CD28 costimulation provided through a CD19-specific chimeric antigen receptor enhances in vivo persistence and antitumor efficacy of adoptively transferred T cells

The Evolving Protein Engineering in the Design of Chimeric Antigen Receptor T Cells

The clinical success of chimeric antigen receptor (CAR) T cell immunotherapy in the treatment of haematological cancers has encouraged the extensive development of CAR design to improve their function and increase their applicability. Advancements in protein engineering have seen modifications to both the ecto- and endo-domains of the CAR, with recent designs targeting multiple antigens and including inducible elements. These developments are likely to play an important role in inducing effective CAR T cell responses in a solid tumour context, where clinical responses have not been effective to date. This review highlights the spectrum of novel strategies being employed in CAR design, including for example variations in targeting tumour antigens by utilising different ectodomain designs such as dual chain CARs, natural receptor or ligand-based CARs, and T cell receptor fusion constructs, and also reviews some of the innovative approaches to a "universal" CAR and various multi-antigen targeting CAR strategies. We also explore how choices in the endodomain impact CAR function and how these need to be considered in the overall CAR design.

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.

The Role of Checkpoint Inhibitors and Cytokines in Adoptive Cell-Based Cancer Immunotherapy with Genetically Modified T Cells

This review focuses on the structure and molecular action mechanisms of chimeric antigen receptors (CARs) and major aspects of the manufacturing and clinical application of products for the CAR-T (CAR-modified T lymphocyte) therapy of hematological and solid tumors with special emphasis on the strategies for combined use of CAR-T therapy with immuno-oncological monoclonal antibodies (checkpoint inhibitors) and cytokines to boost survival, persistence, and antitumor efficacy of CAR-T therapy. The review also summarizes preclinical and clinical data on the additive effects of the combined use of CAR-T therapy with interleukins and monoclonal antibodies targeting immune checkpoints.

Activity of Anti-CD19 Chimeric Antigen Receptor T Cells Against B Cell Lymphoma Is Enhanced by Antibody-Targeted Interferon-Alpha

An important emerging form of immunotherapy targeting B cell malignancies is chimeric antigen receptor (CAR) T cell therapy. Despite encouraging response rates of anti-CD19 CAR T cell therapy in B cell lymphomas, limited durability of response necessitates further study to potentiate CAR T cell efficacy. Antibody-targeted interferon (IFN) therapy is a novel approach in immunotherapy. Given the ability of IFNs to promote T cell activation and survival, target cell recognition, and cytotoxicity, we asked whether antibody-targeted IFN could enhance the antitumor effects of anti-CD19 CAR T cells. We produced an anti-CD20-IFN fusion protein containing the potent type 1 IFN isoform alpha14 (α14), and demonstrated its ability to suppress proliferation and induce apoptosis of human B cell lymphomas. Indeed, with the combination of anti-CD20-hIFNα14 and CAR T cells, we found enhanced cell killing among B cell lymphoma lines. Importantly, for all cell lines pretreated with anti-CD20-hIFNα14, the subsequent cytokine production by CAR T cells was markedly increased regardless of the degree of cell killing. Thus, several activities of CD19 CAR T cells were enhanced in the presence of anti-CD20-hIFNα14. These data suggest that antibody-targeted IFN may be an important novel approach to improving the efficacy of CAR T cell therapy.

Adoptive Immunotherapy for B-cell Malignancies Using CD19- Targeted Chimeric Antigen Receptor T-Cells: A Systematic Review of Efficacy and Safety

BACKGROUND

Adoptive infusion of chimeric antigen receptor transduced T- cells (CAR-T) is a powerful tool of immunotherapy for hematological malignancies, as evidenced by recently published and unpublished clinical results.

OBJECTIVE

In this report, we performed a meta-analysis to evaluate the efficacy and side effects of CAR-T on refractory and/or relapsed B-cell malignancies, including leukemia and lymphoma.

METHODS

Clinical studies investigating efficacy and safety of CAR-T in acute and chronic lymphocytic leukemia and lymphoma were identified by searching PubMed and EMBASE. Outcomes of efficacy subjected to analysis were the rates of complete remission (CR) and partial remission (PR). The safety parameters were the prevalence of adverse effects including fever, hypotension, and acute renal failure. Meta analyses were performed using R software. Weighted hazard ratio (HR) with 95% confidence intervals was calculated for each outcome. Fixed or random-effects models were employed depending on the heterogeneity across the included studies.

RESULTS

Nineteen published clinical studies with a total of 391 patients were included for the meta-analysis. The pooled rate of complete remission was 55% (95% CI 41%-69%); the pooled rate of partial remission was 25% (95% CI: 19%-33%). The prevalence of fever was 62% (95% CI: 41%-79%), the hypotension was 22% (95% CI: 15%-31%), and the acute renal failure was 24% (95% CI: 16%-34%). All adverse effects were manageable and no death was reported due to toxicity.

CONCLUSION

CD19-targeted CAR-T is an effective modality in treating refractory B-cell malignancies including leukemia and lymphoma. However, there is still a need to develop strategies to improve the safety in its clinical use.

Genetically engineered T cells for cancer immunotherapy

T cells in the immune system protect the human body from infection by pathogens and clear mutant cells through specific recognition by T cell receptors (TCRs). Cancer immunotherapy, by relying on this basic recognition method, boosts the antitumor efficacy of T cells by unleashing the inhibition of immune checkpoints and expands adaptive immunity by facilitating the adoptive transfer of genetically engineered T cells. T cells genetically equipped with chimeric antigen receptors (CARs) or TCRs have shown remarkable effectiveness in treating some hematological malignancies, although the efficacy of engineered T cells in treating solid tumors is far from satisfactory. In this review, we summarize the development of genetically engineered T cells, outline the most recent studies investigating genetically engineered T cells for cancer immunotherapy, and discuss strategies for improving the performance of these T cells in fighting cancers.

Current Progress in CAR-T Cell Therapy for Solid Tumors

Cancer immunotherapy by chimeric antigen receptor-modified T (CAR-T) cells has shown exhilarative clinical efficacy for hematological malignancies. Recently two CAR-T cell based therapeutics, Kymriah (Tisagenlecleucel) and Yescarta (Axicabtagene ciloleucel) approved by US FDA (US Food and Drug Administration) are now used for treatment of B cell acute lymphoblastic leukemia (B-ALL) and diffuse large B-cell lymphoma (DLBCL) respectively in the US. Despite the progresses made in treating hematological malignancies, challenges still remain for use of CAR-T cell therapy to treat solid tumors. In this landscape, most studies have primarily focused on improving CAR-T cells and overcoming the unfavorable effects of tumor microenvironment on solid tumors. To further understand the current status and trend for developing CAR-T cell based therapies for various solid tumors, this review emphasizes on CAR-T techniques, current obstacles, and strategies for application, as well as necessary companion diagnostics for treatment of solid tumors with CAR-T cells.

Chimeric antigen receptor T-cell therapy for cancer: a basic research-oriented perspective

Chimeric antigen receptor (CAR) T cells have outstanding therapeutic potential for treating blood cancers. The prospects for this technology have accelerated basic research, clinical translation and Big Pharma's investment in the field of T-cell therapeutics. This interest has led to the discovery of key factors that affect CAR T-cell efficacy and play pivotal roles in T-cell immunology. Herein, we introduce advances in adoptive immunotherapy and the birth of CAR T cells, and review CAR T-cell studies that focus on three important features: CAR constructs, target antigens and T-cell phenotypes. At last, we highlight novel strategies that overcome the tumor microenvironment and circumvent CAR T-cell side effects, and consider the future direction of CAR T-cell development.

Bispecific T-Cell Redirection versus Chimeric Antigen Receptor (CAR)-T Cells as Approaches to Kill Cancer Cells

The concepts for T-cell redirecting bispecific antibodies (TRBAs) and chimeric antigen receptor (CAR)-T cells are both at least 30 years old but both platforms are just now coming into age. Two TRBAs and two CAR-T cell products have been approved by major regulatory agencies within the last ten years for the treatment of hematological cancers and an additional 53 TRBAs and 246 CAR cell constructs are in clinical trials today. Two major groups of TRBAs include small, short-half-life bispecific antibodies that include bispecific T-cell engagers (BiTE®s) which require continuous dosing and larger, mostly IgG-like bispecific antibodies with extended pharmacokinetics that can be dosed infrequently. Most CAR-T cells today are autologous, although significant strides are being made to develop off-the-shelf, allogeneic CAR-based products. CAR-Ts form a cytolytic synapse with target cells that is very different from the classical immune synapse both physically and mechanistically, whereas the TRBA-induced synapse is similar to the classic immune synapse. Both TRBAs and CAR-T cells are highly efficacious in clinical trials but both also present safety concerns, particularly with cytokine release syndrome and neurotoxicity. New formats and dosing paradigms for TRBAs and CAR-T cells are being developed in efforts to maximize efficacy and minimize toxicity, as well as to optimize use with both solid and hematologic tumors, both of which present significant challenges such as target heterogeneity and the immunosuppressive tumor microenvironment.

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.

Development of CAR-T cells for long-term eradication and surveillance of HIV-1 reservoir

Human immunodeficiency virus type 1 (HIV-1) reservoir is a pool of latently infected cells harboring replication-competent proviral DNA that limits antiretroviral therapy. Suppression of HIV-1 by combination antiretroviral therapy (cART) delays progression of the disease but does not eliminate the viral reservoir, necessitating lifetime daily administration of antiretroviral drugs. To achieve durable suppression of viremia without daily therapy, various strategies have been developed, including long-acting antiretroviral drugs (LA-ARVs), broadly neutralizing antibodies (bNAbs), and chimeric antigen receptor T (CAR-T) cells. Here, we summarize and discuss recent breakthroughs in CAR-T cell therapies toward the eradication of HIV-1 reservoir. Although substantial challenges exist, CAR-T cell technology may serve as a promising strategy toward HIV-1 functional cure.

Treatment of patients with relapsed or refractory CD19+ lymphoid disease with T lymphocytes transduced by RV-SFG.CD19.CD28.4-1BBzeta retroviral vector: a unicentre phase I/II clinical trial protocol

INTRODUCTION

Chimeric antigen receptor (CAR) T cells spark hope for patients with CD19+ B cell neoplasia, including relapsed or refractory (r/r) acute lymphoblastic leukaemia (ALL) or r/r non-Hodgkin's lymphoma (NHL). Published studies have mostly used second-generation CARs with 4-1BB or CD28 as costimulatory domains. Preclinical results of third-generation CARs incorporating both elements have shown superiority concerning longevity and proliferation. The University Hospital of Heidelberg is the first institution to run an investigator-initiated trial (IIT) CAR T cell trial (Heidelberg Chimeric Antigen Receptor T cell Trial number 1 [HD-CAR-1]) in Germany with third-generation CD19-directed CAR T cells.

METHODS AND ANALYSIS

Adult patients with r/r ALL (stratum I), r/r NHL including chronic lymphocytic leukaemia, diffuse large B-cell lymphoma, follicular lymphoma or mantle cell lymphoma (stratum II) as well as paediatric patients with r/r ALL (stratum III) will be treated with autologous T-lymphocytes transduced by third-generation RV-SFG.CD19.CD28.4-1BB zeta retroviral vector (CD19.CAR T cells). The main purpose of this study is to evaluate safety and feasibility of escalating CD19.CAR T cell doses (1-20×10⁶ transduced cells/m²) after lymphodepletion with fludarabine (flu) and cyclophosphamide (cyc). Patients will be monitored for cytokine release syndrome (CRS), neurotoxicity, i.e. CAR-T-cell-related encephalopathy syndrome (CRES) and/or other toxicities (primary objectives). Secondary objectives include evaluation of in vivo function and survival of CD19.CAR T cells and assessment of CD19.CAR T cell antitumour efficacy.HD-CAR-1 as a prospective, monocentric trial aims to make CAR T cell therapy accessible to patients in Europe. Currently, HD-CAR-1 is the first and only CAR T cell IIT in Germany. A third-generation Good Manufacturing Practice (GMP) grade retroviral vector, a broad spectrum of NHL, treatment of paediatric and adult ALL patients and inclusion of patients even after allogeneic stem cell transplantation (alloSCT) make this trial unique.

ETHICS AND DISSEMINATION

Ethical approval and approvals from the local and federal competent authorities were granted. Trial results will be reported via peer-reviewed journals and presented at conferences and scientific meetings.

TRIAL REGISTRATION NUMBER

Eudra CT 2016-004808-60; NCT03676504; Pre-results.

The Other Side of CAR T-Cell Therapy: Cytokine Release Syndrome, Neurologic Toxicity, and Financial Burden

Immune effector cells, including T cells and natural killer cells, which are genetically engineered to express a chimeric antigen receptor (CAR), constitute a powerful new class of therapeutic agents to treat patients with hematologic malignancies. Several CAR T-cell trials have shown impressive remission rates in patients with relapsed/refractory hematologic cancers. Although the clinical responses of these agents in hematologic malignancies have been very encouraging, they have also produced substantial morbidity and occasionally mortality resulting from toxicity. With more experience and collaboration, hopefully the toxicities and the costs will come down, increasing the availability of CAR T cells to patients in need.

Selecting costimulatory domains for chimeric antigen receptors: functional and clinical considerations

Costimulatory signals are required to achieve robust chimeric antigen receptor (CAR) T cell expansion, function, persistence and antitumor activity. These can be provided by incorporating intracellular signalling domains from one or more T cell costimulatory molecules, such as CD28 or 4-1BB, into the CAR. The selection and positioning of costimulatory domains within a CAR construct influence CAR T cell function and fate, and clinical experience of autologous anti-CD19 CAR T cell therapies suggests that costimulatory domains have differential impacts on CAR T cell kinetics, cytotoxic function and potentially safety profile. The clinical impacts of combining costimulatory domains and of alternative costimulatory domains are not yet clearly established, and may be construct- and disease-specific. The aim of this review is to summarise the function and effect of established and emerging costimulatory domains and their combinations within CAR T cells.

An Antibody Fab Fragment-based Chimeric Antigen Receptor Could Efficiently Eliminate Human Thyroid Cancer Cells

Thyroid cancer remains a significant health problem worldwide. Traditional chemotherapy does generate long-term benefit but are usually accompanied by severe side effects. Immunotherapy by adoptive infusion of T cells is now an attractive alternative to chemotherapy. Chimeric antigen receptor engineered lymphocytes have produced tremendous clinical outcomes in treating leukemia or lymphoma, but not in solid tumors, which is in part due to the low affinity of single chain Fv fragment or the rapid loss of transfused T cells. In present research, we designed a novel Fab based chimeric antigen receptor, which inherits the advantages of Fab fragment as well as the natural TCR receptor. The novel Fab CAR could recognize the tumor antigens independent of MHC/peptide complex, and mimic the natural activation process of endogenous TCR, therefore extend the life span of CAR-engineered T cells and generate durable clinical effects.

Nanobody-based CAR T cells that target the tumor microenvironment inhibit the growth of solid tumors in immunocompetent mice

Chimeric antigen receptor (CAR) T cell therapy has been successful in clinical trials against hematological cancers, but has experienced challenges in the treatment of solid tumors. One of the main difficulties lies in a paucity of tumor-specific targets that can serve as CAR recognition domains. We therefore focused on developing VHH-based, single-domain antibody (nanobody) CAR T cells that target aspects of the tumor microenvironment conserved across multiple cancer types. Many solid tumors evade immune recognition through expression of checkpoint molecules, such as PD-L1, that down-regulate the immune response. We therefore targeted CAR T cells to the tumor microenvironment via the checkpoint inhibitor PD-L1 and observed a reduction in tumor growth, resulting in improved survival. CAR T cells that target the tumor stroma and vasculature through the EIIIB⁺ fibronectin splice variant, which is expressed by multiple tumor types and on neovasculature, are likewise effective in delaying tumor growth. VHH-based CAR T cells can thus function as antitumor agents for multiple targets in syngeneic, immunocompetent animal models. Our results demonstrate the flexibility of VHH-based CAR T cells and the potential of CAR T cells to target the tumor microenvironment and treat solid tumors.

Preclinical Evaluation of Chimeric Antigen Receptor-Modified T Cells Specific to Epithelial Cell Adhesion Molecule for Treating Colorectal Cancer

Chimeric antigen receptor-modified T cells (CAR-T cells) have emerged as a promising cancer immunotherapy for solid tumors. Epithelial cell adhesion molecule (EpCAM) is overexpressed in a variety of tumors and is recognized as a biomarker for circulating tumor cells and cancer stem cells, representing an attractive target for adoptive T-cell immunotherapy. This study generated third-generation CAR-T cells with redirected specificity to EpCAM (EpCAM CAR-T) by lentiviral vector. The study demonstrated that EpCAM CAR-T cells can elicit lytic cytotoxicity to target cells in an EpCAM-dependent manner and secrete cytotoxic cytokines, including interferon gamma and tumor necrosis factor alpha. Furthermore, adoptive transfer of EpCAM CAR-T cells significantly delayed tumor growth and formation in xenograft models. In addition, the safety evaluation showed that CAR-T cells have no systemic toxicity in mice. The data confirmed the antitumor ability and safety of CAR-T cells targeting EpCAM and may provide a new target for CAR-T cell therapies in treating solid tumors.

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

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

An immunoproteomic approach to characterize the CAR interactome and signalosome

Adoptive transfer of T cells that express a chimeric antigen receptor (CAR) is an approved immunotherapy that may be curative for some hematological cancers. To better understand the therapeutic mechanism of action, we systematically analyzed CAR signaling in human primary T cells by mass spectrometry. When we compared the interactomes and the signaling pathways activated by distinct CAR-T cells that shared the same antigen-binding domain but differed in their intracellular domains and their in vivo antitumor efficacy, we found that only second-generation CARs induced the expression of a constitutively phosphorylated form of CD3ζ that resembled the endogenous species. This phenomenon was independent of the choice of costimulatory domains, or the hinge/transmembrane region. Rather, it was dependent on the size of the intracellular domains. Moreover, the second-generation design was also associated with stronger phosphorylation of downstream secondary messengers, as evidenced by global phosphoproteome analysis. These results suggest that second-generation CARs can activate additional sources of CD3ζ signaling, and this may contribute to more intense signaling and superior antitumor efficacy that they display compared to third-generation CARs. Moreover, our results provide a deeper understanding of how CARs interact physically and/or functionally with endogenous T cell molecules, which will inform the development of novel optimized immune receptors.

Preventing Lck Activation in CAR T Cells Confers Treg Resistance but Requires 4-1BB Signaling for Them to Persist and Treat Solid Tumors in Nonlymphodepleted Hosts

PURPOSE

Chimeric antigen receptor (CAR) T cells have shown promise against solid tumors, but their efficacy has been limited, due in part, to immunosuppression by CD4+FoxP3+ regulatory T cells (Tregs). Although lymphodepletion is commonly used to deplete Tregs, these regimens are nonspecific, toxic, and provide only a narrow window before Tregs repopulate hosts. Importantly, CARs have also been shown to inadvertently potentiate Tregs by providing a source of IL2 for Treg consumption. We explored whether disruption of the IL2 axis would confer efficacy against solid tumors without the need for lymphodepletion.

EXPERIMENTAL DESIGN

We developed second- (CD28z) and third- (CD28-4-1BBz) generation CARs targeting EGFRvIII. To eliminate secretion of IL2, 2 amino acid substitutions were introduced in the PYAP Lck-binding motif of the CD28 domain (ΔCD28). We evaluated CARs against B16 melanomas expressing EGFRvIII.

RESULTS

CD28z CARs failed to engraft in vivo. Although 4-1BB addition improved expansion, CD28-4-1BBz CARs required lymphodepletion to treat solid tumors. CARs deficient in Lck signaling, however, significantly retarded tumor growth without a need for lymphodepletion and this was dependent on inclusion of 4-1BB. To evaluate CAR vulnerability to Tregs, we lymphodepleted mice and transferred CARs alone or with purified Tregs. Cotransfer with Tregs abrogated the efficacy of CD28-4-1BBz CARs, whereas the efficacy of ΔCD28-4-1BBz CARs remained unperturbed.

CONCLUSIONS

In the absence of lymphodepletion, CARs targeting solid tumors are hindered by Treg immunosuppression and poor persistence. Here, CARs were modified to circumvent Treg suppression and to simultaneously improve in vivo engraftment. Modified CARs treated solid tumors without a need for lymphodepletion.

Animal Models for Preclinical Development of Allogeneic Hematopoietic Cell Transplantation

Since its inception in the 1950s, hematopoietic cell transplantation (HCT) has become a highly effective clinical treatment for malignant and nonmalignant hematological disorders. This milestone in cancer therapy was only possible through decades of intensive research using murine and canine animal models that overcame what appeared in the early days to be insurmountable obstacles. Conditioning protocols for tumor ablation and immunosuppression of the recipient using irradiation and chemotherapeutic drugs were developed in mouse and dog models as well as postgrafting immunosuppression methods essential for dependable donor cell engraftment. The random-bred canine was particularly important in defining the role of histocompatibility barriers and the development of the nonmyeloablative transplantation procedure, making HCT available to elderly patients with comorbidities. Two complications limit the success of HCT: disease relapse and graft versus host disease. Studies in both mice and dogs have made significant progress toward reducing and to some degree eliminating patient morbidity and mortality associated with both disease relapse and graft versus host disease. However, more investigation is needed to make HCT more effective, safer, and available as a treatment modality for other non-life-threatening diseases such as autoimmune disorders. Here, we focus our review on the contributions made by both the murine and canine models for the successful past and future development of HCT.

DNAX-activating protein 10 co-stimulation enhances the anti-tumor efficacy of chimeric antigen receptor T cells

Chimeric antigen receptor (CAR) T cell immunotherapies have shown remarkable efficacy in treating multiple types of hematological malignancies but are not sufficiently effective at treating solid tumors. NKG2D is a strong activating receptor for NK cells and a co-stimulatory receptor for T cells. NKG2D signal transduction depends on DNAX-activating protein 10 (DAP10). Here, we introduced the cytoplasmic domain of DAP10 into the second-generation CARs M28z and G28z to generate M28z10 and G28z10, which target mesothelin (MSLN) and glypican 3 (GPC3), respectively. T cells expressing M28z10 or G28z10 showed enhanced and prolonged effector function against MSLN+ lung cancer or GPC3+ hepatocellular carcinoma cell lines in culture and secreted elevated levels of cytokines, including IL-2, IFN-γ, granzyme B, and GM-CSF. In addition, M28z10 CAR-T cells showed greater anti-tumor activity than those expressing M28z in both A549 cell line xenografts and human lung cancer patient-derived xenografts (PDX). Similarly, G28z10 exhibited higher efficacy in causing tumor regression than did G28z in hepatocellular carcinoma PDX. Therefore, our results show that DAP10 signaling contributes to the function of CAR-T cells in both lung cancer and hepatocellular carcinoma and can enhance the efficacy of CAR-T cells.

CAR T Cell Therapy for Neuroblastoma

Patients with high risk neuroblastoma have a poor prognosis and survivors are often left with debilitating long term sequelae from treatment. Even after integration of anti-GD2 monoclonal antibody therapy into standard, upftont protocols, 5-year overall survival rates are only about 50%. The success of anti-GD2 therapy has proven that immunotherapy can be effective in neuroblastoma. Adoptive transfer of chimeric antigen receptor (CAR) T cells has the potential to build on this success. In early phase clinical trials, CAR T cell therapy for neuroblastoma has proven safe and feasible, but significant barriers to efficacy remain. These include lack of T cell persistence and potency, difficulty in target identification, and an immunosuppressive tumor microenvironment. With recent advances in CAR T cell engineering, many of these issues are being addressed in the laboratory. In this review, we summarize the clinical trials that have been completed or are underway for CAR T cell therapy in neuroblastoma, discuss the conclusions and open questions derived from these trials, and consider potential strategies to improve CAR T cell therapy for patients with neuroblastoma.

Cancer Immunotherapy in Diffuse Large B-Cell Lymphoma

Remarkable progress has been made in the field of cancer immunotherapy in the past few years. Immunotherapy has become a standard treatment option for patients with various cancers, including melanoma, lymphoma, and carcinomas of the lungs, kidneys, bladder, and head and neck. Promising immunotherapy approaches, such as chimeric antigen receptor (CAR) T cell therapy and therapeutic blockade of immune checkpoints, in particular cytotoxic T lymphocyte-associated protein 4 (CTLA-4) and programmed cell death protein 1 pathway (PD-1/PD-L1), have boosted the development of new therapeutic regimens for patients with cancer. Immunotherapeutic strategies for diffuse large B-cell lymphoma (DLBCL) include monoclonal anti-CD20 antibody (rituximab), monoclonal anti-PD-1 antibodies (nivolumab and pembrolizumab), monoclonal anti-PD-L1 antibodies (avelumab, durvalumab, and atezolizumab) and chimeric antigen receptor (CAR) T cell therapy. In this review, we outline the latest highlights and progress in using immunotherapy to treat patients with DLBCL, with a focus on the therapeutic blockade of PD-1/PD-L1 and CAR T cell therapy in DLBCL. We also discuss current clinical trials of PD-1/PD-L1 and CAR T cell therapy and review the challenges and opportunities of using immunotherapy for the treatment of DLBCL.

Chimeric Antigen Receptor T Cell Therapy: Challenges to Bench-to-Bedside Efficacy

Immunotherapy with T cells genetically modified to express chimeric Ag receptors (CARs) that target tumor-associated molecules have impressive efficacy in hematological malignancies. The field has now embraced the challenge of applying this approach to treat common epithelial malignancies, which make up the majority of cancer cases but evade immunologic attack by a variety of subversive mechanisms. In this study, we review the principles that have guided CAR T cell design and the extraordinary clinical results being achieved in B cell malignancies targeting CD19 with a single infusion of engineered T cells. This success has raised expectations that CAR T cells can be applied to solid tumors, but numerous obstacles must be overcome to achieve the success observed in hematologic cancers. Potential solutions driven by advances in genetic engineering, synthetic biology, T cell biology, and improved tumor models that recapitulate the obstacles in human tumors are discussed.

Chimeric antigen receptor-modified T cells: CD19 and the road beyond

The ability to harness a patient's immune system to target malignant cells is now transforming the treatment of many cancers, including hematologic malignancies. The adoptive transfer of T cells selected for tumor reactivity or engineered with natural or synthetic receptors has emerged as an effective modality, even for patients with tumors that are refractory to conventional therapies. The most notable example of adoptive cell therapy is with T cells engineered to express synthetic chimeric antigen receptors (CARs) that reprogram their specificity to target CD19. CAR T cells have shown remarkable antitumor activity in patients with refractory B-cell malignancies. Ongoing research is focused on understanding the mechanisms of incomplete tumor elimination, reducing toxicities, preventing antigen escape, and identifying suitable targets and strategies based on established and emerging principles of synthetic biology for extending this approach to other hematologic malignancies. This review will discuss the current status, challenges, and potential future applications of CAR T-cell therapy in hematologic malignancies.

Human CD19-Targeted Mouse T Cells Induce B Cell Aplasia and Toxicity in Human CD19 Transgenic Mice

The clinical success of chimeric antigen receptor (CAR) T cell therapy for CD19+ B cell malignancies can be limited by acute toxicities and immunoglobulin replacement needs due to B cell aplasia from persistent CAR T cells. Life-threatening complications include cytokine release syndrome and neurologic adverse events, the exact etiologies of which are unclear. To elucidate the underlying toxicity mechanisms and test potentially safer CAR T cells, we developed a mouse model in which human CD19 (hCD19)-specific mouse CAR T cells were adoptively transferred into mice whose normal B cells express a hCD19 transgene at hemizygous levels. Compared to homozygous hCD19 transgenic mice that have ∼75% fewer circulating B cells, hemizygous mice had hCD19 frequencies and antigen density more closely simulating human B cells. Hemizygous mice given a lethal dose of hCD19 transgene-expressing lymphoma cells and treated with CAR T cells had undetectable tumor levels. Recipients experienced B cell aplasia and antigen- and dose-dependent acute toxicities mirroring patient complications. Interleukin-6 (IL-6), interferon γ (IFN-γ), and inflammatory pathway transcripts were enriched in affected tissues. As in patients, antibody-mediated neutralization of IL-6 (and IFN-γ) blunted toxicity. Apparent behavioral abnormalities associated with decreased microglial cells point to CAR-T-cell-induced neurotoxicity. This model will prove useful in testing strategies designed to improve hCD19-specific CAR T cell safety.

CAR-T cells and allogeneic hematopoietic stem cell transplantation for relapsed/refractory B-cell acute lymphoblastic leukemia

Relapsed/refractory acute lymphoblastic leukemia (ALL) has a low remission rate after chemotherapy, a high relapse rate and poor long-term survival even when allogeneic hematopoietic stem cell transplantation (allo-HSCT) is performed. Chimeric antigen receptors redirected T cells (CAR-T cells) can enhance disease remission with a favorable outcome for relapsed/refractory ALL, though some cases quickly relapsed after CAR-T cell treatment. Thus, treatment with CAR-T cells followed by allo-HSCT may be the best way to treat relapsed/refractory ALL. In this review, we first discuss the different types of CAR-T cells. We then discuss the treatment of relapsed/refractory ALL using only CAR-T cells. Finally, we discuss the use of CAR-T cells, followed by allo-HSCT, for the treatment of relapsed/refractory ALL.

Advances on chimeric antigen receptor-modified T-cell therapy for oncotherapy

Tumor treatment is still complicated in the field of medicine. Tumor immunotherapy has been the most interesting research field in cancer therapy. Application of chimeric antigen receptor T (CAR-T) cell therapy has recently achieved excellent clinical outcome in patients, especially those with CD19-positive hematologic malignancies. This phenomenon has induced intense interest to develop CAR-T cell therapy for cancer, especially for solid tumors. However, the performance of CAR-T cell treatment in solid tumor is not as satisfactory as that in hematologic disease. Clinical studies on some neoplasms, such as glioblastoma, ovarian cancer, and cholangiocarcinoma, have achieved desirable outcome. This review describes the history and evolution of CAR-T, generalizes the structure and preparation of CAR-T, and summarizes the latest advances on CAR-T cell therapy in different tumor types. The last section presents the current challenges and prospects of CAR-T application to provide guidance for subsequent research.

Choice of costimulatory domains and of cytokines determines CAR T-cell activity in neuroblastoma

Chimeric antigen receptor (CAR) T-cell therapy has been shown to be dramatically effective in the treatment of B-cell malignancies. However, there are still substantial obstacles to overcome, before similar responses can be achieved in patients with solid tumors. We evaluated both in vitro and in a preclinical murine model the efficacy of different 2nd and 3rd generation CAR constructs targeting GD2, a disial-ganglioside expressed on the surface of neuroblastoma (NB) tumor cells. In order to address potential safety concerns regarding clinical application, an inducible safety switch, namely inducible Caspase-9 (iC9), was also included in the vector constructs. Our data indicate that a 3rd generation CAR incorporating CD28.4-1BB costimulatory domains is associated with improved anti-tumor efficacy as compared with a CAR incorporating the combination of CD28.OX40 domains. We demonstrate that the choice of 4-1BB signaling results into significant amelioration of several CAR T-cell characteristics, including: 1) T-cell exhaustion, 2) basal T-cell activation, 3) in vivo tumor control and 4) T-cell persistence. The fine-tuning of T-cell culture conditions obtained using IL7 and IL15 was found to be synergic with the CAR.GD2 design in increasing the anti-tumor activity of CAR T cells. We also demonstrate that activation of the suicide gene iC9, included in our construct without significantly impairing neither CAR expression nor anti-tumor activity, leads to a prompt induction of apoptosis of GD2.CAR T cells. Altogether, these findings are instrumental in optimizing the function of CAR T-cell products to be employed in the treatment of children with NB.

Logic-gated approaches to extend the utility of chimeric antigen receptor T-cell technology

Chimeric antigen receptor (CAR)-T cell therapy has been clinically validated as a curative treatment for the difficult to treat malignancies of relapsed/refractory B-cell acute lymphoblastic leukaemia and lymphoma. Here, the CAR-T cells are re-directed towards a single antigen, CD19, which is recognised as a virtually ideal CAR target antigen because it has strong, uniform expression on cancer cells, and is otherwise expressed only on healthy B cells, which are 'dispensable'. Notwithstanding the clinical success of CD19-CAR-T cell therapy, its single specificity has driven therapeutic resistance in 30% or more of cases with CD19-negative leukaemic relapses. Immune checkpoint blockade is also a highly successful cancer immunotherapeutic approach, but it will be less useful for many patients whose malignancies either lack a substantial somatic mutation load or whose tumours are intrinsically resistant. Although CAR-T cell therapy could serve this unmet medical need, it is beset by several major limitations. There is a lack of candidate antigens that would satisfy the requirements for ideal CAR targets. Biological properties such as clonal heterogeneity and micro-environmental conditions hostile to T cells are inherent to many solid tumours. Past clinical studies indicate that on-target, off-tumour toxicities of CAR-T cell therapy may severely hamper its application. Therefore, re-designing CARs to increase the number of antigen specificities recognised by CAR-T cells will broaden tumour antigen coverage, potentially overcoming tumour heterogeneity and limiting tumour antigen escape. Tuning the balance of signalling within bi-specific CAR-T cells may enable tumour targeting while sparing normal tissues, and thus minimise on-target, off-tumour toxicities.

Immunological Synapse Predicts Effectiveness of Chimeric Antigen Receptor Cells

Chimeric antigen receptor (CAR)-modified T cell therapy has the potential to improve the overall survival of patients with malignancies by enhancing the effectiveness of CAR T cells. Precisely predicting the effectiveness of various CAR T cells represents one of today’s key unsolved problems in immunotherapy. Here, we predict the effectiveness of CAR-modified cells by evaluating the quality of the CAR-mediated immunological synapse (IS) by quantitation of F-actin, clustering of tumor antigen, polarization of lytic granules (LGs), and distribution of key signaling molecules within the IS. Long-term killing capability, but not secretion of conventional cytokines or standard 4-hr cytotoxicity, correlates positively with the quality of the IS in two different CAR T cells that share identical antigen specificity. Xenograft model data confirm that the quality of the IS in vitro correlates positively with performance of CAR-modified immune cells in vivo. Therefore, we propose that the quality of the IS predicts the effectiveness of CAR-modified immune cells, which provides a novel strategy to guide CAR therapy.

CAR T-cells for cancer therapy

Chimeric antigen receptor (CAR) T-cells are redirected T-cells that can recognize cancer antigens in a major histocompatibility complex (MHC)-independent fashion. A typical CAR is comprised of two main functional domains: an extracellular antigen recognition domain, called a single-chain variable fragment (scFv), and an intracellular signaling domain. Based on the number of intracellular signaling molecules, CARs are categorized into four generations. CAR T-cell therapy has become a promising treatment for hematologic malignancies. However, results of its clinical trials on solid tumors have not been encouraging. Here, we described the structure of CARs and summarized the clinical trials of CD19-targeted CAR T-cells. The side effects, safety management, challenges, and future prospects of CAR T-cells for the treatment of cancer, particularly for solid tumors, were also discussed.

CD137+CD154- Expression As a Regulatory T Cell (Treg)-Specific Activation Signature for Identification and Sorting of Stable Human Tregs from In Vitro Expansion Cultures

Regulatory T cells (Tregs) are an attractive therapeutic tool for several different immune pathologies. Therapeutic Treg application often requires prolonged in vitro culture to generate sufficient Treg numbers or to optimize their functionality, e.g., via genetic engineering of their antigen receptors. However, purity of clinical Treg expansion cultures is highly variable, and currently, it is impossible to identify and separate stable Tregs from contaminating effector T cells, either ex vivo or after prior expansion. This represents a major obstacle for quality assurance of expanded Tregs and raises significant safety concerns. Here, we describe a Treg activation signature that allows identification and sorting of epigenetically imprinted Tregs even after prolonged in vitro culture. We show that short-term reactivation resulted in expression of CD137 but not CD154 on stable FoxP3+ Tregs that displayed a demethylated Treg-specific demethylated region, high suppressive potential, and lack of inflammatory cytokine expression. We also applied this Treg activation signature for rapid testing of chimeric antigen receptor functionality in human Tregs and identified major differences in the signaling requirements regarding CD137 versus CD28 costimulation. Taken together, CD137+CD154- expression emerges as a universal Treg activation signature ex vivo and upon in vitro expansion allowing the identification and isolation of epigenetically stable antigen-activated Tregs and providing a means for their rapid functional testing in vitro.

A novel chimeric antigen receptor containing a JAK-STAT signaling domain mediates superior antitumor effects

The adoptive transfer of T cells engineered with a chimeric antigen receptor (CAR) (hereafter referred to as CAR-T cells) specific for the B lymphocyte antigen CD19 has shown impressive clinical responses in patients with refractory B cell malignancies. However, the therapeutic effects of CAR-T cells that target other malignancies have not yet resulted in significant clinical benefit. Although inefficient tumor trafficking and various immunosuppressive mechanisms can impede CAR-T cell effector responses, the signals delivered by the current CAR constructs may still be insufficient to fully activate antitumor T cell functions. Optimal T cell activation and proliferation requires multiple signals, including T cell receptor (TCR) engagement (signal 1), co-stimulation (signal 2) and cytokine engagement (signal 3). However, CAR constructs currently being tested in the clinic contain a CD3z (TCR signaling) domain and co-stimulatory domain(s) but not a domain that transmits signal 3 (refs. 13, 14, 15, 16, 17, 18). Here we have developed a novel CAR construct capable of inducing cytokine signaling after antigen stimulation. This new-generation CD19 CAR encodes a truncated cytoplasmic domain from the interleukin (IL)-2 receptor β-chain (IL-2Rβ) and a STAT3-binding tyrosine-X-X-glutamine (YXXQ) motif, together with the TCR signaling (CD3z) and co-stimulatory (CD28) domains (hereafter referred to as 28-ΔIL2RB-z(YXXQ)). The 28-ΔIL2RB-z(YXXQ) CAR-T cells showed antigen-dependent activation of the JAK kinase and of the STAT3 and STAT5 transcription factors signaling pathways, which promoted their proliferation and prevented terminal differentiation in vitro. The 28-ΔIL2RB-z(YXXQ) CAR-T cells demonstrated superior in vivo persistence and antitumor effects in models of liquid and solid tumors as compared with CAR-T cells expressing a CD28 or 4-1BB co-stimulatory domain alone. Taken together, these results suggest that our new-generation CAR has the potential to demonstrate superior antitumor effects with minimal toxicity in the clinic and that clinical translation of this novel CAR is warranted.

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.

Synthetic Biology: Immunotherapy by Design

Cellular immunotherapy holds great promise for the treatment of human disease. Clinical evidence suggests that T cell immunotherapies have the potential to combat cancers that evade traditional immunotherapy. Despite promising results, adverse effects leading to fatalities have left scientists seeking tighter control over these therapies, which is reflected in the growing body of synthetic biology literature focused on developing tightly controlled, context-independent parts. In addition, researchers are adapting these tools for other uses, such as for the treatment of autoimmune disease, HIV infection, and fungal interactions. We review this body of work and devote special attention to approaches that may lend themselves to the development of an "ideal" therapy: one that is safe, efficient, and easy to manufacture. We conclude with a look toward the future of immunotherapy: how synthetic biology can shift the paradigm from the treatment of disease to a focus on wellness and human health as a whole.

Redirecting T-Cell Specificity to EGFR Using mRNA to Self-limit Expression of Chimeric Antigen Receptor

Potential for on-target, but off-tissue toxicity limits therapeutic application of genetically modified T cells constitutively expressing chimeric antigen receptors (CARs) from tumor-associated antigens expressed in normal tissue, such as epidermal growth factor receptor (EGFR). Curtailing expression of CAR through modification of T cells by in vitro-transcribed mRNA species is one strategy to mitigate such toxicity. We evaluated expression of an EGFR-specific CAR coded from introduced mRNA in human T cells numerically expanded ex vivo to clinically significant numbers through coculture with activating and propagating cells (AaPC) derived from K562 preloaded with anti-CD3 antibody. The density of AaPC could be adjusted to affect phenotype of T cells such that reduced ratio of AaPC resulted in higher proportion of CD8 and central memory T cells that were more conducive to electrotransfer of mRNA than T cells expanded with high ratios of AaPC. RNA-modified CAR T cells produced less cytokine, but demonstrated similar cytolytic capacity as DNA-modified CAR T cells in response to EGFR-expressing glioblastoma cells. Expression of CAR by mRNA transfer was transient and accelerated by stimulation with cytokine and antigen. Loss of CAR abrogated T-cell function in response to tumor and normal cells expressing EGFR. We describe a clinically applicable method to propagate and modify T cells to transiently express EGFR-specific CAR to target EGFR-expressing tumor cells that may be used to limit on-target, off-tissue toxicity to normal tissue.

Anti-GD2/4-1BB chimeric antigen receptor T cell therapy for the treatment of Chinese melanoma patients

Background

Chimeric antigen receptor (CAR)-engineered T cells have demonstrated promising clinical efficacy in patients with B cell lymphoma. However, the application of CAR-T cell therapy in the treatment of other solid tumors has been limited. We incorporated 4-1BB into the anti-GD2 CAR-T cells to test their cytotoxicity in melanoma in vitro and in vivo. Moreover, we reported the expression of ganglioside GD2 in non-Caucasian melanoma populations for the first time, thus providing a basis for future clinical research.

Methods

This study included tumor samples from 288 melanoma patients at the Peking University Cancer Hospital & Institute. Clinical data were collected. Immunohistochemical assays using antibodies against ganglioside GD2 were performed on formalin-fixed, paraffin-embedded specimens. The ability of ganglioside GD2 CAR-T cells to kill ganglioside GD2⁺ melanoma cells was evaluated in vitro and in a patient-derived xenograft (PDX) model.

Results

Among the 288 samples, 49.3% of cases (142/288) demonstrated positive staining with ganglioside GD2. The median survival time in patients exhibiting ganglioside GD2 expression was significantly shorter than that in patients without ganglioside GD2 expression (31 vs. 47.1 months, P < 0.001). In the present study, CAR was constructed using a GD2-specific scFv (14.G2a), T cell receptor CD3ζ chain, and the CD137 (4-1BB) costimulatory motif. In addition, the GD2.BBζ CAR-T cells demonstrated specific lysis of ganglioside GD2-expressing melanoma cells in vitro. In two PDX models, mice that received intravenous or local intratumor injections of GD2.BBζ CAR-T cells experienced rapid tumor regression.

Conclusions

These data demonstrate that the rate of GD2 expression in Chinese patients is 49.3%. GD2.BBζ CAR-T cells can both efficiently lyse melanoma in a GD2-specific manner and release Th1 cytokines in an antigen-dependent manner in vitro and in vivo. Anti-GD2/4-1BB CAR-T cells represent a clinically appealing treatment strategy for Chinese melanoma patients exhibiting GD2 expression and provide a basis for future studies of the clinical application of immunotherapy for melanoma.

Electronic supplementary material

The online version of this article (10.1186/s13045-017-0548-2) contains supplementary material, which is available to authorized users.

Lenalidomide Enhances the Function of CS1 Chimeric Antigen Receptor-Redirected T Cells Against Multiple Myeloma

Purpose: Multiple myeloma remains an incurable malignancy of plasma cells despite considerable advances in treatment. The purpose of the study was to develop novel chimeric antigen receptors (CAR) for the treatment of multiple myeloma and explore combinatorial therapy using CAR T cells and immunomodulatory drugs such as lenalidomide for increasing treatment efficacy.Experimental Design: We redirected central memory T cells to express second-generation CAR-specific for CS1 and adoptively transferred them into multiple myeloma tumor-bearing mice to test their anti-multiple myeloma activity. CS1 CAR T cells were transduced and expanded in the presence of lenalidomide in vitro The phenotype and effector function of CS1 CAR T cells treated with and without lenalidomide were compared. Finally, CS1 CAR T cells and lenalidomide were administered to treat multiple myeloma-bearing mice as combinatorial therapy.Results: CS1 CAR T cells exhibited efficient antitumor activity when adoptively transferred into mice. Mechanistic studies indicated that the addition of lenalidomide during CS1 CAR T-cell expansion in vitro enhanced the immune functions of CS1 CAR T cells, including cytotoxicity, memory maintenance, Th1 cytokine production, and immune synapse formation. Furthermore, lenalidomide enhanced the antitumor activity and persistence of adoptively transferred CS1 CAR T cells in vivoConclusions: The study demonstrates that lenalidomide improves the anti-multiple myeloma properties of CS1-directed CAR T cells and provides a basis for a planned clinical trial using the combination of lenalidomide with engineered T cells against CS1 in relapsed myeloma. Clin Cancer Res; 24(1); 106-19. ©2017 AACR.

Preclinical Optimization of a CD20-specific Chimeric Antigen Receptor Vector and Culture Conditions

Chimeric antigen receptor (CAR)-based adoptive T-cell therapy is a highly promising treatment for lymphoid malignancies, and CD20 is an ideal target antigen. We previously developed a lentiviral construct encoding a third generation CD20-targeted CAR but identified several features that required additional optimization before clinical translation. We describe here several improvements, including replacement of the immunogenic murine antigen-binding moiety with a fully human domain, streamlining the transgene insert to enhance lentiviral titers, modifications to the extracellular IgG spacer that abrogate nonspecific activation resulting from binding to Fc receptors, and evaluation of CD28, 4-1BB, or CD28 and 4-1BB costimulatory domains. We also found that restimulation of CAR T cells with an irradiated CD20 cell line boosted cell growth, increased the fraction of CAR-expressing cells, and preserved in vivo function despite leading to a reduced capacity for cytokine secretion in vitro. We also found that cryopreservation of CAR T cells did not affect immunophenotype or in vivo antitumor activity compared with fresh cells. These optimization steps resulted in significant improvement in antitumor activity in mouse models, resulting in eradication of established systemic lymphoma tumors in 75% of mice with a single infusion of CAR T cells, and prolonged in vivo persistence of modified cells. These results provide the basis for clinical testing of a lentiviral construct encoding a fully human CD20-targeted CAR with CD28 and 4-1BB costimulatory domains and truncated CD19 (tCD19) transduction marker.

The Evolution and Future of CAR T Cells for B-Cell Acute Lymphoblastic Leukemia

Several CAR T designs with CD19 specificity have been associated with consistent responses in clinical trials with complete remission (CR) rates ranging from 70-90%. Relevant challenges remain to be addressed, such as production time, early loss of CAR T cells, relapse due to loss of the target antigen, and prevention of severe cytokine release syndrome and neurotoxicity. This review describes constructs, clinical trial results, side effects, and future direction of CAR T-cell therapy in B-ALL.

The activated conformation of integrin β7 is a novel multiple myeloma-specific target for CAR T cell therapy

Cancer-specific cell-surface antigens are ideal targets for monoclonal antibody (mAb)-based immunotherapy but are likely to have previously been identified in transcriptome or proteome analyses. Here, we show that the active conformer of an integrin can serve as a specific therapeutic target for multiple myeloma (MM). We screened >10,000 anti-MM mAb clones and identified MMG49 as an MM-specific mAb specifically recognizing a subset of integrin β₇ molecules. The MMG49 epitope, in the N-terminal region of the β₇ chain, is predicted to be inaccessible in the resting integrin conformer but exposed in the active conformation. Elevated expression and constitutive activation of integrin β₇ conferred high MMG49 reactivity on MM cells, whereas MMG49 binding was scarcely detectable in other cell types including normal integrin β₇⁺ lymphocytes. T cells transduced with MMG49-derived chimeric antigen receptor (CAR) exerted anti-MM effects without damaging normal hematopoietic cells. Thus, MMG49 CAR T cell therapy is promising for MM, and a receptor protein with a rare but physiologically relevant conformation can serve as a cancer immunotherapy target.