Targeted antibody-mediated depletion of murine CD19 CAR T cells permanently reverses B cell aplasia

Adapter CAR T Cell Therapy for the Treatment of B-Lineage Lymphomas

CD19CAR T cells facilitate a transformational treatment in various relapsed and refractory aggressive B-lineage cancers. In general, encouraging response rates have been observed in B-lineage-derived non-Hodgkin’s lymphomas treated with CD19CAR T cells. The major cause of death in heavily pretreated NHL patients is lymphoma progression and lymphoma recurrence. Inefficient CAR T cell therapy is the result of the limited potency of the CAR T cell product or is due to loss of the targeted antigen. Target antigen loss has been identified as the key factor that can be addressed stringently by dual- or multitargeted CAR T cell approaches. We have developed a versatile adapter CAR T cell technology (AdCAR) that allows multitargeting. Screening of three different B-lineage lymphoma cell lines has revealed distinct immune target profiles. Cancer-specific adapter molecule combinations may be utilized to prevent antigen immune escape. In general, CD19CAR T cells become non-functional in CD19 negative lymphoma subsets; however, AdCAR T cells can be redirected to alternative target antigens beyond CD19, such as CD20, CD22, CD79B, and ROR-1. The capability to flexibly shift CAR specificity by exchanging the adapter molecule’s specificity broadens the application and significantly increases the anti-leukemic and anti-lymphoma activity. The clinical evaluation of AdCAR T cells in lymphoma as a new concept of CAR T cell immunotherapy may overcome treatment failure due to antigen immune escape in monotargeted conventional CAR T cell therapies.

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.

Research Progress on Nanoparticles-Based CRISPR/Cas9 System for Targeted Therapy of Tumors

Cancer is a genetic mutation disease that seriously endangers the health and life of all human beings. As one of the most amazing academic achievements in the past decade, CRISPR/Cas9 technology has been sought after by many researchers due to its powerful gene editing capability. CRISPR/Cas9 technology shows great potential in oncology, and has become one of the most promising technologies for cancer genome-editing therapeutics. However, its efficiency and the safety issues of in vivo gene editing severely limit its widespread application. Therefore, developing a suitable delivery method for the CRISPR/Cas9 system is an urgent problem to be solved at present. Rapid advances in nanomedicine suggest nanoparticles could be a viable option. In this review, we summarize the latest research on the potential use of nanoparticle-based CRISPR/Cas9 systems in cancer therapeutics, in order to further their clinical application. We hope that this review will provide a novel insight into the CRISPR/Cas9 system and offer guidance for nanocarrier designs that will enable its use in cancer clinical applications.

CAR-T cell development for Cutaneous T cell Lymphoma: current limitations and potential treatment strategies

Chimeric antigen receptor (CAR)-T therapy has demonstrated remarkable outcomes for B cell malignancies, however, its application for T cell lymphoma, particularly cutaneous T cell lymphoma (CTCL), has been limited. Barriers to effective CAR-T cell therapy in treating CTCL include T cell aplasia in autologous transplants, CAR-T product contamination with leukemic T cells, CAR-T fratricide (when the target antigen is present on normal T cells), and tumor heterogeneity. To address these critical challenges, innovative CAR engineering by targeting multiple antigens to strike a balance between efficacy and safety of the therapy is necessary. In this review, we discuss the current obstacles to CAR-T cell therapy and highlight potential targets in treating CTCL. Looking forward, we propose strategies to develop more powerful dual CARs that are advancing towards the clinic in CTCL therapy.

Advances in modular control of CAR-T therapy with adapter-mediated CARs

Protein engineering has contributed to successes in the field of T cell-based immunotherapy, including chimeric antigen receptor (CAR) T cell therapy. CAR T cell therapy has become a pillar of cancer immunotherapy, demonstrating clinical effectiveness against B cell malignancies by targeting the B cell antigen CD19. Current gene editing techniques have limited safety controls over CAR T cell activity, which presents a hurdle for control of CAR T cells in patients. Alternatively, CAR T cell activity can be controlled by engineering CARs to bind soluble adapter molecules that direct the interaction between the CAR T cell and target cell. The flexibility in this adapter-mediated approach overcomes the rigid specificity of traditional CAR T cells to allow targeting of multiple cell types. Here we describe adapter CAR T technologies and how these methods emphasize the growing role of protein engineering in the design of programmable tools for T cell therapies.

CAR-T Cell Therapy in Hematological Malignancies: Current Opportunities and Challenges

Chimeric antigen receptor T (CAR-T) cell therapy represents a major breakthrough in cancer treatment, and it has achieved unprecedented success in hematological malignancies, especially in relapsed/refractory (R/R) B cell malignancies. At present, CD19 and BCMA are the most common targets in CAR-T cell therapy, and numerous novel therapeutic targets are being explored. However, the adverse events related to CAR-T cell therapy might be serious or even life-threatening, such as cytokine release syndrome (CRS), CAR-T-cell-related encephalopathy syndrome (CRES), infections, cytopenia, and CRS-related coagulopathy. In addition, due to antigen escape, the limited CAR-T cell persistence, and immunosuppressive tumor microenvironment, a considerable proportion of patients relapse after CAR-T cell therapy. Thus, in this review, we focus on the progress and challenges of CAR-T cell therapy in hematological malignancies, such as attractive therapeutic targets, CAR-T related toxicities, and resistance to CAR-T cell therapy, and provide some practical recommendations.

B cell targeting in CAR T cell therapy: Side effect or driver of CAR T cell function?

Chimeric antigen receptor (CAR) T cell therapies targeting CD19 and CD22 have been successful for treating B cell cancers, but CAR T cells targeting non-B cell cancers remain unsuccessful. We propose that rather than being strictly a side effect of therapy, the large number of CAR interactions with normal B cells may be a key contributor to clinical CAR T cell responses.

Chimeric Antigen Receptor (CAR) Regulatory T-Cells in Solid Organ Transplantation

Solid organ transplantation is the treatment of choice for various end-stage diseases, but requires the continuous need for immunosuppression to prevent allograft rejection. This comes with serious side effects including increased infection rates and development of malignancies. Thus, there is a clinical need to promote transplantation tolerance to prevent organ rejection with minimal or no immunosuppressive treatment. Polyclonal regulatory T-cells (Tregs) are a potential tool to induce transplantation tolerance, but lack specificity and therefore require administration of high doses. Redirecting Tregs towards mismatched donor HLA molecules by modifying these cells with chimeric antigen receptors (CAR) would render Tregs far more effective at preventing allograft rejection. Several studies on HLA-A2 specific CAR Tregs have demonstrated that these cells are highly antigen-specific and show a superior homing capacity to HLA-A2+ allografts compared to polyclonal Tregs. HLA-A2 CAR Tregs have been shown to prolong survival of HLA-A2+ allografts in several pre-clinical humanized mouse models. Although promising, concerns about safety and stability need to be addressed. In this review the current research, obstacles of CAR Treg therapy, and its potential future in solid organ transplantation will be discussed.

Viral infection in hematopoietic stem cell transplantation: an International Society for Cell & Gene Therapy Stem Cell Engineering Committee review on the role of cellular therapy in prevention and treatment

Despite recent advances in the field of HSCT, viral infections remain a frequent causeof morbidity and mortality among HSCT recipients. Adoptive transfer of viral specific T cells has been successfully used both as prophylaxis and treatment of viral infections in immunocompromised HSCT recipients. Increasingly, precise risk stratification of HSCT recipients with infectious complications should incorporate not only pretransplant clinical criteria, but milestones of immune reconstitution as well. These factors can better identify those at highest risk of morbidity and mortality and identify a population of HSCT recipients in whom adoptive therapy with viral specific T cells should be considered for either prophylaxis or second line treatment early after inadequate response to first line antiviral therapy. Broadening these approaches to improve outcomes for transplant recipients in countries with limited resources is a major challenge. While the principles of risk stratification can be applied, early detection of viral reactivation as well as treatment is challenging in regions where commercial PCR assays and antiviral agents are not readily available.

Engineering Next-Generation CAR-T Cells: Overcoming Tumor Hypoxia and Metabolism

T cells engineered to express chimeric antigen receptors (CARs) have shown remarkable success in treating B-cell malignancies, reflected by multiple US Food and Drug Administration-approved CAR-T cell products currently on the market. However, various obstacles have thus far limited the use of approved products and constrained the efficacy of CAR-T cell therapy against solid tumors. Overcoming these obstacles will necessitate multidimensional CAR-T cell engineering approaches and better understanding of the intricate tumor microenvironment (TME). Key challenges include treatment-related toxicity, antigen escape and heterogeneity, and the highly immunosuppressive profile of the TME. Notably, the hypoxic and nutrient-deprived nature of the TME severely attenuates CAR-T cell fitness and efficacy, highlighting the need for more sophisticated engineering strategies. In this review, we examine recent advances in protein- and cell-engineering strategies to improve CAR-T cell safety and efficacy, with an emphasis on overcoming immunosuppression induced by tumor metabolism and hypoxia.

B7-H3 Specific CAR T Cells for the Naturally Occurring, Spontaneous Canine Sarcoma Model

One obstacle for human solid tumor immunotherapy research is the lack of clinically relevant animal models. In this study, we sought to establish a chimeric antigen receptor (CAR) T-cell treatment model for naturally occurring canine sarcomas as a model for human CAR T-cell therapy. Canine CARs specific for B7-H3 were constructed using a single-chain variable fragment derived from the human B7-H3-specific antibody MGA271, which we confirmed to be cross-reactive with canine B7-H3. After refining activation, transduction, and expansion methods, we confirmed target killing in a tumor spheroid three-dimensional assay. We designed a B7-H3 canine CAR T-cell and achieved consistently high levels of transduction efficacy, expansion, and in vitro tumor killing. Safety of the CAR T cells were confirmed in two purposely bred healthy canine subjects following lymphodepletion by cyclophosphamide and fludarabine. Immune response, clinical parameters, and manifestation were closely monitored after treatments and were shown to resemble that of humans. No severe adverse events were observed. In summary, we demonstrated that similar to human cancers, B7-H3 can serve as a target for canine solid tumors. We successfully generated highly functional canine B7-H3-specific CAR T-cell products using a production protocol that closely models human CAR T-cell production procedure. The treatment regimen that we designed was confirmed to be safe in vivo. Our research provides a promising direction to establish in vitro and in vivo models for immunotherapy for canine and human solid tumor treatment.

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.

Time to evolve: predicting engineered T cell-associated toxicity with next-generation models

Despite promising clinical results in a small subset of malignancies, therapies based on engineered chimeric antigen receptor and T-cell receptor T cells are associated with serious adverse events, including cytokine release syndrome and neurotoxicity. These toxicities are sometimes so severe that they significantly hinder the implementation of this therapeutic strategy. For a long time, existing preclinical models failed to predict severe toxicities seen in human clinical trials after engineered T-cell infusion. However, in recent years, there has been a concerted effort to develop models, including humanized mouse models, which can better recapitulate toxicities observed in patients. The Accelerating Development and Improving Access to CAR and TCR-engineered T cell therapy (T2EVOLVE) consortium is a public–private partnership directed at accelerating the preclinical development and increasing access to engineered T-cell therapy for patients with cancer. A key ambition in T2EVOLVE is to design new models and tools with higher predictive value for clinical safety and efficacy, in order to improve and accelerate the selection of lead T-cell products for clinical translation. Herein, we review existing preclinical models that are used to test the safety of engineered T cells. We will also highlight limitations of these models and propose potential measures to improve them.

Evolving Strategies to Eliminate the CD4 T Cells HIV Viral Reservoir via CAR T Cell Immunotherapy

Although the advent of ART has significantly reduced the morbidity and mortality associated with HIV infection, the stable pool of HIV in latently infected cells requires lifelong treatment adherence, with the cessation of ART resulting in rapid reactivation of the virus and productive HIV infection. Therefore, these few cells containing replication-competent HIV, known as the latent HIV reservoir, act as the main barrier to immune clearance and HIV cure. While several strategies involving HIV silencing or its reactivation in latently infected cells for elimination by immune responses have been explored, exciting cell based immune therapies involving genetically engineered T cells expressing synthetic chimeric receptors (CAR T cells) are highly appealing and promising. CAR T cells, in contrast to endogenous cytotoxic T cells, can function independently of MHC to target HIV-infected cells, are efficacious and have demonstrated acceptable safety profiles and long-term persistence in peripheral blood. In this review, we present a comprehensive picture of the current efforts to target the HIV latent reservoir, with a focus on CAR T cell therapies. We highlight the current challenges and advances in this field, while discussing the importance of novel CAR designs in the efforts to find a HIV cure.

T Cell Defects: New Insights Into the Primary Resistance Factor to CD19/CD22 Cocktail CAR T-Cell Immunotherapy in Diffuse Large B-Cell Lymphoma

Despite impressive progress, a significant portion of patients still experience primary or secondary resistance to chimeric antigen receptor (CAR) T-cell immunotherapy for relapsed/refractory diffuse large B-cell lymphoma (r/r DLBCL). The mechanism of primary resistance involves T-cell extrinsic and intrinsic dysfunction. In the present study, a total of 135 patients of DLBCL treated with murine CD19/CD22 cocktail CAR T-therapy were assessed retrospectively. Based on four criteria (maximal expansion of the transgene/CAR-positive T-cell levels post-infusion [Cmax], initial persistence of the transgene by the CAR transgene level at +3 months [Tlast], CD19+ B-cell levels [B-cell recovery], and the initial response to CAR T-cell therapy), 48 patients were included in the research and divided into two groups (a T-normal group [n=22] and a T-defect [n=26] group). According to univariate and multivariate regression analyses, higher lactate dehydrogenase (LDH) levels before leukapheresis (hazard ratio (HR) = 1.922; p = 0.045) and lower cytokine release syndrome (CRS) grade after CAR T-cell infusion (HR = 0.150; p = 0.026) were independent risk factors of T-cell dysfunction. Moreover, using whole-exon sequencing, we found that germline variants in 47 genes were significantly enriched in the T-defect group compared to the T-normal group (96% vs. 41%; p<0.0001), these genes consisted of CAR structure genes (n=3), T-cell signal 1 to signal 3 genes (n=13), T cell immune regulation- and checkpoint-related genes (n=9), cytokine- and chemokine-related genes (n=13), and T-cell metabolism-related genes (n=9). Heterozygous germline UNC13D mutations had the highest intergroup differences (26.9% vs. 0%; p=0.008). Compound heterozygous CX3CR1I249/M280 variants, referred to as pathogenic and risk factors according to the ClinVar database, were enriched in the T-defect group (3 of 26). In summary, the clinical characteristics and T-cell immunodeficiency genetic features may help explain the underlying mechanism of treatment primary resistance and provide novel insights into CAR T-cell immunotherapy.

Engineered cellular immunotherapies in cancer and beyond

This year marks the tenth anniversary of cell therapy with chimeric antigen receptor (CAR)-modified T cells for refractory leukemia. The widespread commercial approval of genetically engineered T cells for a variety of blood cancers offers hope for patients with other types of cancer, and the convergence of human genome engineering and cell therapy technology holds great potential for generation of a new class of cellular therapeutics. In this Review, we discuss the goals of cellular immunotherapy in cancer, key challenges facing the field and exciting strategies that are emerging to overcome these obstacles. Finally, we outline how developments in the cancer field are paving the way for cellular immunotherapeutics in other diseases.

Next generation automated traceless cell chromatography platform for GMP-compliant cell isolation and activation

Large-scale target cell isolation from patient blood preparations is one of the critical operations during drug product manufacturing for personalized cell therapy in immuno-oncology. Use of high-affinity murine antibody coated magnetic nanoparticles that remain on isolated cells is the current standard applied for this purpose. Here, we present the transformation of previously described technology - non-magnetic immunoaffinity column chromatography-based cell selection with reversible reagents into a new clinical-grade cell isolation platform called Automated Traceless Cell affinity chromatography (ATC). ATC is a fully closed and GMP-compliant cell selection and manufacturing system. Reversibility of reagents enables (sequential) positive cell selection, optionally in combination with depletion columns, enabling capture of highly specific cell subsets. Moreover, synergy with other Streptamer-based technologies allows novel uses beyond cell isolation including integrated and automated on-column target cell activation. In conclusion, ATC technology is an innovative as well as versatile platform to select, stimulate and modify cells for clinical manufacturing and downstream therapies.

Off-the-Shelf Prostate Stem Cell Antigen-Directed Chimeric Antigen Receptor Natural Killer Cell Therapy to Treat Pancreatic Cancer

BACKGROUND & AIMS

Pancreatic cancer (PC) is the third leading cause of cancer-related death with a 5-year survival rate of approximately 10%. It typically presents as a late-stage incurable cancer and chemotherapy provides modest benefit. Here, we demonstrate the feasibility, safety, and potency of a novel human natural killer (NK) cell-based immunotherapy to treat PC.

METHODS

The expression of prostate stem cell antigen (PSCA) was evaluated in primary PC at messenger RNA and protein levels. The processes of retroviral transduction, expansion, activation, and cryopreservation of primary human NK cells obtained from umbilical cord blood were optimized, allowing us to develop frozen, off-the-shelf, allogeneic PSCA chimeric antigen receptor (CAR) NK cells. The safety and efficacy of PSCA CAR NK cells also expressing soluble (s) interleukin 15 (PSCA CAR_s15 NK cells) were evaluated in vitro and in vivo.

RESULTS

PSCA was elevated in primary human PC compared with the adjacent or other normal tissues. PSCA CAR_s15 NK cells displayed significant tumor-suppressive effects against PSCA(+) PC in vitro before and after 1 cycle of freeze-thaw. The viability of frozen PSCA CAR_s15 NK cells persisted more than 90 days in vivo after their last infusion and significantly prolonged the survival of mice engrafted with human PC.

CONCLUSIONS

PSCA CAR_s15 NK cells showed therapeutic efficacy in human metastatic PC models without signs of systematic toxicity, providing a strong rationale to support clinical development.

In Vivo Cellular Expansion of Lisocabtagene Maraleucel and Association With Efficacy and Safety in Relapsed/Refractory Large B-Cell Lymphoma

Lisocabtagene maraleucel (liso‐cel) is an autologous, CD19‐directed, chimeric antigen receptor T‐cell product for the treatment of adult patients with relapsed or refractory large B‐cell lymphoma (LBCL) after 2 or more lines of systemic therapy. In vivo cellular expansion after single‐dose administration of liso‐cel has been characterized. In this article, in vivo liso‐cel expansion in the pivotal study TRANSCEND NHL 001 (ClinicalTrials.gov identifier, NCT02631044) was further characterized to assess the relationship between in vivo cellular expansion after single‐dose administration of liso‐cel and efficacy or safety after adjusting for key baseline characteristics. Two bioanalytical methods, quantitative polymerase chain reaction and flow cytometry, were used for the assessment of cellular kinetics of liso‐cel, which showed high concordance for in vivo cellular expansion. Multivariable logistic regression analyses demonstrated that higher in vivo cellular expansion of liso‐cel was associated with a higher overall response and complete response rate, and a higher incidence of cytokine release syndrome and neurological events in patients with relapsed or refractory LBCL. Age and tumor burden (by sum of the product of perpendicular diameters) were likely to confound the relationship between in vivo cellular expansion and efficacy, where the association became stronger after controlling for these factors. Repeat dosing of liso‐cel was tested in the study; however, in vivo cellular expansion of liso‐cel was lower after repeat dosing than after the initial dose. These findings should enable a comprehensive understanding of the in vivo cellular kinetics of liso‐cel and the association with outcomes in relapsed/refractory LBCL.

Synthetic receptors for logic gated T cell recognition and function

Adoptive cell therapy with T cells engineered with customized receptors that redirect antigen specificity to cancer cells has emerged as an effective therapeutic approach for many malignancies. Toxicity due to on target or off target effects, antigen heterogeneity on cancer cells, and acquired T cell dysfunction have been identified as barriers that can hinder successful therapy. This review will discuss recent advances in T cell engineering that have enabled the application of logic gates in T cells that can mimic the integration of natural signaling pathways and act in a cell intrinsic or extrinsic fashion to precisely target tumor cells and regulate effector functions, potentially overcoming these barriers to effective therapy.

Chimeric antigen receptor engineered T cells and their application in the immunotherapy of solid tumours

In this article, we reviewed the current literature studies and our understanding of the parameters that affect the chimeric antigen receptor T cells (CAR-T's) activation, effector function, in vivo persistence, and antitumour effects. These factors include T cell subsets and their differentiation stages, the components of chimeric antigen receptors (CAR) design, the expression promoters and delivery vectors, and the CAR-T production process. The CAR signalling and CAR-T activation were also studied in comparison to TCR. The last section of the review gave special consideration of CAR design for solid tumours, focusing on strategies to improve CAR-T tumour infiltration and survival in the hostile tumour microenvironment. With several hundred clinical trials undergoing worldwide, the pace of CAR-T immunotherapy moves from bench to bedside is unprecedented. We hope that the article will provide readers a clear and comprehensive view of this rapidly evolving field and will help scientists and physician to design effective CAR-Ts immunotherapy for solid tumours.

Chimeric Antigen Receptor T-Cell Therapy in Paediatric B-Cell Precursor Acute Lymphoblastic Leukaemia: Curative Treatment Option or Bridge to Transplant?

Chimeric antigen receptor T-cell therapy (CAR-T) targeting CD19 has been associated with remarkable responses in paediatric patients and adolescents and young adults (AYA) with relapsed/refractory (R/R) B-cell precursor acute lymphoblastic leukaemia (BCP-ALL). Tisagenlecleucel, the first approved CD19 CAR-T, has become a viable treatment option for paediatric patients and AYAs with BCP-ALL relapsing repeatedly or after haematopoietic stem cell transplantation (HSCT). Based on the chimeric antigen receptor molecular design and the presence of a 4-1BB costimulatory domain, tisagenlecleucel can persist for a long time and thereby provide sustained leukaemia control. "Real-world" experience with tisagenlecleucel confirms the safety and efficacy profile observed in the pivotal registration trial. Recent guidelines for the recognition, management and prevention of the two most common adverse events related to CAR-T - cytokine release syndrome and immune-cell-associated neurotoxicity syndrome - have helped to further decrease treatment toxicity. Consequently, the questions of how and for whom CD19 CAR-T could substitute HSCT in BCP-ALL are inevitable. Currently, 40-50% of R/R BCP-ALL patients relapse post CD19 CAR-T with either CD19- or CD19+ disease, and consolidative HSCT has been proposed to avoid disease recurrence. Contrarily, CD19 CAR-T is currently being investigated in the upfront treatment of high-risk BCP-ALL with an aim to avoid allogeneic HSCT and associated treatment-related morbidity, mortality and late effects. To improve survival and decrease long-term side effects in children with BCP-ALL, it is important to define parameters predicting the success or failure of CAR-T, allowing the careful selection of candidates in need of HSCT consolidation. In this review, we describe the current clinical evidence on CAR-T in BCP-ALL and discuss factors associated with response to or failure of this therapy: product specifications, patient- and disease-related factors and the impact of additional therapies given before (e.g., blinatumomab and inotuzumab ozogamicin) or after infusion (e.g., CAR-T re-infusion and/or checkpoint inhibition). We discuss where to position CAR-T in the treatment of BCP-ALL and present considerations for the design of supportive trials for the different phases of disease. Finally, we elaborate on clinical settings in which CAR-T might indeed replace HSCT.

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.

Prospect of CAR T-cell therapy in acute myeloid leukemia

INTRODUCTION

Long-term outcome of patients with acute myeloid leukemia (AML) remains dismal, especially for those with high-risk disease or who are refractory to conventional therapy. CAR T-cell therapy provides unique opportunity to improve outcome by specifically targeting leukemia cells through genetically engineered T-cells.

AREAS COVERED

We summarize the progress of CAR T-cells therapy in AML. We examine its shortcomings in AML therapy and the strategies that are being implemented to improve its safety and effectiveness. PubMed Central, ClinicalTrials.gov and ASH annual meeting abstracts, were searched. Search terms used to identify clinical trials were "CAR T-cells in AML" OR CAR T-cells in leukemia". Relevant clinical trials and CAR T-cell research data was reviewed from June 2009 till July 2021.

EXPERT OPINION

CAR T-cell therapy has shown promise as a novel therapy, but there are number of barriers to overcome to achieve it full therapeutic potential in AML. Targeting leukemia specific antigen such as CLL1, to avoid myelotoxicity; incorporating checkpoint inhibitors to overcome leukemia induced immunosuppression and allogenic CAR T-cells to increases accessibility to patients with proliferative disease are among the strategies that are being explored to make CAR T-cell a successful immunotherapy for patient with AML.

Challenges and Advances in Chimeric Antigen Receptor Therapy for Acute Myeloid Leukemia

The advent of chimeric antigen receptor (CAR) T-cell therapy has led to dramatic remission rates in multiple relapsed/refractory hematologic malignancies. While CAR T-cell therapy has been particularly successful as a treatment for B-cell malignancies, effectively treating acute myeloid leukemia (AML) with CARs has posed a larger challenge. AML not only creates an immunosuppressive tumor microenvironment that dampens CAR T-cell responses, but it also lacks many unique tumor-associated antigens, making leukemic-specific targeting difficult. One advantage of CAR T-cell therapy compared to alternative treatment options is the ability to provide prolonged antigen-specific immune effector and surveillance functions. Since many AML CAR targets under investigation including CD33, CD117, and CD123 are also expressed on hematopoietic stem cells, CAR T-cell therapy can lead to severe and potentially lethal myeloablation. Novel strategies to combat these issues include creation of bispecific CARs, CAR T-cell "safety switches", TCR-like CARs, NK CARs, and universal CARs, but all vary in their ability to provide a sustained remission, and consolidation with an allogeneic hematopoietic cell transplantation (allo-HCT) will be necessary in most cases This review highlights the delicate balance between effectively eliminating AML blasts and leukemic stem cells, while preserving the ability for bone marrow to regenerate. The impact of CAR therapy on treatment landscape of AML and changing scope of allo-HCT is discussed. Continued advances in AML CAR therapy would be of great benefit to a disease that still has high morbidity and mortality.

Therapeutic roles of CAR T cells in infectious diseases: Clinical lessons learnt from cancer

Cancer immunotherapy has made improvements due to the advances in chimaeric antigen receptor (CAR) T cell development, offering a promising treatment option for patients who have failed to respond to traditional treatments. In light of the successful use of adoptive CAR T cell therapy for cancer, researchers have been inspired to develop CARs for the treatment of other diseases beyond cancers such as viral infectious diseases. Nonetheless, various obstacles limit the efficacy of CAR T cell therapies and prevent their widespread usage. Severe toxicities, poor in vivo persistence, antigen escape, and heterogeneity, as well as off-target effect, are key challenges that must all be addressed to broaden the application of CAR T cells to a wider spectrum of diseases. The key advances in CAR T cell treatment for cancer and viral infections are reviewed in this article. We will also discuss revolutionary CAR T cell products developed to improve and enhance the therapeutic advantages of these treatments.

Mechanisms of immune effector cell-associated neurotoxicity syndrome after CAR-T treatment

Chimeric antigen receptor T-cell (CAR-T) treatment has revolutionized the landscape of cancer therapy with significant efficacy on hematologic malignancy, especially in relapsed and refractory B cell malignancies. However, unexpected serious toxicities such as cytokine release syndrome (CRS) and immune effector cell-associated neurotoxicity syndrome (ICANS) still hamper its broad application. Clinical trials using CAR-T cells targeting specific antigens on tumor cell surface have provided valuable information about the characteristics of ICANS. With unclear mechanism of ICANS after CAR-T treatment, unremitting efforts have been devoted to further exploration. Clinical findings from patients with ICANS strongly indicated existence of overactivated peripheral immune response followed by endothelial activation-induced blood-brain barrier (BBB) dysfunction, which triggers subsequent central nervous system (CNS) inflammation and neurotoxicity. Several animal models have been built but failed to fully replicate the whole spectrum of ICANS in human. Hopefully, novel and powerful technologies like single-cell analysis may help decipher the precise cellular response within CNS from a different perspective when ICANS happens. Moreover, multidisciplinary cooperation among the subjects of immunology, hematology, and neurology will facilitate better understanding about the complex immune interaction between the peripheral, protective barriers, and CNS in ICANS. This review elaborates recent findings about ICANS after CAR-T treatment from bed to bench, and discusses the potential cellular and molecular mechanisms that may promote effective management in the future. This article is categorized under: Cancer > Biomedical Engineering Immune System Diseases > Molecular and Cellular Physiology Neurological Diseases > Molecular and Cellular Physiology.

Current Limitations and Perspectives of Chimeric Antigen Receptor-T-Cells in Acute Myeloid Leukemia

Simple Summary

Acute myeloid leukemia (AML) is the most frequent type of acute leukemia in adults. Allogeneic hematopoietic cell transplantation (allo-HCT) has been the only potentially curative treatment for the majority of patients. The ability of chimeric antigen receptor (CAR)-modified T-cell therapy directed against the CD19 antigen to induce durable remissions in patients with acute lymphoblastic leukemia (ALL) has provided optimism that this novel treatment paradigm can be extrapolated to AML. In this review, we provide an overview of candidate target antigens for CAR-T-cells in AML, an update on recent progress in preclinical and clinical development of investigational CAR-T-cell products, and discuss challenges for the clinical implementation of CAR-T-cell therapy in AML.

Abstract

Adoptive transfer of gene-engineered chimeric antigen receptor (CAR)-T-cells has emerged as a powerful immunotherapy for combating hematologic cancers. Several target antigens that are prevalently expressed on AML cells have undergone evaluation in preclinical CAR-T-cell testing. Attributes of an ‘ideal’ target antigen for CAR-T-cell therapy in AML include high-level expression on leukemic blasts and leukemic stem cells (LSCs), and absence on healthy tissues, normal hematopoietic stem and progenitor cells (HSPCs). In contrast to other blood cancer types, where CAR-T therapies are being similarly studied, only a rather small number of AML patients has received CAR-T-cell treatment in clinical trials, resulting in limited clinical experience for this therapeutic approach in AML. For curative AML treatment, abrogation of bulk blasts and LSCs is mandatory with the need for hematopoietic recovery after CAR-T administration. Herein, we provide a critical review of the current pipeline of candidate target antigens and corresponding CAR-T-cell products in AML, assess challenges for clinical translation and implementation in routine clinical practice, as well as perspectives for overcoming them.

Idecabtagene vicleucel (ide-cel) CAR T-cell therapy for relapsed and refractory multiple myeloma

Idecabtagene vicleucel (ide-cel), a novel chimeric antigen receptor (CAR) T-cell therapy targeting B-cell maturation antigen (BCMA), has recently gained approval by the US FDA for relapsed and refractory multiple myeloma (RRMM) after multicenter trials have demonstrated unprecedented results in this difficult-to-treat subgroup of patients. As the first CAR T-cell product approved for myeloma, ide-cel is poised to become a practice-changing treatment option. This first-in-class therapeutic offers hope for more durable remissions, as well as better quality of life, following a single infusion in a group of patients that previously had little hope. This paper reviews the ide-cel product in terms of design, pharmacology, efficacy and toxicity as described in studies reported to date.

Using chimeric antigen receptor T-cell therapy to fight glioblastoma multiforme: past, present and future developments

Introduction

Glioblastoma multiforme (GBM) constitutes one of the deadliest tumors to afflict humans, although it is still considered an orphan disease. Despite testing multiple new and innovative therapies in ongoing clinical trials, the median survival for this type of malignancy is less than two years after initial diagnosis, regardless of therapy. One class of promising new therapies are chimeric antigen receptor T cells or CAR-T which have been shown to be very effective at treating refractory liquid tumors such as B-cell malignancies. However, CAR-T effectivity against solid tumors such as GBM has been limited thus far.

Methods

A Pubmed, Google Scholar, Directory of Open Access Journals, and Web of Science literature search using the terms chimeric antigen receptor or CAR-T, GBM, solid tumor immunotherapy, immunotherapy, and CAR-T combination was performed for publication dates between January 1987 and November 2021.

Results

In the current review, we present a comprehensive list of CAR-T cells developed to treat GBM, we describe new possible T-cell engineering strategies against GBM while presenting a short introductory history to the reader regarding the origin(s) of this cutting-edge therapy. We have also compiled a unique list of anti-GBM CAR-Ts with their specific protein sequences and their functions as well as an inventory of clinical trials involving CAR-T and GBM.

Conclusions

The aim of this review is to introduce the reader to the field of T-cell engineering using CAR-Ts to treat GBM and describe the obstacles that may need to be addressed in order to significantly delay the relentless growth of GBM.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11060-021-03902-8.

Mechanisms of cytokine release syndrome and neurotoxicity of CAR T-cell therapy and associated prevention and management strategies

Chimeric antigen receptor (CAR) T-cell therapy has yielded impressive outcomes and transformed treatment algorithms for hematological malignancies. To date, five CAR T-cell products have been approved by the US Food and Drug Administration (FDA). Nevertheless, some significant toxicities pose great challenges to the development of CAR T-cell therapy, most notably cytokine release syndrome (CRS) and immune effector cell-associated neurotoxicity syndrome (ICANS). Understanding the mechanisms underlying these toxicities and establishing prevention and treatment strategies are important. In this review, we summarize the mechanisms underlying CRS and ICANS and provide potential treatment and prevention strategies.

Optimizing the Clinical Impact of CAR-T Cell Therapy in B-Cell Acute Lymphoblastic Leukemia: Looking Back While Moving Forward

Chimeric antigen receptor T-cell (CAR-T) therapy has been successful in creating extraordinary clinical outcomes in the treatment of hematologic malignancies including relapsed or refractory (R/R) B-cell acute lymphoblastic leukemia (B-ALL). With several FDA approvals, CAR-T therapy is recognized as an alternative treatment option for particular patients with certain conditions of B-ALL, diffuse large B-cell lymphoma, mantle cell lymphoma, follicular lymphoma, or multiple myeloma. However, CAR-T therapy for B-ALL can be surrounded by challenges such as various adverse events including the life-threatening cytokine release syndrome (CRS) and neurotoxicity, B-cell aplasia-associated hypogammaglobulinemia and agammaglobulinemia, and the alloreactivity of allogeneic CAR-Ts. Furthermore, recent advances such as improvements in media design, the reduction of ex vivo culturing duration, and other phenotype-determining factors can still create room for a more effective CAR-T therapy in R/R B-ALL. Herein, we review preclinical and clinical strategies with a focus on novel studies aiming to address the mentioned hurdles and stepping further towards a milestone in CAR-T therapy of B-ALL.

T-Cell Immunotherapy for Pediatric High-Grade Gliomas: New Insights to Overcoming Therapeutic Challenges

Despite decades of research, pediatric central nervous system (CNS) tumors remain the most debilitating, difficult to treat, and deadliest cancers. Current therapies, including radiation, chemotherapy, and/or surgery, are unable to cure these diseases and are associated with serious adverse effects and long-term impairments. Immunotherapy using chimeric antigen receptor (CAR) T cells has the potential to elucidate therapeutic antitumor immune responses that improve survival without the devastating adverse effects associated with other therapies. Yet, despite the outstanding performance of CAR T cells against hematologic malignancies, they have shown little success targeting brain tumors. This lack of efficacy is due to a scarcity of targetable antigens, interactions with the immune microenvironment, and physical and biological barriers limiting the homing and trafficking of CAR T cells to brain tumors. In this review, we summarize experiences with CAR T-cell therapy for pediatric CNS tumors in preclinical and clinical settings and focus on the current roadblocks and novel strategies to potentially overcome those therapeutic challenges.

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.

Fn14-targeted BiTE and CAR-T cells demonstrate potent preclinical activity against glioblastoma

T cell-engaging therapies involving bispecific T cell engager (BiTE) and chimeric antigen receptor T (CAR-T) cells have achieved great success in the treatment of hematological tumors. However, the paucity of ideal cell surface molecules that can be targeted on glioblastoma (GBM) partially reduces the immunotherapeutic efficacy. Recently, high expression of Fn14 has been reported in several solid tumors, so the strategy of exploiting this specific antigen for GBM immunotherapy is worth studying. Consequently, we constructed Fn14× CD3 BiTE and Fn14-specific CAR-T cells and investigated their cytotoxic activity against GBM in vitro and in vivo. First, expression of Fn14 was confirmed in glioma tissues and GBM cells. Then, we designed Fn14-specific BiTE and CAR-T cells and tested their cytotoxicity in GBM cell cultures and mouse models of GBM. Fn14 was highly expressed in GBM tissues and cell lines, while it was undetectable in normal brain samples. Fn14× CD3 BiTE, Fn14 CAR-T cells and Fn14 CAR-T/IL-15 cells were antigen-specific and highly cytotoxic, showing good antitumor activity in vitro and causing significant regression of established solid tumors in xenograft models. However, the xenografts treated with Fn14 CAR-T cells regrew, whereas xenografts treated with Fn14 CAR-T/IL-15 cells did not. IL-15 engineering augmented the antitumor activity of Fn14 CAR-T cells and resulted in significant antitumor effects similar to those of Fn14× CD3 BiTE. Our results suggest that Fn14 is an appropriate target for GBM. Anti-Fn14 BiTE and Fn14-specific CAR-T/IL-15 cells may be exciting immunotherapeutic options for malignant brain cancer.

Titratable Pharmacological Regulation of CAR T Cells Using Zinc Finger-Based Transcription Factors

Simple Summary

Chimeric antigen receptor (CAR) T cell therapy can be associated with substantial side effects primarily due to intense immune activation following treatment, or target antigen recognition on off-tumor tissue. Consequently, temporal and tunable control of CAR T cell activity is of major importance for the clinical translation of innovative CAR designs. This work demonstrates the transcriptional regulation of an anti-CD20 CAR in primary T cells using a drug inducible zinc finger-based transcription factor. The switch system enables titratable induction of CAR expression and CAR T cell effector function with the clinically relevant inducer drug tamoxifen and its metabolites both in vitro and in vivo, whereby CAR activity is strictly dependent on the presence of the inducer drug. The results obtained can readily be transferred to other CARs for which an improved control of expression is required.

Abstract

Chimeric antigen receptor (CAR) T cell therapy has emerged as an attractive strategy for cancer immunotherapy. Despite remarkable success for hematological malignancies, excessive activity and poor control of CAR T cells can result in severe adverse events requiring control strategies to improve safety. This work illustrates the feasibility of a zinc finger-based inducible switch system for transcriptional regulation of an anti-CD20 CAR in primary T cells providing small molecule-inducible control over therapeutic functions. We demonstrate time- and dose-dependent induction of anti-CD20 CAR expression and function with metabolites of the clinically-approved drug tamoxifen, and the absence of background CAR activity in the non-induced state. Inducible CAR T cells executed fine-tuned cytolytic activity against target cells both in vitro and in vivo, whereas CAR-related functions were lost upon drug discontinuation. This zinc finger-based transcriptional control system can be extended to other therapeutically important CARs, thus paving the way for safer cellular therapies.

Chimeric antigen receptor T cells self-neutralizing IL6 storm in patients with hematologic malignancy

IL6 is one of the most elevated cytokines during chimeric antigen receptor (CAR) T cell cytokine release syndrome (CRS), and IL6R blockade by Tocilizumab has successfully relieved the most life-threatening aspects of CRS in patients. In addition, latest studies demonstrated the essential role of IL1 in driving CART induced neurotoxicity in mouse models. Here we present a clinical investigation (ChiCTR2000032124; ChiCTR2000031868) of anti-CD19 and anti-BCMA CART (41BBζ) secreting an anti-IL6 scFv and IL1 receptor antagonist (IL1RA) in treating patients with hematologic malignancy. Our results revealed that IL6 and IL1B were maintained at low levels without significant elevation during CRS, rendering Tocilizumab dispensable. Moreover, treated patients did not show neurotoxicity during CRS and exhibited mild to moderate CRS. Notably, we observed high rate of complete response (CR) and significant CART expansion during treatment. In sum, we conclude that CART-secreting anti-IL6 scFv and IL1RA could self-neutralize IL6 storm and maintain low levels of IL1B during CART therapy to minimize IL6- and IL1-associated cytokine toxicity and neurotoxicity without impairing therapeutic efficacy.

[Comparison of single infusion of anti-BCMA versus combined infusion of anti-CD19 chimeric antigen receptor T cells for immune reconstruction in relapsed/refractory multiple myeloma]

Objective: We observed and compared the differences in immune reconstruction between single-infusion anti-B-cell maturation antigen (BCMA) , chimeric antigen receptor T cells (CAR-T) , and combined infusion of anti-CD19 CAR-T cells in the treatment of recurrent/refractory multiple myeloma (RRMM) . Methods: Sixty-one patients with RRMM who underwent CAR-T cell therapy in our hospital from June 2017 to December 2020 were selected. Among them, 26 patients received anti-BCMA target, and 35 patients received anti-BCMA combined with anti-CD19 target. Using flow cytometry, we determined T cell subsets (CD3(+), CD4(+), CD8(+), CD4(+)/CD8(+)) , B cells (CD19(+)) , and NK cells (CD16(+) CD56(+)) at different time points before and after CAR-T treatment, and detected immunoglobulin IgG, IgA and IgM levels by immunoturbidimetry. We compared the reconstruction rules of lymphocyte subsets and immunoglobulins in the two groups. Results: CD8(+) T lymphocytes recovered most rapidly after the infusion of CAR-T cells, returning to pre-infusion levels at 3 months and 1 month after infusion, respectively[BCMA: 695 (357, 1264) /μl vs 424 (280, 646) /μl; BCMA+CD19: 546 (279, 1672) /μl vs 314 (214, 466) /μl]. NK cells returned to normal levels at 3 months after infusion in both groups[BCMA: 171 (120, 244) /μl, BCMA+CD19: 153 (101, 218) /μl (Normal reference range 150-1100/μl) ]; however, the NK cells were not maintained at stable levels in the BCMA CAR-T cells group. The recovery of CD4(+) T lymphocytes in both groups was slow and remained persistently low within 12 months after infusion, and no recovery was observed in most patients. The reversal of the ratio of CD4(+)/CD8(+) lasted for more than a year. The levels of CD19(+) B cells in both groups returned to baseline 3 months after infusion[BCMA: 62 (10, 72) /μl vs 57 (24, 78) /μl; BCMA+CD19: 40 (4, 94) /μl vs 29 (14, 46) /μl]. IgG returned to the pre-infusion level 12 months after infusion in the group with anti-BCMA cells alone, but not in the group with combined infusion of CD19 CAR T cells[7.82 (6.03, 9.64) g/L vs 6.92 (4.62, 12.76) g/L]. IgA returned to pre-infusion levels at 9 and 12 months after infusion, respectively[BCMA: 0.46 (0.07, 0.51) g/L vs 0.22 (0.12, 4.01) g/L; BCMA+CD19: 0.46 (0.22, 0.98) g/L vs 0.27 (0.10, 0.53) g/L]. IgM in both groups returned to pre-infusion levels 6 months after infusion[BCMA: 0.43 (0.06, 0.60) g/L vs 0.20 (0.13, 0.37) g/L; BCMA+CD19: 0.53 (0.10, 0.80) g/L vs 0.16 (0.11, 0.28) g/L]. There was no significant difference in the indexes of lymphocyte subpopulation reconstruction and immunoglobulin recovery between the two groups at each time point. Conclusion: This study showed that in patients with RRMM treated with CAR-T cells, the appropriate target antigen can be selected without considering the difference of immune reconstruction between anti-BCMA CAR-T and combined anti-CD19 CAR-T therapy.

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.

T-cell receptor-based therapy: an innovative therapeutic approach for solid tumors

T-cell receptor (TCR)-based adoptive therapy employs genetically modified lymphocytes that are directed against specific tumor markers. This therapeutic modality requires a structured and integrated process that involves patient screening (e.g., for HLA-A*02:01 and specific tumor targets), leukapheresis, generation of transduced TCR product, lymphodepletion, and infusion of the TCR-based adoptive therapy. In this review, we summarize the current technology and early clinical development of TCR-based therapy in patients with solid tumors. The challenges of TCR-based therapy include those associated with TCR product manufacturing, patient selection, and preparation with lymphodepletion. Overcoming these challenges, and those posed by the immunosuppressive microenvironment, as well as developing next-generation strategies is essential to improving the efficacy and safety of TCR-based therapies. Optimization of technology to generate TCR product, treatment administration, and patient monitoring for adverse events is needed. The implementation of novel TCR strategies will require expansion of the TCR approach to patients with HLA haplotypes beyond HLA-A*02:01 and the discovery of novel tumor markers that are expressed in more patients and tumor types. Ongoing clinical trials will determine the ultimate role of TCR-based therapy in patients with solid tumors.

New CARs on and off the road: challenges and new developments in CAR-T cell therapy

Building on the tremendous success of chimeric antigen receptor T-cell therapy in hematological malignancies, there are efforts under way to overcome the challenges associated with this treatment and expand its application to solid tumors. In this fast-evolving field, new therapeutic options are constantly generated, tested in model systems, and further evaluated in clinical trials. In this review, we provide an overview of recent challenges and developments associated with engineered T cells and chimeric antigen receptor T-cell applications. We report on the most recent progress in hematological malignancies and highlight technical advances for applications in solid tumors.

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.

Population Cellular Kinetics of Lisocabtagene Maraleucel, an Autologous CD19-Directed Chimeric Antigen Receptor T-Cell Product, in Patients with Relapsed/Refractory Large B-Cell Lymphoma

Background and Objectives

Lisocabtagene maraleucel (liso-cel) is a CD19-directed, defined composition, 4-1BB chimeric antigen receptor (CAR) T-cell product administered at equal target doses of CD8⁺ and CD4⁺ CAR⁺ T cells. Large between-subject variability has been noted with CAR T-cell therapies; patient characteristics might contribute to CAR T-cell expansion variability. We developed a population cellular kinetic model to characterize the kinetics of the liso-cel transgene, via quantitative polymerase chain reaction assessment after intravenous infusion of liso-cel, and to understand covariates that might influence liso-cel kinetics in individual patients.

Methods

We employed nonlinear mixed-effects modeling to develop a population cellular kinetic model for liso-cel. The population cellular kinetic analysis was performed using 2524 post-infusion transgene observations from 261 patients with relapsed/refractory large B-cell lymphoma who were treated with a single dose of liso-cel in TRANSCEND NHL 001. Covariates for the analysis included baseline intrinsic factors such as age, baseline disease characteristics, and liso-cel and coadministration factors.

Results

Liso-cel cellular kinetics were well described by a piecewise model of cellular growth kinetics that featured lag, exponential growth, and biexponential decay phases. Population means (95% confidence interval) of lag phase duration, doubling time, time to maximum levels, initial decline half-life, and terminal half-life were 3.27 (2.71–3.97), 0.755 (0.667–0.821), 9.29 (8.81–9.70), 5.00 (4.15–5.90), and 352 (241–647) days, respectively. The magnitude of effect on liso-cel expansion metrics demonstrated that the covariate associations were smaller than the residual between-subject variability in the population.

Conclusions

The covariates tested were not considered to have a meaningful impact on liso-cel kinetics.

Clinical Trial Registration

NCT02631044.

Current Status of CAR T Cell Therapy for Leukemias

OPINION STATEMENT

Chimeric antigen receptor (CAR) T-cell therapy has become the standard of care for children and young adults with relapsed and refractory B-cell acute lymphoblastic leukemia (B-ALL), and it is a highly promising therapy under investigation for adults with relapsed disease. Despite having potentially life-threatening toxicities, such as cytokine release syndrome and immune effector cell-associated neurotoxicity syndrome, the benefits of CAR T-cell therapy far outweigh these risks, particularly as increased experience and improved supportive care measures are mitigating these toxicities. CAR T cells can result in complete remission for significant proportion of patients with relapsed and refractory B-ALL and permit them to proceed to potentially curative allogeneic hematopoietic stem cell transplantation (allo-HSCT). CAR T cells may also be curative by themselves. Herein lie the greatest challenges and questions for clinical investigators, specifically, how are CAR T cells best employed and how do we overcome mechanisms of resistance to them? The primary clinical question is the timing and even the necessity of allo-HSCT. Relative to resistance, we know that target antigen loss, specifically CD19, is a major contributor to resistance. However, current investigations of alternative targets, such CD22, and CAR T cells expressing dual targeting antigen receptors have demonstrated encouraging initial results and provide a high degree of optimism that the efficacy and the broader application of CAR T-cell therapy will gradually increase in B-ALL. That optimism is not as high and the challenges are increased for the application of CAR T cells in T-cell leukemias and acute myeloid leukemia due to the relative lack of suitable leukemia surface targets that are not also expressed on normal hematopoietic progenitors. Despite these significant challenges, considerable research is being conducted into the development of CAR T cells for these diseases utilizing unique technologies, which may be applicable to other diseases.

CAR T-Cell Therapy in Hematologic Malignancies: Clinical Role, Toxicity, and Unanswered Questions

At the time of writing, five anti-CD19 CAR T-cell products are approved by the U.S. Food and Drug Administration for seven different indications in lymphoid malignancies, including B-cell non-Hodgkin lymphoma, pediatric B-cell acute lymphoblastic leukemia, and multiple myeloma. CAR T cells for chronic lymphocytic leukemia, acute myeloid leukemia, and less common malignancies such as T-cell lymphomas and Hodgkin lymphoma are being tested in early-phase clinical trials worldwide. The purpose of this overview is to describe the current landscape of CAR T cells in hematologic malignancies, outline their outcomes and toxicities, and explain the outstanding questions that remain to be addressed.

Cellular based treatment modalities for unresectable hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the most common primary malignancy of the liver and is unfortunately associated with an overall poor prognosis and high mortality. Early and intermediate stages of HCC allow for treatment with surgical resection, ablation and even liver transplantation, however disease progression warrants conventional systemic therapy. For years treatment options were limited to molecular-targeting medications, of which sorafenib remains the standard of care. The recent development and success of immune checkpoint inhibitors has proven to be a breakthrough in the treatment of HCC, but there is an urgent need for the development of further novel therapeutic treatments that prolong overall survival and minimize recurrence. Current investigation is focused on adoptive cell therapy including chimeric antigen receptor-T cells (CAR-T cells), T cell receptor (TCR) engineered T cells, dendritic cells, natural killer cells, and tumor infiltrating lymphocyte cells, which have shown remarkable success in the treatment of hematological and solid tumor malignancies. In this review we briefly introduce readers to the currently approved systemic treatment options and present clinical and experimental evidence of HCC immunotherapeutic treatments that will hopefully one day allow for revolutionary change in the treatment modalities used for unresectable HCC. We also provide an up-to-date compilation of ongoing clinical trials investigating CAR-T cells, TCR engineered T cells, cancer vaccines and oncolytic viruses, while discussing strategies that can help overcome commonly faced challenges when utilizing cellular based treatments.

Obstacles and Coping Strategies of CAR-T Cell Immunotherapy in Solid Tumors

Chimeric antigen receptor (CAR) T-cell immunotherapy refers to an adoptive immunotherapy that has rapidly developed in recent years. It is a novel type of treatment that enables T cells to express specific CARs on their surface, then returns these T cells to tumor patients to kill the corresponding tumor cells. Significant strides in CAR-T cell immunotherapy against hematologic malignancies have elicited research interest among scholars in the treatment of solid tumors. Nonetheless, in contrast with the efficacy of CAR-T cell immunotherapy in the treatment of hematologic malignancies, its general efficacy against solid tumors is insignificant. This has been attributed to the complex biological characteristics of solid tumors. CAR-T cells play a better role in solid tumors, for instance by addressing obstacles including the lack of specific targets, inhibition of tumor microenvironment (TME), homing barriers of CAR-T cells, differentiation and depletion of CAR-T cells, inhibition of immune checkpoints, trogocytosis of CAR-T cells, tumor antigen heterogeneity, etc. This paper reviews the obstacles influencing the efficacy of CAR-T cell immunotherapy in solid tumors, their mechanism, and coping strategies, as well as economic restriction of CAR-T cell immunotherapy and its solutions. It aims to provide some references for researchers to better overcome the obstacles that affect the efficacy of CAR-T cells in solid tumors.

Composite CD79A/CD40 co-stimulatory endodomain enhances CD19CAR-T cell proliferation and survival

Adoptively transferred CD19 chimeric antigen receptor (CAR) T cells have led to impressive clinical outcomes in B cell malignancies. Beyond induction of remission, the persistence of CAR-T cells is required to prevent relapse and provide long-term disease control. To improve CAR-T cell function and persistence, we developed a composite co-stimulatory domain of a B cell signaling moiety, CD79A/CD40, to induce a nuclear translocating signal, NF-κB, to synergize with other T cell signals and improve CAR-T cell function. CD79A/CD40 incorporating CD19CAR-T cells (CD19.79a.40z) exhibited higher NF-κB and p38 activity upon CD19 antigen exposure compared with the CD28 or 4-1BB incorporating CD19CAR-T cells (CD19.28z and CD19.BBz). Notably, we found that CD19.79a.40z CAR-T cells continued to suppress CD19⁺ target cells throughout the co-culture assay, whereas a tendency for tumor growth was observed with CD19.28z CAR-T cells. Moreover, CD19.79a.40z CAR-T cells exhibited robust T cell proliferation after culturing with CD19⁺ target cells, regardless of exogenous interleukin-2. In terms of in vivo efficiency, CD19.79a.40z demonstrated superior anti-tumor activity and in vivo CAR-T cell proliferation compared with CD19.28z and CD19.BBz CD19CAR-T cells in Raji-inoculated mice. Our data demonstrate that the CD79A/CD40 co-stimulatory domain endows CAR-T cells with enhanced proliferative capacity and improved anti-tumor efficacy in a murine model.

CAR-T cell persistence in the treatment of leukemia and lymphoma

Chimeric antigen receptor (CAR) T cells have emerged as a powerful therapeutic modality for cancer. Following encouraging clinical results, autologous anti-CD19 CAR-T cells first secured regulatory approval from the U.S. Food and Drug Administration in 2017 for the treatment of pediatric B cell acute lymphoblastic leukemia and for diffuse large B cell lymphoma (DLBCL), followed recently by mantle cell lymphoma. While long-term immunosurveillance is among the most important requirements for durable remissions in leukemia and a major potential benefit of immunotherapy, the exact determinants of CAR-T cell persistence remain elusive. Furthermore, it is less clear that long-term persistence is required for durable remission in lymphoma. In this review, we aim to describe the factors governing CAR-T cell persistence as well as unique approaches to exert control over engineered lymphocyte populations post-infusion. Additionally, we explore potential risks and associated clinical considerations arising from prolonged surveillance by highly reactive cytotoxic T lymphocytes.