New Chimeric Antigen Receptor Design for Solid Tumors

Current and Future Trends of Colorectal Cancer Treatment: Exploring Advances in Immunotherapy

Cancer of the colon and rectum (CRC) has been identified among the three most prevalent types of cancer and cancer-related deaths for both sexes. Even though significant progress in surgical and chemotherapeutic techniques has markedly improved disease-free and overall survival rates in contrast to those three decades ago, recent years have seen a stagnation in these improvements. This underscores the need for new therapies aiming to augment patient outcomes. A number of emerging strategies, such as immune checkpoint inhibitors (ICIs) and adoptive cell therapy (ACT), have exhibited promising outcomes not only in preclinical but also in clinical settings. Additionally, a thorough appreciation of the underlying biology has expanded the scope of research into potential therapeutic interventions. For instance, the pivotal role of altered telomere length in early CRC carcinogenesis, leading to chromosomal instability and telomere dysfunction, presents a promising avenue for future treatments. Thus, this review explores the advancements in CRC immunotherapy and telomere-targeted therapies, examining potential synergies and how these novel treatment modalities intersect to potentially enhance each other's efficacy, paving the way for promising future therapeutic advancements.

Prospects and challenges of CAR-T cell therapy combined with ICIs

Immune checkpoint molecules are a group of molecules expressed on the surface of immune cells that primarily regulate their immune homeostasis. Chimeric antigen receptor (CAR) T cell therapy is an immunotherapeutic technology that realizes tumor-targeted killing by constructing synthetic T cells expressing specific antigens through biotechnology. Currently, CAR-T cell therapy has achieved good efficacy in non-solid tumors, but its treatment of solid tumors has not yielded the desired results. Immune checkpoint inhibitors (ICIs) combined with CAR-T cell therapy is a novel combination therapy with high expectations to defeat solid tumors. This review addresses the challenges and expectations of this combination therapy in the treatment of solid tumors.

Advances in adoptive cellular therapy for colorectal cancer: a narrative review

Background and Objective

In recent years, adoptive cell therapy (ACT) has shown great potential in antitumor treatment. To significantly improve the clinical efficacy of ACT against solid tumors, we may need to carefully study the latest developments in ACT. As one of the most common malignancies, colorectal cancer (CRC) is a major risk to human health and has become a significant burden on global healthcare systems. This article reviews the recent advances in the treatment of CRC with ACT.

Methods

We searched PubMed for articles related to ACT for CRC published as of August 31, 2022, and retrieved relevant clinical trial information on the National Institutes of Health ClinicalTrials.gov website. Based on search results, comprehensive and systematic review is made.

Key Content and Findings

This article provides an overview of the research progress of ACT for CRC, including chimeric antigen receptor (CAR) T-cell therapy, T-cell receptor (TCR)-engineered T-cell therapy, and tumor-infiltrating lymphocyte (TIL) therapy. Common tumor-associated antigens (TAAs) in clinical trials of CAR-T cell therapy for CRC are described.

Conclusions

Despite many obstacles, ACT shows great promise in treating CRC. Therefore, more basic experimental studies and clinical trials are warranted to further clarify the effectiveness and safety of ACT.

The Dynamic Role of NK Cells in Liver Cancers: Role in HCC and HBV Associated HCC and Its Therapeutic Implications

Hepatocellular carcinoma (HCC) remains an important complication of chronic liver disease, especially when cirrhosis occurs. Existing treatment strategies include surgery, loco-regional techniques, and chemotherapy. Natural killer cells are distinctive cytotoxic lymphocytes that play a vital role in fighting tumors and infections. As an important constituent of the innate immune system against cancer, phenotypic and functional deviations of NK cells have been demonstrated in HCC patients who also exhibit perturbation of the NK-activating receptor/ligand axis. The rate of recurrence of tumor-infiltrating and circulating NK cells are positively associated with survival benefits in HCC and have prognostic significance, suggesting that NK cell dysfunction is closely related to HCC progression. NK cells are the first-line effector cells of viral hepatitis and play a significant role by directly clearing virus-infected cells or by activating antigen-specific T cells by producing IFN-γ. In addition, chimeric antigen receptor (CAR) engineered NK cells suggest an exclusive opportunity to produce CAR-NKs with several specificities with fewer side effects. In the present review, we comprehensively discuss the innate immune landscape of the liver, particularly NK cells, and the impact of tumor immune microenvironment (TIME) on the function of NK cells and the biological function of HCC. Furthermore, the role of NK cells in HCC and HBV-induced HCC has also been comprehensively elaborated. We also elaborate on available NK cell-based immunotherapeutic approaches in HCC treatment and summarize current advancements in the treatment of HCC. This review will facilitate researchers to understand the importance of the innate immune landscape of NK cells and lead to devising innovative immunotherapeutic strategies for the systematic treatment of HCC.

Distinct functions of CAR-T cells possessing a dectin-1 intracellular signaling domain

Chimeric antigen receptor T (CAR-T) cell therapy has demonstrated remarkable efficacies in treating hematopoietic malignancies, but not in the solid tumors. Incorporating costimulatory signaling domains, such as ICOS or 4-1BB, can positively influence CAR-T cell functions and then the immune responses. These CAR-engineered T cells have showed their enhanced persistence and effector functions with improved antitumor activities, and provided a new approach for the treatment of solid tumors. Here, we designed novel 2nd generation CARs with a costimulatory signaling molecule, dectin-1. The impacts of dectin-1 signaling domain on CAR-T cells were evaluated in vitro and in vivo. Our data show that in vitro cytokine secretions by HER2 or CD19 specific CAR-T cells increase significantly via incorporating this dectin-1 signaling domain. Additional properties of these novel CAR-T cells are affected by this costimulatory domain. Compared with a popular reference (i.e., anti-HER2 CAR-T cells with 4-1BB), in vitro T cell functions and in vivo antitumor activity of the dectin-1 engineered CAR-T cells are similar to the 4-1BB based, and both are discrete to the mock T cells. Furthermore, we found that the CAR-T cells with dectin-1 show distinct phenotype and exhaustion marker expression. These collective results suggest that the incorporation of this new signaling domain, dectin-1, into the CARs may provide the clinical potential of the CAR-T cells through this signaling domain in treating solid tumors.

Preclinical Chimeric Antibody Chimeric Antigen Receptor T Cell Progress in Digestive System Cancers

Digestive system cancers, including hepatocellular carcinoma, colorectal and gastric tumors, are characterized by high rates of incidence and mortality. Digestive cancers are difficult to diagnose during the early stages, and the side effects of chemotherapy are often severe and may outweigh the therapeutic benefits. Chimeric antibody chimeric antigen receptor T cell (CAR-T) therapy, a novel immunotherapy, has achieved excellent results for the treatment of hematological tumors. However, CAR-T treatment of solid tumors has struggled due to a lack of target specificity, a difficult tumor microenvironment, and T cell homing. Despite the challenges, CAR-T treatment of digestive cancers is progressing. Combining CAR-T with other targets and/or modifying the CAR may represent the most promising approaches for future treatment of digestive cancers.

Selecting a Cell Engineering Methodology During Cell Therapy Product Development

When considering the development pathway for a genetically modified cell therapy product, it is critically important that the product is engineered consistent with its intended human use. For scientists looking to develop and commercialize a new technology, the decision to select a genetic modification method depends on several practical considerations. Whichever path is chosen, the developer must understand the key risks and potential mitigations of the cell engineering approach. The developer should also understand the clinical implications: permanent/memory establishment versus transient expression, and clinical manufacturing considerations when dealing with transplantation of genetically engineered cells. This review covers important topics for mapping out a strategy for developers of new cell-based therapeutics. Biological, technological, manufacturing, and clinical considerations are all presented to map out development lanes for the initiation and risk management of new gene-based cell therapeutic products for human use.

Safety and clinical efficacy of BCMA CAR-T-cell therapy in multiple myeloma

Background

B-cell maturation antigen (BCMA)-targeted chimeric antigen receptor (CAR)-T-cell therapy is an emerging treatment option for multiple myeloma. The aim of this systematic review and meta-analysis was to determine its safety and clinical activity and to identify factors influencing these outcomes.

Methods

We performed a database search using the terms “BCMA,” “CAR,” and “multiple myeloma” for clinical studies published between 01/01/2015 and 01/01/2020. The methodology is further detailed in PROSPERO (CRD42020125332).

Results

Twenty-three different CAR-T-cell products have been used so far in 640 patients. Cytokine release syndrome was observed in 80.3% (69.0–88.2); 10.5% (6.8–16.0) had neurotoxicity. A higher neurotoxicity rate was reported in studies that included more heavily pretreated patients: 19.1% (13.3–26.7; I² = 45%) versus 2.8% (1.3–6.1; I² = 0%) (p < 0.0001). The pooled overall response rate was 80.5% (73.5–85.9); complete responses (CR) were observed in 44.8% (35.3–54.6). A pooled CR rate of 71.9% (62.8–79.6; I² = 0%) was noted in studies using alpaca/llama-based constructs, whereas it was only 18.0% (6.5–41.1; I² = 67%) in studies that used retroviral vectors for CAR transduction. Median progression-free survival (PFS) was 12.2 (11.4–17.4) months, which compared favorably to the expected PFS of 1.9 (1.5–3.7) months (HR 0.14; p < 0.0001).

Conclusions

Although considerable toxicity was observed, BCMA-targeted CAR-T-cell therapy is highly efficacious even in advanced multiple myeloma. Subgroup analysis confirmed the anticipated inter-study heterogeneity and identified potential factors contributing to safety and efficacy. The results of this meta-analysis may assist the future design of CAR-T-cell studies and lead to optimized BCMA CAR-T-cell products.

Evaluation of the clinicopathologic features of diffuse large B cell lymphoma after CD19-targeted CAR T-cell therapy emphasizing the potential diagnostic pitfalls

Clinicopathologic data of 16 cases of DLBCL, NOS after CD19-targeted CAR T-cell therapy were retrospectively reviewed. Statistical analyses were performed to investigate the diagnostic agreement and indicate the relationship of the given types or their alterations (Group I versus Group II) to the prognosis. A total of 5 distinct histologic patterns were summarized. The CAR T cells were somewhat atypical, most of which were CD8 positive in the most cases (86.7%, 13/15), with a relatively high Ki-67 (60-90%). The rearrangement of BCR was demonstrated in all cases. The diagnostic test showed that the diagnostic accuracy in cases of types III (7%) and V (7%) was typically low; the diagnostic agreement in cases of type IV (for B, T, or nonlymphoma) and V (for T, or nonlymphoma) was consistently unsatisfactory. The rates of complete response (CR), partial response (PR), and progressive disease (PD) were 18.8% (3/16), 31.3% (5/16), 50% (8/16), respectively. In the follow-up, 25% (4/16) of cases experienced a recurrence and 31.3% (5/16) had died, of which 3 cases succumbed to the side effects. Group II had better disease-free survival (DFS, P=0.009). This study first described the pathologic features of DLBCL after CD19-targeted CAR T-cell therapy. Familiarity with these histologic features and combinations of medical history and genetic analyses facilitate avoiding misdiagnoses. Multiple biopsies are potentially helpful to estimate the treatment effects or prognosis, and stable alterations to any type of III to V, but not a single given one, may indicate a good prognosis.

Epithelial Ovarian Cancer and the Immune System: Biology, Interactions, Challenges and Potential Advances for Immunotherapy

Recent advances in the understanding of immune function and the interactions with tumour cells have led to the development of various cancer immunotherapies and strategies for specific cancer types. However, despite some stunning successes with some malignancies such as melanomas and lung cancer, most patients receive little or no benefit from immunotherapy, which has been attributed to the tumour microenvironment and immune evasion. Although the US Food and Drug Administration have approved immunotherapies for some cancers, to date, only the anti-angiogenic antibody bevacizumab is approved for the treatment of epithelial ovarian cancer. Immunotherapeutic strategies for ovarian cancer are still under development and being tested in numerous clinical trials. A detailed understanding of the interactions between cancer and the immune system is vital for optimisation of immunotherapies either alone or when combined with chemotherapy and other therapies. This article, in two main parts, provides an overview of: (1) components of the normal immune system and current knowledge regarding tumour immunology, biology and their interactions; (2) strategies, and targets, together with challenges and potential innovative approaches for cancer immunotherapy, with attention given to epithelial ovarian cancer.

The Landscape of CAR-T Cell Clinical Trials against Solid Tumors-A Comprehensive Overview

Simple Summary

Certain immune cells, namely T cells, of cancer patients can be genetically manipulated to express so-called chimeric antigen receptors (CARs), which enables these cells to kill the tumor cells after recognition by the receptor. This therapy is very successful in the treatment of hematologic tumors such as lymphoma or leukemia. However, tumors growing as a solid mass are less susceptible to this kind of treatment. This review summarizes known data of all clinical trials using this therapy against solid tumors that are registered at clinicaltrials.gov.

Abstract

CAR-T cells showed great potential in the treatment of patients with hematologic tumors. However, the clinical efficacy of CAR-T cells against solid tumors lags behind. To obtain a comprehensive overview of the landscape of CAR-T cell clinical trials against this type of cancer, this review summarizes all the 196 studies registered at clinicaltrials.gov. Special focus is on: (1) geographical distribution; (2) targeted organs, tumor entities, and antigens; (3) CAR transfer methods, CAR formats, and extra features introduced into the T cells; and (4) patient pretreatments, injection sites, and safety measurements. Finally, the few data on clinical outcome are reported. The last assessment of clinicaltrials.gov for the data summarized in this paper was on 4 August 2020.

Humanized Mice Are Precious Tools for Preclinical Evaluation of CAR T and CAR NK Cell Therapies

Chimeric antigen receptor (CAR) T-cell therapy represents a revolutionary treatment for hematological malignancies. However, improvements in CAR T-cell therapies are urgently needed since CAR T cell application is associated with toxicities, exhaustion, immune suppression, lack of long-term persistence, and low CAR T-cell tumor infiltration. Major efforts to overcome these hurdles are currently on the way. Incrementally improved xenograft mouse models, supporting the engraftment and development of a human hemato-lymphoid system and tumor tissue, represent an important fundamental and preclinical research tool. We will focus here on several CAR T and CAR NK therapies that have benefited from evaluation in humanized mice. These models are of great value for the cancer therapy field as they provide a more reliable understanding of sometimes complicated therapeutic interventions. Additionally, they are considered the gold standard with regard to assessment of new CAR technologies in vivo for safety, efficacy, immune response, design, combination therapies, exhaustion, persistence, and mechanism of action prior to starting a clinical trial. They help to expedite the critical translation from proof-of-concept to clinical CAR T-cell application. In this review, we discuss innovative developments in the CAR T-cell therapy field that benefited from evaluation in humanized mice, illustrated by multiple examples.

CAR T cells and checkpoint inhibition for the treatment of glioblastoma

Introduction: Glioblastoma (GBM) is a highly aggressive brain tumor and is one of the most lethal human cancers. Chimeric antigen receptor (CAR) T cell therapy has markedly improved survival in previously incurable disease; however, this vanguard treatment still faces challenges in GBM. Likewise, checkpoint blockade therapies have not enjoyed the same victories against GBM. As it becomes increasingly evident that a mono-therapeutic approach is unlikely to provide anti-tumor efficacy, there evolves a critical need for combined treatment strategies.Areas covered: This review highlights the clinical successes observed with CAR T cell therapy as well the current efforts to overcome its perceived limitations. The review also explores employed combinations of CAR T cell approaches with immune checkpoint blockade strategies, which aim to potentiate immunotherapeutic benefits while restricting the impact of tumor heterogeneity and T cell exhaustion.Expert opinion: Barriers such as tumor heterogeneity and T cell exhaustion have exposed the weaknesses of various mono-immunotherapeutic approaches to GBM, including CAR T cell and checkpoint blockade strategies. Combining these potentially complementary strategies, however, may proffer a rational means of mitigating these barriers and advancing therapeutic successes against GBM and other solid tumors.

CAR T Cell Therapy Progress and Challenges for Solid Tumors

The past two decades have marked the beginning of an unprecedented success story for cancer therapy through redirecting antitumor immunity [1]. While the mechanisms that control the initial and ongoing immune responses against tumors remain a strong research focus, the clinical development of technologies that engage the immune system to target and kill cancer cells has become a translational research priority. Early attempts documented in the late 1800s aimed at sparking immunity with cancer vaccines were difficult to interpret but demonstrated an opportunity that more than 100 years later has blossomed into the current field of cancer immunotherapy. Perhaps the most recent and greatest illustration of this is the widespread appreciation that tumors actively shut down antitumor immunity, which has led to the emergence of checkpoint pathway inhibitors that re-invigorate the body's own immune system to target cancer [2, 3]. This class of drugs, with first FDA approvals in 2011, has demonstrated impressive durable clinical responses in several cancer types, including melanoma, lung cancer, Hodgkin's lymphoma, and renal cell carcinoma, with the ongoing investigation in others. The biology and ultimate therapeutic successes of these drugs led to the 2018 Nobel Prize in Physiology or Medicine, awarded to Dr. James Allison and Dr. Tasuku Honjo for their contributions to cancer therapy [4]. In parallel to the emerging science that aided in unleashing the body's own antitumor immunity with checkpoint pathway inhibitors, researchers were also identifying ways to re-engineer antitumor immunity through adoptive cellular immunotherapy approaches. Chimeric antigen receptor (CAR)-based T cell therapy has achieved an early head start in the field, with two recent FDA approvals in 2017 for the treatment of B-cell malignancies [5]. There is an explosion of preclinical and clinical efforts to expand the therapeutic indications for CAR T cell therapies, with a specific focus on improving their clinical utility, particularly for the treatment of solid tumors. In this chapter, we will highlight the recent progress, challenges, and future perspectives surrounding the development of CAR T cell therapies for solid tumors.

Humanized mice are precious tools for evaluation of hematopoietic gene therapies and preclinical modeling to move towards a clinical trial

Over the last decade, incrementally improved xenograft mouse models, which support the engraftment and development of a human hemato-lymphoid system, have been developed and represent an important fundamental and preclinical research tool. Immunodeficient mice can be transplanted with human hematopoietic stem cells (HSCs) and this process is accompanied by HSC homing to the murine bone marrow. This is followed by stem cell expansion, multilineage hematopoiesis, long-term engraftment, and functional human antibody and cellular immune responses. The most significant contributions made by these humanized mice are the identification of normal and leukemic hematopoietic stem cells, the characterization of the human hematopoietic hierarchy, screening of anti-cancer therapies and their use as preclinical models for gene therapy applications. This review article focuses on several gene therapy applications that have benefited from evaluation in humanized mice such as chimeric antigen receptor (CAR) T cell therapies for cancer, anti-viral therapies and gene therapies for multiple monogenetic diseases. Humanized mouse models have been and still are of great value for the gene therapy field since they provide a more reliable understanding of sometimes complicated therapeutic approaches such as recently developed therapeutic gene editing strategies, which seek to correct a gene at its endogenous genomic locus. Additionally, humanized mouse models, which are of great importance with regard to testing new vector technologies in vivo for assessing safety and efficacy prior toclinical trials, help to expedite the critical translation from basic findings to clinical applications. In this review, innovative gene therapies and preclinical studies to evaluate T- and B-cell and HSC-based therapies in humanized mice are discussed and illustrated by multiple examples.

Chimeric Antigen Receptors Incorporating D Domains Targeting CD123 Direct Potent Mono- and Bi-specific Antitumor Activity of T Cells

Chimeric antigen receptor (CAR) T cell therapies have demonstrated impressive initial response rates in hematologic malignancies. However, relapse rates are significant, and robust efficacies in other indications, such as solid tumors, will likely require novel therapeutic strategies and CAR designs. To that end, we sought to develop simple, highly selective targeting domains (D domains) that could be incorporated into complex, multifunctional therapeutics. Herein, we describe the identification and characterization of D domains specific for CD123, a therapeutic target for hematologic malignancies, including acute myelogenous leukemia (AML). CARs comprised of these D domains mediate potent T cell activation and cytolysis of CD123-expressing target cells and induce complete durable remission in two AML xenograft models. We describe a strategy of engineering less immunogenic D domains through the identification and removal of putative T cell epitopes and investigate the binding kinetics and affinity requirements of the resultant D domain CARs. Finally, we extended the utility of D domains by generating functional, bi-specific CARs comprised of a CD123-specific D domain and a CD19-specific scFv. The properties of D domains suggest that this class of targeting domain may facilitate the development of multi-functional CARs where conventional, scFv-based designs may be suboptimal.

Radiofrequency ablation of liver metastasis: potential impact on immune checkpoint inhibitor therapy

Percutaneous radiofrequency ablation (RFA), a generally accepted alternative therapy for patients with liver metastases, is a minimally invasive approach with a favorable safety profile and a lower rate of major complications. The use of RFA or combined RFA plus resection can produce total tumor clearance in patients with unresectable liver metastases. However, the relatively high rate of local tumor progression has prevented the widespread use of RFA. Furthermore, its efficacy is controversial because there have been no comparisons for its effect on overall survival compared with standard options such as systemic chemotherapy. Meanwhile, immunotherapy has become a major research focus for oncology based on the recent successes reported for immune checkpoint inhibitors for melanoma, non-small cell lung cancer, gastric cancer, and other cancers. Immune checkpoints negatively regulate T cell function, and inhibition prevents the blockade of the immune system by cancer cells to prevent their destruction. Unfortunately, only some patients (< 25%) respond to immuno-oncology drugs, whereas other patients acquire resistance. However, RFA can induce massive necrotic cell death which might activate immunity and the presentation of cryptic antigens to induce tumor-specific T cell response. Because RFA can induce the rapid release of large amounts of tumor antigens, it can potentially stimulate transient immune responses to much tumor antigens. Combination therapies have induced synergistic enhancement of anticancer immune response in preclinical studies, indicating great promise for the future of oncologic treatment.Key Points • Only some patients respond to immuno-oncology drugs. • RFA causes the release of large amounts of cellular debris, a source of tumor antigens that elicit immune responses against tumors. • Combination RFA for liver metastases and immune checkpoint inhibitor therapies might synergistically enhance antitumor immunity.

Analysis of the Tumor Reactivity of Tumor-Infiltrating Lymphocytes in a Metastatic Melanoma Lesion that Lost Major Histocompatibility Complex Class I Expression after Anti-PD-1 Therapy

Major histocompatibility complex class I loss due to the abnormality of β2-microglobulin gene is one of the mechanisms underlying delayed relapses in melanoma patients long after the initial positive responses to anti-PD-1 therapy. However, the tumor-specific reactivity of tumor-infiltrating lymphocytes in tumor lesions that lost major histocompatibility complex class I expression has not been well evaluated. We report the case of a 55-year-old woman with two metastatic melanoma lesions. After a 12-month period of successful tumor suppression by anti-PD-1 antibody therapy, one lesion started to grow again. We resected both lesions and examined the tumor cells and tumor-infiltrating lymphocytes. The shrinking lesion consisted of necrotic tissue and macrophages, and the enlarged lesion consisted of both necrotic tissue and viable tumor cells. The tumor cells completely lost major histocompatibility complex class I expression, but it was restored upon retroviral transduction of the normal β2-microglobulin gene. When we checked the tumor-specific reactivity of tumor-infiltrating lymphocytes derived from the relapsing lesion, we found that these tumor-infiltrating lymphocytes failed to recognize the native tumor cells derived from the lesion, but strongly recognized the major histocompatibility complex class-I-recovered cells by β2-microglobulin transduction. Our report emphasizes the limitations of T-cell-based immunotherapy and highlights the importance of developing alternative strategies for such cases.

The expansion of targetable biomarkers for CAR T cell therapy

Biomarkers are an integral part of cancer management due to their use in risk assessment, screening, differential diagnosis, prognosis, prediction of response to treatment, and monitoring progress of disease. Recently, with the advent of Chimeric Antigen Receptor (CAR) T cell therapy, a new category of targetable biomarkers has emerged. These biomarkers are associated with the surface of malignant cells and serve as targets for directing cytotoxic T cells. The first biomarker target used for CAR T cell therapy was CD19, a B cell marker expressed highly on malignant B cells. With the success of CD19, the last decade has shown an explosion of new targetable biomarkers on a range of human malignancies. These surface targets have made it possible to provide directed, specific therapy that reduces healthy tissue destruction and preserves the patient's immune system during treatment. As of May 2018, there are over 100 clinical trials underway that target over 25 different surface biomarkers in almost every human tissue. This expansion has led to not only promising results in terms of patient outcome, but has also led to an exponential growth in the investigation of new biomarkers that could potentially be utilized in CAR T cell therapy for treating patients. In this review, we discuss the biomarkers currently under investigation and point out several promising biomarkers in the preclinical stage of development that may be useful as targets.

Chimeric Antigen Receptor T-Cells (CAR T-Cells) for Cancer Immunotherapy - Moving Target for Industry?

The first CD19 CAR T-cell products, Kymriah and Yescarta, are entering the US market and also being evaluated for marketing authorization in the EU. This breakthrough has expanded the interest and also investments towards novel chimeric antigen receptor (CAR) designs, both for hematological malignancies and solid tumors. At the same time, there is active development in moving from autologous products to allogeneic, off-the-shelf -products. New manufacturing technologies are also emerging for production of these complex genetically-modified cells and even decentralized manufacturing in hospitals is under consideration. However, the high potency of CAR T-cells is associated with toxicity and not all patients respond to the treatment. In addition, the number of patient and product variables impacting the clinical outcome is high. The race towards novel CAR T treatment options for cancer patients has begun, but without careful design of the constructs and overall understanding of the factors that impact the ultimate outcome in each case, the road towards commercial success may be long and winding. This review discusses the product- and patient-related variables that may pose challenges for the industry and developers both from the scientific and regulatory perspective.

Perspectives on Chimeric Antigen Receptor T-Cell Immunotherapy for Solid Tumors

Chimeric antigen receptor (CAR) T-cell therapy entails the genetic engineering of a patient's T-cells to express membrane spanning fusion receptors with defined specificities for tumor-associated antigens. These CARs are capable of eliciting robust T-cell activation to initiate killing of the target tumor cells. This therapeutic approach has produced unprecedented clinical outcomes in the treatment of "liquid" hematologic cancers, but to date has not produced comparable responses in targeting solid malignancies. Advances in our understanding of the immunobiology of solid tumors have highlighted several hurdles which currently hinder the efficacy of this therapy. These barriers include the insufficient accumulation of CAR T-cells in the tumor due to poor trafficking or physical exclusion and the exposure of infiltrating CAR T-cells to a panoply of immune suppressive checkpoint molecules, cytokines, and metabolic stresses that are not conducive to efficient immune reactions and can thereby render these cells anergic, exhausted, or apoptotic. This mini-review summarizes these hurdles and describes some recent approaches and innovations to genetically re-engineer CAR T-cells to counter inhibitory influences found in the tumor microenvironment. Novel immunotherapy drug combinations to potentiate the activity of CAR T-cells are also discussed. As our understanding of the immune landscape of tumors improves and our repertoire of immunotherapeutic drugs expands, it is envisaged that the efficacy of CAR T-cells against solid tumors might be potentiated using combination therapies, which it is hoped may lead to meaningful improvements in clinical outcome for patients with refractory solid malignancies.

CD99: A Cell Surface Protein with an Oncojanus Role in Tumors

The cell surface molecule CD99 has gained interest because of its involvement in regulating cell differentiation and adhesion/migration of immune and tumor cells. However, the molecule plays an intriguing and dual role in different cell types. In particular, it acts as a requirement for cell malignancy or as an oncosuppressor in tumors. In addition, the gene encodes for two different isoforms, which also act in opposition inside the same cell. This review highlights key studies focusing on the dual role of CD99 and its isoforms and discusses major critical issues, challenges, and strategies for overcoming those challenges. The review specifically underscores the properties that make the molecule an attractive therapeutic target and identifies new relationships and areas of study that may be exploited. The elucidation of the spatial and temporal control of the expression of CD99 in normal and tumor cells is required to obtain a full appreciation of this molecule and its signaling.