Beyond the antigen receptor: editing the genome of T-cells for cancer adoptive cellular therapies

Updated Clinical Perspectives and Challenges of Chimeric Antigen Receptor-T Cell Therapy in Colorectal Cancer and Invasive Breast Cancer

In recent years, the incidence of colorectal cancer (CRC) and breast cancer (BC) has increased worldwide and caused a higher mortality rate due to the lack of selective anti-tumor therapies. Current chemotherapies and surgical interventions are significantly preferred modalities to treat CRC or BC in advanced stages but the prognosis for patients with advanced CRC and BC remains dismal. The immunotherapy technique of chimeric antigen receptor (CAR)-T cells has resulted in significant clinical outcomes when treating hematologic malignancies. The novel CAR-T therapy target antigens include GUCY2C, CLEC14A, CD26, TEM8/ANTXR1, PDPN, PTK7, PODXL, CD44, CD19, CD20, CD22, BCMA, GD2, Mesothelin, TAG-72, CEA, EGFR, B7H3, HER2, IL13Ra2, MUC1, EpCAM, PSMA, PSCA, NKG2D. The significant aim of this review is to explore the recently updated information pertinent to several novel targets of CAR-T for CRC, and BC. We vividly described the challenges of CAR-T therapies when treating CRC or BC. The immunosuppressive microenvironment of solid tumors, the shortage of tumor-specific antigens, and post-treatment side effects are the major hindrances to promoting the development of CAR-T cells. Several clinical trials related to CAR-T immunotherapy against CRC or BC have already been in progress. This review benefits academicians, clinicians, and clinical oncologists to explore more about the novel CAR-T targets and overcome the challenges during this therapy.

Challenges of Anti-Mesothelin CAR-T-Cell Therapy

Chimeric antigen receptor (CAR)-T-cell therapy is a kind of adoptive T-cell therapy (ACT) that has developed rapidly in recent years. Mesothelin (MSLN) is a tumor-associated antigen (TAA) that is highly expressed in various solid tumors and is an important target antigen for the development of new immunotherapies for solid tumors. This article reviews the clinical research status, obstacles, advancements and challenges of anti-MSLN CAR-T-cell therapy. Clinical trials on anti-MSLN CAR-T cells show that they have a high safety profile but limited efficacy. At present, local administration and introduction of new modifications are being used to enhance proliferation and persistence and to improve the efficacy and safety of anti-MSLN CAR-T cells. A number of clinical and basic studies have shown that the curative effect of combining this therapy with standard therapy is significantly better than that of monotherapy.

Strategies to overcome the main challenges of the use of CRISPR/Cas9 as a replacement for cancer therapy

CRISPR/Cas9 (clustered regularly interspaced short palindromic repeats-associated protein 9) shows the opportunity to treat a diverse array of untreated various genetic and complicated disorders. Therapeutic genome editing processes that target disease-causing genes or mutant genes have been greatly accelerated in recent years as a consequence of improvements in sequence-specific nuclease technology. However, the therapeutic promise of genome editing has yet to be explored entirely, many challenges persist that increase the risk of further mutations. Here, we highlighted the main challenges facing CRISPR/Cas9-based treatments and proposed strategies to overcome these limitations, for further enhancing this revolutionary novel therapeutics to improve long-term treatment outcome human health.

The role of the CRISPR-Cas system in cancer drug development: Mechanisms of action and therapy

BACKGROUND

The recent emergence of gene editing using Clustered regularly interspaced short palindromic repeats (CRISPR)-CRISPR associated system (Cas) tools and advances in genomics and proteomics has revolutionized drug discovery and personalized medicine.

PURPOSE AND SCOPE

The CRISPR-Cas system has enabled gene and cell-based therapies, screening for novel drug targets, a new generation of disease models, elucidation of drug resistance mechanisms, and drug efficacy testing. Here, we summarized recent investigations and strategies involved in cancer-related drug discovery using the CRISPR-Cas system.

CONCLUSION

CRISPR-Cas-mediated gene editing has shown great potential in the development of next generation drugs for treatment of Mendelian disorders and various cancer types. In this review, we focused on the impact of the CRISPR-Cas system in drug discovery and its application to biomarker identification and validation, high-end target genes, and breakthrough anticancer cell therapies. We also highlighted the role of CRISPR-Cas in precision disease modeling and functional drug screening. This article is protected by copyright. All rights reserved.

Increased antitumor efficacy of PD-1-deficient melanoma-specific human lymphocytes

Background

Genome editing offers unique perspectives for optimizing the functional properties of T cells for adoptive cell transfer purposes. So far, PDCD1 editing has been successfully tested mainly in chimeric antigen receptor T (CAR-T) cells and human primary T cells. Nonetheless, for patients with solid tumors, the adoptive transfer of effector memory T cells specific for tumor antigens remains a relevant option, and the use of high avidity T cells deficient for programmed cell death-1 (PD-1) expression is susceptible to improve the therapeutic benefit of these treatments.

Methods

Here we used the transfection of CAS9/sgRNA ribonucleoproteic complexes to edit PDCD1 gene in human effector memory CD8⁺ T cells specific for the melanoma antigen Melan-A. We cloned edited T cell populations and validated PDCD1 editing through sequencing and cytometry in each T cell clone, together with T-cell receptor (TCR) chain’s sequencing. We also performed whole transcriptomic analyses on wild-type (WT) and edited T cell clones. Finally, we documented in vitro and in vivo through adoptive transfer in NOD scid gamma (NSG) mice, the antitumor properties of WT and PD-1KO T cell clones, expressing the same TCR.

Results

Here we demonstrated the feasibility to edit PDCD1 gene in human effector memory melanoma-specific T lymphocytes. We showed that PD-1 expression was dramatically reduced or totally absent on PDCD1-edited T cell clones. Extensive characterization of a panel of T cell clones expressing the same TCR and exhibiting similar functional avidity demonstrated superior antitumor reactivity against a PD-L1 expressing melanoma cell line. Transcriptomic analysis revealed a downregulation of genes involved in proliferation and DNA replication in PD-1-deficient T cell clones, whereas genes involved in metabolism and cell signaling were upregulated. Finally, we documented the superior ability of PD-1-deficient T cells to significantly delay the growth of a PD-L1 expressing human melanoma tumor in an NSG mouse model.

Conclusion

The use of such lymphocytes for adoptive cell transfer purposes, associated with other approaches modulating the tumor microenvironment, would be a promising alternative to improve immunotherapy efficacy in solid tumors.

Emerging role of RNA interference in immune cells engineering and its therapeutic synergism in immunotherapy

RNAi effectors (e.g. siRNA, shRNA and miRNA) can trigger the silencing of specific genes causing alteration of genomic functions becoming a new therapeutic area for the treatment of infectious diseases, neurodegenerative disorders and cancer. In cancer treatment, RNAi effectors showed potential immunomodulatory actions by down-regulating immuno-suppressive proteins, such as PD-1 and CTLA-4, which restrict immune cell function and present challenges in cancer immunotherapy. Therefore, compared with extracellular targeting by antibodies, RNAi-mediated cell-intrinsic disruption of inhibitory pathways in immune cells could promote an increased anti-tumour immune response. Along with non-viral vectors, DNA-based RNAi strategies might be a more promising method for immunomodulation to silence multiple inhibitory pathways in T cells than immune checkpoint blockade antibodies. Thus, in this review, we discuss diverse RNAi implementation strategies, with recent viral and non-viral mediated RNAi synergism to immunotherapy that augments the anti-tumour immunity. Finally, we provide the current progress of RNAi in clinical pipeline.

CRISPR-Cas9 in cancer therapeutics

Cancer is a disease mainly caused by an accumulation of mutations in cells. Consequently, correcting those genetic aberrations could be a potential treatment strategy. The traditional route for cancer drug development is tedious, laborious, and time-consuming. Due to target identification, drug formulation, pre-clinical testing, clinical testing, and regulatory hurdles, on average, it takes 10-15 years for a cancer drug to go from target discovery to a marketable oncology drug. The advent of CRISPR-Cas9 technology has greatly expedited this procedure. CRISPR-Cas9 has single-handedly accelerated target identification and pre-clinical testing. Furthermore, CRISPR-Cas9 has also been used in ex vivo editing of T-cells to specifically target tumor cells. In this chapter, we will discuss the various ways in which CRISPR-Cas9 has been used for the betterment of the cancer drug development process. Additionally, we will discuss various ways in which it is currently being used as therapy and the drawbacks which restrict the use of this groundbreaking technology as direct therapy.

Progress and challenges towards CRISPR/Cas clinical translation

CRISPR/Cas systems (clustered regularly interspaced short palindromic repeats) have emerged as powerful tools to manipulate the genome for both research and therapeutic purposes. However, the clinical use of this system is hindered by multiple challenges, such as the rate of off-target effects, editing efficiency, the efficacy of HDR, immunogenicity, as well as development of efficient and safe delivery vehicles that can carry these compounds. Tremendous efforts are being conducted to overcome these challenges, including the discovery and engineering of more precise and efficacious Cas nucleases. Moreover, in recent years multiple viral and non-viral delivery approaches have been explored for in vivo delivery of CRISPR components. Here, we summarize the available CRISPR/Cas toolbox for genome editing as well as the recently developed in vivo delivery vehicles for CRISPR/Cas system. Furthermore, we discuss the remaining challenges for successful clinical translation of this system and highlight the current clinical applications.

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.

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.

Overexpression of PDE4A Acts as Checkpoint Inhibitor Against cAMP-Mediated Immunosuppression in vitro

Malignant cells acquire physiological mechanisms of immunosuppression to escape immune surveillance. Strategies to counteract this suppression could help to improve adoptive immunotherapy regimen. The intracellular second messenger cyclic AMP (cAMP) acts as a potent immunosuppressive signaling molecule in T-cells and is up-regulated by multiple tumor-relevant suppressive factors including prostaglandin E2 (PGE2), adenosine and the functions of regulatory T-cells. Consequently, we aimed to abrogate cAMP signaling in human T-cells by ectopic overexpression of phosphodiesterase 4A (PDE4A). We could show that retroviral transduction of PDE4A into T-cells led to efficient degradation of cAMP in response to induction of adenylate cyclase. Retroviral transduction of PDE4A into CD4⁺ and CD8⁺ T-cells restored proliferation, cytokine secretion as well as cytotoxicity under immunosuppression by PGE2 and A2A-R agonists. PDE4A-transgenic T-cells were also partially protected from suppression by regulatory T-cells. Furthermore, PGE2-mediated upregulation of the inhibitory surface markers CD73 and CD94 on CD8⁺ T-cells was efficiently counteracted by PDE4A. Importantly, no differences in the functionality under non-suppressive conditions between PDE4A- and control-vector transduced T-cells were observed, indicating that PDE4A does not interfere with T-cell activation per se. Similarly, expression of surface markers associated with T-cell exhaustion were not influenced by PDE4A overexpression in long term cultures. Thus, we provide first in vitro evidence that PDE4A can be exploited as immune checkpoint inhibitor against multiple suppressive factors.

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.

Disruption of PD-1 Enhanced the Anti-tumor Activity of Chimeric Antigen Receptor T Cells Against Hepatocellular Carcinoma

Cancer immunotherapy has made unprecedented breakthrough in the fields of chimeric antigen receptor-redirected T (CAR T) cell therapy and immune modulation. Combination of CAR modification and the disruption of endogenous inhibitory immune checkpoints on T cells represent a promising immunotherapeutic modality for cancer treatment. However, the potential for the treatment of hepatocellular carcinoma (HCC) has not been explored. In this study, the gene expressing the programmed death 1 receptor (PD-1) on the Glypican-3 (GPC3)-targeted second-generation CAR T cells employing CD28 as the co-stimulatory domain was disrupted using the CRISPR/Cas9 gene-editing system. It was found that, in vitro, the CAR T cells with the deficient PD-1 showed the stronger CAR-dependent anti-tumor activity against native programmed death 1 ligand 1-expressing HCC cell PLC/PRF/5 compared with the wild-type CAR T cells, and meanwhile, the CD4 and CD8 subsets, and activation status of CAR T cells were stable with the disruption of endogenous PD-1. Additionally, the disruption of PD-1 could protect the GPC3-CAR T cells from exhaustion when combating with native PD-L1-expressing HCC, as the levels of Akt phosphorylation and anti-apoptotic protein Bcl-xL expression in PD-1 deficient GPC3-CAR T cells were significantly higher than those in wild-type GPC3-CAR T cells after coculturing with PLC/PRF/5. Furthermore, the in vivo anti-tumor activity of the CAR T cells with the deficient PD-1 was investigated using the subcutaneous xenograft tumor model established by the injection of PLC/PRF/5 into NOD-scid-IL-2Rγ-/- (NSG) mice. The results indicated that the disruption of PD-1 enhanced the in vivo anti-tumor activity of CAR T cells against HCC, improved the persistence and infiltration of CAR T cells in the NSG mice bearing the tumor, and strengthened the inhibition of tumor-related genes expression in the xenograft tumors caused by the GPC3-CAR T cells. This study indicates the enhanced anti-tumor efficacy of PD-1-deficient CAR T cells against HCC and suggests the potential of precision gene editing on the immune checkpoints to enhance the CAR T cell therapies against HCC.

Applications and advances of CRISPR-Cas9 in cancer immunotherapy

Immunotherapy has emerged as one of the most promising therapeutic strategies in cancer. The clustered regularly interspaced short palindromic repeat (CRISPR)-associated protein 9 (CRISPR-Cas9) system, as an RNA-guided genome editing technology, is triggering a revolutionary change in cancer immunotherapy. With its versatility and ease of use, CRISPR-Cas9 can be implemented to fuel the production of therapeutic immune cells, such as construction of chimeric antigen receptor T (CAR-T) cells and programmed cell death protein 1 knockout. Therefore, CRISPR-Cas9 technology holds great promise in cancer immunotherapy. In this review, we will introduce the origin, development and mechanism of CRISPR-Cas9. Also, we will focus on its various applications in cancer immunotherapy, especially CAR-T cell-based immunotherapy, and discuss the potential challenges it faces.

Translation of CRISPR Genome Surgery to the Bedside for Retinal Diseases

In recent years, there has been accelerated growth of clustered regularly interspaced short palindromic repeats (CRISPR) genome surgery techniques. Genome surgery holds promise for diseases for which a cure currently does not exist. In the field of ophthalmology, CRISPR offers possibilities for treating inherited retinal dystrophies. The retina has little regenerative potential, which makes treatment particularly difficult. For such conditions, CRISPR genome surgery methods have shown great potential for therapeutic applications in animal models of retinal dystrophies. Much anticipation surrounds the potential for CRISPR as a therapeutic, as clinical trials of ophthalmic genome surgery are expected to begin as early as 2018. This mini-review summarizes preclinical CRISPR applications in the retina and current CRISPR clinical trials.

Extracellular ISG15 Signals Cytokine Secretion through the LFA-1 Integrin Receptor

ISG15 is a ubiquitin-like protein that functions in innate immunity both as an intracellular protein modifier and as an extracellular signaling molecule that stimulates IFN-γ secretion. The extracellular function, important for resistance to mycobacterial disease, has remained biochemically uncharacterized. We have established an NK-92 cell-based assay for IFN-γ release, identified residues critical for ISG15 signaling, and identified the cell surface receptor as LFA-1 (CD11a/CD18; αLβ2 integrin). LFA-1 inhibition blocked IFN-γ secretion, splenocytes from CD11a^-/- mice did not respond to ISG15, and ISG15 bound directly to the αI domain of CD11a in vitro. ISG15 also enhanced secretion of IL-10, indicating a broader role for ISG15 in cytokine signaling. ISG15 engagement of LFA-1 led to the activation of SRC family kinases (SFKs) and SFK inhibition blocked cytokine secretion. These findings establish the molecular basis of the extracellular function of ISG15 and the initial outside-in signaling events that drive ISG15-dependent cytokine secretion.

PD-1 expression on tumor-specific T cells: Friend or foe for immunotherapy?

Inhibitory properties of PD-1 receptor engagement on activated T cells are well established in physiologic and pathological contexts. In cancer, the use of checkpoint blockade, such as anti-PD-1 antibodies, becomes progressively a reference treatment of a growing number of tumors. Nonetheless, it is also established that PD-1 expression on antigen-specific T cells reflects the functional avidity and anti-tumor reactivity of these T cells. We will discuss this dual significance of PD-1 expression on tumor-specific T cells, due to a complex regulation and the opportunity to exploit this expression to define, monitor and exploit tumor-reactive T cells for immunotherapy purposes.

Engineered cells for costimulatory enhancement combined with IL-21 enhance the generation of PD-1-disrupted CTLs for adoptive immunotherapy

Blockade of the immune cell checkpoint inhibitors programmed death 1 (PD-1) and programmed death-ligand 1 (PD-L1) has become a powerful tool in cancer treatment, which is effective across various solid cancer types and hematologic malignancies. Our previous studies showed that by reducing immune tolerance, clustered regularly interspaced short palindromic repeats-associated protein 9 (CRISPR-Cas9) modified cytotoxic T lymphocytes (CTLs) rank highly in terms of immune responses and cytotoxicity. In this study, a genetically modified K562 cell line with surface expression of 4-1BBL was developed to expand PD-1-disrupted CTLs in vitro for further adoptive immunotherapy against cancer. Our findings demonstrate that after a long-term, up to 28days, engineered cells for costimulatory enhancement (ECCE) combined with IL-21 promote the expansion of PD-1-disrupted CTLs with a less differentiated "young" phenotype, enhanced immune response and superior cytotoxic effector characteristics. These new in vitro conditions represent a nimble and cost-effective approach to developing PD-1-disrupted CTLs with improved therapeutic potential.

Advancing chimeric antigen receptor T cell therapy with CRISPR/Cas9

The clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated 9 (CRISPR/Cas9) system, an RNA-guided DNA targeting technology, is triggering a revolution in the field of biology. CRISPR/Cas9 has demonstrated great potential for genetic manipulation. In this review, we discuss the current development of CRISPR/Cas9 technologies for therapeutic applications, especially chimeric antigen receptor (CAR) T cell-based adoptive immunotherapy. Different methods used to facilitate efficient CRISPR delivery and gene editing in T cells are compared. The potential of genetic manipulation using CRISPR/Cas9 system to generate universal CAR T cells and potent T cells that are resistant to exhaustion and inhibition is explored. We also address the safety concerns associated with the use of CRISPR/Cas9 gene editing and provide potential solutions and future directions of CRISPR application in the field of CAR T cell immunotherapy. As an integration-free gene insertion method, CRISPR/Cas9 holds great promise as an efficient gene knock-in platform. Given the tremendous progress that has been made in the past few years, we believe that the CRISPR/Cas9 technology holds immense promise for advancing immunotherapy.

SHP-1: the next checkpoint target for cancer immunotherapy?

The immense power of the immune system is harnessed in healthy individuals by a range of negative regulatory signals and checkpoints. Manipulating these checkpoints through inhibition has resulted in striking immune-mediated clearance of otherwise untreatable tumours and metastases; unfortunately, not all patients respond to treatment with the currently available inhibitors of cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) and programmed cell death protein 1 (PD-1). Combinatorial studies using both anti-CTLA-4 and anti-PD-1 demonstrate synergistic effects of targeting multiple checkpoints, paving the way for other immune checkpoints to be targeted. Src homology 2 domain-containing protein tyrosine phosphatase 1 (SHP-1) is a widely expressed inhibitory protein tyrosine phosphatase (PTP). In T-cells, it is a negative regulator of antigen-dependent activation and proliferation. It is a cytosolic protein, and therefore not amenable to antibody-mediated therapies, but its role in activation and proliferation makes it an attractive target for genetic manipulation in adoptive transfer strategies, such as chimeric antigen receptor (CAR) T-cells. This review will discuss the potential value of SHP-1 inhibition in future tumour immunotherapy.

Cornerstones of CRISPR-Cas in drug discovery and therapy

The recent development of CRISPR-Cas systems as easily accessible and programmable tools for genome editing and regulation is spurring a revolution in biology. Paired with the rapid expansion of reference and personalized genomic sequence information, technologies based on CRISPR-Cas are enabling nearly unlimited genetic manipulation, even in previously difficult contexts, including human cells. Although much attention has focused on the potential of CRISPR-Cas to cure Mendelian diseases, the technology also holds promise to transform the development of therapies to treat complex heritable and somatic disorders. In this Review, we discuss how CRISPR-Cas can affect the next generation of drugs by accelerating the identification and validation of high-value targets, uncovering high-confidence biomarkers and developing differentiated breakthrough therapies. We focus on the promises, pitfalls and hurdles of this revolutionary gene-editing technology, discuss key aspects of different CRISPR-Cas screening platforms and offer our perspectives on the best practices in genome engineering.

CRISPR-Cas9-mediated disruption of PD-1 on human T cells for adoptive cellular therapies of EBV positive gastric cancer

The successful use of immune cell checkpoint inhibitors PD-1 and PD-L1, over the past 5 y has raised the concern of using immunotherapy to treat various cancers. Epstein-Barr virus-associated gastric cancer (EBVaGC) exhibits high infiltration of lymphocytes and high amplification of immune-related genes including PD-L1 as distinguished from Epstein-Barr virus-non-associated gastric cancer (EBVnGC). Here, we presume that this PD-1/PD-L1 pathway may hinder the efficacy of adoptive T cell therapy toward EBVaGC. These studies reveal possibility of generating PD-1-disrupted CTL by CRISPR-Cas9 system and demonstrate enhanced immune response of these PD-1-disrupted CTLs to the EBV-LMP2A antigen and superior cytotoxicity to the EBV-positive gastric cancer cell. In addition, when combined with low-dose radiotherapy, these PD-1-disrupted CTLs mediated an impressive antitumor effect in a xenograft mouse model of EBVaGC. Taken together, these studies illustrate PD-1/PD-L1-mediated immune tolerance of EBVaGC and provide a new strategy for targeting immune checkpoints to break the tolerance for the T cell-based adoptive therapy.

Chimeric antigen receptors for treatment of glioblastoma: a practical review of challenges and ways to overcome them

Glioblastoma (GBM) is by far the most common and the most aggressive of all the primary brain malignancies. No curative therapy exists, and median life expectancy hovers at around 1 year after diagnosis, with a minute fraction surviving beyond 5 years. The difficulty in treating GBM lies in the cancer's protected niche within the blood-brain barrier and the heterogeneity of the cancer cells, which possess varying degrees of susceptibility to various common modalities of treatment. Over time, it is the tumor heterogeneity of GBM and the ability of the cancer stem cells to evolve in response treatment that renders the cancer refractory to conventional treatment. Therefore, research has increasingly focused on treatment that incorporates knowledge of GBM molecular biology to therapeutic strategies. One type of therapy that shows great promise is the area of T-cell immunotherapy to target GBM-specific tumor antigens. One attractive strategy is to use T cells that have undergone genetic modification to express a chimeric antigen receptor capable of interacting with tumor antigens. In this article, we will review chimeric antigen receptor T-cell therapy, their advantages, drawbacks, challenges facing their use and how those challenges may be overcome.

Purity of transferred CD8(+) T cells is crucial for safety and efficacy of combinatorial tumor immunotherapy in the absence of SHP-1

Adoptive transfer of tumor-specific cytotoxic T cells is a promising advance in cancer therapy. Similarly, checkpoint inhibition has shown striking clinical results in some patients. Here we combine adoptive cell transfer with ablation of the checkpoint protein Src homology 2-domain-containing phosphatase 1 (SHP-1, Ptpn6). Naturally occurring motheaten mice lack SHP-1 and do not survive weaning due to extensive immunopathology. To circumvent this limitation, we created a novel SHP-1^null mouse that is viable up to 12 weeks of age by knocking out IL1r1. Using this model, we demonstrate that the absence of SHP-1 augments the ability of adoptively transferred CD8⁺ T cells to control tumor growth. This therapeutic effect was only observed in situations where T-cell numbers were limited, analogous to clinical settings. However, adoptive transfer of non-CD8⁺ SHP-1^null hematopoietic cells resulted in lethal motheaten-like pathology, indicating that systemic inhibition of SHP-1 could have serious adverse effects. Despite this caveat, our findings support the development of SHP-1 inhibition strategies in human T cells to complement adoptive transfer therapies in the clinic.

Targeting CD73 in the tumor microenvironment with MEDI9447

MEDI9447 is a human monoclonal antibody that is specific for the ectoenzyme CD73 and currently undergoing Phase I clinical trials. Here we show that MEDI9447 is a potent inhibitor of CD73 ectonucleotidase activity, with wide ranging immune regulatory consequences. MEDI9447 results in relief from adenosine monophosphate (AMP)-mediated lymphocyte suppression in vitro and inhibition of mouse syngeneic tumor growth in vivo. In contrast with other cancer immunotherapy agents such as checkpoint inhibitors or T-cell agonists, MEDI9447 drives changes in both myeloid and lymphoid infiltrating leukocyte populations within the tumor microenvironment of mouse models. Changes include significant alterations in a number of tumor micro-environmental subpopulations including increases in CD8⁺ effector cells and activated macrophages. Furthermore, these changes correlate directly with responder and non-responder subpopulations within animal studies using syngeneic tumors. Combination data showing additive activity between MEDI9447 and anti-PD-1 antibodies using human cells in vitro and mouse tumor models further demonstrate the potential value of relieving adenosine-mediated immunosuppression. Based on these data, a Phase I study to test the safety, tolerability, and clinical activity of MEDI9447 in cancer patients was initiated (NCT02503774).

RNA Interference in the Age of CRISPR: Will CRISPR Interfere with RNAi?

The recent emergence of multiple technologies for modifying gene structure has revolutionized mammalian biomedical research and enhanced the promises of gene therapy. Over the past decade, RNA interference (RNAi) based technologies widely dominated various research applications involving experimental modulation of gene expression at the post-transcriptional level. Recently, a new gene editing technology, Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) and the CRISPR-associated protein 9 (Cas9) (CRISPR/Cas9) system, has received unprecedented acceptance in the scientific community for a variety of genetic applications. Unlike RNAi, the CRISPR/Cas9 system is bestowed with the ability to introduce heritable precision insertions and deletions in the eukaryotic genome. The combination of popularity and superior capabilities of CRISPR/Cas9 system raises the possibility that this technology may occupy the roles currently served by RNAi and may even make RNAi obsolete. We performed a comparative analysis of the technical aspects and applications of the CRISPR/Cas9 system and RNAi in mammalian systems, with the purpose of charting out a predictive picture on whether the CRISPR/Cas9 system will eclipse the existence and future of RNAi. The conclusion drawn from this analysis is that RNAi will still occupy specific domains of biomedical research and clinical applications, under the current state of development of these technologies. However, further improvements in CRISPR/Cas9 based technology may ultimately enable it to dominate RNAi in the long term.

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

Strategies that enhance the function of T cells are critical for immunotherapy. One negative regulator of T-cell activity is ligand PD-L1, which is expressed on dentritic cells (DCs) or some tumor cells, and functions through binding of programmed death-1 (PD-1) receptor on activated T cells. Here we described for the first time a non-viral mediated approach to reprogram primary human T cells by disruption of PD-1. We showed that the gene knockout of PD-1 by electroporation of plasmids encoding sgRNA and Cas9 was technically feasible. The disruption of inhibitory checkpoint gene PD-1 resulted in significant reduction of PD-1 expression but didn't affect the viability of primary human T cells during the prolonged in vitro culture. Cellular immune response of the gene modified T cells was characterized by up-regulated IFN-γ production and enhanced cytotoxicity. These results suggest that we have demonstrated an approach for efficient checkpoint inhibitor disruption in T cells, providing a new strategy for targeting checkpoint inhibitors, which could potentialy be useful to improve the efficacy of T-cell based adoptive therapies.

Synthetic biology in cell-based cancer immunotherapy

The adoptive transfer of genetically engineered T cells with cancer-targeting receptors has shown tremendous promise for eradicating tumors in clinical trials. This form of cellular immunotherapy presents a unique opportunity to incorporate advanced systems and synthetic biology approaches to create cancer therapeutics with novel functions. We first review the development of synthetic receptors, switches, and circuits to control the location, duration, and strength of T cell activity against tumors. In addition, we discuss the cellular engineering and genome editing of host cells (or the chassis) to improve the efficacy of cell-based cancer therapeutics, and to reduce the time and cost of manufacturing.