CRISPR-Cas9 mediated efficient PD-1 disruption on human primary T cells from cancer patients

TCR Redirected T Cells for Cancer Treatment: Achievements, Hurdles, and Goals

Adoptive T cell therapy (ACT) is a rapidly evolving therapeutic approach designed to harness T cell specificity and function to fight diseases. Based on the evidence that T lymphocytes can mediate a potent anti-tumor response, initially ACT solely relied on the isolation, in vitro expansion, and infusion of tumor-infiltrating or circulating tumor-specific T cells. Although effective in a subset of cases, in the first ACT clinical trials several patients experienced disease progression, in some cases after temporary disease control. This evidence prompted researchers to improve ACT products by taking advantage of the continuously evolving gene engineering field and by improving manufacturing protocols, to enable the generation of effective and long-term persisting tumor-specific T cell products. Despite recent advances, several challenges, including prioritization of antigen targets, identification, and optimization of tumor-specific T cell receptors, in the development of tools enabling T cells to counteract the immunosuppressive tumor microenvironment, still need to be faced. This review aims at summarizing the major achievements, hurdles and possible solutions designed to improve the ACT efficacy and safety profile in the context of liquid and solid tumors.

CRISPR/Cas9 in Cancer Immunotherapy: Animal Models and Human Clinical Trials

Even though chemotherapy and immunotherapy emerged to limit continual and unregulated proliferation of cancer cells, currently available therapeutic agents are associated with high toxicity levels and low success rates. Additionally, ongoing multi-targeted therapies are limited only for few carcinogenesis pathways, due to continually emerging and evolving mutations of proto-oncogenes and tumor-suppressive genes. CRISPR/Cas9, as a specific gene-editing tool, is used to correct causative mutations with minimal toxicity, but is also employed as an adjuvant to immunotherapy to achieve a more robust immunological response. Some of the most critical limitations of the CRISPR/Cas9 technology include off-target mutations, resulting in nonspecific restrictions of DNA upstream of the Protospacer Adjacent Motifs (PAM), ethical agreements, and the lack of a scientific consensus aiming at risk evaluation. Currently, CRISPR/Cas9 is tested on animal models to enhance genome editing specificity and induce a stronger anti-tumor response. Moreover, ongoing clinical trials use the CRISPR/Cas9 system in immune cells to modify genomes in a target-specific manner. Recently, error-free in vitro systems have been engineered to overcome limitations of this gene-editing system. The aim of the article is to present the knowledge concerning the use of CRISPR Cas9 technique in targeting treatment-resistant cancers. Additionally, the use of CRISPR/Cas9 is aided as an emerging supplementation of immunotherapy, currently used in experimental oncology. Demonstrating further, applications and advances of the CRISPR/Cas9 technique are presented in animal models and human clinical trials. Concluding, an overview of the limitations of the gene-editing tool is proffered.

A brief review concerning Chimeric Antigen Receptors T cell therapy

The understanding concerning the function of immune system in cancer has achieved considerable advance with time passes by. Manipulating genetically engineered immune cells were investigated as a novel strategy for treating cancer. Chimeric antigen receptors (CARs) are recombinant protein molecules by merging the exquisite targeting the potent cytotoxicity of T cells and specificity of monoclonal antibodies and, which could trigger serial cascades of signal transduction and thereby activate T cells to directly destroy the tumor cells. Manufacturing CAR-modified T lymphocytes were successfully implemented in treating cancer derived from they could specifically retarget tumor-associated antigens, causing effective elimination of tumor cells, which spurred the optimization and development of new CAR-T cell technology. The advancement of synthetic biology methodologies of cell therapy in CAR-T would ultimately provide us with a much safer, reliable and efficient modality to against cancer. This review primarily described the emergence, development and application of cell therapy in CAR-T, then discuss the side effects and the potential factors of tumor reccurrence caused by CAR-T cell therapy, in addition to the corresponding countermeasure concerning complications.

Identification of Clonal Neoantigens Derived From Driver Mutations in an EGFR-Mutated Lung Cancer Patient Benefitting From Anti-PD-1

Epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors (TKIs) have been recommended as the first-line therapy for non-small cell lung cancer (NSCLC) patients harboring EGFR mutations. However, acquired resistance to EGFR-TKIs is inevitable. Although immune checkpoint blockades (ICBs) targeting the programmed cell death 1 (PD-1)/PD-ligand (L)1 axis have achieved clinical success for many cancer types, the clinical efficacy of anti-PD-1/PD-L1 blockades in EGFR mutated NSCLC patients has been demonstrated to be lower than those without EGFR mutations. Here, we reported an advanced NSCLC patient with EGFR driver mutations benefitting from anti-PD-1 blockade therapy after acquiring resistance to EGFR-TKI. We characterized the mutational landscape of the patient with next-generation sequencing (NGS) and successfully identified specific T-cell responses to clonal neoantigens encoded by EGFR exon 19 deletion, TP53 A116T and DENND6B R398Q mutations. Our findings support the potential application of immune checkpoint blockades in NSCLC patients with acquired resistance to EGFR-TKIs in the context of specific clonal neoantigens with high immunogenicity. Personalized immunomodulatory therapy targeting these neoantigens should be explored for better clinical outcomes in EGFR mutated NSCLC patients.

A high-throughput small molecule screen identifies farrerol as a potentiator of CRISPR/Cas9-mediated genome editing

Directly modulating the choice between homologous recombination (HR) and non-homologous end joining (NHEJ) - two independent pathways for repairing DNA double-strand breaks (DSBs) - has the potential to improve the efficiency of gene targeting by CRISPR/Cas9. Here, we have developed a rapid and easy-to-score screening approach for identifying small molecules that affect the choice between the two DSB repair pathways. Using this tool, we identified a small molecule, farrerol, that promotes HR but does not affect NHEJ. Further mechanistic studies indicate that farrerol functions through stimulating the recruitment of RAD51 to DSB sites. Importantly, we demonstrated that farrerol effectively promotes precise targeted integration in human cells, mouse cells and mouse embryos at multiple genomic loci. In addition, treating cells with farrerol did not have any obvious negative effect on genomic stability. Moreover, farrerol significantly improved the knock-in efficiency in blastocysts, and the subsequently generated knock-in mice retained the capacity for germline transmission.

T-Cell Receptor-Based Immunotherapy for Hematologic Malignancies

Adoptive immunotherapy with engineered T cells is at the forefront of cancer treatment. T cells can be engineered to express T-cell receptors (TCRs) specific for tumor-associated antigens (TAAs) derived from intracellular or cell surface proteins. T cells engineered with TCRs (TCR-T) allow for targeting diverse types of TAAs, including proteins overexpressed in malignant cells, those with lineage-restricted expression, cancer-testis antigens, and neoantigens created from abnormal, malignancy-restricted proteins. Minor histocompatibility antigens can also serve as TAAs for TCR-T to treat relapsed hematologic malignancies after allogeneic hematopoietic cell transplantation. Moreover, TCR constructs can be modified to improve safety and enhance function and persistence of TCR-T. Transgenic T-cell receptor therapies targeting 3 different TAAs are in early-phase clinical trials for treatment of hematologic malignancies. Preclinical studies of TCR-T specific for many other TAAs are underway and offer great promise as safe and effective therapies for a wide range of cancers.

Engineering Strategies to Enhance TCR-Based Adoptive T Cell Therapy

T cell receptor (TCR)-based adoptive T cell therapies (ACT) hold great promise for the treatment of cancer, as TCRs can cover a broad range of target antigens. Here we summarize basic, translational and clinical results that provide insight into the challenges and opportunities of TCR-based ACT. We review the characteristics of target antigens and conventional αβ-TCRs, and provide a summary of published clinical trials with TCR-transgenic T cell therapies. We discuss how synthetic biology and innovative engineering strategies are poised to provide solutions for overcoming current limitations, that include functional avidity, MHC restriction, and most importantly, the tumor microenvironment. We also highlight the impact of precision genome editing on the next iteration of TCR-transgenic T cell therapies, and the discovery of novel immune engineering targets. We are convinced that some of these innovations will enable the field to move TCR gene therapy to the next level.

Generation, ex vivo expansion and safety of engineered PD1-knockout primary T cells from cynomolgus macaques

Programmed cell death protein 1 (PD1) is a cell-surface receptor that plays a vital regulatory role in suppressing inflammatory T cell activity; therefore, it is an ideal target for T cell-redirecting therapies. Here, we describe a cynomolgus macaque model for studying the transfer of PD1-modified T cells. We developed the first T cell engager targeting the disruption of PD1 by electroporation of plasmids encoding sgRNA and Cas9. There were no significant differences between mock T cells and PD1-knockout (PD1-KO) T cells in terms of cell viability, T cell signature marker expression, cell apoptosis, or cell cycling during prolonged in vitro culture. However, in a mixed lymphocyte reaction, PD1-KO T cells exhibited increased proliferation for both CD4+ and CD8+T cells and enhanced IFNγ release. We adoptively transferred autologous PD1-KO T cells into three cynomolgus monkeys. The PD1-KO T cells did not cause overt toxicity as measured by evaluating body weight, hematological parameters, and blood chemistry parameters. Histopathological analyses of tissues showed no lesions related to the infused PD1-KO T cells. Our findings demonstrate the utility of cynomolgus monkeys in expanding PD1-KO T cells and evaluating the safety of this immunotherapy and provide a new strategy for T cell-based adoptive cell therapies.

The Role of Immune Checkpoints after Cellular Therapy

Cellular therapies utilize the powerful force of the human immune system to target malignant cells. Allogeneic hematopoietic stem cell transplantation (allo-HCT) is the most established cellular therapy, but chimeric antigen receptor (CAR) T cell therapies have gained attention in recent years. While in allo-HCT an entirely novel allogeneic immune system facilitates a so-called Graft-versus-tumor, respectively, Graft-versus-leukemia (GvT/GvL) effect against high-risk hematologic malignancies, in CAR T cell therapies genetically modified autologous T cells specifically attack target molecules on malignant cells. These therapies have achieved high success rates, offering potential cures in otherwise detrimental diseases. However, relapse after cellular therapy remains a serious clinical obstacle. Checkpoint Inhibition (CI), which was recently designated as breakthrough in cancer treatment and consequently awarded with the Nobel prize in 2018, is a different way to increase anti-tumor immunity. Here, inhibitory immune checkpoints are blocked on immune cells in order to restore the immunological force against malignant diseases. Disease relapse after CAR T cell therapy or allo-HCT has been linked to up-regulation of immune checkpoints that render cancer cells resistant to the cell-mediated anti-cancer immune effects. Thus, enhancing immune cell function after cellular therapies using CI is an important treatment option that might re-activate the anti-cancer effect upon cell therapy. In this review, we will summarize current data on this topic with the focus on immune checkpoints after cellular therapy for malignant diseases and balance efficacy versus potential side effects.

Pooled Knockin Targeting for Genome Engineering of Cellular Immunotherapies

Adoptive transfer of genetically modified immune cells holds great promise for cancer immunotherapy. CRISPR knockin targeting can improve cell therapies, but more high-throughput methods are needed to test which knockin gene constructs most potently enhance primary cell functions in vivo. We developed a widely adaptable technology to barcode and track targeted integrations of large non-viral DNA templates and applied it to perform pooled knockin screens in primary human T cells. Pooled knockin of dozens of unique barcoded templates into the T cell receptor (TCR)-locus revealed gene constructs that enhanced fitness in vitro and in vivo. We further developed pooled knockin sequencing (PoKI-seq), combining single-cell transcriptome analysis and pooled knockin screening to measure cell abundance and cell state ex vivo and in vivo. This platform nominated a novel transforming growth factor β (TGF-β) R2-41BB chimeric receptor that improved solid tumor clearance. Pooled knockin screening enables parallelized re-writing of endogenous genetic sequences to accelerate discovery of knockin programs for cell therapies.

Therapeutic status and the prospect of CRISPR/Cas9 gene editing in multiple myeloma

In recent years, CRISPR/Cas9, a novel gene-editing technology, has shown considerable potential in the design of novel research methods and future options for treating multiple myeloma (MM). The use of CRISPR/Cas9 promises faster and more accurate identification and validation of target genes. In this review, we summarize the current research status of the application of CRISPR technology in MM, especially in detecting the expression of MM gene, exploring the mechanism of drug action, screening for drug-resistant genes, developing immunotherapy and screening for new drug targets. Given the tremendous progress that has been made, we believe that CRISPR/Cas9 possesses great potential in MM-related clinical practice.

Genetic Ablation of HLA Class I, Class II, and the T-cell Receptor Enables Allogeneic T Cells to Be Used for Adoptive T-cell Therapy

Adoptive immunotherapy can induce sustained therapeutic effects in some cancers. Antitumor T-cell grafts are often individually prepared in vitro from autologous T cells, which requires an intensive workload and increased costs. The quality of the generated T cells can also be variable, which affects the therapy's antitumor efficacy and toxicity. Standardized production of antitumor T-cell grafts from third-party donors will enable widespread use of this modality if allogeneic T-cell responses are effectively controlled. Here, we generated HLA class I, HLA class II, and T-cell receptor (TCR) triple-knockout (tKO) T cells by simultaneous knockout of the B2M, CIITA, and TRAC genes through Cas9/sgRNA ribonucleoprotein electroporation. Although HLA-deficient T cells were targeted by natural killer cells, they persisted better than HLA-sufficient T cells in the presence of allogeneic peripheral blood mononuclear cells (PBMC) in immunodeficient mice. When transduced with a CD19 chimeric antigen receptor (CAR) and stimulated by tumor cells, tKO CAR-T cells persisted better when cultured with allogeneic PBMCs compared with TRAC and B2M double-knockout T cells. The CD19 tKO CAR-T cells did not induce graft-versus-host disease but retained antitumor responses. These results demonstrated the benefit of HLA class I, HLA class II, and TCR deletion in enabling allogeneic-sourced T cells to be used for off-the-shelf adoptive immunotherapy.

Effect of CRISPR/Cas9-Mediated PD-1-Disrupted Primary Human Third-Generation CAR-T Cells Targeting EGFRvIII on In Vitro Human Glioblastoma Cell Growth

Glioblastoma (GBM), which is the most common malignant brain tumor, is resistant to standard treatments. Immunotherapy might be a promising alternative for the treatment of this cancer. Chimeric antigen receptor (CAR) is an artificially modified fusion protein that can be engineered to direct the specificity and function of T cells against tumor antigens. However, the antitumor effects of EGFRvIII-targeting CAR-T (EvCAR-T) cells in GBM are limited. The inhibitory effect is induced by the interaction between programmed cell death protein 1 (PD-1) on activated EvCAR-T cells and its ligands on GBM cells. In the present study, PD-1-disrupted EvCAR-T cells were established using the clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9). The sgRNA/Cas9 expression vectors designed precisely disrupted the target region of PD-1 and inhibited the expression of PD-1 in EvCAR-T cells. The PD-1-disrupted EvCAR-T cells had an in vitro growth inhibitory effect on EGFRvIII-expressing GBM cells without altering the T-cell phenotype and the expression of other checkpoint receptors. In the future, the in vivo antitumor effect of this vector should be evaluated in order to determine if it could be applied clinically for improving the efficacy of EvCAR-T cell-based adoptive immunotherapy for GBM.

Ex vivo cell-based CRISPR/Cas9 genome editing for therapeutic applications

The recently developed CRISPR/Cas9 technology has revolutionized the genome engineering field. Since 2016, increasing number of studies regarding CRISPR therapeutics have entered clinical trials, most of which are focusing on the ex vivo genome editing. In this review, we highlight the ex vivo cell-based CRISPR/Cas9 genome editing for therapeutic applications. In these studies, CRISPR/Cas9 tools were used to edit cells in vitro and the successfully edited cells were considered as therapeutics, which can be introduced into patients to treat diseases. Considering a large number of previous reviews have been focused on the CRISPR/Cas9 delivery methods and materials, this review provides a different perspective, by mainly introducing the targeted conditions and design strategies for ex vivo CRISPR/Cas9 therapeutics. Brief descriptions of the history, functionality, and applications of CRISPR/Cas9 systems will be introduced first, followed by the design strategies and most significant results from previous research that used ex vivo CRISPR/Cas9 genome editing for the treatment of conditions or diseases. The last part of this review includes general information about the status of CRISPR/Cas9 therapeutics in clinical trials. We also discuss some of the challenges as well as the opportunities in this research area.

CRISPR-engineered T cells in patients with refractory cancer

CRISPR-Cas9 gene editing provides a powerful tool to enhance the natural ability of human T cells to fight cancer. We report a first-in-human phase 1 clinical trial to test the safety and feasibility of multiplex CRISPR-Cas9 editing to engineer T cells in three patients with refractory cancer. Two genes encoding the endogenous T cell receptor (TCR) chains, TCRα (TRAC) and TCRβ (TRBC), were deleted in T cells to reduce TCR mispairing and to enhance the expression of a synthetic, cancer-specific TCR transgene (NY-ESO-1). Removal of a third gene encoding programmed cell death protein 1 (PD-1; PDCD1), was performed to improve antitumor immunity. Adoptive transfer of engineered T cells into patients resulted in durable engraftment with edits at all three genomic loci. Although chromosomal translocations were detected, the frequency decreased over time. Modified T cells persisted for up to 9 months, suggesting that immunogenicity is minimal under these conditions and demonstrating the feasibility of CRISPR gene editing for cancer immunotherapy.

Locus-specific DNA methylation of Mecp2 promoter leads to autism-like phenotypes in mice

Autism spectrum disorder (ASD) is a neurodevelopmental disease with a strong heritability, but recent evidence suggests that epigenetic dysregulation may also contribute to the pathogenesis of ASD. Especially, increased methylation at the MECP2 promoter and decreased MECP2 expression were observed in the brains of ASD patients. However, the causative relationship of MECP2 promoter methylation and ASD has not been established. In this study, we achieved locus-specific methylation at the transcription start site (TSS) of Mecp2 in Neuro-2a cells and in mice, using nuclease-deactivated Cas9 (dCas9) fused with DNA methyltransferase catalytic domains, together with five locus-targeting sgRNAs. This locus-specific epigenetic modification led to a reduced Mecp2 expression and a series of behavioral alterations in mice, including reduced social interaction, increased grooming, enhanced anxiety/depression, and poor performance in memory tasks. We further found that specifically increasing the Mecp2 promoter methylation in the hippocampus was sufficient to induce most of the behavioral changes. Our finding therefore demonstrated for the first time the casual relationship between locus-specific DNA methylation and diseases symptoms in vivo, warranting potential therapeutic application of epigenetic editing.

Sharpening the Molecular Scissors: Advances in Gene-Editing Technology

The ability to precisely modify human genes has been made possible by the development of tools such as meganucleases, zinc finger nucleases, TALENs, and CRISPR/Cas. These now make it possible to generate targeted deletions, insertions, gene knock outs, and point variants; to modulate gene expression by targeting transcription factors or epigenetic machineries to DNA; or to target and modify RNA. Endogenous repair mechanisms are used to make the modifications required in DNA; they include non-homologous end joining, homology-directed repair, homology-independent targeted integration, microhomology-mediated end joining, base-excision repair, and mismatch repair. Off-target effects can be monitored using in silico prediction and sequencing and minimized using Cas proteins with higher accuracy, such as high-fidelity Cas9, enhanced-specificity Cas9, and hyperaccurate Cas9. Alternatives to Cas9 have been identified, including Cpf1, Cas12a, Cas12b, and smaller Cas9 orthologs such as CjCas9. Delivery of gene-editing components is performed ex vivo using standard techniques or in vivo using AAV, lipid nanoparticles, or cell-penetrating peptides. Clinical development of gene-editing technology is progressing in several fields, including immunotherapy in cancer treatment, antiviral therapy for HIV infection, and treatment of genetic disorders such as β-thalassemia, sickle cell disease, lysosomal storage disorders, and retinal dystrophy. Here we review these technological advances and the challenges to their clinical implementation.

Engineering T Cells Using CRISPR/Cas9 for Cancer Therapy

Recent advances in the development of gene editing technologies, especially the CRISPR/Cas 9 system, have substantially enhanced our ability to make precise and efficient changes in the genomes of various cells. In particular, the genetic engineering of T cells holds huge potential to improve the efficacy and safety of T cells-based cancer therapy. Due to its ease of use and high efficiency, CRISPR/Cas9 enables efficient gene knockout, site-specific knock-in, and genome-wide screen in T cells. Here we review the current progress of applying gene editing to T-cell therapy, focusing on the technical aspects of the CRISPR/Cas9 platform. We also discuss the challenges and future prospects.

PD-1 disrupted CAR-T cells in the treatment of solid tumors: Promises and challenges

Unprecedented efficacy of chimeric antigen receptor (CAR) T cell therapy in the treatment of hematologic malignancies brings new hope for patients with many cancer types including solid tumors. However, the challenges for CAR-T cell therapy in eradicating solid tumors are immense. To overcome these seemingly intractable hurdles, more "powerful" CAR-T cells with enhanced antitumor efficacy are required. Emerging data support that the anti-tumor activity of CAR-T cells can be enhanced significantly without evident toxicity through simultaneous PD-1 disruption by genome editing. This review focuses on the current progress of PD-1 gene disrupted CAR-T cells in cancer therapy. Here we discuss key rationales for this new combination strategy and summarize the available pre-clinical studies. An update is provided on human clinical studies and available registered cancer clinical trials using CAR-T cells with PD-1 disruption. Future prospects and challenges are also discussed.

Chimeric antigen receptor T cells in solid tumors: a war against the tumor microenvironment

Chimeric antigen receptor (CAR) T cell is a novel approach, which utilizes anti-tumor immunity for cancer treatment. As compared to the traditional cell-mediated immunity, CAR-T possesses the improved specificity of tumor antigens and independent cytotoxicity from major histocompatibility complex molecules through a monoclonal antibody in addition to the T-cell receptor. CAR-T cell has proven its effectiveness, primarily in hematological malignancies, specifically where the CD 19 CAR-T cells were used to treat B-cell acute lymphoblastic leukemia and B-cell lymphomas. Nevertheless, there is little progress in the treatment of solid tumors despite the fact that many CAR agents have been created to target tumor antigens such as CEA, EGFR/EGFRvIII, GD2, HER2, MSLN, MUC1, and other antigens. The main obstruction against the progress of research in solid tumors is the tumor microenvironment, in which several elements, such as poor locating ability, immunosuppressive cells, cytokines, chemokines, immunosuppressive checkpoints, inhibitory metabolic factors, tumor antigen loss, and antigen heterogeneity, could affect the potency of CAR-T cells. To overcome these hurdles, researchers have reconstructed the CAR-T cells in various ways. The purpose of this review is to summarize the current research in this field, analyze the mechanisms of the major barriers mentioned above, outline the main solutions, and discuss the outlook of this novel immunotherapeutic modality.

Overcoming malignant cell-based mechanisms of resistance to immune checkpoint blockade antibodies

Traditional cancer treatment approaches have focused on surgery, radiation therapy, and cytotoxic chemotherapy. However, with rare exceptions, metastatic cancers were considered to be incurable by traditional therapy. Over the past 20 years a fourth modality - immunotherapy - has emerged as a potentially curative approach for patients with advanced metastatic cancer. However, in many patients cancer "finds a way" to evade the anti-tumor effects of immunotherapy. Immunotherapy resistance mechanisms can be employed by both cancer cells and the non-cancer elements of tumor microenvironment. This review focuses on the resistance mechanisms that are specifically mediated by cancer cells. In order to extend the impact of immunotherapy to more patients and across all cancer types, and to inhibit the development of acquired resistance, the underlying biology driving immune escape needs to be better understood. Elucidating mechanisms of immune escape may shed light on new therapeutic targets, and lead to successful combination therapeutic strategies.

Knockout Of BIRC5 Gene By CRISPR/Cas9 Induces Apoptosis And Inhibits Cell Proliferation In Leukemic Cell Lines, HL60 And KG1

INTRODUCTION

Human Baculoviral inhibitor of apoptosis repeat-containing 5 (BIRC5) which encodes survivin exhibits multiple biological activities, such as cell proliferation and apoptosis. Survivin is overexpressed in numerous malignant diseases including acute myeloid leukemia (AML). Recent studies have shown that the CRISPR/Cas9 nuclease-mediated gene-editing systems are suitable approach's for editing or knocking out various genes including oncogenes.

METHODS AND MATERIALS

We used CRISPR-Cas9 to knockout the BIRC5 in the human leukemic cell line, HL60, and KG1, and these cell lines were transfected with either the Cas9- and three sgRNAs expressing plasmids or negative control (scramble) using Lipofectamine 3000. The efficacy of the transfection was determined by quantitative reverse transcription-polymerase chain (RT-qPCR) and surveyor mutation assays. Cell proliferation and apoptosis were measured by MTT assay and flow cytometry, respectively.

RESULTS

We have successfully knocked out the BIRC5 gene in these leukemic cells and observed that the BIRC5-knocked out cells by CRISPR/Cas9 showed a significant decrease (30 folds) of survivin at mRNA levels. Moreover, cell death and apoptosis were significantly induced in BIRC5-CRISPR/Cas9-transfected cells compared to the scramble vector.

CONCLUSION

We demonstrated for the first time that targeting BIRC5 by CRISPR/Cas9 technology is a suitable approach for the induction of apoptosis in leukemic cells. However, further studies targeting this gene in primary leukemic cells are required.

CRISPR-Cas9 disruption of PD-1 enhances activity of universal EGFRvIII CAR T cells in a preclinical model of human glioblastoma

Despite remarkable success in the treatment of hematological malignancies, CAR T-cell therapies for solid tumors have floundered, in large part due to local immune suppression and the effects of prolonged stimulation leading to T-cell dysfunction and exhaustion. One mechanism by which gliomas and other cancers can hamper CAR T cells is through surface expression of inhibitory ligands such as programmed cell death ligand 1 (PD-L1). Using the CRIPSR-Cas9 system, we created universal CAR T cells resistant to PD-1 inhibition through multiplexed gene disruption of endogenous T-cell receptor (TRAC), beta-2 microglobulin (B2M) and PD-1 (PDCD1). Triple gene-edited CAR T cells demonstrated enhanced activity in preclinical glioma models. Prolonged survival in mice bearing intracranial tumors was achieved after intracerebral, but not intravenous administration. CRISPR-Cas9 gene-editing not only provides a potential source of allogeneic, universal donor cells, but also enables simultaneous disruption of checkpoint signaling that otherwise impedes maximal antitumor functionality.

Nanoparticles for nucleic acid delivery: Applications in cancer immunotherapy

Immunotherapy has recently emerged as a powerful tool for cancer treatment. Early clinical successes from cancer immunotherapy have led to a growing list of FDA approvals, and many new therapies are in clinical and preclinical development. Nucleic acid therapeutics, including DNA, mRNA, and genome editing systems, hold significant potential as a form of immunotherapy due to its robust use in cancer vaccination, adoptive T-cell therapy, and gene regulation. However, these therapeutics must overcome numerous delivery obstacles to be successful, including rapid in vivo degradation, poor uptake into target cells, required nuclear entry, and potential in vivo toxicity in healthy cells and tissues. Nanoparticle delivery systems have been engineered to overcome several of these barriers as a means to safely and effectively deliver nucleic acid therapeutics to immune cells. In this Review, we discuss the applications of nucleic acid therapeutics in cancer immunotherapy, and we detail how nanoparticle platforms have been designed to deliver mRNA, DNA, and genome editing systems to enhance the potency and safety of these therapeutics.

Systematic Immunotherapy Target Discovery Using Genome-Scale In Vivo CRISPR Screens in CD8 T Cells

CD8 T cells play essential roles in anti-tumor immune responses. Here, we performed genome-scale CRISPR screens in CD8 T cells directly under cancer immunotherapy settings and identified regulators of tumor infiltration and degranulation. The in vivo screen robustly re-identified canonical immunotherapy targets such as PD-1 and Tim-3, along with genes that have not been characterized in T cells. The infiltration and degranulation screens converged on an RNA helicase Dhx37. Dhx37 knockout enhanced the efficacy of antigen-specific CD8 T cells against triple-negative breast cancer in vivo. Immunological characterization in mouse and human CD8 T cells revealed that DHX37 suppresses effector functions, cytokine production, and T cell activation. Transcriptomic profiling and biochemical interrogation revealed a role for DHX37 in modulating NF-κB. These data demonstrate high-throughput in vivo genetic screens for immunotherapy target discovery and establishes DHX37 as a functional regulator of CD8 T cells.

PD-1 silencing impairs the anti-tumor function of chimeric antigen receptor modified T cells by inhibiting proliferation activity

BACKGROUND

Blocking programmed death-1 (PD-1) is considered to be a promising strategy to improve T cell function, and this is being explored in many ongoing clinical trials. In fact, our knowledge about PD-1 is primarily based on the results of short-term experiments or observations, but how long-lasting PD-1 blockade can affect T cell function remains unclear.

METHODS

We planned to use shRNA-based gene knockdown technology to mimic long-lasting PD-1 blockade. We constructed PD-1 steadily blocked chimeric antigen receptor modified T (CAR-T) cells, and with these cells we can clearly study the effects of PD-1 knockdown on T cell function. The anti-tumor function, proliferation ability and differentiation status of PD-1 silenced CAR-T cells were studied by in vitro and animal experiments.

RESULTS

According to short-term in vitro results, it was reconfirmed that the resistance to programmed death-ligand 1 (PD-L1)-mediated immunosuppression could be enhanced by PD-1 blockade. However, better anti-tumor function was not presented by PD-1 blocked CAR-T cells in vitro or in vivo experiments. It was found that PD-1 knockdownmight impair the anti-tumor potential of CAR-T cells because it inhibited T cells' proliferation activity. In addition, we observed that PD-1 blockade would accelerate T cells' early differentiation and prevent effector T cells from differentiating into effect memory T cells, and this might be the reason for the limited proliferation of PD-1 silenced CAR-T cells.

CONCLUSION

These results suggest that PD-1 might play an important role in maintaining the proper proliferation and differentiation of T cells, and PD-1 silencing would impair T cells' anti-tumor function by inhibiting their proliferation activity.

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.

Therapeutic potential of CRISPR/Cas9 gene editing in engineered T-cell therapy

Cancer patients have been treated with various types of therapies, including conventional strategies like chemo-, radio-, and targeted therapy, as well as immunotherapy like checkpoint inhibitors, vaccine and cell therapy etc. Among the therapeutic alternatives, T-cell therapy like CAR-T (Chimeric Antigen Receptor Engineered T cell) and TCR-T (T Cell Receptor Engineered T cell), has emerged as the most promising therapeutics due to its impressive clinical efficacy. However, there are many challenges and obstacles, such as immunosuppressive tumor microenvironment, manufacturing complexity, and poor infiltration of engrafted cells, etc still, need to be overcome for further treatment with different forms of cancer. Recently, the antitumor activities of CAR-T and TCR-T cells have shown great improvement with the utilization of CRISPR/Cas9 gene editing technology. Thus, the genome editing system could be a powerful genetic tool to use for manipulating T cells and enhancing the efficacy of cell immunotherapy. This review focuses on pros and cons of various gene delivery methods, challenges, and safety issues of CRISPR/Cas9 gene editing application in T-cell-based immunotherapy.

Acquired resistance to cancer immunotherapy: Role of tumor-mediated immunosuppression

In the tumor microenvironment (TME), tumor cells are constantly evolving to reduce neoantigen generation and the mutational burden to escape the anti-tumor response. This will lower tumor reactivity to the adaptive immune response and give rise to tumor intrinsic factors, such as altered expression of immune regulatory molecules on tumor cells. Tumor-extrinsic factors, such as immunosuppressive cells, soluble suppressive molecules or inhibitory receptors expressed by immune cells will alter the composition and activity of tumor-infiltrating lymphocytes (TILs) (by increasing T regulatory cells:T effector cells ratio and inhibiting T effector cell function) and promote tumor growth and metastasis. Together, these factors limit the response rates and clinical outcomes to a particular cancer therapy. Within the TME, the cross-talks between immune and non-immune cells result in the generation of positive feedback loops, which augment immunosuppression and support tumor growth and survival (termed as tumor-mediated immunosuppression). Cancer immunotherapies, such as immune checkpoint inhibitors (ICIs) and adoptive cell transfer (ACT), have shown therapeutic efficacy in hematologic cancers and different types of solid tumors. However, achieving durable response rates in some cancer patients remains a challenge as a result of acquired resistance and tumor immune evasion. This could be driven by the cellular and molecular suppressive network within the TME or due to the loss of tumor antigens. In this review, we describe the contribution of the immunosuppressive cellular and molecular tumor network to the development of acquired resistance against cancer immunotherapies. We also discuss potential combined therapeutic strategies which could help to overcome such resistance against cancer immunotherapies, and to enhance anti-tumor immune responses and improve clinical outcomes in patients.

Engineered Adoptive T-cell Therapy Prolongs Survival in a Preclinical Model of Advanced-Stage Ovarian Cancer

Adoptive T-cell therapy using high-affinity T-cell receptors (TCR) to target tumor antigens has potential for improving outcomes in high-grade serous ovarian cancer (HGSOC) patients. Ovarian tumors develop a hostile, multicomponent tumor microenvironment containing suppressive cells, inhibitory ligands, and soluble factors that facilitate evasion of antitumor immune responses. Developing and validating an immunocompetent mouse model of metastatic ovarian cancer that shares antigenic and immunosuppressive qualities of human disease would facilitate establishing effective T-cell therapies. We used deep transcriptome profiling and IHC analysis of human HGSOC tumors and disseminated mouse ID8_VEGF tumors to compare immunologic features. We then evaluated the ability of CD8 T cells engineered to express a high-affinity TCR specific for mesothelin, an ovarian cancer antigen, to infiltrate advanced ID8_VEGF murine ovarian tumors and control tumor growth. Human CD8 T cells engineered to target mesothelin were also evaluated for ability to kill HLA-A2⁺ HGSOC lines. IHC and gene-expression profiling revealed striking similarities between tumors of both species, including processing/presentation of a leading candidate target antigen, suppressive immune cell infiltration, and expression of molecules that inhibit T-cell function. Engineered T cells targeting mesothelin infiltrated mouse tumors but became progressively dysfunctional and failed to persist. Treatment with repeated doses of T cells maintained functional activity, significantly prolonging survival of mice harboring late-stage disease at treatment onset. Human CD8 T cells engineered to target mesothelin were tumoricidal for three HGSOC lines. Treatment with engineered T cells may have clinical applicability in patients with advanced-stage HGSOC.

Clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 with improved proof-reading enhances homology-directed repair

Genome editing using clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) predominantly induces non-homologous end joining (NHEJ), which generates random insertions or deletions, whereas homology-directed repair (HDR), which generates precise recombination products, is useful for wider applications. However, the factors that determine the ratio of HDR to NHEJ products after CRISPR/Cas9 editing remain unclear, and methods by which the proportion of HDR products can be increased have not yet been fully established. We systematically analyzed the HDR and NHEJ products after genome editing using various modified guide RNAs (gRNAs) and Cas9 variants with an enhanced conformational checkpoint to improve the fidelity at endogenous gene loci in HEK293T cells and HeLa cells. We found that these modified gRNAs and Cas9 variants were able to enhance HDR in both single-nucleotide substitutions and a multi-kb DNA fragment insertion. Our results suggest that the original CRISPR/Cas9 system from the bacterial immune system is not necessarily the best option for the induction of HDR in genome editing and indicate that the modulation of the kinetics of conformational checkpoints of Cas9 can optimize the HDR/NHEJ ratio.

Programmable CRISPR-Cas Repression, Activation, and Computation with Sequence-Independent Targets and Triggers

The programmability of CRISPR-derived Cas9 as a sequence-specific DNA-targeting protein has made it a powerful tool for genomic manipulation in biological research and translational applications. Cas9 activity can be programmably engineered to respond to nucleic acids, but these efforts have focused primarily on single-input control of Cas9, and until recently, they were limited by sequence dependence between parts of the guide RNA and the sequence to be detected. Here, we not only design and present DNA- and RNA-sensing conditional guide RNA (cgRNA) that have no such sequence constraints, but also demonstrate a complete set of logical computations using these designs on DNA and RNA sequence inputs, including AND, OR, NAND, and NOR. The development of sequence-independent nucleic acid-sensing CRISPR-Cas9 systems with multi-input logic computation capabilities could lead to improved genome engineering and regulation as well as the construction of synthetic circuits with broader functionality.

Application of CRISPR/Cas9 gene editing technique in the study of cancer treatment

In recent years, gene editing, especially that using clustered regularly interspaced short palindromic repeat (CRISPR)/Cas9, has made great progress in the field of gene function. Rapid development of gene editing techniques has contributed to their significance in the field of medicine. Because the CRISPR/Cas9 gene editing tool is not only powerful but also has features such as strong specificity and high efficiency, it can accurately and rapidly screen the whole genome, facilitating the administration of gene therapy for specific diseases. In the field of tumor research, CRISPR/Cas9 can be used to edit genomes to explore the mechanisms of tumor occurrence, development, and metastasis. In these years, this system has been increasingly applied in tumor treatment research. CRISPR/Cas9 can be used to treat tumors by repairing mutations or knocking out specific genes. To date, numerous preliminary studies have been conducted on tumor treatment in related fields. CRISPR/Cas9 holds great promise for gene-level tumor treatment. Personalized and targeted therapy based on CRISPR/Cas9 will possibly shape the development of tumor therapy in the future. In this study, we review the findings of CRISPR/Cas9 for tumor treatment research to provide references for related future studies on the pathogenesis and clinical treatment of tumors.

Translatable gene therapy for lung cancer using Crispr CAS9-an exploratory review

Gene therapy using CRISPR Cas9 technique is rapidly gaining popularity among the scientific community primarily because of its versatility, cost-effectiveness, and high efficacy. While the laboratory-based experiments and findings making use of CRISPR as a gene editing tool are available in ample amounts, the question arises that how much of these findings are actually translatable into measures helping in combating particular disease conditions. In this review, we highlight the important studies and findings done till now in the perspective of lung cancer with an in-depth analysis of various clinical trials associated with the use of CRISPR Cas9 technology in the field of cancer research.

Advancements and Obstacles of CRISPR-Cas9 Technology in Translational Research

The expanding CRISPR-Cas9 technology is an easily accessible, programmable, and precise gene-editing tool with numerous applications, most notably in biomedical research. Together with advancements in genome and transcriptome sequencing in the era of metadata, genomic engineering with CRISPR-Cas9 meets the developmental requirements of precision medicine, and clinical tests using CRISPR-Cas9 are now possible. This review summarizes developments and established preclinical applications of CRISPR-Cas9 technology, along with its current challenges, and highlights future applications in translational research.

A CRISPR/Cas9 based polymeric nanoparticles to treat/inhibit microbial infections

The latest breakthrough towards the adequate and decisive methods of gene editing tools provided by CRISPR/Cas9 (Clustered Regularly Interspaced Short Palindromic Repeat/CRISPR Associated System), has been repurposed into a tool for genetically engineering eukaryotic cells and now considered as the major innovation in gene-related disorders. Nanotechnology has provided an alternate way to overcome the conventional problems where methods to deliver therapeutic agents have failed. The use of nanotechnology has the potential to safe-side the CRISPR/Cas9 components delivery by using customized polymeric nanoparticles for safety and efficacy. The pairing of two (CRISPR/Cas9 and nanotechnology) has the potential for opening new avenues in therapeutic use. In this review, we will discuss the most recent advances in developing nanoparticle-based CRISPR/Cas9 gene editing cargo delivery with a focus on several polymeric nanoparticles including fabrication proposals to combat microbial infections.

Disruption of CTLA-4 expression on peripheral blood CD8 + T cell enhances anti-tumor efficacy in bladder cancer

Activation of programmed death-1 (PD-1) and cytotoxic T-lymphocyte antigen-4 (CTLA-4) on T cells leads to T cell exhaustion and ultimately facilitates tumor progression. Recent success of using immune cell checkpoint inhibitors offers a great promise to treat various cancers, including bladder cancer. However, the expression pattern and therapeutic value of PD-1 and CTLA-4 in peripheral blood T cells remain largely unexplored. In this study, we presume that disruption of the potential dysregulated checkpoint molecules in peripheral blood T cells may improve the anti-tumor efficacy of cytotoxic T cells in bladder cancer. We showed that both PD-1 and CTLA-4 expression were specifically elevated on CD8 + T cells but not CD4 + T cells in peripheral blood of patients with bladder cancer compared with that in healthy donors. Notably, CTLA-4 expression was significantly higher in muscle-invasive bladder cancer (MIBC) and correlated with tumor size. By blocking CTLA-4 with anti-CTLA-4 antibody and CRISPR-Cas9-mediated CTLA-4 disruption, we revealed that CTLA-4-disrupted CTLs had enhanced cellular immune response and superior cytotoxicity to the CD80/CD86-positive bladder cancer cells in vitro. Moreover, the CTLA-4-disrupted CTLs exhibited a pronounced anti-tumor effect in vivo as demonstrated by prophylactic assay and therapeutic assay in the subcutaneous xenograft model. Collectively, our findings confirm improved therapeutic efficacy of CTLA-4-disrupted CTLs and provides the potential strategy for targeting immune checkpoints to enhance the promising immunotherapy.

CRISPR/Cas9-based genome editing in the era of CAR T cell immunotherapy

The advent of engineered T cells as a form of immunotherapy marks the beginning of a new era in medicine, providing a transformative way to combat complex diseases such as cancer. Following FDA approval of CAR T cells directed against the CD19 protein for the treatment of acute lymphoblastic leukemia and diffuse large B cell lymphoma, CAR T cells are poised to enter mainstream oncology. Despite this success, a number of patients are unable to receive this therapy due to inadequate T cell numbers or rapid disease progression. Furthermore, lack of response to CAR T cell treatment is due in some cases to intrinsic autologous T cell defects and/or the inability of these cells to function optimally in a strongly immunosuppressive tumor microenvironment. We describe recent efforts to overcome these limitations using CRISPR/Cas9 technology, with the goal of enhancing potency and increasing the availability of CAR-based therapies. We further discuss issues related to the efficiency/scalability of CRISPR/Cas9-mediated genome editing in CAR T cells and safety considerations. By combining the tools of synthetic biology such as CARs and CRISPR/Cas9, we have an unprecedented opportunity to optimally program T cells and improve adoptive immunotherapy for most, if not all future patients.

Neoantigen identification strategies enable personalized immunotherapy in refractory solid tumors

BACKGROUND

Recent genomic and bioinformatic technological advances have made it possible to dissect the immune response to personalized neoantigens encoded by tumor-specific mutations. However, timely and efficient identification of neoantigens is still one of the major obstacles to using personalized neoantigen-based cancer immunotherapy.

METHODS

Two different pipelines of neoantigens identification were established in this study: (1) Clinical grade targeted sequencing was performed in patients with refractory solid tumor, and mutant peptides with high variant allele frequency and predicted high HLA-binding affinity were de novo synthesized. (2) An inventory-shared neoantigen peptide library of common solid tumors was constructed, and patients' hotspot mutations were matched to the neoantigen peptide library. The candidate neoepitopes were identified by recalling memory T-cell responses in vitro. Subsequently, neoantigen-loaded dendritic cell vaccines and neoantigen-reactive T cells were generated for personalized immunotherapy in six patients.

RESULTS

Immunogenic neo-epitopes were recognized by autologous T cells in 3 of 4 patients who utilized the de novo synthesis mode and in 6 of 13 patients who performed shared neoantigen peptide library, respectively. A metastatic thymoma patient achieved a complete and durable response beyond 29 months after treatment. Immune-related partial response was observed in another patient with metastatic pancreatic cancer. The remaining four patients achieved the prolonged stabilization of disease with a median PFS of 8.6 months.

CONCLUSIONS

The current study provided feasible pipelines for neoantigen identification. Implementing these strategies to individually tailor neoantigens could facilitate the neoantigen-based translational immunotherapy research.TRIAL REGSITRATION. ChiCTR.org ChiCTR-OIC-16010092, ChiCTR-OIC-17011275, ChiCTR-OIC-17011913; ClinicalTrials.gov NCT03171220.

FUNDING

This work was funded by grants from the National Key Research and Development Program of China (Grant No. 2017YFC1308900), the National Major Projects for "Major New Drugs Innovation and Development" (Grant No.2018ZX09301048-003), the National Natural Science Foundation of China (Grant No. 81672367, 81572329, 81572601), and the Key Research and Development Program of Jiangsu Province (No. BE2017607).

CRISPR/Cas9: a powerful tool for identification of new targets for cancer treatment

Clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR associated nuclease 9 (Cas9), as a powerful genome-editing tool, has revolutionized genetic engineering. It is widely used to investigate the molecular basis of different cancer types. In this review, we present an overview of recent studies in which CRISPR/Cas9 has been used for the identification of potential molecular targets. Based on the collected data, we suggest here that CRISPR/Cas9 is an effective system to distinguish between mutant and wild-type alleles in cancer. We show that several new potential therapeutic targets, such as CD38, CXCR2, MASTL, and RBX2, as well as several noncoding (nc)RNAs have been identified using CRISPR/Cas9 technology. We also discuss the obstacles and challenges that we face for using CRISPR/Cas9 as a therapeutic.

T-cells "à la CAR-T(e)" - Genetically engineering T-cell response against cancer

The last decade will be remembered as the dawn of the immunotherapy era during which we have witnessed the approval by regulatory agencies of genetically engineered CAR T-cells and of checkpoint inhibitors for cancer treatment. Understandably, T-lymphocytes represent the essential player in these approaches. These cells can mediate impressive tumor regression in terminally-ill cancer patients. Moreover, they are amenable to genetic engineering to improve their function and specificity. In the present review, we will give an overview of the most recent developments in the field of T-cell genetic engineering including TCR-gene transfer and CAR T-cells strategies. We will also elaborate on the development of other types of genetic modifications to enhance their anti-tumor immune response such as the use of co-stimulatory chimeric receptors (CCRs) and unconventional CARs built on non-antibody molecules. Finally, we will discuss recent advances in genome editing and synthetic biology applied to T-cell engineering and comment on the next challenges ahead.

Reprogramming lymphocytes for the treatment of melanoma: From biology to therapy

This decade has introduced drastic changes in melanoma therapy, predominantly due to the materialization of the long promise of immunotherapy. Cytotoxic T cells are the chief component of the immune system, which are targeted by different strategies aimed to increase their capacity against melanoma cells. To this end, reprogramming of T cells occurs by T cell centered manipulation, targeting the immunosuppressive tumor microenvironment or altering the whole patient. These are enabled by delivery of small molecules, functional monoclonal antibodies, different subunit vaccines, as well as living lymphocytes, native or genetically engineered. Current FDA-approved therapies are focused on direct T cell manipulation, such as immune checkpoint inhibitors blocking CTLA-4 and/or PD-1, which paves the way for an effective immunotherapy backbone available for combination with other modalities. Here we review the biology and clinical developments that enable melanoma immunotherapy today and in the future.

CRISPR-Cas9 a boon or bane: the bumpy road ahead to cancer therapeutics

Genome editing allows for the precise manipulation of DNA sequences in a cell making this technology essential for understanding gene function. CRISPR/Cas9 is a targeted genome-editing platform derived from bacterial adaptive immune system and has been repurposed into a genome-editing tool. The RNA-guided DNA endonuclease, Cas9 can be easily programmed to target new sites by altering its guide RNA sequence, making this technology easier, more efficient, scalable and an indispensable tool in biological research. This technology has helped genetically engineer animal models to understand disease mechanisms and elucidate molecular details that can be exploited for improved therapeutic outcomes. In this review, we describe the CRISPR-Cas9 gene-editing mechanism, CRISPR-screening methods, therapeutic targeting of CRISPR in animal models and in cancer immunotherapy. We also discuss the ongoing clinical trials using this tool, limitations of this tool that might impede the clinical applicability of CRISPR-Cas9 and future directions for developing effective CRISPR-Cas9 delivery systems that may improve cancer therapeutics.

Delivery systems of CRISPR/Cas9-based cancer gene therapy

CRISPR/Cas9 (Clustered Regularly Interspaced Short Palindromic Repeats) is today one of the most reliable method for gene-editing, supporting previous gene therapies technologies such as TALEN, Meganucleases and ZFNs. There is a growing up number of manuscripts reporting several successful gene-edited cancer cell lines, but the real challenge is to translate this technique to the clinical practice. While treatments for diseases based on a single gene mutation is closer, being possible to target and repair the mutant allele in a selective way generating specific guide RNAs (gRNAs), many steps need to be done to apply CRISPR to face cancer. In this review, we want to give a general overview to the recent advancements in the delivery systems of the CRISPR/Cas9 machinery in cancer therapy.

CRISPR/Cas9 for Cancer Therapy: Hopes and Challenges

Cancer is the second leading cause of death globally and remains a major economic and social burden. Although our understanding of cancer at the molecular level continues to improve, more effort is needed to develop new therapeutic tools and approaches exploiting these advances. Because of its high efficiency and accuracy, the CRISPR-Cas9 genome editing technique has recently emerged as a potentially powerful tool in the arsenal of cancer therapy. Among its many applications, CRISPR-Cas9 has shown an unprecedented clinical potential to discover novel targets for cancer therapy and to dissect chemical-genetic interactions, providing insight into how tumours respond to drug treatment. Moreover, CRISPR-Cas9 can be employed to rapidly engineer immune cells and oncolytic viruses for cancer immunotherapeutic applications. Perhaps more importantly, the ability of CRISPR-Cas9 to accurately edit genes, not only in cell culture models and model organisms but also in humans, allows its use in therapeutic explorations. In this review, we discuss important considerations for the use of CRISPR/Cas9 in therapeutic settings and major challenges that will need to be addressed prior to its clinical translation for a complex and polygenic disease such as cancer.