Fifteen years of gene therapy based on chimeric antigen receptors: "are we nearly there yet?"

Current Trends and Innovative Approaches in Cancer Immunotherapy

Immunotherapy is one of the most promising therapeutic approaches in the field of cancer treatment. As a tumor progresses, tumor cells employ an array of immune-regulatory mechanisms to suppress immune responses within the tumor microenvironment. Using our understanding of these mechanisms, cancer immunotherapy has been developed to enhance the immune system's effectiveness in treating cancer. Numerous cancer immunotherapies are currently in clinical use, yet many others are either in different stages of development or undergoing clinical studies. In this paper, we briefly discuss the features and current status of cancer immunotherapies. This includes the application of monoclonal antibodies, immune checkpoint inhibitors, adoptive cell therapy, cytokine therapy, cancer vaccines, and gene therapy, all of which have gained significant recognition in clinical practice. Additionally, we discuss limitations that may hinder successful clinical utilization and promising strategies, such as combining immunotherapy with nanotechnology.

The synergistic immunotherapeutic impact of engineered CAR-T cells with PD-1 blockade in lymphomas and solid tumors: a systematic review

Currently, therapies such as chimeric antigen receptor-T Cell (CAR-T) and immune checkpoint inhibitors like programmed cell death protein-1 (PD-1) blockers are showing promising results for numerous cancer patients. However, significant advancements are required before CAR-T therapies become readily available as off-the-shelf treatments, particularly for solid tumors and lymphomas. In this review, we have systematically analyzed the combination therapy involving engineered CAR-T cells and anti PD-1 agents. This approach aims at overcoming the limitations of current treatments and offers potential advantages such as enhanced tumor inhibition, alleviated T-cell exhaustion, heightened T-cell activation, and minimized toxicity. The integration of CAR-T therapy, which targets tumor-associated antigens, with PD-1 blockade augments T-cell function and mitigates immune suppression within the tumor microenvironment. To assess the impact of combination therapy on various tumors and lymphomas, we categorized them based on six major tumor-associated antigens: mesothelin, disialoganglioside GD-2, CD-19, CD-22, CD-133, and CD-30, which are present in different tumor types. We evaluated the efficacy, complete and partial responses, and progression-free survival in both pre-clinical and clinical models. Additionally, we discussed potential implications, including the feasibility of combination immunotherapies, emphasizing the importance of ongoing research to optimize treatment strategies and improve outcomes for cancer patients. Overall, we believe combining CAR-T therapy with PD-1 blockade holds promise for the next generation of cancer immunotherapy.

CAR products from novel sources: a new avenue for the breakthrough in cancer immunotherapy

Chimeric antigen receptor (CAR) T cell therapy has transformed cancer immunotherapy. However, significant challenges limit its application beyond B cell-driven malignancies, including limited clinical efficacy, high toxicity, and complex autologous cell product manufacturing. Despite efforts to improve CAR T cell therapy outcomes, there is a growing interest in utilizing alternative immune cells to develop CAR cells. These immune cells offer several advantages, such as major histocompatibility complex (MHC)-independent function, tumor microenvironment (TME) modulation, and increased tissue infiltration capabilities. Currently, CAR products from various T cell subtypes, innate immune cells, hematopoietic progenitor cells, and even exosomes are being explored. These CAR products often show enhanced antitumor efficacy, diminished toxicity, and superior tumor penetration. With these benefits in mind, numerous clinical trials are underway to access the potential of these innovative CAR cells. This review aims to thoroughly examine the advantages, challenges, and existing insights on these new CAR products in cancer treatment.

Modulating Cholesterol Metabolism via ACAT1 Knockdown Enhances Anti-B-Cell Lymphoma Activities of CD19-Specific Chimeric Antigen Receptor T Cells by Improving the Cell Activation and Proliferation

CD19-specific CAR-T immunotherapy has been extensively studied for the treatment of B-cell lymphoma. Recently, cholesterol metabolism has emerged as a modulator of T lymphocyte function and can be exploited in immunotherapy to increase the efficacy of CAR-based systems. Acetyl-CoA acetyltransferase 1 (ACAT1) is the major cholesterol esterification enzyme. ACAT1 inhibitors previously shown to modulate cardiovascular diseases are now being implicated in immunotherapy. In the present study, we achieved knockdown of ACAT1 in T cells via RNA interference technology by inserting ACAT1-shRNA into anti-CD19-CAR-T cells. Knockdown of ACAT1 led to an increased cytotoxic capacity of the anti-CD19-CAR-T cells. In addition, more CD69, IFN-γ, and GzmB were expressed in the anti-CD19-CAR-T cells. Cell proliferation was also enhanced in both antigen-independent and antigen-dependent manners. Degranulation was also improved as evidenced by an increased level of CD107a. Moreover, the knockdown of ACAT1 led to better anti-tumor efficacy of anti-CD19 CAR-T cells in the B-cell lymphoma mice model. Our study demonstrates novel CAR-T cells containing ACAT1 shRNA with improved efficacy compared to conventional anti-CD19-CAR-T cells in vitro and in vivo.

CAR-T treatment for cancer: prospects and challenges

Chimeric antigen receptor (CAR-T) cell therapy has been widely used in hematological malignancies and has achieved remarkable results, but its long-term efficacy in solid tumors is greatly limited by factors such as the tumor microenvironment (TME). In this paper, we discuss the latest research and future views on CAR-T cell cancer immunotherapy, compare the different characteristics of traditional immunotherapy and CAR-T cell therapy, introduce the latest progress in CAR-T cell immunotherapy, and analyze the obstacles that hinder the efficacy of CAR-T cell therapy, including immunosuppressive factors, metabolic energy deficiency, and physical barriers. We then further discuss the latest therapeutic strategies to overcome these barriers, as well as management decisions regarding the possible safety issues of CAR-T cell therapy, to facilitate solutions to the limited use of CAR-T immunotherapy.

Clinical Trials of Cellular Therapies in Solid Tumors

In the past years cancer treatments have drastically changed, mainly due to the development of immune checkpoint inhibitors capable of immune modulation in vivo, thus providing major clinical benefit in a number of malignancies. Simultaneously, considerable technical refinements have opened new prospects for the development of immune cell-based medicinal products and unprecedented success with chimeric antigen receptor (CAR)-T cells targeting B-cell hematologic malignancies has been obtained. However, T cell therapies introduced and performed in the field of solid tumors have produced so far only limited responses in selected patient populations. This standstill is attributable to the difficulty in identifying target antigens which are homogeneously expressed by all tumor cells while absent from normal tissues, and the limited T cell persistence and proliferation in a hostile tumor microenvironment that favors immune escape. Replicating the results observed in hematology is a major scientific challenge in solid tumors, and ongoing translational and clinical research is focused on obtaining insight into the mechanisms of tumor recognition and evasion, and how to improve the efficacy of cellular therapies, also combining them with immune checkpoint inhibitors or other agents targeting either the cancer cell or the tumor environment. This paper provides an overview of current adaptive T cell therapy approaches in solid tumors, the research performed to increase their efficacy and safety, and results from ongoing clinical trials.

Comprehensive clinical evaluation of CAR-T cell immunotherapy for solid tumors: a path moving forward or a dead end?

INTRODUCTION

Chimeric Antigen Receptor (CAR)-T cell therapy is a form of adoptive cell therapy that has demonstrated tremendous results in the treatment of hematopoietic malignancies, leading to the US Food and Drug Administration (FDA) approval of four CD19-targeted CAR-T cell products. With the unprecedented success of CAR-T cell therapy in hematological malignancies, hundreds of preclinical studies and clinical trials are currently undergoing to explore the translation of this treatment to solid tumors. However, the clinical experience in non-hematologic malignancies has been less encouraging, with only a few patients achieving complete responses. Tumor-associated antigen heterogeneity, inefficient CAR-T cell trafficking and the immunosuppressive tumor microenvironment are considered as the most pivotal roadblocks in solid tumor CAR-T cell therapy.

MATERIALS AND METHODS

We reviewed the relevant literature/clinical trials for CAR-T cell immunotherapy for solid tumors from Pubmed and ClinicalTrials.gov.

CONCLUSION

Herein, we provide an update on solid tumor CAR-T cell clinical trials, focusing on the studies with published results. We further discuss some of the key hurdles that CAR-T cell therapy is encountering for solid tumor treatment as well as the strategies that are exploited to overcome these obstacles.

Advanced Cell Therapy: Beyond the last Frontier in the Treatment of Cancer. A Historical Perspective Emphasizing the Work of Nobel Prize Laureates

During the last five decades different therapies have been developed for the treatment of cancer, and as a result, patients can now live longer and better lives. Among such therapies, hematopoietic cell transplantation and immunotherapy have played key roles. In this short article, we present our particular point of view on the development of these two cellular therapies. We have focused on a historical perspective emphasizing the work of some of the Nobel Prize winners whose studies constituted cornerstones in our knowledge of the biology of cancer and in our fight against this devastating disease.

CAR-based cell therapy: evaluation with bibliometrics and patent analysis

Chimeric antigen receptors-based cell therapies have shown impressive preclinical and clinical success and revolutionized biomedicine. However, the link between science and invention, the impact of international cooperation, and the influence and prestige of CARs research have not been explored. This study analyzed the landscape of peer-reviewed articles and patents related to CARs. A total of 5,681 publications were analyzed using bibliometrics and machine learning-based text mining to assess publication metrics, subject areas, and research hotspots. 5,010 Inpadoc families were also analyzed for patent filing trends, priority countries, and applicant and inventor rankings. The results show that CARs research has the following distinctive features: high research prestige among research community; strong global geographical bias in both academic output and patenting patterns; strong links between science and invention, but significant differences among countries; and an inverse relationship between country size and international collaboration rates.

Cellular Immunotherapy Targeting Cancer Stem Cells: Preclinical Evidence and Clinical Perspective

The term “cancer stem cells” (CSCs) commonly refers to a subset of tumor cells endowed with stemness features, potentially involved in chemo-resistance and disease relapses. CSCs may present peculiar immunogenic features influencing their homeostasis within the tumor microenvironment. The susceptibility of CSCs to recognition and targeting by the immune system is a relevant issue and matter of investigation, especially considering the multiple emerging immunotherapy strategies. Adoptive cellular immunotherapies, especially those strategies encompassing the genetic redirection with chimeric antigen receptors (CAR), hold relevant promise in several tumor settings and might in theory provide opportunities for selective elimination of CSC subsets. Initial dedicated preclinical studies are supporting the potential targeting of CSCs by cellular immunotherapies, indirect evidence from clinical studies may be derived and new studies are ongoing. Here we review the main issues related to the putative immunogenicity of CSCs, focusing on and highlighting the existing evidence and opportunities for cellular immunotherapy approaches with T and non-T antitumor lymphocytes.

Preclinical Evaluation of Invariant Natural Killer T Cells Modified with CD38 or BCMA Chimeric Antigen Receptors for Multiple Myeloma

Due to the CD1d restricted recognition of altered glycolipids, Vα24-invariant natural killer T (iNKT) cells are excellent tools for cancer immunotherapy with a significantly reduced risk for graft-versus-host disease when applied as off-the shelf-therapeutics across Human Leukocyte Antigen (HLA) barriers. To maximally harness their therapeutic potential for multiple myeloma (MM) treatment, we here armed iNKT cells with chimeric antigen receptors (CAR) directed against the MM-associated antigen CD38 and the plasma cell specific B cell maturation antigen (BCMA). We demonstrate that both CD38- and BCMA-CAR iNKT cells effectively eliminated MM cells in a CAR-dependent manner, without losing their T cell receptor (TCR)-mediated cytotoxic activity. Importantly, iNKT cells expressing either BCMA-CARs or affinity-optimized CD38-CARs spared normal hematopoietic cells and displayed a Th1-like cytokine profile, indicating their therapeutic utility. While the costimulatory domain of CD38-CARs had no influence on the cytotoxic functions of iNKT cells, CARs containing the 4-1BB domain showed a better expansion capacity. Interestingly, when stimulated only via CD1d+ dendritic cells (DCs) loaded with α-galactosylceramide (α-GalCer), both CD38- and BCMA-CAR iNKT cells expanded well, without losing their CAR- or TCR-dependent cytotoxic activities. This suggests the possibility of developing an off-the-shelf therapy with CAR iNKT cells, which might even be boostable in vivo by administration α-GalCer pulsed DCs.

Hepatoblastoma: current knowledge and promises from preclinical studies

The survival rate for patients with metastatic hepatoblastoma (HB) is steadily increased in the last thirty years from 27% to 79%. These achievements result from accurate risk stratification and effective chemotherapy and surgical care. However, patients with poor prognosis require more effective therapies. Recent years have witnessed new insights on the biology of HB, setting the stage for molecular classification and new targets of therapy. We review here the molecular pathology of HB, focusing on the driver genes involved in the process of oncogenesis and the identification of novel targets. We also address the role of in vivo models in elucidating the mechanisms of development of this disease and the pre-clinical phase of new treatment modalities.

Recent advances in tumor associated carbohydrate antigen based chimeric antigen receptor T cells and bispecific antibodies for anti-cancer immunotherapy

Tumor associated carbohydrate antigens (TACAs) are a class of attractive antigens for the development of anti-cancer immunotherapy. Besides monoclonal antibodies and vaccines, chimeric antigen receptor (CAR) T cells and bispecific antibodies (BsAbs) targeting TACA are exciting directions to harness the power of the immune system to fight cancer. In this review, we focus on two TACAs, i.e., the GD2 ganglioside and the mucin-1 (MUC1) protein. The latest advances in CAR T cells and bispecific antibodies targeting these two antigens are presented. The roles of co-stimulatory molecules, structures of the sequences for antigen binding, methods for CAR and antibody construction, as well as strategies to enhance solid tumor penetration and reduce T cell exhaustion and death are discussed. Furthermore, approaches to reduce "on target, off tumor" side effects are introduced. With further development, CAR T cells and BsAbs targeting GD2 and MUC1 can become powerful agents to effectively treat solid tumor.

CAR-Based Strategies beyond T Lymphocytes: Integrative Opportunities for Cancer Adoptive Immunotherapy

Chimeric antigen receptor (CAR)-engineered T lymphocytes (CAR Ts) produced impressive clinical results against selected hematological malignancies, but the extension of CAR T cell therapy to the challenging field of solid tumors has not, so far, replicated similar clinical outcomes. Many efforts are currently dedicated to improve the efficacy and safety of CAR-based adoptive immunotherapies, including application against solid tumors. A promising approach is CAR engineering of immune effectors different from αβT lymphocytes. Herein we reviewed biological features, therapeutic potential, and safety of alternative effectors to conventional CAR T cells: γδT, natural killer (NK), NKT, or cytokine-induced killer (CIK) cells. The intrinsic CAR-independent antitumor activities, safety profile, and ex vivo expansibility of these alternative immune effectors may favorably contribute to the clinical development of CAR strategies. The proper biological features of innate immune response effectors may represent an added value in tumor settings with heterogeneous CAR target expression, limiting the risk of tumor clonal escape. All these properties bring out CAR engineering of alternative immune effectors as a promising integrative option to be explored in future clinical studies.

Fluorine-19 MRI for detection and quantification of immune cell therapy for cancer

Over the past two decades, immune cell therapy has emerged as a potent treatment for multiple cancers, first through groundbreaking leukemia therapy, and more recently, by tackling solid tumors. Developing successful therapeutic strategies using live cells could benefit from the ability to rapidly determine their in vivo biodistribution and persistence. Assaying cell biodistribution is unconventional compared to traditional small molecule drug pharmacokinetic readouts used in the pharmaceutical pipeline, yet this information is critical towards understanding putative therapeutic outcomes and modes of action. Towards this goal, efforts are underway to visualize and quantify immune cell therapy in vivo using advanced magnetic resonance imaging (MRI) techniques. Cell labeling probes based on perfluorocarbon nanoemulsions, paired with fluorine-19 MRI detection, enables background-free quantification of cell localization and survival. Here, we highlight recent preclinical and clinical uses of perfluorocarbon probes and ¹⁹F MRI for adoptive cell transfer (ACT) studies employing experimental T lymphocytes, NK, PBMC, and dendritic cell therapies. We assess the forward looking potential of this emerging imaging technology to aid discovery and preclinical phases, as well as clinical trials. The limitations and barriers towards widespread adoption of this technology, as well as alternative imaging strategies, are discussed.

Immune Cell Hacking: Challenges and Clinical Approaches to Create Smarter Generations of Chimeric Antigen Receptor T Cells

T cells equipped with chimeric antigen receptors (CAR T cells) have recently provided promising advances as a novel immunotherapeutic approach for cancer treatment. CAR T cell therapy has shown stunning results especially in B-cell malignancies; however, it has shown less success against solid tumors, which is more supposed to be related to the specific characteristics of the tumor microenvironment. In this review, we discuss the structure of the CAR, current clinical advantages from finished and ongoing trials, adverse effects, challenges and controversies, new engineering methods of CAR, and clinical considerations that are associated with CAR T cell therapy both in hematological malignancies and solid tumors. Also, we provide a comprehensive description of recently introduced modifications for designing smarter models of CAR T cells. Specific hurdles and problems that limit the optimal function of CAR T cells, especially on solid tumors, and possible solutions according to new modifications and generations of CAR T cells have been introduced here. We also provide information of the future directions on how to enhance engineering the next smarter generations of CAR T cells in order to decrease the adverse effects and increase the potency and efficacy of CAR T cells against cancer.

Diagnostic molecular techniques in haematology: recent advances

Hematopoietic disorders are often driven by genetic mutations and epigenetic alterations. New advanced technologies including next-generation sequencing, ultra-deep PCR and whole-genome and exome sequencing were proved very efficient in detecting several mutations implicated in the pathogenesis of hematological diseases. Emerging evidence indicates that genomic data can be useful in all aspects of clinical practice including diagnosis, prognosis and prediction of response to specific treatments, as well as in the development of novel targeted treatments for patients with hematological disorders.

Immunotherapy for Hepatocellular Carcinoma: Current Advances and Future Expectations

Primary liver cancer is a common kind of digestive cancers with high malignancy, causing 745,500 deaths each year. Hepatocellular carcinoma is the major pathological type of primary liver cancer. Traditional treatment methods for patients with hepatocellular carcinoma have shown poor efficacy in killing residual cancer cells for a long time. In recent years, tumor immunotherapy has emerged as a promising method owing to its safety and efficacy with respect to delaying the progression of advanced tumors and protecting postoperative patients against tumor relapse and metastasis. Immune tolerance and suppression in tumor microenvironments are the theoretical basis of immunotherapy. Adoptive cell therapy functions by stimulating and cultivating autologous lymphocytes ex vivo and then reinfusing them into the patient to kill cancer cells. Cancer vaccination is performed using antigenic substances to activate tumor-specific immune responses. Immune checkpoint inhibitors can reactivate tumor-specific T cells and develop an antitumor effect by suppressing checkpoint-mediated signaling. Oncolytic viruses may selectively replicate in tumor cells and cause lysis without harming normal tissues. Here, we briefly introduce the mechanism of immunosuppression in hepatocellular carcinoma and summarize the rationale of the four major immunotherapeutic approaches with their current advances.

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.

CD44v6 as innovative sarcoma target for CAR-redirected CIK cells

Purpose of our study was to explore a new immunotherapy for high grade soft tissue sarcomas (STS) based on cytokine-induced killer cells (CIK) redirected with a chimeric antigen receptor (CAR) against the tumor-promoting antigen CD44v6. We aimed at generating bipotential killers, combining the CAR specificity with the intrinsic tumor-killing ability of CIK cells (CAR⁺.CIK). We set a patient-derived experimental platform. CAR⁺.CIK were generated by transduction of CIK precursors with a lentiviral vector encoding for anti-CD44v6-CAR. CAR⁺.CIK were characterized and assessed in vitro against multiple histotypes of patient-derived STS. The anti-sarcoma activity of CAR⁺.CIK was confirmed in a STS xenograft model. CD44v6 was expressed by 40% (11/27) of patient-derived STS. CAR⁺.CIK were efficiently expanded from patients (n = 12) and killed multiple histotypes of STS (including autologous targets, n = 4). The killing activity was significantly higher compared with unmodified CIK, especially at low effector/target (E/T) ratios: 98% vs 82% (E/T = 10:1) and 68% vs 26% (1:4), (p<0.0001). Specificity of tumor killing was confirmed by blocking with anti-CD44v6 antibody. CAR⁺.CIK produced higher amounts of IL6 and IFN-γ compared to control CIK. CAR⁺.CIK were highly active in mice bearing subcutaneous STS xenografts, with significant delay of tumor growth (p<0.0001) without toxicities.

We report first evidence of CAR⁺.CIK's activity against high grade STS and propose CD44v6 as an innovative target in this setting. CIK are a valuable platform for the translation of CAR-based strategies to challenging field of solid tumors. Our findings support the exploration of CAR⁺.CIK in clinical trials against high grade STS.

Chimeric antigen receptor T cell (CAR-T) immunotherapy for solid tumors: lessons learned and strategies for moving forward

Recently, the US Food and Drug Administration (FDA) approved the first chimeric antigen receptor T cell (CAR-T) therapy for the treatment CD19-positive B cell acute lymphoblastic leukemia. While CAR-T has achieved remarkable success in the treatment of hematopoietic malignancies, whether it can benefit solid tumor patients to the same extent is still uncertain. Even though hundreds of clinical trials are undergoing exploring a variety of tumor-associated antigens (TAA), no such antigen with comparable properties like CD19 has yet been identified regarding solid tumors CAR-T immunotherapy. Inefficient T cell trafficking, immunosuppressive tumor microenvironment, suboptimal antigen recognition specificity, and lack of safety control are currently considered as the main obstacles in solid tumor CAR-T therapy. Here, we reviewed the solid tumor CAR-T clinical trials, emphasizing the studies with published results. We further discussed the challenges that CAR-T is facing for solid tumor treatment and proposed potential strategies to improve the efficacy of CAR-T as promising immunotherapy.

Natural Killer Cells: Angels and Devils for Immunotherapy

In recent years, the relevance of the immune system to fight cancer has led to the development of immunotherapy, including the adoptive cell transfer of immune cells, such as natural killer (NK) cells and chimeric antigen receptors (CAR)-modified T cells. The discovery of donor NK cells’ anti-tumor activity in acute myeloid leukemia patients receiving allogeneic stem cell transplantation (allo-SCT) was the trigger to conduct many clinical trials infusing NK cells. Surprisingly, many of these studies did not obtain optimal results, suggesting that many different NK cell parameters combined with the best clinical protocol need to be optimized. Various parameters including the high array of activating receptors that NK cells have, the source of NK cells selected to treat patients, different cytotoxic mechanisms that NK cells activate depending on the target cell and tumor cell survival mechanisms need to be considered before choosing the best immunotherapeutic strategy using NK cells. In this review, we will discuss these parameters to help improve current strategies using NK cells in cancer therapy. Moreover, the chimeric antigen receptor (CAR) modification, which has revolutionized the concept of immunotherapy, will be discussed in the context of NK cells. Lastly, the dark side of NK cells and their involvement in inflammation will also be discussed.

Engineering CAR-T cells

Chimeric antigen receptor redirected T cells (CAR-T cells) have achieved inspiring outcomes in patients with B cell malignancies, and are now being investigated in other hematologic malignancies and solid tumors. CAR-T cells are generated by the T cells from patients’ or donors’ blood. After the T cells are expanded and genetically modified, they are reinfused into the patients. However, many challenges still need to be resolved in order for this technology to gain widespread adoption. In this review, we first discuss the structure and evolution of chimeric antigen receptors. We then report on the tools used for production of CAR-T cells. Finally, we address the challenges posed by CAR-T cells.

Pre-clinical development of gene modification of haematopoietic stem cells with chimeric antigen receptors for cancer immunotherapy

Patients with refractory or recurrent B-lineage hematologic malignancies have less than 50% of chance of cure despite intensive therapy and innovative approaches are needed. We hypothesize that gene modification of haematopoietic stem cells (HSC) with an anti-CD19 chimeric antigen receptor (CAR) will produce a multi-lineage, persistent immunotherapy against B-lineage malignancies that can be controlled by the HSVsr39TK suicide gene. High-titer third-generation self-inactivating lentiviral constructs were developed to deliver a second-generation CD19-specific CAR and the herpes simplex virus thymidine kinase HSVsr39TK to provide a suicide gene to allow ablation of gene-modified cells if necessary. Human HSC were transduced with such lentiviral vectors and evaluated for function of both CAR and HSVsr39TK. Satisfactory transduction efficiency was achieved; the addition of the suicide gene did not impair CAR expression or antigen-specific cytotoxicity, and determined marked cytotoxicity to ganciclovir. NSG mice transplanted with gene-modified human HSC showed CAR expression not significantly different between transduced cells with or without HSVsr39TK, and expression of anti-CD19 CAR conferred anti-tumor survival advantage. Treatment with ganciclovir led to significant ablation of gene-modified cells in mouse tissues. Haematopoietic stem cell transplantation is frequently part of the standard of care for patients with relapsed and refractory B cell malignancies; following HSC collection, a portion of the cells could be modified to express the CD19-specific CAR and give rise to a persistent, multi-cell lineage, HLA-independent immunotherapy, enhancing the graft-versus-malignancy activity.

Targeting O-Acetyl-GD2 Ganglioside for Cancer Immunotherapy

Target selection is a key feature in cancer immunotherapy, a promising field in cancer research. In this respect, gangliosides, a broad family of structurally related glycolipids, were suggested as potential targets for cancer immunotherapy based on their higher abundance in tumors when compared with the matched normal tissues. GD2 is the first ganglioside proven to be an effective target antigen for cancer immunotherapy with the regulatory approval of dinutuximab, a chimeric anti-GD2 therapeutic antibody. Although the therapeutic efficacy of anti-GD2 monoclonal antibodies is well documented, neuropathic pain may limit its application. O-Acetyl-GD2, the O-acetylated-derivative of GD2, has recently received attention as novel antigen to target GD2-positive cancers. The present paper examines the role of O-acetyl-GD2 in tumor biology as well as the available preclinical data of anti-O-acetyl-GD2 monoclonal antibodies. A discussion on the relevance of O-acetyl-GD2 in chimeric antigen receptor T cell therapy development is also included.

Redirecting T Cells to Glypican-3 with 4-1BB Zeta Chimeric Antigen Receptors Results in Th1 Polarization and Potent Antitumor Activity

T cells engineered to express CD19-specific chimeric antigen receptors (CARs) have shown breakthrough clinical successes in patients with B-cell lymphoid malignancies. However, similar therapeutic efficacy of CAR T cells in solid tumors is yet to be achieved. In this study we systematically evaluated a series of CAR constructs targeting glypican-3 (GPC3), which is selectively expressed on several solid tumors. We compared GPC3-specific CARs that encoded CD3ζ (Gz) alone or with costimulatory domains derived from CD28 (G28z), 4-1BB (GBBz), or CD28 and 4-1BB (G28BBz). All GPC3-CARs rendered T cells highly cytotoxic to GPC3-positive hepatocellular carcinoma, hepatoblastoma, and malignant rhabdoid tumor cell lines in vitro. GBBz induced the preferential production of Th1 cytokines (interferon γ/granulocyte macrophage colony-stimulating factor) while G28z preferentially induced Th2 cytokines (interleukin-4/interleukin-10). Inclusion of 4-1BB in G28BBz could only partially ameliorate the Th2-polarizing effect of CD28. 4-1BB induced superior expansion of CAR T cells in vitro and in vivo. T cells expressing GPC3-CARs incorporating CD28, 4-1BB, or both induced sustained tumor regressions in two xenogeneic tumor models. Thus, GBBz CAR endows T cells with superior proliferative potential, potent antitumor activity, and a Th1-biased cytokine profile, justifying further clinical development of GBBz CAR for immunotherapy of GPC3-positive solid tumors.

Chimeric Antigen Receptor T Cell Therapy Targeting CD19-Positive Leukemia and Lymphoma in the Context of Stem Cell Transplantation

Novel therapies with chimeric antigen receptor (CAR)-transduced T cells (TCs) sparked new hope for patients with relapsed or refractory CD19-positive leukemia or lymphoma even after stem cell therapies. This review focuses on CARs recognizing the B cell antigen CD19. Both retroviral and lentiviral vectors are used, encoding various anti-CD19 CAR constructs comprising costimulatory molecules such as CD28, CD137/4-1BB, and OX40 either alone (second-generation CARs) or in combination (third-generation CARs). Current, up-to-date published studies on anti-CD19 CAR therapy for acute lymphoblastic leukemia (ALL), chronic lymphocytic leukemia (CLL), and non-Hodgkin lymphoma (NHL) with observed side effects are discussed and an outlook on 58 ongoing trials is given. Clinical responses were achieved in up to 81% of ALL, 50% of CLL, and 40% of NHL patients. Factors with potential influence on the clinical outcome might be the design of the vector, the preconditioning regimen, and the number and quality of transfused CAR TCs. The applicability of clinical CAR TC therapy might include relapse after allogeneic stem cell transplantation (alloSCT), and ineligibility for or "bridging" until alloSCT. In summary, CAR therapy represents a highly promising treatment option even in heavily pretreated patients.

Taking up Cancer Immunotherapy Challenges: Bispecific Antibodies, the Path Forward?

As evidenced by the recent approvals of Removab (EU, Trion Pharma) in 2009 and of Blincyto (US, Amgen) in 2014, the high potential of bispecific antibodies in the field of immuno-oncology is eliciting a renewed interest from pharmaceutical companies. Supported by rapid advances in antibody engineering and the development of several technological platforms such as Triomab or bispecific T cell engagers (BiTEs), the “bispecifics” market has increased significantly over the past decade and may occupy a pivotal space in the future. Over 30 bispecific molecules are currently in different stages of clinical trials and more than 70 in preclinical phase. This review focuses on the clinical potential of bispecific antibodies as immune effector cell engagers in the onco-immunotherapy field. We summarize current strategies targeting various immune cells and their clinical interests. Furthermore, perspectives of bispecific antibodies in future clinical developments are addressed.

Immunotherapy for hepatocellular carcinoma: From basic research to clinical use

Hepatocellular carcinoma (HCC) is a common cancer worldwide with a poor prognosis. Few strategies have been proven efficient in HCC treatment, particularly for those patients not indicated for curative resection or transplantation. Immunotherapy has been developed for decades for cancer control and is attaining more attention as a result of encouraging outcomes of new strategies such as chimeric antigen receptor T cells and immune checkpoint blockade. Right at the front of the new era of immunotherapy, we review the immunotherapy in HCC treatment, from basic research to clinical trials, covering anything from immunomodulators, tumor vaccines and adoptive immunotherapy. The mechanisms, efficacy and safety as well as the approach particulars are unveiled to assist readers to gain a concise but extensive understanding of immunotherapy of HCC.

Immunotherapeutic approaches for cancer therapy: An updated review

In spite of specific immune effector mechanisms raised against tumor cells, there are mechanisms employed by the tumor cells to keep them away from immune recognition and elimination; some of these mechanisms have been identified, while others are still poorly understood. Manipulation or augmentation of specific antitumor immune responses are now the preferred approaches for treatment of malignancies, and traditional therapeutic approaches are being replaced by the use of agents which potentiate immune effector mechanisms, broadly called "immunotherapy". Cancer immunotherapy is generally classified into two main classes including active and passive methods. Interventions to augment the immune system of the patient, for example, vaccination or adjuvant therapy, actively promote antitumor effector mechanisms to improve cancer elimination. On the other hand, administration of specific monoclonal antibodies (mAbs) against different tumor antigens and adoptive transfer of genetically-modified specific T cells are currently the most rapidly developing approaches for cancer targeted therapy. In this review, we will discuss the different modalities for active and passive immunotherapy for cancer.

Matrix-specific anchors: a new concept for targeted delivery and retention of therapeutic cells

Biomedical strategies for tissue engineering and repair utilize specific cells, scaffolds, and growth factors to reconstruct elements of damaged tissue. The cellular element of these strategies is limited, however, by poor efficiency of delivery and retention of therapeutic cells in target sites. We propose that the presence of a cellular anchor that is able to specifically bind a defined element of target tissue will facilitate efficient binding and retention of therapeutic cells, thereby promoting repair of the target site. To do so, we engineered an artificial collagen-specific anchor (ACSA) that is able to specifically bind collagen I. The ACSA was engineered by creating a construct comprising rationally designed consecutive domains. The binding specificity of the ACSA was achieved by employing variable regions of a monoclonal antibody that recognizes a unique epitope present in human collagen I. Meanwhile, cell membrane localization of the ACSA was provided by the presence of a transmembrane domain. We determined that the ACSA was localized within cell membranes and interacted with its intended target, that is, collagen I. We have demonstrated that, in comparison to the control, the cells expressing the ACSA attached better to collagen I and exhibited improved retention in sites of seeding. We have also demonstrated that the presence of the ACSA did not interfere with cell proliferation, the biosynthesis of endogenous collagen I, or the biological functions of native collagen receptors. Since the presented cell delivery system utilizes a common characteristic of major connective tissues, namely the presence of collagen I, the findings described here could have a broad positive impact for improving the repair processes of tendon, ligament, bone, intervertebral disc, skin, and other collagen I-rich connective tissues. If successful, the ACSA approach to deliver cells will serve as an outline for developing cell delivery methods that target other elements of extracellular matrices, including other collagen types, laminins, and fibronectins.

Adoptive immunotherapy against sarcomas

INTRODUCTION

Conventional treatments reached an unsatisfactory therapeutic plateau in the treatment of advanced unresectable bone and soft tissue sarcomas that remain an unsolved medical need. Several evidences support the concept that adoptive immunotherapy may effectively integrate within the complex and multidisciplinary treatment of sarcomas.

AREAS COVERED

In this work we reviewed adoptive immunotherapy strategies that have been explored in sarcoma settings, with specific focus on issues related to their clinic transferability. We schematically divided approaches based on T lymphocytes specific for MHC-restricted tumor-associated antigens or relying on MHC-independent immune effectors such as natural killer (NK), cytokine-induced killer (CIK) or γδ T cells.

EXPERT OPINION

Preclinical findings and initial clinical reports showed the potentialities and drawbacks of different adoptive immunotherapy strategies. The expansion of tumor infiltrating lymphocytes is difficult to be reproduced outside melanoma. Genetically redirected T cells appear to be a promising option and initial reports are encouraging against patients with sarcomas. Adoptive immunotherapy with MHC-unrestricted effectors such as NK, CIK or γδ T cells has recently shown great preclinical potential in sarcoma setting and biologic features that may favor clinical transferability. Combination of different immunotherapy approaches and integration with conventional treatments appear to be key issues for successful designing of next clinical trials.

Invariant NKT cells with chimeric antigen receptor provide a novel platform for safe and effective cancer immunotherapy

Advances in the design of chimeric antigen receptors (CARs) have improved the antitumor efficacy of redirected T cells. However, functional heterogeneity of CAR T cells limits their therapeutic potential and is associated with toxicity. We proposed that CAR expression in Vα24-invariant natural killer T (NKT) cells can build on the natural antitumor properties of these cells while their restriction by monomorphic CD1d limits toxicity. Primary human NKT cells were engineered to express a CAR against the GD2 ganglioside (CAR.GD2), which is highly expressed by neuroblastoma (NB). We compared CAR.GD2 constructs that encoded the CD3ζ chain alone, with CD28, 4-1BB, or CD28 and 4-1BB costimulatory endodomains. CAR.GD2 expression rendered NKT cells highly cytotoxic against NB cells without affecting their CD1d-dependent reactivity. We observed a striking T helper 1-like polarization of NKT cells by 4-1BB-containing CARs. Importantly, expression of both CD28 and 4-1BB endodomains in the CAR.GD2 enhanced in vivo persistence of NKT cells. These CAR.GD2 NKT cells effectively localized to the tumor site had potent antitumor activity, and repeat injections significantly improved the long-term survival of mice with metastatic NB. Unlike T cells, CAR.GD2 NKT cells did not induce graft-versus-host disease. These results establish the potential of NKT cells to serve as a safe and effective platform for CAR-directed cancer immunotherapy.

Recombination-deletion between homologous cassettes in retrovirus is suppressed via a strategy of degenerate codon substitution

Transduction and expression procedures in gene therapy protocols may optimally transfer more than a single gene to correct a defect and/or transmit new functions to recipient cells or organisms. This may be accomplished by transduction with two (or more) vectors, or, more efficiently, in a single vector. Occasionally, it may be useful to coexpress homologous genes or chimeric proteins with regions of shared homology. Retroviridae include the dominant vector systems for gene transfer (e.g., gamma-retro and lentiviruses) and are capable of such multigene expression. However, these same viruses are known for efficient recombination–deletion when domains are duplicated within the viral genome. This problem can be averted by resorting to two-vector strategies (two-chain two-vector), but at a penalty to cost, convenience, and efficiency. Employing a chimeric antigen receptor system as an example, we confirm that coexpression of two genes with homologous domains in a single gamma-retroviral vector (two-chain single-vector) leads to recombination–deletion between repeated sequences, excising the equivalent of one of the chimeric antigen receptors. Here, we show that a degenerate codon substitution strategy in the two-chain single-vector format efficiently suppressed intravector deletional loss with rescue of balanced gene coexpression by minimizing sequence homology between repeated domains and preserving the final protein sequence.

Construction and molecular characterization of a T-cell receptor-like antibody and CAR-T cells specific for minor histocompatibility antigen HA-1H

The genetic transfer of T-cell receptors (TCRs) directed toward target antigens into T lymphocytes has been used to generate antitumor T cells efficiently without the need for the in vitro induction and expansion of T cells with cognate specificity. Alternatively, T cells have been gene-modified with a TCR-like antibody or chimeric antigen receptor (CAR). We show that immunization of HLA-A2 transgenic mice with tetramerized recombinant HLA-A2 incorporating HA-1 H minor histocompatibility antigen (mHag) peptides and β2-microglobulin (HA-1 H/HLA-A2) generate highly specific antibodies. One single-chain variable region moiety (scFv) antibody, #131, demonstrated high affinity (KD=14.9 nM) for the HA-1 H/HLA-A2 complex. Primary human T cells transduced with #131 scFV coupled to CD28 transmembrane and CD3ζ domains were stained with HA-1 H/HLA-A2 tetramers slightly more intensely than a cytotoxic T lymphocyte (CTL) clone specific for endogenously HLA-A2- and HA-1 H-positive cells. Although #131 scFv CAR-T cells required >100-fold higher antigen density to exert cytotoxicity compared with the cognate CTL clone, they could produce inflammatory cytokines against cells expressing HLA-A2 and HA-1 H transgenes. These data implicate that T cells with high-affinity antigen receptors reduce the ability to lyse targets with low-density peptide/MHC complexes (~100 per cell), while they could respond at cytokine production level.

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

T cells engrafted with chimeric AgRs (CAR) are showing exciting potential for targeting B cell malignancies in early-phase clinical trials. To determine whether the second-generation CAR was essential for optimal antitumor activity, two CD28-based CAR constructs targeting CD19 were tested for their ability to redirect mouse T cell function against established B cell lymphoma in a BALB/c syngeneic model system. T cells armed with either CAR eliminated A20 B cell lymphoma in vivo; however, one construct induced a T cell dose-dependent acute toxicity associated with a raised serum Th1 type cytokine profile on transfer into preconditioned mice. Moreover, a chronic toxicity manifested as granuloma-like formation in spleen, liver, and lymph nodes was observed in animals receiving T cells bearing either CD28 CAR, albeit with different kinetics dependent upon the specific receptor used. This phenotype was associated with an expansion of CD4+ CAR+ T cells and CD11b+ Gr-1(+) myeloid cells and increased serum Th2-type cytokines, including IL-10 and IL-13. Mouse T cells engrafted with a first-generation CAR failed to develop such autotoxicity, whereas toxicity was not apparent when T cells bearing the same receptors were transferred into C57BL/6 or C3H animals. In summary, the adoptive transfer of second-generation CD19-specific CAR T cells can result in a cell dose-dependent acute toxicity, whereas the prolonged secretion of high levels of Th2 cytokines from these CAR T cells in vivo drives a granulomatous reaction resulting in chronic toxicity. Strategies that prevent a prolonged Th2-cytokine biased CAR T cell response are clearly warranted.

Engineered cell-based therapies: a vanguard of design-driven medicine

Engineered cell-based therapies are uniquely capable of performing sophisticated therapeutic functions in vivo, and this strategy is yielding promising clinical benefits for treating cancer. In this review, we discuss key opportunities and challenges for engineering customized cellular functions using cell-based therapy for cancer as a representative case study. We examine the historical development of chimeric antigen receptor (CAR) therapies as an illustration of the engineering design cycle. We also consider the potential roles that the complementary disciplines of systems biology and synthetic biology may play in realizing safe and effective treatments for a broad range of patients and diseases. In particular, we discuss how systems biology may facilitate both fundamental research and clinical translation, and we describe how the emerging field of synthetic biology is providing novel modalities for building customized cellular functions to overcome existing clinical barriers. Together, these approaches provide a powerful set of conceptual and experimental tools for transforming information into understanding, and for translating understanding into novel therapeutics to establish a new framework for design-driven medicine.

EGFRvIII mCAR-modified T-cell therapy cures mice with established intracerebral glioma and generates host immunity against tumor-antigen loss

PURPOSE

Chimeric antigen receptor (CAR) transduced T cells represent a promising immune therapy that has been shown to successfully treat cancers in mice and humans. However, CARs targeting antigens expressed in both tumors and normal tissues have led to significant toxicity. Preclinical studies have been limited by the use of xenograft models that do not adequately recapitulate the immune system of a clinically relevant host. A constitutively activated mutant of the naturally occurring epidermal growth factor receptor (EGFRvIII) is antigenically identical in both human and mouse glioma, but is also completely absent from any normal tissues.

EXPERIMENTAL DESIGN

We developed a third-generation, EGFRvIII-specific murine CAR (mCAR), and performed tests to determine its efficacy in a fully immunocompetent mouse model of malignant glioma.

RESULTS

At elevated doses, infusion with EGFRvIII mCAR T cells led to cures in all mice with brain tumors. In addition, antitumor efficacy was found to be dependent on lymphodepletive host conditioning. Selective blockade with EGFRvIII soluble peptide significantly abrogated the activity of EGFRvIII mCAR T cells in vitro and in vivo, and may offer a novel strategy to enhance the safety profile for CAR-based therapy. Finally, mCAR-treated, cured mice were resistant to rechallenge with EGFRvIII(NEG) tumors, suggesting generation of host immunity against additional tumor antigens.

CONCLUSION

All together, these data support that third-generation, EGFRvIII-specific mCARs are effective against gliomas in the brain and highlight the importance of syngeneic, immunocompetent models in the preclinical evaluation of tumor immunotherapies.

T lymphocytes redirected against the chondroitin sulfate proteoglycan-4 control the growth of multiple solid tumors both in vitro and in vivo

PURPOSE

Because of its high expression on various types of tumors and its restricted distribution in normal tissues, chondroitin sulfate proteoglycan-4 (CSPG4) represents an attractive target for the antibody-based therapy of several solid tumors. We tested whether T cells transduced with a CSPG4-specific chimeric antigen receptor (CAR) inhibited the growth of CSPG4-expressing tumor cells both in vitro and in vivo.

EXPERIMENTAL DESIGN

We first independently validated by immunohistochemistry (IHC) the expression of CSPG4 in an extensive panel of tumor arrays and normal tissues as well as queried public gene expression profiling datasets of human tumors. We constructed a second-generation CSPG4-specific CAR also encoding the CD28 costimulatory endodomain (CAR.CSPG4). We then evaluated human T lymphocytes expressing this CAR for their ex vivo and in vivo antitumor activity against a broad panel of solid tumors.

RESULTS

IHC showed that CSPG4 is highly expressed in melanoma, breast cancer, head and neck squamous cell carcinoma (HNSCC), and mesothelioma. In addition, in silico analysis of microarray expression data identified other important potential tumors expressing this target, including glioblastoma, clear cell renal carcinoma, and sarcomas. T lymphocytes genetically modified with a CSPG4-CAR controlled tumor growth in vitro and in vivo in NSG mice engrafted with human melanoma, HNSCC, and breast carcinoma cell lines.

CONCLUSIONS

CAR.CSPG4-redirected T cells should provide an effective treatment modality for a variety of solid tumors.

[At the crossroads of cancer]

Since the introduction of the concept of immunosurveillance in 1970 by Macfarlane Burnet and Lewis Thomas, cancer immunology has known a significant revolution and an explosion of discoveries. In this regard, manipulation of the immune system in cancer pathology has been a succession of enthusiasms and failures. Thanks to the fundamental achievements during the past three decades, non-specific passive immunotherapy of cancer has shifted to active specific immunotherapy. Thanks to the immunological arsenal (tumor peptides, dendritic cells), the clinical trials have increased but the results were not encouraging. It became clear that the escape of immunosurveillance by tumor cells is under the control of the complex tumor microenvironment and its heterogeneity, complexity and plasticity. The future of immunotherapy lies in an integrative approach to simultaneously boost the immune system and target the tumor microenvironment or combine immunotherapy with conventional treatments. In this review, we will focus on the development of cancer immunotherapy, its realities, failure and hope it raises as the fourth modality of cancer therapy.

Immune targeting of fibroblast activation protein triggers recognition of multipotent bone marrow stromal cells and cachexia

Transfer of FAP-reactive T cells into mice bearing a variety of subcutaneous tumors mediated limited antitumor effects and induced significant cachexia and lethal bone toxicities

Fibroblast activation protein (FAP) is a candidate universal target antigen because it has been reported to be selectively expressed in nearly all solid tumors by a subset of immunosuppressive tumor stromal fibroblasts. We verified that 18/18 human tumors of various histologies contained pronounced stromal elements staining strongly for FAP, and hypothesized that targeting tumor stroma with FAP-reactive T cells would inhibit tumor growth in cancer-bearing hosts. T cells genetically engineered with FAP-reactive chimeric antigen receptors (CARs) specifically degranulated and produced effector cytokines upon stimulation with FAP or FAP-expressing cell lines. However, adoptive transfer of FAP-reactive T cells into mice bearing a variety of subcutaneous tumors mediated limited antitumor effects and induced significant cachexia and lethal bone toxicities in two mouse strains. We found that FAP was robustly expressed on PDGFR-α⁺, Sca-1⁺ multipotent bone marrow stromal cells (BMSCs) in mice, as well as on well-characterized, clinical-grade multipotent human BMSCs. Accordingly, both mouse and human multipotent BMSCs were recognized by FAP-reactive T cells. The lethal bone toxicity and cachexia observed after cell-based immunotherapy targeting FAP cautions against its use as a universal target. Moreover, the expression of FAP by multipotent BMSCs may point toward the cellular origins of tumor stromal fibroblasts.

Cytotoxic T lymphocytes for the treatment of viral infections and posttransplant lymphoproliferative disorders in transplant recipients

PURPOSE OF REVIEW

The continuous and successful expansion of organ transplants is unfortunately associated with increased incidence of severe opportunistic viral infections and Epstein-Barr virus (EBV)-related lymphomas secondary to immunosuppression. Here, we review the strengths and limitations of T-cell-based strategies used to treat viral infections in immunocompromised individuals.

RECENT FINDINGS

While current antiviral drugs are often suboptimal because of associated toxicities, a promising approach in the management of infections with viruses like cytomegalovirus (CMV), adenovirus (AdV) and EBV is the adoptive transfer of T cells targeting these viruses that can be directly isolated from the peripheral blood of the donor or expanded ex vivo prior to infusions in patients.

SUMMARY

T-cell-based immunotherapies are now being included in the clinical practice of transplant recipients to prevent and treat infections and complications associated with CMV, AdV and EBV. Improvement of current limitations will enable the extension of these approaches to all patients at risk and to other clinically relevant viruses and pathogens that are emerging as significant complications for immunocompromised patients.

Targeted immunotherapy of cancer with CAR T cells: achievements and challenges

The adoptive transfer of chimeric antigen receptor (CAR)-expressing T cells is a relatively new but promising approach in the field of cancer immunotherapy. This therapeutic strategy is based on the genetic reprogramming of T cells with an artificial immune receptor that redirects them against targets on malignant cells and enables their destruction by exerting T cell effector functions. There has been an explosion of interest in the use of CAR T cells as an immunotherapy for cancer. In the pre-clinical setting, there has been a considerable focus upon optimizing the structural and signaling potency of the CAR while advances in bio-processing technology now mean that the clinical testing of these gene-modified T cells has become a reality. This review will summarize the concept of CAR-based immunotherapy and recent clinical trial activity and will further discuss some of the likely future challenges facing CAR-modified T cell therapies.

Dual targeting of ErbB2 and MUC1 in breast cancer using chimeric antigen receptors engineered to provide complementary signaling

PURPOSE

Chimeric antigen receptor (CAR) engineered T-cells occupy an increasing niche in cancer immunotherapy. In this context, CAR-mediated CD3ζ signaling is sufficient to elicit cytotoxicity and interferon-γ production while the additional provision of CD28-mediated signal 2 promotes T-cell proliferation and interleukin (IL)-2 production. This compartmentalisation of signaling opens the possibility that complementary CARs could be used to focus T-cell activation within the tumor microenvironment.

METHODS

Here, we have tested this principle by co-expressing an ErbB2- and MUC1-specific CAR that signal using CD3ζ and CD28 respectively. Stoichiometric co-expression of transgenes was achieved using the SFG retroviral vector containing an intervening Thosea asigna peptide.

RESULTS

We found that "dual-targeted" T-cells kill ErbB2(+) tumor cells efficiently and proliferate in a manner that requires co-expression of MUC1 and ErbB2 by target cells. Notably, however, IL-2 production was modest when compared to control CAR-engineered T-cells in which signaling is delivered by a fused CD28 + CD3ζ endodomain.

CONCLUSIONS

These findings demonstrate the principle that dual targeting may be achieved using genetically targeted T-cells and pave the way for testing of this strategy in vivo.

Protein L: a novel reagent for the detection of chimeric antigen receptor (CAR) expression by flow cytometry

Background

There has been significant progress in the last two decades on the design of chimeric antigen receptors (CAR) for adoptive immunotherapy targeting tumor-associated antigens. Structurally CARs consist of a single chain antibody fragment directed against a tumor-associated antigen fused to an extracellular spacer and transmembrane domain followed by T cell cytoplasmic signaling moieties. Currently several clinical trials are underway using gene modified peripheral blood lymphocytes (PBL) with CARs directed against a variety of tumor associated antigens. Despite the improvements in the design of CARs and expansion of the number of target antigens, there is no universal flow cytometric method available to detect the expression of CARs on the surface of transduced lymphocytes.

Methods

Currently anti-fragment antigen binding (Fab) conjugates are most widely used to determine the expression of CARs on gene-modified lymphocytes by flow cytometry. The limitations of these reagents are that many of them are not commercially available, generally they are polyclonal antibodies and often the results are inconsistent. In an effort to develop a simple universal flow cytometric method to detect the expression of CARs, we employed protein L to determine the expression of CARs on transduced lymphocytes. Protein L is an immunoglobulin (Ig)-binding protein that binds to the variable light chains (kappa chain) of Ig without interfering with antigen binding site. Protein L binds to most classes of Ig and also binds to single-chain antibody fragments (scFv) and Fab fragments.

Results

We used CARs derived from both human and murine antibodies to validate this novel protein L based flow cytometric method and the results correlated well with other established methods. Activated human PBLs were transduced with retroviral vectors expressing two human antibody based CARs (anti-EGFRvIII, and anti-VEGFR2), two murine antibody derived CARs (anti-CSPG4, and anti-CD19), and two humanized mouse antibody based CARs (anti-ERBB2, and anti-PSCA). Transduced cells were stained first with biotin labeled protein L followed by phycoerythrin (PE)-conjugated streptavidin (SA) and analyzed by flow cytometry. For comparison, cells were stained in parallel with biotin conjugated goat-anti-mouse Fab or CAR specific fusion proteins. Using protein L, all CAR transduced lymphocytes exhibited specific staining pattern ranging from 40 to 80% of positive cells (compared to untransduced cells) and staining was comparable to the pattern observed with anti-Fab antibodies.

Conclusion

Our data demonstrate the feasibility of employing Protein L as a general reagent for the detection of CAR expression on transduced lymphocytes by flow cytometry.

Combining mTor inhibitors with rapamycin-resistant T cells: a two-pronged approach to tumor elimination

Despite activity as single agent cancer therapies, Rapamycin (rapa) and its rapalogs may have their greatest effects when combined with other therapeutic modalities. In addition to direct antitumor activity, rapalogs reverse multiple tumor-intrinsic immune evasion mechanisms. These should facilitate tumor-specific T cell activity, but since rapa directly inhibits effector T cells, this potential immune enhancement is lost. We hypothesized that if T cells were rendered resistant to rapa they could capitalize on its downregulation of tumor immune evasion. We therefore modified T cells with a rapa-resistant mutant of mTor, mTorRR, and directed them to B lymphomas by coexpressing a chimeric antigen receptor (CAR) for CD19 (CAR.CD19-28ζ). T cells expressing transgenic mTorRR from a piggyBac transposon maintain mTor signaling, proliferate in the presence of rapa and retain their cytotoxic function and ability to secrete interferon-γ (IFNγ) after stimulation, effector functions that were inhibited by rapa in control T cells. In combination, rapa and rapa-resistant-CAR.CD19-28ζ-expressing T cells produced greater antitumor activity against Burkitt's lymphoma and pre-B ALL cell lines in vitro than CAR.CD19-28ζ T cells or rapa alone. In conclusion, the combination of rapa and rapa-resistant, CAR.CD19-28ζ-expressing T cells may provide a novel therapy for the treatment of B cell malignancies and other cancers.