A highly compact epitope-based marker/suicide gene for easier and safer T-cell therapy

The Future of Regulatory T Cell Therapy: Promises and Challenges of Implementing CAR Technology

Cell therapy with polyclonal regulatory T cells (Tregs) has been translated into the clinic and is currently being tested in transplant recipients and patients suffering from autoimmune diseases. Moreover, building on animal models, it has been widely reported that antigen-specific Tregs are functionally superior to polyclonal Tregs. Among various options to confer target specificity to Tregs, genetic engineering is a particularly timely one as has been demonstrated in the treatment of hematological malignancies where it is in routine clinical use. Genetic engineering can be exploited to express chimeric antigen receptors (CAR) in Tregs, and this has been successfully demonstrated to be robust in preclinical studies across various animal disease models. However, there are several caveats and a number of strategies should be considered to further improve on targeting, efficacy and to understand the in vivo distribution and fate of CAR-Tregs. Here, we review the differing approaches to confer antigen specificity to Tregs with emphasis on CAR-Tregs. This includes an overview and discussion of the various approaches to improve CAR-Treg specificity and therapeutic efficacy as well as addressing potential safety concerns. We also discuss different imaging approaches to understand the in vivo biodistribution of administered Tregs. Preclinical research as well as suitability of methodologies for clinical translation are discussed.

Promoter choice: Who should drive the CAR in T cells?

Chimeric antigen receptor (CAR) T cell therapy is an effective treatment for B cell malignancies, with emerging potential for the treatment of other hematologic cancers and solid tumors. The strength of the promoter within the CAR cassette will alter CAR-polypeptide levels on the cell surface of the T cell-impacting on the kinetics of activation, survival and memory cell formation in T cells. In addition to the CAR, promoters can be used to drive other genes of interest to enhance CAR T cell function. Expressing multiple genes from a single RNA transcript can be effectively achieved by linking the genes via a ribosomal skip site. However, promoters may differ in their ability to transcribe longer RNAs, or could interfere with lentiviral production, or transduction frequencies. In this study we compared the ability of the strong well-characterized promoters CMV, EF-1, hPGK and RPBSA to drive functional expression of a single RNA encoding three products: GFP, CAR, plus an additional cell-survival gene, Mcl-1. Although the four promoters produced similarly high lentiviral titres, EF-1 gave the best transduction efficacy of primary T cells. Major differences were found in the ability of the promoters to drive expression of long RNA encoding GFP, CAR and Mcl-1, highlighting promoter choice as an important consideration for gene therapy applications requiring the expression of long and complex mRNA.

CRISPR/Cas systems to overcome challenges in developing the next generation of T cells for cancer therapy

Genetically engineered immune cells with chimeric antigen receptors (CAR) or modified T cell receptors (TCR) have demonstrated their potential as a potent class of new cancer therapeutic strategy. Despite the clinical success of autologous CD19 CAR T cells in hematological malignancies, allogeneic T cells exhibit many advantages over their autologous counterparts and have recently gathered widespread attention due to the emergence of multiplex genome editing techniques, particularly CRISPR/Cas systems. Furthermore, genetically engineered T cells face a host of major challenges in solid tumors that are not as significant for blood cancers such as T cell targeted delivery, target specificity, proliferation, persistence, and the immunosuppressive tumor microenvironment. We take this opportunity to analyze recent strategies to develop allogeneic T cells, specifically in consideration of CRISPR/Cas and its delivery systems for multiplex gene editing. Additionally, we discuss the current methods used to delivery CRISPR/Cas systems for immunotherapeutic applications, and the challenges to continued development of novel delivery systems. We also provide a comprehensive analysis of the major challenges that genetically engineered T cells face in solid tumors along with the most recent strategies to overcome these barriers, with an emphasis on CRISPR-based approaches. We illustrate the synergistic prospects for how the combination of synthetic biology and immune-oncology could pave the way for designing the next generation of precision cancer therapy.

Engineering Strategies to Enhance TCR-Based Adoptive T Cell Therapy

T cell receptor (TCR)-based adoptive T cell therapies (ACT) hold great promise for the treatment of cancer, as TCRs can cover a broad range of target antigens. Here we summarize basic, translational and clinical results that provide insight into the challenges and opportunities of TCR-based ACT. We review the characteristics of target antigens and conventional αβ-TCRs, and provide a summary of published clinical trials with TCR-transgenic T cell therapies. We discuss how synthetic biology and innovative engineering strategies are poised to provide solutions for overcoming current limitations, that include functional avidity, MHC restriction, and most importantly, the tumor microenvironment. We also highlight the impact of precision genome editing on the next iteration of TCR-transgenic T cell therapies, and the discovery of novel immune engineering targets. We are convinced that some of these innovations will enable the field to move TCR gene therapy to the next level.

convertibleCARs: A chimeric antigen receptor system for flexible control of activity and antigen targeting

We have developed a chimeric antigen receptor (CAR) platform that functions as a modular system to address limitations of traditional CAR therapies. An inert form of the human NKG2D extracellular domain (iNKG2D) was engineered as the ectodomain of the CAR to generate convertibleCARTM-T cells. These cells were specifically directed to kill antigen-expressing target cells only in the presence of an activating bispecific adapter comprised of an iNKG2D-exclusive ULBP2-based ligand fused to an antigen-targeting antibody (MicAbodyTM). Efficacy against Raji tumors in NSG mice was dependent upon doses of both a rituximab-based MicAbody and convertibleCAR-T cells. We have also demonstrated that the exclusive ligand-receptor partnering enabled the targeted delivery of a mutant form of IL-2 to selectively promote the expansion of convertibleCAR-T cells in vitro and in vivo. By altering the Fv domains of the MicAbody or the payload fused to the orthogonal ligand, convertibleCAR-T cells can be readily targeted or regulated.

Neurotoxicity-CAR T-cell therapy: what the neurologist needs to know

Chimeric antigen receptor (CAR) T-cell therapy is one of the most innovative therapies for haematological malignancies to emerge in a generation. Clinical studies have shown that a single dose of CAR T-cells can deliver durable clinical remissions for some patients with B-cell cancers where conventional therapies have failed.A significant complication of CAR therapy is the immune effector cell-associated neurotoxicity syndrome (ICANS). This syndrome presents a continuum from mild tremor to cerebral oedema and in a minority of cases, death. Management of ICANS is mainly supportive, with a focus on seizure prevention and attenuation of the immune system, often using corticosteroids. Parallel investigation to exclude other central nervous system pathologies (infection, disease progression) is critical. In this review, we discuss current paradigms around CAR T-cell therapy, with a focus on appropriate investigation and management of ICANS.

Overcoming Chimeric Antigen Receptor (CAR) Modified T-Cell Therapy Limitations in Multiple Myeloma

Multiple myeloma (MM) remains an incurable disease regardless of recent advances in the field. Therefore, a substantial unmet need exists to treat patients with relapsed/refractory myeloma. The use of novel agents such as daratumumab, elotuzumab, carfilzomib, or pomalidomide, among others, usually cannot completely eradicate myeloma cells. Although these new drugs have had a significant impact on the prognosis of MM patients, the vast majority ultimately become refractory or can no longer be treated due to toxicity of prior treatment, and thus succumb to the disease. Cellular therapies represent a novel approach with a unique mechanism of action against myeloma with the potential to defeat drug resistance and achieve long-term remissions. Genetic modification of cells to express a novel receptor with tumor antigen specificity is currently being explored in myeloma. Chimeric antigen receptor gene-modified T-cells (CAR T-cells) have shown to be the most promising approach so far. CAR T-cells have shown to induce durable complete remissions in other advanced hematologic malignancies like acute lymphocytic leukemia (ALL) and diffuse large B-cell lymphoma (DLBCL). With this background, significant efforts are underway to develop CAR-based therapies for MM. Currently, several antigen targets, including CD138, CD19, immunoglobulin kappa (Ig-Kappa) and B-cell maturation antigen (BCMA), are being used in clinical trials to treat myeloma patients. Some of these trials have shown promising results, especially in terms of response rates. However, the absence of a plateau is observed in most studies which correlates with the absence of durable remissions. Therefore, several potential limitations such as lack of effectiveness, off-tumor toxicities, and antigen loss or interference with soluble proteins could hamper the efficacy of CAR T-cells in myeloma. In this review, we will focus on clinical outcomes reported with CAR T-cells in myeloma, as well as on CAR T-cell limitations and how to overcome them with next generation of CAR T-cells.

Streamlined production of genetically modified T cells with activation, transduction and expansion in closed-system G-Rex bioreactors

BACKGROUND

Gas Permeable Rapid Expansion (G-Rex) bioreactors have been shown to efficiently expand immune cells intended for therapeutic use, but do not address the complexity of the viral transduction step required for many engineered T-cell products. Here we demonstrate a novel method for transduction of activated T cells with Vectofusin-1 reagent. Transduction is accomplished in suspension, in G-Rex bioreactors. The simplified transduction step is integrated into a streamlined process that uses a single bioreactor with limited operator intervention.

METHODS

Peripheral blood mononuclear cells (PBMCs) from healthy donors were thawed, washed and activated with soluble anti-CD3 and anti-CD28 antibodies either in cell culture bags or in G-Rex bioreactors. Cells were cultured in TexMACS GMP medium with interleukin (IL)-7 and IL-15 and transduced with RetroNectin in bags or Vectorfusin-1 in the G-Rex. Total viable cell number, fold expansion, viability, transduction efficiency, phenotype and function were compared between the two processes.

RESULTS

The simplified process uses a single vessel from activation through harvest and achieves 56% transduction with 29-fold expansion in 11 days. The cells generated in the simplified process do not differ from cells produced in the conventional bag-based process functionally or phenotypically.

DISCUSSION

This study demonstrates that T cells can be transduced in suspension. Further, the conventional method of generating engineered T cells in bags for clinical use can be streamlined to a much simpler, less-expensive process without compromising the quality or function of the cell product.

Non-invasive Reporter Gene Imaging of Cell Therapies, including T Cells and Stem Cells

Cell therapies represent a rapidly emerging class of new therapeutics. They are intended and developed for the treatment of some of the most prevalent human diseases, including cancer, diabetes, and for regenerative medicine. Currently, they are largely developed without precise assessment of their in vivo distribution, efficacy, or survival either clinically or preclinically. However, it would be highly beneficial for both preclinical cell therapy development and subsequent clinical use to assess these parameters in situ to enable enhancements in efficacy, applicability, and safety. Molecular imaging can be exploited to track cells non-invasively on the whole-body level and can enable monitoring for prolonged periods in a manner compatible with rapidly expanding cell types. In this review, we explain how in vivo imaging can aid the development and clinical translation of cell-based therapeutics. We describe the underlying principles governing non-invasive in vivo long-term cell tracking in the preclinical and clinical settings, including available imaging technologies, reporter genes, and imaging agents as well as pitfalls related to experimental design. Our emphasis is on adoptively transferred T cell and stem cell therapies.

Adaptor CAR Platforms-Next Generation of T Cell-Based Cancer Immunotherapy

The success of conventional chimeric antigen receptor (CAR) therapy in the treatment of refractory hematologic malignancies has triggered the development of novel exciting experimental CAR technologies. Among them, adaptor CAR platforms have received much attention. They combine the flexibility and controllability of recombinant antibodies with the power of CARs. Due to their modular design, adaptor CAR systems propose answers to the central problems of conventional CAR therapy, such as safety and antigen escape. This review provides an overview on the different adaptor CAR platforms available, discusses the possibilities and challenges of adaptor CAR therapy, and summarizes the first clinical experiences.

Anti-human CD117 CAR T-cells efficiently eliminate healthy and malignant CD117-expressing hematopoietic cells

Acute myeloid leukemia (AML) initiating and sustaining cells maintain high cell-surface similarity with their cells-of-origin, i.e., hematopoietic stem and progenitor cells (HSPCs), and identification of truly distinguishing leukemia-private antigens has remained elusive to date. To nonetheless utilize surface antigen-directed immunotherapy in AML, we here propose targeting both, healthy and malignant human HSPC, by chimeric antigen receptor (CAR) T-cells with specificity against CD117, the cognate receptor for stem cell factor. This approach should spare most mature hematopoietic cells and would require CAR T termination followed by subsequent transplantation of healthy HSPCs to rescue hematopoiesis. We successfully generated anti-CD117 CAR T-cells from healthy donors and AML patients. Anti-CD117 CAR T-cells efficiently targeted healthy and leukemic CD117-positive cells in vitro. In mice xenografted with healthy human hematopoiesis, they eliminated CD117-expressing, but not CD117-negative human cells. Importantly, in mice xenografted with primary human CD117-positive AML, they eradicated disease in a therapeutic setting. Administration of ATG in combination with rituximab, which binds to the co-expressed CAR T-cell transduction/selection marker RQR8, led to CAR T-cell depletion. Thus, we here provide the first proof of concept for the generation and preclinical efficacy of CAR T-cells directed against CD117-expressing human hematopoietic cells.

New directions in chimeric antigen receptor T cell [CAR-T] therapy and related flow cytometry

Chimeric antigen receptor (CAR) T cells provide a promising approach to the treatment of hematologic malignancies and solid tumors. Flow cytometry is a powerful analytical modality, which plays an expanding role in all stages of CAR T therapy, from lymphocyte collection, to CAR T cell manufacturing, to in vivo monitoring of the infused cells and evaluation of their function in the tumor environment. Therefore, a thorough understanding of the new directions is important for designing and implementing CAR T-related flow cytometry assays in the clinical and investigational settings. However, the speed of new discoveries and the multitude of clinical and preclinical trials make it challenging to keep up to date in this complex field. In this review, we summarize the current state of CAR T therapy, highlight the areas of emergent research, discuss applications of flow cytometry in modern cell therapy, and touch upon several considerations particular to CAR detection and assessing the effectiveness of CAR T therapy.

Engineering T Cells to Treat Cancer: The Convergence of Immuno-Oncology and Synthetic Biology

T cells engineered to recognize and kill tumor cells have emerged as powerful agents for combating cancer. Nonetheless, our ability to engineer T cells remains relatively primitive. Aside from CAR T cells for treating B cell malignancies, most T cell therapies are risky, toxic, and often ineffective, especially those that target solid cancers. To fulfill the promise of cell-based therapies, we must transform cell engineering into a systematic and predictable science by applying the principles and tools of synthetic biology. Synthetic biology uses a hierarchical approach—assembling sets of modular molecular parts that can be combined into larger circuits and systems that perform defined target tasks. We outline the toolkit of synthetic modules that are needed to overcome the challenges of solid cancers, progress in building these components, and how these modules could be used to reliably engineer more effective and precise T cell therapies.

Treg cell-based therapies: challenges and perspectives

Cellular therapies using regulatory T (Treg) cells are currently undergoing clinical trials for the treatment of autoimmune diseases, transplant rejection and graft-versus-host disease. In this Review, we discuss the biology of Treg cells and describe new efforts in Treg cell engineering to enhance specificity, stability, functional activity and delivery. Finally, we envision that the success of Treg cell therapy in autoimmunity and transplantation will encourage the clinical use of adoptive Treg cell therapy for non-immune diseases, such as neurological disorders and tissue repair.

Emerging Approaches for Regulation and Control of CAR T Cells: A Mini Review

Chimeric antigen receptor (CAR) T cells have emerged as a promising treatment for patients with advanced B-cell cancers. However, widespread application of the therapy is currently limited by potentially life-threatening toxicities due to a lack of control of the highly potent transfused cells. Researchers have therefore developed several regulatory mechanisms in order to control CAR T cells in vivo. Clinical adoption of these control systems will depend on several factors, including the need for temporal and spatial control, the immunogenicity of the requisite components as well as whether the system allows reversible control or induces permanent elimination. Here we describe currently available and emerging control methods and review their function, advantages, and limitations.

Recent Advances in Allogeneic CAR-T Cells

In recent decades, great advances have been made in the field of tumor treatment. Especially, cell-based therapy targeting tumor associated antigen (TAA) has developed tremendously. T cells were engineered to have the ability to attack tumor cells by generating CAR constructs consisting of genes encoding scFv, a co-stimulatory domain (CD28 or TNFRSF9), and CD247 signaling domains for T cell proliferation and activation. Principally, CAR-T cells are activated by recognizing TAA by scFv on the T cell surface, and then signaling domains inside cells connected by scFv are subsequently activated to induce downstream signaling pathways involving T cell proliferation, activation, and production of cytokines. Many efforts have been made to increase the efficacy and persistence and also to decrease T cell exhaustion. Overall, allogeneic and universal CAR-T generation has attracted much attention because of their wide and prompt usage for patients. In this review, we summarized the current techniques for generation of allogeneic and universal CAR-T cells along with their disadvantages and limitations that still need to be overcome.

The clinical potential of gene editing as a tool to engineer cell-based therapeutics

The clinical application of ex vivo gene edited cell therapies first began a decade ago with zinc finger nuclease editing of autologous CD4+ T-cells. Editing aimed to disrupt expression of the human immunodeficiency virus co-receptor gene CCR5, with the goal of yielding cells resistant to viral entry, prior to re-infusion into the patient. Since then the field has substantially evolved with the arrival of the new editing technologies transcription activator-like effector nucleases (TALENs) and clustered regularly interspaced short palindromic repeats (CRISPR), and the potential benefits of gene editing in the arenas of immuno-oncology and blood disorders were quickly recognised. As the breadth of cell therapies available clinically continues to rise there is growing interest in allogeneic and off-the-shelf approaches and multiplex editing strategies are increasingly employed. We review here the latest clinical trials utilising these editing technologies and consider the applications on the horizon.

Advances and Challenges of CAR T Cells in Clinical Trials

As a specifically programmable, living immunotherapeutic drug, chimeric antigen receptor (CAR)-modified T cells are providing an alternative treatment option for a broad variety of diseases including so far refractory cancer. By recognizing a tumor-associated antigen, the CAR triggers an anti-tumor response of engineered patient's T cells achieving lasting remissions in the treatment of leukemia and lymphoma. During the last years, significant progress was made in optimizing the CAR design, in manufacturing CAR-engineered T cells, and in the clinical management of patients showing promise to establish adoptive CAR T cell therapy as an effective treatment option in the forefront.

Current advances in chimeric antigen receptor T-cell therapy for refractory/relapsed multiple myeloma

Multiple myeloma (MM), considered an incurable hematological malignancy, is characterized by its clonal evolution of malignant plasma cells. Although the application of autologous stem cell transplantation (ASCT) and the introduction of novel agents such as immunomodulatory drugs (IMiDs) and proteasome inhibitors (PIs) have doubled the median overall survival to eight years, relapsed and refractory diseases are still frequent events in the course of MM. To achieve a durable and deep remission, immunotherapy modalities have been developed for relapsed/refractory multiple myeloma (RRMM). Among these approaches, chimeric antigen receptor (CAR) T-cell therapy is the most promising star, based on the results of previous success in B-cell neoplasms. In this immunotherapy, autologous T cells are engineered to express an artificial receptor which targets a tumor-associated antigen and initiates the T-cell killing procedure. Tisagenlecleucel and Axicabtagene, targeting the CD19 antigen, are the two pacesetters of CAR T-cell products. They were approved by the US Food and Drug Administration (FDA) in 2017 for the treatment of acute lymphocytic leukemia (ALL) and diffuse large B-cell lymphoma (DLBCL). Their development enabled unparalleled efficacy in combating hematopoietic neoplasms. In this review article, we summarize six promising candidate antigens in MM that can be targeted by CARs and discuss some noteworthy studies of the safety profile of current CAR T-cell therapy.

CAR T Cell Therapy Progress and Challenges for Solid Tumors

The past two decades have marked the beginning of an unprecedented success story for cancer therapy through redirecting antitumor immunity [1]. While the mechanisms that control the initial and ongoing immune responses against tumors remain a strong research focus, the clinical development of technologies that engage the immune system to target and kill cancer cells has become a translational research priority. Early attempts documented in the late 1800s aimed at sparking immunity with cancer vaccines were difficult to interpret but demonstrated an opportunity that more than 100 years later has blossomed into the current field of cancer immunotherapy. Perhaps the most recent and greatest illustration of this is the widespread appreciation that tumors actively shut down antitumor immunity, which has led to the emergence of checkpoint pathway inhibitors that re-invigorate the body's own immune system to target cancer [2, 3]. This class of drugs, with first FDA approvals in 2011, has demonstrated impressive durable clinical responses in several cancer types, including melanoma, lung cancer, Hodgkin's lymphoma, and renal cell carcinoma, with the ongoing investigation in others. The biology and ultimate therapeutic successes of these drugs led to the 2018 Nobel Prize in Physiology or Medicine, awarded to Dr. James Allison and Dr. Tasuku Honjo for their contributions to cancer therapy [4]. In parallel to the emerging science that aided in unleashing the body's own antitumor immunity with checkpoint pathway inhibitors, researchers were also identifying ways to re-engineer antitumor immunity through adoptive cellular immunotherapy approaches. Chimeric antigen receptor (CAR)-based T cell therapy has achieved an early head start in the field, with two recent FDA approvals in 2017 for the treatment of B-cell malignancies [5]. There is an explosion of preclinical and clinical efforts to expand the therapeutic indications for CAR T cell therapies, with a specific focus on improving their clinical utility, particularly for the treatment of solid tumors. In this chapter, we will highlight the recent progress, challenges, and future perspectives surrounding the development of CAR T cell therapies for solid tumors.

Monitoring Allogeneic CAR-T Cells Using Flow Cytometry

Chimeric antigen receptor T cell (CAR-T) therapies have now entered mainstream clinical practice with two approved autologous CAR-T products targeting CD19 and numerous other products in early and late phase clinical trials. This has led to a demand for highly sensitive, specific, and easily reproducible methods to monitor CAR-T cells in patients. Here we describe a flow cytometry based protocol for detection of allogeneic CAR-T cells and for monitoring their phenotype and numbers in blood and bone marrow of patients following CAR-T treatment.

Targeting T cell malignancies using CAR-based immunotherapy: challenges and potential solutions

Chimeric antigen receptor (CAR) T cell therapy has been successful in treating B cell malignancies in clinical trials; however, fewer studies have evaluated CAR T cell therapy for the treatment of T cell malignancies. There are many challenges in translating this therapy for T cell disease, including fratricide, T cell aplasia, and product contamination. To the best of our knowledge, no tumor-specific antigen has been identified with universal expression on cancerous T cells, hindering CAR T cell therapy for these malignancies. Numerous approaches have been assessed to address each of these challenges, such as (i) disrupting target antigen expression on CAR-modified T cells, (ii) targeting antigens with limited expression on T cells, and (iii) using third party donor cells that are either non-alloreactive or have been genome edited at the T cell receptor α constant (TRAC) locus. In this review, we discuss CAR approaches that have been explored both in preclinical and clinical studies targeting T cell antigens, as well as examine other potential strategies that can be used to successfully translate this therapy for T cell disease.

Engineering strategies to overcome the current roadblocks in CAR T cell therapy

T cells genetically engineered to express chimeric antigen receptors (CARs) have proven — and impressive — therapeutic activity in patients with certain subtypes of B cell leukaemia or lymphoma, with promising efficacy also demonstrated in patients with multiple myeloma. Nevertheless, various barriers restrict the efficacy and/or prevent the widespread use of CAR T cell therapies in these patients as well as in those with other cancers, particularly solid tumours. Key challenges relating to CAR T cells include severe toxicities, restricted trafficking to, infiltration into and activation within tumours, suboptimal persistence in vivo, antigen escape and heterogeneity, and manufacturing issues. The evolution of CAR designs beyond the conventional structures will be necessary to address these limitations and to expand the use of CAR T cells to a wider range of malignancies. Investigators are addressing the current obstacles with a wide range of engineering strategies in order to improve the safety, efficacy and applicability of this therapeutic modality. In this Review, we discuss the innovative designs of novel CAR T cell products that are being developed to increase and expand the clinical benefits of these treatments in patients with diverse cancers.

Chimeric antigen receptor (CAR) T cell therapy, the first approved therapeutic approach with a genetic engineering component, holds substantial promise in the treatment of a range of cancers but is nevertheless limited by various challenges, including toxicities, intrinsic and acquired resistance mechanisms, and manufacturing issues. In this Review, the authors describe the innovative approaches to the engineering of CAR T cell products that are providing solutions to these challenges and therefore have the potential to considerably improve the safety and effectiveness of treatment.

Chimeric antigen receptor (CAR) T cells have induced remarkable responses in patients with certain haematological malignancies, yet various barriers restrict the efficacy and/or prevent the widespread use of this treatment.

Investigators are addressing these challenges with engineering strategies designed to improve the safety, efficacy and applicability of CAR T cell therapy.

CARs have modular components, and therefore the optimal molecular design of the CAR can be achieved through many variations of the constituent protein domains.

Toxicities currently associated with CAR T cell therapy can be mitigated using engineering strategies to make CAR T cells safer and that potentially broaden the range of tumour-associated antigens that can be targeted by overcoming on-target, off-tumour toxicities.

CAR T cell efficacy can be enhanced by using engineering strategies to address the various challenges relating to the unique biology of diverse haematological and solid malignancies.

Strategies to address the manufacturing challenges can lead to an improved CAR T cell product for all patients.

Highly efficient multiplex human T cell engineering without double-strand breaks using Cas9 base editors

The fusion of genome engineering and adoptive cellular therapy holds immense promise for the treatment of genetic disease and cancer. Multiplex genome engineering using targeted nucleases can be used to increase the efficacy and broaden the application of such therapies but carries safety risks associated with unintended genomic alterations and genotoxicity. Here, we apply base editor technology for multiplex gene modification in primary human T cells in support of an allogeneic CAR-T platform and demonstrate that base editor can mediate highly efficient multiplex gene disruption with minimal double-strand break induction. Importantly, multiplex base edited T cells exhibit improved expansion and lack double strand break-induced translocations observed in T cells edited with Cas9 nuclease. Our findings highlight base editor as a powerful platform for genetic modification of therapeutically relevant primary cell types.

Development of adaptive immune effector therapies in solid tumors

State-of-the-art treatment strategies have drastically ameliorated the outcome of patients affected by cancer. However, resistant and recurrent solid tumors are generally nonresponsive to conventional therapies. A central factor in the sequence of events that lead to cancer is an alteration in antitumor immune surveillance, which results in failure to recognize and eliminate the transformed tumor cell. A greater understanding of the dysregulation and evasion of the immune system in the evolution and progression of cancer provides the basis for improved therapies. Targeted strategies, such as T-cell therapy, not only generally spare normal tissues, but also use alternative antineoplastic mechanisms that synergize with other therapeutics. Despite encouraging success in hematologic malignancies, adaptive cellular therapies for solid tumors face unique challenges because of the immunosuppressive tumor microenvironment, and the hurdle of T-cell trafficking within scarcely accessible tumor sites. This review provides a brief overview of current cellular therapeutic strategies for solid tumors, research carried out to increase efficacy and safety, and results from ongoing clinical trials.

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.

Engineering γδT cells limits tonic signaling associated with chimeric antigen receptors

Despite the benefits of chimeric antigen receptor (CAR)-T cell therapies against lymphoid malignancies, responses in solid tumors have been more limited and off-target toxicities have been more marked. Among the possible design limitations of CAR-T cells for cancer are unwanted tonic (antigen-independent) signaling and off-target activation. Efforts to overcome these hurdles have been blunted by a lack of mechanistic understanding. Here, we showed that single-cell analysis with time course mass cytometry provided a rapid means of assessing CAR-T cell activation. We compared signal transduction in expanded T cells to that in T cells transduced to express second-generation CARs and found that cell expansion enhanced the response to stimulation. However, expansion also induced tonic signaling and reduced network plasticity, which were associated with expression of the T cell exhaustion markers PD-1 and TIM-3. Because this was most evident in pathways downstream of CD3ζ, we performed similar analyses on γδT cells that expressed chimeric costimulatory receptors (CCRs) lacking CD3ζ but containing DAP10 stimulatory domains. These CCR-γδT cells did not exhibit tonic signaling but were efficiently activated and mounted cytotoxic responses in the presence of CCR-specific stimuli or cognate leukemic cells. Single-cell signaling analysis enabled detailed characterization of CAR-T and CCR-T cell activation to better understand their functional activities. Furthermore, we demonstrated that CCR-γδT cells may offer the potential to avoid on-target, off-tumor toxicity and allo-reactivity in the context of myeloid malignancies.

Next generation chimeric antigen receptor T cells: safety strategies to overcome toxicity

Chimeric antigen receptor T (CAR-T) cell therapy is an emerging and effective cancer immunotherapy. Especially in hematological malignancies, CAR-T cells have achieved exciting results. Two Anti-CD19 CAR-T therapies have been approved for the treatment of CD19-positive leukemia or lymphoma. However, the application of CAR-T cells is obviously hampered by the adverse effects, such as cytokines release syndrome and on-target off-tumor toxicity. In some clinical trials, patients quitted the treatment of CAR-T cells due to life-threatening toxicity. Seeking to alleviate these toxicities or prevent the occurrence, researchers have developed a number of safety strategies of CAR-T cells, including suicide genes, synthetic Notch receptor, on-switch CAR, combinatorial target-antigen recognition, bispecific T cell engager and inhibitory CAR. This review summarized the preclinical studies and clinical trials of the safety strategies of CAR-T cells and their respective strengths and weaknesses.

Anti-CAR-engineered T cells for epitope-based elimination of autologous CAR T cells

Although CAR T-cell therapy has demonstrated tremendous clinical efficacy especially in hematological malignancies, severe treatment-associated toxicities still compromise the widespread application of this innovative technology. Therefore, developing novel approaches to abrogate CAR T-cell-mediated side effects is of great relevance. Several promising strategies pursue the selective antibody-based depletion of adoptively transferred T cells via elimination markers. However, given the limited half-life and tissue penetration, dependence on the patients’ immune system and on-target/off-side effects of proposed monoclonal antibodies, we sought to exploit αCAR-engineered T cells to efficiently eliminate CAR T cells. For comprehensive and specific recognition, a small peptide epitope (E-tag) was incorporated into the extracellular spacer region of CAR constructs. We provide first proof-of-concept for targeting this epitope by αE-tag CAR T cells, allowing an effective killing of autologous E-tagged CAR T cells both in vitro and in vivo whilst sparing cells lacking the E-tag. In addition to CAR T-cell cytotoxicity, the αE-tag-specific T cells can be empowered with cancer-fighting ability in case of relapse, hence, have versatile utility. Our proposed methodology can most probably be implemented in CAR T-cell therapies regardless of the targeted tumor antigen aiding in improving overall safety and survival control of highly potent gene-modified cells.

Tumor infiltrating lymphocytes expanded from pediatric neuroblastoma display heterogeneity of phenotype and function

Adoptive transfer of ex vivo expanded tumor infiltrating lymphocytes (TILs) has led to clinical benefit in some patients with melanoma but has not demonstrated convincing efficacy in other solid cancers. Whilst the presence of TILs in many types of cancer is often associated with better clinical prognosis, their function has not been systematically evaluated across cancer types. Responses to immunological checkpoint inhibitors in a wide range of cancers, including those for which adoptive transfer of expanded TILs has not shown clinical benefit, has clearly delineated a number of tumor type associated with tumor-reactive lymphocytes capable of effecting tumor remissions. Neuroblastoma is an aggressive childhood solid cancer in which immunotherapy with GD2-directed antibodies confers a proven survival advantage through incompletely understood mechanisms. We therefore evaluated the feasibility of ex vivo expansion of TILs from freshly resected neuroblastoma tumors and the potential therapeutic utility of TIL expansions. TILs were successfully expanded from both tumor biopsies or resections. Significant numbers of NKT and γδT cells were identified alongside the mixed population of cytotoxic (CD8⁺) and helper (CD4⁺) T cells of both effector and central memory phenotypes. Isolated TILs were broadly non-reactive against autologous tumor and neuroblastoma cell lines, so enhancement of neuroblastoma killing was attained by transducing TILs with a second-generation chimeric antigen receptor (CAR) targeting GD2. CAR-TILs demonstrated antigen-specific cytotoxicity against tumor cell lines. This study is the first to show reproducible expansion of TILs from pediatric neuroblastoma, the high proportion of innate-like lymphocytes, and the feasibility to use CAR-TILs therapeutically.

Adoptive T Cell Therapy Following Haploidentical Hematopoietic Stem Cell Transplantation

Delayed immune reconstitution and the consequently high rates of leukemia relapse and infectious complications are the main limitations of haploidentical hematopoietic stem cell transplantation. Donor T cell addback can accelerate immune reconstitution but the therapeutic window between graft-vs.-host disease and protective immunity is very narrow in the haploidentical transplant setting. Hence, strategies to improve the safety and efficacy of adoptive T cell transfer are particularly relevant in this setting. Adoptive T cell transfer strategies in haploidentical transplantation include the use of antigen-specific T cells, allodepletion and alloanergy induction, immune modulation by the co-infusion of regulatory cell populations, and the use of safety switch gene-modified T cells. Whilst common principles apply, there are features that are unique to haploidentical transplantation, where HLA-mismatching directly impacts on immune reconstitution, and shared vs. non-shared HLA-allele can be an important consideration in antigen-specific T cell therapy. This review will also present an update on safety switch gene-modified T cells, which can be conditionally deleted in the event of severe graft- vs.-host disease or other adverse events. Herpes Virus Simplex Thymidine Kinase (HSVtk) and inducible caspase-9 (iCasp9) are safety switches that have undergone multicenter studies in haploidentical transplantation with encouraging results. These gene-modified cells, which are trackable long-term, have also provided important insights on the fate of adoptively transferred T cells. In this review, we will discuss the biology of post-transplant T cell immune reconstitution and the impact of HLA-mismatching, and the different cellular therapy strategies that can help accelerate T cell immune reconstitution after haploidentical transplantation.

A strategy to protect off-the-shelf cell therapy products using virus-specific T-cells engineered to eliminate alloreactive T-cells

Background

The use of “off-the-shelf” cellular therapy products derived from healthy donors addresses many of the challenges associated with customized cell products. However, the potential of allogeneic cell products to produce graft-versus-host disease (GVHD), and their likely rejection by host alloreactive T-cells are major barriers to their clinical safety and efficacy. We have developed a molecule that when expressed in T-cells, can eliminate alloreactive T-cells and hence can be used to protect cell therapy products from allospecific rejection. Further, expression of this molecule in virus-specific T-cells (VSTs) should virtually eliminate the potential for recipients to develop GVHD.

Methods

To generate a molecule that can mediate killing of cognate alloreactive T-cells, we fused beta-2 microglobulin (B2M), a universal component of all human leukocyte antigen (HLA) class I molecules, to the cytolytic endodomain of the T cell receptor ζ chain, to create a chimeric HLA accessory receptor (CHAR). To determine if CHAR-modified human VSTs could eliminate alloreactive T-cells, we co-cultured them with allogeneic peripheral blood mononuclear cells (PBMC), and assessed proliferation of PBMC-derived alloreactive T-cells and the survival of CHAR-modified VSTs by flow cytometry.

Results

The CHAR was able to transport HLA molecules to the cell surface of Daudi cells, that lack HLA class I expression due to defective B2M expression, illustrating its ability to complex with human HLA class I molecules. Furthermore, VSTs expressing CHAR were protected from allospecific elimination in co-cultures with allogeneic PBMCs compared to unmodified VSTs, and mediated killing of alloreactive T-cells. Unexpectedly, CHAR-modified VSTs eliminated not only alloreactive HLA class I restricted CD8 T-cells, but also alloreactive CD4 T-cells. This beneficial effect resulted from non-specific elimination of activated T-cells. Of note, we confirmed that CHAR-modified VSTs did not affect pathogen-specific T-cells which are essential for protective immunity.

Conclusions

Human T-cells can be genetically modified to eliminate alloreactive T-cells, providing a unique strategy to protect off-the-shelf cell therapy products. Allogeneic cell therapies have already proved effective in treating viral infections in the stem cell transplant setting, and have potential in other fields such as regenerative medicine. A strategy to prevent allograft rejection would greatly increase their efficacy and commercial viability.

Electronic supplementary material

The online version of this article (10.1186/s12967-019-1988-y) contains supplementary material, which is available to authorized users.

Synergistic combination of oncolytic virotherapy with CAR T-cell therapy

For patients with advanced hematological malignancies the therapeutic landscape has been transformed by the emergence of adoptive cell transfer utilizing autologous chimeric antigen receptor (CAR)-redirected T-cells. However, solid tumors have proved far more resistant to this approach. Here, we summarize the numerous challenges faced by CAR T-cells designed to target solid tumors, highlighting, in particular, issues related to impaired trafficking, expansion, and persistence. In parallel, we draw attention to exciting developments in the burgeoning field of oncolytic virotherapy and posit strategies for the synergistic combination of oncolytic viruses with CAR T-cells to improve outcomes for patients with advanced solid tumors.

Production of CAR T-cells by GMP-grade lentiviral vectors: latest advances and future prospects

Chimeric antigen receptor (CAR) T-cells represent a paradigm shift in cancer immunotherapy and a new milestone in the history of oncology. In 2017, the Food and Drug Administration approved two CD19-targeted CAR T-cell therapies (Kymriah™, Novartis, and Yescarta™, Kite Pharma/Gilead Sciences) that have remarkable efficacy in some B-cell malignancies. The CAR approach is currently being evaluated in multiple pivotal trials designed for the immunotherapy of hematological malignancies as well as solid tumors. To generate CAR T-cells ex vivo, lentiviral vectors (LVs) are particularly appealing due to their ability to stably integrate relatively large DNA inserts, and to efficiently transduce both dividing and nondividing cells. This review discusses the latest advances and challenges in the design and production of CAR T-cells, and the good manufacturing practices (GMP)-grade production process of LVs used as a gene transfer vehicle. New developments in the application of CAR T-cell therapy are also outlined with particular emphasis on next-generation allogeneic CAR T-cells.

Bispecific T-Cell Redirection versus Chimeric Antigen Receptor (CAR)-T Cells as Approaches to Kill Cancer Cells

The concepts for T-cell redirecting bispecific antibodies (TRBAs) and chimeric antigen receptor (CAR)-T cells are both at least 30 years old but both platforms are just now coming into age. Two TRBAs and two CAR-T cell products have been approved by major regulatory agencies within the last ten years for the treatment of hematological cancers and an additional 53 TRBAs and 246 CAR cell constructs are in clinical trials today. Two major groups of TRBAs include small, short-half-life bispecific antibodies that include bispecific T-cell engagers (BiTE®s) which require continuous dosing and larger, mostly IgG-like bispecific antibodies with extended pharmacokinetics that can be dosed infrequently. Most CAR-T cells today are autologous, although significant strides are being made to develop off-the-shelf, allogeneic CAR-based products. CAR-Ts form a cytolytic synapse with target cells that is very different from the classical immune synapse both physically and mechanistically, whereas the TRBA-induced synapse is similar to the classic immune synapse. Both TRBAs and CAR-T cells are highly efficacious in clinical trials but both also present safety concerns, particularly with cytokine release syndrome and neurotoxicity. New formats and dosing paradigms for TRBAs and CAR-T cells are being developed in efforts to maximize efficacy and minimize toxicity, as well as to optimize use with both solid and hematologic tumors, both of which present significant challenges such as target heterogeneity and the immunosuppressive tumor microenvironment.

Photothermal Therapy Promotes Tumor Infiltration and Antitumor Activity of CAR T Cells

Chimeric antigen receptor (CAR)-redirected T lymphocytes (CAR T cells) show modest therapeutic efficacy in solid tumors. The desmoplastic structure of the tumor and the immunosuppressive tumor microenvironment usually account for the reduced efficacy of CAR T cells in solid tumors. Mild hyperthermia of the tumor reduces its compact structure and interstitial fluid pressure, increases blood perfusion, releases antigens, and promotes the recruitment of endogenous immune cells. Therefore, the combination of mild hyperthermia with the adoptive transfer of CAR T cells can potentially increase the therapeutic index of these cells in solid tumors. It is found that the chondroitin sulfate proteoglycan-4 (CSPG4)-specific CAR T cells infused in Nod scid gamma mice engrafted with the human melanoma WM115 cell line have superior antitumor activity after photothermal ablation of the tumor. The findings suggest that photothermal therapy facilitates the accumulation and effector function of CAR T cells within solid tumors.

Adoptive Cell Therapy for Acute Myeloid Leukemia and T-Cell Acute Lymphoblastic Leukemia

Refractory and relapsed acute myeloid leukemia (AML) and T-lineage leukemia have poor prognosis and limited therapeutic options. Adoptive cellular immunotherapies are emerging as an effective treatment for patients with chemotherapy refractory hematological malignancies. Indeed, the use of unselected donor lymphocyte infusions has demonstrated successes in treating patients with AML and T-lineage leukemia post-allogeneic transplantation. The development of ex vivo manipulation techniques such as genetic modification or selection and expansion of individual cellular components has permitted the clinical translation of a wide range of promising cellular therapies for AML and T-cell acute lymphoblastic leukemia. Here, we will review clinical studies to date using adoptive cell therapy approaches and outline the major challenges limiting the development of safe and effective cell therapies for both types of acute leukemia.

The nephrotoxicity of new immunotherapies

Introduction: Advanced cancers that did not respond to chemotherapy were once a death sentence, but now there are newer therapies utilizing the patient's own immune system to fight cancer that are proving effective in chemotherapy-refractory malignancies. However, this success against cancer cells may be accompanied by immune-related adverse events that can affect the kidneys. Areas covered: Using Medline and Scopus, we compiled all publications through February 2019 that pertained to immune checkpoint inhibitors (ICPIs) and chimeric antigen receptor T-cells (CAR T-cells).  The focus of this review is the discussion of these new cancer therapies, with attention to the reported kidney-related adverse effects.. Expert opinion: Autoimmunity is repressed by molecular pathways that inhibit T-cell activation against selected antigens. These self-protective mechanisms have been appropriated by tumor cells as a means of evading immune detection and destruction. New immunotherapies such as immune checkpoint inhibitors and chimeric antigen receptor T-cell therapy incite an aggressive immune response directed against tumor cells. This unrestrained activation of the immune system may result in kidney injury via multiple mechanisms.

Switching on the green light for chimeric antigen receptor T-cell therapy

Adoptive cellular therapy involving genetic modification of T cells with chimeric antigen receptor (CAR) transgene offers a promising strategy to broaden the efficacy of this approach for the effective treatment of cancer. Although remarkable antitumor responses have been observed following CAR T‐cell therapy in a subset of B‐cell malignancies, this has yet to be extended in the context of solid cancers. A number of promising strategies involving reprogramming the tumor microenvironment, increasing the specificity and safety of gene‐modified T cells and harnessing the endogenous immune response have been tested in preclinical models that may have a significant impact in patients with solid cancers. This review will discuss these exciting new developments and the challenges that must be overcome to deliver a more sustained and potent therapeutic response.

Preclinical Evaluation of Allogeneic CAR T Cells Targeting BCMA for the Treatment of Multiple Myeloma

Clinical success of autologous CD19-directed chimeric antigen receptor T cells (CAR Ts) in acute lymphoblastic leukemia and non-Hodgkin lymphoma suggests that CAR Ts may be a promising therapy for hematological malignancies, including multiple myeloma. However, autologous CAR T therapies have limitations that may impact clinical use, including lengthy vein-to-vein time and manufacturing constraints. Allogeneic CAR T (AlloCAR T) therapies may overcome these innate limitations of autologous CAR T therapies. Unlike autologous cell therapies, AlloCAR T therapies employ healthy donor T cells that are isolated in a manufacturing facility, engineered to express CARs with specificity for a tumor-associated antigen, and modified using gene-editing technology to limit T cell receptor (TCR)-mediated immune responses. Here, transcription activator-like effector nuclease (TALEN) gene editing of B cell maturation antigen (BCMA) CAR Ts was used to confer lymphodepletion resistance and reduced graft-versus-host disease (GvHD) potential. The safety profile of allogeneic BCMA CAR Ts was further enhanced by incorporating a CD20 mimotope-based intra-CAR off switch enabling effective CAR T elimination in the presence of rituximab. Allogeneic BCMA CAR Ts induced sustained antitumor responses in mice supplemented with human cytokines, and, most importantly, maintained their phenotype and potency after scale-up manufacturing. This novel off-the-shelf allogeneic BCMA CAR T product is a promising candidate for clinical evaluation.

Quantitative in vivo dual-color bioluminescence imaging in the mouse brain

Bioluminescence imaging (BLI) is an optical imaging method that can be translated from the cell culture dish in vitro to cell tracking in small animal models in vivo. In contrast to the more widely used fluorescence imaging, which requires light excitation, in BLI the light is exclusively generated by the enzyme luciferase. The luciferase gene can be engineered to target and monitor almost every cell and biological process quantitatively in vitro and even from deep tissue in vivo. While initially used for tumor imaging, bioluminescence was recently optimized for mouse brain imaging of neural cells and monitoring of viability or differentiation of grafted stem cells. Here, we describe the use of bright color-shifted firefly luciferases (Flucs) based on the thermostable x5 Fluc that emit red and green for effective and quantitative unmixing of two human cell populations in vitro and after transplantation into the mouse brain in vivo. Spectral unmixing predicts the ratio of luciferases in vitro and a mixture of cells precisely for cortical grafts, however, with less accuracy for striatal grafts. This dual-color approach enables the simultaneous visualization and quantification of two cell populations on the whole brain scale, with particular relevance for translational studies of neurological disorders providing information on stem cell survival and differentiation in one imaging session in vivo.

The Emergence of Universal Immune Receptor T Cell Therapy for Cancer

Chimeric antigen receptor (CAR) T cells have shown great success in the treatment of CD19+ hematological malignancies, leading to their recent approval by the FDA as a new cancer treatment modality. However, their broad use is limited since a CAR targets a single tumor associated antigen (TAA), which is not effective against tumors with heterogeneous TAA expression or emerging antigen loss variants. Further, stably engineered CAR T cells can continually and uncontrollably proliferate and activate in response to antigen, potentially causing fatal on-target off-tumor toxicity, cytokine release syndrome, or neurotoxicity without a method of control or elimination. To address these issues, our lab and others have developed various universal immune receptors (UIRs) that allow for targeting of multiple TAAs by T cells expressing a single receptor. UIRs function through the binding of an extracellular adapter domain which acts as a bridge between intracellular T cell signaling domains and a soluble tumor antigen targeting ligand (TL). The dissociation of TAA targeting and T cell signaling confers many advantages over standard CAR therapy, such as dose control of T cell effector function, the ability to simultaneously or sequentially target multiple TAAs, and control of immunologic synapse geometry. There are currently four unique UIR platform types: ADCC-mediating Fc-binding immune receptors, bispecific protein engaging immune receptors, natural binding partner immune receptors, and anti-tag CARs. These UIRs all allow for potential benefits over standard CARs, but also bring unique engineering challenges that will have to be addressed to achieve maximal efficacy and safety in the clinic. Still, UIRs present an exciting new avenue for adoptive T cell transfer therapies and could lead to their expanded use in areas which current CAR therapies have failed. Here we review the development of each UIR platform and their unique functional benefits, and detail the potential hurdles that may need to be overcome for continued clinical translation.

Constitutively active MyD88/CD40 costimulation enhances expansion and efficacy of chimeric antigen receptor T cells targeting hematological malignancies

Successful adoptive chimeric antigen receptor (CAR) T-cell therapies against hematological malignancies require CAR-T expansion and durable persistence following infusion. Balancing increased CAR-T potency with safety, including severe cytokine-release syndrome (sCRS) and neurotoxicity, warrants inclusion of safety mechanisms to control in vivo CAR-T activity. Here, we describe a novel CAR-T cell platform that utilizes expression of the toll-like receptor (TLR) adaptor molecule, MyD88, and tumor-necrosis factor family member, CD40 (MC), tethered to the CAR molecule through an intentionally inefficient 2A linker system, providing a constitutive signal that drives CAR-T survival, proliferation, and antitumor activity against CD19⁺ and CD123⁺ hematological cancers. Robust activity of MC-enhanced CAR-T cells was associated with cachexia in animal models that corresponded with high levels of human cytokine production. However, toxicity could be successfully resolved by using the inducible caspase-9 (iC9) safety switch to reduce serum cytokines, by administration of a neutralizing antibody against TNF-α, or by selecting “low” cytokine-producing CD8⁺ T cells, without loss of antitumor activity. Interestingly, high basal activity was essential for in vivo CAR-T expansion. This study shows that co-opting novel signaling elements (i.e., MyD88 and CD40) and development of a unique CAR-T architecture can drive T-cell proliferation in vivo to enhance CAR-T therapies.

Fueling Cancer Immunotherapy With Common Gamma Chain Cytokines

Adoptive T cell transfer therapy (ACT) using tumor infiltrating lymphocytes or lymphocytes redirected with antigen receptors (CAR or TCR) has revolutionized the field of cancer immunotherapy. Although CAR T cell therapy mediates robust responses in patients with hematological malignancies, this approach has been less effective for treating patients with solid tumors. Additionally, toxicities post T cell infusion highlight the need for safer ACT protocols. Current protocols traditionally expand T lymphocytes isolated from patient tumors or from peripheral blood to large magnitudes in the presence of high dose IL-2 prior to infusion. Unfortunately, this expansion protocol differentiates T cells to a full effector or terminal phenotype in vitro, consequently reducing their long-term survival and antitumor effectiveness in vivo. Post-infusion, T cells face further obstacles limiting their persistence and function within the suppressive tumor microenvironment. Therapeutic manipulation of T cells with common γ chain cytokines, which are critical growth factors for T cells, may be the key to bypass such immunological hurdles. Herein, we discuss the primary functions of the common γ chain cytokines impacting T cell survival and memory and then elaborate on how these distinct cytokines have been used to augment T cell-based cancer immunotherapy.

CAR T Cells: A Snapshot on the Growing Options to Design a CAR

Adoptive cell therapy of malignant diseases with chimeric antigen receptor (CAR) modified T cells rapidly advanced from pre-clinical models to commercial approvals within 2 decades. CARs redirect patient's T cells towards cancer cells and activate the engineered cells for a cytolytic attack resulting in the destruction of the cognate target cell. CAR T cells have demonstrated their powerful capacities in inducing complete and lasting remissions of leukemia/lymphoma in an increasing number of trials worldwide. Since the early 90's, the design of CARs went through various steps of optimization until the very recent developments which include CARs with logic gating in the recognition of antigen patterns on target cells and TRUCKs with a target recognition induced delivery of immune modulating agents. Here we review the generations in CAR design, the impact of specific modifications, the strategies to improve the safety of CAR T cell therapy, and the challenges to adapt the CAR design for broader applications.