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

Car T Cells in Solid Tumors: Overcoming Obstacles

Chimeric antigen receptor T cell (CAR T cell) therapy has emerged as a prominent adoptive cell therapy and a therapeutic approach of great interest in the fight against cancer. This approach has shown notorious efficacy in refractory hematological neoplasm, which has bolstered its exploration in the field of solid cancers. However, successfully managing solid tumors presents considerable intrinsic challenges, which include the necessity of guiding the modified cells toward the tumoral region, assuring their penetration and survival in adverse microenvironments, and addressing the complexity of identifying the specific antigens for each type of cancer. This review focuses on outlining the challenges faced by CAR T cell therapy when used in the treatment of solid tumors, as well as presenting optimizations and emergent approaches directed at improving its efficacy in this particular context. From precise localization to the modulation of the tumoral microenvironment and the adaptation of antigen recognition strategies, diverse pathways will be examined to overcome the current limitations and buttress the therapeutic potential of CAR T cells in the fight against solid tumors.

Immune modulation in transplant medicine: a comprehensive review of cell therapy applications and future directions

Balancing the immune response after solid organ transplantation (SOT) and vascularized composite allotransplantation (VCA) remains an ongoing clinical challenge. While immunosuppressants can effectively reduce acute rejection rates following transplant surgery, some patients still experience recurrent acute rejection episodes, which in turn may progress to chronic rejection. Furthermore, these immunosuppressive regimens are associated with an increased risk of malignancies and metabolic disorders. Despite significant advancements in the field, these IS related side effects persist as clinical hurdles, emphasizing the need for innovative therapeutic strategies to improve transplant survival and longevity. Cellular therapy, a novel therapeutic approach, has emerged as a potential pathway to promote immune tolerance while minimizing systemic side-effects of standard IS regiments. Various cell types, including chimeric antigen receptor T cells (CAR-T), mesenchymal stromal cells (MSCs), regulatory myeloid cells (RMCs) and regulatory T cells (Tregs), offer unique immunomodulatory properties that may help achieve improved outcomes in transplant patients. This review aims to elucidate the role of cellular therapies, particularly MSCs, T cells, Tregs, RMCs, macrophages, and dendritic cells in SOT and VCA. We explore the immunological features of each cell type, their capacity for immune regulation, and the prospective advantages and obstacles linked to their application in transplant patients. An in-depth outline of the current state of the technology may help SOT and VCA providers refine their perioperative treatment strategies while laying the foundation for further trials that investigate cellular therapeutics in transplantation surgery.

Current advances in experimental and computational approaches to enhance CAR T cell manufacturing protocols and improve clinical efficacy

Since the FDA's approval of chimeric antigen receptor (CAR) T cells in 2017, significant improvements have been made in the design of chimeric antigen receptor constructs and in the manufacturing of CAR T cell therapies resulting in increased in vivo CAR T cell persistence and improved clinical outcome in certain hematological malignancies. Despite the remarkable clinical response seen in some patients, challenges remain in achieving durable long-term tumor-free survival, reducing therapy associated malignancies and toxicities, and expanding on the types of cancers that can be treated with this therapeutic modality. Careful analysis of the biological factors demarcating efficacious from suboptimal CAR T cell responses will be of paramount importance to address these shortcomings. With the ever-expanding toolbox of experimental approaches, single-cell technologies, and computational resources, there is renowned interest in discovering new ways to streamline the development and validation of new CAR T cell products. Better and more accurate prognostic and predictive models can be developed to help guide and inform clinical decision making by incorporating these approaches into translational and clinical workflows. In this review, we provide a brief overview of recent advancements in CAR T cell manufacturing and describe the strategies used to selectively expand specific phenotypic subsets. Additionally, we review experimental approaches to assess CAR T cell functionality and summarize current in silico methods which have the potential to improve CAR T cell manufacturing and predict clinical outcomes.

Progress, implications, and challenges in using humanized immune system mice in CAR-T therapy-Application evaluation and improvement

In recent years, humanized immune system (HIS) mice have been gradually used as models for preclinical research in pharmacotherapies and cell therapies with major breakthroughs in tumor and other fields, better mimicking the human immune system and the tumor immune microenvironment, compared to traditional immunodeficient mice. To better promote the application of HIS mice in preclinical research, we selectively summarize the current prevalent and breakthrough research and evaluation of chimeric antigen receptor (CAR) -T cells in various antiviral and antitumor treatments. By exploring its application in preclinical research, we find that it can better reflect the actual clinical patient condition, with the advantages of providing high-efficiency detection indicators, even for progressive research and development. We believe that it has better clinical patient simulation and promotion for the updated design of CAR-T cell therapy than directly transplanted immunodeficient mice. The characteristics of the main models are proposed to improve the use defects of the existing models by reducing the limitation of antihost reaction, combining multiple models, and unifying sources and organoid substitution. Strategy study of relapse and toxicity after CAR-T treatment also provides more possibilities for application and development.

CAR-T Therapy in Relapsed Refractory Multiple Myeloma

Multiple myeloma is a plasma cell neoplasm. The emergence of proteasome inhibitors, immunomodulatory drugs, and anti-CD38 monoclonal antibodies has improved the prognosis of multiple myeloma patients. However, some patients are still insensitive to conventional therapy or frequently relapse after remission. Chemotherapy based on proteasome inhibitors or immunomodulatory drugs is ineffective in controlling the progression of relapsed refractory multiple myeloma. No consensus has been reached on treating relapsed refractory multiple myeloma to date. Recently chimeric antigen receptor T cells therapy has shown promising results that could achieve rapid remissions of patients and improve their prognoses. Additionally, most patients in chimeric antigen receptor T cell clinical trials were triple-refractory multiple myeloma patients, indicating that chimeric antigen receptor T cell immunotherapy could overcome drug resistance to new drugs. Since single immunotherapies are prone to acquired resistance, combination immunotherapies based on emerging immunotherapies may solve this issue. Achieving complete remission and minimal residual disease negative status as soon as possible is beneficial to patients. This paper reviewed the main chimeric antigen receptor T cell products in relapsed refractory multiple myeloma, and it explained the drug resistance mechanism and improvement methods of chimeric antigen receptor T cells therapy. This review summarized the best beneficiaries of chimeric antigen receptor T cell therapy and the salvage treatment of disease recurrence after chimeric antigen receptor T cell therapy, providing some ideas for the clinical application of chimeric antigen receptor T cells.

Strategies for modifying the chimeric antigen receptor (CAR) to improve safety and reduce toxicity in CAR T cell therapy for cancer

Immune cell therapy with chimeric antigen receptor (CAR) T cells, which has shown promising efficacy in patients with some hematologic malignancies, has introduced several successfully approved CAR T cell therapy products. Nevertheless, despite significant advances, treatment with these products has major challenges regarding potential toxicity and sometimes fatal adverse effects for patients. These toxicities can result from cytokine release or on-target off-tumor toxicity that targets healthy host tissue following CAR T cell therapy. The present study focuses on the unexpected side effects of targeting normal host tissues with off-target toxicity. Also, recent safety strategies such as replacing or adding different components to CARs and redesigning CAR structures to eliminate the toxic impact of CAR T cells, including T cell antigen coupler (TAC), switch molecules, suicide genes, and humanized monoclonal antibodies in the design of CARs, are discussed in this review.

Engineered Treg cells as putative therapeutics against inflammatory diseases and beyond

Regulatory T (Treg) cells ensure tolerance against self-antigens, limit excessive inflammation, and support tissue repair processes. Therefore, Treg cells are currently attractive candidates for the treatment of certain inflammatory diseases, autoimmune disorders, or transplant rejection. Early clinical trials have proved the safety and efficacy of certain Treg cell therapies in inflammatory diseases. We summarize recent advances in engineering Treg cells, including the concept of biosensors for inflammation. We assess Treg cell engineering possibilities for novel functional units, including Treg cell modifications influencing stability, migration, and tissue adaptation. Finally, we outline perspectives of engineered Treg cells going beyond inflammatory diseases by using custom-designed receptors and read-out systems, aiming to use Treg cells as in vivo diagnostic tools and drug delivery vehicles.

How I treat high-risk acute myeloid leukemia using preemptive adoptive cellular immunotherapy

Allogeneic hematopoietic stem cell transplantation (alloHSCT) is a potentially curative treatment for patients with high-risk acute leukemias, but unfortunately disease recurrence remains the major cause of death in these patients. Infusion of donor lymphocytes (DLI) has the potential to restore graft-versus-leukemia immunologic surveillance; however, efficacy varies across different hematologic entities. Although relapsed chronic myeloid leukemia, transplanted in chronic phase, has proven remarkably susceptible to DLI, response rates are more modest for relapsed acute myeloid leukemia and acute lymphoblastic leukemia. To prevent impending relapse, a number of groups have explored administering DLI preemptively on detection of measurable residual disease (MRD) or mixed chimerism. Evidence for the effectiveness of this strategy, although encouraging, comes from only a few, mostly single-center retrospective, nonrandomized studies. This article seeks to (1) discuss the available evidence supporting this approach while highlighting some of the inherent challenges of MRD-triggered treatment decisions post-transplant, (2) portray other forms of postremission cellular therapies, including the role of next-generation target-specific immunotherapies, and (3) provide a practical framework to support clinicians in their decision-making process when considering preemptive cellular therapy for this difficult-to-treat patient population.

The CD8α hinge is intrinsically disordered with a dynamic exchange that includes proline cis-trans isomerization

T cells engineered to express artificial chimeric antigen receptors (CARs) that selectively target tumor-specific antigens or deleterious cell types offer transformative therapeutic possibilities. CARs contain an N-terminal extracellular antigen recognition domain, C-terminal intracellular signal transduction domains, and connecting hinge and transmembrane regions, each of which have been varied to optimize targeting and minimize toxicity. We find that a CD22-targeting CAR harboring a CD8α hinge (H) exhibits greater cytotoxicity against a low antigen density CD22⁺ leukemia as compared to an equivalent CAR with a CD28 H. We therefore studied the biophysical and dynamic properties of the CD8α H by nuclear magnetic resonance (NMR) spectroscopy. We find that a large region of the CD8α H undergoes dynamic chemical exchange between distinct and observable states. This exchanging region contains proline residues dispersed throughout the sequence that undergo cis-trans isomerization. Up to four signals of differing intensity are observed, with the most abundantly populated being intrinsically disordered and with all prolines in the trans isomerization state. The lesser populated states all contain cis prolines and evidence of local structural motifs. Altogether, our data suggest that the CD8α H lacks long-range structural order but has local structural motifs that transiently exchange with a dominant disordered state. We propose that structural plasticity and local structural motifs promoted by cis proline states within the CD8α H are important for relaying and amplifying antigen-binding effects to the transmembrane and signal transduction domains.

Influence of Culture Conditions on Ex Vivo Expansion of T Lymphocytes and Their Function for Therapy: Current Insights and Open Questions

Ex vivo expansion of T lymphocytes is a central process in the generation of cellular therapies targeted at tumors and other disease-relevant structures, which currently cannot be reached by established pharmaceuticals. The influence of culture conditions on T cell functions is, however, incompletely understood. In clinical applications of ex vivo expanded T cells, so far, a relatively classical standard cell culture methodology has been established. The expanded cells have been characterized in both preclinical models and clinical studies mainly using a therapeutic endpoint, for example antitumor response and cytotoxic function against cellular targets, whereas the influence of manipulations of T cells ex vivo including transduction and culture expansion has been studied to a much lesser detail, or in many contexts remains unknown. This includes the circulation behavior of expanded T cells after intravenous application, their intracellular metabolism and signal transduction, and their cytoskeletal (re)organization or their adhesion, migration, and subsequent intra-tissue differentiation. This review aims to provide an overview of established T cell expansion methodologies and address unanswered questions relating in vivo interaction of ex vivo expanded T cells for cellular therapy.

CAR T Cell Therapy in Hematological Malignancies: Implications of the Tumor Microenvironment and Biomarkers on Efficacy and Toxicity

Chimeric antigen receptor (CAR) T cell therapy has ushered in a new era in cancer treatment. Remarkable outcomes have been demonstrated in patients with previously untreatable relapsed/refractory hematological malignancies. However, optimizing efficacy and reducing the risk of toxicities have posed major challenges, limiting the success of this therapy. The tumor microenvironment (TME) plays an important role in CAR T cell therapy’s effectiveness and the risk of toxicities. Increasing research studies have also identified various biomarkers that can predict its effectiveness and risk of toxicities. In this review, we discuss the various aspects of the TME and biomarkers that have been implicated thus far and discuss the role of creating scoring systems that can aid in further refining clinical applications of CAR T cell therapy and establishing a safe and efficacious personalised medicine for individuals.

Immunotherapy for lung cancer: Focusing on chimeric antigen receptor (CAR)-T cell therapy

Besides traditional treatment strategies, including surgery, radiotherapy, and chemotherapy for lung cancer as the leading cause of cancer incidence and death, immunotherapy has also emerged as a new treatment strategy. The goal of immunotherapy is to stimulate the immune system responses against cancer, using various approaches such as therapeutic vaccines, monoclonal antibodies, immune checkpoint inhibitors, and T-cell therapy. Chimeric antigen receptor (CAR)-T cells, one of the most popular cancer immunotherapy approaches in the last decade, are genetically engineered T-cells to redirect patients' immune responses to recognize and eliminate tumor-associated antigens (TAA)-expressing tumor cells. CAR-T cell therapy provides promising benefits in lung tumors. In this review, we summarize different immunotherapy approaches for lung cancer, the structure of CAR-T cells, currently undergoing CARs in clinical trials, and various TAAs are being investigated as potential targets in designing CAR-T cells for lung cancer.

The potential of CAR T cell therapy for prostate cancer

Chimeric antigen receptor (CAR) T cell immunotherapy involves the genetic modification of the patient's own T cells so that they specifically recognize and destroy tumour cells. Considerable clinical success has been achieved using this technique in patients with lymphoid malignancies, but clinical studies that investigated treating solid tumours using this emerging technology have been disappointing. A number of developments might be able to increase the efficacy of CAR T cell therapy for treatment of prostate cancer, including improved trafficking to the tumour, techniques to overcome the immunosuppressive tumour microenvironment, as well as methods to enhance CAR T cell persistence, specificity and safety. Furthermore, CAR T cell therapy has the potential to be combined with other treatment modalities, such as androgen deprivation therapy, radiotherapy or chemotherapy, and could be applied as focal CAR T cell therapy for prostate cancer.

Evaluation of switch-mediated costimulation in trans on universal CAR-T cells (UniCAR) targeting CD123-positive AML

Chimeric antigen receptor T cells (CAR-T) targeting CD19 have achieved significant success in patients with B cell malignancies. To date, implementation of CAR-T in other indications remains challenging due to the lack of truly tumor-specific antigens as well as control of CAR-T activity in patients. CD123 is highly expressed in acute myeloid leukemia (AML) blasts including leukemia-initiating cells making it an attractive immunotherapeutic target. However, CD123 expression in normal hematopoietic progenitor cells and endothelia bears the risk of severe toxicities and may limit CAR-T applications lacking fine-tuned control mechanisms. Therefore, we recently developed a rapidly switchable universal CAR-T platform (UniCAR), in which CAR-T activity depends on the presence of a soluble adapter called targeting module (TM), and confirmed clinical proof-of-concept for targeting CD123 in AML with improved safety. As costimulation via 4–1BB ligand (4–1BBL) can enhance CAR-T expansion, persistence, and effector functions, a novel CD123-specific TM variant (TM123-4-1BBL) comprising trimeric single-chain 4–1BBL was developed for transient costimulation of UniCAR-T cells (UniCAR-T) at the leukemic site in trans. TM123-4-1BBL-directed UniCAR-T efficiently eradicated CD123-positive AML cells in vitro and in a CDX in vivo model. Moreover, additional costimulation via TM123-4-1BBL enabled enhanced expansion and persistence with a modulated UniCAR-T phenotype. In addition, the increased hydrodynamic volume of TM123-4-1BBL prolonged terminal plasma half-life and ensured a high total drug exposure in vivo. In conclusion, expanding the soluble adapter optionality for CD123-directed UniCAR-T maintains the platforms high anti-leukemic efficacy and immediate control mechanism for a flexible, safe, and individualized CAR-T therapy of AML patients.

CAR T-cell therapy in multiple myeloma: more room for improvement

The emergence of various novel therapies over the last decade has changed the therapeutic landscape for multiple myeloma. While the clinical outcomes have improved significantly, the disease remains incurable, typically in patients with relapsed and refractory disease. Chimeric antigen receptor (CAR) T-cell therapies have achieved remarkable clinical success in B-cell malignancies. This scope of research has more recently been extended to the field of myeloma. While B-cell maturation antigen (BCMA) is currently the most well-studied CAR T antigen target in this disease, many other antigens are also undergoing intensive investigations. Some studies have shown encouraging results, whereas some others have demonstrated unfavorable results due to reasons such as toxicity and lack of clinical efficacy. Herein, we provide an overview of CAR T-cell therapies in myeloma, highlighted what has been achieved over the past decade, including the latest updates from ASH 2020 and discussed some of the challenges faced. Considering the current hits and misses of CAR T therapies, we provide a comprehensive analysis on the current manufacturing technologies, and deliberate on the future of CAR T-cell domain in MM.

Adoptive Cell Therapy in Hepatocellular Carcinoma: Biological Rationale and First Results in Early Phase Clinical Trials

The mortality of hepatocellular carcinoma (HCC) is quickly increasing worldwide. In unresectable HCC, the cornerstone of systemic treatments is switching from tyrosine kinase inhibitors to immune checkpoints inhibitors (ICI). Next to ICI, adoptive cell transfer represents another promising field of immunotherapy. Targeting tumor associated antigens such as alpha-fetoprotein (AFP), glypican-3 (GPC3), or New York esophageal squamous cell carcinoma-1 (NY-ESO-1), T cell receptor (TCR) engineered T cells and chimeric antigen receptors (CAR) engineered T cells are emerging as potentially effective therapies, with objective responses reported in early phase trials. In this review, we address the biological rationale of TCR/CAR engineered T cells in advanced HCC, their mechanisms of action, and results from recent clinical trials.

Bioengineered tissue models for the development of dynamic immuno-associated tumor models and high-throughput immunotherapy cytotoxicity assays

Cancer immunotherapy is rapidly developing, with numerous therapies approved over the past decade and more therapies expected to gain approval in the future. However, immunotherapy of solid tumors has been less successful because immunosuppressive barriers limit immune cell trafficking and function against cancer cells. Interactions between suppressive immune cells, cytokines, and inhibitory factors are central to cancer immunotherapy approaches. In this review, we discuss recent advances in utilizing microfluidic platforms for understanding cancer-suppressive immune system interactions. Dendritic cell (DC)-mediated tumor models, infiltrated lymphocyte-mediated tumor models [e.g., natural killer (NK) cells, T cells, chimeric antigen receptor (CAR) T cells, and macrophages], monocyte-mediated tumor models, and immune checkpoint blockade (ICB) tumor models are among the various bioengineered immune cell-cancer cell interactions that we reviewed herein.

Current Immunotherapy Approaches in Non-Hodgkin Lymphomas

Non-Hodgkin lymphomas (NHLs) are lymphoid malignancies of B- or T-cell origin. Despite great advances in treatment options and significant improvement of survival parameters, a large part of NHL patients either present with a chemotherapy-refractory disease or experience lymphoma relapse. Chemotherapy-based salvage therapy of relapsed/refractory NHL is, however, capable of re-inducing long-term remissions only in a minority of patients. Immunotherapy-based approaches, including bispecific antibodies, immune checkpoint inhibitors and genetically engineered T-cells carrying chimeric antigen receptors, single-agent or in combination with therapeutic monoclonal antibodies, immunomodulatory agents, chemotherapy or targeted agents demonstrated unprecedented clinical activity in heavily-pretreated patients with NHL, including chemotherapy-refractory cases with complex karyotype changes and other adverse prognostic factors. In this review, we recapitulate currently used immunotherapy modalities in NHL and discuss future perspectives of combinatorial immunotherapy strategies, including patient-tailored approaches.

Anti-CD19 CAR-T cells: Digging in the dark side of the golden therapy

The unprecedented technological advances in genetic engineering have resulted in the advent of the very promising chimeric antigen receptor (CAR)-T cell therapy. Based on the striking outcomes of clinical trials, the first two commercial CAR-T cell products, tisagenlecleucel and axicabtagene ciloleucel, have been approved in both the United States and Europe for the treatment of patients with highly aggressive CD19-positive hematological malignancies. Despite the initial remarkable responses many patients finally relapse, implying the presence of resistance mechanisms. In this review, we describe the limitations and resistance mechanisms to anti-CD19 CAR-T cells and address potential strategies to overcome CAR-T cell barriers.

The Landscape of CAR-T Cell Clinical Trials against Solid Tumors-A Comprehensive Overview

Simple Summary

Certain immune cells, namely T cells, of cancer patients can be genetically manipulated to express so-called chimeric antigen receptors (CARs), which enables these cells to kill the tumor cells after recognition by the receptor. This therapy is very successful in the treatment of hematologic tumors such as lymphoma or leukemia. However, tumors growing as a solid mass are less susceptible to this kind of treatment. This review summarizes known data of all clinical trials using this therapy against solid tumors that are registered at clinicaltrials.gov.

Abstract

CAR-T cells showed great potential in the treatment of patients with hematologic tumors. However, the clinical efficacy of CAR-T cells against solid tumors lags behind. To obtain a comprehensive overview of the landscape of CAR-T cell clinical trials against this type of cancer, this review summarizes all the 196 studies registered at clinicaltrials.gov. Special focus is on: (1) geographical distribution; (2) targeted organs, tumor entities, and antigens; (3) CAR transfer methods, CAR formats, and extra features introduced into the T cells; and (4) patient pretreatments, injection sites, and safety measurements. Finally, the few data on clinical outcome are reported. The last assessment of clinicaltrials.gov for the data summarized in this paper was on 4 August 2020.

CAR-T Cells Targeting Epstein-Barr Virus gp350 Validated in a Humanized Mouse Model of EBV Infection and Lymphoproliferative Disease

Epstein-Barr virus (EBV) is a latent and oncogenic human herpesvirus. Lytic viral protein expression plays an important role in EBV-associated malignancies. The EBV envelope glycoprotein 350 (gp350) is expressed abundantly during EBV lytic reactivation and sporadically on the surface of latently infected cells. Here we tested T cells expressing gp350-specific chimeric antigen receptors (CARs) containing scFvs derived from two novel gp350-binding, highly neutralizing monoclonal antibodies. The scFvs were fused to CD28/CD3ζ signaling domains in a retroviral vector. The produced gp350CAR-T cells specifically recognized and killed gp350⁺ 293T cells in vitro. The best-performing 7A1-gp350CAR-T cells were cytotoxic against the EBV⁺ B95-8 cell line, showing selectivity against gp350⁺ cells. Fully humanized Nod.Rag.Gamma mice transplanted with cord blood CD34⁺ cells and infected with the EBV/M81/fLuc lytic strain were monitored dynamically for viral spread. Infected mice recapitulated EBV-induced lymphoproliferation, tumor development, and systemic inflammation. We tested adoptive transfer of autologous CD8⁺gp350CAR-T cells administered protectively or therapeutically. After gp350CAR-T cell therapy, 75% of mice controlled or reduced EBV spread and showed lower frequencies of EBER⁺ B cell malignant lymphoproliferation, lack of tumor development, and reduced inflammation. In summary, CD8⁺gp350CAR-T cells showed proof-of-concept preclinical efficacy against impending EBV⁺ lymphoproliferation and lymphomagenesis.

CAR-Tregs as a Strategy for Inducing Graft Tolerance

Purpose of the review

The adoptive transfer of alloantigen-specific regulatory T cells (Tregs) following organ transplantation is an emerging treatment paradigm that may induce tolerance and reduce the risk for graft rejection. In particular, redirecting Treg specificity via expression of synthetic chimeric antigen receptors (CARs) has demonstrated therapeutic promise in several preclinical studies. In this review, we highlight recent progress and remaining barriers to the clinical translation of CAR-Treg therapies.

Recent findings

CAR Tregs targeting human leukocyte antigen (HLA)-A2 showed antigen-specific in vitro activation and superior in vivo protective function relative to polyclonal Tregs. Adoptively transferred anti-HLA-A2 CAR Tregs prolonged the survival of HLA-A2-positive grafts in humanized mouse models.

Summary

Donor HLA molecules are attractive candidate antigens to target with CAR Tregs in transplantation due to mismatched HLA only expressed on the transplanted organ. The feasibility of this approach has been demonstrated by several independent groups in recent years. However, substantial challenges in CAR design and preclinical modeling must be more extensively addressed prior to clinical application.

Structure-guided engineering of the affinity and specificity of CARs against Tn-glycopeptides

The potency of adoptive T cell therapies targeting the cell surface antigen CD19 has been demonstrated in hematopoietic cancers. It has been difficult to identify appropriate targets in nonhematopoietic tumors, but one class of antigens that have shown promise is aberrant O-glycoprotein epitopes. It has long been known that dysregulated synthesis of O-linked (threonine or serine) sugars occurs in many cancers, and that this can lead to the expression of cell surface proteins containing O-glycans comprised of a single N-acetylgalactosamine (GalNAc, known as Tn antigen) rather than the normally extended carbohydrate. Previously, we used the scFv fragment of antibody 237 as a chimeric antigen receptor (CAR) to mediate recognition of mouse tumor cells that bear its cognate Tn-glycopeptide epitope in podoplanin, also called OTS8. Guided by the structure of the 237 Fab:Tn-OTS8-glycopeptide complex, here we conducted a deep mutational scan showing that residues flanking the Tn-glycan contributed significant binding energy to the interaction. Design of 237-scFv libraries in the yeast display system allowed us to isolate scFv variants with higher affinity for Tn-OTS8. Selection with a noncognate human antigen, Tn-MUC1, yielded scFv variants that were broadly reactive with multiple Tn-glycoproteins. When configured as CARs, engineered T cells expressing these scFv variants showed improved activity against mouse and human cancer cell lines defective in O-linked glycosylation. This strategy provides CARs with Tn-peptide specificities, all based on a single scFv scaffold, that allows the same CAR to be tested for toxicity in mice and efficacy against mouse and human tumors.

Development of CAR-T cell therapies for multiple myeloma

Currently available data on chimeric antigen receptor (CAR)-T cell therapy has demonstrated efficacy and manageable toxicity in heavily pretreated multiple myeloma (MM) patients. The CAR-T field in MM is rapidly evolving with >50 currently ongoing clinical trials across all phases, different CAR-T design, or targets. Most of the CAR-T trials are performed in China and the United States, while European centers organize or participate in only a small fraction of current clinical investigations. Autologous CAR-T cell therapy against B cell maturation antigen shows the best evidence of efficacy so far but main issues remain to be addressed: duration of response, longer follow-up, prolonged cytopenia, patients who may benefit the most such as those with extramedullary disease, outcome prediction, and the integration of CAR-T cell therapy within the MM treatment paradigm. Other promising targets are, i.a.,: CD38, SLAMF7/CS1, or GPRC5D. Although no product has been approved to date, cost and production time for autologous products are expected to be the main obstacles for broad use, for which reason allogeneic CAR-T cells are currently explored. However, the inherent risk of graft-versus-host disease requires additional modification which still need to be validated. This review aims to present the current status of CAR-T cell therapy in MM with an overview on current targets, designs, and stages of CAR-T cell development. Main challenges to CAR-T cell therapy will be highlighted as well as strategies to structurally improve the CAR-T cell product, and thereby its efficacy and safety. The need for comparability of the most promising therapies will be emphasized to balance risks and benefits in an evidence-based but personalized approach to further improve outcome of patients with MM.

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

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

CSPG4 as Target for CAR-T-Cell Therapy of Various Tumor Entities-Merits and Challenges

Targeting cancer cells using chimeric-antigen-receptor (CAR-)T cells has propelled adoptive T-cell therapy (ATT) to the next level. A plentitude of durable complete responses using CD19-specific CAR-T cells in patients suffering from various lymphoid malignancies resulted in the approval by the food and drug administration (FDA) of CD19-directed CAR-T cells for the treatment of acute lymphoblastic leukemia (ALL) and diffuse large B-cell lymphoma (DLBCL). A substantial portion of this success in hematological malignancies can be traced back to the beneficial properties of the target antigen CD19, which combines a universal presence on target cells with no detectable expression on indispensable host cells. Hence, to replicate response rates achieved in ALL and DLBCL in the realm of solid tumors, where ideal target antigens are scant and CAR-T cells are still lagging behind expectations, the quest for appropriate target antigens represents a crucial task to expedite the next steps in the evolution of CAR-T-cell therapy. In this review, we want to highlight the potential of chondroitin sulfate proteoglycan 4 (CSPG4) as a CAR-target antigen for a variety of different cancer entities. In particular, we discuss merits and challenges associated with CSPG4-CAR-T cells for the ATT of melanoma, leukemia, glioblastoma, and triple-negative breast cancer.

Role of CAR-T cell therapy in B-cell acute lymphoblastic leukemia

Chimeric antigen receptor (CAR) T cells are genetically engineered cells containing fusion proteins combining an extracellular epitope-specific binding domain, a transmembrane and signaling domains of the T cell receptor. The CD19-CAR T cell product tisagenlecleucel has been approved by the US Food and Drug Administration and the European Medicines Agency for therapy of children and young adults under 25 years with relapsed/refractory B‑cell acute lymphoblastic leukemia (ALL) due to a high overall response rate of 81% at 3 months after therapy. The rates of event-free and overall survival were 50 and 76% at 12 months. Despite the high initial response rate with CD19-CAR‑T cells in B‑ALL, relapses occur in a significant fraction of patients. Current strategies to improve CAR‑T cell efficacy focus on improved persistence of CAR‑T cells in vivo, use of multispecific CARs to overcome immune escape and new CAR designs. The approved CAR‑T cell products are from autologous T cells generated on a custom-made basis with an inherent risk of production failure. For large scale clinical applications, universal CAR‑T cells serving as “off-the-shelf” agents would be of advantage. During recent years CAR‑T cells have been frequently used for bridging to allogeneic hematopoietic stem cell transplantation (HSCT) in patients with relapsed/refractory B‑ALL since we currently are not able to distinguish those CAR‑T cell induced CRs that will persist without further therapy from those that are likely to be short-lived. CAR‑T cells are clearly of benefit for treatment following relapse after allogeneic HSCT. Future improvements in CAR‑T cell constructs may allow longer term remissions without additional HSCT.