Remote control of therapeutic T cells through a small molecule-gated chimeric receptor

Chimeric antigen receptors: driving immunology towards synthetic biology

The advent of second generation chimeric antigen receptors and the CD19 paradigm have ushered a new therapeutic modality in oncology. In contrast to earlier forms of adoptive cell therapy, which were based on the isolation and expansion of naturally occurring T cells, CAR therapy is based on the design and manufacture of engineered T cells with optimized properties. A new armamentarium, comprising not only CARs but also chimeric costimulatory receptors, chimeric cytokine receptors, inhibitory receptors and synthetic Notch receptors, expressed in naïve, central memory or stem cell-like memory T cells, is being developed for clinical use in a wide range of cancers. Immunological principles are thus finding a new purpose thanks to advances in genetic engineering, synthetic biology and cell manufacturing sciences.

A Tet-On Inducible System for Controlling CD19-Chimeric Antigen Receptor Expression upon Drug Administration

T cells genetically modified with a CD19 chimeric antigen receptor (CD19CAR) are remarkably effective against B-cell malignancies in clinical trials. However, major concerns remain regarding toxicities, such as hypogammaglobulinemia, due to B-cell aplasia or severe cytokine release syndrome after overactivation of CAR T cells. To resolve these adverse events, we aimed to develop an inducible CAR system by using a tetracycline regulation system that would be activated only in the presence of doxycycline (Dox). In this study, the second-generation CD19CAR was fused into the third-generation Tet-On vector (Tet-CD19CAR) and was retrovirally transduced into primary CD8(+) T cells. Tet-CD19CAR T cells were successfully generated and had minimal background CD19CAR expression without Dox. Tet-CD19CAR T cells in the presence of Dox were equivalently cytotoxic against CD19(+) cell lines and had equivalent cytokine production and proliferation upon CD19 stimulation, compared with conventional CD19CAR T cells. The Dox(+) Tet-CD19CAR T cells also had significant antitumor activity in a xenograft model. However, without Dox, Tet-CD19CAR T cells lost CAR expression and CAR T-cell functions in vitro and in vivo, clearly segregating the "On" and "Off" status of Tet-CD19CAR cells by Dox administration. In addition to suicide-gene technology, controlling the expression and the functions of CAR with an inducible vector is a potential solution for CAR T-cell therapy-related toxicities, and may improve the safety profile of CAR T-cell therapy. This strategy might also open the way to treat other malignancies in combination with other CAR or TCR gene-modified T cells. Cancer Immunol Res; 4(8); 658-68. ©2016 AACRSee related Spotlight by June, p. 643.

How Chimeric Antigen Receptor Design Affects Adoptive T Cell Therapy

Chimeric antigen receptor (CAR) T cells have been developed to treat tumors and have shown great success against B cell malignancies. Exploiting modular designs and swappable domains, CARs can target an array of cell surface antigens and, upon receptor-ligand interactions, direct signaling cascades, thereby driving T cell effector functions. CARs have been designed using receptors, ligands, or scFv binding domains. Different regions of a CAR have each been found to play a role in determining the overall efficacy of CAR T cells. Therefore, this review provides an overview of CAR construction and common designs. Each CAR region is discussed in the context of its importance to a CAR's function. Additionally, the review explores how various engineering strategies have been applied to CAR T cells in order to regulate CAR T cell function and activity. J. Cell. Physiol. 231: 2590-2598, 2016. © 2016 Wiley Periodicals, Inc.

The best of both worlds: reaping the benefits from mammalian and bacterial therapeutic circuits

Synthetic biology has revolutionized the field of biology in the last two decades. By taking apart natural systems and recombining engineered parts in novel constellations, it has not only unlocked a staggering variety of biological control mechanisms but it has also created a panoply of biomedical achievements, such as innovative diagnostics and therapies. The most common mode of action in the field of synthetic biology is mediated by synthetic gene circuits assembled in a systematic and rational manner. This review covers the most recent therapeutic gene circuits implemented in mammalian and bacterial cells designed for the diagnosis and therapy of an extensive array of diseases. Highlighting new tools for therapeutic gene circuits, we describe a future that holds a plethora of potentialities for the medicine of tomorrow.

CAR models: next-generation CAR modifications for enhanced T-cell function

T cells genetically targeted with a chimeric antigen receptor (CAR) to B-cell malignancies have demonstrated tremendous clinical outcomes. With the proof in principle for CAR T cells as a therapy for B-cell malignancies being established, current and future research is being focused on adapting CAR technology to other cancers, as well as enhancing its efficacy and/or safety. The modular nature of the CAR, extracellular antigen-binding domain fused to a transmembrane domain and intracellular T-cell signaling domains, allows for optimization by replacement of the various components. These modifications are creating a whole new class of therapeutic CARs. In this review, we discuss the recent major advances in CAR design and how these modifications will impact its clinical application.

Cybernetics, Redux: An Outside-In Strategy for Unraveling Cellular Function

A new paper in Science reveals how repetitive stimulation can identify and help to repair fragilities within a signaling network, while using linear mathematical models inspired by engineering, thereby suggesting how cybernetic methods can be integrated into systems and synthetic biology.

Toxicity and management in CAR T-cell therapy

T cells can be genetically modified to target tumors through the expression of a chimeric antigen receptor (CAR). Most notably, CAR T cells have demonstrated clinical efficacy in hematologic malignancies with more modest responses when targeting solid tumors. However, CAR T cells also have the capacity to elicit expected and unexpected toxicities including: cytokine release syndrome, neurologic toxicity, “on target/off tumor” recognition, and anaphylaxis. Theoretical toxicities including clonal expansion secondary to insertional oncogenesis, graft versus host disease, and off-target antigen recognition have not been clinically evident. Abrogating toxicity has become a critical step in the successful application of this emerging technology. To this end, we review the reported and theoretical toxicities of CAR T cells and their management.

Synthetic biology approaches in cancer immunotherapy, genetic network engineering, and genome editing

Investigations into cells and their contents have provided evolving insight into the emergence of complex biological behaviors. Capitalizing on this knowledge, synthetic biology seeks to manipulate the cellular machinery towards novel purposes, extending discoveries from basic science to new applications. While these developments have demonstrated the potential of building with biological parts, the complexity of cells can pose numerous challenges. In this review, we will highlight the broad and vital role that the synthetic biology approach has played in applying fundamental biological discoveries in receptors, genetic circuits, and genome-editing systems towards translation in the fields of immunotherapy, biosensors, disease models and gene therapy. These examples are evidence of the strength of synthetic approaches, while also illustrating considerations that must be addressed when developing systems around living cells.

Chimeric antigen receptor-modified T cells strike back

Chimeric antigen receptors (CARs) are engineered molecules designed to endow a polyclonal T-cell population with the ability to recognize tumor-associated surface antigens. In their simplest form, CARs comprise a targeting moiety in the form of a single-chain variable fragment from an antibody connected to various intracellular signaling domains allowing for T-cell activation. This powerful approach combines the specificity of an antibody with the cytotoxic ability of a T cell. There has been much excitement since early phase trials of CAR-T cells targeting CD19 expressed on B-cell malignancies demonstrated remarkable efficacy in inducing long-term, stable remissions in otherwise relapsed/refractory disease. Despite these successes, we have just begun to understand the intricacies of CAR biology with efforts underway to utilize this platform in the treatment of other, previously refractory malignancies. Challenges currently include identification of viable cancer targets, management strategies for potentially severe and irreversible toxicities and overcoming the immunosuppressive nature of the tumor microenvironment. This review will focus on basic CAR structure and function, previous success and new approaches aimed at the broader application of CAR-T-cell therapy.

Spotlight on chimeric antigen receptor engineered T cell research and clinical trials in China

T cell mediated adoptive immune response has been characterized as the key to anti-tumor immunity. Scientists around the world including in China, have been trying to harness the power of T cells against tumors for decades. Recently, the biosynthetic chimeric antigen receptor engineered T cell (CAR-T) strategy was developed and exhibited encouraging clinical efficacy, especially in hematological malignancies. Chimeric antigen receptor research reports began in 2009 in China according to our PubMed search results. Clinical trials have been ongoing in China since 2013 according to the trial registrations on clinicaltrials. gov.. After years of assiduous efforts, research and clinical scientists in China have made their own achievements in the CAR-T therapy field. In this review, we aim to highlight CAR-T research and clinical trials in China, to provide an informative reference for colleagues in the field.

On-Demand Targeting: Investigating Biology with Proximity-Directed Chemistry

Proximity enhancement is a central chemical tenet underpinning an exciting suite of small-molecule toolsets that have allowed us to unravel many biological complexities. The leitmotif of this opus is "tethering"-a strategy in which a multifunctional small molecule serves as a template to bring proteins/biomolecules together. Scaffolding approaches have been powerfully applied to control diverse biological outcomes such as protein-protein association, protein stability, activity, and improve imaging capabilities. A new twist on this strategy has recently appeared, in which the small-molecule probe is engineered to unleash controlled amounts of reactive chemical signals within the microenvironment of a target protein. Modification of a specific target elicits a precisely timed and spatially controlled gain-of-function (or dominant loss-of-function) signaling response. Presented herein is a unique personal outlook conceptualizing the powerful proximity-enhanced chemical biology toolsets into two paradigms: "multifunctional scaffolding" versus "on-demand targeting". By addressing the latest advances and challenges in the established yet constantly evolving multifunctional scaffolding strategies as well as in the emerging on-demand precision targeting (and related) systems, this Perspective is aimed at choosing when it is best to employ each of the two strategies, with an emphasis toward further promoting novel applications and discoveries stemming from these innovative chemical biology platforms.

Treatment of solid tumors with chimeric antigen receptor-engineered T cells: current status and future prospects

Chimeric antigen receptors (CARs) are artificial recombinant receptors that generally combine the antigen-recognition domain of a monoclonal antibody with T cell activation domains. Recent years have seen great success in clinical trials employing CD19-specific CAR-T cell therapy for B cell leukemia. Nevertheless, solid tumors remain a major challenge for CAR-T cell therapy. This review summarizes the preclinical and clinical studies on the treatment of solid tumors with CAR-T cells. The major hurdles for the success of CAR-T and the novel strategies to address these hurdles have also been described and discussed.

Combinatorial Antigen Targeting: Ideal T-Cell Sensing and Anti-Tumor Response

T cells expressing chimeric antigen receptors (CARs) are a formidable platform for the study and application of synthetic biology approaches to study customized and flexible control of cellular functions. Recent reports in the journal Cell provide a new twist on combinatorial antigen targeting, profiting from the singular cleavage and signaling of the Notch receptor to conditionally express CARs.

Bispecific antibodies and CARs: generalized immunotherapeutics harnessing T cell redirection

To realize the full potential of cancer immunotherapy, the latest generation immunotherapeutics are designed to harness the potent tumor-killing capacity of T cells. Thus, to mobilize T cells, new optimized bispecific antibody (BsAb) designs, enabling efficient polyclonal redirection of cytotoxic activity through binding to CD3 and a Tumor Associated Antigen (TAA) and refined genetically modified T cells have recently expanded the arsenal of available options for cancer treatment. This review presents the current understanding of the parameters crucial to the design of optimal T cell redirecting BsAb and chimeric antigen receptor (CAR)-modified T cells. However, there are additional questions that require thorough elucidation. Both modalities will benefit from design changes that may increase the therapeutic window. One such approach could employ the discrimination afforded by multiple TAA to significantly increase selectivity.

Versatile strategy for controlling the specificity and activity of engineered T cells

The adoptive transfer of autologous T cells engineered to express a chimeric antigen receptor (CAR) has emerged as a promising cancer therapy. Despite impressive clinical efficacy, the general application of current CAR-T--cell therapy is limited by serious treatment-related toxicities. One approach to improve the safety of CAR-T cells involves making their activation and proliferation dependent upon adaptor molecules that mediate formation of the immunological synapse between the target cancer cell and T-cell. Here, we describe the design and synthesis of structurally defined semisynthetic adaptors we refer to as "switch" molecules, in which anti-CD19 and anti-CD22 antibody fragments are site-specifically modified with FITC using genetically encoded noncanonical amino acids. This approach allows the precise control over the geometry and stoichiometry of complex formation between CD19- or CD22-expressing cancer cells and a "universal" anti-FITC-directed CAR-T cell. Optimization of this CAR-switch combination results in potent, dose-dependent in vivo antitumor activity in xenograft models. The advantage of being able to titrate CAR-T-cell in vivo activity was further evidenced by reduced in vivo toxicity and the elimination of persistent B-cell aplasia in immune-competent mice. The ability to control CAR-T cell and cancer cell interactions using intermediate switch molecules may expand the scope of engineered T-cell therapy to solid tumors, as well as indications beyond cancer therapy.

Versatile strategy for controlling the specificity and activity of engineered T cells

The adoptive transfer of autologous T cells engineered to express a chimeric antigen receptor (CAR) has emerged as a promising cancer therapy. Despite impressive clinical efficacy, the general application of current CAR-T--cell therapy is limited by serious treatment-related toxicities. One approach to improve the safety of CAR-T cells involves making their activation and proliferation dependent upon adaptor molecules that mediate formation of the immunological synapse between the target cancer cell and T-cell. Here, we describe the design and synthesis of structurally defined semisynthetic adaptors we refer to as "switch" molecules, in which anti-CD19 and anti-CD22 antibody fragments are site-specifically modified with FITC using genetically encoded noncanonical amino acids. This approach allows the precise control over the geometry and stoichiometry of complex formation between CD19- or CD22-expressing cancer cells and a "universal" anti-FITC-directed CAR-T cell. Optimization of this CAR-switch combination results in potent, dose-dependent in vivo antitumor activity in xenograft models. The advantage of being able to titrate CAR-T-cell in vivo activity was further evidenced by reduced in vivo toxicity and the elimination of persistent B-cell aplasia in immune-competent mice. The ability to control CAR-T cell and cancer cell interactions using intermediate switch molecules may expand the scope of engineered T-cell therapy to solid tumors, as well as indications beyond cancer therapy.

Chimeric antigen receptor-redirected T cells return to the bench

While the clinical progress of chimeric antigen receptor T cell (CAR-T) immunotherapy has garnered attention to the field, our understanding of the biology of these chimeric molecules is still emerging. Our aim within this review is to bring to light the mechanistic understanding of these multi-modular receptors and how these individual components confer particular properties to CAR-Ts. In addition, we will discuss extrinsic factors that can be manipulated to influence CAR-T performance such as choice of cellular population, culturing conditions and additional modifications that enhance their activity particularly in solid tumors. Finally, we will also consider the emerging toxicity associated with CAR-Ts. By breaking apart the CAR and examining the role of each piece, we can build a better functioning cellular vehicle for optimized treatment of cancer patients.

Switch-mediated activation and retargeting of CAR-T cells for B-cell malignancies

Chimeric antigen receptor T (CAR-T) cell therapy has produced impressive results in clinical trials for B-cell malignancies. However, safety concerns related to the inability to control CAR-T cells once infused into the patient remain a significant challenge. Here we report the engineering of recombinant antibody-based bifunctional switches that consist of a tumor antigen-specific Fab molecule engrafted with a peptide neo-epitope, which is bound exclusively by a peptide-specific switchable CAR-T cell (sCAR-T). The switch redirects the activity of the bio-orthogonal sCAR-T cells through the selective formation of immunological synapses, in which the sCAR-T cell, switch, and target cell interact in a structurally defined and temporally controlled manner. Optimized switches specific for CD19 controlled the activity, tissue-homing, cytokine release, and phenotype of sCAR-T cells in a dose-titratable manner in a Nalm-6 xenograft rodent model of B-cell leukemia. The sCAR-T-cell dosing regimen could be tuned to provide efficacy comparable to the corresponding conventional CART-19, but with lower cytokine levels, thereby offering a method of mitigating cytokine release syndrome in clinical translation. Furthermore, we demonstrate that this methodology is readily adaptable to targeting CD20 on cancer cells using the same sCAR-T cell, suggesting that this approach may be broadly applicable to heterogeneous and resistant tumor populations, as well as other liquid and solid tumor antigens.

Design of chimeric antigen receptors with integrated controllable transient functions

The ability to control T cells engineered to permanently express chimeric antigen receptors (CARs) is a key feature to improve safety. Here, we describe the development of a new CAR architecture with an integrated switch-on system that permits to control the CAR T-cell function. This system offers the advantage of a transient CAR T-cell for safety while letting open the possibility of multiple cytotoxicity cycles using a small molecule drug.

Synthetic biology: insights into biological computation

Synthetic biology attempts to rationally engineer biological systems in order to perform desired functions. Our increasing understanding of biological systems guides this rational design, while the huge background in electronics for building circuits defines the methodology.

Prospects for gene-engineered T cell immunotherapy for solid cancers

Adoptive transfer of receptor-engineered T cells has produced impressive results in treating patients with B cell leukemias and lymphomas. This success has captured public imagination and driven academic and industrial researchers to develop similar 'off-the-shelf' receptors targeting shared antigens on epithelial cancers, the leading cause of cancer-related deaths. However, the successful treatment of large numbers of people with solid cancers using this strategy is unlikely to be straightforward. Receptor-engineered T cells have the potential to cause lethal toxicity from on-target recognition of normal tissues, and there is a paucity of truly tumor-specific antigens shared across tumor types. Here we offer our perspective on how expanding the use of genetically redirected T cells to treat the majority of patients with solid cancers will require major technical, manufacturing and regulatory innovations centered around the development of autologous gene therapies targeting private somatic mutations.

The quest for spatio-temporal control of CAR T cells

Chimeric antigen receptors (CARs) are synthetic receptors capable of directing potent antigen-specific anti-tumor T cell responses. A recent report by Wu et al. extends a series of strategies aiming to curb excessive T cell activity, utilizing in this instance a chemical dimerizer to aggregate antigen-binding, T cell-activating and costimulatory domains.

T-cell receptor gene therapy--ready to go viral?

T lymphocytes can be redirected to recognize a tumor target and harnessed to combat cancer by genetic introduction of T-cell receptors of a defined specificity. This approach has recently mediated encouraging clinical responses in patients with cancers previously regarded as incurable. However, despite the great promise, T-cell receptor gene therapy still faces a multitude of obstacles. Identification of epitopes that enable effective targeting of all the cells in a heterogeneous tumor while sparing normal tissues remains perhaps the most demanding challenge. Experience from clinical trials has revealed the dangers associated with T-cell receptor gene therapy and highlighted the need for reliable preclinical methods to identify potentially hazardous recognition of both intended and unintended epitopes in healthy tissues. Procedures for manufacturing large and highly potent T-cell populations can be optimized to enhance their antitumor efficacy. Here, we review the current knowledge gained from preclinical models and clinical trials using adoptive transfer of T-cell receptor-engineered T lymphocytes, discuss the major challenges involved and highlight potential strategies to increase the safety and efficacy to make T-cell receptor gene therapy a standard-of-care for large patient groups.