Regulation of CAR T cell-mediated cytokine release syndrome-like toxicity using low molecular weight adapters

Electrophilic proximity-inducing synthetic adapters enhance universal T cell function by covalently enforcing immune receptor signaling

Proximity-induction of cell-cell interactions via small molecules represents an emerging field in basic and translational sciences. Covalent anchoring of these small molecules represents a useful chemical strategy to enforce proximity; however, it remains largely unexplored for driving cell-cell interactions. In immunotherapeutic applications, bifunctional small molecules are attractive tools for inducing proximity between immune effector cells like T cells and tumor cells to induce tumoricidal function. We describe a two-component system composed of electrophilic bifunctional small molecules and paired synthetic antigen receptors (SARs) that elicit T cell activation. The molecules, termed covalent immune recruiters (CIRs), were designed to affinity label and covalently engage SARs. We evaluated the utility of CIRs to direct anti-tumor function of human T cells engineered with three biologically distinct classes of SAR. Irrespective of the electrophilic chemistry, tumor-targeting moiety, or SAR design, CIRs outperformed equivalent non-covalent bifunctional adapters, establishing a key role for covalency in maximizing functionality. We determined that covalent linkage enforced early T cell activation events in a manner that was dependent upon each SARs biology and signaling threshold. These results provide a platform to optimize universal SAR-T cell functionality and more broadly reveal new insights into how covalent adapters modulate cell-cell proximity-induction.

A Flow Cytometry-Based Method for Assessing CAR Cell Binding Kinetics Using Stable CAR Jurkat Cells

Chimeric antigen receptors (CARs) are synthetic fusion proteins that can reprogram immune cells to target specific antigens. CAR-expressing T cells have emerged as an effective treatment method for hematological cancers; despite this success, the mechanisms and structural properties that govern CAR responses are not fully understood. Here, we provide a simple assay to assess cellular avidity using a standard flow cytometer. This assay measures the interaction kinetics of CAR-expressing T cells and targets antigen-expressing target cells. By co-culturing stably transfected CAR Jurkat cells with target positive and negative cells for short periods of time in a varying effector-target gradient, we were able to observe the formation of CAR-target cell doublets, providing a readout of actively bound cells. When using the optimized protocol reported here, we observed unique cellular binding curves that varied between CAR constructs with differing antigen binding domains. The cellular binding kinetics of unique CARs remained consistent, were dependent on specific target antigen expression, and required active biological signaling. While existing literature is not clear at this time whether higher or lower CAR cell binding is beneficial to CAR therapeutic activity, the application of this simplified protocol for assessing CAR binding could lead to a better understanding of the proximal signaling events that regulate CAR functionality. Key features • Determines CAR receptor cellular interaction kinetics using a Jurkat cell model. • Can be used for a wide variety of CAR target antigens, including both hematological and solid tumor targets. • Experiments can be performed in under two hours with no staining using a standard flow cytometer. • Requires stable CAR Jurkat cells and target cells with stable fluorescent marker expression for optimal results.

Fluorescein-Based SynNotch Adaptors for Regulating Gene Expression Responses to Diverse Extracellular Cues

We introduce an adaptor-based strategy for regulating fluorescein-binding synthetic Notch (SynNotch) receptors using ligands based on conjugates of fluorescein isomers and analogs. To develop a versatile system, we evaluated the surface expression and activities of multiple constructs containing distinct extracellular fluorescein-binding domains. Using an optimized receptor, we devised ways to regulate signaling via fluorescein-based chemical transformations, including an approach based on a bio-orthogonal chemical ligation and a spatially controllable strategy via the photo-patterned uncaging of an o -nitrobenzyl-caged fluorescein conjugate. We further demonstrate that fluorescein-conjugated extracellular matrix (ECM)-binding peptides can regulate SynNotch activity depending on the folding state of collagen-based ECM networks. Treatment with these conjugates enabled cells to distinguish between folded versus denatured collagen proteins and enact dose-dependent gene expression responses depending on the nature of the signaling adaptors presented. To demonstrate the utility of these tools, we applied them to control the myogenic conversion of fibroblasts into myocytes with spatial and temporal precision and in response to denatured collagen-I, a biomarker of multiple pathological states. Overall, we introduce an optimized fluorescein-binding SynNotch as a versatile tool for regulating transcriptional responses to extracellular ligands based on the widely used and clinically-approved fluorescein dye.

Synthetic biology approaches for improving the specificity and efficacy of cancer immunotherapy

Immunotherapy has shown robust efficacy in treating a broad spectrum of hematological and solid cancers. Despite the transformative impact of immunotherapy on cancer treatment, several outstanding challenges remain. These challenges include on-target off-tumor toxicity, systemic toxicity, and the complexity of achieving potent and sustainable therapeutic efficacy. Synthetic biology has emerged as a promising approach to overcome these obstacles, offering innovative tools for engineering living cells with customized functions. This review provides an overview of the current landscape and future prospects of cancer immunotherapy, particularly emphasizing the role of synthetic biology in augmenting its specificity, controllability, and efficacy. We delineate and discuss two principal synthetic biology strategies: those targeting tumor surface antigens with engineered immune cells and those detecting intratumoral disease signatures with engineered gene circuits. This review concludes with a forward-looking perspective on the enduring challenges in cancer immunotherapy and the potential breakthroughs that synthetic biology may contribute to the field.

Control of the antitumour activity and specificity of CAR T cells via organic adapters covalently tethering the CAR to tumour cells

On-target off-tumour toxicity limits the anticancer applicability of chimaeric antigen receptor (CAR) T cells. Here we show that the tumour-targeting specificity and activity of T cells with a CAR consisting of an antibody with a lysine residue that catalytically forms a reversible covalent bond with a 1,3-diketone hapten can be regulated by the concentration of a small-molecule adapter. This adapter selectively binds to the hapten and to a chosen tumour antigen via a small-molecule binder identified via a DNA-encoded library. The adapter therefore controls the formation of a covalent bond between the catalytic antibody and the hapten, as well as the tethering of the CAR T cells to the tumour cells, and hence the cytotoxicity and specificity of the cytotoxic T cells, as we show in vitro and in mice with prostate cancer xenografts. Such small-molecule switches of T-cell cytotoxicity and specificity via an antigen-independent 'universal' CAR may enhance the control and safety profile of CAR-based cellular immunotherapies.

Enhancing the safety of CAR-T cell therapy: Synthetic genetic switch for spatiotemporal control

Chimeric antigen receptor T (CAR-T) cell therapy is a promising and precise targeted therapy for cancer that has demonstrated notable potential in clinical applications. However, severe adverse effects limit the clinical application of this therapy and are mainly caused by uncontrollable activation of CAR-T cells, including excessive immune response activation due to unregulated CAR-T cell action time, as well as toxicity resulting from improper spatial localization. Therefore, to enhance controllability and safety, a control module for CAR-T cells is proposed. Synthetic biology based on genetic engineering techniques is being used to construct artificial cells or organisms for specific purposes. This approach has been explored in recent years as a means of achieving controllability in CAR-T cell therapy. In this review, we summarize the recent advances in synthetic biology methods used to address the major adverse effects of CAR-T cell therapy in both the temporal and spatial dimensions.

Chimeric antigen receptor T-cell therapy in hematologic malignancies: Successes, challenges, and opportunities

The success of chimeric antigen receptor T-cell (CAR-T) therapy in hematologic malignancies has realized a longstanding effort toward harnessing the immune system to fight cancer in a truly personalized fashion. Second generation chimeric antigen receptors (CAR) incorporating co-stimulatory molecules like 4-1BB or CD28 were able to overcome some of the hindrances with initial CAR constructs resulting in efficacious products. Many second-generation CAR-T products have been approved in the treatment of relapsed/refractory hematologic malignancies including multiple myeloma (MM), non-Hodgkin lymphoma (NHL), and acute lymphoblastic leukemia. However, challenges remain in optimizing the manufacturing, timely access, limiting the toxicity from CAR-T infusions and improving sustainability of responses derived with CAR-T therapy. Here, we summarize the clinical trial data leading to approval CAR-T therapies in MM and NHL, discuss the limitations with current CAR-T therapy strategies and review emerging strategies for overcoming these limitations.

Mechanisms and strategies for safe chimeric antigen receptor T-cell activity control

The clinical application of chimeric antigen receptor (CAR) T-cell therapy has rapidly changed the treatment options for terminally ill patients with defined blood-borne cancer types. However, CAR T-cell therapy can lead to severe therapy-associated toxicities including CAR-related hematotoxicity, ON-target OFF-tumor toxicity, cytokine release syndrome (CRS) or immune effector cell-associated neurotoxicity syndrome (ICANS). Just as CAR T-cell therapy has evolved regarding receptor design, gene transfer systems and production protocols, the management of side effects has also improved. However, because of measures taken to abrogate adverse events, CAR T-cell viability and persistence might be impaired before complete remission can be achieved. This has fueled efforts for the development of extrinsic and intrinsic strategies for better control of CAR T-cell activity. These approaches can mediate a reversible resting state or irreversible T-cell elimination, depending on the route chosen. Control can be passive or active. By combination of CAR T-cells with T-cell inhibiting compounds, pharmacologic control, mostly independent of the CAR construct design used, can be achieved. Other strategies involve the genetic modification of T-cells or further development of the CAR construct by integration of molecular ON/OFF switches such as suicide genes. Alternatively, CAR T-cell activity can be regulated intracellularly through a self-regulation function or extracellularly through titration of a CAR adaptor or of a priming small molecule. In this work, we review the current strategies and mechanisms to control activity of CAR T-cells reversibly or irreversibly for preventing and for managing therapy-associated toxicities.

Discovery of a selective TC-PTP degrader for cancer immunotherapy

T-cell protein tyrosine phosphatase (TC-PTP), encoded by PTPN2, has emerged as a promising target for cancer immunotherapy. TC-PTP deletion in B16 melanoma cells promotes tumor cell antigen presentation, while loss of TC-PTP in T-cells enhances T-cell receptor (TCR) signaling and stimulates cell proliferation and activation. Therefore, there is keen interest in developing TC-PTP inhibitors as novel immunotherapeutic agents. Through rational design and systematic screening, we discovered the first highly potent and selective TC-PTP PROTAC degrader, TP1L, which induces degradation of TC-PTP in multiple cell lines with low nanomolar DC50s and >110-fold selectivity over the closely related PTP1B. TP1L elevates the phosphorylation level of TC-PTP substrates including pSTAT1 and pJAK1, while pJAK2, the substrate of PTP1B, is unaffected by the TC-PTP degrader. TP1L also intensifies interferon gamma (IFN-γ) signaling and increases MHC-I expression. In Jurkat cells, TP1L activates TCR signaling through increased phosphorylation of LCK. Furthermore, in a CAR-T cell and KB tumor cell co-culture model, TP1L enhances CAR-T cell mediated tumor killing efficacy through activation of the CAR-T cells. Thus, we surmise that TP1L not only provides a unique opportunity for in-depth interrogation of TC-PTP biology but also serves as an excellent starting point for the development of novel immunotherapeutic agents targeting TC-PTP.

Design and preclinical testing of an anti-CD41 CAR T cell for the treatment of acute megakaryoblastic leukaemia

Acute megakaryoblastic leukaemia (AMkL) is a rare subtype of acute myeloid leukaemia (AML) representing 5% of all reported cases, and frequently diagnosed in children with Down syndrome. Patients diagnosed with AMkL have low overall survival and have poor outcome to treatment, thus novel therapies such as CAR T cell therapy could represent an alternative in treating AMkL. We investigated the effect of a new CAR T cell which targets CD41, a specific surface antigen for M7-AMkL, against an in vitro model for AMkL, DAMI Luc2 cell line. The performed flow cytometry evaluation highlighted a percentage of 93.8% CAR T cells eGFP-positive and a limited acute effect on lowering the target cell population. However, the interaction between effector and target (E:T) cells, at a low ratio, lowered the cell membrane integrity, and reduced the M7-AMkL cell population after 24 h of co-culture, while the cytotoxic effect was not significant in groups with higher E:T ratio. Our findings suggest that the anti-CD41 CAR T cells are efficient for a limited time spawn and the cytotoxic effect is visible in all experimental groups with low E:T ratio.

Adapter CAR T cells to counteract T-cell exhaustion and enable flexible targeting in AML

Although the landscape for treating acute myeloid leukemia (AML) patients has changed substantially in recent years, the majority of patients will eventually relapse and succumb to their disease. Allogeneic stem cell transplantation provides the best anti-AML treatment strategy, but is only suitable in a minority of patients. In contrast to B-cell neoplasias, chimeric antigen receptor (CAR) T-cell therapy in AML has encountered challenges in target antigen heterogeneity, safety, and T-cell dysfunction. We established a Fab-based adapter CAR (AdCAR) T-cell platform with flexibility of targeting and control of AdCAR T-cell activation. Utilizing AML cell lines and a long-term culture assay for primary AML cells, we were able to demonstrate AML-specific cytotoxicity using anti-CD33, anti-CD123, and anti-CLL1 adapter molecules in vitro and in vivo. Notably, we show for the first time the feasibility of sequential application of adapter molecules of different specificity in primary AML co-cultures. Importantly, using the AML platform, we were able to demonstrate that chronic T-cell stimulation and exhaustion can be counteracted through introduction of treatment-free intervals. As T-cell exhaustion and target antigen heterogeneity are well-known causes of resistance, the AdCAR platform might offer effective strategies to ameliorate these limitations.

CAR-neutrophil mediated delivery of tumor-microenvironment responsive nanodrugs for glioblastoma chemo-immunotherapy

Glioblastoma (GBM) is one of the most aggressive and lethal solid tumors in human. While efficacious therapeutics, such as emerging chimeric antigen receptor (CAR)-T cells and chemotherapeutics, have been developed to treat various cancers, their effectiveness in GBM treatment has been hindered largely by the blood-brain barrier and blood-brain-tumor barriers. Human neutrophils effectively cross physiological barriers and display effector immunity against pathogens but the short lifespan and resistance to genome editing of primary neutrophils have limited their broad application in immunotherapy. Here we genetically engineer human pluripotent stem cells with CRISPR/Cas9-mediated gene knock-in to express various anti-GBM CAR constructs with T-specific CD3ζ or neutrophil-specific γ-signaling domains. CAR-neutrophils with the best anti-tumor activity are produced to specifically and noninvasively deliver and release tumor microenvironment-responsive nanodrugs to target GBM without the need to induce additional inflammation at the tumor sites. This combinatory chemo-immunotherapy exhibits superior and specific anti-GBM activities, reduces off-target drug delivery and prolongs lifespan in female tumor-bearing mice. Together, this biomimetic CAR-neutrophil drug delivery system is a safe, potent and versatile platform for treating GBM and possibly other devastating diseases.

Expressing IL-15/IL-18 and CXCR2 improve infiltration and survival of EGFRvIII-targeting CAR-T cells in breast cancer

Previously, we have generated EGFRvIII-targeting CAR-T cells and brought hope for treating advanced breast cancer. However, EGFRvIII-targeting CAR-T cells were defined limited anti-tumor efficacy, which might be due to reduced accumulation, persistence of therapeutic T cells in tumor site of breast cancer. CXCLs were highly expressed in tumor environment of breast cancer and CXCR2 is the main receptor for CXCLs. Here, CXCR2 could significantly improve the trafficking and tumor specific accumulation of CAR-T cells both in vivo and in vitro. However, the anti-tumor effect of CXCR2 CAR-T cells were weaken which might be results of the apoptosis of T cells. Cytokines could stimulate Tcell proliferation, such as interleukin (IL)-15 and IL-18. Then, we generated CXCR2 CAR with synthetic IL-15 or IL-18 production. Co-expressing IL-15 or IL-18 could significantly suppress the exhaustion and apoptosis of T cells and enhanced the anti-tumor activity of CXCR2 CAR-T cells in vivo. Further, coexpression IL-15 or IL-18 in CXCR2 CAR-T cells did not cause toxicity. These findings provide a potential therapy strategy of co-expression IL-15 or IL-18 in CXCR2 CAR-T cells for the treatment of advancing breast cancer in the future.

Generation of anti-GD2 CAR macrophages from human pluripotent stem cells for cancer immunotherapies

Macrophages armed with chimeric antigen receptors (CARs) provide a potent new option for treating solid tumors. However, genetic engineering and scalable production of somatic macrophages remains significant challenges. Here, we used CRISPR-Cas9 gene editing methods to integrate an anti-GD2 CAR into the AAVS1 locus of human pluripotent stem cells (hPSCs). We then established a serum- and feeder-free differentiation protocol for generating CAR macrophages (CAR-Ms) through arterial endothelial-to-hematopoietic transition (EHT). CAR-M produced by this method displayed a potent cytotoxic activity against GD2-expressing neuroblastoma and melanoma in vitro and neuroblastoma in vivo. This study provides a new platform for the efficient generation of off-the-shelf CAR-Ms for antitumor immunotherapy.

Switchable targeting of solid tumors by BsCAR T cells

The development of chimeric antigen receptor (CAR) T cell therapy has become a critical milestone in modern oncotherapy. Despite the remarkable in vitro effectiveness, the problem of safety and efficacy of CAR T cell therapy against solid tumors is challenged by the lack of tumor-specific antigens required to avoid on-target off-tumor effects. Spatially separating the cytotoxic function of CAR T cells from tumor antigen recognition provided by protein mediators allows for the precise control of CAR T cell cytotoxicity. Here, the high affinity and capability of the bacterial toxin-antitoxin barnase-barstar system were adopted to guide CAR T cells to solid tumors. The complementary modules based on (1) ankyrin repeat (DARPin)-barnase proteins and (2) barstar-based CAR (BsCAR) were designed to provide switchable targeting to tumor cells. The alteration of the DARPin-barnase switches enabled the targeting of different tumor antigens with a single BsCAR. A gradual increase in cytokine release and tunable BsCAR T cell cytotoxicity was achieved by varying DARPin-barnase loads. Switchable BsCAR T cell therapy was able to eradicate the HER2⁺ ductal carcinoma in vivo. Guiding BsCAR T cells by DARPin-barnase switches provides a universal approach for a controlled multitargeted adoptive immunotherapy.

Emerging approaches for preventing cytokine release syndrome in CAR-T cell therapy

Chimeric antigen receptor (CAR) T cells have demonstrated remarkable anti-tumor efficacy against hematological malignancies, such as leukemia and lymphoma. However, patients treated with CAR-T cells frequently experience cytokine release syndrome (CRS), one of the most life-threatening adverse events of the therapy induced by systemic concentrations of pro-inflammatory cytokines throughout the body. Immunosuppressants such as tocilizumab are currently administered to treat the onset and progression of CRS symptoms. In order to reduce the risk of CRS, newly designed next-generation CAR-T treatments are being developed for both hematopoietic malignancies and solid tumors. In this review, we discuss six classes of interesting approaches that control cytokine production of CAR-T cell therapy: adaptor-based strategies, orthogonal cytokine-receptor pairs, regulation of macrophage cytokine activity, autonomous neutralization of key cytokines, kill switches and methods of reversible suppression of CARs. With these strategies, future CAR-T cell therapies will be designed to preemptively inhibit CRS, minimize the patients' suffering, and maximize the number of benefiting patients.

Understanding CAR T cell-tumor interactions: Paving the way for successful clinical outcomes

Since their approval 5 years ago, chimeric antigen receptor (CAR) T cells have gained great importance in the daily clinical practice and treatment of hematological malignancies, although many challenges to their use remain, such as limited long-term CAR T cell efficacy due to disease resistance or recurrence. After a brief overview of CAR T cells, their approval, therapeutic successes, and ongoing limitations, this review discusses what is known about CAR T cell activation, their expansion and persistence, their mechanisms of cytotoxicity, and how the CAR design and/or tumor-intrinsic factors influence these functions. This review also examines the role of cytokines in CAR T cell-associated toxicity and their effects on CAR T cell function. Furthermore, we discuss several resistance mechanisms, including obstacles associated with CAR treatment of solid tumors. Finally, we provide a future outlook on next-generation strategies to further optimize CARs and improve clinical outcomes.

ROR1-targeting switchable CAR-T cells for cancer therapy

The success of chimeric antigen receptor T cell (CAR-T) therapy in the treatment of hematologic malignancies has prompted the development of numerous CAR-T technologies, including switchable CAR-T (sCAR-T) systems that combine a universal CAR-T with bispecific adapter proteins. Owing to their controllability and versatility, sCAR-Ts have received considerable attention. To explore the therapeutic utility of sCAR-Ts targeting the receptor tyrosine kinase ROR1, which is expressed in hematologic and solid malignancies, and to identify bispecific adaptor proteins that efficiently mediate universal CAR-T engagement, a panel of switches based on ROR1-targeting Fabs with different epitopes and affinities was compared in in vitro and in vivo models of ROR1-expressing cancers. For switches targeting overlapping or identical epitopes, potency correlated with affinity. Surprisingly, however, we identified a switch targeting a unique epitope with low affinity but mediating potent and selective antitumor activity in vitro and in vivo. Converted to a conventional CAR-T, the same anti-ROR1 mAb (324) outperformed a clinically investigated conventional CAR-T that is based on an anti-ROR1 mAb (R12) with ~200-fold higher affinity. Thus, demonstrating therapeutic utility on their own, sCAR-Ts also facilitate higher throughput screening for the identification of conventional CAR-T candidates for preclinical and clinical studies.

Application and Design of Switches Used in CAR

Among the many oncology therapies, few have generated as much excitement as CAR-T. The success of CAR therapy would not have been possible without the many discoveries that preceded it, most notably, the Nobel Prize-winning breakthroughs in cellular immunity. However, despite the fact that CAR-T already offers not only hope for development, but measurable results in the treatment of hematological malignancies, CAR-T still cannot be safely applied to solid tumors. The reason for this is, among other things, the lack of tumor-specific antigens which, in therapy, threatens to cause a lethal attack of lymphocytes on healthy cells. In the case of hematological malignancies, dangerous complications such as cytokine release syndrome may occur. Scientists have responded to these clinical challenges with molecular switches. They make it possible to remotely control CAR lymphocytes after they have already been administered to the patient. Moreover, they offer many additional capabilities. For example, they can be used to switch CAR antigenic specificity, create logic gates, or produce local activation under heat or light. They can also be coupled with costimulatory domains, used for the regulation of interleukin secretion, or to prevent CAR exhaustion. More complex modifications will probably require a combination of reprogramming (iPSc) technology with genome editing (CRISPR) and allogenic (off the shelf) CAR-T production.

Design, Synthesis, and Targeted Delivery of an Immune Stimulant that Selectively Reactivates Exhausted CAR T Cells

Although chimeric antigen receptor (CAR) T cells have demonstrated significant promise in suppressing hematopoietic cancers, their applications in treating solid tumors have been limited by onset of CAR T cell exhaustion that accompanies continuous CAR T cell exposure to tumor antigen. To address this limitation, we have exploited the abilities of recently designed universal CARs to bind fluorescein and internalize a fluorescein-TLR7 agonist conjugate by CAR-mediated endocytosis. We demonstrate here that anti-fluorescein CAR-mediated uptake of a fluorescein-TLR7-3 conjugate can reactivate exhausted CAR T cells, leading to dramatic reduction in T cell exhaustion markers (PD-1⁺ Tim-3⁺ ) and shrinkage of otherwise resistant tumors without inducing systemic activation of the immune system. We conclude that CAR T cell exhaustion can be reversed by administration of a CAR-targeted TLR7 agonist, thereby enabling the CAR T cells to successfully treat solid tumors without incurring the systemic toxicity that commonly accompanies administration of nontargeted TLR7 agonists.

Improving CAR-T immunotherapy: Overcoming the challenges of T cell exhaustion

Chimeric antigen receptor (CAR) T cell therapy has emerged as a cancer treatment with enormous potential, demonstrating impressive antitumor activity in the treatment of hematological malignancies. However, CAR T cell exhaustion is a major limitation to their efficacy, particularly in the application of CAR T cells to solid tumors. CAR T cell exhaustion is thought to be due to persistent antigen stimulation, as well as an immunosuppressive tumor microenvironment, and mitigating exhaustion to maintain CAR T cell effector function and persistence and achieve clinical potency remains a central challenge. Here, we review the underlying mechanisms of exhaustion and discuss emerging strategies to prevent or reverse exhaustion through modifications of the CAR receptor or CAR independent pathways. Additionally, we discuss the potential of these strategies for improving clinical outcomes of CAR T cell therapy.

Recent advances in the prevention and management of cytokine release syndrome after chimeric antigen receptor T-cell therapy

Adoptive immunotherapy has recently garnered widespread interests owing to the successful application of chimeric antigen receptor T cell therapy. CAR-T cells are “living drugs” that can live in patients for several years and act as an effective antitumor agent. Over the last few years, five types of CAR-T cells have been approved by Food and Drug Administration (FDA) for treatment of hematologic malignancies. Despite their impressive clinical efficacy, the current application of CAR-T cell therapy is restricted by the uncontrollable release of cytokines (cytokine release syndrome and cytokine release syndrome) due to serious treatment-related toxicities resulting from synchronous activation and rapid proliferation of CAR-T cells. CRS is the most common toxicity and its severity can range from low-grade physical symptoms to a high-grade syndrome linked with life-threatening multiple organ dysfunction. Treatment-related deaths from severe CRS have been reported, suggesting the importance of appropriate intervention. Gaining a better understanding of CRS and developing new treatments for CRS are active areas of laboratory and clinical research. Herein, we summarize the current studies on prevention and management of CRS to expand the safety and applicability of CAR-T cell therapy in various malignancies.

Novel systemic treatment approaches for metastatic pancreatic cancer

INTRODUCTION

Pancreatic ductal adenocarcinoma (PDAC) has a 5-year overall survival rate of 10 %, emphasizing the need for more effective therapies, especially in metastatic disease. The immunosuppressive tumor microenvironment, poor vascularization, and dense tumor stroma typical for PDAC are hurdles that need to be overcome by novel drugs. Investigations are moving towards more targeted treatments including immunotherapy and cell-based approaches.

AREAS COVERED

This article reviews emerging drugs in clinical development for metastatic PDAC, focusing on cellular therapies and novel treatments targeting metabolism, tumor stroma, oncogenic pathways and immunosuppression. With immunotherapy and CAR T cell therapy on the rise in hematological malignancies, the transfer to solid tumors remains intriguing. Multiple exciting clinical trials investigating innovative therapeutic strategies for PDAC are currently ongoing and reviewed herein. ClinicalTrials.gov, conference abstracts and PubMed were searched in August 2021 and assessed for information on ongoing and published clinical studies.

EXPERT OPINION

With many challenges to overcome, the optimal therapy for patients with metastatic PDAC is likely to consist of a combination of different agents. We are slowly moving from entity-dependent approaches to ones more focused on molecular and pathological features. Increasingly personalized treatment plans tailored to each patient may be the future of PDAC therapy.

Synthetic Biology in Chimeric Antigen Receptor T (CAR T) Cell Engineering

Synthetic biology is a novel interdisciplinary research area following engineering principles to redesign and construct biological systems for useful purposes. As one of the most notable clinically relevant application of synthetic biology, chimeric antigen receptor (CAR) T cells have demonstrated tremendous success for the treatment of advanced hematological malignancies in recent years. However, various unsolved obstacles limit the widespread application of CAR T cell therapies, including treatment-associated toxicities, antigen heterogeneity, antigen escape, poor CAR T cell persistence and expansion, and particularly inefficient homing, infiltrating into, and surviving within solid tumors. Accordingly, to improve therapeutic efficacy and minimize side effects, innovative CAR design becomes urgently necessary, and researchers are developing numerous methods to overcome the limitations. Here we summarize currently available bioengineering strategies and discuss the future development from a viewpoint of synthetic biology.

Systematic review of nutrition support interventions in adult haematology and oncology patients receiving CAR T cell therapy

BACKGROUND & AIMS

Chimeric Antigen Receptor (CAR) T cell therapy is a novel adoptive immunotherapy that is revolutionising the treatment of haematological malignancies and solid tumours. Maintaining a patient's nutritional status and implementing nutrition support interventions have been shown to improve certain patient outcomes in standard anti-cancer therapies; however, guidance for nutrition support interventions in CAR T cell therapy are lacking. The primary aim of this review was to determine the impact of nutrition support interventions on patient-centred outcomes for adult CAR T cell therapy haematology and oncology patients. The patient-centred outcomes of interest included nutritional status and dietary intake, morbidity, functional status, and mortality. Our secondary aim was to describe the nutrition implications that have been acknowledged (but not fully evaluated) in CAR T cell therapy, and to guide future research and practice.

METHODS

Four electronic databases (CENTRAL, Embase, MEDLINE and CINAHL) were searched to January 2021, with additional records identified through handsearching and snowballing. Studies considered eligible for inclusion were randomised control trials (RCT), quasi-RCTs, cohort and observational studies, assessing nutrition support interventions (oral, enteral and/or parenteral) in adult haematology and oncology patients receiving CAR T cell therapy or adoptive immunotherapy. No publication status, year or language restrictions were applied.

RESULTS

Two authors reviewed the title and abstracts of 1181 retrieved records; however no studies were eligible for inclusion in this systematic review.

CONCLUSIONS

We are currently unable to identify if there is an association between nutrition support interventions and outcomes in CAR T cell therapy for adults with haematological malignancies or solid tumours. Lower quality clinical studies and animal models were identified that permitted us to qualitatively describe the risks for poor nutritional status in this population. This empty review confirms the need for research into the potential impact of nutrition support in CAR T cell therapy, including well-designed RCTs.

Gene dosage effects of poly(A) track-engineered hypomorphs

Manipulation of gene activity through creation of hypomorphic mutants has been a long-standing tool in examining gene function. Our previous studies have indicated that hypomorphic mutants could be created by inserting cis-regulatory sequences composed of consecutive adenosine nucleotides called poly(A) tracks. Here we use poly(A) tracks to create hypomorphic mutants and functional characterization of membrane, secretory, and endogenous proteins. Insertion of poly(A) tracks into the sequences of interleukin-2 and membrane protein CD20 results in a programmable reduction of mRNA stability and attenuation of protein expression regardless of the presence of a signaling sequence. Likewise, CRISPR-Cas9 targeted insertion of poly(A) tracks into the coding sequence of the endogenous human genes AUF1 and TP53 results in a programmable reduction of targeted protein and mRNA levels. Functional analyses of AUF1-engineered hypomorphs indicate a direct correlation between AUF1 gene levels and the stability of AUF1-regulated mRNAs. Hypomorphs of TP53 affect expression of the target genes differentially depending on the severity of the hypomorphic mutation. Finally, decreases in TP53 protein affect the same cellular pathways in poly(A) track-engineered cells as in cancer cells, indicating these variants’ biological relevance. These results highlight this technology’s power to create predictable, stable hypomorphs in recombinant or endogenous genes in combination with CRISPR-Cas9 engineering tools.

T Cell Engaging Immunotherapies, Highlighting Chimeric Antigen Receptor (CAR) T Cell Therapy

In the past decade, chimeric antigen receptor (CAR) T cell technology has revolutionized cancer immunotherapy. This strategy uses synthetic CARs to redirect the patient's own immune cells to recognize specific antigens expressed on the surface of tumor cells. The unprecedented success of anti-CD19 CAR T cell therapy against B cell malignancies has resulted in its approval by the US Food and Drug Administration (FDA) in 2017. However, major scientific challenges still remain to be addressed for the broad use of CAR T cell therapy. These include severe toxicities, limited efficacy against solid tumors, and immune suppression in the hostile tumor microenvironment. Furthermore, CAR T cell therapy is a personalized medicine of which the production is time- and resource-intensive, which makes it very expensive. All these factors drive new innovations to engineer more powerful CAR T cells with improved antitumor activity, which are reviewed in this manuscript.

Signaling pathways in the regulation of cytokine release syndrome in human diseases and intervention therapy

Cytokine release syndrome (CRS) embodies a mixture of clinical manifestations, including elevated circulating cytokine levels, acute systemic inflammatory symptoms and secondary organ dysfunction, which was first described in the context of acute graft-versus-host disease after allogeneic hematopoietic stem-cell transplantation and was later observed in pandemics of influenza, SARS-CoV and COVID-19, immunotherapy of tumor, after chimeric antigen receptor T (CAR-T) therapy, and in monogenic disorders and autoimmune diseases. Particularly, severe CRS is a very significant and life-threatening complication, which is clinically characterized by persistent high fever, hyperinflammation, and severe organ dysfunction. However, CRS is a double-edged sword, which may be both helpful in controlling tumors/viruses/infections and harmful to the host. Although a high incidence and high levels of cytokines are features of CRS, the detailed kinetics and specific mechanisms of CRS in human diseases and intervention therapy remain unclear. In the present review, we have summarized the most recent advances related to the clinical features and management of CRS as well as cutting-edge technologies to elucidate the mechanisms of CRS. Considering that CRS is the major adverse event in human diseases and intervention therapy, our review delineates the characteristics, kinetics, signaling pathways, and potential mechanisms of CRS, which shows its clinical relevance for achieving both favorable efficacy and low toxicity.

Structure identification of soybean peptides and their immunomodulatory activity

Soybean peptides are functional food with good health benefits. The health benefits presented are highly dependent on the peptide structure. In this work, soybean peptides were prepared by alkaline protease hydrolysis of soybean proteins. The peptide structure was identified by UPLC-MS/MS. The full peptide composition was revealed. The sequences of 51 peptides were identified and 46 peptides were assigned as immunomodulatory peptides. By evaluating the immumonodulatory activity and mechanism, soybean peptides could facilitate the proliferation of macrophages. The pinocytotic activity and NO level were increased. Induction of iNOS mRNA expression by soybean peptides was responsible for the increased NO production. The release of cytokines IL-6 and TNF-α was elevated and their levels were equal to positive control. The mRNA expression levels of IL-6 and TNF-α were also improved by soybean peptides, but much lower than positive control. The results were helpful for application of soybean peptides in functional foods.

Conditional control of chimeric antigen receptor T-cell activity through a destabilizing domain switch and its chemical ligand

BACKGROUND AIMS

Despite the impressive efficacy of chimeric antigen receptor (CAR) T-cell therapy, adverse effects, including cytokine release syndrome and neurotoxicity, impede its therapeutic application, thus making the modulation of CAR T-cell activity a priority. The destabilizing domain mutated from Escherichia coli dihydrofolate reductase (DHFR) is inherently unstable and degraded by proteasomes unless it is stabilized by its chemical ligand trimethoprim (TMP), a Food and Drug Administration-approved drug. Here the authors reveal a strategy to modulate CAR T-cell activity at the protein level by employing DHFR and TMP as a chemical switch system.

METHODS

First, the system was demonstrated to work in human primary T cells. To introduce the system to CAR T cells, DHFR was genetically fused to the carboxyl terminal of a third-generation CAR molecule targeting CD19 (CD19-CAR), constructing the CD19-CAR-DHFR fusion.

RESULTS

The CD19-CAR-DHFR molecule level was shown to be modulated by TMP. Importantly, the incorporation of DHFR had no impact on the recognition specificity and normal function of the CAR molecule. Little adverse effect on cell proliferation and apoptosis was detected. It was proved that TMP could regulate cytokine secretion and the in vitro cytotoxicity of CD19-CAR-DHFR T cells. Furthermore, the in vivo anti-tumor efficacy was demonstrated to be controllable through the manipulation of TMP administration. The approach to control CD19-CAR also succeeded in 19-BBZ(71), another CD19-targeting CAR with a different structure.

CONCLUSIONS

The proposed approach based on DHFR and TMP provides a facile strategy to bring CAR T-cell therapy under conditional user control, and the strategy may have the potential to be transplantable.

Quantitative radio-thin-layer chromatography and positron emission tomography studies for measuring streptavidin transduced chimeric antigen receptor T cells

The proliferation of chimeric antigen receptor (CAR) T cells is closely related to their efficacy, but it is still a great challenge to monitor and quantify CAR T cells in vivo. Based on the high affinity (Kd ≈ 10^-15 M) of streptavidin (SA) and biotin, radiolabeled biotin may be used to quantify SA-transduced CAR T cells (SA-CAR T cells). Radio-thin-layer chromatography (radio-TLC) and positron emission tomography (PET) are highly sensitive for trace analysis. Our aim was to develop radio-TLC and PET methods to quantify SA-CAR T cells in vitro and in vivo. First, we developed [⁶⁸Ga]-DOTA-biotin. Commercially available SA was used as a standard, and quantitative standard curves were established in vitro and in vivo by radio-TLC and PET. Furthermore, the feasibility of the method was verified in Raji model mice. The linear range of radio-TLC was 0.02 ∼ 0.15 pmol/μL with R² = 0.9993 in vitro. The linear range of PET was 0.02 ∼ 0.76 pmol/μL with R² = 0.9986 in vivo. SA in CAR T cells can also be accurately quantified in a Raji leukemia model according to PET imaging. The radio-TLC/PET method established in this study is promising for using in the dynamic monitoring and analysis of SA-CAR T cells during therapy.

Focused evaluation of the roles of macrophages in chimeric antigen receptor (CAR) T cell therapy associated cytokine release syndrome

Cytokine release syndrome (CRS) is a major obstacle to the widespread clinical application of chimeric antigen receptor (CAR) T cell therapies. CRS can also be induced by infections (such as SARS-CoV-2), drugs (such as therapeutic antibodies), and some autoimmune diseases. Myeloid-derived macrophages play key roles in the pathogenesis of CRS, and participate in the production and release of the core CRS cytokines, including interleukin (IL)-1, IL-6, and interferon-γ. In this review, we summarize the roles of macrophages in CRS and discuss new developments in macrophage activation and the related mechanisms of cytokine regulation in CRS.

Insight into next-generation CAR therapeutics: designing CAR T cells to improve clinical outcomes

Chimeric antigen receptor (CAR) T cell therapy has shown considerable promise for hematologic malignancies, leading to the US Food and Drug Administration approval of two CAR T cell-based therapies for the treatment of B cell acute lymphoblastic leukemia and large B cell lymphoma. Despite success in hematologic malignancies, the treatment landscape of CAR T cell therapy for solid tumors has been limited. There are unique challenges in the development of novel CAR T cell therapies to improve both safety and efficacy. Improved understanding of the immunosuppressive tumor microenvironment and resistance mechanisms has led to encouraging approaches to mitigating these obstacles. This Review will characterize challenges with current CAR T designs for hematologic malignancies and solid tumors and emphasize preclinical and clinical strategies to overcome them with novel CAR T cell therapies.

Design of Neuraminidase-Targeted Imaging and Therapeutic Agents for the Diagnosis and Treatment of Influenza Virus Infections

The last step in influenza virus replication involves the assembly of viral components on the infected cell's plasma membrane followed by budding of intact virus from the host cell surface. Because viral neuraminidase and hemagglutinin are both inserted into the host cell's membrane during this process, influenza virus-infected cells are distinguished from uninfected cells by the presence of viral neuraminidase and hemagglutinin on their cell surfaces. In an effort to exploit this difference in cell surface markers for development of diagnostic and therapeutic agents, we have modified an influenza neuraminidase inhibitor, zanamivir, for targeting of attached imaging and therapeutic agents selectively to influenza viruses and virus-infected cells. We have designed here a zanamivir-conjugated rhodamine dye that allows visual monitoring of binding, internalization, and intracellular trafficking of the fluorescence-labeled neuraminidase in virus-infected cells. We also synthesize a zanamivir-^99mTc radioimaging conjugate that permits whole body imaging of the virus's biodistribution and abundance in infected mice. Finally, we create both a zanamivir-targeted cytotoxic drug (i.e., zanamivir-tubulysin B) and a viral neuraminidase-targeted CAR T cell and demonstrate that they are both able to kill viral neuraminidase-expressing cells without damaging healthy cells. Taken together, these data suggest that the influenza virus neuraminidase inhibitor, zanamivir, can be exploited to improve the diagnosis, imaging, and treatment of influenza virus infections.

Toci or not toci: innovations in the diagnosis, prevention, and early management of cytokine release syndrome

Cytokine release syndrome (CRS) remains a significant toxicity of chimeric antigen receptor T-cell (CAR-T) therapy for hematologic malignancies. While established guidelines exist for the management of Grade 2+ CRS with immunosuppressive agents such as tocilizumab or corticosteroids, the management of early-grade CRS (i.e. Grade 1 CRS with isolated fevers) has no such consensus beyond supportive care. In this review, we discuss early-grade CRS with an emphasis on its diagnosis, management, and prevention. Strategies to target early-grade CRS include immunosuppression preemptively (once CRS develops) or prophylactically (before CRS develops) as well as novel small-molecule inhibitors or fractionated CAR-T dosing. In the near future, next-generation CAR-T therapies may be able to target CRS precisely or obviate CRS entirely. If shown to prevent CRS-associated morbidity while maintaining therapeutic anti-neoplastic efficacy, these innovative strategies will enhance the safety of CAR-T therapy while also improving its operationalization and accessibility in the real-world setting.

Stereo- and regiodefined DNA-encoded chemical libraries enable efficient tumour-targeting applications

The encoding of chemical compounds with amplifiable DNA tags facilitates the discovery of small-molecule ligands for proteins. To investigate the impact of stereo- and regiochemistry on ligand discovery, we synthesized a DNA-encoded library of 670,752 derivatives based on 2-azido-3-iodophenylpropionic acids. The library was selected against multiple proteins and yielded specific ligands. The selection fingerprints obtained for a set of protein targets of pharmaceutical relevance clearly showed the preferential enrichment of ortho-, meta- or para-regioisomers, which was experimentally verified by affinity measurements in the absence of DNA. The discovered ligands included novel selective enzyme inhibitors and binders to tumour-associated antigens, which enabled conditional chimeric antigen receptor T-cell activation and tumour targeting.

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.

Safety profile of chimeric antigen receptor T-cell immunotherapies (CAR-T) in clinical practice

Purpose

Two chimeric antigen receptor T-cell (CAR-T) therapies have been approved in the United States (USA) in 2017 and Europe (EU) in 2018: axicabtagene ciloleucel and tisagenlecleucel. They contain the patient’s own T cells, which are extracted, genetically modified, and reinfused. Alongside the good efficacy results, the assessment of safety profile of these new therapies represents a great challenge. Our aim was to analyze the reports of the adverse drug reactions (ADR) after CAR-T administration as occurred in the real clinical setting.

Methods

We performed a retrospective observational study, collecting all the reports in EU (EudraVigilance, EV) and US (FAERS) databases of ADRs regarding axicabtagene ciloleucel and tisagenlecleucel. Both descriptive and statistical analyses were performed, the latter by using Reporting Odds Ratio (ROR).

Results

A total number of 1426 reports of suspected ADRs were retrieved in EudraVigilance and FAERS. Patients’ reported age reflected the age range for which the drugs are approved (18–64 years for axicabtagene ciloleucel and patients aged under 25 years for tisagenlecleucel). The most reported event was cytokine release syndrome (CRS), 185 events for tisagenlecleucel and 462 for axicabtagene ciloleucel in FAERS and 137 and 498, respectively, in EudraVigilance. A disproportionality was found comparing axicabtagene ciloleucel with tisagenlecleucel for the above-mentioned event: EV ROR 2.47, 95% CI 2.22–2.74, FAERS 1.89, 1.70–2.10.

Conclusion

CRS represents the major problem with the administration of CAR-T therapies. Our analysis has not revealed new ADRs; however, it supports the safety profile of CAR-T with new data from real clinical setting.

Toxicities of Chimeric Antigen Receptor T Cell Therapy in Multiple Myeloma: An Overview of Experience From Clinical Trials, Pathophysiology, and Management Strategies

In the last few years, monoclonal antibodies (mAbs) such as elotuzumab and daratutumab have brought the treatment of multiple myeloma (MM) into the new era of immunotherapy. More recently, chimeric antigen receptor (CAR) modified T cell, a novel cellular immunotherapy, has been developed for treatment of relapsed/refractory (RR) MM, and early phase clinical trials have shown promising efficacy of CAR T cell therapy. Many patients with end stage RRMM regard CAR T cell therapy as their “last chance” and a “hope of cure”. However, severe adverse events (AEs) and even toxic death related to CAR T cell therapy have been observed. The management of AEs related to CAR T cell therapy represents a new challenge, as the pathophysiology is not fully understood and there is still no well-established standard of management. With regard to CAR T cell associated toxicities in MM, in this review, we will provide an overview of experience from clinical trials, pathophysiology, and management strategies.

Chimeric antigen receptor T cells immunotherapy: challenges and opportunities in hematological malignancies

Taking advantage of the cellular immune system is the mainstay of the adoptive cell therapy, to induce recognition and destruction of cancer cells. The impressive demonstration of this principle is chimeric antigen receptor-modified T (CAR-T)-cell therapy, which had a major impact on treating relapsed and refractory hematological malignancies. Despite the great results of the CAR-T-cell therapy, many tumors are still able to avoid immune detection and further elimination, as well as the possible associated adverse events. Herein, we highlighted the recent advances in CAR-T-cell therapy, discussing their applications beneficial functions and side effects in hematological malignancies, illustrating the underlying challenges and opportunities. Furthermore, we provide an overview to overcome different obstacles using potential manufacture and treatment strategies.

Sensitive manipulation of CAR T cell activity using a chimeric endocytosing receptor

Background

Most adoptive cell therapies (ACTs) suffer from an inability to control the therapeutic cell’s behavior following its transplantation into a patient. Thus, efforts to inhibit, activate, differentiate or terminate an ACT after patient reinfusion can be futile, because the required drug adversely affects other cells in the patient.

Methods

We describe here a two domain fusion receptor composed of a ligand-binding domain linked to a recycling domain that allows constitutive internalization and trafficking of the fusion receptor back to the cell surface. Because the ligand-binding domain is designed to bind a ligand not normally present in humans, any drug conjugated to this ligand will bind and endocytose selectively into the ACT.

Results

In two embodiments of our strategy, we fuse the chronically endocytosing domain of human folate receptor alpha to either a murine scFv that binds fluorescein or human FK506 binding protein that binds FK506, thereby creating a fusion receptor composed of largely human components. We then create the ligand-targeted drug by conjugating any desired drug to either fluorescein or FK506, thereby generating a ligand-drug conjugate with ~10^-9 M affinity for its fusion receptor. Using these tools, we demonstrate that CAR T cell activities can be sensitively tuned down or turned off in vitro as well as tightly controlled following their reinfusion into tumor-bearing mice.

Conclusions

We suggest this ‘chimeric endocytosing receptor’ can be exploited to manipulate not only CAR T cells but other ACTs following their reinfusion into patients. With efforts to develop ACTs to treat diseases including diabetes, heart failure, osteoarthritis, cancer and sickle cell anemia accelerating, we argue an ability to manipulate ACT activities postinfusion will be important.

Photoswitchable CAR-T Cell Function In Vitro and In Vivo via a Cleavable Mediator

Chimeric antigen receptor (CAR)-T-based therapeutics are a breakthrough in cancer treatment; however, they are hampered by constitutive activation, which leads to worrisome side effects. Engineering CAR-T cells to be as tightly controllable as possible remains a topic of ongoing investigation. Here, we report a photoswitchable approach that uses a mediator for the at-will regulation of CAR-T cells. This mediator carries dual folate and fluorescein isothiocyanate moieties tethered by an ortho-nitrobenzyl ester photocleavable linker. CAR-T cells were shown to be highly cytotoxic to targeted cells only in the presence of the mediator and acted in a dose-dependent manner. The toxicity of CAR-T cells can be rapidly terminated by cleavage of the mediator, and the effects of CAR-T cells can be activated again by resupplementation with the mediator without compromising tumor therapy. The approach described here provides a direction for enhancing the controllability of CAR-T cells and can likely be applied in other immunotherapies.

Engineering CAR-T Cells for Next-Generation Cancer Therapy

T cells engineered to express chimeric antigen receptors (CARs) with tumor specificity have shown remarkable success in treating patients with hematologic malignancies and revitalized the field of adoptive cell therapy. However, realizing broader therapeutic applications of CAR-T cells necessitates engineering approaches on multiple levels to enhance efficacy and safety. Particularly, solid tumors present unique challenges due to the biological complexity of the solid-tumor microenvironment (TME). In this review, we highlight recent strategies to improve CAR-T cell therapy by engineering (1) the CAR protein, (2) T cells, and (3) the interaction between T cells and other components in the TME.

Identification of Targets to Redirect CAR T Cells in Glioblastoma and Colorectal Cancer: An Arduous Venture

The chimeric antigen receptor (CAR) is an artificial molecule engineered to induce cytolytic T cell reactions in tumors. Generally, this molecule combines an extracellular single-chain variable fragment (scFv) able to recognize tumor-associated epitopes together with the intracellular signaling domains that are required for T cell activation. When expressed by T cells, the CAR enables the recognition and subsequent destruction of cancer cells expressing the complementary antigen on their surface. Although the clinical application for CAR T cells is currently limited to some hematological malignancies, researchers are trying to develop CAR T cell-based therapies for the treatment of solid tumors. However, while in the case of CD19, or other targets restricted to the hematopoietic compartment, the toxicity is limited and manageable, the scarcity of specific antigens expressed by solid tumors and not by healthy cells from vital organs makes the clinical development of CAR T cells in this context particularly challenging. Here we summarize relevant research and clinical trials conducted to redirect CAR T cells to surface antigens in solid tumors and cancer stem cells with a focus on colorectal cancer and glioblastoma. Finally, we will discuss current knowledge of altered glycosylation of CSCs and cancer cells and how these novel epitopes may help to target CAR T cell-based immunotherapy in the future.

Macrophage, the potential key mediator in CAR-T related CRS

Chimeric antigen receptor (CAR) T cell therapy is a new frontier in cancer therapy. The toxicity of cytokine release syndrome (CRS) has become one of the major challenges that limits the wider use of CAR T cells to fight cancer. Exploration of CRS pathogenesis and treatment is becoming the main focus of ongoing studies. Myeloid-derived macrophages were found to play a critical role in CRS pathogenesis, and these cells mediate the major production of core cytokines, including IL-6, IL-1 and interferon (IFN)-γ. Colocalization of macrophages and CAR T cells was also identified as necessary for inducing CRS, and CD40L-CD40 signaling might be the key cell–cell interaction in the tumor microenvironment. Macrophages might also take part in endocrine and self-amplified catecholamine loops that can directly activate cytokine production and release by macrophages during CRS. In addition to tocilizumab and corticosteroids, several novel CRS therapies targeting macrophage-centered pathways have shown much potential, including GM-CSF blockade and administration of atrial natriuretic peptide (ANP) and α-methyltyrosine (metyrosine, MTR). In the present review, we summarized the role of macrophages in CRS and new developments in therapeutic strategies for CRS-associated toxicities.

Next-generation CAR T cells to overcome current drawbacks

As a rapidly emerging treatment in the oncology field, adoptive transfer of autologous, genetically modified chimeric antigen receptor (CAR) T cells has shown striking efficacy and is curative in certain relapsed/refractory patients with hematologic malignancy. This treatment modality of using a "living drug" offers many tantalizing and novel therapeutic strategies for cancer patients whose remaining treatment options may have otherwise been limited. Despite the early success of CAR T cells in hematologic malignancies, many barriers remain for widespread adoption. General barriers include cellular manufacturing limitations, baseline quality of the T cells, adverse events post-infusion such as cytokine release syndrome (CRS) and neurotoxicity, and host rejection of non-human CARs. Additionally, each hematologic disease presents unique mechanisms of relapse which have to be addressed in future clinical trials if we are to augment the efficacy of CAR T treatment. In this review, we will describe current barriers to hindering efficacy of CAR T-cell treatment for hematologic malignancies in a disease-specific manner and review recent innovations aimed at enhancing the potency and applicability of CAR T cells, with the overall goal of building a framework to begin incorporating this form of therapy into the standard medical management of blood cancers.