Hypoxia Selectively Impairs CAR-T Cells In Vitro

Prospects of Synergy: Local Interventions and CAR T Cell Therapy in Solid Tumors

Chimeric antigen receptor T cell therapy has been established in the treatment of various B cell malignancies. However, translating this therapeutic effect to treat solid tumors has been challenging because of their inter-tumoral as well as intratumoral heterogeneity and immunosuppressive microenvironment. Local interventions, such as surgery, radiotherapy, local ablation, and locoregional drug delivery, can enhance chimeric antigen receptor T cell therapy in solid tumors by improving tumor infiltration and reducing systemic toxicities. Additionally, ablation and radiotherapy have proven to (re-)activate systemic immune responses via abscopal effects and reprogram the tumor microenvironment on a physical, cellular, and chemical level. This review highlights the potential synergy of the combined approaches to overcome barriers of chimeric antigen receptor T cell therapy and summarizes recent studies that may pave the way for new treatment regimens.

Ex vivo T cell differentiation in adoptive immunotherapy manufacturing: Critical process parameters and analytical technologies

Adoptive immunotherapy shows great promise as a treatment for cancer and other diseases. Recent evidence suggests that the therapeutic efficacy of these cell-based therapies can be enhanced by the enrichment of less-differentiated T cell subpopulations in the therapeutic product, giving rise to a need for advanced manufacturing technologies capable of enriching of these subpopulations through regulation of T cell differentiation. Studies have shown that modifying certain critical process control parameters, such as cytokines, metabolites, amino acids, and culture environment, can effectively manipulate T cell differentiation in ex vivo cultures. Advanced process analytical technologies (PATs) are crucial for monitoring these parameters and the assessment of T cell differentiation during culture. In this review, we examine such critical process parameters and PATs, with an emphasis on their impact on enriching less-differentiated T cell population. We also discuss the limitations of current technologies and advocate for further efforts from the community to establish more stringent critical process parameters (CPPs) and develop more at-line/online PATs that are specific to T cell differentiation. These advancements will be essential to enable the manufacturing of more efficacious adoptive immunotherapy products.

CAR-T cell technologies that interact with the tumour microenvironment in solid tumours

INTRODUCTION

Chimeric antigen receptor (CAR) T-cells have emerged as a ground-breaking therapy for the treatment of hematological malignancies due to their capacity for rapid tumor-specific killing and long-lasting tumor immunity. However, the same success has not been observed in patients with solid tumors. Largely, this is due to the additional challenges imposed by safe and uniform target selection, inefficient CAR T-cell access to sites of disease and the presence of a hostile immunosuppressive tumor microenvironment.

AREAS COVERED

Literature was reviewed on the PubMed database from the first description of a CAR by Kuwana, Kurosawa and colleagues in December 1987 through to the present day. This literature indicates that in order to tackle solid tumors, CAR T-cells can be further engineered with additional armoring strategies that facilitate trafficking to and infiltration of malignant lesions together with reversal of suppressive immune checkpoints that operate within solid tumor lesions.

EXPERT OPINION

In this review, we describe a number of recent advances in CAR T-cell technology that set out to combat the problems imposed by solid tumors including tumor recruitment, infiltration, immunosuppression, metabolic compromise, and hypoxia.

Regulatory T cells and immune escape in HCC: understanding the tumor microenvironment and advancing CAR-T cell therapy

Liver cancer, which most commonly manifests as hepatocellular carcinoma (HCC), is the sixth most common cancer in the world. In HCC, the immune system plays a crucial role in the growth and proliferation of tumor cells. HCC achieve immune escape through the tumor microenvironment, which significantly promotes the development of this cancer. Here, this article introduces and summarizes the functions and effects of regulatory T cells (Tregs) in the tumor microenvironment, highlighting how Tregs inhibit and regulate the functions of immune and tumor cells, cytokines, ligands and receptors, etc, thereby promoting tumor immune escape. In addition, it discusses the mechanism of CAR-T therapy for HCC and elaborate on the relationship between CAR-T and Tregs.

CAR-T cell expansion platforms yield distinct T cell differentiation states

With investigators looking to expand engineered T cell therapies such as CAR-T to new tumor targets and patient populations, a variety of cell manufacturing platforms have been developed to scale manufacturing capacity using closed and/or automated systems. Such platforms are particularly useful for solid tumor targets, which typically require higher CAR-T cell doses. Although T cell phenotype and function are key attributes that often correlate with therapeutic efficacy, how manufacturing platforms influence the final CAR-T cell product is currently unknown. We compared 4 commonly used T cell manufacturing platforms (CliniMACS Prodigy, Xuri W25 rocking platform, G-Rex gas-permeable bioreactor, static bag culture) using identical media, stimulation, culture length, and donor starting material. Selected CD4+CD8+ cells were transduced with lentiviral vector incorporating a CAR targeting FGFR4, a promising target for pediatric sarcoma. We observed significant differences in overall expansion over the 14-day culture; bag cultures had the highest capacity for expansion while the Prodigy had the lowest (481-fold versus 84-fold, respectively). Strikingly, we also observed considerable differences in the phenotype of the final product, with the Prodigy significantly enriched for CCR7+CD45RA+ naïve/stem central memory (Tn/scm)-like cells at 46% compared to bag and G-Rex with 16% and 13%, respectively. Gene expression analysis also showed that Prodigy CAR-Ts are more naïve, less cytotoxic and less exhausted than bag, G-Rex, and Xuri CAR-Ts, and pointed to differences in cell metabolism that were confirmed via metabolic assays. We hypothesized that dissolved oxygen level, which decreased substantially during the final 3 days of the Prodigy culture, may contribute to the observed differences in T cell phenotype. By culturing bag and G-Rex cultures in 1% O2 from day 5 onward, we could generate >60% Tn/scm-like cells, with longer time in hypoxia correlating with a higher percentage of Tn/scm-like cells. Intriguingly, our results suggest that oxygenation is responsible, at least in part, for observed differences in T cell phenotype among bioreactors and suggest hypoxic culture as a potential strategy prevent T cell differentiation during expansion. Ultimately, our study demonstrates that selection of bioreactor system may have profound effects not only on the capacity for expansion, but also on the differentiation state of the resulting CAR-T cells.

Aptamer-Based Nongenetic Reprogramming of CARs Enables Flexible Modulation of T Cell-Mediated Tumor Immunotherapy

Innovating the design of chimeric antigen receptors (CARs) beyond conventional structures would be necessary to address the challenges of efficacy, safety, and applicability in T cell-based cancer therapy, whereas excessive genetic modification might complicate CAR design and manufacturing, and increase gene editing risks. In this work, we used aptamers as the antigen-recognition unit to develop a nongenetic CAR engineering strategy for programming the antitumor activity and specificity of CAR T cells. Our results demonstrated that aptamer-functionalized CAR (Apt-CAR) T cells could be directly activated by recognizing target antigens on cancer cells, and then impart a cytotoxic effect for cancer elimination in vitro and in vivo. The designable antigen recognition capability of Apt-CAR T cells allows for easy modulation of their efficacy and specificity. Additionally, multiple features, e.g., tunable antigen-binding avidity and the tumor microenvironment responsiveness, could be readily integrated into Apt-CAR design without T cell re-engineering, offering a new paradigm for developing adaptable immunotherapeutics.

A Roadmap of CAR-T-Cell Therapy in Glioblastoma: Challenges and Future Perspectives

Glioblastoma (GBM) is the most common primary malignant brain tumor, with a median overall survival of less than 2 years and a nearly 100% mortality rate under standard therapy that consists of surgery followed by combined radiochemotherapy. Therefore, new therapeutic strategies are urgently needed. The success of chimeric antigen receptor (CAR) T cells in hematological cancers has prompted preclinical and clinical investigations into CAR-T-cell treatment for GBM. However, recent trials have not demonstrated any major success. Here, we delineate existing challenges impeding the effectiveness of CAR-T-cell therapy for GBM, encompassing the cold (immunosuppressive) microenvironment, tumor heterogeneity, T-cell exhaustion, local and systemic immunosuppression, and the immune privilege inherent to the central nervous system (CNS) parenchyma. Additionally, we deliberate on the progress made in developing next-generation CAR-T cells and novel innovative approaches, such as low-intensity pulsed focused ultrasound, aimed at surmounting current roadblocks in GBM CAR-T-cell therapy.

PX-478, an HIF-1α inhibitor, impairs mesoCAR T cell antitumor function in cervical cancer

Introduction

Chimeric Antigen Receptor (CAR) T cell therapy has demonstrated remarkable success in treating hematological malignancies. However, its efficacy against solid tumors, including cervical cancer, remains a challenge. Hypoxia, a common feature of the tumor microenvironment, profoundly impacts CAR T cell function, emphasizing the need to explore strategies targeting hypoxia-inducible factor-1α (HIF-1α).

Methods

In this study, we evaluated the effects of the HIF-1α inhibitor PX-478 on mesoCAR T cell function through in-silico and in vitro experiments. We conducted comprehensive analyses of HIF-1α expression in cervical cancer patients and examined the impact of PX-478 on T cell proliferation, cytokine production, cytotoxicity, and exhaustion markers.

Results

Our in-silico analyses revealed high expression of HIF-1α in cervical cancer patients, correlating with poor prognosis. PX-478 effectively reduced HIF-1α levels in T and HeLa cells. While PX-478 exhibited dose-dependent inhibition of antigen-nonspecific T and mesoCAR T cell proliferation, it had minimal impact on antigen-specific mesoCAR T cell proliferation. Notably, PX-478 significantly impaired the cytotoxic function of mesoCAR T cells and induced terminally exhausted T cells.

Discussion

Our results underscore the significant potential and physiological relevance of the HIF-1α pathway in determining the fate and function of both T and CAR T cells. However, we recognize the imperative for further molecular investigations aimed at unraveling the intricate downstream targets associated with HIF-1α and its influence on antitumor immunity, particularly within the context of hypoxic tumors. These insights serve as a foundation for the careful development of combination therapies tailored to counter immunosuppressive pathways within hypoxic environments and fine-tune CAR T cell performance in the intricate tumor microenvironment.

Hypoxia-Responsive CAR-T Cells Exhibit Reduced Exhaustion and Enhanced Efficacy in Solid Tumors

Expanding the utility of chimeric antigen receptor (CAR)-T cells in solid tumors requires improving their efficacy and safety. Hypoxia is a feature of most solid tumors that could be used to help CAR-T cells discriminate tumors from normal tissues. In this study, we developed hypoxia-responsive CAR-T cells by engineering the CAR to be under regulation of hypoxia-responsive elements and selected the optimal structure (5H1P-CEA CAR), which can be activated in the tumor hypoxic microenvironment to induce CAR-T cells with high polyfunctionality. Hypoxia-responsive CAR T cells were in a "resting" state with low CAR expression under normoxic conditions. Compared with conventional CAR-T cells, hypoxia-responsive CAR-T cells maintained lower differentiation and displayed enhanced oxidative metabolism and proliferation during cultivation, and they sowed a capacity to alleviate the negative effects of hypoxia on T-cell proliferation and metabolism. Furthermore, 5H1P-CEA CAR-T cells exhibited decreased T-cell exhaustion and improved T-cell phenotype in vivo. In patient-derived xenograft models, hypoxia-responsive CAR-T cells induced more durable antitumor activity than their conventional counterparts. Overall, this study provides an approach to limit CAR expression to the hypoxic tumor microenvironment that could help to enhance CAR T-cell efficacy and safety in solid tumors.

SIGNIFICANCE

Engineering CAR-T cells to upregulate CAR expression under hypoxic conditions induces metabolic reprogramming, reduces differentiation, and increases proliferation to enhance their antitumor activity, providing a strategy to improve efficacy and safety.

Engineering metabolism to modulate immunity

Metabolic programming and reprogramming have emerged as pivotal mechanisms for altering immune cell function. Thus, immunometabolism has become an attractive target area for treatment of immune-mediated disorders. Nonetheless, many hurdles to delivering metabolic cues persist. In this review, we consider how biomaterials are poised to transform manipulation of immune cell metabolism through integrated control of metabolic configurations to affect outcomes in autoimmunity, regeneration, transplant, and cancer. We emphasize the features of nanoparticles and other biomaterials that permit delivery of metabolic cues to the intracellular compartment of immune cells, or strategies for altering signals in the extracellular space. We then provide perspectives on the potential for reciprocal regulation of immunometabolism by the physical properties of materials themselves. Lastly, opportunities for clinical translation are highlighted. This discussion contributes to our understanding of immunometabolism, biomaterials-based strategies for altering metabolic configurations in immune cells, and emerging concepts in this evolving field.

Challenges and solutions to superior chimeric antigen receptor-T design and deployment for B-cell lymphomas

Chimeric antigen receptor-T (CAR-T) therapies represent a major breakthrough in cancer medicine, given the ex vivo-based technology that harnesses the power of one's own immune system. These therapeutics have demonstrated remarkable success for relapsed/refractory B-cell lymphomas. Although more than a decade has passed since the initial introduction of CAR-T therapeutics for patients with leukaemia and lymphoma, there is still significant debate as to where CAR-T therapeutics fit into the management paradigm, as consensus guidelines are limited. Competing interventions deployed in subsequent lines of therapy for aggressive lymphoma include novel targeted agents, bispecific antibodies, and time-honoured stem cell transplant. In this focused review, we discuss the major obstacles to advancing the therapeutic reach for CAR-T products in early lines of therapy. Such barriers include antigen escape, "cold" tumour microenvironments, host inflammation and CAR-T cell exhaustion. We highlight solutions including point-of-care CAR-T manufacturing and early T lymphopheresis. We review the evidence basis for early CAR-T deployment for B-cell lymphomas in light of the recent Food and Drug Administration (FDA) approval of three first-in-class anti-CD3/CD20 bispecific antibodies-mosunetuzumab, epcoritamab and glofitamab. We propose practical recommendations for 2024.

Hypoxia-specific imaging in patients with lymphoma undergoing CAR-T therapy

PURPOSE

Intratumoral hypoxia in non-Hodgkin's Lymphoma (NHL) may interfere with chimeric antigen receptor T-cell (CAR-T) function. We conducted a single-center pilot study (clinicaltrials.gov ID NCT04409314) of [18F]fluoroazomycin arabinoside, a hypoxia-specific radiotracer abbreviated as [18F]FAZA, to assess the feasibility of this positron emission tomography (PET) imaging modality in this population.

METHODS

Patients with relapsed NHL being evaluated for CAR-T therapy received a one-time [18F]FAZA PET scan before pre-CAR-T lymphodepletion. A tumor to mediastinum (T/M) ratio of 1.2 or higher with regard to [18F]FAZA uptake was defined as positive for intratumoral hypoxia. We planned to enroll 30 patients with an interim futility analysis after 16 scans.

RESULTS

Of 16 scanned patients, 3 had no evidence of disease by standard [18F]fluorodeoxyglucose PET imaging before CAR-T therapy. Six patients (38%) had any [18F]FAZA uptake above background. Using a T/M cutoff of 1.20, only one patient (a 68-year-old male with relapsed diffuse large B-cell lymphoma) demonstrated intratumoral hypoxia in an extranodal chest wall lesion (T/M 1.35). Interestingly, of all 16 scanned patients, he was the only patient with progressive disease within 1 month of CAR-T therapy. However, because of our low overall proportion of positive scans, our study was stopped for futility.

CONCLUSIONS

Our pilot study identified low-level [18F]FAZA uptake in a small number of patients with NHL receiving CAR-T therapy. The only patient who met our pre-specified threshold for intratumoral hypoxia was also the only patient with early CAR-T failure. Future plans include exploration of [18F]FAZA in a more selected patient population.

Modulation of Radiation Doses and Chimeric Antigen Receptor T Cells: A Promising New Weapon in Solid Tumors-A Narrative Review

Tumor behavior is determined by its interaction with the tumor microenvironment (TME). Chimeric antigen receptor (CART) cell therapy represents a new form of cellular immunotherapy (IT). Immune cells present a different sensitivity to radiation therapy (RT). RT can affect tumor cells both modifying the TME and inducing DNA damage, with different effects depending on the low and high doses delivered, and can favor the expression of CART cells. CART cells are patients' T cells genetically engineered to recognize surface structure and to eradicate cancer cells. High-dose radiation therapy (HDRT, >10-20 Gy/fractions) converts immunologically "cold" tumors into "hot" ones by inducing necrosis and massive inflammation and death. LDRT (low-dose radiation therapy, >5-10 Gy/fractions) increases the expansion of CART cells and leads to non-immunogenetic death. An innovative approach, defined as the LATTICE technique, combines a high dose in higher FDG- uptake areas and a low dose to the tumor periphery. The association of RT and immune checkpoint inhibitors increases tumor immunogenicity and immune response both in irradiated and non-irradiated sites. The aim of this narrative review is to clarify the knowledge, to date, on CART cell therapy and its possible association with radiation therapy in solid tumors.

The role of bone marrow microenvironment on CAR-T efficacy in haematologic malignancies

In recent years, chimeric antigen receptor-T (CAR-T) cell therapy has emerged as a novel immunotherapy method. It has shown significant therapeutic efficacy in the treatment of haematological B cell malignancies. In particular, the CAR-T therapy targeting CD19 has yielded unprecedented efficacy for acute B-lymphocytic leukaemia (B-ALL) and non-Hodgkin's lymphoma (NHL). In haematologic malignancies, tumour stem cells are more prone to stay in the regulatory bone marrow (BM) microenvironment (called niches), which provides a protective environment against immune attack. However, how the BM microenvironment affects the anti-tumour efficacy of CAR-T cells and its underlying mechanism is worthy of attention. In this review, we discuss the role of the BM microenvironment on the efficacy of CAR-T in haematological malignancies and propose corresponding strategies to enhance the anti-tumour activity of CAR-T therapy.

Current and potential roles of immuno-PET/-SPECT in CAR T-cell therapy

Chimeric antigen receptor (CAR) T-cell therapies have evolved as breakthrough treatment options for the management of hematological malignancies and are also being developed as therapeutics for solid tumors. However, despite the impressive patient responses from CD19-directed CAR T-cell therapies, ~ 40%-60% of these patients' cancers eventually relapse, with variable prognosis. Such relapses may occur due to a combination of molecular resistance mechanisms, including antigen loss or mutations, T-cell exhaustion, and progression of the immunosuppressive tumor microenvironment. This class of therapeutics is also associated with certain unique toxicities, such as cytokine release syndrome, immune effector cell-associated neurotoxicity syndrome, and other "on-target, off-tumor" toxicities, as well as anaphylactic effects. Furthermore, manufacturing limitations and challenges associated with solid tumor infiltration have delayed extensive applications. The molecular imaging modalities of immunological positron emission tomography and single-photon emission computed tomography (immuno-PET/-SPECT) offer a target-specific and highly sensitive, quantitative, non-invasive platform for longitudinal detection of dynamic variations in target antigen expression in the body. Leveraging these imaging strategies as guidance tools for use with CAR T-cell therapies may enable the timely identification of resistance mechanisms and/or toxic events when they occur, permitting effective therapeutic interventions. In addition, the utilization of these approaches in tracking the CAR T-cell pharmacokinetics during product development and optimization may help to assess their efficacy and accordingly to predict treatment outcomes. In this review, we focus on current challenges and potential opportunities in the application of immuno-PET/-SPECT imaging strategies to address the challenges encountered with CAR T-cell therapies.

mRNA-Lipid Nanoparticle (LNP) Delivery of Humanized EpCAM-CD3 Bispecific Antibody Significantly Blocks Colorectal Cancer Tumor Growth

The epithelial cell adhesion molecule (EpCAM) is often overexpressed in many types of tumors, including colorectal cancer. We sequenced and humanized an EpCAM mouse antibody and used it to develop bispecific EpCAM-CD3 antibodies. Three different designs were used to generate bispecific antibodies such as EpCAM-CD3 CrossMab knob-in-hole, EpCAM ScFv-CD3 ScFv (BITE), and EpCAM ScFv-CD3 ScFv-human Fc designs. These antibody designs showed strong and specific binding to the EpCAM-positive Lovo cell line and T cells, specifically killed EpCAM-positive Lovo cells and not EpCAM-negative Colo741 cells in the presence of T cells, and increased T cells' IFN-gamma secretion in a dose-dependent manner. In addition, transfection of HEK-293 cells with EpCAM ScFv-CD3 ScFv human Fc mRNA-LNPs resulted in antibody secretion that killed Lovo cells and did not kill EpCAM-negative Colo741 cells. The antibody increased IFN-gamma secretion against Lovo target cells and did not increase it against Colo741 target cells. EpCAM-CD3 hFc mRNA-LNP transfection of several cancer cell lines (A1847, C30, OVCAR-5) also demonstrated functional bispecific antibody secretion. In addition, intratumoral delivery of the EpCAM-CD3 human Fc mRNA-LNPs into OVCAR-5 tumor xenografts combined with intravenous injection of T cells significantly blocked xenograft tumor growth. Thus, EpCAM-CD3 hFc mRNA-LNP delivery to tumor cells shows strong potential for future clinical studies.

Cell Therapy as Target Therapy against Colon Cancer Stem Cells

Cancer stem cells (CSCs) are a small subpopulation of cells within tumors with properties, such as self-renewal, differentiation, and tumorigenicity. CSCs have been proposed as a plausible therapeutic target as they are responsible for tumor recurrence, metastasis, and conventional therapy resistance. Selectively targeting CSCs is a promising strategy to eliminate the propagation of tumor cells and impair overall tumor development. Recent research shows that several immune cells play a crucial role in regulating tumor cell proliferation by regulating different CSC maintenance or proliferation pathways. There have been great advances in cellular immunotherapy using T cells, natural killer (NK) cells, macrophages, or stem cells for the selective targeting of tumor cells or CSCs in colorectal cancer (CRC). This review summarizes the CRC molecular profiles that may benefit from said therapy and the main vehicles used in cell therapy against CSCs. We also discuss the challenges, limitations, and advantages of combining conventional and/or current targeted treatments in the late stages of CRC.

Hypoxia switches TET1 from being tumor-suppressive to oncogenic

The classical oxidizing enzymatic activity of Ten Eleven Translocation 1 (TET1) and its tumor suppressor role are well known. Here, we find that high TET1 expression is associated with poor patient survival in solid cancers often having hypoxia, which is inconsistent with its tumor suppressor role. Through a series of in vitro and in vivo studies, using thyroid cancer as a model, we demonstrate that TET1 plays a tumor suppressor function in normoxia and, surprisingly, an oncogenic function in hypoxia. Mechanistically, TET1 mediates HIF1α-p300 interaction by acting as a co-activator of HIF1α to promote CK2B transcription under hypoxia, which is independent of its enzymatic activity; CK2 activates the AKT/GSK3β signaling pathway to promote oncogenesis. Activated AKT/GSK3β signaling in turn maintains HIF1α at elevated levels by preventing its K48-linked ubiquitination and degradation, creating a feedback loop to enhance the oncogenicity of TET1 in hypoxia. Thus, this study uncovers a novel oncogenic mechanism in which TET1 promotes oncogenesis and cancer progression through a non-enzymatic interaction between TET1 and HIF1α in hypoxia, providing novel therapeutic targeting implications for cancer.

Radiotherapy as a means to increase the efficacy of T-cell therapy in solid tumors

Chimeric antigen receptor (CAR)-T cells have demonstrated significant improvements in the treatment of refractory B-cell malignancies that previously showed limited survival. In contrast, early-phase clinical studies targeting solid tumors have been disappointing. This may be due to both a lack of specific and homogeneously expressed targets at the surface of tumor cells, as well as intrinsic properties of the solid tumor microenvironment that limit homing and activation of adoptive T cells. Faced with these antagonistic conditions, radiotherapy (RT) has the potential to change the overall tumor landscape, from depleting tumor cells to reshaping the tumor microenvironment. In this article, we describe the current landscape and discuss how RT may play a pivotal role for enhancing the efficacy of adoptive T-cell therapies in solid tumors. Indeed, by improving homing, expansion and activation of infused T cells while reducing tumor volume and heterogeneity, the use of RT could help the implementation of engineered T cells in the treatment of solid tumors.

Engineering chimeric antigen receptor T cells for solid tumour therapy

Cell-based immunotherapy, for example, chimeric antigen receptor T (CAR-T) cell immunotherapy, has revolutionized cancer treatment, particularly for blood cancers. However, factors such as insufficient T cell tracking, tumour heterogeneity, inhibitory tumour microenvironment (TME) and T cell exhaustion limit the broad application of CAR-based immunotherapy for solid tumours. In particular, the TME is a complex and evolving entity, which is composed of cells of different types (e.g., cancer cells, immune cells and stromal cells), vasculature, soluble factors and extracellular matrix (ECM), with each component playing a critical role in CAR-T immunotherapy. Thus, developing approaches to mitigate the inhibitory TME factors is critical for future success in applying CAR-T cells for solid tumour treatment. Accordingly, understanding the bilateral interaction of CAR-T cells with the TME is in pressing need to pave the way for more efficient therapeutics. In the following review, we will discuss TME-associated aspects with an emphasis on T cell trafficking, ECM barriers, abnormal vasculature, solid tumour heterogenicity and immune suppressive microenvironment. We will then summarize current engineering strategies to overcome the challenges posed by the TME-associated factors. Lastly, the future directions for engineering efficient CAR-T cells for solid tumour therapy will be discussed.

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.

Remodelling of tumour microenvironment by microwave ablation potentiates immunotherapy of AXL-specific CAR T cells against non-small cell lung cancer

The complex immunosuppressive tumour microenvironment (TME) and lack of tumour-specific targets hinder the application of chimeric antigen receptor (CAR) T cells in the treatment of solid tumours. Combining local treatment with CAR T cell immunotherapy may regulate the TME and enhance the killing potency of CAR T cells in solid tumours. Here, we show that AXL, which is highly expressed in non-small cell lung cancer (NSCLC) but not in normal tissues, might be a target for CAR T cell therapy. AXL-CAR T cells alone cause moderate tumour regression in subcutaneous and pulmonary metastatic lung cancer cell-derived xenograft models. Combination of microwave ablation (MWA) and AXL-CAR T cells have superior antitumour efficacy. MWA enhances the activation, infiltration, persistence and tumour suppressive properties of AXL-CAR T cells in AXL-positive NSCLC patient-derived xenograft tumours via TME remodelling. The combination therapy increases the mitochondrial oxidative metabolism of tumour-infiltrating CAR T cells. Combination treatment induces significant tumour suppression without observed toxicities in humanized immunocompetent mice. The synergistic therapeutic effect of MWA and AXL-CAR T cells may be valuable for NSCLC treatment.

Advances and Hurdles in CAR T Cell Immune Therapy for Solid Tumors

Chimeric antigen receptor (CAR) T cells in solid tumors have so far yielded limited results, in terms of therapeutic effects, as compared to the dramatic results observed for hematological malignancies. Many factors involve both the tumor cells and the microenvironment. The lack of specific target antigens and severe, potentially fatal, toxicities caused by on-target off-tumor toxicities constitute major hurdles. Furthermore, the tumor microenvironment is usually characterized by chronic inflammation, the presence of immunosuppressive molecules, and immune cells that can reduce CAR T cell efficacy and facilitate antigen escape. Nonetheless, solid tumors are under investigation as possible targets despite their complexity, which represents a significant challenge. In preclinical mouse models, CAR T cells are able to efficiently recognize and kill several tumor xenografts. Overall, in the next few years, there will be intensive research into optimizing novel cell therapies to improve their effector functions and keep untoward effects in check. In this review, we provide an update on the state-of-the-art CAR T cell therapies in solid tumors, focusing on the preclinical studies and preliminary clinical findings aimed at developing optimal strategies to reduce toxicity and improve efficacy.

Targeting glycans for CAR therapy: The advent of sweet CARs

Chimeric antigen receptor (CAR) T cell therapy has created a paradigm shift in the treatment of hematologic malignancies but has not been as effective toward solid tumors. For such tumors, the primary obstacles facing CAR T cells are scarcity of tumor-specific antigens and the hostile and complex tumor microenvironment. Glycosylation, the process by which sugars are post-translationally added to proteins or lipids, is profoundly dysregulated in cancer. Abnormally glycosylated glycoproteins expressed on cancer cells offer unique targets for CAR T therapy as they are specific to tumor cells. Tumor stromal cells also express abnormal glycoproteins and thus also have the potential to be targeted by glycan-binding CAR T cells. This review will discuss the state of CAR T cells in the therapy of solid tumors, the cancer glycoproteome and its potential for use as a therapeutic target, and the landscape and future of glycan-binding CAR T cell therapy.

Road testing new CAR design strategies in multiple myeloma

A deeper understanding of basic immunology principles and advances in bioengineering have accelerated the mass production of genetically-reprogrammed T-cells as living drugs to treat human diseases. Autologous and allogeneic cytotoxic T-cells have been weaponized to brandish MHC-independent chimeric antigen receptors (CAR) that specifically engage antigenic regions on tumor cells. Two distinct CAR-based therapeutics designed to target BCMA are now FDA-approved based upon robust, sustained responses in heavily-pretreated multiple myeloma (MM) patients enrolled on the KarMMa and CARTITUDE-1 studies. While promising, CAR T-cells present unique challenges such as antigen escape and T-cell exhaustion. Here, we review novel strategies to design CARs that overcome current limitations. Co-stimulatory signaling regions were added to second-generation CARs to promote IL-2 synthesis, activate T-cells and preclude apoptosis. Third-generation CARs are composed of multiple co-stimulatory signaling units, e.g., CD28, OX40, 4-1BB, to reduce exhaustion. Typically, CAR T-cells incorporate a potent constitutive promoter that maximizes long-term CAR expression but extended CAR activation may also promote T-cell exhaustion. Hypoxia-inducible elements can be incorporated to conditionally drive CAR expression and selectively target MM cells within bone marrow. CAR T-cell survival and activity is further realized by blocking intrinsic regulators of T-cell inactivation. T-Cells Redirected for Universal Cytokine Killing (TRUCKs) bind a specific tumor antigen and produce cytokines to recruit endogenous immune cells. Suicide genes have been engineered into CAR T-cells given the potential for long-term on-target, off-tumor effects. Universal allo-CAR T-cells represent an off-the-shelf source, while logic-gated CAR T-cells are designed to recognize tumor-specific features coupled with Boolean-generated binary gates that then dictate cell-fate decisions. Future generations of CARs should further revitalize immune responses, enhance tumor specificity and reimagine strategies to treat myeloma and other cancers.

Advances and challenges of CAR T therapy and suitability of animal models (Review)

Chimeric antigen receptors (CARs) recently gained momentum in cancer treatment due to their ability to promote T-cell mediated responses to a specific tumor-associated antigen. CARs are part of the adoptive cell transfer (ACT) strategies that utilize patients' T lymphocytes, genetically engineered to kill cancer cells. However, despite the therapy's success against blood-related malignancies, treating solid tumors has not reached its fullest potential yet. The reasons include the complex suppressive tumor microenvironment, mutations on cancer cells' target receptors, lethal side-effects, restricted trafficking into the tumor, suboptimal persistence in vivo and the lack of animal models that faithfully resemble human tumor's immunological responses. Currently, rodent models are used to investigate the safety and efficacy of CAR therapies. However, these models are limited in representing the human disease faithfully, fail to predict the adverse treatment events and overestimate the efficacy of the therapy. On the other hand, spontaneously developed tumors in dogs are more suited in CAR research and their efficacy has been demonstrated in a number of diseases, including lymphoma, osteosarcoma and mammary tumors. The present review discusses the design and evolution of CARs, challenges of CAR in solid tumors, human and canine clinical trials and advantages of the canine model.

CAR T Cell Locomotion in Solid Tumor Microenvironment

The promising outcomes of chimeric antigen receptor (CAR) T cell therapy in hematologic malignancies potentiates its capability in the fight against many cancers. Nevertheless, this immunotherapy modality needs significant improvements for the treatment of solid tumors. Researchers have incrementally identified limitations and constantly pursued better CAR designs. However, even if CAR T cells are armed with optimal killer functions, they must overcome and survive suppressive barriers imposed by the tumor microenvironment (TME). In this review, we will discuss in detail the important role of TME in CAR T cell trafficking and how the intrinsic barriers contribute to an immunosuppressive phenotype and cancer progression. It is of critical importance that preclinical models can closely recapitulate the in vivo TME to better predict CAR T activity. Animal models have contributed immensely to our understanding of human diseases, but the intensive care for the animals and unreliable representation of human biology suggest in vivo models cannot be the sole approach to CAR T cell therapy. On the other hand, in vitro models for CAR T cytotoxic assessment offer valuable insights to mechanistic studies at the single cell level, but they often lack in vivo complexities, inter-individual heterogeneity, or physiologically relevant spatial dimension. Understanding the advantages and limitations of preclinical models and their applications would enable more reliable prediction of better clinical outcomes.

Engineering Next-Generation CAR-T Cells: Overcoming Tumor Hypoxia and Metabolism

T cells engineered to express chimeric antigen receptors (CARs) have shown remarkable success in treating B-cell malignancies, reflected by multiple US Food and Drug Administration-approved CAR-T cell products currently on the market. However, various obstacles have thus far limited the use of approved products and constrained the efficacy of CAR-T cell therapy against solid tumors. Overcoming these obstacles will necessitate multidimensional CAR-T cell engineering approaches and better understanding of the intricate tumor microenvironment (TME). Key challenges include treatment-related toxicity, antigen escape and heterogeneity, and the highly immunosuppressive profile of the TME. Notably, the hypoxic and nutrient-deprived nature of the TME severely attenuates CAR-T cell fitness and efficacy, highlighting the need for more sophisticated engineering strategies. In this review, we examine recent advances in protein- and cell-engineering strategies to improve CAR-T cell safety and efficacy, with an emphasis on overcoming immunosuppression induced by tumor metabolism and hypoxia.

Hypoxia-inducible lentiviral gene expression in engineered human macrophages

Background

Human immune cells, including monocyte-derived macrophages, can be engineered to deliver proinflammatory cytokines, bispecific antibodies, and chimeric antigen receptors to support immune responses in different disease settings. When gene expression is regulated by constitutively active promoters, lentiviral payload gene expression is unregulated, and can result in potentially toxic quantities of proteins. Regulated delivery of lentivirally encoded proteins may allow localized or conditional therapeutic protein expression to support safe delivery of adoptively transferred, genetically modified cells with reduced capacity for systemic toxicities.

Methods

In this study, we engineered human macrophages to express genes regulated by hypoxia responsive elements included in the lentiviral promoter region to drive conditional lentiviral gene expression only under hypoxic conditions. We tested transduced macrophages cultured in hypoxic conditions for the transient induced expression of reporter genes and the secreted cytokine, interleukin-12. Expression of hypoxia-regulated genes was investigated both transcriptionally and translationally, and in the presence of human tumor cells in a slice culture system. Finally, hypoxia-regulated gene expression was evaluated in a subcutaneous humanized-mouse cancer model.

Results

Engineered macrophages were shown to conditionally and tranisently express lentivirally encoded gene protein products, including IL-12 in hypoxic conditions in vitro. On return to normoxic conditions, lentiviral payload expression returned to basal levels. Reporter genes under the control of hypoxia response elements were upregulated under hypoxic conditions in the presence of human colorectal carcinoma cells and in the hypoxic xenograft model of glioblastoma, suggesting utility for systemic engineered cell delivery capable of localized gene delivery in cancer.

Conclusions

Macrophages engineered to express hypoxia-regulated payloads have the potential to be administered systemically and conditionally express proteins in tissues with hypoxic conditions. In contrast to immune cells that function or survive poorly in hypoxic conditions, macrophages maintain a proinflammatory phenotype that may support continued gene and protein expression when regulated by conditional hypoxia responsive elements and naturally traffic to hypoxic microenvironments, making them ideal vehicles for therapeutic payloads to hypoxic tissues, such as solid tumors. With the ability to fine-tune delivery of potent proteins in response to endogenous microenvironments, macrophage-based cellular therapies may therefore be designed for different disease settings.

Bispecific BCMA-CD3 Antibodies Block Multiple Myeloma Tumor Growth

BCMA antigen is overexpressed in multiple myeloma cells and has been shown to be a promising target for novel cellular and antibody therapeutics. The humanized BCMA (clone 4C8A) antibody that effectively targeted multiple myeloma in a CAR (chimeric antigen receptor) format was used for designing several formats of bispecific BCMA-CD3 antibodies. Several different designs of univalent and bivalent humanized BCMA-CD3 CrossMAB and BCMA-FAB-CD3 ScFv-Fc antibodies were tested for binding with BCMA-positive cells and T cells and for killing by real time cytotoxic activity and IFN-gamma secretion with CHO-BCMA target cells and with multiple myeloma MM1S and H929 cell lines. All BCMA-CD3 antibodies demonstrated specific binding by FACS to CHO-BCMA, multiple myeloma cells, and to T cells with affinity Kd in the nM range. All antibodies with T cells specifically killed CHO-BCMA and multiple myeloma cells in a dose-dependent manner. The BCMA-CD3 antibodies with T cells secreted IFN-gamma with EC50 in the nM range. In addition, three BCMA bispecific antibodies had high in vivo efficacy using an MM1S xenograft NSG mouse model. The data demonstrate the high efficacy of novel hBCMA-CD3 antibodies with multiple myeloma cells and provide a basis for future pre-clinical and clinical development.

Challenges to the broad application of allogeneic natural killer cell immunotherapy of cancer

Natural killer (NK) cells are innate immune cells that recognize malignant cells through a wide array of germline-encoded receptors. Triggering of activating receptors results in cytotoxicity and broad immune system activation. The former is achieved through release of cytotoxic granules and presentation of death receptor ligands, while the latter is mediated by inflammatory cytokines, such as interferon-γ and tumor necrosis factor α. Early success with ex vivo activation of NK cells and adoptive transfer suggest they are a safe therapeutic with promising responses in advanced hematologic malignancies. In particular, adoptive NK cell therapies can serve as a 'bridge' to potentially curative allogeneic stem cell transplantation. In addition, strategies are being developed that expand large numbers of cells from limited starting material and mature NK cells from precursors. Together, these make 'off-the-shelf' NK cells possible to treat a wide range of cancers. Research efforts have focused on creating a range of tools that increase targeting of therapeutic NK cells toward cancer-from therapeutic antibodies that drive antibody-dependent cellular cytotoxicity, to chimeric antigen receptors. As these novel therapies start to show promise in clinical trials, the field is rapidly moving toward addressing other challenges that limit NK cell therapeutics and the goal to treat solid tumors. This review describes the state of therapeutic NK cell targeting of tumors; discusses the challenges that need to be addressed before NK cells can be applied as a wide-ranging treatment for cancer; and points to some of the innovations that are being developed to surmount these challenges. Suppressive cells in the tumor microenvironment pose a direct threat to therapeutic NK cells, through presentation of inhibitory ligands and secretion of suppressive cytokines and metabolites. The nutrient- and oxygen-starved conditions under which NK cells must function necessitate an understanding of therapeutic NK cell metabolism that is still emerging. Prior to these challenges, NK cells must find their way into and persist in the tumor itself. Finally, the desirability of a 'single-shot' NK cell treatment and the problems and benefits of a short-lived rejection-prone NK cellular product are discussed.

Targeting Type I Collagen for Cancer Treatment

Collagen is the most abundant protein in animals. Interactions between tumor cells and collagen influence every step of tumor development. Type I collagen is the main fibrillar collagen in the extracellular matrix and is frequently up-regulated during tumorigenesis. The binding of type I collagen to its receptors on tumor cells promotes tumor cell proliferation, epithelial-mesenchymal transition, and metastasis. Type I collagen also regulates the efficacy of tumor therapies, such as chemotherapy, radiotherapy, and immunotherapy. Furthermore, type I collagen fragments are diagnostic markers of metastatic tumors and have prognostic value. Inhibition of type I collagen synthesis has been reported to have anti-tumor effects in animal models. However, collagen has also been shown to possess anti-tumor activity. Therefore, the roles that type I collagen plays in tumor biology are complex and tumor type-dependent. In this review, we discuss the expression and regulation of synthesis of type I collagen, as well as the role up-regulated type I collagen plays in various stages of cancer progression. We also discuss the role of collagen in tumor therapy. Finally, we highlight several recent approaches targeting type I collagen for cancer treatment. This article is protected by copyright. All rights reserved.

Multifaceted Interplay between Hormones, Growth Factors and Hypoxia in the Tumor Microenvironment

Hormones and growth factors (GFs) are signaling molecules implicated in the regulation of a variety of cellular processes. They play important roles in both healthy and tumor cells, where they function by binding to specific receptors on target cells and activating downstream signaling cascades. The stages of tumor progression are influenced by hormones and GF signaling. Hypoxia, a hallmark of cancer progression, contributes to tumor plasticity and heterogeneity. Most solid tumors contain a hypoxic core due to rapid cellular proliferation that outgrows the blood supply. In these circumstances, hypoxia-inducible factors (HIFs) play a central role in the adaptation of tumor cells to their new environment, dramatically reshaping their transcriptional profile. HIF signaling is modulated by a variety of factors including hormones and GFs, which activate signaling pathways that enhance tumor growth and metastatic potential and impair responses to therapy. In this review, we summarize the role of hormones and GFs during cancer onset and progression with a particular focus on hypoxia and the interplay with HIF proteins. We also discuss how hypoxia influences the efficacy of cancer immunotherapy, considering that a hypoxic environment may act as a determinant of the immune-excluded phenotype and a major hindrance to the success of adoptive cell therapies.

Addressing the obstacles of CAR T cell migration in solid tumors: wishing a heavy traffic

Chimeric antigen receptor T cell (CAR-T) therapy has been recognized as one of the most prosperous treatment options against certain blood-based malignancies. However, the same clinical and commercial success have been out of range in the case of solid tumors. The main contributing factor in this regard is the hostile environment the tumor cells impose that results in the exhaustion of immune effector cells alongside the abrogation of their infiltration capacity. The discovery of the underlying mechanisms and the development of reliable counterstrategies to overcome the inaccessibility of CAR-Ts to their target cells might correlate with encouraging clinical outcomes in advanced solid tumors. Here, we highlight the successive physical and metabolic barriers that systemically administered CAR-Ts face on their journey toward their target cells. Moreover, we propose meticulously-devised countertactics and combination therapies that can be applied to maximize the therapeutic benefits of CAR-T therapies against solid tumors.

Editorial on Special Issue “Immunotherapy, Tumor Microenvironment and Survival Signaling”

Recently, novel types of immunotherapies such as CAR-T cell therapy demonstrated efficacy in leukemia, lymphoma, and multiple myeloma [...]

Hypoxia as a driver of resistance to immunotherapy

Hypoxia, a hallmark of solid tumors, determines the selection of invasive and aggressive malignant clones displaying resistance to radiotherapy, conventional chemotherapy or targeted therapy. The recent introduction of immunotherapy, based on immune checkpoint inhibitors (ICPIs) and chimeric antigen receptor (CAR) T-cells, has markedly transformed the prognosis in some tumors but also revealed the existence of intrinsic or acquired drug resistance. In the current review we highlight hypoxia as a culprit of immunotherapy failure. Indeed, multiple metabolic cross talks between tumor and stromal cells determine the prevalence of immunosuppressive populations within the hypoxic tumor microenvironment and confer upon tumor cells resistance to ICPIs and CAR T-cells. Notably, hypoxia-triggered angiogenesis causes immunosuppression, adding another piece to the puzzle of hypoxia-induced immunoresistance. If these factors concurrently contribute to the resistance to immunotherapy, they also unveil an unexpected Achille's heel of hypoxic tumors, providing the basis for innovative combination therapies that may rescue the efficacy of ICPIs and CAR T-cells. Although these treatments reveal both a bright side and a dark side in terms of efficacy and safety in clinical trials, they represent the future solution to enhance the efficacy of immunotherapy against hypoxic and therapy-resistant solid tumors.

CAR T cell therapy in solid tumors; with an extensive focus on obstacles and strategies to overcome the challenges

The application of the CAR T cell therapy in hematologic malignancies holds prosperous results that intensified the unprecedented enthusiasm to employ this fascinating strategy in other types of human malignancies. Although the researchers invested a great deal of effort to exploit the utmost efficacy of these cells in the context of solid tumors, few articles reviewed obstacles and opportunities. The current review aims to provide comprehensive literature of recent advances of CAR T cell therapy in a wide range of solid tumors; and also, to discuss the original data obtained from international research laboratories on this topic. Despite promising results, several radical obstacles are on the way of this approach. This review discusses the most important drawbacks and also responds to questions on how the intrinsic features of solid tumors in addition to the tumor microenvironment-related challenges and the immune-relating adverse effects can curb satisfactory outcomes of CAR T cells. The last section allocates a special focus on innovative and contemporary policies which have already been adopted to surmount these challenges. Finally, we comment on the future research aspects in which the efficacy, as well as the safety of CAR T cell therapy, might be improved.

Improved Immunotherapy Efficacy by Vascular Modulation

Several strategies have been developed to modulate the tumour vasculature for cancer therapy including anti-angiogenesis and vascular normalisation. Vasculature modulation results in changes to the tumour microenvironment including oxygenation and immune cell infiltration, therefore lending itself to combination with cancer therapy. The development of immunotherapies has led to significant improvements in cancer treatment. Particularly promising are immune checkpoint blockade and CAR T cell therapies, which use antibodies against negative regulators of T cell activation and T cells reprogrammed to better target tumour antigens, respectively. However, while immunotherapy is successful in some patients, including those with advanced or metastatic cancers, only a subset of patients respond. Therefore, better predictors of patient response and methods to overcome resistance warrant investigation. Poor, or periphery-limited, T cell infiltration in the tumour is associated with poor responses to immunotherapy. Given that (1) lymphocyte recruitment requires leucocyte-endothelial cell adhesion and (2) the vasculature controls tumour oxygenation and plays a pivotal role in T cell infiltration and activation, vessel targeting strategies including anti-angiogenesis and vascular normalisation in combination with immunotherapy are providing possible new strategies to enhance therapy. Here, we review the progress of vessel modulation in enhancing immunotherapy efficacy.

Engineered in vitro tumor models for cell-based immunotherapy

Tumor immunotherapy is rapidly evolving as one of the major pillars of cancer treatment. Cell-based immunotherapies, which utilize patient's own immune cells to eliminate cancer cells, have shown great promise in treating a range of malignancies, especially those of hematopoietic origins. However, their performance on a broader spectrum of solid tumor types still fall short of expectations in the clinical stage despite promising preclinical assessments. In this review, we briefly introduce cell-based immunotherapies and the inhibitory mechanisms in tumor microenvironments that may have contributed to this discrepancy. Specifically, a major obstacle to the clinical translation of cell-based immunotherapies is in the lack of preclinical models that can accurately assess the efficacies and mechanisms of these therapies in a (patho-)physiologically relevant manner. Lately, tissue engineering and organ-on-a-chip tools and microphysiological models have allowed for more faithful recapitulation of the tumor microenvironments, by incorporating crucial tumor tissue features such as cellular phenotypes, tissue architecture, extracellular matrix, physical parameters, and their dynamic interactions. This review summarizes the existing engineered tumor models with a focus on tumor immunology and cell-based immunotherapy. We also discuss some key considerations for the future development of engineered tumor models for immunotherapeutics. STATEMENT OF SIGNIFICANCE: Cell-based immunotherapies have shown great promise in treating hematological malignancies and some epithelial tumors. However, their performance on a broader spectrum of solid tumor types still fall short of expectations. Major obstacles include the inhibitory mechanisms in tumor microenvironments (TME) and the lack of preclinical models that can accurately assess the efficacies and mechanisms of cellular therapies in a (patho-)physiologically relevant manner. In this review, we introduce recent progress in tissue engineering and microphysiological models for more faithful recapitulation of TME for cell-based immunotherapies, and some key considerations for the future development of engineered tumor models. This overview will provide a better understanding on the role of engineered models in accelerating immunotherapeutic discoveries and clinical translations.

Stem cell-like memory T cells: The generation and application

Stem cell-like memory T cells (Tscm), are a newly defined memory T cell subset with characteristics of long life span, consistent self-renewing, rapid differentiation into effector T cells, and apoptosis resistance. These features indicate that Tscm have great therapeutic or preventive purposes, including being applied in chimeric Ag receptor-engineered T cells, TCR gene-modified T cells, and vaccines. However, the little knowledge about Tscm development restrains their applications. Strength and duration of TCR signaling, cytokines and metabolism in the T cells during activation all influence the Tscm development via regulating transcriptional factors and cell signaling pathways. Here, we summarize the molecular and cellular pathways involving Tscm differentiation, and its clinical application for cancer immunotherapy and prevention.

Radiotherapy to Enhance Chimeric Antigen Receptor T-Cell Therapeutic Efficacy in Solid Tumors: A Narrative Review

Importance

Immunotherapy has emerged as a new pillar of cancer therapy over the past decade. Adoptive immunotherapy in particular has become a major area of research interest, with advances seen in the development of T-cell engineering. As a result, chimeric antigen receptor (CAR) T-cell therapy has become a new and highly effective treatment option, especially for patients with refractory or resistant blood cell cancers. However, CAR T-cell therapy has shown limited efficacy for the treatment of solid tumors thus far.

Observations

Combinatorial treatment approaches, such as addition of radiotherapy to CAR T cells, may provide a strategy to prevent resistance to CAR T-cell therapy of solid tumors. These approaches need to overcome obstacles that include abnormal vessels and adhesion molecule expression on tumor vasculature, leading to reduced transmigration of effector immune cells, including CAR T cells, and immunosuppressive cues in the tumor microenvironment, including regional hypoxia.

Conclusions and Relevance

This review provides an overview of the current developments in CAR T-cell therapy and highlights the unique opportunities and challenges in combining CAR T-cell therapy with radiotherapy.

Obstacles and Coping Strategies of CAR-T Cell Immunotherapy in Solid Tumors

Chimeric antigen receptor (CAR) T-cell immunotherapy refers to an adoptive immunotherapy that has rapidly developed in recent years. It is a novel type of treatment that enables T cells to express specific CARs on their surface, then returns these T cells to tumor patients to kill the corresponding tumor cells. Significant strides in CAR-T cell immunotherapy against hematologic malignancies have elicited research interest among scholars in the treatment of solid tumors. Nonetheless, in contrast with the efficacy of CAR-T cell immunotherapy in the treatment of hematologic malignancies, its general efficacy against solid tumors is insignificant. This has been attributed to the complex biological characteristics of solid tumors. CAR-T cells play a better role in solid tumors, for instance by addressing obstacles including the lack of specific targets, inhibition of tumor microenvironment (TME), homing barriers of CAR-T cells, differentiation and depletion of CAR-T cells, inhibition of immune checkpoints, trogocytosis of CAR-T cells, tumor antigen heterogeneity, etc. This paper reviews the obstacles influencing the efficacy of CAR-T cell immunotherapy in solid tumors, their mechanism, and coping strategies, as well as economic restriction of CAR-T cell immunotherapy and its solutions. It aims to provide some references for researchers to better overcome the obstacles that affect the efficacy of CAR-T cells in solid tumors.

Metabolic barriers to cancer immunotherapy

Several non-redundant features of the tumour microenvironment facilitate immunosuppression and limit anticancer immune responses. These include physical barriers to immune infiltration, the recruitment of suppressive immune cells and the upregulation of ligands on tumour cells that bind to inhibitory receptors on immune cells. Recent insights into the importance of the metabolic restrictions imposed by the tumour microenvironment on antitumour T cells have begun to inform immunotherapeutic anticancer strategies. Therapeutics that target metabolic restrictions, such as low glucose levels, a low pH, hypoxia and the generation of suppressive metabolites, have shown promise as combination therapies for different types of cancer. In this Review, we discuss the metabolic aspects of the antitumour T cell response in the context of immune checkpoint blockade, adoptive cell therapy and treatment with oncolytic viruses, and discuss emerging combination strategies.

CAR-T in Cancer Treatment: Develop in Self-Optimization, Win-Win in Cooperation

Simple Summary

Chimeric antigen receptor (CAR)-T cell therapy has exhibited good application prospects in the treatment of hematologic malignancies. However, there are still many unsolved problems, such as the limited antitumor effect of CAR-T on solid tumors and the potential risk of CAR-T therapy in clinical applications. In order to meet these challenges, more and more solutions are proposed. Therefore, in this review, we have discussed the recent breakthroughs in CAR-T therapy for cancer treatment, with an emphasis on the potentially effective CAR-T modifications and combined strategies.

Abstract

Despite remarkable achievements in the treatment of hematologic malignancies, chimeric antigen receptor (CAR)-T cell therapy still faces many obstacles. The limited antitumor activity and persistence of infused CAR-T cells, especially in solid tumors, are the main limiting factors for CAR-T therapy. Moreover, clinical security and accessibility are important unmet needs for the application of CAR-T therapy. In view of these challenges, many potentially effective solutions have been proposed and confirmed. Both the independent and combined strategies of CAR-T therapy have exhibited good application prospects. Thus, in this review, we have discussed the cutting-edge breakthroughs in CAR-T therapy for cancer treatment, with the aim of providing a reference for addressing the current challenges.

Fine-Tuning the Tumour Microenvironment: Current Perspectives on the Mechanisms of Tumour Immunosuppression

Immunotherapy has revolutionised the treatment of cancers by harnessing the power of the immune system to eradicate malignant tissue. However, it is well recognised that some cancers are highly resistant to these therapies, which is in part attributed to the immunosuppressive landscape of the tumour microenvironment (TME). The contexture of the TME is highly heterogeneous and contains a complex architecture of immune, stromal, vascular and tumour cells in addition to acellular components such as the extracellular matrix. While understanding the dynamics of the TME has been instrumental in predicting durable responses to immunotherapy and developing new treatment strategies, recent evidence challenges the fundamental paradigms of how tumours can effectively subvert immunosurveillance. Here, we discuss the various immunosuppressive features of the TME and how fine-tuning these mechanisms, rather than ablating them completely, may result in a more comprehensive and balanced anti-tumour response.

Manipulating the Metabolism to Improve the Efficacy of CAR T-Cell Immunotherapy

The adoptive transfer of the chimeric antigen receptor (CAR) expressing T-cells has produced unprecedented successful results in the treatment of B-cell malignancies. However, the use of this technology in other malignancies remains less effective. In the setting of solid neoplasms, CAR T-cell metabolic fitness needs to be optimal to reach the tumor and execute their cytolytic function in an environment often hostile. It is now well established that both tumor and T cell metabolisms play critical roles in controlling the immune response by conditioning the tumor microenvironment and the fate and activity of the T cells. In this review, after a brief description of the tumoral and T cell metabolic reprogramming, we summarize the latest advances and new strategies that have been developed to improve the metabolic fitness and efficacy of CAR T-cell products.

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.

CAR-T TREK through the lymphoma universe, to boldly go where no other therapy has gone before

Chimeric antigen receptor (CAR) T cells (CART) therapies have changed and continue to change the treatment paradigms for B-cell malignancies because they can achieve durable complete remission in patients in whom multiple lines of treatment have failed. These unprecedented results have led to the widespread use of anti-CD19 CART therapy for patients with relapsed and refractory aggressive large B-cell lymphomas. While long-term follow-up data show that about one-third of patients achieve prolonged complete remission and are potentially cured, the majority of patients either do not respond to CD19 CART therapy or eventually relapse after CD19 CART therapy. These results are, on the one hand, driving intense research into identifying mechanisms of relapse and, on the other hand, inspiring the development of novel strategies to overcome resistance. This review summarizes current clinical outcomes of CART immunotherapy in B-cell non-Hodgkin lymphomas, describes the most up-to-date understanding of mechanisms of relapse and discusses novel strategies to address resistance to CART therapy. We are indeed at the beginning of a scientific trek to explore the mechanisms of resistance, seek out new, more effective treatment approaches based on these discoveries and to boldly go where no other therapy has gone before!