Differential role of Th1 and Th2 cytokines in autotoxicity driven by CD19-specific second-generation chimeric antigen receptor T cells in a mouse model

A major role for CD4+ T cells in driving cytokine release syndrome during CAR T cell therapy

Anti-CD19 chimeric antigen receptor (CAR) T cell therapy represents a breakthrough for the treatment of B cell malignancies. Yet, it can lead to severe adverse events, including cytokine release syndrome (CRS), which may require urgent clinical management. Whether interpatient variability in CAR T cell subsets contributes to CRS is unclear. Here, we show that CD4+ CAR T cells are the main drivers of CRS. Using an immunocompetent model of anti-CD19 CAR T cell therapy, we report that CD4+, but not CD8+, CAR T cells elicit physiological CRS-like manifestations associated with the release of inflammatory cytokines. In CAR T cell-treated patients, CRS occurrence and severity are significantly associated with high absolute values of CD4+ CAR T cells in the blood. CRS in mice occurs independently of CAR T cell-derived interferon γ (IFN-γ) but requires elevated tumor burden. Thus, adjusting the CD4:CD8 CAR T cell ratio to patient tumor load may help mitigate CAR T cell-associated toxicities.

Tumor-intrinsic sensitivity to the pro-apoptotic effects of IFN-γ is a major determinant of CD4+ CAR T-cell antitumor activity

CD4+ T cells and CD4+ chimeric antigen receptor (CAR) T cells display highly variable antitumor activity in preclinical models and in patients; however, the mechanisms dictating how and when CD4+ T cells promote tumor regression are incompletely understood. With the help of functional intravital imaging, we report that interferon (IFN)-γ production but not perforin-mediated cytotoxicity was the dominant mechanism for tumor elimination by anti-CD19 CD4+ CAR T cells. Mechanistically, mouse or human CD4+ CAR T-cell-derived IFN-γ diffused extensively to act on tumor cells at distance selectively killing tumors sensitive to cytokine-induced apoptosis, including antigen-negative variants. In anti-CD19 CAR T-cell-treated patients exhibiting elevated CAR CD4:CD8 ratios, strong induction of serum IFN-γ was associated with increased survival. We propose that the sensitivity of tumor cells to the pro-apoptotic activity of IFN-γ is a major determinant of CD4+ CAR T-cell efficacy and may be considered to guide the use of CD4+ T cells during immunotherapy.

High-Dimensional Cytometry Dissects Immunological Fingerprints of Idiopathic Inflammatory Myopathies

Chronic inflammation of skeletal muscle is the common feature of idiopathic inflammatory myopathies (IIM). Given the rarity of the disease and potential difficulty of routinely obtaining target tissue, i.e., standardized skeletal muscle, our understanding of immune signatures of the IIM spectrum remains incomplete. Further insight into the immune topography of IIM is needed to determine specific treatment targets according to clinical and immunological phenotypes. Thus, we used high-dimensional flow cytometry to investigate the immune phenotypes of anti-synthetase syndrome (ASyS), dermatomyositis (DM) and inclusion-body myositis (IBM) patients as representative entities of the IIM spectrum and compared them to healthy controls. We studied the CD8, CD4 and B cell compartments in the blood aiming to provide a contemporary overview of the immune topography of the IIM spectrum. ASyS was characterized by altered CD4 composition and expanded T follicular helper cells supporting B cell-mediated autoimmunity. For DM, unsupervised clustering identified expansion of distinct B cell subtypes highly expressing immunoglobulin G4 (IgG4) and CD38. Lastly, terminally differentiated, cytotoxic CD8 T cells distinguish IBM from other IIM. Interestingly, these terminally differentiated CD8 T cells highly expressed the integrin CD18 mediating cellular adhesion and infiltration. The distinct immune cell topography of IIM might provide the framework for targeted treatment approaches potentially improving therapeutic outcomes.

Applying a Clinical Lens to Animal Models of CAR-T Cell Therapies

Chimeric antigen receptor (CAR)-T cells have emerged as a promising treatment modality for various hematologic and solid malignancies over the past decade. Animal models remain the cornerstone of pre-clinical evaluation of human CAR-T cell products and are generally required by regulatory agencies prior to clinical translation. However, pharmacokinetics and pharmacodynamics of adoptively transferred T cells are dependent on various recipient factors, posing challenges for accurately predicting human engineered T cell behavior in non-human animal models. For example, murine xenograft models did not forecast now well-established cytokine-driven systemic toxicities of CAR-T cells seen in humans, highlighting the limitations of animal models that do not perfectly recapitulate complex human immune systems. Understanding the concordance as well as discrepancies between existing pre-clinical animal data and human clinical experiences, along with established advantages and limitations of each model, will facilitate investigators’ ability to appropriately select and design animal models for optimal evaluation of future CAR-T cell products. We summarize the current state of animal models in this field, and the advantages and disadvantages of each approach depending on the pre-clinical questions being asked.

CAR-T Cell Performance: How to Improve Their Persistence?

Adoptive cell therapy with T cells reprogrammed to express chimeric antigen receptors (CAR-T cells) has been highly successful in patients with hematological neoplasms. However, its therapeutic benefits have been limited in solid tumor cases. Even those patients who respond to this immunotherapy remain at risk of relapse due to the short-term persistence or non-expansion of CAR-T cells; moreover, the hostile tumor microenvironment (TME) leads to the dysfunction of these cells after reinfusion. Some research has shown that, in adoptive T-cell therapies, the presence of less differentiated T-cell subsets within the infusion product is associated with better clinical outcomes. Naive and memory T cells persist longer and exhibit greater antitumor activity than effector T cells. Therefore, new methods are being studied to overcome the limitations of this therapy to generate CAR-T cells with these ideal phenotypes. In this paper, we review the characteristics of T-cell subsets and their implications in the clinical outcomes of adoptive therapy with CAR-T cells. In addition, we describe some strategies developed to overcome the reduced persistence of CAR T-cells and alternatives to improve this therapy by increasing the expansion ability and longevity of modified T cells. These methods include cell culture optimization, incorporating homeostatic cytokines during the expansion phase of manufacturing, modulation of CAR-T cell metabolism, manipulating signaling pathways involved in T-cell differentiation, and strategies related to CAR construct designs.

Brain capillary obstruction during neurotoxicity in a mouse model of anti-CD19 chimeric antigen receptor T-cell therapy

Immunotherapy for haematologic malignancies with CD19-directed chimeric antigen receptor T cells has been highly successful at eradicating cancer but is associated with acute neurotoxicity in ∼40% of patients. This neurotoxicity correlates with systemic cytokine release syndrome, endothelial activation and disruption of endothelial integrity, but it remains unclear how these mechanisms interact and how they lead to neurologic dysfunction. We hypothesized that dysfunction of the neurovascular unit is a key step in the development of neurotoxicity. To recapitulate the interaction of the intact immune system with the blood-brain barrier, we first developed an immunocompetent mouse model of chimeric antigen receptor T-cell treatment-associated neurotoxicity. We treated wild-type mice with cyclophosphamide lymphodepletion followed by escalating doses of murine CD19-directed chimeric antigen receptor T cells. Within 3-5 days after chimeric antigen receptor T-cell infusion, these mice developed systemic cytokine release and abnormal behaviour as measured by daily neurologic screening exams and open-field testing. Histologic examination revealed widespread brain haemorrhages, diffuse extravascular immunoglobulin deposition, loss of capillary pericyte coverage and increased prevalence of string capillaries. To measure any associated changes in cerebral microvascular blood flow, we performed in vivo two-photon imaging through thinned-skull cranial windows. Unexpectedly, we found that 11.9% of cortical capillaries were plugged by Day 6 after chimeric antigen receptor T-cell treatment, compared to 1.1% in controls treated with mock transduced T cells. The capillary plugs comprised CD45+ leucocytes, a subset of which were CD3+ T cells. Plugging of this severity is expected to compromise cerebral perfusion. Indeed, we found widely distributed patchy hypoxia by hypoxyprobe immunolabelling. Increased serum levels of soluble ICAM-1 and VCAM-1 support a putative mechanism of increased leucocyte-endothelial adhesion. These data reveal that brain capillary obstruction may cause sufficient microvascular compromise to explain the clinical phenotype of chimeric antigen receptor T-cell neurotoxicity. The translational impact of this finding is strengthened by the fact that our mouse model closely approximates the kinetics and histologic findings of the chimeric antigen receptor T-cell neurotoxicity syndrome seen in human patients. This new link between systemic immune activation and neurovascular unit injury may be amenable to therapeutic intervention.

Associação Brasileira de Hematologia, Hemoterapia e Terapia Celular Consensus on genetically modified cells. VIII: CAR-T cells: preclinical development - Safety and efficacy evaluation

Currently, there are four CAR-T products commercially available on the market. CAR-T cells have shown high remission rates and they represent an effective treatment option for patients with resistant or refractory B cell malignancies. Approval of these cell therapy products came after an extended period of preclinical evaluation that demonstrated unprecedented efficacy in this difficult-to-treat patient population. This review article outlines the main preclinical evaluations needed for CAR T cell product development.

Preclinical pharmacology modeling of chimeric antigen receptor T therapies

Chimeric antigen receptor (CAR) T cells have largely been successful in treating hematological malignancies in the clinic but have not been as effective in treating solid tumors, in part, owing to poor access and the immunosuppressive tumor microenvironment. In addition, CAR-T therapy can cause potentially life-threatening side effects, including cytokine release syndrome and neurotoxicity. Current preclinical testing of CAR-T therapy efficacy is typically performed in mouse tumor models, which often fails to predict toxicity. Recent developments in humanized models and transgenic mice as well as in vitro three-dimensional organoids in early development and nonhuman primate models are being adopted for CAR-T cell efficacy and toxicity assessment. However, because no single model perfectly recapitulates the human immune system and tumor microenvironment, careful model selection based on their respective pros and cons is crucial for adequate evaluation of different CAR-T treatments, so that their clinical development can be better supported.

New CARs on and off the road: challenges and new developments in CAR-T cell therapy

Building on the tremendous success of chimeric antigen receptor T-cell therapy in hematological malignancies, there are efforts under way to overcome the challenges associated with this treatment and expand its application to solid tumors. In this fast-evolving field, new therapeutic options are constantly generated, tested in model systems, and further evaluated in clinical trials. In this review, we provide an overview of recent challenges and developments associated with engineered T cells and chimeric antigen receptor T-cell applications. We report on the most recent progress in hematological malignancies and highlight technical advances for applications in solid tumors.

Combined tumor-directed recruitment and protection from immune suppression enable CAR T cell efficacy in solid tumors

CAR T cell therapy remains ineffective in solid tumors, due largely to poor infiltration and T cell suppression at the tumor site. T regulatory (Treg) cells suppress the immune response via inhibitory factors such as transforming growth factor-β (TGF-β). Treg cells expressing the C-C chemokine receptor 8 (CCR8) have been associated with poor prognosis in solid tumors. We postulated that CCR8 could be exploited to redirect effector T cells to the tumor site while a dominant-negative TGF-β receptor 2 (DNR) can simultaneously shield them from TGF-β. We identified that CCL1 from activated T cells potentiates a feedback loop for CCR8+ T cell recruitment to the tumor site. This sustained and improved infiltration of engineered T cells synergized with TGF-β shielding for improved therapeutic efficacy. Our results demonstrate that addition of CCR8 and DNR into CAR T cells can render them effective in solid tumors.

A cross-talk between CAR T cell subsets and the tumor microenvironment is essential for sustained cytotoxic activity

Chimeric antigen receptor (CAR) T cell therapy relies on the activity of a large pool of tumor-targeting cytotoxic effectors. Whether CAR T cells act autonomously or require interactions with the tumor microenvironment (TME) remains incompletely understood. Here, we report an essential cross-talk between CAR T cell subsets and the TME for tumor control in an immunocompetent mouse B cell lymphoma model of anti-CD19 CAR T cell therapy. Using single-cell RNA sequencing, we revealed substantial modification of the TME during CAR T cell therapy. Interferon-γ (IFN-γ) produced by CAR T cells not only enhanced endogenous T and natural killer cell activity but was also essential for sustaining CAR T cell cytotoxicity, as revealed by intravital imaging. CAR T cell-derived IFN-γ facilitated host interleukin-12 production that supported host immune and CAR T cell responses. Compared with CD8⁺ CAR T cells, CD4⁺ CAR T cells were more efficient at host immune activation but less capable of direct tumor killing. In summary, CAR T cells do not act independently in vivo but rely instead on cytokine-mediated cross-talk with the TME for optimal activity. Invigorating CAR T cell interplay with the host represents an attractive strategy to prevent relapses after therapy.

CAR-T cell-mediated depletion of immunosuppressive tumor-associated macrophages promotes endogenous antitumor immunity and augments adoptive immunotherapy

The immunosuppressive tumor microenvironment (TME) represents a major barrier for effective immunotherapy. Tumor-associated macrophages (TAMs) are highly heterogeneous and plastic cell components of the TME which can either promote tumor progression (M2-like) or boost antitumor immunity (M1-like). Here, we demonstrate that a subset of TAMs that express folate receptor β (FRβ) possess an immunosuppressive M2-like profile. In syngeneic tumor mouse models, chimeric antigen receptor (CAR)-T cell-mediated selective elimination of FRβ⁺ TAMs in the TME results in an enrichment of pro-inflammatory monocytes, an influx of endogenous tumor-specific CD8⁺ T cells, delayed tumor progression, and prolonged survival. Preconditioning of the TME with FRβ-specific CAR-T cells also improves the effectiveness of tumor-directed anti-mesothelin CAR-T cells, while simultaneous co-administration of both CAR products does not. These results highlight the pro-tumor role of FRβ⁺ TAMs in the TME and the therapeutic implications of TAM-depleting agents as preparative adjuncts to conventional immunotherapies that directly target tumor antigens.

Acellular Wharton's Jelly, Potentials in T-Cell Subtypes Differentiation, Activation and Proliferation

Purpose: Because of different potentials of T-cell subtypes in T-cell based cellular immunotherapy approaches such as CAR-T cell therapies; Regarding the high cost of the serum-free specific culture media, having distinct control on T-cell subset activation, expansion and differentiation seem crucial in T-cell expansion step of cell preparation methods. By the way, there was no clear data about the effect of acellular Wharton’s Jelly (AWJ) on T-cells expansion, activation or differentiation status. So, we have launched to study the effect of AWJ on T-cell’s immunobiological properties.

Methods: CD3+ T-cells were isolated from healthy bone marrow allogeneic donors, sorted by FACS method and cultured on either routine phyto-hemagglutinin complemented and different concentrations of AWJ, lag phase and doubling time of the cells calculated from cell growth curve. After 3, 7 and 14-days T-cell subtypes cell markers and cell activity related genes expression rate have been evaluated by flow cytometry and real-time polymerase chain reaction (PCR) methods respectively.

Results: AWJ in a 1:1 ratio compared with contemporary lymphocyte culture media showed significant activating and proliferative capacities. The introduced condition has not affected the frequency of CD4+ subpopulation of T-cells, but significantly increased even CD8+ cells and immune-activator genes in T-cells. The regulatory and memory subsets of T-cells in this study have not affected significantly.

Conclusion: the study results revealed that AWJ can be utilized as a supportive substance to increase the memory properties of the T-cells, gives control to design a selective medium for expanding and differentiating memory T-cells, relatively.

CAR T cells targeting tumor endothelial marker CLEC14A inhibit tumor growth

Engineering T cells to express chimeric antigen receptors (CARs) specific for antigens on hematological cancers has yielded remarkable clinical responses, but with solid tumors, benefit has been more limited. This may reflect lack of suitable target antigens, immune evasion mechanisms in malignant cells, and/or lack of T cell infiltration into tumors. An alternative approach, to circumvent these problems, is targeting the tumor vasculature rather than the malignant cells directly. CLEC14A is a glycoprotein selectively overexpressed on the vasculature of many solid human cancers and is, therefore, of considerable interest as a target antigen. Here, we generated CARs from 2 CLEC14A-specific antibodies and expressed them in T cells. In vitro studies demonstrated that, when exposed to their target antigen, these engineered T cells proliferate, release IFN-γ, and mediate cytotoxicity. Infusing CAR engineered T cells into healthy mice showed no signs of toxicity, yet these T cells targeted tumor tissue and significantly inhibited tumor growth in 3 mouse models of cancer (Rip-Tag2, mPDAC, and Lewis lung carcinoma). Reduced tumor burden also correlated with significant loss of CLEC14A expression and reduced vascular density within malignant tissues. These data suggest the tumor vasculature can be safely and effectively targeted with CLEC14A-specific CAR T cells, offering a potent and widely applicable therapy for cancer.

T cells expressing a chimeric antigen receptor specific for the tumor vascular marker CLEC14A inhibited tumor growth in three mouse cancer models.

Perforin-deficient CAR T cells recapitulate late-onset inflammatory toxicities observed in patients

Late-onset inflammatory toxicities resembling hemophagocytic lymphohistiocytosis (HLH) or macrophage activation syndrome (MAS) occur after chimeric antigen receptor T cell (CAR T cell) infusion and represent a therapeutic challenge. Given the established link between perforin deficiency and primary HLH, we investigated the role of perforin in anti-CD19 CAR T cell efficacy and HLH-like toxicities in a syngeneic murine model. Perforin contributed to both CD8+ and CD4+ CAR T cell cytotoxicity but was not required for in vitro or in vivo leukemia clearance. Upon CAR-mediated in vitro activation, perforin-deficient CAR T cells produced higher amounts of proinflammatory cytokines compared with WT CAR T cells. Following in vivo clearance of leukemia, perforin-deficient CAR T cells reexpanded, resulting in splenomegaly with disruption of normal splenic architecture and the presence of hemophagocytes, which are findings reminiscent of HLH. Notably, a substantial fraction of patients who received anti-CD22 CAR T cells also experienced biphasic inflammation, with the second phase occurring after the resolution of cytokine release syndrome, resembling clinical manifestations of HLH. Elevated inflammatory cytokines such as IL-1β and IL-18 and concurrent late CAR T cell expansion characterized the HLH-like syndromes occurring in the murine model and in humans. Thus, a murine model of perforin-deficient CAR T cells recapitulated late-onset inflammatory toxicities occurring in human CAR T cell recipients, providing therapeutically relevant mechanistic insights.

Development and Significance of Mouse Models in Lymphoma Research

PURPOSE OF REVIEW

Animal models have played an indispensable role in interpreting cancer gene functions, pathogenesis of disease, and in the development of innovative therapeutic approaches targeting aberrant biological pathways in human cancers.

RECENT FINDINGS

These models have guided the therapeutic targeting of cancer-causing mutations and paved the way for assessing anti-cancer drug responses and the preclinical development of immunotherapies. The mammalian models of cancer utilize genetically edited or transplanted mice that develop fairly accurate disease histopathology. The mouse model also allows us to study the effect of tumor microenvironment in the development of lymphoma. The emergence of patient-derived xenografts provides a better opportunity for recapitulating primary lymphoma characteristics and researching personalized drug therapy. In conclusion, the refinement and advancement of available mouse models in lymphoma significantly minimize the therapeutic translational failures in patients.

Experimental treatment of colorectal cancer in mice with human T cells electroporated with NKG2D RNA CAR

Aim: Peritoneal metastasis is often present in end-stage neoplastic diseases, including recurrent colorectal cancer and is associated with decreased overall survival. Novel methods are needed. Materials & methods: We constructed first-, second- and third-generation chimeric antigen receptors (CARs) specific for NKG2D ligands and modified human T cells with mRNA electroporation. Results: NKG2D CAR expression was detectable for at least 6 days postelectroporation and mediated efficient cytotoxicity against NKG2DL+ tumor cells, but not NKG2DL-cells. Multiple infusions of the first-generation CAR-T cells into immunodeficient mice bearing established peritoneal colorectal xenografts led to significantly reduced tumor burden. Conclusion: mRNA CAR is an economical way to test new CARs and potentiates controlling on-target/off-tumor toxicity and cytokine storms. The use of NKG2D RNA CARs to treat colorectal peritoneal metastasis warrants further investigation.

Mouse Tumor Models for Advanced Cancer Immunotherapy

Recent advances in the development of new methods of cancer immunotherapy require the production of complex cancer animal models that reliably reflect the complexity of the tumor and its microenvironment. Mice are good animals to create tumor models because they are low cost, have a short reproductive cycle, exhibit high tumor growth rates, and can be easily genetically modified. However, the obvious problem of these models is the high failure rate observed in human clinical trials after promising results obtained in mouse models. In order to increase the reliability of the results obtained in mice, the tumor model should reflect the heterogeneity of the tumor, contain components of the tumor microenvironment, in particular immune cells, to which the action of immunotherapeutic drugs are directed. This review discusses the current immunocompetent and immunocompromised mouse models of human tumors that are used to evaluate the effectiveness of immunotherapeutic agents, in particular chimeric antigen receptor (CAR) T-cells and immune checkpoint inhibitors.

Signaling from T cell receptors (TCRs) and chimeric antigen receptors (CARs) on T cells

T cells react to foreign or self-antigens through T cell receptor (TCR) signaling. Several decades of research have delineated the mechanism of TCR signal transduction and its impact on T cell performance. This knowledge provides the foundation for chimeric antigen receptor T cell (CAR-T cell) technology, by which T cells are redirected in a major histocompatibility complex-unrestricted manner. TCR and CAR signaling plays a critical role in determining the T cell state, including exhaustion and memory. Given its artificial nature, CARs might affect or rewire signaling differently than TCRs. A better understanding of CAR signal transduction would greatly facilitate improvements to CAR-T cell technology and advance its usefulness in clinical practice. Herein, we systematically review the knowns and unknowns of TCR and CAR signaling, from the contact of receptors and antigens, proximal signaling, immunological synapse formation, and late signaling outcomes. Signaling through different T cell subtypes and how signaling is translated into practice are also discussed.

Electroporation of NKG2D RNA CAR Improves Vγ9Vδ2 T Cell Responses against Human Solid Tumor Xenografts

Vγ9Vδ2 T cell-based anticancer immunotherapy has shown some promise in early-phase clinical trials but there is still large room for improvement. Using the extracellular domain of the human NKG2D, a stimulatory receptor expressed by Vγ9Vδ2 T cells, we constructed NKG2D ligand-specific chimeric antigen receptors (CARs). We adopted a non-viral CAR approach via mRNA electroporation to modify Vγ9Vδ2 T cells and demonstrated that, upon interaction with the NKG2D ligand-positive cancer cells, the CARs substantially enhanced the cytotoxic activity of the modified cells toward multiple cultured solid tumor cell lines, including those resistant to Zometa treatment. Repeated doses of the CAR-expressing cells resulted in tumor regression in mice with established tumors, extending median survival time by up to 132% as compared to the PBS control group. The findings suggest clinical potential for RNA CAR-modified Vγ9Vδ2 T cells to treat a wide variety of NKG2D ligand-expressing cancers.

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.

Preclinical safety evaluation of chimeric antigen receptor-modified T cells against CD19 in NSG mice

Background

With the increase of chimeric antigen receptor-modified T (CAR-T) cell therapy, serious complications initiated by CAR-T cells have garnered wide attention. We have previously developed a 4-1BB/CD3-ζ-costimulated CAR-T cells against CD19 (CART19) for adult acute lymphoblastic leukemia (ALL). In this study, a preclinical safety assessment of CART19 was performed on NSG mice, to evaluate the preclinical toxicity along with its efficacy and tissue distribution.

Methods

A total of 120 NSG mice were used for a combined pharmacodynamics and toxicity study for 56 days. Ninety-six mice of which were single dosed with Raji-Luc (5×10⁵ per animal, i.p.) and different concentrations of CART19 (0.2×10⁷, 0.6×10⁷ and 1.8×10⁷ per animal, i.v.), while the rest were assigned to the Untreated group. Optical intensity of Raji-Luc in mice, clinical symptoms, body mass, hematological analysis, humanized cytokine, lymphocyte subset counting, necropsy and histopathological examinations were performed. In addition, a single dose of 0.6×10⁷ CART19 was intravenously administered to 48 NSG mice, and the distribution of CART19 in different tissues was analyzed using quantitative PCR.

Results

CART19 is widely distributed in organs well-perfused with blood, including the lungs, blood, bone marrow, liver and spleen. Significant proliferation of CART19 was also found in the blood by through recognition using humanized CD3⁺ for T lymphocytes. The survival rate and leukemia related clinical symptoms in mice administered CART19 were markedly ameliorated, and the proliferation of Raji cells in mice was effectively inhibited. However, CART19 had no obvious effects on either the mean body mass or the blood cell counts, and no cytokine release syndrome and graft versus host disease were observed.

Conclusions

NSG mice given CART19 treatment demonstrated a longer survival period without significant immunotoxicity, suggesting encouraging clinical prospects for CART19 in patients with R/R ALL. Our study shed light on evaluation and supervision strategies for CAR-T products for the treatment of hematological diseases or leukemia.

TEM8/ANTXR1-specific CAR T cells mediate toxicity in vivo

Engineering T-cells to express receptors specific for antigens present on tumour tissue is proving a highly effective treatment for some leukaemias. However, extending this to solid tumours requires antigens that can be safely and effectively targeted. TEM8, a marker overexpressed on the vasculature of some solid tumours, has been proposed as one such target. A recent report stated that T-cells engineered to express a TEM8-specific chimeric antigen receptor (CAR), when injected into mouse models of triple negative breast cancer, are both safe and effective in controlling tumour growth. Here we report contrasting data with a panel of TEM8-specific CAR-T-cells including one generated from the same antibody used in the other study. We found that the CAR-T-cells demonstrated clear TEM8-specific cytotoxic and cytokine release responses in vitro, but when injected into healthy C57BL6 and NSG mice they rapidly and selectively disappeared from the circulation and in most cases caused rapid toxicity. Infusing CAR-T-cells into a TEM8-knockout mouse indicated that selective loss of cells from the circulation was due to targeting of TEM8 in healthy tissues. Histological analysis of mice treated with a TEM8-specific CAR revealed evidence of inflammation in the lung and spleen with large collections of infiltrating neutrophils. Therefore our data raise concerns over potential on-target off-tumour toxicity with CARs targeting TEM8 and these should be considered carefully before embarking upon clinical trials with such agents.

The making and function of CAR cells

Genetically engineered T cells expressing chimeric antigen receptors (CAR) present a new treatment option for patients with cancer. Recent clinical trials of B cell leukemia have demonstrated a response rate of up to 90%. However, CAR cell therapy is frequently accompanied by severe side effects such as cytokine release syndrome and the development of target cell resistance. Consequently, further optimization of CARs to obtain greater long-term efficacy and increased safety is urgently needed. Here we high-light the various efforts of adjusting the intracellular signaling domains of CARs to these major requirements to eventually obtain high-level target cell cytotoxicity paralleled by the establishment of longevity of the CAR expressing cell types to guarantee for extended tumor surveillance over prolonged periods of time. We are convinced that it will be crucial to identify the molecular pathways and signaling requirements utilized by such ‘efficient CARs’ in order to provide a rational basis for their further hypothesis-based improvement. Furthermore, we here discuss timely attempts of how to: i) control ‘on-tumor off-target’ effects; ii) introduce Signal 3 (cytokine responsiveness of CAR cells) as an important building-block into the CAR concept; iii) most efficiently eliminate CAR cells once full remission has been obtained. We also argue that universal systems for the variable and pharmacokinetically-controlled attachment of extracellular ligand recognition domains of choice along with the establishment of ‘off-the-shelf’ cell preparations with suitability for all patients in need of a highly-potent cellular therapy may become future mainstays of CAR cell therapy. Such therapies would have the attraction to work independent of the patients’ histo-compatibility make-up and the availability of functionally intact patient’s cells. Finally, we summarize the evidence that CAR cells may obtain a prominent place in the treatment of non-malignant and auto-reactive T and B lymphocyte expansions in the near future, e.g., for the alleviation of autoimmune diseases and allergies. After the introduction of red blood cell transfusions, which were made possible by the landmark discoveries of the ABO blood groups by Karl Landsteiner, and the establishment of bone marrow transplantation by E. Donnall Thomas to exchange the entire hematopoietic system of a patient suffering from leukemia, the introduction of patient-tailored cytotoxic cellular populations to eradicate malignant cell populations in vivo pioneered by Carl H. June, represents the third major and broadly applicable milestone in the development of human cellular therapies within the rapidly developing field of applied biomedical research of the last one hundred years.

Single-cell imaging of CAR T cell activity in vivo reveals extensive functional and anatomical heterogeneity

Cazaux et al. use intravital imaging to dissect anti-CD19 CAR T cell activity. This study uncovers both anatomical and functional diversity in the outcome of anti-CD19 CAR T cell interactions with tumor cells impacting engraftment, killing dynamics, and tumor immunoediting.

CAR T cells represent a potentially curative strategy for B cell malignancies. However, the outcome and dynamics of CAR T cell interactions in distinct anatomical sites are poorly understood. Using intravital imaging, we tracked interactions established by anti-CD19 CAR T cells in B cell lymphoma–bearing mice. Circulating targets trapped CAR T cells in the lungs, reducing their access to lymphoid organs. In the bone marrow, tumor apoptosis was largely due to CAR T cells that engaged, killed, and detached from their targets within 25 min. Notably, not all CAR T cell contacts elicited calcium signaling or killing while interacting with tumors, uncovering extensive functional heterogeneity. Mathematical modeling revealed that direct killing was sufficient for tumor regression. Finally, antigen-loss variants emerged in the bone marrow, but not in lymph nodes, where CAR T cell cytotoxic activity was reduced. Our results identify a previously unappreciated level of diversity in the outcomes of CAR T cell interactions in vivo, with important clinical implications.

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.

The impact of antibiotic usage on the efficacy of chemoimmunotherapy is contingent on the source of tumor-reactive T cells

In recent years the combined use of chemotherapy and immunotherapy, collectively termed chemoimmunotherapy, has emerged as a promising treatment option for patients with cancer. Antibiotics are commonly used to reduce infection-related complications in patients undergoing chemotherapy. Intriguingly, accumulating evidence has implicated gut microbiota as a critical determinant of host antitumor immune responses, raising the question as to whether the use of broad-spectrum antibiotics would invariably diminish tumor response to chemoimmunotherapies. We investigated the impact of antibiotics on the therapeutic outcomes of cyclophosphamide (CTX) chemotherapy and adoptive T-cell therapy (ACT) where CTX was used as the host-conditioning regimen in mice. We show that antibiotic prophylaxis dampened the endogenous T cell responses elicited by CTX, and reduced the efficacy of CTX against B-cell lymphoma. In the ACT setting, antibiotics administration impaired the therapeutic effects of adoptively transferred tumor-specific CD4+ T cells in mice with implanted colorectal tumors. In contrast, long-term antibiotic exposure did not affect the efficacy of ACT using CD19-targeting chimeric antigen receptor (CAR) T cells in mice with systemic B-cell lymphoma, although it correlated with prolonged CAR expression and sustained B-cell aplasia. Our study demonstrates that chemoimmunotherapies may have variable reliance on intestinal microbiota for T cell activation and function, and thus have different sensitivities to antibiotic prophylaxis. These findings may have implications for the judicial use of antibiotics in cancer patients receiving chemoimmunotherapies.

'Atypical' CAR T cells: NKG2D and Erb-B as examples of natural receptor/ligands to target recalcitrant solid tumors

Chimeric antigen receptor (CAR) T-cell therapy has recently been recommended for approval for certain B-cell malignancies bringing the approach closer to mainstream cancer treatment. This rapid rise to prominence has been driven by impressive clinical results and the means to successfully commercialize the approach now being actively pursued. The current success of CAR T cells in B-cell malignancies relies upon the absolute lineage specificity of the CD19 antigen. CARs can also be targeted using non-antibody approaches, including the use of receptors and ligands to provide target specificity that have different specificities and binding kinetics. The specific examples of NKG2D and Erb-B are used that provide different characteristics and target profiles for CAR T-cell therapy of cancer.

Adoptive transfer of murine T cells expressing a chimeric-PD1-Dap10 receptor as an immunotherapy for lymphoma

Adoptive transfer of T cells is a promising cancer therapy and expression of chimeric antigen receptors can enhance tumour recognition and T-cell effector functions. The programmed death protein 1 (PD1) receptor is a prospective target for a chimeric antigen receptor because PD1 ligands are expressed on many cancer types, including lymphoma. Therefore, we developed a murine chimeric PD1 receptor (chPD1) consisting of the PD1 extracellular domain fused to the cytoplasmic domain of CD3ζ. Additionally, chimeric antigen receptor therapies use various co-stimulatory domains to enhance efficacy. Hence, the inclusion of a Dap10 or CD28 co-stimulatory domain in the chPD1 receptor was compared to determine which domain induced optimal anti-tumour immunity in a mouse model of lymphoma. The chPD1 T cells secreted pro-inflammatory cytokines and lysed RMA lymphoma cells. Adoptive transfer of chPD1 T cells significantly reduced established tumours and led to tumour-free survival in lymphoma-bearing mice. When comparing chPD1 receptors containing a Dap10 or CD28 domain, both receptors induced secretion of pro-inflammatory cytokines; however, chPD1-CD28 T cells also secreted anti-inflammatory cytokines whereas chPD1-Dap10 T cells did not. Additionally, chPD1-Dap10 induced a central memory T-cell phenotype compared with chPD1-CD28, which induced an effector memory phenotype. The chPD1-Dap10 T cells also had enhanced in vivo persistence and anti-tumour efficacy compared with chPD1-CD28 T cells. Therefore, adoptive transfer of chPD1 T cells could be a novel therapy for lymphoma and inclusion of the Dap10 co-stimulatory domain in chimeric antigen receptors may induce a preferential cytokine profile and T-cell differentiation phenotype for anti-tumour therapies.

Different Subsets of T Cells, Memory, Effector Functions, and CAR-T Immunotherapy

This review is focused on different subsets of T cells: CD4 and CD8, memory and effector functions, and their role in CAR-T therapy--a cellular adoptive immunotherapy with T cells expressing chimeric antigen receptor. The CAR-T cells recognize tumor antigens and induce cytotoxic activities against tumor cells. Recently, differences in T cell functions and the role of memory and effector T cells were shown to be important in CAR-T cell immunotherapy. The CD4⁺ subsets (Th1, Th2, Th9, Th17, Th22, Treg, and Tfh) and CD8⁺ memory and effector subsets differ in extra-cellular (CD25, CD45RO, CD45RA, CCR-7, L-Selectin [CD62L], etc.); intracellular markers (FOXP3); epigenetic and genetic programs; and metabolic pathways (catabolic or anabolic); and these differences can be modulated to improve CAR-T therapy. In addition, CD4⁺ Treg cells suppress the efficacy of CAR-T cell therapy, and different approaches to overcome this suppression are discussed in this review. Thus, next-generation CAR-T immunotherapy can be improved, based on our knowledge of T cell subsets functions, differentiation, proliferation, and signaling pathways to generate more active CAR-T cells against tumors.

CAR T-cell therapy: toxicity and the relevance of preclinical models

Chimeric antigen receptor (CAR) T cells form part of a broad wave of immunotherapies that are showing promise in early phase cancer clinical trials. This clinical delivery has been based upon preclinical efficacy testing that confirmed the proof of principle of the therapy. However, CAR T-cell therapy does not exist alone as T cells are generally given in combination with patient preconditioning, most commonly in the form of chemotherapy, and may also include systemic cytokine support, both of which are associated with toxicity. Consequently, complete CAR T-cell therapy includes elements where the toxicity profile is well known, but also includes the CAR T cell itself, for which toxicity profiles are largely unknown. With recent reports of adverse events associated with CAR T-cell therapy, there is now concern that current preclinical models may not be fit for purpose with respect to CAR T-cell toxicity profiling. Here, we explore the preclinical models used to validate CAR T-cell function and examine their potential to predict CAR T-cell driven toxicities for the future.

The pharmacology of second-generation chimeric antigen receptors

Second-generation chimeric antigen receptors (CARs) retarget and reprogramme T cells to augment their antitumour efficacy. The combined activating and co-stimulatory domains incorporated in these CARs critically determine the function, differentiation, metabolism and persistence of engineered T cells. CD19-targeted CARs that incorporate CD28 or 4-1BB signalling domains are the best known to date. Both have shown remarkable complete remission rates in patients with refractory B cell malignancies. Recent data indicate that CD28-based CARs direct a brisk proliferative response and boost effector functions, whereas 4-1BB-based CARs induce a more progressive T cell accumulation that may compensate for less immediate potency. These distinct kinetic features can be exploited to further develop CAR-based T cell therapies for a variety of cancers. A new field of immunopharmacology is emerging.

Adoptive T-cell therapy for cancer in the United kingdom: a review of activity for the British Society of Gene and Cell Therapy annual meeting 2015

Adoptive T-cell therapy is delivering objective clinical responses across a number of cancer indications in the early phase clinical setting. Much of this clinical activity is taking place at major clinical academic centers across the United States. This review focuses upon cancer-focused cell therapy activity within the United Kingdom as a contribution to the 2015 British Society of Gene and Cell Therapy annual general meeting. This overview reflects the diversity and expansion of clinical and preclinical studies within the United Kingdom while considering the background context of this work against new infrastructural developments and the requirements of nationalized healthcare delivery within the UK National Health Service.

Adoptive immunotherapy for hematological malignancies using T cells gene-modified to express tumor antigen-specific receptors

Accumulating clinical evidence suggests that adoptive T-cell immunotherapy could be a promising option for control of cancer; evident examples include the graft-vs-leukemia effect mediated by donor lymphocyte infusion (DLI) and therapeutic infusion of ex vivo-expanded tumor-infiltrating lymphocytes (TIL) for melanoma. Currently, along with advances in synthetic immunology, gene-modified T cells retargeted to defined tumor antigens have been introduced as “cellular drugs”. As the functional properties of the adoptive immune response mediated by T lymphocytes are decisively regulated by their T-cell receptors (TCRs), transfer of genes encoding target antigen-specific receptors should enable polyclonal T cells to be uniformly redirected toward cancer cells. Clinically, anticancer adoptive immunotherapy using genetically engineered T cells has an impressive track record. Notable examples include the dramatic benefit of chimeric antigen receptor (CAR) gene-modified T cells redirected towards CD19 in patients with B-cell malignancy, and the encouraging results obtained with TCR gene-modified T cells redirected towards NY-ESO-1, a cancer-testis antigen, in patients with advanced melanoma and synovial cell sarcoma. This article overviews the current status of this treatment option, and discusses challenging issues that still restrain the full effectiveness of this strategy, especially in the context of hematological malignancy.