Armored BCMA CAR T Cells Eliminate Multiple Myeloma and Are Resistant to the Suppressive Effects of TGF-β

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.

Rediscovering hemostasis abnormalities in multiple myeloma: The new era

Multiple myeloma (MM) is a malignancy arisen from the abnormal proliferation of clonal plasma cells. It has a high risk of developing bleeding and thrombotic complications, which are related to poor prognosis and decreased survival. Multiple factors are involved in the breaking of the hemostasis balance, including disease specific factors, patient-specific factors, and drug factors that change pro-and anticoagulant and fibrinolysis. Recently, with the introduction of new treatments such as monoclonal antibodies, chimeric antigen receptor modified T-cell therapy, antibody-drug conjugates directed against BCMA, programmed death-1 inhibitor, export protein 1 inhibitors, histone deacetylase inhibitors, immunomodulatory drugs, proteasome inhibitors and Bcl-2 inhibitors, the therapy of MM patients has entered into a new era. Furthermore, it arouses a question whether these new treatments would alter the hemostasis balance in MM patients, which highlights the importance of the underlying pathophysiology of hemostasis abnormalities in MM, and on prophylaxis approaches. In this review, we updated the mechanisms of hemostasis abnormalities in MM, the impact of the new drugs on hemostasis balance and reliable therapeutic strategies.

CD4+ CAR T-cell exhaustion associated with early relapse of multiple myeloma after BCMA CAR T-cell therapy

ABSTRACT

Multiple myeloma is characterized by frequent clinical relapses after conventional therapy. Recently, chimeric antigen receptor (CAR) T cells targeting B-cell maturation antigen (BCMA) has been established as a treatment option for patients with relapsed or refractory disease. However, although >70% of patients initially respond to this treatment, clinical relapse and disease progression occur in most cases. Recent studies showed persistent expression of BCMA at the time of relapse, indicating that immune-intrinsic mechanisms may contribute to this resistance. Although there were no preexisting T-cell features associated with clinical outcomes, we found that patients with a durable response to CAR T-cell treatment had greater persistence of their CAR T cells than patients with transient clinical responses. They also possessed a significantly higher proportion of CD8+ T-effector memory cells. In contrast, patients with short-lived responses to treatment have increased frequencies of cytotoxic CD4+ CAR T cells. These cells expand in vivo early after infusion but express exhaustion markers (hepatitis A virus cellular receptor 2 [HAVCR2] and T-cell immunoglobulin and mucin domain-containing-3 [TIGIT]) and remain polyclonal. Finally, we demonstrate that nonclassical monocytes are enriched in the myeloma niche and may induce CAR T-cell dysfunction through mechanisms that include transforming growth factor β. These findings shed new light on the role of cytotoxic CD4+ T cells in disease progression after CAR T-cell therapy.

Charting the Course: Sequencing Immunotherapy for Multiple Myeloma

Multiple chimeric antigen receptor (CAR) T-cell and bispecific antibody (bsAb) therapies have been approved, demonstrating impressive clinical efficacy in relapsed/refractory multiple myeloma (MM). Currently, these treatment share overlapping approval indications in the relapsed/refractory space, highlighting the importance of optimal selection and sequencing to maximize clinical efficacy. For patients previously unexposed to T-cell-directed therapies, several factors should be weighed when both options are available. These factors include access and logistical challenges associated with CAR T-cell therapy, disease-specific factors such as tempo of disease relapse, in addition to patient-specific factors such as frailty, and distinct toxicity profiles across these agents. Sequential therapy, whether it involves CAR T-cell therapy followed by bsAb or vice versa, has demonstrated clinical efficacy. When sequencing these agents, it is crucial to consider various factors that contribute to treatment resistance with careful selection of treatments for subsequent therapy in order to achieve favorable long-term patient outcomes.

CAR T therapies in multiple myeloma: unleashing the future

In recent years, the field of cancer treatment has witnessed remarkable breakthroughs that have revolutionized the landscape of care for cancer patients. While traditional pillars such as surgery, chemotherapy, and radiation therapy have long been available, a cutting-edge therapeutic approach called CAR T-cell therapy has emerged as a game-changer in treating multiple myeloma (MM). This novel treatment method complements options like autologous stem cell transplants and immunomodulatory medications, such as proteasome inhibitors, by utilizing protein complexes or anti-CD38 antibodies with potent complement-dependent cytotoxic effects. Despite the challenges and obstacles associated with these treatments, the recent approval of the second FDA multiple myeloma CAR T-cell therapy has sparked immense promise in the field. Thus far, the results indicate its potential as a highly effective therapeutic solution. Moreover, ongoing preclinical and clinical trials are exploring the capabilities of CAR T-cells in targeting specific antigens on myeloma cells, offering hope for patients with relapsed/refractory MM (RRMM). These advancements have shown the potential for CAR T cell-based medicines or combination therapies to elicit greater treatment responses and minimize side effects. In this context, it is crucial to delve into the history and functions of CAR T-cells while acknowledging their limitations. We can strategize and develop innovative approaches to overcome these barriers by understanding their challenges. This article aims to provide insights into the application of CAR T-cells in treating MM, shedding light on their potential, limitations, and strategies employed to enhance their efficacy.

Armored TGFβRIIDN ROR1-CAR T cells reject solid tumors and resist suppression by constitutively-expressed and treatment-induced TGFβ1

BACKGROUND

Chimeric antigen receptor (CAR) T-cell therapy target receptor tyrosine kinase-like orphan receptor 1 (ROR1) is broadly expressed in hematologic and solid tumors, however clinically-characterized ROR1-CAR T cells with single chain variable fragment (scFv)-R12 targeting domain failed to induce durable remissions, in part due to the immunosuppressive tumor microenvironment (TME). Herein, we describe the development of an improved ROR1-CAR with a novel, fully human scFv9 targeting domain, and augmented with TGFβRIIDN armor protective against a major TME factor, transforming growth factor beta (TGFβ).

METHODS

CAR T cells were generated by lentiviral transduction of enriched CD4+ and CD8+ T cells, and the novel scFv9-based ROR1-CAR-1 was compared with the clinically-characterized ROR1-R12-scFv-based CAR-2 in vitro and in vivo.

RESULTS

CAR-1 T cells exhibited greater CAR surface density than CAR-2 when normalized for %CAR+, and produced more interferon (IFN)-γ tumor necrosis factor (TNF)-α and interleukin (IL)-2 in response to hematologic (Jeko-1, RPMI-8226) and solid (OVCAR-3, Capan-2, NCI-H226) tumor cell lines in vitro. In vivo, CAR-1 and CAR-2 both cleared hematologic Jeko-1 lymphoma xenografts, however only CAR-1 fully rejected ovarian solid OVCAR-3 tumors, concordantly with greater expansion of CD8+ and CD4+CAR T cells, and enrichment for central and effector memory phenotype. When equipped with TGFβ-protective armor TGFβRIIDN, CAR-1 T cells resisted TGFβ-mediated pSmad2/3 phosphorylation, as compared with CAR-1 alone. When co-cultured with ROR-1+ AsPC-1 pancreatic cancer line in the presence of TGFβ1, armored CAR-1 demonstrated improved recovery of killing function, IFN-γ, TNF-α and IL-2 secretion. In mouse AsPC-1 pancreatic tumor xenografts overexpressing TGFβ1, armored CAR-1, in contrast to CAR-1 alone, achieved complete tumor remissions, and yielded accelerated expansion of CAR+ T cells, diminished circulating active TGFβ1, and no apparent toxicity or weight loss. Unexpectedly, in AsPC-1 xenografts without TGFβ overexpression, TGFβ1 production was specifically induced by ROR-1-CAR T cells interaction with ROR-1 positive tumor cells, and the TGFβRIIDN armor conferred accelerated tumor clearance.

CONCLUSIONS

The novel fully human TGFßRIIDN-armored ROR1-CAR-1 T cells are highly potent against ROR1-positive tumors, and withstand the inhibitory effects of TGFß in solid TME. Moreover, TGFβ1 induction represents a novel, CAR-induced checkpoint in the solid TME, which can be circumvented by co-expressing the TGβRIIDN armor on T cells.

Exploiting the CD200-CD200R immune checkpoint axis in multiple myeloma to enhance CAR T-cell therapy

ABSTRACT

Patients with multiple myeloma (MM) treated with B-cell maturation antigen (BCMA)-specific chimeric antigen receptor (CAR) T cells usually relapse with BCMA+ disease, indicative of CAR T-cell suppression. CD200 is an immune checkpoint that is overexpressed on aberrant plasma cells (aPCs) in MM and is an independent negative prognostic factor for survival. However, CD200 is not present on MM cell lines, a potential limitation of current preclinical models. We engineered MM cell lines to express CD200 at levels equivalent to those found on aPCs in MM and show that these are sufficient to suppress clinical-stage CAR T-cells targeting BCMA or the Tn glycoform of mucin 1 (TnMUC1), costimulated by 4-1BB and CD2, respectively. To prevent CD200-mediated suppression of CAR T cells, we compared CRISPR-Cas9-mediated knockout of the CD200 receptor (CD200RKO), to coexpression of versions of the CD200 receptor that were nonsignaling, that is, dominant negative (CD200RDN), or that leveraged the CD200 signal to provide CD28 costimulation (CD200R-CD28 switch). We found that the CD200R-CD28 switch potently enhanced the polyfunctionality of CAR T cells, and improved cytotoxicity, proliferative capacity, CAR T-cell metabolism, and performance in a chronic antigen exposure assay. CD200RDN provided modest benefits, but surprisingly, the CD200RKO was detrimental to CAR T-cell activity, adversely affecting CAR T-cell metabolism. These patterns held up in murine xenograft models of plasmacytoma, and disseminated bone marrow predominant disease. Our findings underscore the importance of CD200-mediated immune suppression in CAR T-cell therapy of MM, and highlight a promising approach to enhance such therapies by leveraging CD200 expression on aPCs to provide costimulation via a CD200R-CD28 switch.

Advances in the pathogenesis of multiple myeloma bone disease

Multiple myeloma (MM) is a clonal proliferative malignant tumor of plasma cells in bone marrow. With the aging of population in China, the incidence of MM is on the rise. Multiple myeloma bone disease (MBD) is one of the common clinical manifestations of MM, and 80%-90% of MM patients are accompanied by osteolytic lesions at the time of their first visit to the clinic. MBD not only increases the disability rate of patients, but also severely reduces the physical function of patients due to skeletal lesions and bone-related events. Currently available drugs for treating of MBD are ineffective and associated with side effects. Therefore, it is important to find new therapeutic approaches for the treatment of MBD. It is generally believed that the increased osteoclast activity and suppressed osteoblast function are the main pathologic mechanisms for MBD. However, more and more studies have suggested that soluble molecules in the bone marrow microenvironment, including cytokines, extracellular bodies, and metabolites, play an important role in the development of MBD. Therefore, exploring the occurrence and potential molecular mechanisms for MBD from multiple perspectives, and identifying the predictive biomarkers and potential therapeutic targets are of significance for the clinical treatment of MBD.

What Can De Novo Protein Design Bring to the Treatment of Hematological Disorders?

Protein therapeutics have been widely used to treat hematological disorders. With the advent of de novo protein design, protein therapeutics are not limited to ameliorating natural proteins but also produce novel protein sequences, folds, and functions with shapes and functions customized to bind to the therapeutic targets. De novo protein techniques have been widely used biomedically to design novel diagnostic and therapeutic drugs, novel vaccines, and novel biological materials. In addition, de novo protein design has provided new options for treating hematological disorders. Scientists have designed protein switches called Colocalization-dependent Latching Orthogonal Cage-Key pRoteins (Co-LOCKR) that perform computations on the surface of cells. De novo designed molecules exhibit a better capacity than the currently available tyrosine kinase inhibitors in chronic myeloid leukemia therapy. De novo designed protein neoleukin-2/15 enhances chimeric antigen receptor T-cell activity. This new technique has great biomedical potential, especially in exploring new treatment methods for hematological disorders. This review discusses the development of de novo protein design and its biological applications, with emphasis on the treatment of hematological disorders.

Targeting TGF-β signaling in the multiple myeloma microenvironment: Steering CARs and T cells in the right direction

Multiple myeloma (MM) remains a lethal hematologic cancer characterized by the expansion of transformed plasma cells within the permissive bone marrow (BM) milieu. The emergence of relapsed and/or refractory MM (RRMM) is provoked through clonal evolution of malignant plasma cells that harbor genomic, metabolic and proteomic perturbations. For most patients, relapsed disease remains a major cause of overall mortality. Transforming growth factors (TGFs) have pleiotropic effects that regulate myelomagenesis as well as the emergence of drug resistance. Moreover, TGF-β modulates numerous cell types present with the tumor microenvironment, including many immune cell types. While numerous agents have been FDA-approved over the past 2 decades and significantly expanded the treatment options available for MM patients, the molecular mechanisms responsible for drug resistance remain elusive. Multiple myeloma is uniformly preceded by a premalignant state, monoclonal gammopathy of unknown significance, and both conditions are associated with progressive deregulation in host immunity characterized by reduced T cell, natural killer (NK) cell and antigen-presenting dendritic cell (DC) activity. TGF-β promotes myelomagenesis as well as intrinsic drug resistance by repressing anti-myeloma immunity to promote tolerance, drug resistance and disease progression. Hence, repression of TGF-β signaling is a prerequisite to enhance the efficacy of current and future immunotherapeutics. Novel strategies that incorporate T cells that have been modified to express chimeric antigen receptor (CARs), T cell receptors (TCRs) and bispecific T cell engagers (BiTEs) offer promise to block TGF-β signaling, overcome chemoresistance and enhance anti-myeloma immunity. Here, we describe the effects of TGF-β signaling on immune cell effectors in the bone marrow and emerging strategies to overcome TGF-β-mediated myeloma growth, drug resistance and survival.

Innovation in BCMA CAR-T therapy: Building beyond the Model T

Autologous chimeric antigen receptor T-cell (CAR-T) therapies targeting B-cell maturation antigen (BCMA) have revolutionized the field of multiple myeloma in the same way that the Ford Model T revolutionized the original CAR world a century ago. However, we are only beginning to understand how to improve the efficacy and usability of these cellular therapies. In this review, we explore three automotive analogies for innovation with BCMA CAR-T therapies: stronger engines, better mileage, and hassle-free delivery. Firstly, we can build stronger engines in terms of BCMA targeting: improved antigen binding, tools to modulate antigen density, and armoring to better reach the antigen itself. Secondly, we can improve "mileage" in terms of response durability through ex vivo CAR design and in vivo immune manipulation. Thirdly, we can implement hassle-free delivery through rapid manufacturing protocols and off-the-shelf products. Just as the Model T set a benchmark for car manufacturing over 100 years ago, idecabtagene vicleucel and ciltacabtagene autoleucel have now set the starting point for BCMA CAR-T therapy with their approvals. As with any emerging technology, whether automotive or cellular, the best in innovation and optimization is yet to come.

Combined targeting of soluble latent TGF-ß and a solid tumor-associated antigen with adapter CAR T cells

Solid tumors consist of malignant and nonmalignant cells that together create the local tumor microenvironment (TME). Additionally, the TME is characterized by the expression of numerous soluble factors such as TGF-β. TGF-β plays an important role in the TME by suppressing T cell effector function and promoting tumor invasiveness. Up to now CAR T cells exclusively target tumor-associated antigens (TAA) located on the cell membrane. Thus, strategies to exploit soluble antigens as CAR targets within the TME are needed. This study demonstrates a novel approach using Adapter CAR (AdCAR) T cells for the detection of soluble latent TGF-β within the TME of a pancreatic tumor model. We show that AdCARs in combination with the respective adapter can be used to sense soluble tumor-derived latent TGF-β, both in vitro and in vivo. Sensing of the soluble antigen induced cellular activation and effector cytokine production in AdCAR T cells. Moreover, we evaluated AdCAR T cells for the combined targeting of soluble latent TGF-β and tumor cell killing by targeting CD66c as TAA in vivo. In sum, our study broadens the spectrum of targetable moieties for AdCAR T cells by soluble latent TGF-β.

Combination of a Novel Fusion Protein CD3εζ28 and Bispecific T Cell Engager Enhances the Persistance and Anti-Cancer Effects of T Cells

Bi-specific T cell engager (BiTE), an artificial bi-functional fusion protein, has shown promising therapeutic potential in preclinical and clinical studies. However, T cells cannot be sufficiently activated by BiTE, most likely due to lacking co-stimulatory signal. We reasoned that incorporating co-stimulatory signal might have the potential to enhance the T cell activation mediated by BiTE. We, therefore, designed a chimeric fusion protein, named as CD3εζ28, which consists of the CD3ε extracellular region, the CD28 costimulatory signal and the intracellular region of CD3ζ in tandem. T cells genetically modified to express both CD3εζ28 and GFP (T-CD3εζ28-GFP) were generated by retroviral transduction. The results from in vitro experiments showed that T-CD3εζCD28-GFP cells had superior cytotoxic effects on tumor cells in presence of BiTE compared with control T cells, as evidenced by IL-2 and IFN-γ production, T cell proliferation and sequential killing assay. In vivo, T-CD3εζCD28-GFP cells showed superior anti-tumor effects in Hela-BiTE. EGFRvIII xenograft tumor model, as evaluated by tumor growth rate and T cell persistence in comparison with control T cells. In order to further confirm these findings, we generated T cells modified to express both CD3εζCD28 on cell surface and BiTE.CD19 by autocrine manner (T-CD3εζCD28-BiTE.19). The superior anti-tumor effects of T-CD3εζCD28-BiTE.19 cells could also be evidenced by the similar in vitro and in vivo experiments; thus, incorporating co-stimulatory signal may be an effective approach to improve the effector function of T cells mediated by BiTE.

Circular RNA in multiple myeloma: A new target for therapeutic intervention

Circular RNAs (circRNAs) are RNA molecules with a stable closed-loop structure that are found in a variety of organisms. CircRNAs are highly stable and conserved, and they play important roles in transcriptional regulation and splicing. Multiple Myeloma (MM) is a malignant proliferative disease for which there are currently no effective and comprehensive treatments. Numerous circRNAs may contribute to the development and progression of MM by acting as oncogenes or regulators. Due to the unique function of circRNAs, they have a high potential for regulating the biological functions (including proliferation and apoptosis) of MM cells, and their expression levels and molecular mechanism are closely related to their diagnostic value, therapeutic sensitivity, and clinical prognosis of MM patients. In this review, we aim to provide a detailed overview of the structure and function of circRNAs and demonstrate the potential therapeutic value and potential mechanism of circRNAs in MM via experiments and clinical trials.

m5C Regulator-mediated methylation modification clusters contribute to the immune microenvironment regulation of multiple myeloma

Background: Multiple myeloma (MM) is a hematological malignancy in which plasma cells proliferate abnormally. 5-methylcytosine (m5C) methylation modification is the primary epigenetic modification and is involved in regulating the occurrence, development, invasion, and metastasis of various tumors; however, its immunological functions have not been systematically described in MM. Thus, this study aimed to clarify the significance of m5C modifications and how the immune microenvironment is linked to m5C methylation in MM.

Method: A total of 483 samples (60 healthy samples, 423 MM samples) from the Gene Expression Omnibus dataset were acquired to assess the expression of m5C regulators. A nomogram model was established to predict the occurrence of MM. We investigated the impact of m5C modification on immune microenvironment characteristics, such as the infiltration of immunocytes and immune response reactions. We then systematically evaluated three different m5C expression patterns to assess immune characteristics and metabolic functional pathways and established m5C-related differentially expressed genes (DEGs). In addition, biological process analysis was performed and an m5C score was constructed to identify potentially significant immunological functions in MM.

Result: Differential expressions of m5C regulators were identified between healthy and MM samples. The nomogram revealed that m5C regulators could predict higher disease occurrence of MM. We identified three distinct m5C clusters with unique immunological and metabolic characteristics. Among the three different m5C clusters, cluster C had more immune characteristics and more metabolism-related pathways than clusters A and B. We analyzed 256 m5C-related DEGs and classified the samples into three different m5C gene clusters. Based on the m5C and m5C gene clusters, we calculated m5C scores and classified each patient into high- and low-m5C score groups.

Conclusion: Our study demonstrated that m5C modification is involved in and contributes to the diversity and complexity of the immune microenvironment, which offers promise for the development of accurate therapeutic strategies.

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.

Gaps and opportunities in the treatment of relapsed-refractory multiple myeloma: Consensus recommendations of the NCI Multiple Myeloma Steering Committee

A wide variety of new therapeutic options for Multiple Myeloma (MM) have recently become available, extending progression-free and overall survival for patients in meaningful ways. However, these treatments are not curative, and patients eventually relapse, necessitating decisions on the appropriate choice of treatment(s) for the next phase of the disease. Additionally, an important subset of MM patients will prove to be refractory to the majority of the available treatments, requiring selection of effective therapies from the remaining options. Immunomodulatory agents (IMiDs), proteasome inhibitors, monoclonal antibodies, and alkylating agents are the major classes of MM therapies, with several options in each class. Patients who are refractory to one agent in a class may be responsive to a related compound or to a drug from a different class. However, rules for selection of alternative treatments in these situations are somewhat empirical and later phase clinical trials to inform those choices are ongoing. To address these issues the NCI Multiple Myeloma Steering Committee formed a relapsed/refractory working group to review optimal treatment choices, timing, and sequencing and provide recommendations. Additional issues considered include the role of salvage autologous stem cell transplantation, risk stratification, targeted approaches for genetic subsets of MM, appropriate clinical trial endpoints, and promising investigational agents. This report summarizes the deliberations of the working group and suggests potential avenues of research to improve the precision, timing, and durability of treatments for Myeloma.

CAR-T Cell Therapy in Hematological Malignancies: Current Opportunities and Challenges

Chimeric antigen receptor T (CAR-T) cell therapy represents a major breakthrough in cancer treatment, and it has achieved unprecedented success in hematological malignancies, especially in relapsed/refractory (R/R) B cell malignancies. At present, CD19 and BCMA are the most common targets in CAR-T cell therapy, and numerous novel therapeutic targets are being explored. However, the adverse events related to CAR-T cell therapy might be serious or even life-threatening, such as cytokine release syndrome (CRS), CAR-T-cell-related encephalopathy syndrome (CRES), infections, cytopenia, and CRS-related coagulopathy. In addition, due to antigen escape, the limited CAR-T cell persistence, and immunosuppressive tumor microenvironment, a considerable proportion of patients relapse after CAR-T cell therapy. Thus, in this review, we focus on the progress and challenges of CAR-T cell therapy in hematological malignancies, such as attractive therapeutic targets, CAR-T related toxicities, and resistance to CAR-T cell therapy, and provide some practical recommendations.