CD19 CAR-targeted T cells induce long-term remission and B Cell Aplasia in an immunocompetent mouse model of B cell acute lymphoblastic leukemia

CAR T cells: Building on the CD19 paradigm

Spearheaded by the therapeutic use of chimeric antigen receptors (CARs) targeting CD19, synthetic immunology has entered the clinical arena. CARs are recombinant receptors for antigen that engage cell surface molecules through the variable region of an antibody and signal through arrayed T-cell activating and costimulatory domains. CARs allow redirection of T-cell cytotoxicity against any antigen of choice, independent of MHC expression. Patient T cells engineered to express CARs specific for CD19 have yielded remarkable outcomes in subjects with relapsed/refractory B- cell malignancies, setting off unprecedented interest in T-cell engineering and cell-based cancer immunotherapy. In this review, we present the challenges to extend the use of CAR T cells to solid tumors and other pathologies. We further highlight progress in CAR design, cell manufacturing, and genome editing, which in aggregate hold the promise of generating safer and more effective genetically instructed immunity. Novel engineered cell types, including innate T-cell types, natural killer (NK) cells, macrophages, and induced pluripotent stem cell-derived immune cells, are on the horizon, as are applications of CAR T cells to treat autoimmunity, severe infections, and senescence-associated pathologies.

Cytokine release syndrome and associated neurotoxicity in cancer immunotherapy

A paradigm shift has recently occurred in the field of cancer therapeutics. Traditional anticancer agents, such as chemotherapy, radiotherapy and small-molecule drugs targeting specific signalling pathways, have been joined by cellular immunotherapies based on T cell engineering. The rapid adoption of novel, patient-specific cellular therapies builds on scientific developments in tumour immunology, genetic engineering and cell manufacturing, best illustrated by the curative potential of chimeric antigen receptor (CAR) T cell therapy targeting CD19-expressing malignancies. However, the clinical benefit observed in many patients may come at a cost. In up to one-third of patients, significant toxicities occur that are directly associated with the induction of powerful immune effector responses. The most frequently observed immune-mediated toxicities are cytokine release syndrome and immune effector cell-associated neurotoxicity syndrome. This Review discusses our current understanding of their pathophysiology and clinical features, as well as the development of novel therapeutics for their prevention and/or management.

This Review discusses our current understanding of the pathophysiological mechanisms of cytokine release syndrome and immune effector cell-associated neurotoxicity syndrome associated with chimeric antigen receptor (CAR) T cell therapies, and how this might be used for the prevention or management of these toxicities.

Armored CAR T-Cells: The Next Chapter in T-Cell Cancer Immunotherapy

Chimeric antigen receptor (CAR) T-cell therapy engineers T-cells to express a synthetic receptor which redirects effector function to the tumor, to improve efficacy and reduce toxicities associated with conventional treatments, such as radiotherapy and chemotherapy. This approach has proved effective in treating hematological malignancies; however, the same effects have not been observed in solid tumors. The immunosuppressive tumor microenvironment (TME) creates a significant barrier to solid tumor efficacy and reduces the anti-cancer activity of endogenous tumor-resident immune cells, enabling cancer progression. In recent years, researchers have attempted to enhance CAR T-cell function in the TME by engineering the cells to express various proteins alongside the CAR. Examples of this engineering include inducing CAR T-cells to secrete cytokines or express cytokine receptors to modulate the cytokine milieu of the TME. Alternatively, the CAR T-cell may secrete antibody-like proteins to target a range of tumor antigens. Collectively, these methods are termed armored CAR T-cell therapy, and in this review, we will discuss the range of armored CAR T-cell approaches which have been investigated to date.

Deletion of Cbl-b inhibits CD8+ T-cell exhaustion and promotes CAR T-cell function

Background

Chimeric antigen receptor (CAR) T-cell therapy is an emerging option for cancer treatment, but its efficacy is limited, especially in solid tumors. This is partly because the CAR T cells become dysfunctional and exhausted in the tumor microenvironment. However, the key pathways responsible for impaired function of exhausted cells remain unclear, which is essential to overcome CAR T-cell exhaustion.

Methods

Analysis of RNA-sequencing data from CD8⁺ tumor-infiltrating lymphocytes (TILs) led to identification of Cbl-b as a potential target. The sequencing data were validated using a syngeneic MC38 colon cancer model. To analyze the in vivo role of Cbl-b in T-cell exhaustion, tumor growth, % PD1⁺Tim3⁺ cells, and expression of effector cytokines were analyzed in cbl-b^+/+ and cbl-b^–/– mice. To evaluate the therapeutic potential of Cbl-b depletion, we generated a new CAR construct, hCEAscFv-CD28-CD3ζ.GFP, that recognizes human carcinoembryonic antigen (CEA). cbl-b^+/+ and cbl-b^–/– CEA-CAR T cells were generated by retroviral transduction. Rag^–/– mice bearing MC38-CEA cells were injected with cbl-b^+/+ and cbl-b^–/–; CEA-CAR T cells, tumor growth, % PD1⁺Tim3⁺ cells and expression of effector cytokines were analyzed.

Results

Our results show that the E3 ubiquitin ligase Cbl-b is upregulated in exhausted (PD1⁺Tim3⁺) CD8⁺ TILs. CRISPR-Cas9-mediated inhibition of Cbl-b restores the effector function of exhausted CD8⁺ TILs. Importantly, the reduced growth of syngeneic MC38 tumors in cbl-b^–/– mice was associated with a marked reduction of PD1⁺Tim3⁺ CD8⁺ TILs. Depletion of Cbl-b inhibited CAR T-cell exhaustion, resulting in reduced MC38-CEA tumor growth, reduced PD1⁺Tim3⁺ cells and increased expression of interferon gamma, tumor necrosis factor alpha, and increased tumor cell killing.

Conclusion

Our studies demonstrate that deficiency of Cbl-b overcomes endogenous CD8⁺ T-cell exhaustion, and deletion of Cbl-b in CAR T cells renders them resistant to exhaustion. Our results could facilitate the development of efficient CAR T-cell therapy for solid tumors by targeting Cbl-b.

CD28 Costimulatory Domain-Targeted Mutations Enhance Chimeric Antigen Receptor T-cell Function

An obstacle to the development of chimeric antigen receptor (CAR) T cells is the limited understanding of CAR T-cell biology and the mechanisms behind their antitumor activity. We and others have shown that CARs with a CD28 costimulatory domain drive high T-cell activation, which leads to exhaustion and shortened persistence. This work led us to hypothesize that by incorporating null mutations of CD28 subdomains (YMNM, PRRP, or PYAP), we could optimize CAR T-cell costimulation and enhance function. In vivo, we found that mice given CAR T cells with only a PYAP CD28 endodomain had a significant survival advantage, with 100% of mice alive after 62 days compared with 50% for mice with an unmutated endodomain. We observed that mutant CAR T cells remained more sensitive to antigen after ex vivo antigen and PD-L1 stimulation, as demonstrated by increased cytokine production. The mutant CAR T cells also had a reduction of exhaustion-related transcription factors and genes such as Nfatc1, Nr42a, and Pdcd1 Our results demonstrated that CAR T cells with a mutant CD28 endodomain have better survival and function. This work allows for the development of enhanced CAR T-cell therapies by optimizing CAR T-cell costimulation.

Advances in Supportive Care for Acute Lymphoblastic Leukemia

PURPOSE OF REVIEW

Tremendous advances have been made in the treatment armamentarium for acute lymphoblastic leukemia in recent years, which have substantially improved outcomes for these patients. At the same time, unique toxicities have emerged, and without early intervention, are life-threatening. This article will review the novel therapies in acute leukemias and highlight the clinically relevant supportive care advances.

RECENT FINDINGS

The American Society for Transplantation and Cellular Therapy (ASTCT) has put forth the most recent recommendations in managing the cytokine release syndrome and neurotoxicity after chimeric antigen receptor T cells (CAR-T) and blinatumomab. The hepatic injury incurred by inotuzumab, and the vascular toxicity of tyrosine kinase inhibitors, other relatively novel agents, require subspecialist intervention and multidisciplinary care. Asparaginase, a long-established and key element of pediatric regimens, has made a comeback in the young adult leukemia population. Updated guidelines have been outlined for management of asparaginase thrombotic complications. Lastly, although there have been few changes in the applications of growth factor, antimicrobial prophylaxis, and management of neuropathy, these encompass exceedingly important aspects of care. While the rapidly changing treatment paradigms for acute lymphoblastic leukemia have transformed leukemia-specific outcomes, treatment emergent toxicities have forced much necessary attention to better definitions of these toxicities and on improving supportive care guidelines in acute lymphoblastic leukemia.

CD103+ cDC1 and endogenous CD8+ T cells are necessary for improved CD40L-overexpressing CAR T cell antitumor function

While effective in specific settings, adoptive chimeric antigen receptor (CAR) T cell therapy for cancer requires further improvement and optimization. Our previous results show that CD40L-overexpressing CAR T cells mobilize endogenous immune effectors, resulting in improved antitumor immunity. However, the cell populations required for this protective effect remain to be identified. Here we show, by analyzing Batf3-/- mice lacking the CD103+ conventional dendritic cell type 1 (cDC1) subpopulation important for antigen cross-presentation, that CD40L-overexpressing CAR T cells elicit an impaired antitumor response in the absence of cDC1s. We further find that CD40L-overexpressing CAR T cells stimulate tumor-resident CD11b-CD103- double-negative (DN) cDCs to proliferate and differentiate into cDC1s in wild-type mice. Finally, re-challenge experiments show that endogenous CD8+ T cells are required for protective antitumor memory in this setting. Our findings thus demonstrate the stimulatory effect of CD40L-overexpressing CAR T cells on innate and adaptive immune cells, and provide a rationale for using CD40L-overexpressing CAR T cells to improve immunotherapy responses.

In vitro-transcribed antigen receptor mRNA nanocarriers for transient expression in circulating T cells in vivo

Engineering chimeric antigen receptors (CAR) or T cell receptors (TCR) helps create disease-specific T cells for targeted therapy, but the cost and rigor associated with manufacturing engineered T cells ex vivo can be prohibitive, so programing T cells in vivo may be a viable alternative. Here we report an injectable nanocarrier that delivers in vitro-transcribed (IVT) CAR or TCR mRNA for transiently reprograming of circulating T cells to recognize disease-relevant antigens. In mouse models of human leukemia, prostate cancer and hepatitis B-induced hepatocellular carcinoma, repeated infusions of these polymer nanocarriers induce sufficient host T cells expressing tumor-specific CARs or virus-specific TCRs to cause disease regression at levels similar to bolus infusions of ex vivo engineered lymphocytes. Given their ease of manufacturing, distribution and administration, these nanocarriers, and the associated platforms, could become a therapeutic for a wide range of diseases.

Ex vivo engineering of antigen-specific T cells has shown therapeutic efficacy but can be costly and scarce. Here the authors show that in vitro-transcribed antigen receptor mRNA packaged in nanocarriers can directly induce, in vivo, transient their expression in circulating T cells to provide therapeutic effects in mouse models of cancer or viral infection.

Optimized gene engineering of murine CAR-T cells reveals the beneficial effects of IL-15 coexpression

Limited clinical benefit has been demonstrated for chimeric antigen receptor (CAR) therapy of solid tumors, but coengineering strategies to generate so-called fourth-generation (4G) CAR-T cells are advancing toward overcoming barriers in the tumor microenvironment (TME) for improved responses. In large part due to technical challenges, there are relatively few preclinical CAR therapy studies in immunocompetent, syngeneic tumor-bearing mice. Here, we describe optimized methods for the efficient retroviral transduction and expansion of murine T lymphocytes of a predominantly central memory T cell (T_CM cell) phenotype. We present a bicistronic retroviral vector encoding both a tumor vasculature–targeted CAR and murine interleukin-15 (mIL-15), conferring enhanced effector functions, engraftment, tumor control, and TME reprogramming, including NK cell activation and reduced presence of M2 macrophages. The 4G-CAR-T cells coexpressing mIL-15 were further characterized by up-regulation of the antiapoptotic marker Bcl-2 and lower cell-surface expression of the inhibitory receptor PD-1. Overall, this work introduces robust tools for the development and evaluation of 4G-CAR-T cells in immunocompetent mice, an important step toward the acceleration of effective therapies reaching the clinic.

Adapter chimeric antigen receptor (AdCAR)-engineered NK-92 cells: an off-the-shelf cellular therapeutic for universal tumor targeting

Despite the recent success of CAR T cells targeting CD19 and CD22 in hematological malignancies, the production of CAR T cells still requires an extensive manufacturing process. The well-established NK-92 cell line provides a promising alternative to produce CAR-modified effector cells in a GMP-compliant, cost-effective way. NK-92 can be redirected against a variety of surface antigens by our adapter CAR (AdCAR) system utilizing biotinylated antibodies (bAb) as adapter molecules. Selected bAb were capable of inducing significant AdCAR NK-92-mediated lysis of non-Hodgkin lymphoma (NHL) and mantle-cell lymphoma (MCL) cell lines as well as primary MCL and chronic lymphocytic leukemia (CLL) cells. AdCAR specificity was proven using a JeKo-1 CD19/CD20 knockout antigen-loss model. Moreover, through combinations of bAb, AdCAR NK-92 cells are capable of combatting tumor antigen evasion mechanisms. In conclusion, we successfully generated the AdCAR NK-92 cell line which can be manufactured as an “off-the-shelf, on-demand” product allowing universal and tunable tumor targeting.

A rational relationship: Oncolytic virus vaccines as functional partners for adoptive T cell therapy

Tumours employ a variety of immune-evasion and suppression mechanisms to impair development of functional tumor-specific T cells and subvert T cell-mediated immunity in the tumour microenvironment. Adoptive T cell therapy (ACT) aims to overcome these barriers and overwhelm tumor defenses with a bolus of T cells that were selectively expanded ex vivo. Although this strategy has been effective in liquid tumors and melanomas, many tumors appear to be resistant to ACT. Several factors are thought to play into this resistance, including poor engraftment and persistence of transferred cells, tumour cell heterogeneity and antigen loss, poor immune cell recruitment and infiltration into the tumour, and susceptibility to local immunosuppression in the tumor microenvironment. Oncolytic viruses (OV) have been identified as powerful stimulators of the anti-tumour immune response. As such, OVs are inherently well-positioned to act in synergy with ACT to bolster the anti-tumour T cell response. Further, OV vaccines, wherein tumour-associated antigens are encoded into the viral backbone, have proven to be remarkable in boosting antigen-specific T cell response. Pre-clinical studies have revealed remarkable therapeutic outcomes when OV vaccines are paired with ACT. In this scenario, OV vaccines are thought to function in a "push and pull" manner, where push refers to expanding T cells in the periphery and pull refers to recruiting those cells into the tumour that has been rendered amenable to T cell attack by the actions of the OV. In this review, we discuss barriers that limit eradication of tumors by T cells, highlight attributes of OVs that break down these barriers and present strategies for rational combinations of ACT with OV vaccines.

Senolytic CAR T cells reverse senescence-associated pathologies

Cellular senescence is characterized by stable cell-cycle arrest and a secretory program that modulates the tissue microenvironment1,2. Physiologically, senescence serves as a tumour-suppressive mechanism that prevents the expansion of premalignant cells3,4 and has a beneficial role in wound-healing responses5,6. Pathologically, the aberrant accumulation of senescent cells generates an inflammatory milieu that leads to chronic tissue damage and contributes to diseases such as liver and lung fibrosis, atherosclerosis, diabetes and osteoarthritis1,7. Accordingly, eliminating senescent cells from damaged tissues in mice ameliorates the symptoms of these pathologies and even promotes longevity1,2,8-10. Here we test the therapeutic concept that chimeric antigen receptor (CAR) T cells that target senescent cells can be effective senolytic agents. We identify the urokinase-type plasminogen activator receptor (uPAR)11 as a cell-surface protein that is broadly induced during senescence and show that uPAR-specific CAR T cells efficiently ablate senescent cells in vitro and in vivo. CAR T cells that target uPAR extend the survival of mice with lung adenocarcinoma that are treated with a senescence-inducing combination of drugs, and restore tissue homeostasis in mice in which liver fibrosis is induced chemically or by diet. These results establish the therapeutic potential of senolytic CAR T cells for senescence-associated diseases.

Excessive Costimulation Leads to Dysfunction of Adoptively Transferred T Cells

Although clinical responses with CD19-targeting chimeric antigen receptor (CAR) T-cell treatment have been observed in patients with certain hematologic malignancies, high rates of disease relapse highlight the necessity to understand and improve mechanisms of CAR T-cell failure. Because T-cell dysfunction is thought to contribute to CAR T-cell treatment failure, understanding what mechanisms drive T cells into this dysfunctional state may aid optimal design of efficacious CAR T cells. Dysfunctional CAR T cells have been characterized as having upregulated inhibitory receptors and decreased cytolytic capabilities. Previous studies have identified a role for sustained CAR CD3ζ signaling in CAR T-cell dysfunction. Here, we demonstrate a mechanism that drives dysfunction in CAR T cells through excessive costimulation. Fully activated CD19-targeted CAR T cells were rendered dysfunctional upon stimulation with both endogenous CD28 stimulation and CAR-mediated CD28 costimulation. Costimulation-driven dysfunction of CAR T cells was demonstrated in a syngeneic immunocompetent mouse model, in which CAR T cells were activated with signals 1 (CD3ζ), 2 (CD28), and 3 (IL12). Thus, we show that CAR T-cell dysfunction can be driven through excessive CD28 and 4-1BB costimulation.See related article by Drakes et al., p. 743.

A New Era in Endothelial Injury Syndromes: Toxicity of CAR-T Cells and the Role of Immunity

Immunotherapy with chimeric antigen receptor T (CAR-T cells) has been recently approved for patients with relapsed/refractory B-lymphoproliferative neoplasms. Along with great efficacy in patients with poor prognosis, CAR-T cells have been also linked with novel toxicities in a significant portion of patients. Cytokine release syndrome (CRS) and neurotoxicity present with unique clinical phenotypes that have not been previously observed. Nevertheless, they share similar characteristics with endothelial injury syndromes developing post hematopoietic cell transplantation (HCT). Evolution in complement therapeutics has attracted renewed interest in these life-threatening syndromes, primarily concerning transplant-associated thrombotic microangiopathy (TA-TMA). The immune system emerges as a key player not only mediating cytokine responses but potentially contributing to endothelial injury in CAR-T cell toxicity. The interplay between complement, endothelial dysfunction, hypercoagulability, and inflammation seems to be a common denominator in these syndromes. As the indications for CAR-T cells and patient populations expand, there in an unmet clinical need of better understanding of the pathophysiology of CAR-T cell toxicity. Therefore, this review aims to provide state-of-the-art knowledge on cellular therapies in clinical practice (indications and toxicities), endothelial injury syndromes and immunity, as well as potential therapeutic targets.

Targeting Cancer Stem Cells by Genetically Engineered Chimeric Antigen Receptor T Cells

The term cancer stem cell (CSC) starts 25 years ago with the evidence that CSC is a subpopulation of tumor cells that have renewal ability and can differentiate into several distinct linages. Therefore, CSCs play crucial role in the initiation and the maintenance of cancer. Moreover, it has been proposed throughout several studies that CSCs are behind the failure of the conventional chemo-/radiotherapy as well as cancer recurrence due to their ability to resist the therapy and their ability to re-regenerate. Thus, the need for targeted therapy to eliminate CSCs is crucial; for that reason, chimeric antigen receptor (CAR) T cells has currently been in use with high rate of success in leukemia and, to some degree, in patients with solid tumors. This review outlines the most common CSC populations and their common markers, in particular CD133, CD90, EpCAM, CD44, ALDH, and EGFRVIII, the interaction between CSCs and the immune system, CAR T cell genetic engineering and signaling, CAR T cells in targeting CSCs, and the barriers in using CAR T cells as immunotherapy to treat solid cancers.

Generation of Antitumor T Cells For Adoptive Cell Therapy With Artificial Antigen Presenting Cells

Adoptive cell therapy with ex vivo expanded tumor infiltrating lymphocytes or gene engineering T cells expressing chimeric antigen receptors (CAR) is a promising treatment for cancer patients. This production utilizes T-cell activation and transduction with activation beads and RetroNectin, respectively. However, the high cost of production is an obstacle for the broad clinical application of novel immunotherapeutic cell products. To facilitate production we refined our approach by using artificial antigen presenting cells (aAPCs) with receptors that ligate CD3, CD28, and the CD137 ligand (CD137L or 41BBL), as well as express the heparin binding domain (HBD), which binds virus for gene-transfer. We have used these aAPC for ex vivo gene engineering and expansion of tumor infiltrating lymphocytes and CAR T cells. We found that aAPCs can support efficacious T-cell expansion and transduction. Moreover, aAPCs expanded T cells exhibit higher production of IFN-γ and lower traits of T-cell exhaustion compared with bead expanded T cells. Our results suggest that aAPC provide a more physiological stimulus for T-cell activation than beads that persistently ligate T cells. The use of a renewable cell line to replace 2 critical reagents (beads and retronectin) for CAR T-cell production can significantly reduce the cost of production and make these therapies more accessible to patients.

Enhanced CAR-T cell activity against solid tumors by vaccine boosting through the chimeric receptor

Chimeric antigen receptor-T cell (CAR-T) therapy has been effective in the treatment of hematologic malignancies, but it has shown limited efficacy against solid tumors. Here we demonstrate an approach to enhancing CAR-T function in solid tumors by directly vaccine-boosting donor cells through their chimeric receptor in vivo. We designed amphiphile CAR-T ligands (amph-ligands) that, upon injection, trafficked to lymph nodes and decorated the surfaces of antigen-presenting cells, thereby priming CAR-Ts in the native lymph node microenvironment. Amph-ligand boosting triggered massive CAR-T expansion, increased donor cell polyfunctionality, and enhanced antitumor efficacy in multiple immunocompetent mouse tumor models. We demonstrate two approaches to generalizing this strategy to any chimeric antigen receptor, enabling this simple non-human leukocyte antigen-restricted approach to enhanced CAR-T functionality to be applied to existing CAR-T designs.

CAR T cells: continuation in a revolution of immunotherapy

The recent clinical successes of immunotherapy, as a result of a broader and more profound understanding of cancer immunobiology, and the leverage of this knowledge to effectively eradicate malignant cells, has revolutionised the field of cancer therapeutics. Immunotherapy is now considered the fifth pillar of cancer care, alongside surgery, chemotherapy, radiotherapy, and targeted therapy. Recently, the success of genetically modified T cells that express chimeric antigen receptors (CAR T cells) has generated considerable excitement. CAR T-cell therapy research and development has built on experience generated by laboratory research and clinical investigation of lymphokine-activated killer cells, tumour-infiltrating lymphocytes, and allogeneic haemopoietic stem-cell transplantation for cancer treatment. This Review aims to provide a background on the field of adoptive T-cell therapy and the development of genetically modified T cells, most notably CAR T-cell therapy. Many challenges exist to optimise efficacy, minimise toxicity, and broaden the application of immunotherapies based on T cells.

Sustained B cell depletion by CD19-targeted CAR T cells is a highly effective treatment for murine lupus

The failure of anti-CD20 antibody (Rituximab) as therapy for lupus may be attributed to the transient and incomplete B cell depletion achieved in clinical trials. Here, using an alternative approach, we report that complete and sustained CD19⁺ B cell depletion is a highly effective therapy in lupus models. CD8⁺ T cells expressing CD19-targeted chimeric antigen receptors (CARs) persistently depleted CD19⁺ B cells, eliminated autoantibody production, reversed disease manifestations in target organs, and extended life spans well beyond normal in the (NZB × NZW) F₁ and MRL ^fas/fas mouse models of lupus. CAR T cells were active for 1 year in vivo and were enriched in the CD44⁺CD62L⁺ T cell subset. Adoptively transferred splenic T cells from CAR T cell-treated mice depleted CD19⁺ B cells and reduced disease in naive autoimmune mice, indicating that disease control was cell-mediated. Sustained B cell depletion with CD19-targeted CAR T cell immunotherapy is a stable and effective strategy to treat murine lupus, and its effectiveness should be explored in clinical trials for lupus.

Is Hematopoietic Stem Cell Transplantation Required to Unleash the Full Potential of Immunotherapy in Acute Myeloid Leukemia?

From monoclonal antibodies (mAbs) to Chimeric Antigen Receptor (CAR) T cells, immunotherapies have enhanced the efficacy of treatments against B cell malignancies. The same has not been true for Acute Myeloid Leukemia (AML). Hematologic toxicity has limited the potential of modern immunotherapies for AML at preclinical and clinical levels. Gemtuzumab Ozogamicin has demonstrated hematologic toxicity, but the challenge of preserving normal hematopoiesis has become more apparent with the development of increasingly potent immunotherapies. To date, no single surface molecule has been identified that is able to differentiate AML from Hematopoietic Stem and Progenitor Cells (HSPC). Attempts have been made to spare hematopoiesis by targeting molecules expressed only on later myeloid progenitors as well as AML or using toxins that selectively kill AML over HSPC. Other strategies include targeting aberrantly expressed lymphoid molecules or only targeting monocyte-associated proteins in AML with monocytic differentiation. Recently, some groups have accepted that stem cell transplantation is required to access potent AML immunotherapy and envision it as a rescue to avoid severe hematologic toxicity. Whether it will ever be possible to differentiate AML from HSPC using surface molecules is unclear. Unless true specific AML surface targets are discovered, stem cell transplantation could be required to harness the true potential of immunotherapy in AML.

Safety and efficacy of axicabtagene ciloleucel in refractory large B-cell lymphomas

Aggressive large B-cell lymphomas represent a diverse population of diseases that are typically treated with anti-CD20 based immunochemotherapy. While this treatment is effective for a large proportion of patients, those that become refractory to induction therapy or experience disease relapse suffer an inferior overall prognosis, and novel treatment options are needed. Adoptive T-cell immunotherapy in the form of chimeric antigen receptor (CAR) T-cell therapy is one of the most revolutionary breakthroughs in the past several decades for the treatment of relapsed/refractory aggressive large B-cell lymphomas. Based on data from the pivotal ZUMA-1 study, axicabtagene ciloleucel (axi-cel) became the first-in-class anti-CD19 directed CAR T-cell therapy approved for patients with diffuse large B-cell lymphoma and other aggressive B-cell lymphoma variants. In this review, we provide an overview of CAR T-cell therapy, including its biology, manufacturing, and treatment course. In addition, we highlight the available efficacy data, review pertinent safety concerns, including cytokine release syndrome and neurologic toxicity, as well as provide an overview of emerging therapeutic strategies in the cellular therapy arena.

Updates on CAR T-cell therapy in B-cell malignancies

By increasing disease-free survival and offering the potential for long-term cure, chimeric antigen receptor (CAR) T-cell therapy has dramatically expanded therapeutic options among those with high-risk B-cell malignancies. As CAR T-cell utilization evolves however, novel challenges are generated. These include determining how to optimally integrate CAR T cells into standard of care and overcoming mechanisms of resistance to CAR T-cell therapy, such as evolutionary stress induced on cancer cells leading to immunophenotypic changes that allow leukemia to evade this targeted therapy. Compounding these challenges are the limited ability to determine differences between various CAR T-cell constructs, understanding the generalizability of trial outcomes from multiple sites utilizing unique CAR manufacturing strategies, and comparing distinct criteria for toxicity grading while defining optimal management. Additionally, as understanding of CAR behavior in humans has developed, strategies have appropriately evolved to proactively mitigate toxicities. These challenges offer complimentary insights and guide next steps to enhance the efficacy of this novel therapeutic modality. With a focus on B-cell malignancies as the paradigm for effective CAR T-cell therapy, this review describes advances in the field as well as current challenges and future directions.

Chimeric Antigen Receptors for the Tumour Microenvironment

Chimeric antigen receptor T (CAR-T) cell therapy has dramatically revolutionised cancer treatment. The FDA approval of two CAR-T cell products for otherwise incurable refractory B-cell acute lymphoblastic leukaemia (B-ALL) and aggressive B-cell non-Hodgkin lymphoma has established this treatment as an effective immunotherapy option. The race for extending CAR-T therapy for various tumours is well and truly underway. However, response rates in solid organ cancers have been inadequate thus far, partly due to challenges posed by the tumour microenvironment (TME). The TME is a complex structure whose role is to subserve the persistence and proliferation of tumours as well as support their escape from immune surveillance. It presents several obstacles like inhibitory immune checkpoint proteins, immunosuppressive cells, cytokines, chemokines, stromal factors and adverse metabolic pathways. CAR structure and CAR-T therapies have evolved to overcome these obstacles, and we now have several novel CARs with improved anti-tumour activity demonstrated in xenograft models and in some clinical trials. This chapter provides a discussion of the evolution of CAR-T therapies to enable targeting specific aspects of the TME.

Recent Advancements and Applications of Human Immune System Mice in Preclinical Immuno-Oncology

Significant advances in immunotherapies have resulted in the increasing need of predictive preclinical models to improve immunotherapeutic drug development, treatment combination, and to prevent or minimize toxicity in clinical trials. Immunodeficient mice reconstituted with human immune system (HIS), termed humanized mice or HIS mice, permit detailed analysis of human immune biology, development, and function. Although this model constitutes a great translational model, some aspects need to be improved as the incomplete engraftment of immune cells, graft versus host disease and the lack of human cytokines and growth factors. In this review, we discuss current HIS platforms, their pathology, and recent advances in their development to improve the quality of human immune cell reconstitution. We also highlight new technologies that can be used to better understand these models and how improved characterization is needed for their application in immuno-oncology safety, efficacy, and new modalities therapy development.

Donor-Derived CD123-Targeted CAR T Cell Serves as a RIC Regimen for Haploidentical Transplantation in a Patient With FUS-ERG+ AML

Background: Allogeneic hematopoietic stem cell transplantation (allo-HSCT) following chemotherapy is part of standard treatment protocol for patients with acute myeloid leukemia (AML). FUS-ERG+ AML is rare but has an extremely poor prognosis even with allo-HSCT in remission, possibly due to its a leukemia stem cell (LSC)-driven disease resulting in chemotherapy resistance and a novel therapy is urgently required. It has been reported that FUS-ERG-positive AML expresses CD123, a marker of LSC, in some cases. CD123-targeted CAR T cell (CART123) is promising immunotherapy, but how to improve the complete remission (CR) rate and rescue potential hematopoietic toxicity still need to explore.

Case Presentation: We used donor-derived CART123 as part of conditioning regimen for haploidentical HSCT (haplo-HSCT) in a patient with FUS-ERG+ AML who relapsed after allogeneic transplantation within 3 months, resists to multi-agent chemotherapy and donor lymphocyte infusion (DLI) and remained non-remission, aiming to reduce these chemotherapy-resistant blasts and rescue potential hematopoietic toxicity. The blasts in BM were reduced within 2 weeks and coincided with CAR copies expansion after CART123 infusion. The patient achieved full donor chimerism, CR with incomplete blood count recovery, and myeloid implantation.

Conclusion: Our results hints that CART123 reduces the chemotherapy-resistant AML blasts for FUS-ERG+ AML without affecting the full donor chimerism and myeloid implantation.

Multiple cancer-specific antigens are targeted by a chimeric antigen receptor on a single cancer cell

Human cancer cells were eradicated by adoptive transfer of T cells transduced with a chimeric antigen receptor (CAR) made from an antibody (237Ab) that is highly specific for the murine Tn-glycosylated podoplanin (Tn-PDPN). The objectives were to determine the specificity of these CAR-transduced T (CART) cells and the mechanism for the absence of relapse. We show that although the 237Ab bound only to cell lines expressing murine Tn-PDPN, the 237Ab-derived 237CART cells lysed multiple different human and murine cancers not predicted by the 237Ab binding. Nevertheless, the 237CART cell reactivities remained cancer specific because all recognitions were dependent on the Tn glycosylation that resulted from COSMC mutations that were not present in normal tissues. While Tn was required for the recognition by 237CART, Tn alone was not sufficient for 237CART cell activation. Activation of 237CART cells required peptide backbone recognition but tolerated substitutions of up to 5 of the 7 amino acid residues in the motif recognized by 237Ab. Together, these findings demonstrate what we believe is a new principle whereby simultaneous recognition of multiple independent Tn-glycopeptide antigens on a cancer cell makes tumor escape due to antigen loss unlikely.

Cell transfer-based immunotherapies in cancer: A review

In cell transfer therapy (CTT), immune cells such as innate immune-derived natural killer cells and dendritic cells as well as acquired immune-related T lymphocytes such as tumor-infiltrating lymphocytes and cytokine-activated or genetically modified peripheral blood T cells are used in the management of cancer. These therapies are increasingly becoming the most used treatment modality in cancer after tumor resection, chemotherapy, and radiotherapy. In adoptive cell transfer, the lymphocytes isolated from either a donor or the patient are modified ex vivo and reinfused to target malignant cells. Transferring in vitro-manipulated immune cells produces a continuous antitumor immune response. In this review, we evaluate the recent advances in CTT for the management of various malignancies.

Preclinical Targeting of Human Acute Myeloid Leukemia Using CD4-specific Chimeric Antigen Receptor (CAR) T Cells and NK Cells

Acute myeloid leukemia (AML) is an aggressive malignancy lacking targeted therapy due to shared molecular and transcriptional circuits as well as phenotypic markers with normal hematopoietic stem cells (HSCs). Identifying leukemia specific markers expressed on AML or AML subtypes for therapeutic targeting is of exquisite clinical value. Here we show that CD4, a T lymphocytes membrane glycoprotein that interacts with major histocompatibility complex class II antigens and is also expressed in certain AML subsets but not on HSCs is a proper target for genetically engineered chimeric antigen receptor T cells (CAR-T cells). Treatment with CD4 redirected CAR-T cell (CD4CAR) specifically eliminated CD4-expressing AML cell lines in vitro and exhibited a potent anti-leukemic effect in a systemic AML murine model in vivo. We also utilized natural killers as another vehicle for CAR engineered cells and this strategy similarly and robustly eliminated CD4- expressing AML cells in vitro and had a potent in vivo anti-leukemic effect and was noted to have shorter in vivo persistence. Our data offer a proof of concept for immunotherapeutic targeting of CD4 as a strategy to treat CD4 expressing refractory AML as a bridge to stem cell transplant (SCT) in a first in human clinical trial.

Cancer Immunotherapy Based on Natural Killer Cells: Current Progress and New Opportunities

Cancer immunotherapy has been firmly established as a new milestone for cancer therapy, with the development of multiple immune cells as therapeutic tools. Natural killer (NK) cells are innate immune cells endowed with potent cytolytic activity against tumors, and meanwhile act as regulatory cells for the immune system. The efficacy of NK cell-mediated immunotherapy can be enhanced by immune stimulants such as cytokines and antibodies, and adoptive transfer of activated NK cells expanded ex vivo. In addition, NK cells can arm themselves with chimeric antigen receptors (CARs), which may greatly enhance their anti-tumor activity. Most recently, extracellular vesicles (EVs) derived from NK cells show promising anti-tumor effects in preclinical studies. Herein, we carefully review the current progress in these NK cell-based immunotherapeutic strategies (NK cells combined with stimulants, adoptive transfer of NK cells, CAR-NK cells, and NK EVs) for the treatment of cancers, and discussed the challenges and opportunities for opening a new horizon for cancer immunotherapy.

CAR T Cell Toxicity: Current Management and Future Directions

By late 2018, 2 chimeric antigen receptor T (CAR T) cell products have been approved by US and European regulatory authorities. Tisagenlecleucel (Kymriah, Novartis) is indicated in the treatment of patients up to 25 years of age with B-cell acute lymphoblastic leukemia (ALL) that is refractory or in second or later relapse, or adult patients with large B-cell lymphoma relapsed or refractory (r/r) after 2 or more lines of systemic therapy, including diffuse large B-cell lymphoma (DLBCL) not otherwise specified, high grade B-cell lymphoma and DLBCL arising from follicular lymphoma. Axicabtagene ciloleucel (Yescarta, Kite) is indicated for the treatment of adult patients with large B-cell lymphoma relapsed or refractory after 2 or more lines of systemic therapy, including DLBCL not otherwise specified, primary mediastinal large B-cell lymphoma, high grade B-cell lymphoma, and DLBCL arising from follicular lymphoma (ZUMA-1 trial). This review will offer a practical guide for the recognition and management of the most important toxicities related to the use of the current commercial CAR T cells, and also highlight strategies to diminish these side effects in the future.

CD40 Ligand-Modified Chimeric Antigen Receptor T Cells Enhance Antitumor Function by Eliciting an Endogenous Antitumor Response

Chimeric antigen receptor (CAR) T cells provide great efficacy in B cell malignancies. However, improved CAR T cell therapies are still needed. Here, we engineered tumor-targeted CAR T cells to constitutively express the immune-stimulatory molecule CD40 ligand (CD40L) and explored efficacy in different mouse leukemia/lymphoma models. We observed that CD40L⁺ CAR T cells circumvent tumor immune escape via antigen loss through CD40/CD40L-mediated cytotoxicity and induction of a sustained, endogenous immune response. After adoptive cell transfer, the CD40L⁺ CAR T cells displayed superior antitumor efficacy, licensed antigen-presenting cells, enhanced recruitment of immune effectors, and mobilized endogenous tumor-recognizing T cells. These effects were absent in Cd40^-/- mice and provide a rationale for the use of CD40L⁺ CAR T cells in cancer treatment.

Challenges of driving CD30-directed CAR-T cells to the clinic

Chimeric antigen receptor T (CAR-T) cells are a promising new treatment for patients with relapsed or refractory hematologic malignancies, including lymphoma. Given the success of CAR-T cells directed against CD19, new targets are being developed and tested, since not all lymphomas express CD19. CD30 is promising target as it is universally expressed in virtually all classical Hodgkin lymphomas, anaplastic large cell lymphomas, and in a proportion of other lymphoma types, including cutaneous T cell lymphomas and diffuse large B cell lymphomas. Preclinical studies with CD30-directed CAR-T cells support the feasibility of this approach. Recently, two clinical trials of CD30-directed CAR-T cells in relapsed/refractory CD30+ lymphomas, including Hodgkin lymphoma, have been reported with minimal toxicities noted and preliminary efficacy seen in a proportion of patients. However, improving the persistence and expansion of CAR-T cells is key to further enhancing the efficacy of this treatment approach. Future directions include optimizing the lymphodepletion regimen, enhancing migration to the tumor site, and combination with other immune regulators. Several ongoing and upcoming clinical trials of CD30-directed CAR-T cells are expected to further enhance this approach to treat patients with relapsed and refractory CD30+ lymphomas.

T-cell receptor-α CDR3 domain chemical features correlate with survival rates in bladder cancer

PURPOSE

In certain cancer settings, a T-cell response to cancer represents a relatively favorable outcome. Thus, the near-future challenges include a better understanding of exactly which T-cell features contribute to a response to which cancer antigen-groups, to maximize the opportunities for tumor-infiltrating lymphocyte (TIL)-based therapies and other immunotherapies.

METHODS

The immune receptor complementarity determining region-3 (CDR3) is considered to be important for antigen binding, hence, in this report, we evaluated the chemical features of the CDR3 of 846 T-cell receptor-α (TCR-α) coding regions associated with bladder tumor tissue, using bioinformatics databases.

RESULTS

Results indicated that statistically significantly distinct, low value, CDR3 region isoelectric points associate with a better outcome (log rank p < 0.027, overall survival). Moreover, in samples representing the more favorable isoelectric points, known driver mutations, for example, PIK3CA (E → K) with chemically complementary features overlap the better-outcome, low isoelectric point samples. Further work extended these results, i.e., survival rate-CDR3 associations, to other CDR3 chemical features and other cancers, consistent with the initial isoelectric point-related, bladder cancer findings.

CONCLUSIONS

A bioinformatics assessment of cancer-associated TCR biochemical features may improve the accuracy of the predictions of which TILs will be best for ex-vivo amplification and which patients will benefit from other immunotherapies.

Clinical Utilization of Chimeric Antigen Receptor T Cells in B Cell Acute Lymphoblastic Leukemia: An Expert Opinion from the European Society for Blood and Marrow Transplantation and the American Society for Blood and Marrow Transplantation

On August 30, 2017 the US Food and Drug Administration approved tisagenlecleucel (Kymriah; Novartis, Basel, Switzerland), a synthetic bioimmune product of anti-CD19 chimeric antigen receptor T cells (CAR-T), for the treatment of children and young adults with relapsed/refractory B cell acute lymphoblastic leukemia (B-ALL). With this new era of personalized cancer immunotherapy, multiple challenges are present, ranging from implementation of a CAR-T program to safe delivery of the drug, long-term toxicity monitoring, and disease assessments. To address these issues experts representing the American Society for Blood and Marrow Transplant, the European Society for Blood and Marrow Transplantation, the International Society of Cell and Gene Therapy, and the Foundation for the Accreditation of Cellular Therapy formed a global CAR-T task force to identify and address key questions pertinent for hematologists and transplant physicians regarding the clinical use of anti CD19 CAR-T therapy in patients with B-ALL. This article presents an initial roadmap for navigating common clinical practice scenarios that will become more prevalent now that the first commercially available CAR-T product for B-ALL has been approved.

Clinical utilization of Chimeric Antigen Receptor T-cells (CAR-T) in B-cell acute lymphoblastic leukemia (ALL)-an expert opinion from the European Society for Blood and Marrow Transplantation (EBMT) and the American Society for Blood and Marrow Transplantation (ASBMT)

On August 30, 2017, the U.S. Food and Drug Administration (US-FDA) approved tisagenlecleucel (KYMRIAH, Novartis, Basel, Switzerland), a synthetic bioimmune product of anti-CD19 chimeric antigen receptor-T cells (CAR-T), for the treatment of children and young adults with relapsed/refractory B-cell acute lymphoblastic leukemia (B-ALL). With this new era of personalized cancer immunotherapy, multiple challenges are present ranging from implementation of a CAR-T program to safe delivery of the drug, long-term toxicity monitoring and disease assessments. To address these issues, experts representing the American Society for Blood and Marrow Transplant (ASBMT), the European Group for Blood and Marrow Transplantation (EBMT), the International Society of Cell and Gene Therapy (ISCT), and the Foundation for the Accreditation of Cellular Therapy (FACT), formed a global CAR-T task force to identify and address key questions pertinent for hematologists and transplant physicians regarding the clinical use of anti CD19 CAR-T therapy in patients with B-ALL. This article presents an initial roadmap for navigating common clinical practice scenarios that will become more prevalent now that the first commercially available CAR-T product for B-ALL has been approved.

Distinct Regulation of Th17 and Th1 Cell Differentiation by Glutaminase-Dependent Metabolism

Activated T cells differentiate into functional subsets with distinct metabolic programs. Glutaminase (GLS) converts glutamine to glutamate to support the tricarboxylic acid cycle and redox and epigenetic reactions. Here, we identify a key role for GLS in T cell activation and specification. Though GLS deficiency diminished initial T cell activation and proliferation and impaired differentiation of Th17 cells, loss of GLS also increased Tbet to promote differentiation and effector function of CD4 Th1 and CD8 CTL cells. This was associated with altered chromatin accessibility and gene expression, including decreased PIK3IP1 in Th1 cells that sensitized to IL-2-mediated mTORC1 signaling. In vivo, GLS null T cells failed to drive Th17-inflammatory diseases, and Th1 cells had initially elevated function but exhausted over time. Transient GLS inhibition, however, led to increased Th1 and CTL T cell numbers. Glutamine metabolism thus has distinct roles to promote Th17 but constrain Th1 and CTL effector cell differentiation.

Disruption of a self-amplifying catecholamine loop reduces cytokine release syndrome

Cytokine release syndrome (CRS) is a life-threatening complication of several new immunotherapies used to treat cancers and autoimmune diseases^1-5. Here we report that atrial natriuretic peptide can protect mice from CRS induced by such agents by reducing the levels of circulating catecholamines. Catecholamines were found to orchestrate an immunodysregulation resulting from oncolytic bacteria and lipopolysaccharide through a self-amplifying loop in macrophages. Myeloid-specific deletion of tyrosine hydroxylase inhibited this circuit. Cytokine release induced by T-cell-activating therapeutic agents was also accompanied by a catecholamine surge and inhibition of catecholamine synthesis reduced cytokine release in vitro and in mice. Pharmacologic catecholamine blockade with metyrosine protected mice from lethal complications of CRS resulting from infections and various biotherapeutic agents including oncolytic bacteria, T-cell-targeting antibodies and CAR-T cells. Our study identifies catecholamines as an essential component of the cytokine release that can be modulated by specific blockers without impairing the therapeutic response.

Switchable control over in vivo CAR T expansion, B cell depletion, and induction of memory

Chimeric antigen receptor (CAR) T cell therapy represents a powerful strategy in immuno-oncology. Nevertheless, associated life-threatening toxicities and chronic B cell aplasia have underscored the need to control engineered T cells in the patient. To address these challenges, we have previously developed a switchable CAR (sCAR) T cell platform that allows dose-titratable control over CAR T cell activity by using antibody-based switches. Here, we demonstrate in a syngeneic murine model that the switchable platform can impart antitumor efficacy while dissociating long-term persistence from chronic B cell aplasia. Further, the functional reversibility of the switchable platform can be leveraged to incorporate “rest” phases through cyclical dosing of the switch to enable the induction of a robust central memory population for in vivo, on-demand expansion of sCAR T cells.

Chimeric antigen receptor (CAR) T cells with a long-lived memory phenotype are correlated with durable, complete remissions in patients with leukemia. However, not all CAR T cell products form robust memory populations, and those that do can induce chronic B cell aplasia in patients. To address these challenges, we previously developed a switchable CAR (sCAR) T cell system that allows fully tunable, on/off control over engineered cellular activity. To further evaluate the platform, we generated and assessed different murine sCAR constructs to determine the factors that afford efficacy, persistence, and expansion of sCAR T cells in a competent immune system. We find that sCAR T cells undergo significant in vivo expansion, which is correlated with potent antitumor efficacy. Most importantly, we show that the switch dosing regimen not only allows control over B cell populations through iterative depletion and repopulation, but that the “rest” period between dosing cycles is the key for induction of memory and expansion of sCAR T cells. These findings introduce rest as a paradigm in enhancing memory and improving the efficacy and persistence of engineered T cell products.

4-1BB enhancement of CAR T function requires NF-κB and TRAFs

Chimeric antigen receptors (CARs) have an antigen-binding domain fused to transmembrane, costimulatory, and CD3ζ domains. Two CARs with regulatory approval include a CD28 or 4-1BB costimulatory domain. While both CARs achieve similar clinical outcomes, biologic differences have become apparent but not completely understood. Therefore, in this study we aimed to identify mechanistic differences between 4-1BB and CD28 costimulation that contribute to the biologic differences between the 2 CARs and could be exploited to enhance CAR T cell function. Using CD19-targeted CAR T cells with 4-1BB we determined that enhancement of T cell function is driven by NF-κB. Comparison to CAR T cells with CD28 also revealed that 4-1BB is associated with more antiapoptotic proteins and dependence on persistence for B cell killing. While TNF receptor-associated factor 2 (TRAF2) has been presupposed to be required for 4-1BB costimulation in CAR T cells, we determined that TRAF1 and TRAF3 are also critical. We observed that TRAFs impacted CAR T viability and proliferation, as well as cytotoxicity and/or cytokines, in part by regulating NF-κB. Our study demonstrates how 4-1BB costimulation in CAR T cells impacts antitumor eradication and clinical outcomes and has implications for enhanced CAR design.

Viral and Nonviral Engineering of Natural Killer Cells as Emerging Adoptive Cancer Immunotherapies

Natural killer (NK) cells are powerful immune effectors whose antitumor activity is regulated through a sophisticated network of activating and inhibitory receptors. As effectors of cancer immunotherapy, NK cells are attractive as they do not attack healthy self-tissues nor do they induce T cell-driven inflammatory cytokine storm, enabling their use as allogeneic adoptive cellular therapies. Clinical responses to adoptive NK-based immunotherapy have been thwarted, however, by the profound immunosuppression induced by the tumor microenvironment, particularly severe in the context of solid tumors. In addition, the short postinfusion persistence of NK cells in vivo has limited their clinical efficacy. Enhancing the antitumor immunity of NK cells through genetic engineering has been fueled by the promise that impaired cytotoxic functionality can be restored or augmented with the use of synthetic genetic approaches. Alongside expressing chimeric antigen receptors to overcome immune escape by cancer cells, enhance their recognition, and mediate their killing, NK cells have been genetically modified to enhance their persistence in vivo by the expression of cytokines such as IL-15, avoid functional and metabolic tumor microenvironment suppression, or improve their homing ability, enabling enhanced targeting of solid tumors. However, NK cells are notoriously adverse to endogenous gene uptake, resulting in low gene uptake and transgene expression with many vector systems. Though viral vectors have achieved the highest gene transfer efficiencies with NK cells, nonviral vectors and gene transfer approaches—electroporation, lipofection, nanoparticles, and trogocytosis—are emerging. And while the use of NK cell lines has achieved improved gene transfer efficiencies particularly with viral vectors, challenges with primary NK cells remain. Here, we discuss the genetic engineering of NK cells as they relate to NK immunobiology within the context of cancer immunotherapy, highlighting the most recent breakthroughs in viral vectors and nonviral approaches aimed at genetic reprogramming of NK cells for improved adoptive immunotherapy of cancer, and, finally, address their clinical status.

Steering CAR T cells to distinguish friend from foe

CD19-specific chimeric antigen receptor (CAR)⁺ T cells have demonstrated clinical efficacy and long-lasting remissions, concomitant with tolerable normal B-cell aplasia. However, many tumor-associated antigens (TAAs) are expressed on normal tissues, the destruction of which would lead to intolerable toxicity. Thus, there is a need to engineer CAR⁺ T cells with improved safety profiles to restrict toxicity against TAA-expressing normal tissues. Bioengineering approaches include: (i) targeting CAR⁺ T cells to the tumor site, (ii) limiting CAR⁺ T-cell persistence, and (iii) restricting CAR activation. We review and evaluate strategies to engineer CAR⁺ T cells to reduce the potential of on-target, off-tissue toxicity.

Interferon gene therapy reprograms the leukemia microenvironment inducing protective immunity to multiple tumor antigens

Immunotherapy is emerging as a new pillar of cancer treatment with potential to cure. However, many patients still fail to respond to these therapies. Among the underlying factors, an immunosuppressive tumor microenvironment (TME) plays a major role. Here we show that monocyte-mediated gene delivery of IFNα inhibits leukemia in a mouse model. IFN gene therapy counteracts leukemia-induced expansion of immunosuppressive myeloid cells and imposes an immunostimulatory program to the TME, as shown by bulk and single-cell transcriptome analyses. This reprogramming promotes T-cell priming and effector function against multiple surrogate tumor-specific antigens, inhibiting leukemia growth in our experimental model. Durable responses are observed in a fraction of mice and are further increased combining gene therapy with checkpoint blockers. Furthermore, IFN gene therapy strongly enhances anti-tumor activity of adoptively transferred T cells engineered with tumor-specific TCR or CAR, overcoming suppressive signals in the leukemia TME. These findings warrant further investigations on the potential development of our gene therapy strategy towards clinical testing.

An immune suppressive tumor microenvironment (TME) is a limitation for immunotherapy. Here the authors show that, in a B cell acute lymphoblastic leukemia mouse model, gene-based delivery of IFNα  reprograms the leukemia-induced immunosuppressive TME into immunostimulatory and enhances T-cell responses.

Preclinical Efficacy and Safety of CD19CAR Cytokine-Induced Killer Cells Transfected with Sleeping Beauty Transposon for the Treatment of Acute Lymphoblastic Leukemia

Infusion of patient-derived CD19-specific chimeric antigen receptor (CAR) T cells engineered by viral vectors achieved complete remission and durable response in relapsed and refractory (r/r) B-lineage neoplasms. Here, we expand on those findings by providing a preclinical evaluation of allogeneic non-viral cytokine-induced killer (CIK) cells transfected with the Sleeping Beauty (SB) transposon CD19CAR (CARCIK-CD19). Specifically, thanks to a large-scale 18-day manufacturing process, it was possible to achieve stable CD19CAR expression (62.425 ± 6.399%) and efficient T-cell expansion (23.36 ± 3.00-fold). Frozen/thawed CARCIK-CD19 remained fully functional both in vitro and in an established patient-derived xenograft (PDX) of MLL-ENL rearranged acute lymphoblastic leukemia (ALL). CARCIK-CD19 showed a dose-dependent antitumor response and prolonged persistence in a PDX, bearing the feature of a Philadelphia-like ALL with PAX5/AUTS2 translocation, and in a survival model of lymphoma, achieving complete eradication of disseminated tumors. Finally, the infusion of CARCIK-CD19 proved to be safe and well tolerated in a biodistribution and toxicity model. The infused cells persisted in the hematopoietic and post-injection perfused organs until the end of the study and consisted of CD8⁺, CD56⁺, and CAR⁺ T cells. Overall, these findings provide important implications for non-viral technology and the proof-of-concept that donor-derived CARCIK-CD19 are indeed effective against relapsed ALL, a possibility that will be tested in Phase I/II clinical trials after allogeneic hematopoietic stem-cell transplantation.

Preclinical Models in Chimeric Antigen Receptor-Engineered T-Cell Therapy

Cancer immunotherapy has enormous potential in inducing long-term remission in cancer patients, and chimeric antigen receptor (CAR)-engineered T cells have been largely successful in treating hematological malignancies in the clinic. CAR-T therapy has not been as effective in treating solid tumors, in part due to the immunosuppressive tumor microenvironment. Additionally, CAR-T therapy can cause dangerous side effects, including off-tumor toxicity, cytokine release syndrome, and neurotoxicity. Animal models of CAR-T therapy often fail to predict such adverse events and frequently overestimate the efficacy of the treatment. Nearly all preclinical CAR-T studies have been performed in mice, including syngeneic, xenograft, transgenic, and humanized mouse models. Recently, a few studies have used primate models to mimic clinical side effects better. To date, no single model perfectly recapitulates the human immune system and tumor microenvironment, and some models have revealed CAR-T limitations that were contradicted or missed entirely in other models. Careful model selection based on the primary goals of the study is a crucial step in evaluating CAR-T treatment. Advancements are being made in preclinical models, with the ultimate objective of providing safer, more effective CAR-T therapy to patients.

Myeloid Conditioning with c-kit-Targeted CAR-T Cells Enables Donor Stem Cell Engraftment

We report a novel approach to bone marrow (BM) conditioning using c-kit-targeted chimeric antigen receptor T (c-kit CAR-T) cells in mice. Previous reports using anti-c-kit or anti-CD45 antibody linked to a toxin such as saporin have been promising. We developed a distinctly different approach using c-kit CAR-T cells. Initial studies demonstrated in vitro killing of hematopoietic stem cells by c-kit CAR-T cells but poor expansion in vivo and poor migration of CAR-T cells into BM. Pre-treatment of recipient mice with low-dose cyclophosphamide (125 mg/kg) together with CXCR4 transduction in the CAR-T cells enhanced trafficking to and expansion in BM (<1%-13.1%). This resulted in significant depletion of the BM c-kit⁺ population (9.0%-0.1%). Because congenic Thy1.1 CAR-T cells were used in the Thy1.2-recipient mice, anti-Thy1.1 antibody could be used to deplete CAR-T cells in vivo before donor BM transplant. This achieved 20%-40% multilineage engraftment. We applied this conditioning to achieve an average of 28% correction of chronic granulomatous disease mice by wild-type BM transplant. Our findings provide a proof of concept that c-kit CAR-T cells can achieve effective BM conditioning without chemo-/radiotherapy. Our work also demonstrates that co-expression of a trafficking receptor can enhance targeting of CAR-T cells to a designated tissue.

Versatile CAR T-cells for cancer immunotherapy

Chimeric antigen receptor (CAR) T-cell therapy has been clinically proven to efficiently combat haematological malignancies. However, continuous efforts are required to increase the specificity of CAR T-cells against tumour versus normal tissues, and are essential to improve their antitumour activity in solid tumours. This review summarises the structure of major CAR designs, and strategies to overcome immunosuppressive tumour microenvironment, and reduce toxicities. Along with reviewing currently available techniques that allow the elimination of CAR T-cells after they fulfil their desired functions, using suicide genes, drug elimination strategies are also introduced. A better understanding of the strengths and pitfalls of CAR T-cell therapy will provide fundamental knowledge for the improvement of engineered T-cell therapy in the near future.

Highly Efficient and Versatile Plasmid-Based Gene Editing in Primary T Cells

Adoptive cell transfer is an important approach for basic research and emerges as an effective treatment for various diseases, including infections and blood cancers. Direct genetic manipulation of primary immune cells opens up unprecedented research opportunities and could be applied to enhance cellular therapeutic products. In this article, we report highly efficient genome engineering in primary murine T cells using a plasmid-based RNA-guided CRISPR system. We developed a straightforward approach to ablate genes in up to 90% of cells and to introduce precisely targeted single nucleotide polymorphisms in up to 25% of the transfected primary T cells. We used gene editing-mediated allele switching to quantify homology-directed repair, systematically optimize experimental parameters, and map a native B cell epitope in primary T cells. Allele switching of a surrogate cell surface marker can be used to enrich cells, with successful simultaneous editing of a second gene of interest. Finally, we applied the approach to correct two disease-causing mutations in the Foxp3 gene. Repairing the cause of the scurfy syndrome, a 2-bp insertion in Foxp3, and repairing the clinically relevant Foxp3^K276X mutation restored Foxp3 expression in primary T cells.

T-cell Immunotherapies and the Role of Nonclinical Assessment: The Balance between Efficacy and Pathology

Gene-engineered T-cell therapies have the potential to revolutionize the treatment of cancer. These therapies have shown exceptional clinical efficacy specifically in the field of B-cell malignancies and the first products (Kymriah™ and Yescarta™) have recently been approved in the United States for specific indications. The power of these treatments is also linked with a distinct set of toxicities both predicted and unpredicted, including off-tumor activity, cytokine release syndromes, and neurotoxicity, occasionally with fatal consequences. As these therapies begin to reach more patients, it is critical to develop the nonclinical tools to adequately determine the mechanisms driving these toxicities, to assess the safety risks of candidate products, and to develop strategies for safety management.