Therapeutic Potential of T Cell Chimeric Antigen Receptors (CARs) in Cancer Treatment: Counteracting Off-Tumor Toxicities for Safe CAR T Cell Therapy

FGFR4-specific CAR-T cells with inducible caspase-9 suicide gene as an approach to treat rhabdomyosarcoma

Metastatic rhabdomyosarcoma is associated with poor survival and unsatisfactory treatment outcomes. Therefore, new immunotherapeutic methods are urgently required. Fibroblast growth factor receptor 4 (FGFR4), a new therapeutic target for rhabdomyosarcoma, plays a crucial role in its onset and development. This study aimed to generate FGFR4 single-chain variable fragment-based chimeric antigen receptor (CAR) T cells without causing evident toxicity and incorporating an inducible caspase-9 (iCasp9) suicide gene system to enhance their safety. FGFR4 antigen expression was evaluated in normal murine tissues, normal human tissues, and specimens from patients with rhabdomyosarcoma. Combined with a 4-1BB co-stimulatory domain, a CD3ζ signaling domain, and an iCasp9 suicide gene, CAR-T cells with an FGFR4-specific single-chain variable fragment were developed. The specific cytotoxic effects, T-cell proliferation, cytokine secretion, apoptosis induction by chemical dimerization (AP20187), and toxicity of FGFR4 CAR-T cells were investigated in vitro and in vivo. FGFR4 CAR-T cells generated a variety of immune-promoting cytokines, including tumor necrosis factor α, interleukin 2, and interferon γ, and displayed effective cytotoxic activity against FGFR4-overexpressing rhabdomyosarcoma cells in vitro. FGFR4 CAR-T cells were relatively effective against FGFR4-overexpressing rhabdomyosarcoma, with tumor regression and poor survival in a subcutaneous xenograft model. The iCasp9 gene was incorporated into FGFR4 CAR-T cells and it was demonstrated that effective and reliable suicide gene activity depends on the administration of AP20187. By making use of the cross-reaction of FGFR4 CAR-T cells with murine FGFR4 in a syngeneic tumor model, this study found that FGFR4 CAR-T cells could regulate the growth of tumors without evident toxicity. Our study demonstrates that FGFR4 is a prospective target for CAR-T cell therapy in rhabdomyosarcoma without serious on-target off-tumor toxicity. FGFR4 CAR-T cells with the iCasp9 suicide gene system as a safety switch to limit toxicity may broaden the clinical applications of cellular therapy.

The peptide-based bispecific CAR T cells target EGFR and tumor stroma for effective cancer therapy

BACKGROUND AND PURPOSE

The efficacy of chimeric antigen receptor (CAR)-T cell for solid tumors is limited partially because of the lack of tumor-specific antigens and off-target effects. Low molecular weight peptides allowed CAR T cell to display several antigen receptors to reduce off-target effects. Here, we develop a peptide-based bispecific CAR for EGFR and tumor stroma, which are expressed in a variety of tumor types.

EXPERIMENTAL APPROACH AND KEY RESULTS

The peptide-based CAR T cells show excellent proliferation, cytotoxicity activity and are only activated by tumor cells overexpressing EGFR instead of normal cells with low EGFR expressing. In mouse xenograft models, the peptide bispecific CAR T cells can be delivered into the inner of tumor masses and thus are effective in inhibiting tumor growth. Meanwhile, they show strong expansion capacity and the property of maintaining long-term function in vivo. During treatment, no off-tumor toxicity is observed on healthy organs expressing lower levels of EGFR.

CONCLUSIONS & IMPLICATIONS

Our findings demonstrate that peptide-based bispecific CAR T holds great potential in solid tumor therapy due to an excellent targeting ability towards tumors and tumor microenvironment.

The method for assessing the specificity of developing CAR therapies

The effectiveness of antitumor chimeric antigen receptor (CAR) therapy mainly dealt with an elevated sensitivity of CAR cells to target cells. However, CAR therapies are associated with nonspecific side effects: on-target off-tumor toxicity. Sensitivity and specificity of CAR cells are the most important properties of the recognition process of target cells among other cells. Current developments are mainly concentrated on exploring molecular biology methods for designing CAR cells with the highest sensitivity, while the problem of the CAR cell specificity is rarely considered. For the assessment of CAR cell specificity, we suggest that, in addition to an elevated level of CAR-antigen affinity, the ability of CARs for clustering should be taken into account. We assume that the CAR cell cytotoxicity is determined by CAR clustering. The latter is treated within the framework of nucleation theory. The master equation for the probability of CAR cell cytotoxicity is derived. The size of a critical CAR cluster is found to be one of two most essential parameters. The conditions for necessary sensitivity and sufficient specificity are explored. Relevant parametric diagrams are derived. Possible applications of the method for assessing the specificity of developing CAR therapies are discussed.

NK/DC crosstalk-modulating antitumor activity via Sema3E/PlexinD1 axis for enhanced cancer immunotherapy

The complex relationship between natural killer (NK) cells and dendritic cells (DCs) within the tumor microenvironment significantly impacts the success of cancer immunotherapy. Recent advancements in cancer treatment have sought to bolster innate and adaptive immune responses through diverse modalities, aiming to tilt the immune equilibrium toward tumor elimination. Optimal antitumor immunity entails a multifaceted interplay involving NK cells, T cells and DCs, orchestrating immune effector functions. Although DC-based vaccines and NK cells' cytotoxic capabilities hold substantial therapeutic potential, their interaction is frequently hindered by immunosuppressive elements such as myeloid-derived suppressor cells (MDSCs) and regulatory T cells. Chemokines and cytokines, such as CXCL12, CCL2, interferons, and interleukins, play crucial roles in modulating NK/DC interactions and enhancing immune responses. This review elucidates the mechanisms underlying NK/DC interaction, emphasizing their pivotal roles in augmenting antitumor immune responses and the impediments posed by tumor-induced immunosuppression. Furthermore, it explores the therapeutic prospects of restoring NK/DC crosstalk, highlighting the significance of molecules like Sema3E/PlexinD1 in this context, offering potential avenues for enhancing the effectiveness of current immunotherapeutic strategies and advancing cancer treatment paradigms. Harnessing the dynamic interplay between NK and DC cells, including the modulation of Sema3E/PlexinD1 signaling, holds promise for developing more potent therapies that harness the immune system's full potential in combating cancer.

CAR-T lymphocyte-based cell therapies; mechanistic substantiation, applications and biosafety enhancement with suicide genes: new opportunities to melt side effects

Immunotherapy has made significant strides in cancer treatment with strategies like checkpoint blockade antibodies and adoptive T cell transfer. Chimeric antigen receptor T cells (CAR-T) have emerged as a promising approach to combine these strategies and overcome their limitations. This review explores CAR-T cells as a living drug for cancer treatment. CAR-T cells are genetically engineered immune cells designed to target and eliminate tumor cells by recognizing specific antigens. The study involves a comprehensive literature review on CAR-T cell technology, covering structure optimization, generations, manufacturing processes, and gene therapy strategies. It examines CAR-T therapy in haematologic cancers and solid tumors, highlighting challenges and proposing a suicide gene-based mechanism to enhance safety. The results show significant advancements in CAR-T technology, particularly in structure optimization and generation. The manufacturing process has improved for broader clinical application. However, a series of inherent challenges and side effects still need to be addressed. In conclusion, CAR-T cells hold great promise for cancer treatment, but ongoing research is crucial to improve efficacy and safety for oncology patients. The proposed suicide gene-based mechanism offers a potential solution to mitigate side effects including cytokine release syndrome (the most common toxic side effect of CAR-T therapy) and the associated neurotoxicity.

Expression of modified FcγRI enables myeloid cells to elicit robust tumor-specific cytotoxicity

Despite the central role of T cells in tumor immunity, attempts to harness their cytotoxic capacity as a therapy have met limited efficacy, partially as a result of the suppressive microenvironment which limits their migration and activation. In contrast, myeloid cells massively infiltrate tumors and are well adapted to survive these harsh conditions. While they are equipped with cell-killing abilities, they often adopt an immunosuppressive phenotype upon migration to tumors. Therefore, the questions of how to modify their activation programming against cancer, and what signaling cascades should be activated in myeloid cells to elicit their cytotoxicity have remained unclear. Here, we found that activation of IgM-induced signaling in murine myeloid cells results in secretion of lytic granules and massive tumor cell death. These findings open venues for designing novel immunotherapy by equipping monocytes with chimeric receptors that target tumor antigens and consequently, signal through IgM receptor. Nonetheless, we found that myeloid cells do not express the antibody-derived portion used to recognize the tumor antigen due to the induction of an ER stress response. To overcome this limitation, we designed chimeric receptors that are based on the high-affinity FcγRI for IgG. Incubation of macrophages expressing these receptors along with tumor-binding IgG induced massive tumor cell killing and secretion of reactive oxygen species and Granzyme B. Overall, this work highlights the challenges involved in genetically reprogramming the signaling in myeloid cells and provides a framework for endowing myeloid cells with antigen-specific cytotoxicity.

Small-molecule-mediated control of the anti-tumour activity and off-tumour toxicity of a supramolecular bispecific T cell engager

The broader clinical use of bispecific T cell engagers for inducing anti-tumour toxicity is hindered by their on-target off-tumour toxicity and the associated neurotoxicity and cytokine-release syndrome. Here we show that the off-tumour toxicity of a supramolecular bispecific T cell engager binding to the T cell co-receptor CD3 and to the human epidermal growth factor receptor 2 on breast tumour cells can be halted by disengaging the T cells from the tumour cells via the infusion of the small-molecule drug amantadine, which disassembles the supramolecular aggregate. In mice bearing human epidermal growth factor receptor 2-expressing tumours and with a human immune system, high intravenous doses of such a 'switchable T cell nanoengager' elicited strong tumour-specific adaptive immune responses that prevented tumour relapse, while the infusion of amantadine restricted off-tumour toxicity, cytokine-release syndrome and neurotoxicity. Supramolecular chemistry may be further leveraged to control the anti-tumour activity and off-tumour toxicity of bispecific antibodies.

The role of intestinal flora on tumor immunotherapy: recent progress and treatment implications

Immunotherapy, specifically immune checkpoint inhibitors, has emerged as a promising approach for treating malignant tumors. The gut, housing approximately 70 % of the body's immune cells, is abundantly populated with gut bacteria that actively interact with the host's immune system. Different bacterial species within the intestinal flora are in a delicate equilibrium and mutually regulate each other. However, when this balance is disrupted, pathogenic microorganisms can dominate, adversely affecting the host's metabolism and immunity, ultimately promoting the development of disease. Emerging researches highlight the potential of interventions such as fecal microflora transplantation (FMT) to improve antitumor immune response and reduce the toxicity of immunotherapy. These remarkable findings suggest the major role of intestinal flora in the development of cancer immunotherapy and led us to the hypothesis that intestinal flora transplantation may be a new breakthrough in modifying immunotherapy side effects.

A genetically encoded protein tag for control and quantitative imaging of CAR T cell therapy

Chimeric antigen receptor (CAR) T cell therapy has been successful for hematological malignancies. Still, a lack of efficacy and potential toxicities have slowed its application for other indications. Furthermore, CAR T cells undergo dynamic expansion and contraction in vivo that cannot be easily predicted or controlled. Therefore, the safety and utility of such therapies could be enhanced by engineered mechanisms that engender reversible control and quantitative monitoring. Here, we use a genetic tag based on the enzyme Escherichia coli dihydrofolate reductase (eDHFR), and derivatives of trimethoprim (TMP) to modulate and monitor CAR expression and T cell activity. We fused eDHFR to the CAR C terminus, allowing regulation with TMP-based proteolysis-targeting chimeric small molecules (PROTACs). Fusion of eDHFR to the CAR does not interfere with cell signaling or its cytotoxic function, and the addition of TMP-based PROTACs results in a reversible and dose-dependent inhibition of CAR activity via the proteosome. We show the regulation of CAR expression in vivo and demonstrate imaging of the cells with TMP radiotracers. In vitro immunogenicity assays using primary human immune cells and overlapping peptide fragments of eDHFR showed no memory immune repertoire for eDHFR. Overall, this translationally-orientied approach allows for temporal monitoring and image-guided control of cell-based therapies.

Regulation of eDHFR-tagged proteins with trimethoprim PROTACs

Temporal control of protein levels in cells and living animals can be used to improve our understanding of protein function. In addition, control of engineered proteins could be used in therapeutic applications. PRoteolysis-TArgeting Chimeras (PROTACs) have emerged as a small-molecule-driven strategy to achieve rapid, post-translational regulation of protein abundance via recruitment of an E3 ligase to the target protein of interest. Here, we develop several PROTAC molecules by covalently linking the antibiotic trimethoprim (TMP) to pomalidomide, a ligand for the E3 ligase, Cereblon. These molecules induce degradation of proteins of interest (POIs) genetically fused to a small protein domain, E. coli dihydrofolate reductase (eDHFR), the molecular target of TMP. We show that various eDHFR-tagged proteins can be robustly degraded to 95% of maximum expression with PROTAC molecule 7c. Moreover, TMP-based PROTACs minimally affect the expression of immunomodulatory imide drug (IMiD)-sensitive neosubstrates using proteomic and biochemical assays. Finally, we show multiplexed regulation with another known degron-PROTAC pair, as well as reversible protein regulation in a rodent model of metastatic cancer, demonstrating the formidable strength of this system. Altogether, TMP PROTACs are a robust approach for selective and reversible degradation of eDHFR-tagged proteins in vitro and in vivo.

Editorial on "Cell Therapy, Bispecific Antibodies and Other Immunotherapies against Cancer"

This Special Issue in Cancers, "Cell Therapy, Bispecific Antibodies and other Immunotherapies Against Cancer", includes interesting reports and reviews on cell therapies and bispecific antibodies [...].

Decoding the expression pattern of MUC3A in gastric adenocarcinoma: unveiling the key to successful immunotherapy

AIMS

Despite the promise of immunotherapy for gastric adenocarcinoma, resistance is common, necessitating the validation of new targets. Based on our previous bioinformatics analysis, the MUC3A antigen emerged as a promising candidate for immunotherapy against gastric adenocarcinoma. However, a comprehensive understanding of its expression at protein level remains elusive, despite its crucial role in determining clinical response. We also sought to establish a connection between the expression pattern and relevant clinical variables of the disease, whenever feasible.

METHODS

Immunohistochemistry was used to determine the percentage of MUC3A-positive tumor cells in primary (PT) and metastatic tumor (MT) sites of 190 gastric adenocarcinoma patients. We also evaluated the association between MUC3A expression and variables such as Lauren classification, history of neoadjuvant chemotherapy and/or radiotherapy, and overall patient survival.

RESULTS

Median MUC3A expression was 50% in PT and 70% in MT sites, exhibiting a positive correlation. MT intestinal type showed significantly higher MUC3A expression compared to other types. Neoadjuvant therapy history did not affect MUC3A expression. Higher MUC3A expression correlated with improved survival.

CONCLUSIONS

Based on our previous bioinformatics data and the consistently high expression of MUC3A on gastric tumor cells, we propose advancing experimental aspects of anti-MUC3A immunotherapy for gastric adenocarcinoma.

Tuning CARs: recent advances in modulating chimeric antigen receptor (CAR) T cell activity for improved safety, efficacy, and flexibility

Cancer immunotherapies utilizing genetically engineered T cells have emerged as powerful personalized therapeutic agents showing dramatic preclinical and clinical results, particularly in hematological malignancies. Ectopically expressed chimeric antigen receptors (CARs) reprogram immune cells to target and eliminate cancer. However, CAR T cell therapy's success depends on the balance between effective anti-tumor activity and minimizing harmful side effects. To improve CAR T cell therapy outcomes and mitigate associated toxicities, scientists from different fields are cooperating in developing next-generation products using the latest molecular cell biology and synthetic biology tools and technologies. The immunotherapy field is rapidly evolving, with new approaches and strategies being reported at a fast pace. This comprehensive literature review aims to provide an up-to-date overview of the latest developments in controlling CAR T cell activity for improved safety, efficacy, and flexibility.

Current advances and challenges in CAR T-Cell therapy for solid tumors: tumor-associated antigens and the tumor microenvironment

The past decade has witnessed ongoing progress in immune therapy to ameliorate human health. As an emerging technique, chimeric antigen receptor (CAR) T-cell therapy has the advantages of specific killing of cancer cells, a high remission rate of cancer-induced symptoms, rapid tumor eradication, and long-lasting tumor immunity, opening a new window for tumor treatment. However, challenges remain in CAR T-cell therapy for solid tumors due to target diversity, tumor heterogeneity, and the complex microenvironment. In this review, we have outlined the development of the CAR T-cell technique, summarized the current advances in tumor-associated antigens (TAAs), and highlighted the importance of tumor-specific antigens (TSAs) or neoantigens for solid tumors. We also addressed the challenge of the TAA binding domain in CARs to overcome off-tumor toxicity. Moreover, we illustrated the dominant tumor microenvironment (TME)-induced challenges and new strategies based on TME-associated antigens (TMAs) for solid tumor CAR T-cell therapy.

Monoclonal antibodies: Trends in therapeutic success and commercial focus

Monoclonal antibody products have risen from obscurity in the 1990s to a position that increasingly dominates both revenue generation and patient impact. This success has occurred largely over the past two decades, and we have identified factors associated with the remarkable advances that have contributed to the discovery, development and approval of monoclonal antibodies. Although consolidation has increased in recent years, the net number of monoclonal antibody developers continues to grow, bucking the general trend in the biopharmaceutical industry.

Forced expression of the non-coding RNA miR-17∼92 restores activation and function in CD28-deficient CD4+ T cells

CD28 provides the prototypical costimulatory signal required for productive T-cell activation. Known molecular consequences of CD28 costimulation are mostly based on studies of protein signaling molecules. The microRNA cluster miR-17∼92 is induced by T cell receptor stimulation and further enhanced by combined CD28 costimulation. We demonstrate that transgenic miR-17∼92 cell-intrinsically largely overcomes defects caused by CD28 deficiency. Combining genetics, transcriptomics, bioinformatics, and biochemical miRNA:mRNA interaction maps we empirically validate miR-17∼92 target genes that include several negative regulators of T cell activation. CD28-deficient T cells exhibit derepressed miR-17∼92 target genes during activation. CRISPR/Cas9-mediated ablation of the miR-17∼92 targets Pten and Nrbp1 in naive CD28-/- CD4+ T cells differentially increases proliferation and expression of the activation markers CD25 and CD44, respectively. Thus, we propose that miR-17∼92 constitutes a central mediator for T cell activation, integrating signals by the TCR and CD28 costimulation by dampening multiple brakes that prevent T cell activation.

PD-1 engineered cytomembrane cloaked molybdenum nitride for synergistic photothermal and enhanced immunotherapy of breast cancer

Incomplete tumor ablation and subsequent tumor metastasis usually occur during photothermal anti-tumor processes. The combination of photothermal and immunotherapy has proven to be a promising method to conquer technical challenges. Inhibiting the programmed death ligand-1 (PD-L1)/programmed cell death protein 1 (PD-1) immune pathway represents one of the most successful immunotherapy strategies. Whereas, the PD-L1 expression level significantly differs, leading to a relatively low response rate to the immune checkpoint blockade (ICB) approaches. Therefore, improving the expression level of PD-L1 becomes one potential method to enhance the response rate. Herein, NIH 3T3 cells were educated to steadily express PD-1 protein. Furthermore, the synthesized molybdenum nitride was then coated with PD-1 protein-modified cytomembrane, which endows it with immune checkpoint blocking capability. Moreover, under the irradiation of near-infrared light, the local mild heat released from the molybdenum nitride causes the apoptosis of tumor cells. More importantly, the elevated temperature simultaneously helps elevate the expression level of PD-L1, further enhancing the response rate of ICB. Finally, the PD-1 cytomembrane coatings interact with the upregulated PD-L1, leading to the activation of the immune system. In summary, we confirmed that the PD-1 protein-coated molybdenum nitride could synergistically ablate tumors and avoid metastasis.

Chimeric antigen receptor-engineered NK cells: new weapons of cancer immunotherapy with great potential

Chimeric antigen receptor (CAR)-engineered T (CAR-T) cells have obtained prominent achievement in the clinical immunotherapy of hematological malignant tumors, leading to a rapid development of cellular immunotherapy in cancer treatment. Scientists are also aware of the prospective advantages of CAR engineering in cellular immunotherapy. Due to various limitations such as the serious side effects of CAR-T therapy, researchers began to investigate other immune cells for CAR modification. Natural killer (NK) cells are critical innate immune cells with the characteristic of non-specifically recognizing target cells and with the potential to become "off-the-shelf" products. In recent years, many preclinical studies on CAR-engineered NK (CAR-NK) cells have shown their remarkable efficacy in cancer therapy and their superiority over autologous CAR-T cells. In this review, we summarize the generation, mechanisms of anti-tumor activity and unique advantages of CAR-NK cells, and then analyze some challenges and recent clinical trials about CAR-NK cells therapy. We believe that CAR-NK therapy is a promising prospect for cancer immunotherapy in the future.

Recent findings on chimeric antigen receptor (CAR)-engineered immune cell therapy in solid tumors and hematological malignancies

Advancements in adoptive cell therapy over the last four decades have revealed various new therapeutic strategies, such as chimeric antigen receptors (CARs), which are dedicated immune cells that are engineered and administered to eliminate cancer cells. In this context, CAR T-cells have shown significant promise in the treatment of hematological malignancies. However, many obstacles limit the efficacy of CAR T-cell therapy in both solid tumors and hematological malignancies. Consequently, CAR-NK and CAR-M cell therapies have recently emerged as novel therapeutic options for addressing the challenges associated with CAR T-cell therapies. Currently, many CAR immune cell trials are underway in various human malignancies around the world to improve antitumor activity and reduce the toxicity of CAR immune cell therapy. This review will describe the comprehensive literature of recent findings on CAR immune cell therapy in a wide range of human malignancies, as well as the challenges that have emerged in recent years.

Generation and Functional Characterization of PLAP CAR-T Cells against Cervical Cancer Cells

Chimeric antigen receptor (CAR) T-cell therapy is one of the cancer treatment modalities that has recently shown promising results in treating hematopoietic malignancies. However, one of the obstacles that need to be addressed in solid tumors is the on-target and off-tumor cytotoxicity due to the lack of specific tumor antigens with low expression in healthy cells. Placental alkaline phosphatase (PLAP) is a shared placenta- and tumor-associated antigen (TAA) that is expressed in ovarian, cervical, colorectal, and prostate cancers and is negligible in normal cells. In this study, we constructed second-generation CAR T cells with a fully human scFv against PLAP antigen andthen evaluated the characteristics of PLAP CAR T cells in terms of tonic signaling and differentiation in comparison with ΔPLAP CAR T cells and CD19 CAR T cells. In addition, by co-culturing PLAP CAR T cells with HeLa and CaSki cells, we analyzed the tumor-killing functions and the secretion of anti-tumor molecules. Results showed that PLAP CAR T cells not only proliferated during co-culture with cancer cells but also eliminated them in vitro. We also observed increased secretion of IL-2, granzyme A, and IFN-γ by PLAP CAR T cells upon exposure to the target cells. In conclusion, PLAP CAR T cells are potential candidates for further investigation in cervical cancer and, potentially, other solid tumors.

Current clinical landscape of oncolytic viruses as novel cancer immunotherapeutic and recent preclinical advancements

Oncolytic viruses (OVs) have been gaining attention in the pharmaceutical industry as a novel immunotherapeutic and therapeutic adjuvant due to their ability to induce and boost antitumor immunity through multiple mechanisms. First, intrinsic mechanisms of OVs that enable exploitation of the host immune system (e.g., evading immune detection) can nullify the immune escape mechanism of tumors. Second, many types of OVs have been shown to cause direct lysis of tumor cells, resulting in an induction of tumor-specific T cell response mediated by release of tumor-associated antigens and danger signal molecules. Third, armed OV-expressing immune stimulatory therapeutic genes could be highly expressed in tumor tissues to further improve antitumor immunity. Last, these OVs can inflame cold tumors and their microenvironment to be more immunologically favorable for other immunotherapeutics. Due to these unique characteristics, OVs have been tested as an adjuvant of choice in a variety of therapeutics. In light of these promising attributes of OVs in the immune-oncology field, the present review will examine OVs in clinical development and discuss various strategies that are being explored in preclinical stages for the next generation of OVs that are optimized for immunotherapy applications.

The Contribution of the Minimal Promoter Element to the Activity of Synthetic Promoters Mediating CAR Expression in the Tumor Microenvironment

Harnessing immune effector cells to benefit cancer patients is becoming more and more prevalent in recent years. However, the increasing number of different therapeutic approaches, such as chimeric antigen receptors and armored chimeric antigen receptors, requires constant adjustments of the transgene expression levels. We have previously demonstrated it is possible to achieve spatial and temporal control of transgene expression as well as tailoring the inducing agents using the Chimeric Antigen Receptor Tumor Induced Vector (CARTIV) platform. Here we describe the next level of customization in our promoter platform. We have tested the functionality of three different minimal promoters, representing three different promoters' strengths, leading to varying levels of CAR expression and primary T cell function. This strategy shows yet another level of CARTIV gene regulation that can be easily integrated into existing CAR T systems.

Reforming the Chimeric Antigen Receptor by Peptide Towards Optimized CAR T Cells With Enhanced Anti-Cancer Potency and Safety

The emerging chimeric antigen receptor (CAR) T cell revolutionized the clinic treatment of hematological cancers, but meet its Waterloo in solid tumor therapy. Although there exist many reasons for this limitation, one of the largest challenges is the scarcity of recognition for tumor cells, resulting in the undesirable side effects and the subsequent ineffectiveness. To overcome it, a lung-cancer-cell-targeting peptide termed A1 was used in this work to reform the scFv domain of CAR by genetic manipulation. As a result, this modified ^A1CAR T exhibited the optimized cancer-cell targeting and cytotoxicity in vitro and in vivo. More importantly, by tuning the sensitivity of CAR to antigen, peptide-based ^A1CAR T cells could distinguish tumors from normal tissue, thereby eliminating the off-tumor toxicity in healthy organs. Collectively, we herein constructed a genetic peptide-engineered CAR T cells by inserting A1 peptide into the scFv domain. Profitted from the optimized recognition pattern and sensitivity, ^A1CAR T cells showed the ascendancy in solid tumor treatment. Our findings demonstrate that peptide-based CAR T holds great potential in solid tumor therapy due to an excellent targeting ability towards tumor cells.

Enhanced safety and efficacy of protease-regulated CAR-T cell receptors

Regulatable CAR platforms could circumvent toxicities associated with CAR-T therapy, but existing systems have shortcomings including leakiness and attenuated activity. Here, we present SNIP CARs, a protease-based platform for regulating CAR activity using an FDA-approved small molecule. Design iterations yielded CAR-T cells that manifest full functional capacity with drug and no leaky activity in the absence of drug. In numerous models, SNIP CAR-T cells were more potent than constitutive CAR-T cells and showed diminished T cell exhaustion and greater stemness. In a ROR1-based CAR lethality model, drug cessation following toxicity onset reversed toxicity, thereby credentialing the platform as a safety switch. In the same model, reduced drug dosing opened a therapeutic window that resulted in tumor eradication in the absence of toxicity. SNIP CARs enable remote tuning of CAR activity, which provides solutions to safety and efficacy barriers that are currently limiting progress in using CAR-T cells to treat solid tumors.

Opportunities and challenges of physiologically based pharmacokinetic modeling in drug delivery

Physiologically based pharmacokinetic (PBPK) modeling is an important in silico tool to bridge drug properties and in vivo PK behaviors during drug development. Over the recent decade, the PBPK method has been largely applied to drug delivery systems (DDS), including oral, inhaled, transdermal, ophthalmic, and complex injectable products. The related therapeutic agents have included small-molecule drugs, therapeutic proteins, nucleic acids, and even cells. Simulation results have provided important insights into PK behaviors of new dosage forms, which strongly support drug regulation. In this review, we comprehensively summarize recent progress in PBPK applications in drug delivery, which shows large opportunities for facilitating drug development. In addition, we discuss the challenges of applying this methodology from a practical viewpoint.

New Developments in T Cell Immunometabolism and Implications for Cancer Immunotherapy

Despite rapid advances in the field of immunotherapy, the elimination of established tumors has not been achieved. Many promising new treatments such as adoptive cell therapy (ACT) fall short, primarily due to the loss of T cell effector function or the failure of long-term T cell persistence. With the availability of new tools and advancements in technology, our understanding of metabolic processes has increased enormously in the last decade. Redundancy in metabolic pathways and overlapping targets that could address the plasticity and heterogenous phenotypes of various T cell subsets have illuminated the need for understanding immunometabolism in the context of multiple disease states, including cancer immunology. Herein, we discuss the developing field of T cell immunometabolism and its crucial relevance to improving immunotherapeutic approaches. This in-depth review details the metabolic pathways and preferences of the antitumor immune system and the state of various metabolism-targeting therapeutic approaches.

Gut microbiota: impacts on gastrointestinal cancer immunotherapy

The association of gut microbiota with gastrointestinal carcinogenesis has been heavily investigated since the recent advance in sequencing technology. Accumulating evidence has revealed the critical roles of commensal microbes in cancer progression. Given by its importance, emerging studies have focussed on targeting microbiota to ameliorate therapeutic effectiveness. It is now clear that the microbial community is closely related to the efficacy of chemotherapy, while the correlation of microbiota with immunotherapy is much less studied. Herein, we review the up-to-date findings on the influence of gut microbiota on three common immunotherapies including adoptive cell transfer, immune checkpoint blockade, and CpG-oligodeoxynucleotide therapy. We then explore three microbiota-targeted strategies that may improve treatment efficacy, involving dietary intervention, probiotics supplementation, and fecal microbiota transplantation.

An AAV gene therapy computes over multiple cellular inputs to enable precise targeting of multifocal hepatocellular carcinoma in mice

[Figure: see text].

Implementing Logic Gates for Safer Immunotherapy of Cancer

Targeting solid tumors with absolute precision is a long-standing challenge in cancer immunotherapy. The identification of antigens, which are expressed by a large fraction of tumors of a given type and, preferably, across various types, but not by normal cells, holds the key to developing safe, off-the-shelf immunotherapies. Although the quest for widely shared, strictly tumor-specific antigens has been the focus of tremendous effort, only few such candidates have been implicated. Almost all antigens that are currently explored as targets for chimeric antigen receptor (CAR) or T cell receptor (TCR)-T cell therapy are also expressed by healthy cells and the risk of on-target off-tumor toxicity has remained a major concern. Recent studies suggest that this risk could be obviated by targeting instead combinations of two or more antigens, which are co-expressed by tumor but not normal cells and, as such, are tumor-specific. Moreover, the expression of a shared tumor antigen along with the lack of a second antigen that is expressed by normal tissues can also be exploited for precise recognition. Additional cues, antigenic or non-antigenic ones, which characterize the tumor microenvironment, could be harnessed to further increase precision. This review focuses on attempts to define the targetable signatures of tumors and assesses different strategies employing advanced synthetic biology for translating such information into safer modes of immunotherapy, implementing the principles of Boolean logic gates.

CAR T cell therapy in solid tumors; with an extensive focus on obstacles and strategies to overcome the challenges

The application of the CAR T cell therapy in hematologic malignancies holds prosperous results that intensified the unprecedented enthusiasm to employ this fascinating strategy in other types of human malignancies. Although the researchers invested a great deal of effort to exploit the utmost efficacy of these cells in the context of solid tumors, few articles reviewed obstacles and opportunities. The current review aims to provide comprehensive literature of recent advances of CAR T cell therapy in a wide range of solid tumors; and also, to discuss the original data obtained from international research laboratories on this topic. Despite promising results, several radical obstacles are on the way of this approach. This review discusses the most important drawbacks and also responds to questions on how the intrinsic features of solid tumors in addition to the tumor microenvironment-related challenges and the immune-relating adverse effects can curb satisfactory outcomes of CAR T cells. The last section allocates a special focus on innovative and contemporary policies which have already been adopted to surmount these challenges. Finally, we comment on the future research aspects in which the efficacy, as well as the safety of CAR T cell therapy, might be improved.

The Immunology of Hepatocellular Carcinoma

Liver cancer is the third leading cause of cancer death worldwide. Hepatocellular carcinoma (HCC) is the most common primary malignant tumor of the liver. Liver resection or transplantation offer the only potentially curative options for HCC; however, many patients are not candidates for surgical resection, either due to presentation at advanced stages or poor liver function and portal hypertension. Liver transplantation is also limited to patients with certain characteristics, such as those that meet the Milan criteria (one tumor ≤ 5 cm, or up to three tumors no larger than 3 cm, along with the absence of gross vascular invasion or extrahepatic spread). Locoregional therapies, such as ablation (radiofrequency, ethanol, cryoablation, microwave), trans-arterial therapies like chemoembolization (TACE) or radioembolization (TARE), and external beam radiation therapy, have been used mainly as palliative measures with poor prognosis. Therefore, emerging novel systemic treatments, such as immunotherapy, have increasingly become popular. HCC is immunogenic, containing infiltrating tumor-specific T-cell lymphocytes and other immune cells. Immunotherapy may provide a more effective and discriminatory targeting of tumor cells through induction of a tumor-specific immune response in cancer cells and can improve post-surgical recurrence-free survival in HCC. We herein review evidence supporting different immunomodulating cell-based technology relative to cancer therapy in vaccines and targeted therapies, such as immune checkpoint inhibitors, in the management of hepatocellular carcinoma among patients with advanced disease.

Novel CS1 CAR-T Cells and Bispecific CS1-BCMA CAR-T Cells Effectively Target Multiple Myeloma

Multiple myeloma (MM) is a hematological cancer caused by abnormal proliferation of plasma cells in the bone marrow, and novel types of treatment are needed for this deadly disease. In this study, we aimed to develop novel CS1 CAR-T cells and bispecific CS1-BCMA CAR-T cells to specifically target multiple myeloma. We generated a new CS1 (CD319, SLAM-7) antibody, clone (7A8D5), which specifically recognized the CS1 antigen, and we applied it for the generation of CS1-CAR. CS1-CAR-T cells caused specific killing of CHO-CS1 target cells with secretion of IFN-gamma and targeted multiple myeloma cells. In addition, bispecific CS1-BCMA-41BB-CD3 CAR-T cells effectively killed CHO-CS1 and CHO-BCMA target cells, killed CS1/BCMA-positive multiple myeloma cells, and secreted IFN-gamma. Moreover, CS1-CAR-T cells and bispecific CS1-BCMA CAR-T cells effectively blocked MM1S multiple myeloma tumor growth in vivo. These data for the first time demonstrate that novel CS1 and bispecific CS1-BCMA-CAR-T cells are effective in targeting MM cells and provide a basis for future clinical trials.

Rationally Designed Transgene-Encoded Cell-Surface Polypeptide Tag for Multiplexed Programming of CAR T-cell Synthetic Outputs

Synthetic immunology, as exemplified by chimeric antigen receptor (CAR) T-cell immunotherapy, has transformed the treatment of relapsed/refractory B cell-lineage malignancies. However, there are substantial barriers-including limited tumor homing, lack of retention of function within a suppressive tumor microenvironment, and antigen heterogeneity/escape-to using this technology to effectively treat solid tumors. A multiplexed engineering approach is needed to equip effector T cells with synthetic countermeasures to overcome these barriers. This, in turn, necessitates combinatorial use of lentiviruses because of the limited payload size of current lentiviral vectors. Accordingly, there is a need for cell-surface human molecular constructs that mark multi-vector cotransduced T cells, to enable their purification ex vivo and their tracking in vivo. To this end, we engineered a cell surface-localizing polypeptide tag based on human HER2, designated HER2t, that was truncated in its extracellular and intracellular domains to eliminate ligand binding and signaling, respectively, and retained the membrane-proximal binding epitope of the HER2-specific mAb trastuzumab. We linked HER2t to CAR coexpression in lentivirally transduced T cells and showed that co-transduction with a second lentivirus expressing our previously described EGFRt tag linked to a second CAR efficiently generated bispecific dual-CAR T cells. Using the same approach, we generated T cells expressing a CAR and a second module, a chimeric cytokine receptor. The HER2txEGFRt multiplexing strategy is now being deployed for the manufacture of CD19xCD22 bispecific CAR T-cell products for the treatment of acute lymphoblastic leukemia (NCT03330691).

P32-specific CAR T cells with dual antitumor and antiangiogenic therapeutic potential in gliomas

Glioblastoma is considered one of the most aggressive malignancies in adult and pediatric patients. Despite decades of research no curative treatment is available and it thus remains associated with a very dismal prognosis. Although recent pre-clinical and clinical studies have demonstrated the feasibility of chimeric antigen receptors (CAR) T cell immunotherapeutic approach in glioblastoma, tumor heterogeneity and antigen loss remain among one of the most important challenges to be addressed. In this study, we identify p32/gC1qR/HABP/C1qBP to be specifically expressed on the surface of glioma cells, making it a suitable tumor associated antigen for redirected CAR T cell therapy. We generate p32 CAR T cells and find them to recognize and specifically eliminate p32 expressing glioma cells and tumor derived endothelial cells in vitro and to control tumor growth in orthotopic syngeneic and xenograft mouse models. Thus, p32 CAR T cells may serve as a therapeutic option for glioblastoma patients.

Chimeric antigen receptor (CAR) T cell therapy has been proposed as a promising approach for treating glioblastoma. Here the authors show that p32 is expressed in murine and human glioma and that p32-directed CAR-T cells promote anti-tumor responses in preclinical models by targeting glioma cells and tumor derived endothelial cells.

Materials for Improving Immune Cell Transfection

Chimeric antigen receptor T cell (CAR-T) therapy holds great promise for preventing and treating deadly diseases such as cancer. However, it remains challenging to transfect and engineer primary immune cells for clinical cell manufacturing. Conventional tools using viral vectors and bulk electroporation suffer from low efficiency while posing risks like viral transgene integration and excessive biological perturbations. Emerging techniques using microfluidics, nanoparticles, and high-aspect-ratio nanostructures can overcome these challenges, and on top of that, provide universal and high-throughput cargo delivery. Herein, the strengths and limitations of traditional and emerging materials for immune cell transfection, and commercial development of these tools, are discussed. To enhance the characterization of transfection techniques and uptake by the clinical community, a list of in vitro and in vivo assays to perform, along with relevant protocols, is recommended. The overall aim, herein, is to motivate the development of novel materials to meet rising demand in transfection for clinical CAR-T cell manufacturing.

CAR T cell therapy as a promising approach in cancer immunotherapy: challenges and opportunities

BACKGROUND

Chimeric antigen receptor (CAR)-modified T cell therapy has shown great potential in the immunotherapy of patients with hematologic malignancies. In spite of this striking achievement, there are still major challenges to overcome in CAR T cell therapy of solid tumors, including treatment-related toxicity and specificity. Also, other obstacles may be encountered in tackling solid tumors, such as their immunosuppressive microenvironment, the heterogeneous expression of cell surface markers, and the cumbersome arrival of T cells at the tumor site. Although several strategies have been developed to overcome these challenges, aditional research aimed at enhancing its efficacy with minimum side effects, the design of precise yet simplified work flows and the possibility to scale-up production with reduced costs and related risks is still warranted.

CONCLUSIONS

Here, we review main strategies to establish a balance between the toxicity and activity of CAR T cells in order to enhance their specificity and surpass immunosuppression. In recent years, many clinical studies have been conducted that eventually led to approved products. To date, the FDA has approved two anti-CD19 CAR T cell products for non-Hodgkin lymphoma therapy, i.e., axicbtagene ciloleucel and tisagenlecleucel. With all the advances that have been made in the field of CAR T cell therapy for hematologic malignancies therapy, ongoing studies are focused on optimizing its efficacy and specificity, as well as reducing the side effects. Also, the efforts are poised to broaden CAR T cell therapeutics for other cancers, especially solid tumors.

Renaissance of armored immune effector cells, CAR-NK cells, brings the higher hope for successful cancer therapy

In recent decades, a new method of cellular immunotherapy was introduced based on engineering and empowering the immune effector cells. In this type of immunotherapy, the immune effector cells are equipped with chimeric antigen receptor (CAR) to specifically target cancer cells. In much of the trials and experiments, CAR-modified T cell immunotherapy has achieved very promising therapeutic results in the treatment of some types of cancers and infectious diseases. However, there are also some considerable drawbacks in the clinical application of CAR-T cells although much effort is in progress to rectify the issues. In some conditions, CAR-T cells initiate over-activated and strong immune responses, therefore, causing unexpected side-effects such as systemic cytokine toxicity (i.e., cytokine release syndrome), neurotoxicity, on-target, off-tumor toxicity, and graft-versus-host disease (GvHD). To overcome these limitations in CAR-T cell immunotherapy, NK cells as an alternative source of immune effector cells have been utilized for CAR-engineering. Natural killer cells are key players of the innate immune system that can destroy virus-infected cells, tumor cells, or other aberrant cells with their efficient recognizing capability. Compared to T cells, CAR-transduced NK cells (CAR-NK) have several advantages, such as safety in clinical use, non-MHC-restricted recognition of tumor cells, and renewable and easy cell sources for their preparation. In this review, we will discuss the recent preclinical and clinical studies, different sources of NK cells, transduction methods, possible limitations and challenges, and clinical considerations.

First immunotherapeutic CAR-T cells against the immune checkpoint protein HLA-G

BACKGROUND

CAR-T cells immunotherapy is a breakthrough in the treatment of hematological malignancies such as acute lymphoblastic leukemia (ALL) and B-cell malignancies. However, CAR-T therapies face major hurdles such as the lack of tumor-specific antigen (TSA), and immunosuppressive tumor microenvironment sometimes caused by the tumorous expression of immune checkpoints (ICPs) such as HLA-G. Indeed, HLA-G is remarkable because it is both a potent ICP and a TSA. HLA-G tumor expression causes immune escape by impairing innate and adaptive immune responses and by inducing a suppressive microenvironment. Yet, to date, no immunotherapy targets it.

METHODS

We have developed two anti-HLA-G third-generation CARs based on new anti-HLA-G monoclonal antibodies.

RESULTS

Anti-HLA-G CAR-T cells were specific for immunosuppressive HLA-G isoforms. HLA-G-activated CAR-T cells polarized toward T helper 1, and became cytotoxic against HLA-G+ tumor cells. In vivo, anti-HLA-G CAR-T cells were able to control and eliminate HLA-G+ tumor cells. The interaction of tumor-HLA-G with interleukin (IL)T2-expressing T cells is known to result in effector T cell functional inhibition, but anti-HLA-G CAR-T cells were insensitive to this inhibition and still exerted their function even when expressing ILT2. Lastly, we show that anti-HLA-G CAR-T cells differentiated into long-term memory effector cells, and seemed not to lose function even after repeated stimulation by HLA-G-expressing tumor cells.

CONCLUSION

We report for the first time that HLA-G, which is both a TSA and an ICP, constitutes a valid target for CAR-T cell therapy to specifically target and eliminate both tumor cells and HLA-G+ suppressive cells.

CAR-T Therapy, the End of a Chapter or the Beginning of a New One?

Simple Summary

CAR-T therapy is a breakthrough treatment in our fight against cancer. It was recently approved for the treatment of advanced diffuse large B-cell lymphoma and acute lymphoblastic leukaemia after the failure of previous multiple therapies. The positive results achieved in the registration studies for those patients were remarkable. Unfortunately, this was not the end of this chapter. Disease relapses occur in the range of 30–60% of patients treated with CAR-T therapy. Cytokine release syndrome represents a major side effect for treatment with CAR-T therapy. Notwithstanding, the high positive results triggered the start of a huge research activity of CAR-T therapy in other haematologic malignancies such as acute myelogenous leukaemia, Hodgkin’s disease, chronic lymphocytic leukaemia, and multiple myeloma. The research is also trying to overcome the hurdles stated above. These activities represent a new chapter in the management of haematologic malignancies with CAR-T therapy.

Abstract

Chimeric antigen receptor-T (CAR-T) therapy targeting CD19 has revolutionised the treatment of advanced acute lymphoblastic leukaemia (ALL) and diffuse large B-cell lymphoma (DLBCL). The ability to specifically target the cancer cells has shown high positive results as reported in the registration studies. The success of CAR-T therapy in the first two indications led to the initiation of a large number of studies testing CAR-T therapy in different haematologic tumours such as acute myelogenous leukaemia (AML), Hodgkin’s disease (HD), chronic lymphocytic leukaemia (CLL), multiple myeloma (MM), as well as different solid tumours. Unfortunately, relapses occurred in patients treated with CAR-T therapy, calling for the development of effective subsequent therapies. Likewise, this novel mechanism of action was also accompanied by a different toxicity profile, such as cytokine release syndrome (CRS). Patients’ access to the treatment is still limited by its cost. Notwithstanding, this did not prohibit further development of this new therapy to treat other malignancies. This research activity of CAR-T therapy moves it from being used as an end-stage treatment for ALL and DLBCL to a new therapeutic option for a wide range of patients with different haematologic and solid tumours.

An IgG-based bispecific antibody for improved dual targeting in PSMA-positive cancer

The prostate-specific membrane antigen (PSMA) has been demonstrated in numerous studies to be expressed specifically on prostate carcinoma cells and on the neovasculature of several other cancer entities. However, the simultaneous expression of PSMA on both, tumor cells as well as tumor vessels remains unclear, even if such "dual" expression would constitute an important asset to facilitate sufficient influx of effector cells to a given tumor site. We report here on the generation of a PSMA antibody, termed 10B3, which exerts superior dual reactivity on sections of prostate carcinoma and squamous cell carcinoma of the lung. 10B3 was used for the construction of T-cell recruiting bispecific PSMAxCD3 antibodies in Fab- and IgG-based formats, designated Fabsc and IgGsc, respectively. In vitro, both molecules exhibited comparable activity. In contrast, only the larger IgGsc molecule induced complete and durable elimination of established tumors in humanized mice due to favorable pharmacokinetic properties. Upon treatment of three patients with metastasized prostate carcinoma with the IgGsc reagent, marked activation of T cells and rapid reduction of elevated PSA levels were observed.

Synthetic promoters to induce immune-effectors into the tumor microenvironment

Harnessing the immune-system to eradicate cancer is becoming a reality in recent years. Engineered immune cells, such as chimeric antigen receptor (CAR) T cells, are facing the danger of an overt life-threatening immune response due to the ON-target OFF-tumor cytotoxicity and Cytokine Release Syndrome. We therefore developed synthetic promoters for regulation of gene expression under the control of inflammation and Hypoxia-induced signals that are associated with the tumor microenvironment (TME). We termed this methodology as chimeric-antigen-receptor-tumor-induced-vector (CARTIV). For proof of concept, we studied synthetic promoters based on promoter-responsive elements (PREs) of IFNγ, TNFα and hypoxia; triple PRE-based CARTIV promoter manifested a synergistic activity in cell-lines and potent activation in human primary T-cells. CARTIV platform can improve safety of CAR T-cells or other engineered immune-cells, providing TME-focused activity and opening a therapeutic window for many tumor-associated antigens that are also expressed by non-tumor healthy tissues.

From the T-cell receptor to cancer therapy: an interview with Tak W. Mak

This interview is part of a series of articles to mark the 25th anniversary of the launching of Cell Death and Differentiation.

CAR T-cells profiling in carcinogenesis and tumorigenesis: An overview of CAR T-cells cancer therapy

Immunotherapy of cancer by chimeric antigen receptors (CAR) modified T-cell has a remarkable clinical potential for malignancies. Meaningly, it is a suitable cancer therapy to treat different solid tumors. CAR is a special recombinant protein combination with an antibody targeting structure alongside with signaling domain capacity on order to activate T cells. It is confirmed that the CAR-modified T cells have this ability to terminate and remove B cell malignancies. So, methodologies for investigations the pro risks and also strategies for neutralizing possible off-tumor consequences of are great importance successful protocols and strategies of CAR T-cell therapy can improve the efficacy and safety of this type of cancers. In this review article, we try to classify and illustrate main optimized plans in cancer CAR T-cell therapy.

Emerging vistas in CAR T-cell therapy: challenges and opportunities in solid tumors

INTRODUCTION

Despite advances in modern evidence-based medicine, cancer remains a major cause of global disease-associated mortality. CAR T-cell therapy is a major histocompatibility complex (MHC)-independent immunotherapy involving adoptive cell transfer. Cancer immunotherapy witnessed a major breakthrough with the US FDA approval of the first chimeric antigen receptor (CAR) T-cell therapy Kymriah^TM (tisagenlecleucel) for relapsed or refractory (R/R) acute lymphoblastic leukemia (ALL) in August 2017 followed by approval of Yescarta® (axicabtagene ciloleucel) for R/R non-Hodgkin's lymphoma (NHL) in October 2017.

AREAS COVERED

We review the potential of CAR T-cell therapy which, despite showing great promise in hematological malignancies, faces significant challenges in targeting solid tumors. We address these challenges and discuss proposed strategies to overcome them in solid tumors. We highlight the potential of CAR T-cell therapy as cancer precision medicine and briefly discuss the 'financial toxicity' of CAR T-cell therapy.

EXPERT OPINION

Taken together, we discuss various strategies to circumvent the limitations of CAR T-cell therapy in solid tumors. Despite the rapid advances in CAR NK-cell therapies, there is immense scope for CAR T-cell therapy in solid tumors. We provide a synthetic review of CAR T-cell therapy that will drive future research and harness its full potential in cancer precision medicine for solid tumors.

Editor's Pick: Tumour-Associated Hypoxia: Can We Give Chimeric Antigen Receptor T Cells More Breathing Space?

Immunotherapy using chimeric antigen receptor (CAR)-engineered T cells has encountered important limitations in the transition of their use from liquid to solid tumours. Success is dependent upon T-cell trafficking to, and functional persistence within, tumours that often present a metabolically and immunologically hostile microenvironment. Moreover, CAR targets that are tumour specific are extremely scarce. To address these issues, several strategies have been proposed to improve both tumour selectivity and safety. One approach involves the engineering of CAR-T cells that only deploy their effector function at tumour sites. Conceptually, a solution for this exploits the oxygen-limited nature of advanced tumour deposits through the engineering of CAR that are exclusively expressed or activated under conditions of profound hypoxia. T cells have a complex inter-relationship with oxygen, which also needs to be factored into the refinement of these technologies. Ideally, oxygen-sensing CAR should only function when oxygen tension is below 2%, as is commonly the case in solid tumours but rare in healthy tissue. Successful advancement of such technologies presents opportunities for solid tumour immunotherapy because it should broaden the target repertoire that may safely be exploited in this context.

Potential lung attack and lethality generated by EpCAM-specific CAR-T cells in immunocompetent mouse models

The tumoricidal efficiency of human CAR-T cells is generally evaluated using immune-deficient mouse models; however, due to their immune-incompetency and the species-specific reactivity of a target antigen, these models are problematic to imitate CAR-T-induced adverse effects in the clinic. Epithelial cell adhesion molecule (EpCAM) is a tumor-associated antigen overtly presented on the cell surface of various carcinomas, making it an attractive target for CAR-T therapy. Here, we developed an anti-mouse EpCAM CAR to evaluate its safety and efficacy in immunocompetent mouse models. As previously reported for their human equivalents, murine EpCAM CAR-T cells exhibit promising anti-tumor efficacy in vitro and in vivo. However, after CAR-T infusion, various dose-depended toxicities including body weight loss, cytokine-release syndrome (CRS), and death were observed in both tumor-bearing and tumor-free mice. Pathological examination revealed unexpected and severe pulmonary immunopathology due to basal EpCAM expression in normal lung. While our study validates EpCAM CAR-T's potent anti-tumor efficacy, it also reveals that EpCAM CAR-T cells used for the treatment of solid tumors may cause lethal toxicity and should, therefore, be evaluated in patients with caution.

Surmounting the obstacles that impede effective CAR T cell trafficking to solid tumors

Innovative immunotherapies based on immune checkpoint targeting antibodies and engineered T cells are transforming the way we approach cancer treatment. However, although these T cell centered strategies result in marked and durable responses in patients across many different tumor types, they provide therapeutic efficacy only in a proportion of patients. A major challenge of immuno‐oncology is thereby to identify mechanisms responsible for resistance to cancer immunotherapy in order to overcome them via adapted strategies that will ultimately improve intrinsic efficacy and response rates. Here, we focus on the barriers that restrain the trafficking of chimeric antigen receptor (CAR)‐expressing T cells to solid tumors. Upon infusion, CAR T cells need to home into malignant sites, navigate within complex tumor environments, form productive interactions with cancer cells, deliver their cytotoxic activities, and finally persist. We review the accumulating evidence that the microenvironment of solid tumors contains multiple obstacles that hinder CAR T cells in the dynamic steps underlying their trafficking. We focus on how these hurdles may in part account for the failure of CAR T cell clinical trials in human carcinomas. Given the engineered nature of CAR T cells and possibilities to modify the tumor environment, there are ample opportunities to augment CAR T cell ability to efficiently find and combat tumors. We present some of these strategies, which represent a dynamic field of research with high potential for clinical applicability.

Combined Expression of Genetic Adjuvants Via mRNA Electroporation Exerts Multiple Immunostimulatory Effects on Antitumor T Cells

Adoptive transfer of tumor-infiltrating lymphocytes (TILs) or gene-modified T cells expressing antitumor TCRs or chimeric antigen receptors often yields a high rate of clinical response in several types of cancer. New approaches for enhancing the functional properties of antitumor T cells could improve the clinical outcome of these treatments. To this end, we created 3 classes of genes, each designed to operate autonomously upon expression in T cells. We recently reported on the enhancing effects of constitutively active toll-like receptor 4 (caTLR4), membrane (mem) interleukin-2, memIL-12, and memIL-15, and self-oligomerizing, constitutively active CD40 (caCD40). Here, we evaluated their combined effects on peripheral blood CD8 T cells and different antimelanoma TIL cultures following mRNA electroporation. Expression in CD8 T cells induced transient production of interferon-γ and prolonged and robust upregulation of CD25, CD69, 4-1BB, and OX40. The adjuvants enhanced cytolytic activity of TILs and production of interferon-γ and TNF-α in the presence of autologous, but not mismatched, melanoma for at least 3 days after electroporation. Expression of the 3 adjuvants in young TILs from different patients markedly increased the expression of CD25, OX40, 4-1BB, CD127, and CD28 and exhibited cooperative and, at times, synergistic effects. Furthermore, predefined mixtures of mRNA encoding these adjuvants markedly enhanced the specific antitumor response of selected TILs and killing of autologous melanoma cells by young TILs. Our findings suggest that combinations of these new genetic adjuvants can substantially improve the functional properties of antitumor T cells, offering a new tool of unique versatility in adoptive cell therapy.

Self-Assembled Multivalent Aptamer Nanoparticles with Potential CAR-like Characteristics Could Activate T Cells and Inhibit Melanoma Growth

In this study, the CAR-like multivalent aptamer nanoparticles (X-polymers) were assembled with the dimer of murine CD28 RNA aptamer (CD28Apt7), the tetramer of CTLA-4 (cytotoxic T-lymphocyte-associated protein 4) RNA aptamer (Del60), and a folic acid labeled ssDNA fragment in a stable nucleic acid three-way junction scaffold (3WJ). Results showed that the X-polymers could recognize both the mCD28 and mCTLA-4 molecules. Confocal imaging and flow cytometry assays showed that the X-polymers could target both T cells and B16 cells in vitro. With the first costimulatory signals provided by the CD3 antibodies, the X-polymers could increase T cell proliferation and reverse the inhibitory effect of interleukin-2 (IL-2) secreting caused by exogenous B7.1 molecules on T cells in vitro. Results of our study also showed that X-polymers could inhibit mouse melanoma B16 cell growth both in vitro and in vivo. Our study demonstrated for the first time that the multivalent aptamer nanoparticle-activated T cells could fulfill the function of CAR-T, which promised a novel approach to developing a multi-functional design of aptamer drugs with potential CAR-like characteristics to enhance the safety of CAR-T cell immunotherapy.

CAR T‑cell therapy for gastric cancer: Potential and perspective (Review)

Gastric cancer (GC) is one of the most frequently diagnosed digestive malignancies and is the third leading cause of cancer‑associated death worldwide. Delayed diagnosis and poor prognosis indicate the urgent need for new therapeutic strategies. The success of chimeric antigen receptor (CAR) T‑cell therapy for chemotherapy‑refractory hematological malignancies has inspired the development of a similar strategy for GC treatment. Although using CAR T‑cells against GC is not without difficulty, results from preclinical studies remain encouraging. The current review summarizes relevant preclinical studies and ongoing clinical trials for the use of CAR T‑cells for GC treatment and investigates possible toxicities, as well as current clinical experiences and emerging approaches. With a deeper understanding of the tumor microenvironment, novel target epitopes and scientific‑technical progress, the potential of CAR T‑cell therapy for GC is anticipated in the near future.