CAR affinity modulates the sensitivity of CAR-T cells to PD-1/PD-L1-mediated inhibition.

Chimeric antigen receptor (CAR)-T cell therapy for solid tumors faces significant hurdles, including T-cell inhibition mediated by the PD-1/PD-L1 axis. The effects of disrupting this pathway on T-cells are being actively explored and controversial outcomes have been reported. Here, we hypothesize that CAR-antigen affinity may be a key factor modulating T-cell susceptibility towards the PD-1/PD-L1 axis. We systematically interrogate CAR-T cells targeting HER2 with either low (LA) or high affinity (HA) in various preclinical models. Our results reveal an increased sensitivity of LA CAR-T cells to PD-L1-mediated inhibition when compared to their HA counterparts by using in vitro models of tumor cell lines and supported lipid bilayers modified to display varying PD-L1 densities. CRISPR/Cas9-mediated knockout (KO) of PD-1 enhances LA CAR-T cell cytokine secretion and polyfunctionality in vitro and antitumor effect in vivo and results in the downregulation of gene signatures related to T-cell exhaustion. By contrast, HA CAR-T cell features remain unaffected following PD-1 KO. This behavior holds true for CD28 and ICOS but not 4-1BB co-stimulated CAR-T cells, which are less sensitive to PD-L1 inhibition albeit targeting the antigen with LA. Our findings may inform CAR-T therapies involving disruption of PD-1/PD-L1 pathway tailored in particular for effective treatment of solid tumors.

The role of chimeric antigen receptor T cells targeting more than one antigen in the treatment of B-cell malignancies.

Several products containing chimeric antigen receptor T cells targeting CD19 (CART19) have been approved for the treatment of patients with relapsed/refractory non-Hodgkin's lymphoma (NHL) and acute lymphoblastic leukaemia (ALL). Despite very impressive response rates, a significant percentage of patients experience disease relapse and die of progressive disease. A major cause of CART19 failure is loss or downregulation of CD19 expression in tumour cells, which has prompted a myriad of novel strategies aimed at targeting more than one antigen (e.g. CD19 and CD20 or CD22). Dual targeting can the accomplished through co-administration of two separate products, co-transduction with two different vectors, bicistronic cassettes or tandem receptors. In this manuscript, we review the pros and cons of each strategy and the clinical results obtained so far.

Genome Editing in CAR-T Cells Using CRISPR/Cas9 Technology.

CAR-T cell therapy is revolutionizing the treatment of hematologic malignancies. However, there are still many challenges ahead before CAR-T cells can be used effectively to treat solid tumors and certain hematologic cancers, such as T-cell malignancies. Next-generation CAR-T cells containing further genetic modifications are being developed to overcome some of the current limitations of this therapy. In this regard, genome editing is being explored to knock out or knock in genes with the goal of enhancing CAR-T cell efficacy or increasing access. In this chapter, we describe in detail a protocol to knock out genes on CAR-T cells using CRISPR-Cas9 technology. Among various gene editing protocols, due to its simplicity, versatility, and reduced toxicity, we focused on the electroporation of ribonucleoprotein complexes containing the Cas9 protein together with sgRNA. All together, these protocols allow for the design of the knockout strategy, CAR-T cell expansion and genome editing, and analysis of knockout efficiency.

Genome Editing in Engineered T Cells for Cancer Immunotherapy.

Advanced gene transfer technologies and profound immunological insights have enabled substantial increases in the efficacy of anticancer adoptive cellular therapy (ACT). In recent years, the U.S. Food and Drug Administration and European Medicines Agency have approved six engineered T cell therapeutic products, all chimeric antigen receptor-engineered T cells directed against B cell malignancies. Despite encouraging clinical results, engineered T cell therapy is still constrained by challenges, which could be addressed by genome editing. As RNA-guided Clustered Regularly Interspaced Short Palindromic Repeats technology passes its 10-year anniversary, we review emerging applications of genome editing approaches designed to (1) overcome resistance to therapy, including cancer immune evasion mechanisms; (2) avoid unwanted immune reactions related to allogeneic T cell products; (3) increase fitness, expansion capacity, persistence, and potency of engineered T cells, while preserving their safety profile; and (4) improve the ability of therapeutic cells to resist immunosuppressive signals active in the tumor microenvironment. Overall, these innovative approaches should widen the safe and effective use of ACT to larger number of patients affected by cancer.

Type I Interferon Signaling via the EGR2 Transcriptional Regulator Potentiates CAR T Cell-Intrinsic Dysfunction.

Chimeric antigen receptor (CAR) T cell therapy has shown promise in treating hematologic cancers, but resistance is common and efficacy is limited in solid tumors. We found that CAR T cells autonomously propagate epigenetically programmed type I interferon signaling through chronic stimulation, which hampers antitumor function. EGR2 transcriptional regulator knockout not only blocks this type I interferon-mediated inhibitory program but also independently expands early memory CAR T cells with improved efficacy against liquid and solid tumors. The protective effect of EGR2 deletion in CAR T cells against chronic antigen-induced exhaustion can be overridden by interferon-ß exposure, suggesting that EGR2 ablation suppresses dysfunction by inhibiting type I interferon signaling. Finally, a refined EGR2 gene signature is a biomarker for type I interferon-associated CAR T cell failure and shorter patient survival. These findings connect prolonged CAR T cell activation with deleterious immunoinflammatory signaling and point to an EGR2-type I interferon axis as a therapeutically amenable biological system. SIGNIFICANCE: To improve CAR T cell therapy outcomes, modulating molecular determinants of CAR T cell-intrinsic resistance is crucial. Editing the gene encoding the EGR2 transcriptional regulator renders CAR T cells impervious to type I interferon pathway-induced dysfunction and improves memory differentiation, thereby addressing major barriers to progress for this emerging class of cancer immunotherapies. This article is highlighted in the In This Issue feature, p. 1501.

mRNAs encoding IL-12 and a decoy-resistant variant of IL-18 synergize to engineer T cells for efficacious intratumoral adoptive immunotherapy.

Interleukin-12 (IL-12) gene transfer enhances the therapeutic potency of adoptive T cell therapies. We previously reported that transient engineering of tumor-specific CD8 T cells with IL-12 mRNA enhanced their systemic therapeutic efficacy when delivered intratumorally. Here, we mix T cells engineered with mRNAs to express either single-chain IL-12 (scIL-12) or an IL-18 decoy-resistant variant (DRIL18) that is not functionally hampered by IL-18 binding protein (IL-18BP). These mRNA-engineered T cell mixtures are repeatedly injected into mouse tumors. Pmel-1 T cell receptor (TCR)-transgenic T cells electroporated with scIL-12 or DRIL18 mRNAs exert powerful therapeutic effects in local and distant melanoma lesions. These effects are associated with T cell metabolic fitness, enhanced miR-155 control on immunosuppressive target genes, enhanced expression of various cytokines, and changes in the glycosylation profile of surface proteins, enabling adhesiveness to E-selectin. Efficacy of this intratumoral immunotherapeutic strategy is recapitulated in cultures of tumor-infiltrating lymphocytes (TILs) and chimeric antigen receptor (CAR) T cells on IL-12 and DRIL18 mRNA electroporation.

Time 2EVOLVE: predicting efficacy of engineered T-cells - how far is the bench from the bedside?

Immunotherapy with gene engineered CAR and TCR transgenic T-cells is a transformative treatment in cancer medicine. There is a rich pipeline with target antigens and sophisticated technologies that will enable establishing this novel treatment not only in rare hematological malignancies, but also in common solid tumors. The T2EVOLVE consortium is a public private partnership directed at accelerating the preclinical development of and increasing access to engineered T-cell immunotherapies for cancer patients. A key ambition in T2EVOLVE is to assess the currently available preclinical models for evaluating safety and efficacy of engineered T cell therapy and developing new models and test parameters with higher predictive value for clinical safety and efficacy in order to improve and accelerate the selection of lead T-cell products for clinical translation. Here, we review existing and emerging preclinical models that permit assessing CAR and TCR signaling and antigen binding, the access and function of engineered T-cells to primary and metastatic tumor ligands, as well as the impact of endogenous factors such as the host immune system and microbiome. Collectively, this review article presents a perspective on an accelerated translational development path that is based on innovative standardized preclinical test systems for CAR and TCR transgenic T-cell products.

Overcoming CAR-Mediated CD19 Downmodulation and Leukemia Relapse with T Lymphocytes Secreting Anti-CD19 T-cell Engagers.

Chimeric antigen receptor (CAR)-modified T cells have revolutionized the treatment of CD19-positive hematologic malignancies. Although anti-CD19 CAR-engineered autologous T cells can induce remission in patients with B-cell acute lymphoblastic leukemia, a large subset relapse, most of them with CD19-positive disease. Therefore, new therapeutic strategies are clearly needed. Here, we report a comprehensive study comparing engineered T cells either expressing a second-generation anti-CD19 CAR (CAR-T19) or secreting a CD19/CD3-targeting bispecific T-cell engager antibody (STAb-T19). We found that STAb-T19 cells are more effective than CAR-T19 cells at inducing cytotoxicity, avoiding leukemia escape in vitro, and preventing relapse in vivo. We observed that leukemia escape in vitro is associated with rapid and drastic CAR-induced internalization of CD19 that is coupled with lysosome-mediated degradation, leading to the emergence of transiently CD19-negative leukemic cells that evade the immune response of engineered CAR-T19 cells. In contrast, engineered STAb-T19 cells induce the formation of canonical immunologic synapses and prevent the CD19 downmodulation observed in anti-CD19 CAR-mediated interactions. Although both strategies show similar efficacy in short-term mouse models, there is a significant difference in a long-term patient-derived xenograft mouse model, where STAb-T19 cells efficiently eradicated leukemia cells, but leukemia relapsed after CAR-T19 therapy. Our findings suggest that the absence of CD19 downmodulation in the STAb-T19 strategy, coupled with the continued antibody secretion, allows an efficient recruitment of the endogenous T-cell pool, resulting in fast and effective elimination of cancer cells that may prevent CD19-positive relapses frequently associated with CAR-T19 therapies.

Soluble CD137 as a dynamic biomarker to monitor agonist CD137 immunotherapies.

BACKGROUND: On the basis of efficacy in mouse tumor models, multiple CD137 (4-1BB) agonist agents are being preclinically and clinically developed. The costimulatory molecule CD137 is inducibly expressed as a transmembrane or as a soluble protein (sCD137). Moreover, the CD137 cytoplasmic signaling domain is a key part in approved chimeric antigen receptors (CARs). Reliable pharmacodynamic biomarkers for CD137 ligation and costimulation of T cells will facilitate clinical development of CD137 agonists in the clinic. METHODS: We used human and mouse CD8 T cells undergoing activation to measure CD137 transcription and protein expression levels determining both the membrane-bound and soluble forms. In tumor-bearing mice plasma sCD137 concentrations were monitored on treatment with agonist anti-CD137 monoclonal antibodies (mAbs). Human CD137 knock-in mice were treated with clinical-grade agonist anti-human CD137 mAb (Urelumab). Sequential plasma samples were collected from the first patients intratumorally treated with Urelumab in the INTRUST clinical trial. Anti-mesothelin CD137-encompassing CAR-transduced T cells were stimulated with mesothelin coated microbeads. sCD137 was measured by sandwich ELISA and Luminex. Flow cytometry was used to monitor CD137 surface expression. RESULTS: CD137 costimulation upregulates transcription and protein expression of CD137 itself including sCD137 in human and mouse CD8 T cells. Immunotherapy with anti-CD137 agonist mAb resulted in increased plasma sCD137 in mice bearing syngeneic tumors. sCD137 induction is also observed in human CD137 knock-in mice treated with Urelumab and in mice transiently humanized with T cells undergoing CD137 costimulation inside subcutaneously implanted Matrigel plugs. The CD137 signaling domain-containing CAR T cells readily released sCD137 and acquired CD137 surface expression on antigen recognition. Patients treated intratumorally with low dose Urelumab showed increased plasma concentrations of sCD137. CONCLUSION: sCD137 in plasma and CD137 surface expression can be used as quantitative parameters dynamically reflecting therapeutic costimulatory activity elicited by agonist CD137-targeted agents.

An NK-like CAR T cell transition in CAR T cell dysfunction.

Chimeric antigen receptor (CAR) T cell therapy has achieved remarkable success in hematological malignancies but remains ineffective in solid tumors, due in part to CAR T cell exhaustion in the solid tumor microenvironment. To study dysfunction of mesothelin-redirected CAR T cells in pancreatic cancer, we establish a robust model of continuous antigen exposure that recapitulates hallmark features of T cell exhaustion and discover, both in vitro and in CAR T cell patients, that CAR dysregulation is associated with a CD8+ T-to-NK-like T cell transition. Furthermore, we identify a gene signature defining CAR and TCR dysregulation and transcription factors, including SOX4 and ID3 as key regulators of CAR T cell exhaustion. Our findings shed light on the plasticity of human CAR T cells and demonstrate that genetic downmodulation of ID3 and SOX4 expression can improve the efficacy of CAR T cell therapy in solid tumors by preventing or delaying CAR T cell dysfunction.

Choosing the Right Tool for Genetic Engineering: Clinical Lessons from Chimeric Antigen Receptor-T Cells.

T cell modification with genes that encode chimeric antigen receptors (CAR-T cells) has shown tremendous promise for the treatment of B cell malignancies. The successful translation of CAR-T cell therapy to other tumor types, including solid tumors, is the next big challenge. As the field advances from second- to next-generation CAR-T cells comprising multiple genetic modifications, more sophisticated methods and tools to engineer T cells are being developed. Viral vectors, especially γ-retroviruses and lentiviruses, are traditionally used for CAR-T cell engineering due to their high transduction efficiency. However, limited genetic cargo, high costs of production under good manufacturing practice (GMP) conditions, and the high regulatory demands are obstacles for widespread clinical translation. To overcome these limitations, different nonviral approaches are being explored at a preclinical or clinical level, including transposon/transposase systems and mRNA electroporation and nonintegrating DNA nanovectors. Genome editing tools that allow efficient knockout of particular genes and/or site-directed integration of the CAR and/or other transgenes into the genome are also being evaluated for CAR-T cell engineering. In this review, we discuss the development of viral and nonviral vectors used to generate CAR-T cells, focusing on their advantages and limitations. We also discuss the lessons learned from clinical trials using the different genetic engineering tools, with special focus on safety and efficacy.

CAR-T Cells Hit the Tumor Microenvironment: Strategies to Overcome Tumor Escape.

Chimeric antigen receptor (CAR) T cell therapies have demonstrated remarkable efficacy for the treatment of hematological malignancies. However, in patients with solid tumors, objective responses to CAR-T cell therapy remain sporadic and transient. A major obstacle for CAR-T cells is the intrinsic ability of tumors to evade immune responses. Advanced solid tumors are largely composed of desmoplastic stroma and immunosuppressive modulators, and characterized by aberrant cell proliferation and vascularization, resulting in hypoxia and altered nutrient availability. To mount a curative response after infusion, CAR-T cells must infiltrate the tumor, recognize their cognate antigen and perform their effector function in this hostile tumor microenvironment, to then differentiate and persist as memory T cells that confer long-term protection. Fortunately, recent advances in synthetic biology provide a wide set of tools to genetically modify CAR-T cells to overcome some of these obstacles. In this review, we provide a comprehensive overview of the key tumor intrinsic mechanisms that prevent an effective CAR-T cell antitumor response and we discuss the most promising strategies to prevent tumor escape to CAR-T cell therapy.

Single residue in CD28-costimulated CAR-T cells limits long-term persistence and antitumor durability.

Chimeric antigen receptor-T (CAR-T) cell therapies can eliminate relapsed and refractory tumors, but the durability of antitumor activity requires in vivo persistence. Differential signaling through the CAR costimulatory domain can alter the T cell metabolism, memory differentiation, and influence long-term persistence. CAR-T cells costimulated with 4-1BB or ICOS persist in xenograft models but those constructed with CD28 exhibit rapid clearance. Here, we show that a single amino acid residue in CD28 drove T cell exhaustion and hindered the persistence of CD28-based CAR-T cells and changing this asparagine to phenylalanine (CD28-YMFM) promoted durable antitumor control. In addition, CD28-YMFM CAR-T cells exhibited reduced T cell differentiation and exhaustion as well as increased skewing toward Th17 cells. Reciprocal modification of ICOS-containing CAR-T cells abolished in vivo persistence and antitumor activity. This finding suggests modifications to the costimulatory domains of CAR-T cells can enable longer persistence and thereby improve antitumor response.

Analysis of CAR-Mediated Tonic Signaling.

CARs are synthetic receptors designed to drive antigen-specific activation upon binding of the scFv to its cognate antigen. However, CARs can also elicit different levels of ligand-independent constitutive signaling, also known as tonic signaling. Chronic T cell activation is observed in certain combinations of scFv, hinge, and costimulatory domains and may be increased due to high levels of CAR expression. Tonic signaling can be identified during primary T cell expansion due to differences in the phenotype and growth of CAR-T cells compared to control T cells. CARs displaying tonic signaling are associated with accelerated T cell differentiation and exhaustion and impaired antitumor effects. Selecting CARs which configuration does not induce tonic signaling is important to enhance antigen-specific T cell responses. In this chapter, we describe in detail different protocols to identify tonic signaling driven by CARs during primary T cell ex vivo expansion.

Analysis of Antitumor Effects of CAR-T Cells in Mice with Solid Tumors.

Animal models provide an essential tool to study the efficacy of CAR-T cell treatments. Most of the current works test human CAR-T cells in immunodeficient animals, typically NOD Scid Gamma (NSG) mice transplanted with human tumors. Despite the limitations of this model, including the difficulty to study the interaction between CAR-T cells and the human innate system and to assess the toxicity of this therapy, NSG are extensively used for adoptive T cell transfer studies. In this chapter, we will describe the protocols to test CAR-T cells in NSG animals with solid tumors. We first describe the implantation of human xenograft tumors in NSG animals, followed by CAR-T cell administration and assessment of antitumor responses. We will also review the protocols to analyze T cell persistence in the blood of treated animals. Finally, we will focus on the analysis of the tumors at the end point of the experiment, including the percentage, phenotype, and function of tumor infiltrating T cells, and loss of antigen expression.

Immobilizing A Moving Target: CAR T Cells Hit CD22.

A key mechanism of resistance to chimeric antigen receptor-modified T cells (CAR-T) is loss or downregulation of target antigens. Low antigen expression on cancer cells prevents full CAR-T-cell activation and persistence. Pharmacologic modulation of target antigen expression offers a novel therapeutic strategy to drive more potent and durable responses.See related article by Ramakrishna et al., p. 5329.

Engineering and Design of Chimeric Antigen Receptors.

T cells engineered with chimeric antigen receptors (CARs) have emerged as a potent new class of therapeutics for cancer, based on their remarkable potency in blood cancers. Since the first clinical reports of their efficacy emerged 7 years ago, investigators have focused on the mechanisms and properties that make CARs effective or toxic, and their effects on T cell biology. Novel CAR designs coupled with improvements in gene transfer technology, incorporating advances in gene editing, have the potential to increase access to engineered cell therapies, as well as improve their potency in solid tumors.

Emerging Cellular Therapies for Cancer.

Genetically engineered T cells are powerful new medicines, offering hope for curative responses in patients with cancer. Chimeric antigen receptor (CAR) T cells were recently approved by the US Food and Drug Administration and are poised to enter the practice of medicine for leukemia and lymphoma, demonstrating that engineered immune cells can serve as a powerful new class of cancer therapeutics. The emergence of synthetic biology approaches for cellular engineering provides a broadly expanded set of tools for programming immune cells for enhanced function. Advances in T cell engineering, genetic editing, the selection of optimal lymphocytes, and cell manufacturing have the potential to broaden T cell-based therapies and foster new applications beyond oncology, in infectious diseases, organ transplantation, and autoimmunity.

CAR-T Cells and Oncolytic Viruses: Joining Forces to Overcome the Solid Tumor Challenge.

Adoptive transfer of chimeric antigen receptor (CAR)-modified T cells has resulted in unprecedented rates of long-lasting complete responses in patients with leukemia and lymphoma. However, despite the impressive results in patients with hematologic malignancies, CAR-T cells have showed limited effect against solid cancers. New approaches will need to simultaneously overcome the multiple challenges that CAR-T cells encounter in solid tumors, including the immunosuppressive tumor microenvironment and heterogeneity of antigen expression. Oncolytic viruses are lytic and immunogenic anti-cancer agents with the potential to synergize with CAR-T cells for the treatment of solid tumors. In addition, viruses can be further modified to deliver therapeutic transgenes selectively to the tumor microenvironment, which could enhance the effector functions of tumor-specific T cells. This review summarizes the major limitations of CAR-T cells in solid tumors and discusses the potential role for oncolytic viruses as partners for CAR-T cells in the fight against cancer.

Pancreatic cancer therapy with combined mesothelin-redirected chimeric antigen receptor T cells and cytokine-armed oncolytic adenoviruses.

Pancreatic ductal adenocarcinoma (PDA) is characterized by its highly immunosuppressive tumor microenvironment (TME) that limits T cell infiltration and induces T cell hypofunction. Mesothelin-redirected chimeric antigen receptor T cell (meso-CAR T cell) therapy has shown some efficacy in clinical trials but antitumor efficacy remains modest. We hypothesized that combined meso-CAR T cells with an oncolytic adenovirus expressing TNF-α and IL-2 (Ad5/3-E2F-D24-TNFa-IRES-IL2, or OAd-TNFa-IL2) would improve efficacy. OAd-TNFa-IL2 enhanced the antitumor efficacy of meso-CAR T cells in human-PDA-xenograft immunodeficient mice and efficacy was associated with robustly increased tumor-infiltrating lymphocytes (TILs), enhanced and prolonged T cell function. Mice treated with parental OAd combined with meso-CAR T developed tumor metastasis to the lungs even if primary tumors were controlled. However, no mice treated with combined OAd-TNFa-IL2 and meso-CAR T died of tumor metastasis. We also evaluated this approach in a syngeneic mouse tumor model by combining adenovirus expressing murine TNF-α and IL-2 (Ad-mTNFa-mIL2) and mouse CAR T cells. This approach induced significant tumor regression in mice engrafted with highly aggressive and immunosuppressive PDA tumors. Ad-mTNFa-mIL2 increased both CAR T cell and host T cell infiltration to the tumor and altered host tumor immune status with M1 polarization of macrophages and increased dendritic cell maturation. These findings indicate that combining cytokine-armed oncolytic adenovirus to enhance the efficacy of CAR T cell therapy is a promising approach to overcome the immunosuppressive TME for the treatment of PDA.