Optimizing T-cell receptor gene therapy for hematologic malignancies

Update on B-cell maturation antigen-directed therapies in AL amyloidosis

Systemic light chain (AL) amyloidosis is a rare clonal plasma cell disorder characterized by the production of amyloidogenic immunoglobulin light chains, which causes the formation and deposition of amyloid fibrils, leading to multi-organ dysfunction. Current treatment is directed at the underlying plasma cell clone to achieve a profound reduction in the monoclonal free light chain production. The standard-of-care first-line therapy is a combination of daratumumab, cyclophosphamide, bortezomib and dexamethasone (D-VCd regimen), resulting in high rates of haematological and organ responses. However, AL amyloidosis remains incurable, and all patients inevitably relapse. Hence, novel treatment options are needed for patients with an inadequate response or relapsed/refractory disease. B-cell maturation antigen (BCMA) is a tumour necrosis factor (TNF receptor superfamily receptor overexpressed on plasma cells in multiple myeloma (MM) and AL amyloidosis. Recently, several novel anti-BCMA immunotherapies have been approved for the treatment of relapsed/refractory MM, including antibody-drug conjugate belantamab mafodotin, bispecific antibodies teclistamab and elranatamab and chimeric antigen receptor T-cell therapies idecabtagene vicleucel and ciltacabtagene autoleucel. Despite lower expression than in MM, BCMA is also a promising target in AL amyloidosis. This review aims to provide up-to-date information on the efficacy and toxicity of anti-BCMA therapy in AL amyloidosis.

Insight into the natural regulatory mechanisms and clinical applications of the CRISPR-Cas system

CRISPR-Cas, the adaptive immune system exclusive to prokaryotes, confers resistance against foreign mobile genetic elements. The CRISPR-Cas system is now being exploited by scientists in a diverse range of genome editing applications. CRISPR-Cas systems can be categorized into six different types based on their composition and mechanism, and there are also natural regulatory biomolecules in bacteria and bacteriophages that can either enhance or inhibit the immune function of CRISPR-Cas. The CRISPR-Cas systems are currently being trialed as a new tool for gene therapy to treat various human diseases, including cancers and genetic diseases, offering significant therapeutic potential. This paper comprehensively summarizes various aspects of the CRISPR-Cas system, encompassing its diversity, regulatory mechanisms, its clinical applications and the obstacles encountered.

Key links in the physiological regulation of the immune system and disease induction: T cell receptor -CD3 complex

T cell receptor (TCR) is a kind of surface marker that are specific to T cells. The TCR regulates T cell function and participates in the body's immunological response to prevent immune dysregulation and inflammatory reactions by identifying and binding exogenous antigens. Due to its brief intracellular segment, TCR requires intracellular molecules to assist with signaling. Among these, the CD3 molecule is one of the most important. The CD3 molecule involves in TCR structural stability as well as T cell activation signaling. A TCR-CD3 complex is created when TCR and CD3 form a non-covalent bond. Antigen recognition and T cell signaling are both facilitated by the TCR-CD3 complex. When a CD3 subunit is absent, a TCR-CD3 complex cannot form, and none of the subunits is transported to the cell surface. Thus, T cells cannot develop. Consequently, research on the physiological functions and potential pathogenicity of CD3 subunits can clarify the pathogenesis of immune system diseases and can offer fresh approaches to the treatment of it. In this review, the structure and function of the TCR-CD3 complex in the immune system was summarized, the pathogenicity of each CD3 subunit and therapeutic approaches to related diseases was explored and research directions for the development of new targeted drugs was provided.

Harnessing the evolving CRISPR/Cas9 for precision oncology

The Clustered Regularly Interspaced Short Palindromic Repeat (CRISPR)/Cas9 system, a groundbreaking innovation in genetic engineering, has revolutionized our approach to surmounting complex diseases, culminating in CASGEVY™ approved for sickle cell anemia. Derived from a microbial immune defense mechanism, CRISPR/Cas9, characterized as precision, maneuverability and universality in gene editing, has been harnessed as a versatile tool for precisely manipulating DNA in mammals. In the process of applying it to practice, the consecutive exploitation of novel orthologs and variants never ceases. It's conducive to understanding the essentialities of diseases, particularly cancer, which is crucial for diagnosis, prevention, and treatment. CRISPR/Cas9 is used not only to investigate tumorous genes functioning but also to model disparate cancers, providing valuable insights into tumor biology, resistance, and immune evasion. Upon cancer therapy, CRISPR/Cas9 is instrumental in developing individual and precise cancer therapies that can selectively activate or deactivate genes within tumor cells, aiming to cripple tumor growth and invasion and sensitize cancer cells to treatments. Furthermore, it facilitates the development of innovative treatments, enhancing the targeting efficiency of reprogrammed immune cells, exemplified by advancements in CAR-T regimen. Beyond therapy, it is a potent tool for screening susceptible genes, offering the possibility of intervening before the tumor initiative or progresses. However, despite its vast potential, the application of CRISPR/Cas9 in cancer research and therapy is accompanied by significant efficacy, efficiency, technical, and safety considerations. Escalating technology innovations are warranted to address these issues. The CRISPR/Cas9 system is revolutionizing cancer research and treatment, opening up new avenues for advancements in our understanding and management of cancers. The integration of this evolving technology into clinical practice promises a new era of precision oncology, with targeted, personalized, and potentially curative therapies for cancer patients.

Canine Mammary Tumors: Classification, Biomarkers, Traditional and Personalized Therapies

In recent years, many studies have focused their attention on the dog as a proper animal model for human cancer. In dogs, mammary tumors develop spontaneously, involving a complex interplay between tumor cells and the immune system and revealing several molecular and clinical similarities to human breast cancer. In this review, we summarized the major features of canine mammary tumor, risk factors, and the most important biomarkers used for diagnosis and treatment. Traditional therapy of mammary tumors in dogs includes surgery, which is the first choice, followed by chemotherapy, radiotherapy, or hormonal therapy. However, these therapeutic strategies may not always be sufficient on their own; advancements in understanding cancer mechanisms and the development of innovative treatments offer hope for improved outcomes for oncologic patients. There is still a growing interest in the use of personalized medicine, which should play an irreplaceable role in the research not only in human cancer therapy, but also in veterinary oncology. Moreover, immunotherapy may represent a novel and promising therapeutic option in canine mammary cancers. The study of novel therapeutic approaches is essential for future research in both human and veterinary oncology.

Immunoengineering via Chimeric Antigen Receptor-T Cell Therapy: Reprogramming Nanodrug Delivery

Following its therapeutic effect in hematological metastasis, chimeric antigen receptor (CAR) T cell therapy has gained a great deal of attention during the last years. However, the effectiveness of this treatment has been hampered by a number of challenges, including significant toxicities, difficult access to tumor locations, inadequate therapeutic persistence, and manufacturing problems. Developing novel techniques to produce effective CARs, administer them, and monitor their anti-tumor activity in CAR-T cell treatment is undoubtedly necessary. Exploiting the advantages of nanotechnology may possibly be a useful strategy to increase the efficacy of CAR-T cell treatment. This study outlines the current drawbacks of CAR-T immunotherapy and identifies promising developments and significant benefits of using nanotechnology in order to introduce CAR transgene motifs into primary T cells, promote T cell expansion, enhance T cell trafficking, promote intrinsic T cell activity and rewire the immunosuppressive cellular and vascular microenvironments. Therefore, the development of powerful CART cells can be made possible with genetic and functional alterations supported by nanotechnology. In this review, we discuss the innovative and possible uses of nanotechnology for clinical translation, including the delivery, engineering, execution, and modulation of immune functions to enhance and optimize the anti-tumor efficacy of CAR-T cell treatment.

Evaluation of diversity indices to estimate clonal dominance in gene therapy studies

In cell and gene therapy, achieving the stable engraftment of an abundant and highly polyclonal population of gene-corrected cells is one of the key factors to ensure the successful and safe treatment of patients. Because integrative vectors have been associated with possible risks of insertional mutagenesis leading to clonal dominance, monitoring the relative abundance of individual vector insertion sites in patients' blood cells has become an important safety assessment, particularly in hematopoietic stem cell-based therapies. Clinical studies often express clonal diversity using various metrics. One of the most commonly used is the Shannon index of entropy. However, this index aggregates two distinct aspects of diversity, the number of unique species and their relative abundance. This property hampers the comparison of samples with different richness. This prompted us to reanalyze published datasets and to model the properties of various indices as applied to the evaluation of clonal diversity in gene therapy. A normalized version of the Shannon index, such as Pielou's index, or Simpson's probability index is robust and useful to compare sample evenness between patients and trials. Clinically meaningful standard values for clonal diversity are herein proposed to facilitate the use of vector insertion site analyses in genomic medicine practice.

Knowledge mapping and current trends of global research on CRISPR in the field of cancer

Background: Gene editing tools using clustered regularly interspaced short palindromic repeats (CRISPR) and CRISPR-related systems have revolutionized our understanding of cancer. The purpose of this study was to determine the distribution, collaboration, and direction of cancer research using CRISPR. Methods: Data from the Web of Science (WoS) Core Collection database were collected from 4,408 cancer publications related to CRISPR from 1 January 2013to 31 December 2022. The obtained data were analyzed using VOSviewer software for citation, co-citation, co-authorship, and co-occurrence analysis. Results: The number of annual publications has grown steadily over the past decade worldwide. The United States was shown, by far, to be the leading source of cancer publications, citations, and collaborations involving CRISPR than any other country, followed by China. Li Wei (Jilin University, China), and Harvard Medical School (Boston, MA, United States) were the author and institution with the most publications and active collaborations, respectively. The journal with the most contributions was Nature Communications (n = 147) and the journal with the most citations was Nature (n = 12,111). The research direction of oncogenic molecules, mechanisms, and cancer-related gene editing was indicated based on keyword analysis. Conclusion: The current study has provided a comprehensive overview of cancer research highlights and future trends of CRISPR, combined with a review of CRISPR applications in cancer to summarize and predict research directions and provide guidance to researchers.

Advances in CRISPR/Cas9

CRISPR/Cas9 technology has become the most examined gene editing technology in recent years due to its simple design, yet low cost, high efficiency, and simple operation, which can also achieve simultaneous editing of multiple loci. It can also be carried out without using plasmids, saving lots of troubles caused by plasmids. CRISPR/Cas9 has shown great potential in the study of genes or genomic functions in microorganisms, plants, animals, and human beings. In this review, we will examine the history, structure, and basic mechanisms of the CRISPR/Cas9 system, describe its great value in precision medicine and sgRNA library screening, and dig its great potential in a new field: DNA information storage.

Current applications and future perspective of CRISPR/Cas9 gene editing in cancer

Clustered regularly interspaced short palindromic repeats (CRISPR) system provides adaptive immunity against plasmids and phages in prokaryotes. This system inspires the development of a powerful genome engineering tool, the CRISPR/CRISPR-associated nuclease 9 (CRISPR/Cas9) genome editing system. Due to its high efficiency and precision, the CRISPR/Cas9 technique has been employed to explore the functions of cancer-related genes, establish tumor-bearing animal models and probe drug targets, vastly increasing our understanding of cancer genomics. Here, we review current status of CRISPR/Cas9 gene editing technology in oncological research. We first explain the basic principles of CRISPR/Cas9 gene editing and introduce several new CRISPR-based gene editing modes. We next detail the rapid progress of CRISPR screening in revealing tumorigenesis, metastasis, and drug resistance mechanisms. In addition, we introduce CRISPR/Cas9 system delivery vectors and finally demonstrate the potential of CRISPR/Cas9 engineering to enhance the effect of adoptive T cell therapy (ACT) and reduce adverse reactions.

CAR-T and other adoptive cell therapies for B cell malignancies

B cell malignancies pose challenges due to therapeutic resistance and repeated relapse. Advances in adoptive cellular therapies including chimeric antigen receptor (CAR)-T cells have the potential to transform the treatment landscape in hematological and solid tumor cancers. Improvements in constructs of CAR-T have improved specificity in targeting malignant cells. Multiple clinical trials have demonstrated the efficacy of CAR-T and other cellular treatments. In spite of advances in cellular therapies, hurdles in managing toxicities and lingering resistance remain. This review aims to summarize current innovations in adoptive cellular therapies and introduces future paths of discovery that will enhance these therapies in the era of precision oncology.

CRISPR/Cas9 Gene-Editing in Cancer Immunotherapy: Promoting the Present Revolution in Cancer Therapy and Exploring More

In recent years, immunotherapy has showed fantastic promise in pioneering and accelerating the field of cancer therapy and embraces unprecedented breakthroughs in clinical practice. The clustered regularly interspaced short palindromic repeat (CRISPR)-associated protein 9 (CRISPR-Cas9) system, as a versatile gene-editing technology, lays a robust foundation to efficiently innovate cancer research and cancer therapy. Here, we summarize recent approaches based on CRISPR/Cas9 system for construction of chimeric antigen receptor T (CAR-T) cells and T cell receptor T (TCR-T) cells. Besides, we review the applications of CRISPR/Cas9 in inhibiting immune checkpoint signaling pathways and highlight the feasibility of CRISPR/Cas9 based engineering strategies to screen novel cancer immunotherapy targets. Conclusively, we discuss the perspectives, potential challenges and possible solutions in this vivid growing field.

Overview of Cellular Immunotherapies within Transfusion Medicine for the Treatment of Malignant Diseases

Over the years, transfusion medicine has developed into a broad, multidisciplinary field that covers different clinical patient services such as apheresis technology and the development of stem cell transplantation. Recently, the discipline has found a niche in development and production of advanced therapy medicinal products (ATMPs) for immunotherapy and regenerative medicine purposes. In clinical trials, cell-based immunotherapies have shown encouraging results in the treatment of multiple cancers and autoimmune diseases. However, there are many parameters such as safety, a high level of specificity, and long-lasting efficacy that still need to be optimized to maximize the potential of cell-based immunotherapies. Thus, only a few have gained FDA approval, while the majority of them are studied in the context of investigator-initiated trials (IITs), where modern, academically oriented transfusion centers can play an important role. In this review, we summarize existing and contemporary cellular immunotherapies, which are already a part of modern transfusion medicine or are likely to become so in the future.

Overcoming Resistance to Tumor-Targeted and Immune-Targeted Therapies

Resistance to anticancer therapies includes primary resistance, usually related to lack of target dependency or presence of additional targets, and secondary resistance, mostly driven by adaptation of the cancer cell to the selection pressure of treatment. Resistance to targeted therapy is frequently acquired, driven by on-target, bypass alterations, or cellular plasticity. Resistance to immunotherapy is often primary, orchestrated by sophisticated tumor-host-microenvironment interactions, but could also occur after initial efficacy, mostly when only partial responses are obtained. Here, we provide an overview of resistance to tumor and immune-targeted therapies and discuss challenges of overcoming resistance, and current and future directions of development. SIGNIFICANCE: A better and earlier identification of cancer-resistance mechanisms could avoid the use of ineffective drugs in patients not responding to therapy and provide the rationale for the administration of personalized drug associations. A clear description of the molecular interplayers is a prerequisite to the development of novel and dedicated anticancer drugs. Finally, the implementation of such cancer molecular and immunologic explorations in prospective clinical trials could de-risk the demonstration of more effective anticancer strategies in randomized registration trials, and bring us closer to the promise of cure.

CRISPR/Cas: Advances, Limitations, and Applications for Precision Cancer Research

Cancer is one of the most leading causes of mortalities worldwide. It is caused by the accumulation of genetic and epigenetic alterations in 2 types of genes: tumor suppressor genes (TSGs) and proto-oncogenes. In recent years, development of the clustered regularly interspaced short palindromic repeats (CRISPR) technology has revolutionized genome engineering for different cancer research ranging for research ranging from fundamental science to translational medicine and precise cancer treatment. The CRISPR/CRISPR associated proteins (CRISPR/Cas) are prokaryote-derived genome editing systems that have enabled researchers to detect, image, manipulate and annotate specific DNA and RNA sequences in various types of living cells. The CRISPR/Cas systems have significant contributions to discovery of proto-oncogenes and TSGs, tumor cell epigenome normalization, targeted delivery, identification of drug resistance mechanisms, development of high-throughput genetic screening, tumor models establishment, and cancer immunotherapy and gene therapy in clinics. Robust technical improvements in CRISPR/Cas systems have shown a considerable degree of efficacy, specificity, and flexibility to target the specific locus in the genome for the desired applications. Recent developments in CRISPRs technology offers a significant hope of medical cure against cancer and other deadly diseases. Despite significant improvements in this field, several technical challenges need to be addressed, such as off-target activity, insufficient indel or low homology-directed repair (HDR) efficiency, in vivo delivery of the Cas system components, and immune responses. This study aims to overview the recent technological advancements, preclinical and perspectives on clinical applications of CRISPR along with their advantages and limitations. Moreover, the potential applications of CRISPR/Cas in precise cancer tumor research, genetic, and other precise cancer treatments discussed.

Potentiating the Antitumor Activity of Cytotoxic T Cells via the Transmembrane Domain of IGSF4 That Increases TCR Avidity

A robust T-cell response is an important component of sustained antitumor immunity. In this respect, the avidity of TCR in the antigen-targeting of tumors is crucial for the quality of the T-cell response. This study reports that the transmembrane (TM) domain of immunoglobulin superfamily member 4 (IGSF4) binds to the TM of the CD3 ζ-chain through an interaction between His177 and Asp36, which results in IGSF4-CD3 ζ dimers. IGSF4 also forms homo-dimers through the GxxVA motif in the TM domain, thereby constituting large TCR clusters. Overexpression of IGSF4 lacking the extracellular (IG4ΔEXT) domain potentiates the OTI CD8+ T cells to release IFN-γ and TNF-α and to kill OVA+-B16F10 melanoma cells. In animal models, IG4ΔEXT significantly reduces B16F10 tumor metastasis as well as tumor growth. Collectively, the results indicate that the TM domain of IGSF4 can regulate TCR avidity, and they further demonstrate that TCR avidity regulation is critical for improving the antitumor activity of cytotoxic T cells.

CRISPR/Cas9-mediated knockout of clinically relevant alloantigenes in human primary T cells

Background

The ability of CRISPR/Cas9 to mutate any desired genomic locus is being increasingly explored in the emerging area of cancer immunotherapy. In this respect, current efforts are mostly focused on the use of autologous (i.e. patient-derived) T cells. The autologous approach, however, has drawbacks in terms of manufacturing time, cost, feasibility and scalability that can affect therapeutic outcome or wider clinical application. The use of allogeneic T cells from healthy donors may overcome these limitations. For this strategy to work, the endogenous T cell receptor (TCR) needs to be knocked out in order to reduce off-tumor, graft-versus-host-disease (GvHD). Furthermore, CD52 may be knocked out in the donor T cells, since this leaves them resistant to the commonly used anti-CD52 monoclonal antibody lymphodepletion regimen aiming to suppress rejection of the infused T cells by the recipient. Despite the great prospect, genetic manipulation of human T cells remains challenging, in particular how to deliver the engineering reagents: virus-mediated delivery entails the inherent risk of altering cancer gene expression by the genomically integrated CRISPR/Cas9. This is avoided by delivery of CRISPR/Cas9 as ribonucleoproteins, which, however, are fragile and technically demanding to produce. Electroporation of CRISPR/Cas9 expression plasmids would bypass the above issues, as this approach is simple, the reagents are robust and easily produced and delivery is transient.

Results

Here, we tested knockout of either TCR or CD52 in human primary T cells, using electroporation of CRISPR/Cas9 plasmids. After validating the CRISPR/Cas9 constructs in human 293 T cells by Tracking of Indels by Decomposition (TIDE) and Indel Detection by Amplicon Analysis (IDAA) on-target genomic analysis, we evaluated their efficacy in primary T cells. Four days after electroporation with the constructs, genomic analysis revealed a knockout rate of 12–14% for the two genes, which translated into 7–8% of cells showing complete loss of surface expression of TCR and CD52 proteins, as determined by flow cytometry analysis.

Conclusion

Our results demonstrate that genomic knockout by electroporation of plasmids encoding CRISPR/Cas9 is technically feasible in human primary T cells, albeit at low efficiency.

CRISPR technology: The engine that drives cancer therapy

CRISPR gene editing technology belongs to the third generation of gene editing technology. Since its discovery, it has attracted the attention of a large number of researchers. Investigators have published a series of academic articles and obtained breakthrough research results through in-depth research. In recent years, this technology has developed rapidly and been widely applied in many fields, especially in medicine. This review focuses on concepts of CRISPR gene editing technology, its application in cancer treatments, its existing limitations, and the new progress in recent years for detailed analysis and sharing.

CAR-T cells targeting a nucleophosmin neoepitope exhibit potent specific activity in mouse models of acute myeloid leukaemia

Therapies employing chimeric antigen receptor T cells (CAR-T cells) targeting tumour-associated antigens (TAAs) can lead to on-target-off-tumour toxicity and to resistance, owing to TAA expression in normal tissues and to TAA expression loss in tumour cells. These drawbacks can be circumvented by CAR-T cells targeting tumour-specific driver gene mutations, such as the four-nucleotide duplication in the oncogene nucleophosmin (NPM1c), which creates a neoepitope presented by the human leukocyte antigen with the A2 serotype (HLA-A2) that has been observed in about 35% of patients with acute myeloid leukaemia (AML). Here, we report a human single-chain variable fragment (scFv), identified via yeast surface display, that specifically binds to the NPM1c epitope-HLA-A2 complex but not to HLA-A2 or to HLA-A2 loaded with control peptides. In vitro and in mice, CAR-T cells with the scFv exhibit potent cytotoxicity against NPM1c⁺HLA-A2⁺ leukaemia cells and primary AML blasts, but not NPM1c^-HLA-A2⁺ leukaemia cells or HLA-A2^- tumour cells. Therapies using NPM1c CAR-T cells for the treatment of NPM1c⁺HLA-A2⁺ AML may limit on-target-off-tumour toxicity and tumour resistance.

SYNE1 mutation may enhance the response to immune checkpoint blockade therapy in clear cell renal cell carcinoma patients

As one of the 10 most common cancers in men, the incidence of renal cell carcinoma (RCC) has been increasing in recent years. Clear cell renal cell carcinoma (ccRCC) is the most common pathological type of RCC, counting for 80%-90% of cases. Immunotherapy is becoming increasingly important in the treatment of advanced RCC. Tumor mutation burden (TMB) is a potent marker for predicting the response to immune checkpoint blockade (ICB) treatment. Here, we analyzed somatic mutation data for ccRCC from The Cancer Genome Atlas datasets. We found that the frequently mutated gene SYNE1 is associated with higher TMBs and with a poor clinical prognosis. To further investigate the relationship between SYNE1 mutation and the immune system, we used Gene Set Enrichment Analysis and the CIBERSORT algorithm. They showed that SYNE1 mutations correlate with immune system pathways and immune cell tumor infiltration. We also found that SYNE1 mutation correlated with a better response to ICB therapy. Thus, mutation of SYNE1 correlates with a higher TMB and a poorer outcome in ccRCC, but may mediate better responses to ICB therapy.

CRISPR-Cas, a robust gene-editing technology in the era of modern cancer immunotherapy

Cancer immunotherapy has been emerged as a promising strategy for treatment of a broad spectrum of malignancies ranging from hematological to solid tumors. One of the principal approaches of cancer immunotherapy is transfer of natural or engineered tumor-specific T-cells into patients, a so called "adoptive cell transfer", or ACT, process. Construction of allogeneic T-cells is dependent on the employment of a gene-editing tool to modify donor-extracted T-cells and prepare them to specifically act against tumor cells with enhanced function and durability and least side-effects. In this context, CRISPR technology can be used to produce universal T-cells, equipped with recombinant T cell receptor (TCR) or chimeric antigen receptor (CAR), through multiplex genome engineering using Cas nucleases. The robust potential of CRISPR-Cas in preparing the building blocks of ACT immunotherapy has broaden the application of such therapies and some of them have gotten FDA approvals. Here, we have collected the last investigations in the field of immuno-oncology conducted in partnership with CRISPR technology. In addition, studies that have addressed the challenges in the path of CRISPR-mediated cancer immunotherapy, as well as pre-treatment applications of CRISPR-Cas have been mentioned in detail.

Identification of a tumor-specific allo-HLA-restricted γδTCR

γδT cells are key players in cancer immune surveillance because of their ability to recognize malignant transformed cells, which makes them promising therapeutic tools in the treatment of cancer. However, the biological mechanisms of how γδT-cell receptors (TCRs) interact with their ligands are poorly understood. Within this context, we describe the novel allo-HLA-restricted and CD8α-dependent Vγ5Vδ1TCR. In contrast to the previous assumption of the general allo-HLA reactivity of a minor fraction of γδTCRs, we show that classic anti-HLA-directed, γδTCR-mediated reactivity can selectively act on hematological and solid tumor cells, while not harming healthy tissues in vitro and in vivo. We identified the molecular interface with proximity to the peptide-binding groove of HLA-A*24:02 as the essential determinant for recognition and describe the critical role of CD8 as a coreceptor. We conclude that alloreactive γδT-cell repertoires provide therapeutic opportunities, either within the context of haplotransplantation or as individual γδTCRs for genetic engineering of tumor-reactive T cells.

Engineering CD4+ T Cells to Enhance Cancer Immunity

This review presents key advances in combining T cell receptor (TCR) gene transfer to redirect T-cell specificity with gene engineering in order to enhance cancer-protective immune function. We discuss how emerging insights might be applied to CD4+ T cells. Although much attention has been paid to the role of CD8+ cytotoxic T cells in tumour protection, we provide convincing evidence that CD4+ helper T cells play a critical role in cancer immune responses in animal models and also in patients. We demonstrate that genetic engineering technologies provide exciting opportunities to extend the specificity range of CD4+ T cells from MHC class-II-presented epitopes to include peptides presented by MHC class I molecules. Functional enhancement of tumour immunity can improve the sensitivity of T cells to cancer antigens, promote survival in a hostile tumour microenvironment, boost cancer-protective effector mechanisms and enable the formation of T-cell memory. Engineered cancer-specific CD4+ T cells may contribute to protective immunity by a direct pathway involving cancer cell killing, and by an indirect pathway that boosts the function, persistence and memory formation of CD8+ T cells.

A High-Avidity T-cell Receptor Redirects Natural Killer T-cell Specificity and Outcompetes the Endogenous Invariant T-cell Receptor

T-cell receptor (TCR) gene transfer redirects T cells to target intracellular antigens. However, the potential autoreactivity generated by TCR mispairing and occurrence of graft-versus-host disease in the allogenic setting due to the retention of native TCRs remain major concerns. Natural killer T cells (NKT) have shown promise as a platform for adoptive T-cell therapy in cancer patients. Here, we showed their utility for TCR gene transfer. We successfully engineered and expanded NKTs expressing a functional TCR (TCR NKTs), showing HLA-restricted antitumor activity in xenogeneic mouse models in the absence of graft-versus-mouse reactions. We found that TCR NKTs downregulated the invariant TCR (iTCR), leading to iTCR⁺TCR⁺ and iTCR^-TCR⁺ populations. In-depth analyses of these subsets revealed that in iTCR^-TCR⁺ NKTs, the iTCR, although expressed at the mRNA and protein levels, was retained in the cytoplasm. This effect resulted from a competition for binding to CD3 molecules for cell-surface expression by the transgenic TCR. Overall, our results highlight the feasibility and advantages of using NKTs for TCR expression for adoptive cell immunotherapies. NKT-low intrinsic alloreactivity that associated with the observed iTCR displacement by the engineered TCR represents ideal characteristics for "off-the-shelf" products without further TCR gene editing.

Mesenchymal stem cells as carrier of the therapeutic agent in the gene therapy of blood disorders

Nonhematopoietic stem cells as a delivery platform of therapeutic useful genes have attracted widespread attention in recent years, owing to gained a long lifespan, easy separation, high proliferation, and high transfection capacity. Mesenchymal stem/stromal cells (MSCs) are the choice of the cells for gene and cell therapy due to high self-renewal capacity, high migration rate to the site of the tumor, and with immune suppressive and anti-inflammatory properties. Hence, it has a high potential of safety genetic modification of MSCs for antitumor gene expression and has paved the way for the clinical application of these cells to target the therapy of cancers and other diseases. The aim of gene therapy is targeted treatment of cancers and diseases through recovery, change, or enhancement cell performance to the sustained secretion of useful therapeutic proteins and induction expression of the functional gene in intended tissue. Recent developments in the vectors designing leading to the increase and durability of expression and improvement of the safety of the vectors that overcome a lot of problems, such as durability of expression and the host immune response. Nowadays, gene therapy approach is used by MSCs as a delivery vehicle in the preclinical and the clinical trials for the secretion of erythropoietin, recombinant antibodies, coagulation factors, cytokines, as well as angiogenic inhibitors in many blood disorders like anemia, hemophilia, and malignancies. In this study, we critically discuss the status of gene therapy by MSCs as a delivery vehicle for the treatment of blood disorders. Finally, the results of clinical trial studies are assessed, highlighting promising advantages of this emerging technology in the clinical setting.

The application of CRISPR-Cas9 genome editing tool in cancer immunotherapy

Clustered regularly interspaced short palindromic repeats (CRISPR)-associated protein 9 (CRISPR-Cas9) system was originally discovered in prokaryotes functioned as a part of the adaptive immune system. Because of its high efficiency and easy operability, CRISPR-Cas9 system has been developed to be a powerful and versatile gene editing tool shortly after its discovery. Given that multiple genetic alterations are the main factors that drive genesis and development of tumor, CRISPR-Cas9 system has been applied to correct cancer-causing gene mutations and deletions and to engineer immune cells, such as chimeric antigen receptor T (CAR T) cells, for cancer immunotherapeutic applications. Recently, CRISPR-Cas9-based CAR T-cell preparation has been an important breakthrough in antitumor therapy. Here, we summarize the mechanism, delivery and the application of CRISPR-Cas9 in gene editing, and discuss the challenges and future directions of CRISPR-Cas9 in cancer immunotherapy.

Preclinical assessment of transiently TCR redirected T cells for solid tumour immunotherapy

Off-target toxicity due to the expression of target antigens in normal tissue or TCR cross-reactivity represents a major risk when using T cell receptor (TCR)-engineered T cells for treatment of solid tumours. Due to the inherent cross-reactivity of TCRs it is difficult to accurately predict their target recognition pre-clinically. It has become evident that direct testing in a human being represents the best evaluation of the risks. There is, therefore, a clear unmet need for assessing the safety of a therapeutic TCR in a more controllable manner than by the injection of permanently modified cellular products. Using transiently modified T cells combined with dose escalation has already been shown feasible for chimeric antigen receptor (CAR)-engineered T cells, but nothing is yet reported for TCR. We performed a preclinical evaluation of a therapeutic TCR transiently expressed in T cells by mRNA electroporation. We analyzed if the construct was active in vitro, how long it was detectable for and if this expression format was adapted to in vivo efficacy assessment. Our data demonstrate the potential of mRNA engineered T cells, although less powerful than permanent redirection, to induce a significant response. Thus, these findings support the development of mRNA based TCR-therapy strategies as a feasible and efficacious method for evaluating TCR safety and efficacy in first-in-man testing.

An Ig Transmembrane Domain Motif Improves the Function of TCRs Transduced in Human T Cells: Implications for Immunotherapy

Adoptive transfer of T lymphocytes (ACT) engineered with T-cell receptors (TCRs) of known antitumor specificity is an effective therapeutic strategy. However, a major constraint of ACT is the unpredictable interference of the endogenous TCR α and β chains in pairing of the transduced TCR. This effect reduces the efficacy of the genetically modified primary T cells and carries the risk of generating novel TCR reactivities with unintended functional consequences. Here, we show a powerful approach to overcome these limitations. We engineered TCR α and β chains with mutations encompassing a conserved motif (FXXXFXXS) required to stabilize the pairing of immunoglobulin heavy chain transmembrane domains. Molecular modeling supported the preferential pairing of mutated TCR and impaired pairing between mutated and wild-type TCRs. Expression of the mutated TCR was similar to wild type and conferred the expected specificity. Fluorescence resonance energy transfer analysis in mouse splenocytes transduced with mutated or wild-type TCRs showed a higher proximity of the former over the latter. Importantly, we show that mutated TCRs effectively outcompete endogenous TCRs and improve in vitro antitumor cytotoxicity when expressed in ex vivo isolated human T cells. This approach should contribute to improving current protocols of anticancer immunetherapy protocols.

T-cell receptor gene-modified cells: past promises, present methodologies and future challenges

Immunotherapy constitutes an exciting and rapidly evolving field, and the demonstration that genetically modified T-cell receptors (TCRs) can be used to produce T-lymphocyte populations of desired specificity offers new opportunities for antigen-specific T-cell therapy. Overall, TCR-modified T cells have the ability to target a wide variety of self and non-self targets through the normal biology of a T cell. Although major histocompatibility complex (MHC)-restricted and dependent on co-receptors, genetically engineered TCRs still present a number of characteristics that ensure they are an important alternative strategy to chimeric antigen receptors (CARs), and high-affinity TCRs can now be successfully engineered with the potential to enhance therapeutic efficacy while minimizing adverse events. This review will focus on the main characteristics of TCR gene-modified cells, their potential clinical application and promise to the field of adoptive cell transfer (ACT), basic manufacturing procedures and characterization protocols and overall challenges that need to be overcome so that redirection of TCR specificity may be successfully translated into clinical practice, beyond early-phase clinical trials.

Mutated nucleophosmin 1 as immunotherapy target in acute myeloid leukemia

The most frequent subtype of acute myeloid leukemia (AML) is defined by mutations in the nucleophosmin 1 (NPM1) gene. Mutated NPM1 (ΔNPM1) is an attractive target for immunotherapy, since it is an essential driver gene and 4 bp frameshift insertions occur in the same hotspot in 30%-35% of AMLs, resulting in a C-terminal alternative reading frame of 11 aa. By searching the HLA class I ligandome of primary AMLs, we identified multiple ΔNPM1-derived peptides. For one of these peptides, HLA-A*02:01-binding CLAVEEVSL, we searched for specific T cells in healthy individuals using peptide-HLA tetramers. Tetramer-positive CD8+ T cells were isolated and analyzed for reactivity against primary AMLs. From one clone with superior antitumor reactivity, we isolated the T cell receptor (TCR) and demonstrated specific recognition and lysis of HLA-A*02:01-positive ΔNPM1 AML after retroviral transfer to CD8+ and CD4+ T cells. Antitumor efficacy of TCR-transduced T cells was confirmed in immunodeficient mice engrafted with a human AML cell line expressing ΔNPM1. In conclusion, the data show that ΔNPM1-derived peptides are presented on AML and that CLAVEEVSL is a neoantigen that can be efficiently targeted on AML by ΔNPM1 TCR gene transfer. Immunotherapy targeting ΔNPM1 may therefore contribute to treatment of AML.

mRNA as novel technology for passive immunotherapy

While active immunization elicits a lasting immune response by the body, passive immunotherapy transiently equips the body with exogenously generated immunological effectors in the form of either target-specific antibodies or lymphocytes functionalized with target-specific receptors. In either case, administration or expression of recombinant proteins plays a fundamental role. mRNA prepared by in vitro transcription (IVT) is increasingly appreciated as a drug substance for delivery of recombinant proteins. With its biological role as transient carrier of genetic information translated into protein in the cytoplasm, therapeutic application of mRNA combines several advantages. For example, compared to transfected DNA, mRNA harbors inherent safety features. It is not associated with the risk of inducing genomic changes and potential adverse effects are only temporary due to its transient nature. Compared to the administration of recombinant proteins produced in bioreactors, mRNA allows supplying proteins that are difficult to manufacture and offers extended pharmacokinetics for short-lived proteins. Based on great progress in understanding and manipulating mRNA properties, efficacy data in various models have now demonstrated that IVT mRNA constitutes a potent and flexible platform technology. Starting with an introduction into passive immunotherapy, this review summarizes the current status of IVT mRNA technology and its application to such immunological interventions.

The Emerging World of TCR-T Cell Trials Against Cancer: A Systematic Review

T-cell receptor-engineered T-cell therapy and chimeric antigen receptor T-cell therapy are 2 types of adoptive T-cell therapy that genetically modify natural T cells to treat cancers. Although chimeric antigen receptor T-cell therapy has yielded remarkable efficacy for hematological malignancies of the B-cell lineages, most solid tumors fail to respond significantly to chimeric antigen receptor T cells. T-cell receptor-engineered T-cell therapy, on the other hand, has shown unprecedented promise in treating solid tumors and has attracted growing interest. In order to create an unbiased, comprehensive, and scientific report for this fast-moving field, we carefully analyzed all 84 clinical trials using T-cell receptor-engineered T-cell therapy and downloaded from ClinicalTrials.gov updated by June 11, 2018. Informative features and trends were observed in these clinical trials. The number of trials initiated each year is increasing as expected, but an interesting pattern is observed. NY-ESO-1, as the most targeted antigen type, is the target of 31 clinical trials; melanoma is the most targeted cancer type and is the target of 33 clinical trials. Novel antigens and underrepresented cancers remain to be targeted in future studies and clinical trials. Unlike chimeric antigen receptor T-cell therapy, only about 16% of the 84 clinical trials target against hematological malignancies, consistent with T-cell receptor-engineered T-cell therapy's high potential for solid tumors. Six pharma/biotech companies with novel T-cell receptor-engineered T-cell ideas and products were examined in this review. Multiple approaches have been utilized in these companies to increase the T-cell receptor's affinity and efficiency and to minimize cross-reactivity. The major challenges in the development of the T-cell receptor-engineered T-cell therapy due to tumor microenvironment were also discussed here.

Safety and efficacy of Tet-regulated IL-12 expression in cancer-specific T cells

We explored whether engineering of T cell specificity and effector function improves immunotherapy of solid tumors. Although IL-12 can enhance cancer immunity, a strategy of safe IL-12 delivery without toxicity is currently lacking. We engineered T cells to express IL-12 controlled by the NFAT promoter responsive to TCR stimulation, or by the Tet-On promoter responsive to doxycycline. In vivo, NFAT-engineered T cells caused lethal toxicity, while Tet-engineered T cells were safe in the absence of doxycycline. Combining gene transfer of the melanoma-specific TRP2-TCR with Tet-IL-12 engineering revealed that temporal induction of IL-12 was essential to inhibit the growth of B16F10 melanoma tumors. Induced IL-12 increased the number of tumor-infiltrating T cells and also prevented the down-modulation of the TRP2-TCR and the associated up-regulation of the PD1 marker that was observed in the absence of IL-12. In addition, temporal induction of IL-12 expression also increased the number of plasmacytoid DC in the tumor micro-environment. We show that repeated induction of IL-12 can be used to enhance control of tumor growth without encountering systemic toxicity. The observation that TCR engineering combined with Tet-regulated IL-12 expression can achieve tumor immunity without the side effects that are usually associated with the in vivo use of IL-12 warrants translation of this concept into the clinic.

Chimeric Antigen Receptor (CAR) Treg: A Promising Approach to Inducing Immunological Tolerance

Cellular therapies with polyclonal regulatory T-cells (Tregs) in transplantation and autoimmune diseases have been carried out in both animal models and clinical trials. However, The use of large numbers of polyclonal Tregs with unknown antigen specificities has led to unwanted effects, such as systemic immunosuppression, which can be avoided via utilization of antigen-specific Tregs. Antigen-specific Tregs are also more potent in suppression than polyclonal ones. Although antigen-specific Tregs can be induced in vitro, these iTregs are usually contaminated with effector T cells during in vitro expansion. Fortunately, Tregs can be efficiently engineered with a predetermined antigen-specificity via transfection of viral vectors encoding specific T cell receptors (TCRs) or chimeric antigen receptors (CARs). Compared to Tregs engineered with TCRs (TCR-Tregs), CAR-modified Tregs (CAR-Tregs) engineered in a non-MHC restricted manner have the advantage of widespread applications, especially in transplantation and autoimmunity. CAR-Tregs also are less dependent on IL-2 than are TCR-Tregs. CAR-Tregs are promising given that they maintain stable phenotypes and functions, preferentially migrate to target sites, and exert more potent and specific immunosuppression than do polyclonal Tregs. However, there are some major hurdles that must be overcome before CAR-Tregs can be used in clinic. It is known that treatments with anti-tumor CAR-T cells cause side effects due to cytokine “storm” and neuronal cytotoxicity. It is unclear whether CAR-Tregs would also induce these adverse reactions. Moreover, antibodies specific for self- or allo-antigens must be characterized to construct antigen-specific CAR-Tregs. Selection of antigens targeted by CARs and development of specific antibodies are difficult in some disease models. Finally, CAR-Treg exhaustion may limit their efficacy in immunosuppression. Recently, innovative CAR-Treg therapies in animal models of transplantation and autoimmune diseases have been reported. In this mini-review, we have summarized recent progress of CAR-Tregs and discussed their potential applications for induction of immunological tolerance.

The growing role of precision and personalized medicine for cancer treatment

Cancer is a devastating disease that takes the lives of hundreds of thousands of people every year. Due to disease heterogeneity, standard treatments, such as chemotherapy or radiation, are effective in only a subset of the patient population. Tumors can have different underlying genetic causes and may express different proteins in one patient versus another. This inherent variability of cancer lends itself to the growing field of precision and personalized medicine (PPM). There are many ongoing efforts to acquire PPM data in order to characterize molecular differences between tumors. Some PPM products are already available to link these differences to an effective drug. It is clear that PPM cancer treatments can result in immense patient benefits, and companies and regulatory agencies have begun to recognize this. However, broader changes to the healthcare and insurance systems must be addressed if PPM is to become part of standard cancer care.

Engineering Approaches in Human Gamma Delta T Cells for Cancer Immunotherapy

Sharing both innate and adaptive immune properties, γδT cells are attractive candidates for cellular engineering. As the cancer immunotherapy field becomes increasingly busy, orthogonal approaches are required to drive advancement. Engineering of alternative effector cell types such as γδT cells represents one such approach. γδT cells can be modified using many of the techniques used in αβT cell engineering, with the added advantage of innate-like tumor recognition and killing. Progress has been made in T-cell receptor transfer to and from γδT cells as well as in a number of chimeric antigen receptor-based strategies. As the cancer immunotherapy field moves beyond repetitive iteration of established constructs to more creative solutions, γδT cells may offer an attractive chassis to drive anti-tumor responses that are not only broader, but also possess a more favorable safety profile.

Generation of V α13/β21+T cell specific target CML cells by TCR gene transfer

Adoptive immunotherapy with antigen-specific T cells can be effective for treating melanoma and chronic myeloid leukemia (CML). However, to obtain sufficient antigen-specific T cells for treatment, the T cells have to be cultured for several weeks in vitro, but in vitro T cell expansion is difficult to control. Alternatively, the transfer of T cell receptors (TCRs) with defined antigen specificity into recipient T cells may be a simple solution for generating antigen-specific T cells. The objective of this study was to identify CML-associated, antigen-specific TCR genes and generate CML-associated, antigen-specific T cells with T cell receptor (TCR) gene transfer. Our previous study has screened an oligoclonal Vβ21 with a different oligoclonal Vα partner in peripheral blood mononuclear cells (PBMCs) derived from patients with CML. In this study, oligoclonally expanded TCR α genes, which pair with TCR Vβ21, were cloned into the pIRES eukaryotic expression vector (TCR Vα-IRES-Vβ21). Next, two recombinant plasmids, TCR Vα13-IRES-Vβ21 and TCR Vα18-IRES-Vβ21, were successfully transferred into T cells, and the TCR gene-modified T cells acquired CML-specific cytotoxicity with the best cytotoxic effects for HLA-A11⁺ K562 cells observed for the TCR Vα13/Vβ21 gene redirected T cells. In summary, our data confirmed TCRVα13/Vβ21 as a CML-associated, antigen-specific TCR. This study provided new evidence that genetically engineered antigen-specific TCR may become a druggable approach for gene therapy of CML.

Engineering chimeric antigen receptor-T cells for cancer treatment

Intratumor heterogeneity of tumor clones and an immunosuppressive microenvironment in cancer ecosystems contribute to inherent difficulties for tumor treatment. Recently, chimeric antigen receptor (CAR) T-cell therapy has been successfully applied in the treatment of B-cell malignancies, underscoring its great potential in antitumor therapy. However, functional challenges of CAR-T cell therapy, especially in solid tumors, remain. Here, we describe cancer-immunity phenotypes from a clonal-stromal-immune perspective and elucidate mechanisms of T-cell exhaustion that contribute to tumor immune evasion. Then we assess the functional challenges of CAR-T cell therapy, including cell trafficking and infiltration, targeted-recognition and killing of tumor cells, T-cell proliferation and persistence, immunosuppressive microenvironment and self-control regulation. Finally, we delineate tumor precision informatics and advancements in engineered CAR-T cells to counteract inherent challenges of the CAR-T cell therapy, either alone or in combination with traditional therapeutics, and highlight the therapeutic potential of this approach in future tumor precision treatment.

CRISPR-mediated TCR replacement generates superior anticancer transgenic T cells

Adoptive transfer of T cells genetically modified to express a cancer-specific T-cell receptor (TCR) has shown significant therapeutic potential for both hematological and solid tumors. However, a major issue of transducing T cells with a transgenic TCR is the preexisting expression of TCRs in the recipient cells. These endogenous TCRs compete with the transgenic TCR for surface expression and allow mixed dimer formation. Mixed dimers, formed by mispairing between the endogenous and transgenic TCRs, may harbor autoreactive specificities. To circumvent these problems, we designed a system where the endogenous TCR-β is knocked out from the recipient cells using clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein-9 (Cas9) technology, simultaneously with transduction with a cancer-reactive receptor of choice. This TCR replacement strategy resulted in markedly increased surface expression of transgenic αβ and γδ TCRs, which in turn translated to a stronger, and more polyfunctional, response of engineered T cells to their target cancer cell lines. Additionally, the TCR-plus-CRISPR-modified T cells were up to a thousandfold more sensitive to antigen than standard TCR-transduced T cells or conventional model proxy systems used for studying TCR activity. Finally, transduction with a pan-cancer-reactive γδ TCR used in conjunction with CRISPR/Cas9 knockout of the endogenous αβ TCR resulted in more efficient redirection of CD4+ and CD8+ T cells against a panel of established blood cancers and primary, patient-derived B-cell acute lymphoblastic leukemia blasts compared with standard TCR transfer. Our results suggest that TCR transfer combined with genome editing could lead to new, improved generations of cancer immunotherapies.

Safety Strategies of Genetically Engineered T Cells in Cancer Immunotherapy

T-cell therapy using genetically engineered T cells modified with either T cell receptor or chimeric antigen receptor holds great promise for cancer immunotherapy. The concerns about its toxicities still remain despite recent successes in clinical trials. Temporal and spatial control of the engineered therapeutic T cells may improve the safety profile of these treatment regimens. To achieve these goals, numerous approaches have been tested and utilized including the incorporation of a suicide gene, the switch-mediated activation, the combinatorial antigen recognition, etc. This review will summarize the toxicities caused by engineered T cells and novel strategies to overcome them.

In-vitro blockade of the CD4 receptor co-signal in antigen-specific T-cell stimulation cultures induces the outgrowth of potent CD4 independent T-cell effectors

T-cell receptor (TCR) redirected T cells are promising tools for adoptive cancer immunotherapy. Since not only CD8 but also CD4 T cells are key players for efficient antitumor responses, the targeted redirection of both subsets with the same antigen-specific TCR comes more and more into focus. Although rapidly evolving technologies enable the reliable genetic re-programming of T cells, the limited availability of TCRs that induce T-cell activation in both T-cell subsets without CD4/CD8 co-receptor contribution hampers the broad application of this approach. We developed a novel stimulation approach, which drives the activation and proliferation of CD4 T-cell populations capable of inducing effector functions in a CD4-independent manner. Naive-enriched CD4 T cells were stimulated against dendritic cells (DC) expressing allogeneic HLA-DP antigens upon RNA transfection and CD4/HLA interactions were blocked by the addition of CD4 binding antibody. Evolving CD4 T-cell populations were specifically activated independent of the CD4 co-signal and induced strong TCR-mediated IFN-γ secretion as well as cytolysis upon recognition of leukemia cells expressing HLA-DP antigen. Our novel stimulation approach may facilitate the generation of CD4 T cells as source for co-receptor independent TCRs for future immunotherapies.

T cells expressing chimeric antigen receptor promote immune tolerance

Cellular therapies based on permanent genetic modification of conventional T cells have emerged as a promising strategy for cancer. However, it remains unknown if modification of T cell subsets, such as Tregs, could be useful in other settings, such as allograft transplantation. Here, we use a modular system based on a chimeric antigen receptor (CAR) that binds covalently modified mAbs to control Treg activation in vivo. Transient expression of this mAb-directed CAR (mAbCAR) in Tregs permitted Treg targeting to specific tissue sites and mitigated allograft responses, such as graft-versus-host disease. mAbCAR Tregs targeted to MHC class I proteins on allografts prolonged islet allograft survival and also prolonged the survival of secondary skin grafts specifically matched to the original islet allograft. Thus, transient genetic modification to produce mAbCAR T cells led to durable immune modulation, suggesting therapeutic targeting strategies for controlling alloreactivity in settings such as organ or tissue transplantation.

New targeted therapies for relapsed pediatric acute lymphoblastic leukemia

INTRODUCTION

The improvement in outcomes for children with acute lymphoblastic leukemia (ALL) is one of the greatest success stories of modern oncology however the prognosis for patients who relapse remains dismal. Recent discoveries by high resolution genomic technologies have characterized the biology of relapsed leukemia, most notably pathways leading to the drug resistant phenotype. These observations open the possibility of targeting such pathways to prevent and/or treat relapse. Likewise, early experiences with new immunotherapeutic approaches have shown great promise. Areas covered: We performed a literature search on PubMed and recent meeting abstracts using the keywords below. We focused on the biology and clonal evolution of relapsed disease highlighting potential new targets of therapy. We further summarized the results of early trials of the three most prominent immunotherapy agents currently under investigation. Expert commentary: Discovery of targetable pathways that lead to drug resistance and recent breakthroughs in immunotherapy show great promise towards treating this aggressive disease. The best way to treat relapse, however, is to prevent it which makes incorporation of these new approaches into frontline therapy the best approach. Challenges remain to balance efficacy with toxicity and to prevent the emergence of resistant subclones which is why combining these newer agents with conventional chemotherapy will likely become standard of care.

Tumor-targeting domains for chimeric antigen receptor T cells

Immunotherapy with chimeric antigen receptor (CAR) T cells has been advancing steadily in clinical trials. Since the ability of engineered T cells to recognize intended tumor-associated targets is crucial for the therapeutic success, antigen-binding domains play an important role in shaping T-cell responses. Single-chain antibody and T-cell receptor fragments, natural ligands, repeat proteins, combinations of the above and universal tag-specific domains have all been used in the antigen-binding moiety of chimeric receptors. Here we outline the advantages and disadvantages of different domains, discuss the concepts of affinity and specificity, and highlight the recent progress of each targeting strategy.