CD19 CAR T Cells Expressing IL-12 Eradicate Lymphoma in Fully Lymphoreplete Mice through Induction of Host Immunity

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

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

Oncolytic virus-mediated expansion of dual-specific CAR T cells improves efficacy against solid tumors in mice

Oncolytic viruses (OVs) encoding a variety of transgenes have been evaluated as therapeutic tools to increase the efficacy of chimeric antigen receptor (CAR)-modified T cells in the solid tumor microenvironment (TME). Here, using systemically delivered OVs and CAR T cells in immunocompetent mouse models, we have defined a mechanism by which OVs can potentiate CAR T cell efficacy against solid tumor models of melanoma and glioma. We show that stimulation of the native T cell receptor (TCR) with viral or virally encoded epitopes gives rise to enhanced proliferation, CAR-directed antitumor function, and distinct memory phenotypes. In vivo expansion of dual-specific (DS) CAR T cells was leveraged by in vitro preloading with oncolytic vesicular stomatitis virus (VSV) or reovirus, allowing for a further in vivo expansion and reactivation of T cells by homologous boosting. This treatment led to prolonged survival of mice with subcutaneous melanoma and intracranial glioma tumors. Human CD19 CAR T cells could also be expanded in vitro with TCR reactivity against viral or virally encoded antigens and was associated with greater CAR-directed cytokine production. Our data highlight the utility of combining OV and CAR T cell therapy and show that stimulation of the native TCR can be exploited to enhance CAR T cell activity and efficacy in mice.

Next-Generation CAR T-cell Therapies

SUMMARY

CD19- and B-cell maturation antigen (BCMA)-directed chimeric antigen receptor (CAR) T cells have enabled unprecedented responses in a subset of refractory patients with B-cell and plasma cell malignancies, leading to their approval by the FDA for the treatment of leukemia, lymphoma, and myeloma. These "living drugs" can become part of a synthetic immune system, persisting at least a decade in some patients. However, despite this tremendous impact, significant unmet treatment needs remain for patients with hematologic malignancies and solid cancers. In this perspective, we highlight recent innovations that advance the field toward production of a more potent and universal cellular immunotherapy of the future. Next-generation CAR T cells will incorporate advances in gene engineering and synthetic biology to enhance functionality and persistence, and reduce treatment-associated toxicities. The combination of autologous CAR T cells with various allogeneic cell treatment strategies designed to target the immunosuppressive tumor microenvironment will broaden the impact of future CAR T-cell therapies.

Engineering strategies to enhance oncolytic viruses in cancer immunotherapy

Oncolytic viruses (OVs) are emerging as potentially useful platforms in treatment methods for patients with tumors. They preferentially target and kill tumor cells, leaving healthy cells unharmed. In addition to direct oncolysis, the essential and attractive aspect of oncolytic virotherapy is based on the intrinsic induction of both innate and adaptive immune responses. To further augment this efficacious response, OVs have been genetically engineered to express immune regulators that enhance or restore antitumor immunity. Recently, combinations of OVs with other immunotherapies, such as immune checkpoint inhibitors (ICIs), chimeric antigen receptors (CARs), antigen-specific T-cell receptors (TCRs) and autologous tumor-infiltrating lymphocytes (TILs), have led to promising progress in cancer treatment. This review summarizes the intrinsic mechanisms of OVs, describes the optimization strategies for using armed OVs to enhance the effects of antitumor immunity and highlights rational combinations of OVs with other immunotherapies in recent preclinical and clinical studies.

The next wave of cellular immunotherapies in pancreatic cancer

Pancreatic cancer is an aggressive disease that is predicted to become the second leading cause of cancer-related death worldwide by 2030. The overall 5-year survival rate is around 10%. Pancreatic cancer typically presents late with locally advanced or metastatic disease, and there are limited effective treatments available. Cellular immunotherapy, such as chimeric antigen receptor (CAR) T cell therapy, has had significant success in treating hematological malignancies. However, CAR T cell therapy efficacy in pancreatic cancer has been limited. This review provides an overview of current and ongoing CAR T cell clinical studies of pancreatic cancer and the major challenges and strategies to improve CAR T cell efficacy. These strategies include arming CAR T cells; developing off-the-shelf allogeneic CAR T cells; using other immune CAR cells, like natural killer cells and tumor-infiltrating lymphocytes; and combination therapy. Careful incorporation of preclinical models will enhance management of affected individuals, assisting incorporation of cellular immunotherapies. A multifaceted, personalized approach involving cellular immunotherapy treatment is required to improve pancreatic cancer outcomes.

Engineering interferons and interleukins for cancer immunotherapy

Cytokines are a class of potent immunoregulatory proteins that are secreted in response to various stimuli and act locally to regulate many aspects of human physiology and disease. Cytokines play important roles in cancer initiation, progression, and elimination, and thus, there is a long clinical history associated with the use of recombinant cytokines to treat cancer. However, the use of cytokines as therapeutics has been limited by cytokine pleiotropy, complex biology, poor drug-like properties, and severe dose-limiting toxicities. Nevertheless, cytokines are crucial mediators of innate and adaptive antitumor immunity and have the potential to enhance immunotherapeutic approaches to treat cancer. Development of immune checkpoint inhibitors and combination immunotherapies has reinvigorated interest in cytokines as therapeutics, and a variety of engineering approaches are emerging to improve the safety and effectiveness of cytokine immunotherapy. In this review we highlight recent advances in cytokine biology and engineering for cancer immunotherapy.

Chimeric antigen receptor T cell therapy: challenges and opportunities in lung cancer

Chimeric antigen receptor (CAR) T-cell therapy has revolutionized the paradigm in hematological malignancies treatment, driving an ever-expanding number of basic research and clinical trials of genetically engineering T cells to treat solid tumors. CAR T-cell therapies based on the antibodies targeting Mesothelin, CEA, EGFR, EGFR, MUC1, DLL3, and emerging novel targets provide promising efficacy for lung cancer patients. However, clinical application of CAR T-cell therapy against lung cancer remains limited on account of physical and immune barriers, antigen escape and heterogeneity, on-target off-tumor toxicity, and many other reasons. Understanding the evolution of CAR structure and the generalizable requirements for manufacturing CAR T cells as well as the interplay between lung tumor immunology and CAR T cells will improve clinical translation of this therapeutic modality in lung cancer. In this review, we systematically summarize the latest advances in CAR T-cell therapy in lung cancer, focusing on the CAR structure, target antigens, challenges, and corresponding new strategies.

IL12 integrated into the CAR exodomain converts CD8+ T cells to poly-functional NK-like cells with superior killing of antigen-loss tumors

Chimeric antigen receptor (CAR)-redirected T cell therapy often fails to control tumors in the long term due to selecting cancer cells that downregulated or lost CAR targeted antigen. To reprogram the functional capacities specifically of engineered CAR T cells, we inserted IL12 into the extracellular moiety of a CD28-ζ CAR; both the CAR endodomain and IL12 were functionally active, as indicated by antigen-redirected effector functions and STAT4 phosphorylation, respectively. The IL12-CAR reprogrammed CD8⁺ T cells toward a so far not recognized natural killer (NK) cell-like signature and a CD94⁺CD56⁺CD62L^high phenotype closely similar, but not identical, to NK and cytokine induced killer (CIK) cells. In contrast to conventional CAR T cells, IL12-CAR T cells acquired antigen-independent, human leukocyte antigen E (HLA-E) restricted cytotoxic capacities eliminating antigen-negative cancer cells in addition to eliminating cancer cells with CAR cognate antigen. Simultaneous signaling through both the CAR endodomain and IL12 were required for inducing maximal NK-like cytotoxicity; adding IL12 to conventional CAR T cells was not sufficient. Antigen-negative tumors were attacked by IL12-CAR T cells, but not by conventional CAR T cells. Overall, we present a prototype of a new family of CARs that augments tumor recognition and elimination through expanded functional capacities by an appropriate cytokine integrated into the CAR exodomain.

Chimeric Antigen Receptor T-Cell Therapy in Metastatic Castrate-Resistant Prostate Cancer

Simple Summary

Prostate cancer is one of the most frequently diagnosed cancers amongst men worldwide. Treatment for metastatic disease is often in the form of androgen deprivation therapy. However, over the course of treatment affected men may become castrate-resistant. Options for men with metastatic castrate-resistant cancer are limited. This review focuses on the role of chimeric antigen receptor T-cell therapy (CAR-T) in men with metastatic castrate-resistant prostate cancer. This review is a contemporary appraisal of preclinical and clinical studies conducted in this emerging form of immunotherapy. A thorough evaluation of the role of CAR-T therapy in prostate cancer is provided, as well as the obstacles we must overcome to clinically translate this therapy for men affected with this rapidly fatal disease.

Abstract

Prostate cancer is the most commonly diagnosed solid-organ cancer amongst males worldwide. Metastatic castrate-resistant prostate cancer (mCRPC) is a rapidly fatal end-sequelae of prostate cancer. Therapeutic options for men with mCRPC are limited and are not curative in nature. The recent development of chimeric antigen receptor T-cell (CAR-T) therapy has revolutionised the treatment of treatment-resistant haematological malignancies, and several studies are underway investigating the utility of this technology in the treatment of solid tumours. In this review, we evaluate the current treatment options for men with mCRPC as well as the current landscape of preclinical and clinical trials of CAR-T cell therapy against prostate cancer. We also appraise the various prostate cancer-specific tumour-associated antigens that may be targeted by CAR-T cell technology. Finally, we examine the potential translational barriers of CAR-T cell therapy in solid tumours. Despite preclinical success, preliminary clinical trials in men with prostate cancer have had limited efficacy. Therefore, further clinically translatable preclinical models are required to enhance the understanding of the role of this investigational therapeutic in men with mCRPC. In the era of precision medicine, tailored immunotherapy administered to men in a tumour-agnostic approach provides hope to a group of men who otherwise have few treatment options available.

IL-12 nanochaperone-engineered CAR T cell for robust tumor-immunotherapy

Although chimeric antigen receptor T (CAR T) cell immunotherapy has demonstrated remarkable success in clinical, therapeutic effects are still limited in solid tumor due to lack of activated T cell infiltration in immunosuppression of tumor microenvironment. Herein, we develop IL-12 nanostimulant-engineered CAR T cell (INS-CAR T) biohybrids for boosting antitumor immunity of CAR T cells via immunofeedback. As stimulating nanochaperone, IL-12-loaded human serum albumin (HSA) nanoparticles are effectively conjugated onto CAR T cells via bioorthogonal chemistry without influencing their antitumor capabilities. IL-12 is responsively released from INS-CAR T biohybrids in presence of the increased thiol groups on cell-surface triggered by tumor antigens. In return, released IL-12 obviously promotes the secretion of CCL5, CCL2 and CXCL10, which further selectively recruits and expands CD8⁺ CAR T cells in tumors. Ultimately, the immune-enhancing effects of IL-12 nanochaperone significantly boost CAR T cell antitumor capabilities, dramatically eliminated solid tumor and minimized unwanted side effects. Hence, immunofeedback INS-CAR T biohybrids, which include INS that serves as an intelligent 'nanochaperone', could provide a powerful tool for efficient and safe antitumor immunotherapy.

Allogeneic CAR Invariant Natural Killer T Cells Exert Potent Antitumor Effects through Host CD8 T-Cell Cross-Priming

PURPOSE

The development of allogeneic chimeric antigen receptor (CAR) T-cell therapies for off-the-shelf use is a major goal that faces two main immunologic challenges, namely the risk of graft-versus-host disease (GvHD) induction by the transferred cells and the rejection by the host immune system limiting their persistence. In this work we assessed the direct and indirect antitumor effect of allogeneic CAR-engineered invariant natural killer T (iNKT) cells, a cell population without GvHD-induction potential that displays immunomodulatory properties.

EXPERIMENTAL DESIGN

After assessing murine CAR iNKT cells direct antitumor effects in vitro and in vivo, we employed an immunocompetent mouse model of B-cell lymphoma to assess the interaction between allogeneic CAR iNKT cells and endogenous immune cells.

RESULTS

We demonstrate that allogeneic CAR iNKT cells exerted potent direct and indirect antitumor activity when administered across major MHC barriers by inducing tumor-specific antitumor immunity through host CD8 T-cell cross-priming.

CONCLUSIONS

In addition to their known direct cytotoxic effect, allogeneic CAR iNKT cells induce host CD8 T-cell antitumor responses, resulting in a potent antitumor effect lasting longer than the physical persistence of the allogeneic cells. The utilization of off-the-shelf allogeneic CAR iNKT cells could meet significant unmet needs in the clinic.

Genetic Modification of Cytokine Signaling to Enhance Efficacy of CAR T Cell Therapy in Solid Tumors

Chimeric antigen receptor (CAR) T cell therapy has shown unprecedented success in treating advanced hematological malignancies. Its effectiveness in solid tumors has been limited due to heterogeneous antigen expression, a suppressive tumor microenvironment, suboptimal trafficking to the tumor site and poor CAR T cell persistence. Several approaches have been developed to overcome these obstacles through various strategies including the genetic engineering of CAR T cells to blunt the signaling of immune inhibitory receptors as well as to modulate signaling of cytokine/chemokine molecules and their receptors. In this review we offer our perspective on how genetically modifying cytokine/chemokine molecules and their receptors can improve CAR T cell qualities such as functionality, persistence (e.g. resistance to pro-apoptotic signals) and infiltration into tumor sites. Understanding how such modifications can overcome barriers to CAR T cell effectiveness will undoubtedly enhance the potential of CAR T cells against solid tumors.

Advances in CAR design

Chimeric antigen receptor (CAR) T cells have revolutionized the management of B cell malignancies. These synthetic molecules are composed of peptide fragments from several distinct immune cell proteins and link highly-specific antigen recognition with potent T cell activation. Despite impressive results in many, less than half of patients treated will achieve durable remission after CAR therapy. Recent studies have identified the central role that each structural component of the CAR molecule plays in regulating T cell function. Significant effort has been dedicated to exploring strategies to improve the design of CARs themselves or integrate their activity with other regulatory circuits to enable more precise function. In this review, we will summarize recent pre-clinical and clinical studies that have evaluated novel CAR design formats.

Improving CAR T-Cell Persistence

Over the last decade remarkable progress has been made in enhancing the efficacy of CAR T therapies. However, the clinical benefits are still limited, especially in solid tumors. Even in hematological settings, patients that respond to CAR T therapies remain at risk of relapsing due to several factors including poor T-cell expansion and lack of long-term persistence after adoptive transfer. This issue is even more evident in solid tumors, as the tumor microenvironment negatively influences the survival, infiltration, and activity of T-cells. Limited persistence remains a significant hindrance to the development of effective CAR T therapies due to several determinants, which are encountered from the cell manufacturing step and onwards. CAR design and ex vivo manipulation, including culture conditions, may play a pivotal role. Moreover, previous chemotherapy and lymphodepleting treatments may play a relevant role. In this review, the main causes for decreased persistence of CAR T-cells in patients will be discussed, focusing on the molecular mechanisms underlying T-cell exhaustion. The approaches taken so far to overcome these limitations and to create exhaustion-resistant T-cells will be described. We will also examine the knowledge gained from several key clinical trials and highlight the molecular mechanisms determining T-cell stemness, as promoting stemness may represent an attractive approach to improve T-cell therapies.

The promise and perils of immunotherapy

Advances in understanding the ways in which the immune system fails to control tumor growth or prevent autoimmunity have led to the development of powerful therapeutic strategies to treat these diseases. In contrast to conventional therapies that have a broadly suppressive effect, immunotherapies are more akin to targeted therapies because they are mechanistically driven and are typically developed with the goal of "drugging" a specific underlying pathway or phenotype. This means that their effects and toxicities are, at least in theory, more straightforward to anticipate. The development of functionalized antibodies, genetically engineered T cells, and immune checkpoint inhibitors continues to accelerate, illuminating new biology and bringing new treatment to patients. In the following sections, we provide an overview of immunotherapeutic concepts, highlight recent advances in the field of immunotherapies, and discuss controversies and future directions, particularly as these pertain to hematologic oncology or blood-related diseases. We conclude by illustrating how original research published in this journal fits into and contributes to the overall framework of advances in immunotherapy.

Insight into next-generation CAR therapeutics: designing CAR T cells to improve clinical outcomes

Chimeric antigen receptor (CAR) T cell therapy has shown considerable promise for hematologic malignancies, leading to the US Food and Drug Administration approval of two CAR T cell-based therapies for the treatment of B cell acute lymphoblastic leukemia and large B cell lymphoma. Despite success in hematologic malignancies, the treatment landscape of CAR T cell therapy for solid tumors has been limited. There are unique challenges in the development of novel CAR T cell therapies to improve both safety and efficacy. Improved understanding of the immunosuppressive tumor microenvironment and resistance mechanisms has led to encouraging approaches to mitigating these obstacles. This Review will characterize challenges with current CAR T designs for hematologic malignancies and solid tumors and emphasize preclinical and clinical strategies to overcome them with novel CAR T cell therapies.

Engineered Cytokines for Cancer and Autoimmune Disease Immunotherapy

Cytokine signaling is critical to a range of biological processes including cell development, tissue repair, aging, and immunity. In addition to acting as key signal mediators of the immune system, cytokines can also serve as potent immunotherapies with more than 20 recombinant products currently Food and Drug Administration (FDA)-approved to treat conditions including hepatitis, multiple sclerosis, arthritis, and various cancers. Yet despite their biological importance and clinical utility, cytokine immunotherapies suffer from intrinsic challenges that limit their therapeutic potential including poor circulation, systemic toxicity, and low tissue- or cell-specificity. In the past decade in particular, methods have been devised to engineer cytokines in order to overcome such challenges and here, the myriad strategies are reviewed that may be employed in order to improve the therapeutic potential of cytokine and chemokine immunotherapies with applications in cancer and autoimmune disease therapy, as well as tissue engineering and regenerative medicine. For clarity, these strategies are collected and presented as they vary across size scales, ranging from single amino acid substitutions, to larger protein-polymer conjugates, nano/micrometer-scale particles, and macroscale implants. Together, this work aims to provide readers with a timely view of the field of cytokine engineering with an emphasis on early-stage therapeutic approaches.

Gene-Edited Interleukin CAR-T Cells Therapy in the Treatment of Malignancies: Present and Future

In recent years, chimeric antigen receptor T cells (CAR-T cells) have been faced with the problems of weak proliferation and poor persistence in the treatment of some malignancies. Researchers have been trying to perfect the function of CAR-T by genetically modifying its structure. In addition to the participation of T cell receptor (TCR) and costimulatory signals, immune cytokines also exert a decisive role in the activation and proliferation of T cells. Therefore, genetic engineering strategies were used to generate cytokines to enhance tumor killing function of CAR-T cells. When CAR-T cells are in contact with target tumor tissue, the proliferation ability and persistence of T cells can be improved by structurally or inductively releasing immunoregulatory molecules to the tumor region. There are a large number of CAR-T cells studies on gene-edited cytokines, and the most common cytokines involved are interleukins (IL-7, IL-12, IL-15, IL-18, IL-21, IL-23). Methods for the construction of gene-edited interleukin CAR-T cells include co-expression of single interleukin, two interleukin, interleukin combined with other cytokines, interleukin receptors, interleukin subunits, and fusion inverted cytokine receptors (ICR). Preclinical and clinical trials have yielded positive results, and many more are under way. By reading a large number of literatures, we summarized the functional characteristics of some members of the interleukin family related to tumor immunotherapy, and described the research status of gene-edited interleukin CAR-T cells in the treatment of malignant tumors. The objective is to explore the optimized strategy of gene edited interleukin-CAR-T cell function.

Making Potent CAR T Cells Using Genetic Engineering and Synergistic Agents

Immunotherapies are emerging as powerful weapons for the treatment of malignancies. Chimeric antigen receptor (CAR)-engineered T cells have shown dramatic clinical results in patients with hematological malignancies. However, it is still challenging for CAR T cell therapy to be successful in several types of blood cancer and most solid tumors. Many attempts have been made to enhance the efficacy of CAR T cell therapy by modifying the CAR construct using combination agents, such as compounds, antibodies, or radiation. At present, technology to improve CAR T cell therapy is rapidly developing. In this review, we particularly emphasize the most recent studies utilizing genetic engineering and synergistic agents to improve CAR T cell therapy.

A Deep Insight Into CAR-T Cell Therapy in Non-Hodgkin Lymphoma: Application, Opportunities, and Future Directions

Non-Hodgkin's lymphoma (NHL) is a cancer that starts in the lymphatic system. In NHL, the important part of the immune system, a type of white blood cells called lymphocytes become cancerous. NHL subtypes include marginal zone lymphoma, small lymphocytic lymphoma, follicular lymphoma (FL), and lymphoplasmacytic lymphoma. The disease can emerge in either aggressive or indolent form. 5-year survival duration after diagnosis is poor among patients with aggressive/relapsing form of NHL. Therefore, it is necessary to understand the molecular mechanisms of pathogenesis involved in NHL establishment and progression. In the next step, we can develop innovative therapies for NHL based on our knowledge in signaling pathways, surface antigens, and tumor milieu of NHL. In the recent few decades, several treatment solutions of NHL mainly based on targeted/directed therapies have been evaluated. These approaches include B-cell receptor (BCR) signaling inhibitors, immunomodulatory agents, monoclonal antibodies (mAbs), epigenetic modulators, Bcl-2 inhibitors, checkpoint inhibitors, and T-cell therapy. In recent years, methods based on T cell immunotherapy have been considered as a novel promising anti-cancer strategy in the treatment of various types of cancers, and particularly in blood cancers. These methods could significantly increase the capacity of the immune system to induce durable anti-cancer responses in patients with chemotherapy-resistant lymphoma. One of the promising therapy methods involved in the triumph of immunotherapy is the chimeric antigen receptor (CAR) T cells with dramatically improved killing activity against tumor cells. The CAR-T cell-based anti-cancer therapy targeting a pan-B-cell marker, CD19 is recently approved by the US Food and Drug Administration (FDA) for the treatment of chemotherapy-resistant B-cell NHL. In this review, we will discuss the structure, molecular mechanisms, results of clinical trials, and the toxicity of CAR-T cell-based therapies. Also, we will criticize the clinical aspects, the treatment considerations, and the challenges and possible drawbacks of the application of CAR-T cells in the treatment of NHL.

CAR T Cell Therapy in Pancreaticobiliary Cancers: a Focused Review of Clinical Data

OBJECTIVE

CAR T cell therapy is an innovative approach to treat cancers in the modern era. It utilizes the application of chimeric antigen receptors targeted against specific antigens expressed by the tumor cells. Although its efficacy is established in hematological malignancies, the safety and efficacy of this therapy in solid tumors, especially pancreaticobiliary cancers, is a highly investigated aspect. A focused review of clinical data was conducted to examine the outcomes of this therapy in pancreaticobiliary cancers.

METHODS

A comprehensive literature search was done on Medline and Embase databases through April 24, 2020 for studies that evaluated the outcomes of CAR T cell therapy in pancreaticobiliary cancers.

RESULTS

There were six phase 1 trials, while one was phase 1/2. Some of these trials were specifically done for pancreaticobiliary cancers, while others included patients of various solid organ cancers, including pancreatic and biliary tract cancers. The target antigens for therapy in these trials included mesothelin, CD133, prostate stem cell antigen, claudin 18.2, epidermal growth factor receptor, and human epidermal growth factor receptor 2. CAR T cell therapy has shown very few grade 3 and 4 side effects. Most of the adverse events are associated with cytokine release syndrome.

CONCLUSION

CAR T cell therapy has a manageable safety profile based on phase 1 studies, and efficacy assessments are currently ongoing in dose expansion and phase 2 studies.

How Can We Engineer CAR T Cells to Overcome Resistance?

Chimeric antigen receptor (CAR) T cell therapy has achieved unrivalled success in the treatment of B cell and plasma cell malignancies, with five CAR T cell products now approved by the US Food and Drug Administration (FDA). However, CAR T cell therapies for solid tumours have not been nearly as successful, owing to several additional challenges. Here, we discuss mechanisms of tumour resistance in CAR T cell therapy and the emerging strategies that are under development to engineer CAR T cells to overcome resistance.

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

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

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

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

Peripheral eosinophil counts predict efficacy of anti-CD19 CAR-T cell therapy against B-lineage non-Hodgkin lymphoma

Rationale: The onset of cytokine release syndrome (CRS) and in vivo persistence of anti-CD19 chimeric antigen receptor T (CAR-T) cells after infusion correlate with clinical responsiveness. However, there are no known baseline biomarkers that can predict the prognosis of patients with B-lineage non-Hodgkin lymphoma (B-NHL). The aim of this study was to identify blood cell populations associated with beneficial outcomes in B-NHL patients administered CAR-T cell immunotherapies.

Methods: We enumerated peripheral blood and CAR-T cells by retrospectively analyzing three CAR-T cell trials involving 65 B-NHL patients. We used a preclinical model to elucidate the eosinophil mechanism in CAR-T cell therapy.

Results: During an observation period up to 30 mo, B-NHL patients with higher baseline eosinophil counts had higher objective response rates than those with low eosinophil counts. Higher baseline eosinophil counts were also significantly associated with durable progression-free survival (PFS). The predictive significance of baseline eosinophil counts was validated in two independent cohorts. A preclinical model showed that eosinophil depletion impairs the intratumoral infiltration of transferred CAR-T cells and reduces CAR-T cell antitumor efficacy.

Conclusion: The results of this study suggest that peripheral eosinophils could serve as stratification biomarkers and a recruitment machinery to facilitate anti-CD19 CAR-T cell therapy in B-NHL patients.

Allogeneic CAR T Cells: An Alternative to Overcome Challenges of CAR T Cell Therapy in Glioblastoma

Chimeric antigen receptor (CAR) T cell therapy has emerged as one of the major breakthroughs in cancer immunotherapy in the last decade. Outstanding results in hematological malignancies and encouraging pre-clinical anti-tumor activity against a wide range of solid tumors have made CAR T cells one of the most promising fields for cancer therapies. CAR T cell therapy is currently being investigated in solid tumors including glioblastoma (GBM), a tumor for which survival has only modestly improved over the past decades. CAR T cells targeting EGFRvIII, Her2, or IL-13Rα2 have been tested in GBM, but the first clinical trials have shown modest results, potentially due to GBM heterogeneity and to the presence of an immunosuppressive microenvironment. Until now, the use of autologous T cells to manufacture CAR products has been the norm, but this approach has several disadvantages regarding production time, cost, manufacturing delay and dependence on functional fitness of patient T cells, often reduced by the disease or previous therapies. Universal “off-the-shelf,” or allogeneic, CAR T cells is an alternative that can potentially overcome these issues, and allow for multiple modifications and CAR combinations to target multiple tumor antigens and avoid tumor escape. Advances in genome editing tools, especially via CRISPR/Cas9, might allow overcoming the two main limitations of allogeneic CAR T cells product, i.e., graft-vs.-host disease and host allorejection. Here, we will discuss how allogeneic CAR T cells could allow for multivalent approaches and alteration of the tumor microenvironment, potentially allowing the development of next generation therapies for the treatment of patients with GBM.

Single nucleotide variants in immune-response genes and the tumor microenvironment composition predict progression of mantle cell lymphoma

Background

There is evidence to consider that the tumor microenvironment (TME) composition associates with antitumor immune response, and may predict the outcome of various non-Hodgkin lymphoma subtypes. However, in the case of mantle cell lymphoma (MCL), a rare and aggressive disease, there is lacking a detailed study of the TME components, as well as an integrative approach among them in patients’ samples. Also, from the genetic point of view, it is known that single nucleotide variants (SNVs) in immune-response genes are among important regulators of immunity. At present, it is uncertain whether SNVs in candidate immune-response genes and the TME composition are able to alter the prognosis in MCL.

Methods

We assessed a detailed TME composition in 88 MCL biopsies using immunohistochemistry, which was automatically analyzed by pixel counting (Aperio system). We also genotyped SNVs located in candidate immune-response genes (IL12A, IL2, IL10, TGFB1, TGFBR1, TGFBR2, IL17A, IL17F) in 95 MCL patients. We tested whether the SNVs could modulate the respective protein expression and TME composition in the tumor compartment. Finally, we proposed survival models in rituximab-treated patients, considering immunohistochemical and SNV models.

Results

High FOXP3/CD3 ratios (p = 0.001), high IL17A levels (p = 0.003) and low IL2 levels (p = 0.03) were individual immunohistochemical predictors of poorer survival. A principal component, comprising high quantities of macrophages and high Ki-67 index, also worsened outcome (p = 0.02). In the SNV model, the CC haplotype of IL10 (p < 0.01), the GG genotype of IL2 rs2069762 (p = 0.02) and the AA+AG genotypes of TGFBR2 rs3087465 (p < 0.01) were independent predictors of outcome. Finally, the GG genotype of TGFB1 rs6957 associated with lower tumor TGFβ levels (p = 0.03) and less CD163+ macrophages (p = 0.01), but did not modulate patients’ survival.

Conclusions

Our results indicate that the TME composition has relevant biological roles in MCL. In this setting, immunohistochemical detection of T-reg cells, IL17A and IL2, coupled with SNV genotyping in IL10, TGFBR2 and IL2, may represent novel prognostic factors in this disease, following future validations.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-021-07891-9.

Biomarkers for Chimeric Antigen Receptor T Cell Therapy in Acute Lymphoblastic Leukemia: Prospects for Personalized Management and Prognostic Prediction

Chimeric antigen receptor (CAR) T cell therapy represents a breakthrough in immunotherapy with the potential of ushering in a new era in cancer treatment. Remarkable therapeutic response and complete remission of this innovative management have been observed in patients with relapse/refractory acute lymphoblastic leukemia. With CAR-T cell therapy becoming widely used both in multicenter clinical trials and as a commercial treatment, therapeutic efficacy monitoring and management of toxicities will be indispensable for ensuring safety and improving overall survival. Biomarkers can act not only as effective indicators reflecting patients' baseline characteristics, CAR-T cell potency, and the immune microenvironment, but can also assess side effects during treatment. In this review, we will elaborate on a series of biomarkers associated with therapeutic response as well as treatment-related toxicities, and present their current condition and latent value with respect to the clinical utility. The combination of biomarker research and CAR-T cell therapy will contribute to establishing a safer and more powerful monitoring system and prolonging the event-free survival of patients.

Systematic Review and Meta-analysis of CD19-Specific CAR-T Cell Therapy in Relapsed/Refractory Acute Lymphoblastic Leukemia in the Pediatric and Young Adult Population: Safety and Efficacy Outcomes

Acute lymphoblastic leukemia (ALL) typically responds better when treated with multiagent chemotherapy in the pediatric and young adolescent populations. Treatment of relapsed/refractory (RR) ALL remains a challenge. Even after stem-cell transplantation and intensive chemotherapy, the prognosis of RR-ALL remains grave. The advent of chimeric antigen receptors has demonstrated promising results in RR-ALL. Chimeric antigen receptor-modified T cells (CAR-T) and engineered T cells are used to target cancer cells. In 2017, the US Food and Drug Administration approved CD19-specific CAR-T (tisagenlecleucel) therapy for RR-B-cell ALL in patients under 25 years old. In this systematic review, we discuss the efficacy and safety of CD19-specific CAR-T therapy in RR-B-cell ALL in the pediatric and young adult population. We searched the PubMed, Embase, Web of Science, Cochrane Library, and clinical trials databases. A total of 448 patients received a CD19-specific CAR-T product, and 446 patients had evaluable data. The age range was 0 to 30 years. The incidence rate of complete remission was 82%. The cumulative incidence of relapse after CD19-specific CAR-T therapy is 36%. Similarly, the incidence rate of grade 3 or higher adverse events of neutropenia, thrombocytopenia, neurotoxicity, infections, and cytokine release syndrome were 38%, 23%, 18%, 29%, and 19%, respectively. Our subgroup analysis shows the incidence rate of minimal residual negative complete remission was 69% with the CD28z costimulatory domain, 81% with the 4-1BB domain, and 77% with fourth-generation CD19-specific CAR-T therapy.

Befriending the Hostile Tumor Microenvironment in CAR T-Cell Therapy

T-cells genetically engineered to express a chimeric antigen receptor (CAR) have shown remarkable results in patients with B-cell malignancies, including B-cell acute lymphoblastic leukemia, diffuse large B-cell lymphoma, and mantle cell lymphoma, with some promising efficacy in patients with multiple myeloma. However, the efficacy of CAR T-cell therapy is still hampered by local immunosuppression and significant toxicities, notably cytokine release syndrome (CRS) and neurotoxicity. The tumor microenvironment (TME) has been identified to play a major role in preventing durable responses to immunotherapy in both solid and hematologic malignancies, with this role exaggerated in solid tumors. The TME comprises a diverse set of components, including a heterogeneous population of various cells and acellular elements that collectively contribute towards the interplay of pro-immune and immunosuppressive signaling. In particular, macrophages, myeloid-derived suppressor cells, regulatory T-cells, and cell-free factors such as cytokines are major contributors to local immunosuppression in the TME of patients treated with CAR T-cells. In order to create a more favorable niche for CAR T-cell function, armored CAR T-cells and other combinatorial approaches are being explored for potential improved outcomes compared to conventional CAR T-cell products. While these strategies may potentiate CAR T-cell function and efficacy, they may paradoxically increase the risk of adverse events due to increased pro-inflammatory signaling. Herein, we discuss the mechanisms by which the TME antagonizes CAR T-cells and how innovative immunotherapy strategies are being developed to address this roadblock. Furthermore, we offer perspective on how these novel approaches may affect the risk of adverse events, in order to identify ways to overcome these barriers and expand the clinical benefits of this treatment modality in patients with diverse cancers. Precise immunomodulation to allow for improved tumor control while simultaneously mitigating the toxicities seen with current generation CAR T-cells is integral for the future application of more effective CAR T-cells against other malignancies.

CAR-T cells for Colorectal Cancer: Target-selection and strategies for improved activity and safety

Chimeric antigen receptor-T (CAR-T) cell immunotherapy is a novel method that is genetically engineered to recruit T cells against malignant disease. Administration of CAR-T cells has led to progress in hematological malignancies, and it has been proposed for solid tumors like colorectal cancer (CRC) for years. However, this method was not living up to expectations for the intrinsic challenges posed to CAR-T cells by solid tumors, which mainly due to the lacking of tumor-restricted antigens and adverse effects following treatment. New approaches are proposed to overcome the multiple challenges to alleviate the difficult situation of CAR-T cells in CRC, including engineering T cells with immune-activating molecules, regional administration of T cell, bispecific T cell engager, and combinatorial target-antigen recognition. In this review, we sum up the current stage of knowledge about target-selection, adverse events like on/off-tumor toxicity, the preclinical and clinical studies of CAR-T therapy, and the characteristics of strategies applied in CRC.

Intratumoral IL-12 delivery empowers CAR-T cell immunotherapy in a pre-clinical model of glioblastoma

Glioblastoma multiforme (GBM) is the most common and aggressive form of primary brain cancer, for which effective therapies are urgently needed. Chimeric antigen receptor (CAR)-based immunotherapy represents a promising therapeutic approach, but it is often impeded by highly immunosuppressive tumor microenvironments (TME). Here, in an immunocompetent, orthotopic GBM mouse model, we show that CAR-T cells targeting tumor-specific epidermal growth factor receptor variant III (EGFRvIII) alone fail to control fully established tumors but, when combined with a single, locally delivered dose of IL-12, achieve durable anti-tumor responses. IL-12 not only boosts cytotoxicity of CAR-T cells, but also reshapes the TME, driving increased infiltration of proinflammatory CD4+ T cells, decreased numbers of regulatory T cells (Treg), and activation of the myeloid compartment. Importantly, the immunotherapy-enabling benefits of IL-12 are achieved with minimal systemic effects. Our findings thus show that local delivery of IL-12 may be an effective adjuvant for CAR-T cell therapy for GBM.

IL-12 Family Cytokines in Cancer and Immunotherapy

The IL-12 family cytokines are a group of unique heterodimeric cytokines that include IL-12, IL-23, IL-27, IL-35 and, most recently, IL-39. Recent studies have solidified the importance of IL-12 cytokines in shaping innate and adaptive immune responses in cancer and identified multipronged roles for distinct IL-12 family members, ranging from effector to regulatory immune functions. These cytokines could serve as promising candidates for the development of immunomodulatory therapeutic approaches. Overall, IL-12 can be considered an effector cytokine and has been found to engage anti-tumor immunity by activating the effector Th1 response, which is required for the activation of cytotoxic T and NK cells and tumor clearance. IL-23 and IL-27 play dual roles in tumor immunity, as they can both activate effector immune responses and promote tumor growth by favoring immune suppression. IL-35 is a potent regulatory cytokine and plays a largely pro-tumorigenic role by inhibiting effector T cells. In this review, we summarize the recent findings on IL-12 family cytokines in the control of tumor growth with an emphasis primarily on immune regulation. We underscore the clinical implications for the use of these cytokines either in the setting of monotherapy or in combination with other conventional therapies for the more effective treatment of malignancies.

Targeted Delivery of IL-12 Adjuvants Immunotherapy by Oncolytic Viruses

The great hopes raised by the discovery of the immunoregulatory cytokine interleukin 12 (IL-12) as an anticancer agent were marred during early clinical experimentation because of severe adverse effects, which prompted a search for alternative formulations and routes of administration. Onco-immunotherapeutic viruses (OIVs) are wild-type or genetically engineered viruses that exert antitumor activity by causing death of the tumor cells they infect and by overcoming a variety of immunosuppressive mechanisms put in place by the tumors. OIVs have renewed the interest in IL-12, as they offer the opportunity to encode the cytokine transgenically from the viral genome and to produce it at high concentrations in the tumor bed. A large body of evidence indicates that IL-12 serves as a potent adjuvant for the immunotherapeutic response elicited by OIVs in murine tumor models. The list of OIVs includes onco-immunotherapeutic herpes simplex, adeno, measles, Newcastle disease, and Maraba viruses, among others. The large increase in IL-12-mediated adjuvanticity was invariably observed for all the OIVs analyzed. Indirect evidence suggests that locally delivered IL-12 may also increase tumor antigenicity. Importantly, the OIV/IL-12 treatment was not accompanied by adverse effects and elicited a long-lasting immune response capable of halting the growth of distant tumors. Thus, OIVs provide an avenue for reducing the clinical toxicity associated with systemic IL-12 therapy, by concentrating the cytokine at the site of disease. The changes to the tumor microenvironment induced by the IL-12-armed OIVs primed the tumors to an improved response to the checkpoint blockade therapy, suggesting that the triple combination is worth pursuing in the future. The highly encouraging results in preclinical models have prompted translation to the clinic. How well the IL-12-OIV-checkpoint inhibitors' combination will perform in humans remains to be fully investigated.

Lymphodepletion strategies to potentiate adoptive T-cell immunotherapy - what are we doing; where are we going?

INTRODUCTION

Adoptive immunotherapy of cancer has evolved from the use of ex vivo expanded lymphokine-activated killer cells and tumor-infiltrating lymphocytes to an increasing array of approaches involving genetically engineered T-cells. A pivotal advance in the enablement of these therapies has been the conditioning of patients with lymphodepleting chemotherapy.A broad range of lymphodepleting regimens has been employed in an effort to improve response rates, without any single consistent approach having emerged. Only a limited number of studies involving small numbers of patients has directly compared two or more regimens, making it challenging to infer which are the preferred agents and dosing schedules. This difficulty is compounded by the fact that both response rate and toxicity appear to be disease-, patient- and T-cell product specific.

EXPERT OPINION

This article surveys clinical experience with lymphodepleting regimens that have been used in conjunction with adoptive T-cell immunotherapy, focussing in particular on studies where different approaches have been employed. Harnessing this limited and evolving clinical experience, we set out to provide potential insights into how an optimal balance may be achieved between efficacy and safety. Intermediate dose fludarabine-based regimens are emerging as an increasingly popular option in an attempt to achieve this goal, although further studies are required to provide definitive evidence.

Angiogenesis in Lymph Nodes Is a Critical Regulator of Immune Response and Lymphoma Growth

Tumor-induced remodeling of the microenvironment in lymph nodes (LNs) includes the formation of blood vessels, which goes beyond the regulation of metabolism, and shaping a survival niche for tumor cells. In contrast to solid tumors, which primarily rely on neo-angiogenesis, hematopoietic malignancies usually grow within pre-vascularized autochthonous niches in secondary lymphatic organs or the bone marrow. The mechanisms of vascular remodeling in expanding LNs during infection-induced responses have been studied in more detail; in contrast, insights into the conditions of lymphoma growth and lodging remain enigmatic. Based on previous murine studies and clinical trials in human, we conclude that there is not a universal LN-specific angiogenic program applicable. Instead, signaling pathways that are tightly connected to autochthonous and infiltrating cell types contribute variably to LN vascular expansion. Inflammation related angiogenesis within LNs relies on dendritic cell derived pro-inflammatory cytokines stimulating vascular endothelial growth factor-A (VEGF-A) expression in fibroblastic reticular cells, which in turn triggers vessel growth. In high-grade B cell lymphoma, angiogenesis correlates with poor prognosis. Lymphoma cells immigrate and grow in LNs and provide pro-angiogenic growth factors themselves. In contrast to infectious stimuli that impact on LN vasculature, they do not trigger the typical inflammatory and hypoxia-related stroma-remodeling cascade. Blood vessels in LNs are unique in selective recruitment of lymphocytes via high endothelial venules (HEVs). The dissemination routes of neoplastic lymphocytes are usually disease stage dependent. Early seeding via the blood stream requires the expression of the homeostatic chemokine receptor CCR7 and of L-selectin, both cooperate to facilitate transmigration of tumor and also of protective tumor-reactive lymphocytes via HEV structures. In this view, the HEV route is not only relevant for lymphoma cell homing, but also for a continuous immunosurveillance. We envision that HEV functional and structural alterations during lymphomagenesis are not only key to vascular remodeling, but also impact on tumor cell accessibility when targeted by T cell-mediated immunotherapies.

Fueling chimeric antigen receptor T cells with cytokines

Chimeric antigen receptor (CAR)-T therapy started a new era of tumor treatment, especially for hematological malignancies. However, many challenges remain, including low-level proliferation and short-term persistence, insufficient CAR T-cell trafficking, suppressive tumor microenvironment (TME), frequent adverse events and the unaffordable manufacturing process. Cytokines are pleiotropic hormones involved in multiple processes of immunity, including activation, expansion, differentiation, and migration of immune cells. Both pre-clinical models and clinical trials showed that armoring CAR-T cells with cytokines strengthened the anti-tumor responses of CAR T cells. This review looked into the key role of cytokines as a promoter of anti-tumor activities of CAR-T cells and consequently a facilitator of clinical translation, mainly, from cytokines of the common γ-chains family, chemokines and chemokine receptors, immunosuppressive molecules and pro-inflammatory cytokines.

The Application of CAR-T Cells in Haematological Malignancies

Chimeric antigen receptor (CAR)-T cells (CART) remain one of the most advanced and promising forms of adoptive T-cell immunotherapy. CART represent autologous, genetically engineered T lymphocytes expressing CAR, i.e. fusion proteins that combine components and features of T cells as well as antibodies providing their more effective and direct anti-tumour effect. The technology of CART construction is highly advanced in vitro and every element of their structure influence their mechanism of action in vivo. Patients with haematological malignancies are faced with the possibility of disease relapse after the implementation of conventional chemo-immunotherapy. Since the most preferable result of therapy is a partial or complete remission, cancer treatment regimens are constantly being improved and customized to individual patients. This individualization could be ensured by CART therapy. This paper characterized CART strategy in details in terms of their structure, generations, mechanism of action and published the results of clinical trials in haematological malignancies including acute lymphoblastic leukaemia, diffuse large B-cell lymphoma, chronic lymphocytic leukaemia and multiple myeloma.

Genetically engineered macrophages persist in solid tumors and locally deliver therapeutic proteins to activate immune responses

Background

Though currently approved immunotherapies, including chimeric antigen receptor T cells and checkpoint blockade antibodies, have been successfully used to treat hematological and some solid tumor cancers, many solid tumors remain resistant to these modes of treatment. In solid tumors, the development of effective antitumor immune responses is hampered by restricted immune cell infiltration and an immunosuppressive tumor microenvironment (TME). An immunotherapy that infiltrates and persists in the solid TME, while providing local, stable levels of therapeutic to activate or reinvigorate antitumor immunity could overcome these challenges faced by current immunotherapies.

Methods

Using lentivirus-driven engineering, we programmed human and murine macrophages to express therapeutic payloads, including Interleukin (IL)-12. In vitro coculture studies were used to evaluate the effect of genetically engineered macrophages (GEMs) secreting IL-12 on T cells and on the GEMs themselves. The effects of IL-12 GEMs on gene expression profiles within the TME and tumor burden were evaluated in syngeneic mouse models of glioblastoma and melanoma and in human tumor slices isolated from patients with advanced gastrointestinal malignancies.

Results

Here, we present a cellular immunotherapy platform using lentivirus-driven genetic engineering of human and mouse macrophages to constitutively express proteins, including secreted cytokines and full-length checkpoint antibodies, as well as cytoplasmic and surface proteins that overcomes these barriers. GEMs traffic to, persist in, and express lentiviral payloads in xenograft mouse models of glioblastoma, and express a non-signaling truncated CD19 surface protein for elimination. IL-12-secreting GEMs activated T cells and induced interferon-gamma (IFNγ) in vitro and slowed tumor growth resulting in extended survival in vivo. In a syngeneic glioblastoma model, IFNγ signaling cascades were also observed in mice treated with mouse bone-marrow-derived GEMs secreting murine IL-12. These findings were reproduced in ex vivo tumor slices comprised of intact MEs. In this setting, IL-12 GEMs induced tumor cell death, chemokines and IFNγ-stimulated genes and proteins.

Conclusions

Our data demonstrate that GEMs can precisely deliver titratable doses of therapeutic proteins to the TME to improve safety, tissue penetrance, targeted delivery and pharmacokinetics.

Localized Interleukin-12 for Cancer Immunotherapy

Interleukin-12 (IL-12) is a potent, pro-inflammatory type 1 cytokine that has long been studied as a potential immunotherapy for cancer. Unfortunately, IL-12's remarkable antitumor efficacy in preclinical models has yet to be replicated in humans. Early clinical trials in the mid-1990's showed that systemic delivery of IL-12 incurred dose-limiting toxicities. Nevertheless, IL-12's pleiotropic activity, i.e., its ability to engage multiple effector mechanisms and reverse tumor-induced immunosuppression, continues to entice cancer researchers. The development of strategies which maximize IL-12 delivery to the tumor microenvironment while minimizing systemic exposure are of increasing interest. Diverse IL-12 delivery systems, from immunocytokine fusions to polymeric nanoparticles, have demonstrated robust antitumor immunity with reduced adverse events in preclinical studies. Several localized IL-12 delivery approaches have recently reached the clinical stage with several more at the precipice of translation. Taken together, localized delivery systems are supporting an IL-12 renaissance which may finally allow this potent cytokine to fulfill its considerable clinical potential. This review begins with a brief historical account of cytokine monotherapies and describes how IL-12 went from promising new cure to ostracized black sheep following multiple on-study deaths. The bulk of this comprehensive review focuses on developments in diverse localized delivery strategies for IL-12-based cancer immunotherapies. Advantages and limitations of different delivery technologies are highlighted. Finally, perspectives on how IL-12-based immunotherapies may be utilized for widespread clinical application in the very near future are offered.

Externally-Controlled Systems for Immunotherapy: From Bench to Bedside

Immunotherapy is a very promising therapeutic approach against cancer that is particularly effective when combined with gene therapy. Immuno-gene therapy approaches have led to the approval of four advanced therapy medicinal products (ATMPs) for the treatment of p53-deficient tumors (Gendicine and Imlygic), refractory acute lymphoblastic leukemia (Kymriah) and large B-cell lymphomas (Yescarta). In spite of these remarkable successes, immunotherapy is still associated with severe side effects for CD19+ malignancies and is inefficient for solid tumors. Controlling transgene expression through an externally administered inductor is envisioned as a potent strategy to improve safety and efficacy of immunotherapy. The aim is to develop smart immunogene therapy-based-ATMPs, which can be controlled by the addition of innocuous drugs or agents, allowing the clinicians to manage the intensity and durability of the therapy. In the present manuscript, we will review the different inducible, versatile and externally controlled gene delivery systems that have been developed and their applications to the field of immunotherapy. We will highlight the advantages and disadvantages of each system and their potential applications in clinics.

Potential lung attack and lethality generated by EpCAM-specific CAR-T cells in immunocompetent mouse models

The tumoricidal efficiency of human CAR-T cells is generally evaluated using immune-deficient mouse models; however, due to their immune-incompetency and the species-specific reactivity of a target antigen, these models are problematic to imitate CAR-T-induced adverse effects in the clinic. Epithelial cell adhesion molecule (EpCAM) is a tumor-associated antigen overtly presented on the cell surface of various carcinomas, making it an attractive target for CAR-T therapy. Here, we developed an anti-mouse EpCAM CAR to evaluate its safety and efficacy in immunocompetent mouse models. As previously reported for their human equivalents, murine EpCAM CAR-T cells exhibit promising anti-tumor efficacy in vitro and in vivo. However, after CAR-T infusion, various dose-depended toxicities including body weight loss, cytokine-release syndrome (CRS), and death were observed in both tumor-bearing and tumor-free mice. Pathological examination revealed unexpected and severe pulmonary immunopathology due to basal EpCAM expression in normal lung. While our study validates EpCAM CAR-T's potent anti-tumor efficacy, it also reveals that EpCAM CAR-T cells used for the treatment of solid tumors may cause lethal toxicity and should, therefore, be evaluated in patients with caution.

Analysis and Augmentation of the Immunologic Bystander Effects of CAR T Cell Therapy in a Syngeneic Mouse Cancer Model

The therapeutic efficacy of adoptive transfer of T cells transduced with chimeric antigen receptors (CARs) has been limited in the treatment of solid cancers, partly due to tumor antigen heterogeneity. Overcoming lack of universal tumor antigen expression would be achieved if CAR T cells could induce bystander effects. To study this process, we developed a system where CAR T cells targeting mesothelin could cure tumors containing 100% antigen-positive cells in immunocompetent mice. Using this model, we found that the CAR T cells were unable to cure tumors, even when only 10% of the tumor cells were mesothelin negative. A bystander effect was not induced by co-administration of anti-PD-1, anti-CTLA-4, or anti-TGF-β (transforming growth factor β) antibodies; agonistic CD40 antibodies; or an IDO (indoleamine 2,3-dioxygenase) inhibitor. However, pretreatment with a non-lymphodepleting dose of cyclophosphamide (CTX) prior to CAR T cells resulted in cures of tumors with up to 25% mesothelin-negative cells. The mechanism was dependent on endogenous CD8 T cells but not on basic leucine zipper transcription factor ATF-like 3 (BATF3)-dependent dendritic cells. These data suggest that CAR T cell therapy of solid tumors, in which the targeted antigen is not expressed by the vast majority of tumor cells, will not likely be successful unless combination strategies to enhance bystander effects are used.

Next-generation CAR T cells to overcome current drawbacks

As a rapidly emerging treatment in the oncology field, adoptive transfer of autologous, genetically modified chimeric antigen receptor (CAR) T cells has shown striking efficacy and is curative in certain relapsed/refractory patients with hematologic malignancy. This treatment modality of using a "living drug" offers many tantalizing and novel therapeutic strategies for cancer patients whose remaining treatment options may have otherwise been limited. Despite the early success of CAR T cells in hematologic malignancies, many barriers remain for widespread adoption. General barriers include cellular manufacturing limitations, baseline quality of the T cells, adverse events post-infusion such as cytokine release syndrome (CRS) and neurotoxicity, and host rejection of non-human CARs. Additionally, each hematologic disease presents unique mechanisms of relapse which have to be addressed in future clinical trials if we are to augment the efficacy of CAR T treatment. In this review, we will describe current barriers to hindering efficacy of CAR T-cell treatment for hematologic malignancies in a disease-specific manner and review recent innovations aimed at enhancing the potency and applicability of CAR T cells, with the overall goal of building a framework to begin incorporating this form of therapy into the standard medical management of blood cancers.

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

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

Gene modification strategies for next-generation CAR T cells against solid cancers

Immunotherapies have become the backbone of cancer treatment. Among them, chimeric antigen receptor (CAR) T cells have demonstrated great success in the treatment of hematological malignancies. However, CAR T therapy against solid tumors is less effective. Antigen targeting; an immunosuppressive tumor microenvironment (TME); and the infiltration, proliferation, and persistence of CAR T cells are the predominant barriers preventing the extension of CAR T therapy to solid tumors. To circumvent these obstacles, the next-generation CAR T cells will require more potent antitumor properties, which can be achieved by gene-editing technology. In this review, we summarize innovative strategies to enhance CAR T cell function by improving target identification, persistence, trafficking, and overcoming the suppressive TME. The construction of multi-target CAR T cells improves antigen recognition and reduces immune escape. Enhancing CAR T cell proliferation and persistence can be achieved by optimizing costimulatory signals and overexpressing cytokines. CAR T cells equipped with chemokines or chemokine receptors help overcome their poor homing to tumor sites. Strategies like knocking out immune checkpoint molecules, incorporating dominant negative receptors, and chimeric switch receptors can favor the depletion or reversal of negative T cell regulators in the TME.

Chimeric Antigen Receptor Cell Therapy: Overcoming Obstacles to Battle Cancer

Chimeric antigen receptors (CAR) are fusion proteins engineered from antigen recognition, signaling, and costimulatory domains that can be used to reprogram T cells to specifically target tumor cells expressing specific antigens. Current CAR-T cell technology utilizes the patient's own T cells to stably express CARs and has achieved exciting clinical success in the past few years. However, current CAR-T cell therapy still faces several challenges, including suboptimal persistence and potency, impaired trafficking to solid tumors, local immunosuppression within the tumor microenvironment and intrinsic toxicity associated with CAR-T cells. This review focuses on recent strategies to improve the clinical efficacy of CAR-T cell therapy and other exciting CAR approaches currently under investigation, including CAR natural killer (NK) and NKT cell therapies.

Recent Advances in Allogeneic CAR-T Cells

In recent decades, great advances have been made in the field of tumor treatment. Especially, cell-based therapy targeting tumor associated antigen (TAA) has developed tremendously. T cells were engineered to have the ability to attack tumor cells by generating CAR constructs consisting of genes encoding scFv, a co-stimulatory domain (CD28 or TNFRSF9), and CD247 signaling domains for T cell proliferation and activation. Principally, CAR-T cells are activated by recognizing TAA by scFv on the T cell surface, and then signaling domains inside cells connected by scFv are subsequently activated to induce downstream signaling pathways involving T cell proliferation, activation, and production of cytokines. Many efforts have been made to increase the efficacy and persistence and also to decrease T cell exhaustion. Overall, allogeneic and universal CAR-T generation has attracted much attention because of their wide and prompt usage for patients. In this review, we summarized the current techniques for generation of allogeneic and universal CAR-T cells along with their disadvantages and limitations that still need to be overcome.

Repurposing endogenous immune pathways to tailor and control chimeric antigen receptor T cell functionality

Endowing chimeric antigen receptor (CAR) T cells with additional potent functionalities holds strong potential for improving their antitumor activity. However, because potency could be deleterious without control, these additional features need to be tightly regulated. Immune pathways offer a wide array of tightly regulated genes that can be repurposed to express potent functionalities in a highly controlled manner. Here, we explore this concept by repurposing TCR, CD25 and PD1, three major players of the T cell activation pathway. We insert the CAR into the TCRα gene (TRAC_CAR), and IL-12P70 into either IL2Rα or PDCD1 genes. This process results in transient, antigen concentration-dependent IL-12P70 secretion, increases TRAC_CAR T cell cytotoxicity and extends survival of tumor-bearing mice. This gene network repurposing strategy can be extended to other cellular pathways, thus paving the way for generating smart CAR T cells able to integrate biological inputs and to translate them into therapeutic outputs in a highly regulated manner.

Engineered T cells work as living therapeutics, but are prone to hyperreactivity and exhaustion. Here the authors improve CAR T cell antitumor responses by simultaneously targeting a CAR to TCR locus and IL-12 to PD1 locus, placing the transgenes under a naturally regulated transcriptional network while disrupting unwanted signals.

Long-term in vivo microscopy of CAR T cell dynamics during eradication of CNS lymphoma in mice

Primary central nervous system lymphoma (PCNSL) is a highly malignant brain tumor with limited treatment options. Here, we show that genetically engineered T cells, expressing a chimeric antigen receptor, thoroughly infiltrate these tumors in mice. Combining intravital 2-photon microscopy with chronic cranial windows, we were able to visualize their intratumoral proliferation and intracerebral persistence for up to 159 d, leading to the eradication of large, established PCNSL and to long-term survival.

T cells expressing anti-CD19 chimeric antigen receptors (CARs) demonstrate impressive efficacy in the treatment of systemic B cell malignancies, including B cell lymphoma. However, their effect on primary central nervous system lymphoma (PCNSL) is unknown. Additionally, the detailed cellular dynamics of CAR T cells during their antitumor reaction remain unclear, including their intratumoral infiltration depth, mobility, and persistence. Studying these processes in detail requires repeated intravital imaging of precisely defined tumor regions during weeks of tumor growth and regression. Here, we have combined a model of PCNSL with in vivo intracerebral 2-photon microscopy. Thereby, we were able to visualize intracranial PCNSL growth and therapeutic effects of CAR T cells longitudinally in the same animal over several weeks. Intravenous (i.v.) injection resulted in poor tumor infiltration of anti-CD19 CAR T cells and could not sufficiently control tumor growth. After intracerebral injection, however, anti-CD19 CAR T cells invaded deeply into the solid tumor, reduced tumor growth, and induced regression of PCNSL, which was associated with long-term survival. Intracerebral anti-CD19 CAR T cells entered the circulation and infiltrated distant, nondraining lymph nodes more efficiently than mock CAR T cells. After complete regression of tumors, anti-CD19 CAR T cells remained detectable intracranially and intravascularly for up to 159 d. Collectively, these results demonstrate the great potential of anti-CD19 CAR T cells for the treatment of PCNSL.