of increased T cell responses to PHA in 4 out of 6 patients. One patient showed increased specific proliferative responses to the tumour associated antigen h5T4 coinciding with the nadir of T(reg) cells.

CONCLUSIONS

Given the transient nature of the reduction in CD25(+) subset and the observed toxicity there is a need to explore further strategies to improve the safety and efficacy of this approach. Nevertheless, the results provide proof of concept in potentiation of tumour antigen T cell responses when T(reg) cell levels are depleted.

O6-Methylguanine-DNA methyltransferase inactivation and chemotherapy

INTRODUCTION

Alkylating agents are frequently used in the chemotherapy of many types of cancer. This group of drugs mediates cell death by damaging DNA and therefore, understandably, cellular DNA repair mechanisms can influence both their antitumour efficacy and their dose-limiting toxicities.

SOURCES OF DATA

This review focuses on the mechanism of action of the DNA repair protein, O(6)-methylguanine-DNA methyltransferase (MGMT) and its exploitation in cancer therapy and reviews the current literature.

AREAS OF AGREEMENT

MGMT can provide resistance to alkylating agents by DNA damage reversal. Inhibition of tumour MGMT by pseudosubstrates to overcome tumour resistance is under clinical evaluation. In addition, MGMT overexpression in haematopoietic stem cells has been shown in animal models to protect normal cells against the myelosuppressive effects of chemotherapy: this strategy has also entered clinical trials.

AREAS OF CONTROVERSY

MGMT inhibitors enhance the myelotoxic effect of O(6)-alkylating drugs and therefore reduce the maximum-tolerated dose of these agents. Retroviral vectors used for chemoprotective gene therapy are associated with insertional mutagenesis and leukaemia development.

GROWING POINTS

The results of ongoing preclinical and clinical research involving various aspects of MGMT modulation should provide new prospects for the treatment of glioma, melanoma and other cancer types.

AREAS TIMELY FOR DEVELOPING RESEARCH

Tissue- and tumour-specific approaches to the modulation of MGMT together with other DNA repair functions and in combination with immuno- or radiotherapy are promising strategies to improve alkylating agent therapy.

Eotaxin-2 and colorectal cancer: a potential target for immune therapy

PURPOSE

To study the production of chemokines by colorectal hepatic metastases.

EXPERIMENTAL DESIGN

Biopsies of resected colorectal hepatic metastases and nonneoplastic adjacent liver tissue were screened for chemokines using protein arrays and results were confirmed by ELISA and immunohistochemistry.

RESULTS

Two chemokines, eotaxin-2 and MCP-1, were found at elevated levels within the tumor biopsy compared with adjacent liver. The relative increase in expression from tumor was much higher for eotaxin-2 than MCP-1, with 10 of 25 donors having a >100-fold increase in expression compared with 0 of 24 donors for MCP-1. In a parallel analysis, eotaxin-2 was also found at elevated levels in the tumor region of primary colorectal cancer biopsies. Immunohistochemical staining indicated that carcinoembryonic antigen-positive tumor cells stained strongly for eotaxin-2, implicating these cells as the predominant source of the chemokine. In vitro studies confirmed that several colorectal tumor lines produce eotaxin-2 and that secretion of this chemokine could be depressed by IFN-gamma and enhanced by the Th2-type cytokines interleukin-4 and interleukin-13. Jurkat T cells were engineered to express the receptor for eotaxin-2 (CCR3). These cells effectively migrated in response to eotaxin-2 protein, suggesting that immune cells gene modified to express a chemokine receptor may have improved abilities to home to tumor.

CONCLUSIONS

Taken together, these observations confirm eotaxin-2 as a chemokine strongly associated with primary and metastatic tumors of colorectal origin. Furthermore, the importance of this result may be a useful tool in the development of targeted therapeutic approaches to colorectal tumors.

Cyclin-dependent kinase inhibitors and basement membrane interact to regulate breast epithelial cell differentiation and acinar morphogenesis

OBJECTIVE

The cyclin-dependent kinase inhibitors (CDKIs), p21(CIP1) and p27(KIP1) regulate growth and differentiation in diverse tissue types. We aimed to determine whether p21(CIP1) or p27(KIP1) could induce a terminally differentiated phenotype in breast cells, and to examine if CDKI expression is regulated by basement membrane interactions.

MATERIALS AND METHODS

Effects of increased CDKI expression on the phenotype of MCF-10A breast epithelial cells were examined by retroviral transduction of p21(CIP1) or p27(KIP1) cDNA.

RESULTS

Overexpression of p21(CIP1) or p27(KIP1) reduced MCF-10A growth rates in monolayer cultures, altered cellular morphology and stimulated accumulation of neutral lipid droplets, suggesting partial lactational differentiation. However, markers of luminal differentiation (oestrogen and progesterone receptors, alpha-lactalbumin, beta-casein and adipophilin) were absent when examined by reverse transcriptase-polymerase chain reaction and immunohistochemistry. Cell-basement membrane contacts are known to be essential for full mammary epithelial cell differentiation and therefore parental MCF-10A cells were cultured on a basement membrane preparation (Matrigel) in which they form acini. Immunocytochemistry showed that Ki67, the cell proliferation marker, was initially expressed at high levels and as growth decreased p27(KIP1) expression steadily increased. Surprisingly, p21(CIP1) was highest at the early stages of acinus growth and was detected in proliferating cells, as demonstrated by colocalization in dual Ki67/p21(CIP1) immunofluorescence. Overexpression of p21(CIP1) or p27(KIP1) impaired formation of acini, whereas their knockdown, using siRNA, increased acinus formation.

CONCLUSION

We conclude that both p21(CIP1) and p27(KIP1) induce partial secretory differentiation of mammary cells in monolayer, but during acinus morphogenesis in 3D culture they have a highly regulated temporal expression pattern.

Frequency of regulatory T cells in renal cell carcinoma patients and investigation of correlation with survival

BACKGROUND

Regulatory T cells are important in maintaining immune homeostasis, mediating peripheral tolerance and preventing autoimmunity. Increased frequencies of CD4(+)CD25(high )T regulatory (T(Reg)) cells have been documented in the peripheral blood of patients with several types of cancer consistent with a role in tumour escape from immunological control. We have investigated the presence of T(Reg) cells systemically and in situ in previously untreated patients with renal cell carcinoma (RCC).

RESULTS

We have shown that there is a significant increased frequency of CD4(+)CD25(high) T cells in RCC patients (n = 49) compared to normal donors (n = 38), respectively, 2.47% versus 1.50%; P < 0.0001. We confirmed these data using the FOXP3 marker of T(Reg) cells in a subset of these patients and normal donors. The population of T(Reg) cells identified showed the expected phenotype with CD4(+)CD25(high) population in both RCC patients and normal donors contained higher proportions of CD45RO and GITR than CD4(+)CD25(-/low) populations and exhibiting suppressive activity in an anti-CD3 and anti-CD28 induced proliferation assay. CD4(+)FOXP3(+) T cells were detected in the tumour microenvironment by immunofluorescence and the numbers enumerated in lymphocytes recovered following enzymatic disaggregations of biopsies; their frequency was higher in the tumour than the peripheral blood of the same patients. The early follow up data show an association between higher peripheral blood regulatory T-cell count and adverse overall survival.

CONCLUSION

These data confirm the increase of T(Reg) cells in RCC patients and provide impetus to further investigate modulation of T(Reg) activity in RCC patients as part of therapy.

T cell activation by antibody-like immunoreceptors: the position of the binding epitope within the target molecule determines the efficiency of activation of redirected T cells

Recombinant TCRs confer specificity to T cells and trigger their activation. Receptors with Ab-derived binding domains have the advantages of MHC-independent Ag recognition and of targeting a variety of chemically different molecules. We explored the impact of the position of a defined epitope within the target molecule on the efficacy of receptor-mediated T cell activation. T cells were grafted with recombinant immunoreceptors that recognize either the membrane distal N or the proximal A3 domain of carcinoembryonic Ag (CEA). Upon binding to isolated, solid-phase immobilized CEA, receptor-mediated T cell activation correlates with the binding efficiency, irrespectively, of the epitope position. Upon binding to CEA expressed on the cell membrane, in contrast, the A3 epitope mediates more efficiently T cell activation than the N epitope, although the N epitope is bound with higher affinity. The CEA N epitope when expressed in a more membrane proximal position, however, activated receptor grafted T cells with higher efficiency than in the distal position. The position of the targeted epitope within the molecule obviously has major impact on the efficacy of T cell activation independently of the binding efficiency of the immunoreceptor.

Combination of vaccination and chimeric receptor expressing T cells provides improved active therapy of tumors

We have generated murine T cells expressing chimeric immune receptors (CR) against human 5T4 oncofetal Ag (h5T4) and evaluated their tumor therapeutic efficacy alone and in combination with immunization using a replication-defective adenovirus encoding h5T4 (Rad.h5T4) and bone marrow-derived dendritic cells (BMDC). The h5T4-specific engineered T cells demonstrated Ag-specific, non-MHC-restricted cytolysis of h5T4-positive B16 and CT26 tumor cells in vitro by cytotoxicity assay and antitumor activity in vivo using a Winn assay. In the s.c. injected B16h5T4 melanoma model, early local but not systemic i.v. administration of syngeneic h5T4-specific CR T cells significantly increased mice survival. This improvement was further enhanced when combined with immunization with Rad.h5T4, followed by post-CR T cell treatment with BMDC in the active therapy model, possibly through mechanisms of enhancing Ag-specific cellular immune responses. This synergistic effect was lost without delivery of the BMDC. Our findings suggest that combining engineered T cells with specific vaccination strategies can improve the active tumor therapy.

Human monocytes expressing a CEA-specific chimeric CD64 receptor specifically target CEA-expressing tumour cells in vitro and in vivo

Antibody-dependent cellular cytotoxicity (ADCC) is one means by which macrophages (as well as natural killer cells and granulocytes) elicit a cytotoxic response. This is achieved via interaction of the Fc-gamma-receptor (CD64) with the Fc portion of antibody bound to target cells. We have created a chimeric CD64 molecule that incorporates a single chain Fv molecule, targeted against human carcinoembryonic antigen (CEA), fused to the membrane spanning and cytosolic domains of human CD64. Following adenoviral transfer to primary human monocytes, this chimeric CD64 receptor induced antigen-specific cytokine secretion during culture on immobilised CEA protein or on CEA-expressing tumour cells. Moreover, CEA targeted, but not control, monocytes effectively retarded CEA-positive tumour cell growth in vitro. Importantly, targeted monocyte cultures significantly reduced in vivo tumour growth rates in xenograft studies resulting in improved survival rates over that of control monocyte cultures. These data suggest that genetically directing monocytes against tumour antigens may be a useful means of achieving an immunotherapeutic response.

Engineering T cells for cancer therapy

It is generally accepted that the immune system plays an important role in controlling tumour development. However, the interplay between tumour and immune system is complex, as demonstrated by the fact that tumours can successfully establish and develop despite the presence of T cells in tumour. An improved understanding of how tumours evade T-cell surveillance, coupled with technical developments allowing the culture and manipulation of T cells, has driven the exploration of therapeutic strategies based on the adoptive transfer of tumour-specific T cells. The isolation, expansion and re-infusion of large numbers of tumour-specific T cells generated from tumour biopsies has been shown to be feasible. Indeed, impressive clinical responses have been documented in melanoma patients treated with these T cells. These studies and others demonstrate the potential of T cells for the adoptive therapy of cancer. However, the significant technical issues relating to the production of natural tumour-specific T cells suggest that the application of this approach is likely to be limited at the moment. With the advent of retroviral gene transfer technology, it has become possible to efficiently endow T cells with antigen-specific receptors. Using this strategy, it is potentially possible to generate large numbers of tumour reactive T cells rapidly. This review summarises the current gene therapy approaches in relation to the development of adoptive T-cell-based cancer treatments, as these methods now head towards testing in the clinical trial setting.