Construction and characterisation of a functional CD19 specific single chain Fv fragment for immunotherapy of B lineage leukaemia and lymphoma

Comparison of seven CD19 CAR designs in engineering NK cells for enhancing anti-tumour activity

Chimeric antigen receptor-natural killer (CAR-NK) cell therapy is emerging as a promising cancer treatment, with notable safety and source diversity benefits over CAR-T cells. This study focused on optimizing CAR constructs for NK cells to maximize their therapeutic potential. We designed seven CD19 CAR constructs and expressed them in NK cells using a retroviral system, assessing their tumour-killing efficacy and persistence. Results showed all constructs enhanced tumour-killing and prolonged survival in tumour-bearing mice. In particular, CAR1 (CD8 TMD-CD3ζ SD)-NK cells showed superior efficacy in treating tumour-bearing animals and exhibited enhanced persistence when combined with OX40 co-stimulatory domain. Of note, CAR1-NK cells were most effective at lower effector-to-target ratios, while CAR4 (CD8 TMD-OX40 CD- FcεRIγ SD) compromised NK cell expansion ability. Superior survival rates were noted in mice treated with CAR1-, CAR2 (CD8 TMD- FcεRIγ SD)-, CAR3 (CD8 TMD-OX40 CD- CD3ζ SD)- and CAR4-NK cells over those treated with CAR5 (CD28 TMD- FcεRIγ SD)-, CAR6 (CD8 TMD-4-1BB CD-CD3ζ 1-ITAM SD)- and CAR7 (CD8 TMD-OX40 CD-CD3ζ 1-ITAM SD)-NK cells, with CAR5-NK cells showing the weakest anti-tumour activity. Increased expression of exhaustion markers, especially in CAR7-NK cells, suggests that combining CAR-NK cells with immune checkpoint inhibitors might improve anti-tumour outcomes. These findings provide crucial insights for developing CAR-NK cell products for clinical applications.

Development of a chimeric cytokine receptor that captures IL-6 and enhances the antitumor response of CAR-T cells

The efficacy of chimeric antigen receptor (CAR)-engineered T cell therapy is suboptimal in most cancers, necessitating further improvement in their therapeutic actions. However, enhancing antitumor T cell response inevitably confers an increased risk of cytokine release syndrome associated with monocyte-derived interleukin-6 (IL-6). Thus, an approach to simultaneously enhance therapeutic efficacy and safety is warranted. Here, we develop a chimeric cytokine receptor composed of the extracellular domains of GP130 and IL6RA linked to the transmembrane and cytoplasmic domain of IL-7R mutant that constitutively activates the JAK-STAT pathway (G6/7R or G6/7R-M452L). CAR-T cells with G6/7R efficiently absorb and degrade monocyte-derived IL-6 in vitro. The G6/7R-expressing CAR-T cells show superior expansion and persistence in vivo, resulting in durable antitumor response in both liquid and solid tumor mouse models. Our strategy can be widely applicable to CAR-T cell therapy to enhance its efficacy and safety, irrespective of the target antigen.

Unraveling resistance mechanisms in anti-CD19 chimeric antigen receptor-T therapy for B-ALL: a novel in vitro model and insights into target antigen dynamics

BACKGROUND

Cellular immunotherapy, represented by the chimeric antigen receptor T cell (CAR-T), has exhibited high response rates, durable remission, and safety in vitro and in clinical trials. Unfortunately, anti-CD19 CAR-T (CART-19) treatment alone is prone to relapse and has a particularly poor prognosis in relapsed/refractory (r/r) B-ALL patients. To date, addressing or reducing relapse remains one of the research priorities to achieve broad clinical application.

METHODS

We manufactured second generation CART-19 cells and validated their efficacy and safety in vitro and in vivo. Through co-culture of Nalm-6 cells with short-term cultured CART-19 cells, CD19-negative Nalm-6 cells were detected by flow cytometry, and further investigation of the relapsed cells and their resistance mechanisms was evaluated in vitro.

RESULTS

In this study, we demonstrated that CART-19 cells had enhanced and specific antileukemic activities, and the survival of B-ALL mouse models after CART-19 treatment was significantly prolonged. We then shortened the culture time and applied the serum-free culture to expand CAR-T cells, followed by co-culturing CART-19 cells with Nalm-6 cells. Surprisingly, we observed the proliferation of CD19-negative Nalm-6 cells around 28 days. Identification of potential resistance mechanisms showed that the relapsed cells express truncated CD19 proteins with decreased levels and, more importantly, CAR expression was detected on the relapsed cell surface, which may ultimately keep them antigen-negative. Furthermore, it was validated that CART-22 and tandem CART-22/19 cells could effectively kill the relapsed cells, but neither could completely eradicate them.

CONCLUSIONS

We successfully generated CART-19 cells and obtained a CD19-negative refractory relapsed B-ALL cell line, providing new insights into the underlying mechanisms of resistance and a new in vitro model for the treatment of r/r B-ALL patients with low antigen density.

Novel chimeric antigen receptor-expressing T cells targeting the malignant mesothelioma-specific antigen sialylated HEG1

The selection of highly specific target antigens is critical for the development of clinically efficient and safe chimeric antigen receptors (CARs). In search of diagnostic marker for malignant mesothelioma (MM), we have established SKM9-2 monoclonal antibody (mAb) which recognizes a MM-specific molecule, sialylated Protein HEG homolog 1 (HEG1), with high specificity and sensitivity. In this study, to develop a novel therapeutic approach against MM, we generated SKM9-2 mAb-derived CARs that included the CD28 (SKM-28z) or 4-1BB (SKM-BBz) costimulatory domain. SKM-28z CAR-T cells showed continuous growth and enhanced Tim-3, LAG-3, and PD-1 expression in vitro, which might be induced by tonic signaling caused by self-activation; however, these phenotypes were not observed in SKM-BBz CAR-T cells. In addition, SKM-BBz CAR-T cells exhibited slightly stronger in vitro killing activity against MM cell lines than SKM-28z CAR-T cells. More importantly, only SKM-BBz CAR-T cells, but not SKM-28z CAR-T cells, significantly inhibited tumor growth in vivo in a MM cell line xenograft mouse model. Gene expression profiling and reporter assays revealed differential signaling pathway activation; in particular, SKM-BBz CAR-T cells exhibited enhanced NF-kB signaling and reduced NFAT activation. In addition, SKM-BBz CAR-T cells showed upregulation of early memory markers, such as TCF7 and CCR7, as well as downregulation of pro-apoptotic proteins, such as BAK1 and BID, which may be associated with phenotypical and functional differences between SKM-BBz and SKM-28z CAR-T cells. In conclusion, we developed novel SKM9-2-derived CAR-T cells with the 4-1BB costimulatory domain, which could provide a promising therapeutic approach against refractory MM.

Stealth transgenes enable CAR-T cells to evade host immune responses

BACKGROUND

Adoptive cell therapy, such as chimeric antigen receptor (CAR)-T cell therapy, has improved patient outcomes for hematological malignancies. Currently, four of the six FDA-approved CAR-T cell products use the FMC63-based αCD19 single-chain variable fragment, derived from a murine monoclonal antibody, as the extracellular binding domain. Clinical studies demonstrate that patients develop humoral and cellular immune responses to the non-self CAR components of autologous CAR-T cells or donor-specific antigens of allogeneic CAR-T cells, which is thought to potentially limit CAR-T cell persistence and the success of repeated dosing.

METHODS

In this study, we implemented a one-shot approach to prevent rejection of engineered T cells by simultaneously reducing antigen presentation and the surface expression of both Classes of the major histocompatibility complex (MHC) via expression of the viral inhibitors of transporter associated with antigen processing (TAPi) in combination with a transgene coding for shRNA targeting class II MHC transactivator (CIITA). The optimal combination was screened in vitro by flow cytometric analysis and mixed lymphocyte reaction assays and was validated in vivo in mouse models of leukemia and lymphoma. Functionality was assessed in an autologous setting using patient samples and in an allogeneic setting using an allogeneic mouse model.

RESULTS

The combination of the Epstein-Barr virus TAPi and an shRNA targeting CIITA was efficient and effective at reducing cell surface MHC classes I and II in αCD19 'stealth' CAR-T cells while retaining in vitro and in vivo antitumor functionality. Mixed lymphocyte reaction assays and IFNγ ELISpot assays performed with T cells from patients previously treated with autologous αCD19 CAR-T cells confirm that CAR T cells expressing the stealth transgenes evade allogeneic and autologous anti-CAR responses, which was further validated in vivo. Importantly, we noted anti-CAR-T cell responses in patients who had received multiple CAR-T cell infusions, and this response was reduced on in vitro restimulation with autologous CARs containing the stealth transgenes.

CONCLUSIONS

Together, these data suggest that the proposed stealth transgenes may reduce the immunogenicity of autologous and allogeneic cellular therapeutics. Moreover, patient data indicate that repeated doses of autologous FMC63-based αCD19 CAR-T cells significantly increased the anti-CAR T cell responses in these patients.

Extracellular domains of CARs reprogramme T cell metabolism without antigen stimulation

Metabolism is an indispensable part of T cell proliferation, activation and exhaustion, yet the metabolism of chimeric antigen receptor (CAR)-T cells remains incompletely understood. CARs are composed of extracellular domains-often single-chain variable fragments (scFvs)-that determine ligand specificity and intracellular domains that trigger signalling following antigen binding. Here, we show that CARs differing only in the scFv variously reprogramme T cell metabolism. Even without exposure to antigens, some CARs increase proliferation and nutrient uptake in T cells. Using stable isotope tracers and mass spectrometry, we observed basal metabolic fluxes through glycolysis doubling and amino acid uptake overtaking anaplerosis in CAR-T cells harbouring a rituximab scFv, unlike other similar anti-CD20 scFvs. Disparate rituximab and 14G2a-based anti-GD2 CAR-T cells are similarly hypermetabolic and channel excess nutrients to nitrogen overflow metabolism. Modest overflow metabolism of CAR-T cells and metabolic compatibility between cancer cells and CAR-T cells are identified as features of efficacious CAR-T cell therapy.

Class I HDAC inhibitors enhance antitumor efficacy and persistence of CAR-T cells by activation of the Wnt pathway

Epigenetic modification shapes differentiation trajectory and regulates the exhaustion state of chimeric antigen receptor T (CAR-T) cells. Limited efficacy induced by terminal exhaustion closely ties with intrinsic transcriptional regulation. However, the comprehensive regulatory mechanisms remain largely elusive. Here, we identify class I histone deacetylase inhibitors (HDACi) as boosters of CAR-T cell function by high-throughput screening of chromatin-modifying drugs, in which M344 and chidamide enhance memory maintenance and resistance to exhaustion of CAR-T cells that induce sustained antitumor efficacy both in vitro and in vivo. Mechanistically, HDACi decrease HDAC1 expression and enhance H3K27ac activity. Multi-omics analyses from RNA-seq, ATAC-seq, and H3K27ac CUT&Tag-seq show that HDACi upregulate expression of TCF4, LEF1, and CTNNB1, which subsequently activate the canonical Wnt/β-catenin pathway. Collectively, our findings elucidate the functional roles of class I HDACi in enhancing CAR-T cell function, which provides the basis and therapeutic targets for synergic combination of CAR-T cell therapy and HDACi treatment.

Chimeric Antigen Receptor (CAR) T-Cell Therapy in Hematologic Malignancies: Clinical Implications and Limitations

Chimeric antigen receptor (CAR) T-cell therapy has become a powerful treatment option in B-cell and plasma cell malignancies, and many patients have benefited from its use. To date, six CAR T-cell products have been approved by the FDA and EMA, and many more are being developed and investigated in clinical trials. The whole field of adoptive cell transfer has experienced an unbelievable development process, and we are now at the edge of a new era of immune therapies that will have its impact beyond hematologic malignancies. Areas of interest are, e.g., solid oncology, autoimmune diseases, infectious diseases, and others. Although much has been achieved so far, there is still a huge effort needed to overcome significant challenges and difficulties. We are witnessing a rapid expansion of knowledge, induced by new biomedical technologies and CAR designs. The era of CAR T-cell therapy has just begun, and new products will widen the therapeutic landscape in the future. This review provides a comprehensive overview of the clinical applications of CAR T-cells, focusing on the approved products and emphasizing their benefits but also indicating limitations and challenges.

Targeting branched N-glycans and fucosylation sensitizes ovarian tumors to immune checkpoint blockade

Aberrant glycosylation is a crucial strategy employed by cancer cells to evade cellular immunity. However, it's unclear whether homologous recombination (HR) status-dependent glycosylation can be therapeutically explored. Here, we show that the inhibition of branched N-glycans sensitizes HR-proficient, but not HR-deficient, epithelial ovarian cancers (EOCs) to immune checkpoint blockade (ICB). In contrast to fucosylation whose inhibition sensitizes EOCs to anti-PD-L1 immunotherapy regardless of HR-status, we observe an enrichment of branched N-glycans on HR-proficient compared to HR-deficient EOCs. Mechanistically, BRCA1/2 transcriptionally promotes the expression of MGAT5, the enzyme responsible for catalyzing branched N-glycans. The branched N-glycans on HR-proficient tumors augment their resistance to anti-PD-L1 by enhancing its binding with PD-1 on CD8+ T cells. In orthotopic, syngeneic EOC models in female mice, inhibiting branched N-glycans using 2-Deoxy-D-glucose sensitizes HR-proficient, but not HR-deficient EOCs, to anti-PD-L1. These findings indicate branched N-glycans as promising therapeutic targets whose inhibition sensitizes HR-proficient EOCs to ICB by overcoming immune evasion.

A novel safer CD19CAR with shRNA interference of IFN-γ can reduce multiple cytokine levels without significantly compromising its killing efficacy

Cytokine release syndrome (CRS) is a great challenge for the application of anti-CD19 CAR-T cell therapy. The aim of this study was to investigate the effect of knocking down interferon gamma (IFN-γ) by shRNA as a potential strategy to reduce the cytokine storms. A newly designed short hairpin interference RNA of IFN-γ (shIFN-γ) in CD19CAR gene was constructed. Several cellular model systems of approach using Nalm-6 cell lines including Nalm-6CD19pos and Nalm-6CD19neg with or without monocytes and endothelial cells were used to analyze the different levels of cytokines after shIFN-γ-anti-CD19CAR-T cell targeted therapy. The activity of this novel CD19CAR-T was evaluated both in vitro and in NSG mouse model. The killing efficacy of shIFN-γ-anti-CD19CAR-T at the E:T ratio of 2:1 was similar to that of regular anti-CD19CAR-T at the E:T ratio of 1:1. The IFN-γ level in the shIFN-γ-anti-CD19CAR-T cell group was (2673.1 ± 307.4) pg/ml at the E:T ratio of 2:1 which was significantly lower than that ((8261.5 ± 345.5) pg/ml) in the regular anti-CD19CAR-T group at the E:T ratio of 1:1. Cytotoxicity experiments in vitro showed significantly reduced concentrations of IFN-γ, IL-6 and TNFα in the shIFN-γ-anti-CD19CAR-T cell group compared to regular anti-CD19CAR-T cell group. Both regular anti-CD19CAR and shIFN-γ-CD19CAR-T exerted bystander killing effect in vitro. We conclude that shIFN-γ-anti-CD19CAR-T cells can reduce the generation of cytokine storms without significantly compromising their therapeutic efficacy in the preclinical setting. In mouse model, 3 × 106 shIFN-γ-anti-CD19CAR-T cells/mouse generated the similar killing efficacy to that with 2 × 106 regular anti-CD19CAR-T cells/mouse.

TRBC1-targeting antibody-drug conjugates for the treatment of T cell cancers

Antibody and chimeric antigen receptor (CAR) T cell-mediated targeted therapies have improved survival in patients with solid and haematologic malignancies1-9. Adults with T cell leukaemias and lymphomas, collectively called T cell cancers, have short survival10,11 and lack such targeted therapies. Thus, T cell cancers particularly warrant the development of CAR T cells and antibodies to improve patient outcomes. Preclinical studies showed that targeting T cell receptor β-chain constant region 1 (TRBC1) can kill cancerous T cells while preserving sufficient healthy T cells to maintain immunity12, making TRBC1 an attractive target to treat T cell cancers. However, the first-in-human clinical trial of anti-TRBC1 CAR T cells reported a low response rate and unexplained loss of anti-TRBC1 CAR T cells13,14. Here we demonstrate that CAR T cells are lost due to killing by the patient's normal T cells, reducing their efficacy. To circumvent this issue, we developed an antibody-drug conjugate that could kill TRBC1+ cancer cells in vitro and cure human T cell cancers in mouse models. The anti-TRBC1 antibody-drug conjugate may provide an optimal format for TRBC1 targeting and produce superior responses in patients with T cell cancers.

Identification of cancer-specific cell surface targets for CAR-T cell therapy

One should identify appropriate cell surface targets to develop new CAR-T cells. Currently, lineage-specific antigens such as CD19 or B cell maturation antigen (BCMA) are being used as targets for CAR-T cells. However, in most cancers, lineage-specific antigens cannot be used as targets because targeting normal counterparts expressing them causes fatal toxicity. Cancer-specific transcripts have been extensively searched for using transcriptome analysis, but only a few candidates were reported. We have been working on identifying tumor-specific antigen structures, for example constitutively activated conformer of integrin b7 in multiple myeloma. Recently, several researchers have been working on a logic gate system that can react only when two antigens are expressed on the cell surface.

Dual CAR-T Cells Targeting CD19 and CD37 Are Effective in Target Antigen Loss B-cell Tumor Models

Chimeric antigen receptor T (CAR-T) cells targeting multiple antigens (Ag), may reduce the risk of immune escape following the loss of the target Ag and further increase the efficacy of treatment. We developed dual-targeting CAR-T cells that target CD19 and CD37 Ags and evaluated their antitumor effects. CD19/CD37 dual CAR-T cells were generated using cotransduction and simultaneous gene transfer of two types of lentiviral vectors transferring CD19CAR or CD37CAR genes, including the intracellular domains of CD28 and CD3ζ signaling domains. These dual CAR-T cells contained three fractions: CD19/CD37 bispecific CAR-T cells, single CD19CAR-T cells, and single CD37CAR-T cells. In the functional evaluation of CAR-T cells in vitro, CD19/CD37 dual CAR-T cells showed adequate proliferation and cytokine production in response to CD19 and CD37 antigen stimulation alone or in combination. Evaluation of intracellular signaling revealed that dual CAR-T cell-mediated signals were comparable with single CAR-T cells in response to CD19- and CD37-positive B-cell tumors. Although the cytotoxicity of CD19/CD37 dual CAR-T cells in both CD19- and CD37-positive B-cell tumors was similar to that of single CD19 and CD37CAR-T cells, against CD19 and CD37 Ag-heterogeneous tumor, dual CAR-T cells demonstrated significantly superior tumor lysis compared with single CAR-T cells. Furthermore, CD19/CD37 dual CAR-T cells effectively suppressed Ag-heterogeneous Raji cells in a xenograft mouse model. Collectively, these results suggest that CD19/CD37 dual CAR-T cells may be effective target-Ag-loss B-cell tumor models in vitro and in vivo, which represents a promising treatment for patients with relapsed/refractory B-cell malignancies.

Digital PCR Improves Sensitivity and Quantification in Monitoring CAR-T Cells in B Cell Lymphoma Patients

Chimeric antigen receptor T cells (CAR-T) has emerged as a promising therapy, over 60% of patients fail to sustain a long-term response. The underlying factors that leads to the effectiveness of this therapy are not completely understood, CAR-T cell persistence and monitoring seems to be pivotal for ensuring a successful response. Various monitoring methods such as multiparametric flow cytometry (MFC) or quantitative PCR (qPCR) have been applied. Our objective is to develop digital PCR (dPCR) assays for detection and quantification of CAR-T cells, comparing them with MFC and qPCR. Samples taken at different follow-up times from 45 patients treated with CAR-T therapy were analyzed to assess the correlation between the different methodologies. dPCR presented a high correlation with MFC and qPCR (r = 0.97 and r = 0.87, respectively), while offering a higher sensitivity (0.01%) compared to MFC (0.1%) and qPCR (1%). dPCR emerged as an alternative and highly sensitivity method for monitoring CAR-T cell dynamics. This technique is well-suited for implementation in clinical practice as a complementary technique to MFC.

Inhibition of CD38 enzymatic activity enhances CAR-T cell immune-therapeutic efficacy by repressing glycolytic metabolism

Chimeric antigen receptor (CAR)-T therapy has shown superior efficacy against hematopoietic malignancies. However, many patients failed to achieve sustainable tumor control partially due to CAR-T cell exhaustion and limited persistence. In this study, by performing single-cell multi-omics data analysis on patient-derived CAR-T cells, we identify CD38 as a potential hallmark of exhausted CAR-T cells, which is positively correlated with exhaustion-related transcription factors and further confirmed with in vitro exhaustion models. Moreover, inhibiting CD38 activity reverses tonic signaling- or tumor antigen-induced exhaustion independent of single-chain variable fragment design or costimulatory domain, resulting in improved CAR-T cell cytotoxicity and antitumor response. Mechanistically, CD38 inhibition synergizes the downregulation of CD38-cADPR -Ca2+ signaling and activation of the CD38-NAD+-SIRT1 axis to suppress glycolysis. Collectively, our findings shed light on the role of CD38 in CAR-T cell exhaustion and suggest potential clinical applications of CD38 inhibition in enhancing the efficacy and persistence of CAR-T cell therapy.

Signaling via a CD27-TRAF2-SHP-1 axis during naive T cell activation promotes memory-associated gene regulatory networks

The interaction of the tumor necrosis factor receptor (TNFR) family member CD27 on naive CD8+ T (Tn) cells with homotrimeric CD70 on antigen-presenting cells (APCs) is necessary for T cell memory fate determination. Here, we examined CD27 signaling during Tn cell activation and differentiation. In conjunction with T cell receptor (TCR) stimulation, ligation of CD27 by a synthetic trimeric CD70 ligand triggered CD27 internalization and degradation, suggesting active regulation of this signaling axis. Internalized CD27 recruited the signaling adaptor TRAF2 and the phosphatase SHP-1, thereby modulating TCR and CD28 signals. CD27-mediated modulation of TCR signals promoted transcription factor circuits that induced memory rather than effector associated gene programs, which are induced by CD28 costimulation. CD27-costimulated chimeric antigen receptor (CAR)-engineered T cells exhibited improved tumor control compared with CD28-costimulated CAR-T cells. Thus, CD27 signaling during Tn cell activation promotes memory properties with relevance to T cell immunotherapy.

Epigenetic profiles guide improved CRISPR/Cas9-mediated gene knockout in human T cells

Genetic modification of specific genes is emerging as a useful tool to enhance the functions of antitumor T cells in adoptive immunotherapy. Current advances in CRISPR/Cas9 technology enable gene knockout during in vitro preparation of infused T-cell products through transient transfection of a Cas9-guide RNA (gRNA) ribonucleoprotein complex. However, selecting optimal gRNAs remains a major challenge for efficient gene ablation. Although multiple in silico tools to predict the targeting efficiency have been developed, their performance has not been validated in cultured human T cells. Here, we explored a strategy to select optimal gRNAs using our pooled data on CRISPR/Cas9-mediated gene knockout in human T cells. The currently available prediction tools alone were insufficient to accurately predict the indel percentage in T cells. We used data on the epigenetic profiles of cultured T cells obtained from transposase-accessible chromatin with high-throughput sequencing (ATAC-seq). Combining the epigenetic information with sequence-based prediction tools significantly improved the gene-editing efficiency. We further demonstrate that epigenetically closed regions can be targeted by designing two gRNAs in adjacent regions. Finally, we demonstrate that the gene-editing efficiency of unstimulated T cells can be enhanced through pretreatment with IL-7. These findings enable more efficient gene editing in human T cells.

Solving the mystery of the FMC63-CD19 affinity

The majority of approved CAR T cell products are based on the FMC63-scFv directed against CD19. Surprisingly, although antigen binding affinity is a major determinant for CAR function, the affinity of the benchmark FMC63-scFv has not been unambiguously determined. That is, a wide range of affinities have been reported in literature, differing by more than 100-fold. Using a range of techniques, we demonstrate that suboptimal experimental designs can cause artefacts that lead to over- or underestimation of the affinity. To minimize these artefacts, we performed SPR with strictly monomeric and correctly folded soluble CD19, yielding an FMC63-scFv affinity of 2-6 nM. Together, apart from analyzing the FMC63-scFv affinity under optimized conditions, we also provide potential explanations for the wide range of published affinities. We expect that this study will be highly valuable for interpretations of CAR affinity-function relationships, as well as for the design of future CAR T cell generations.

CRISPR-Cas12a-integrated transgenes in genomic safe harbors retain high expression in human hematopoietic iPSC-derived lineages and primary cells

Discovery of genomic safe harbor sites (SHSs) is fundamental for multiple transgene integrations, such as reporter genes, chimeric antigen receptors (CARs), and safety switches, which are required for safe cell products for regenerative cell therapies and immunotherapies. Here we identified and characterized potential SHS in human cells. Using the CRISPR-MAD7 system, we integrated transgenes at these sites in induced pluripotent stem cells (iPSCs), primary T and natural killer (NK) cells, and Jurkat cell line, and demonstrated efficient and stable expression at these loci. Subsequently, we validated the differentiation potential of engineered iPSC toward CD34+ hematopoietic stem and progenitor cells (HSPCs), lymphoid progenitor cells (LPCs), and NK cells and showed that transgene expression was perpetuated in these lineages. Finally, we demonstrated that engineered iPSC-derived NK cells retained expression of a non-virally integrated anti-CD19 CAR, suggesting that several of the investigated SHSs can be used to engineer cells for adoptive immunotherapies.

Chimeric Antigen Receptor T-Cell Therapy in Aggressive B-Cell Lymphoma

Chimeric antigen receptor (CAR) T-cell therapy is a revolutionary therapy increasingly used in the treatment of non-Hodgkin B-cell lymphoma. This review focuses on the use of CAR T-cell therapy in aggressive B-cell lymphoma including clinical indications, known short- and long-term toxicity, mechanisms of CAR T-cell efficacy and tumor resistance, and future directions in the treatment of aggressive lymphoma with CAR T-cell therapy.

[Long-term follow-up of humanized and murine CD19 CAR-T-cell therapy for B-cell acute lymphoblastic leukemia]

Objective: Murine CD19 chimeric antigen receptor T-cell (CAR-T) products have been approved for the treatment of refractory/relapsed (R/R) B-cell acute lymphocytic leukemia (B-ALL) ; moreover, humanized products are also undergoing clinical trials. This study aimed to explore the differences in safety and short- and long-term follow-up efficacy between humanized and murine CD19 CAR-T-cells for treating relapsed and refractory B-ALL. Methods: Clinical data of 80 patients with R/R B-ALL treated with CD19-targeted CAR-T-cells at the Union Hospital of Tongji Medical College of Huazhong University of Science and Technology between May 2016 and March 2023 were analyzed, which included 31 patients with murine CAR-T and 49 with humanized products. Results: The proportion of patients with cytokine-release syndrome (CRS) in the murine and humanized groups was 63.1% and 65.3%, respectively. Moreover, a higher proportion of patients suffered from severe CRS in the murine group than in the humanized CAR-T group (19.4% vs 8.2%, P=0.174). Furthermore, one patient per group died of grade 5 CRS. The incidence of grade 1-2 immune effector cell-associated neurotoxicity syndrome (ICANS) was 12.9% and 6.1%, respectively; severe ICANS were not observed. Among patients receiving murine CAR-T-cells, an overall response (OR) was observed in 74.2%. Conversely, the OR rate of patients receiving humanized CAR-T-cells was 87.8%. During the median follow-up time of 10.5 months, the median recurrence-free survival (RFS) of patients with murine CAR-T-cells was 12 months, which was as long as that of patients with humanized CAR-T-cells. The median overall survival (OS) were not reached in both groups. Of the 45 patients with a bone marrow burden over 20% at baseline, humanized CAR-T therapy was associated with a significantly improved RFS (43.25% vs 33.33%, P=0.027). Bridging transplantation was an independent factor in prolonging OS (χ(2)=8.017, P=0.005) and PFS (χ(2)=6.584, P=0.010). Common risk factors, such as age, high proportion of bone marrow blasts, and BCR-ABL fusion gene expression, had no significant effect on patients' long-term follow-up outcomes. Three patients reached complete remission after reinfusion of humanized CAR-T-cells. However, one patient relapsed one month after his second infusion of murine CAR-T-cells. Conclusions: The results indicate that humanized CAR-T therapy showed durable efficacy in patients with a higher tumor burden in the bone marrow without any influence on safety. Moreover, it could overcome immunogenicity-induced CAR-T resistance, providing treatment options for patients who were not treated successfully with CAR-T therapies.

Bringing cell therapy to tumors: considerations for optimal CAR binder design

Chimeric antigen receptor (CAR)-T cells have revolutionized the immunotherapy of B-cell malignancies and are poised to expand the range of their impact across a broad range of oncology and non-oncology indications. Critical to the success of a given CAR is the choice of binding domain, as this is the key driver for specificity and plays an important role (along with the rest of the CAR structure) in determining efficacy, potency and durability of the cell therapy. While antibodies have proven to be effective sources of CAR binding domains, it has become apparent that the desired attributes for a CAR binding domain do differ from those of a recombinant antibody. This review will address key factors that need to be considered in choosing the optimal binding domain for a given CAR and how binder properties influence and are influenced by the rest of the CAR.

Hypoxia-regulated secretion of IL-12 enhances antitumor activity and safety of CD19 CAR-T cells in the treatment of DLBCL

CD19-targeted chimeric antigen receptor-modified T (CD19 CAR-T) cell therapy has been demonstrated as one of the most promising therapeutic strategies for treating B cell malignancies. However, it has shown limited treatment efficacy for diffuse large B cell lymphoma (DLBCL). This is, in part, due to the tumor heterogeneity and the hostile tumor microenvironment. Human interleukin-12 (IL-12), as a potent antitumor cytokine, has delivered encouraging outcomes in preclinical studies of DLBCL. However, potentially lethal toxicity associated with systemic administration precludes its clinical application. Here, an armed CD19 CAR expressing hypoxia-regulated IL-12 was developed (CAR19/hIL12ODD). In this vector, IL-12 secretion was restricted to hypoxic microenvironments within the tumor site by fusion of IL-12 with the oxygen degradation domain (ODD) of HIF1α. In vitro, CAR19/hIL12ODD-T cells could only secrete bioactive IL-12 under hypoxic conditions, accompanied by enhanced proliferation, robust IFN-γ secretion, increased abundance of CD4+, and central memory T cell phenotype. In vivo, adoptive transfer of CAR19/hIL12ODD-T cells significantly enhanced regression of large, established DLBCL xenografts in a novel immunodeficient Syrian hamster model. Notably, this targeted and controlled IL-12 treatment was without toxicity in this model. Taken together, our results suggest that armed CD19 CARs with hypoxia-controlled IL-12 (CAR19/hIL12ODD) might be a promising and safer approach for treating DLBCL.

Enhancing CAR T-cell Therapy Using Fab-Based Constitutively Heterodimeric Cytokine Receptors

Adoptive T-cell therapy aims to achieve lasting tumor clearance, requiring enhanced engraftment and survival of the immune cells. Cytokines are paramount modulators of T-cell survival and proliferation. Cytokine receptors signal via ligand-induced dimerization, and this principle has been hijacked utilizing nonnative dimerization domains. A major limitation of current technologies resides in the absence of a module that recapitulates the natural cytokine receptor heterodimeric pairing. To circumvent this, we created a new engineered cytokine receptor able to constitutively recreate receptor-heterodimer utilizing the heterodimerization domain derived from the IgG1 antibody (dFab_CCR). We found that the signal delivered by the dFab_CCR-IL2 proficiently mimicked the cytokine receptor heterodimerization, with transcriptomic signatures like those obtained by activation of the native IL2 receptor. Moreover, we found that this dimerization structure was agnostic, efficiently activating signaling through four cytokine receptor families. Using a combination of in vivo and in vitro screening approaches, we characterized a library of 18 dFab_CCRs coexpressed with a clinically relevant solid tumor-specific GD2-specific chimeric antigen receptor (CAR). Based on this characterization, we suggest that the coexpression of either the common β-chain GMCSF or the IL18 dFab_CCRs is optimal to improve CAR T-cell expansion, engraftment, and efficacy. Our results demonstrate how Fab dimerization is efficient and versatile in recapitulating a cytokine receptor heterodimerization signal. This module could be applied for the enhancement of adoptive T-cell therapies, as well as therapies based on other immune cell types. Furthermore, these results provide a choice of cytokine signal to incorporate with adoptive T-cell therapies.

Complexities in comparing the impact of costimulatory domains on approved CD19 CAR functionality

Chimeric antigen receptors (CARs) are engineered to target T cells specifically to tumor cells, resulting in the engineered T cell killing the tumor cell. This technology has been developed to target a range of cancers, with the most notable successes in the treatment of B-cell malignancies where four approved therapies, all targeting CD19, are on the market. These four products differ in the costimulation domains, with axicabtagene ciloleucel (Yescarta) and brexucabtagene autoleucel (Tecartus) both utilizing the CD28 costimulation domain whilst tisagenlecleucel (Kymriah) and lisocabtagene maraleucel (Breyanzi) both utilizing the 4-1BB costimulation domain. There are clearly defined differences in how the CD28 and 4-1BB domains signal, yet it is difficult to ascertain which domain affords a superior mechanism of action given many other differences between these products, including overall CAR architecture and manufacturing methods. Additionally, while in vitro and preclinical in vivo studies have compared CARs with different costimulation domains, it remains a challenge to extrapolate differences observed in this biology across different experimental systems to the overall product performance. While there has been extensive preclinical and clinical work looking at CARs with a variety of targeting domains and architectures, this review will focus on the differences between the four marketed anti-CD19 CAR-Ts, with an additional focus on the impact of hinge and transmembrane domain on CAR activity and interaction with the target cell as well as other proteins on the surface of the T-cell.

Systematic single amino acid affinity tuning of CD229 CAR T cells retains efficacy against multiple myeloma and eliminates on-target off-tumor toxicity

T cells expressing chimeric antigen receptors (CARs) have shown remarkable therapeutic activity against different types of cancer. However, the wider use of CAR T cells has been hindered by the potential for life-threatening toxicities due to on-target off-tumor killing of cells expressing low amounts of the target antigen. CD229, a signaling lymphocyte-activation molecule (SLAM) family member, has previously been identified as a target for CAR T cell-mediated treatment of multiple myeloma (MM) due to its high expression on the surfaces of MM cells. CD229 CAR T cells have shown effective clearance of MM cells in vitro and in vivo. However, healthy lymphocytes also express CD229, albeit at lower amounts than MM cells, causing their unintended targeting by CD229 CAR T cells. To increase the selectivity of CD229 CAR T cells for MM cells, we used a single amino acid substitution approach of the CAR binding domain to reduce CAR affinity. To identify CARs with increased selectivity, we screened variant binding domains using solid-phase binding assays and biolayer interferometry and determined the cytotoxic activity of variant CAR T cells against MM cells and healthy lymphocytes. We identified a CD229 CAR binding domain with micromolar affinity that, when combined with overexpression of c-Jun, confers antitumor activity comparable to parental CD229 CAR T cells but lacks the parental cells' cytotoxic activity toward healthy lymphocytes in vitro and in vivo. The results represent a promising strategy to improve the efficacy and safety of CAR T cell therapy that requires clinical validation.

Rapid generation of CD19 CAR-T cells by minicircle DNA enables anti-tumor activity and prevents fatal CAR-B leukemia

Manufacturing chimeric antigen receptor (CAR)-T cellsusing viral vectors is expensive and time-consuming. In addition, during viral transduction, genes encoding CARs are randomly integrated into the genome, which can cause oncogenesis or produce devastating CARtumor cells. Here, using a virus-free and non-transgenic minicircle DNA (mcDNA) vector, we enabledthe rapid generation of CD19 CAR-T cells within two days. Furthermore, we demonstrated in vitro and in xenograft models that the antitumor effects of CD19 CAR-T cells produced by mcDNA are as effective as those produced by viral vectors. Finally, we showed that our manufacturing process avoids the production of fatal CARtumor cells. Taken together, we have provided a fast, effective, and therapeutically safe method for generating CD19 CAR-T cells for the treatment of leukemia.

Extracellular Domains of CAR Reprogram T-Cell Metabolism Without Antigen Stimulation

Metabolism is an indispensable part of T-cell proliferation, activation, and exhaustion, yet the metabolism of chimeric antigen receptor (CAR)-T cells remains incompletely understood. CARs are comprised of extracellular domains that determine cancer specificity, often using single-chain variable fragments (scFvs), and intracellular domains that trigger signaling upon antigen binding. Here we show that CARs differing only in the scFv reprogram T-cell metabolism differently. Even in the absence of antigens, some CARs increase proliferation and nutrient uptake in T cells. Using stable isotope tracers and mass spectrometry, we observe basal metabolic fluxes through glycolysis doubling and amino acid uptake overtaking anaplerosis in CAR-T cells harboring rituximab scFv, unlike other similar anti-CD20 scFvs. Disparate rituximab and 14g2a-based anti-GD2 CAR-T cells are similarly hypermetabolic and channel excess nutrients to nitrogen overflow metabolism. Since CAR-dependent metabolic reprogramming alters cellular energetics, nutrient utilization, and proliferation, metabolic profiling should be an integral part of CAR-T cell development.

Strength of CAR signaling determines T cell versus ILC differentiation from pluripotent stem cells

Generation of chimeric antigen receptor (CAR) T cells from pluripotent stem cells (PSCs) will enable advances in cancer immunotherapy. Understanding how CARs affect T cell differentiation from PSCs is important for this effort. The recently described artificial thymic organoid (ATO) system supports in vitro differentiation of PSCs to T cells. Unexpectedly, PSCs transduced with a CD19-targeted CAR resulted in diversion of T cell differentiation to the innate lymphoid cell 2 (ILC2) lineage in ATOs. T cells and ILC2s are closely related lymphoid lineages with shared developmental and transcriptional programs. Mechanistically, we show that antigen-independent CAR signaling during lymphoid development enriched for ILC2-primed precursors at the expense of T cell precursors. We applied this understanding to modulate CAR signaling strength through expression level, structure, and presentation of cognate antigen to demonstrate that the T cell-versus-ILC lineage decision can be rationally controlled in either direction, providing a framework for achieving CAR-T cell development from PSCs.

CD19 CAR antigen engagement mechanisms and affinity tuning

Chimeric antigen receptor (CAR) T cell therapy relies on T cells that are guided by synthetic receptors to target and lyse cancer cells. CARs bind to cell surface antigens through an scFv (binder), the affinity of which is central to determining CAR T cell function and therapeutic success. CAR T cells targeting CD19 were the first to achieve marked clinical responses in patients with relapsed/refractory B cell malignancies and to be approved by the U.S. Food and Drug Administration (FDA). We report cryo-EM structures of CD19 antigen with the binder FMC63, which is used in four FDA-approved CAR T cell therapies (Kymriah, Yescarta, Tecartus, and Breyanzi), and the binder SJ25C1, which has also been used extensively in multiple clinical trials. We used these structures for molecular dynamics simulations, which guided creation of lower- or higher-affinity binders, and ultimately produced CAR T cells endowed with distinct tumor recognition sensitivities. The CAR T cells exhibited different antigen density requirements to trigger cytolysis and differed in their propensity to prompt trogocytosis upon contacting tumor cells. Our work shows how structural information can be applied to tune CAR T cell performance to specific target antigen densities.

Novel scFv against Notch Ligand JAG1 Suitable for Development of Cell Therapies toward JAG1-Positive Tumors

The Notch signaling ligand JAG1 is overexpressed in various aggressive tumors and is associated with poor clinical prognosis. Hence, therapies targeting oncogenic JAG1 hold great potential for the treatment of certain tumors. Here, we report the identification of specific anti-JAG1 single-chain variable fragments (scFvs), one of them endowing chimeric antigen receptor (CAR) T cells with cytotoxicity against JAG1-positive cells. Anti-JAG1 scFvs were identified from human phage display libraries, reformatted into full-length monoclonal antibodies (Abs), and produced in mammalian cells. The characterization of these Abs identified two specific anti-JAG1 Abs (J1.B5 and J1.F1) with nanomolar affinities. Cloning the respective scFv sequences in our second- and third-generation CAR backbones resulted in six anti-JAG1 CAR constructs, which were screened for JAG1-mediated T-cell activation in Jurkat T cells in coculture assays with JAG1-positive cell lines. Studies in primary T cells demonstrated that one CAR harboring the J1.B5 scFv significantly induced effective T-cell activation in the presence of JAG1-positive, but not in JAG1-knockout, cancer cells, and enabled specific killing of JAG1-positive cells. Thus, this new anti-JAG1 scFv represents a promising candidate for the development of cell therapies against JAG1-positive tumors.

Rational Protein Design Yields a CD20 CAR with Superior Antitumor Efficacy Compared with CD19 CAR

Chimeric antigen receptors (CAR) are fusion proteins whose functional domains are often connected in a plug-and-play manner to generate multiple CAR variants. However, CARs with highly similar sequences can exhibit dramatic differences in function. Thus, approaches to rationally optimize CAR proteins are critical to the development of effective CAR T-cell therapies. Here, we report that as few as two amino-acid changes in nonsignaling domains of a CAR were able to significantly enhance in vivo antitumor efficacy. We demonstrate juxtamembrane alanine insertion and single-chain variable fragment sequence hybridization as two strategies that could be combined to maximize CAR functionality, and describe a CD20 CAR that outperformed the CD19 CAR in antitumor efficacy in preclinical in vitro and in vivo assays. Precise changes in the CAR sequence drove dramatically different transcriptomic profiles upon antigen stimulation, with the most efficacious CAR inducing an enrichment in highly functional memory T cells upon antigen stimulation. These findings underscore the importance of sequence-level optimization to CAR T-cell function, and the protein-engineering strategy described here may be applied to the development of additional CARs against diverse antigens. See related Spotlight by Scheller and Hudecek, p. 142.

CAR-tropic extracellular vesicles carry tumor-associated antigens and modulate CAR T cell functionality

Tumor-derived extracellular vesicles (EVs) are active contributors in metastasis and immunosuppression in tumor microenvironment. At least some of the EVs carry tumor surface molecules such as tumor-associated antigens (TAAs) and/or checkpoint inhibitors, and potentially could interact with T cells or CAR T cells. Upon contact with T cells, EVs could alter their phenotype and functions by triggering signaling through TCR or CAR reprogramming them to escape immune response. We hypothesize that EVs that possess TAA on the surface will probably interact with CAR T cells which can recognize and bind corresponding TAA. This interaction between EVs and CAR T cells may change the outcome of CAR T-based cancer immunotherapy since it should affect CAR T cells. Also, EVs could serve as adjuvants and antigenic components of antitumor vaccines. Herein, we isolated EVs from B cell precursor leukemia cell line (pre-B ALL) Nalm-6 and demonstrated that recognition and binding of CD19⁺EVs with CD19-CAR T cells strongly depends on the presence of CD19 antigen. CD19⁺EVs induce secretion of pro-inflammatory cytokines (IL-2 and IFN-y) and upregulated transcription of activation-related genes (IFNG, IFNGR1, FASLG, IL2) in CD19-CAR T cells. Tumor necrosis factor receptor superfamily (TNFRSF4 and TNFRSF9) and T-cell exhaustion markers (CTLA4, LAG3, TIM3 and PDCD1LG2) were also upregulated in CD19-CAR T cells after incubation with CD19⁺EVs. Long-term cultivation of CD19⁺ or PD-L1⁺EVs with CD19-CAR T cells led to increased terminal differentiation and functional exhaustion according to elevated expression of PD-1, TIGIT, CD57. In summary, our results suggest that chronic exposure of CD19-CAR T cells to CD19⁺EVs mediates activation and systemic exhaustion in antigen-specific manner, and this negative effect is accompanied by the impaired cytotoxic activity in vitro.

Monitoring anti-CD19 chimeric antigen receptor T cell population by flow cytometry and its consistency with digital droplet polymerase chain reaction

Anti-CD19 chimeric antigen receptor (CAR19) T cell therapy has produced impressive clinical efficacy in patients with relapsed or refractory B-cell malignancies. As a living drug, monitoring the pharmacokinetics of CAR T cells in vivo is an important part of clinical work, which provides valuable information for assessing therapeutic response and related side effects. However, no guidelines are available regarding the detection and quantification of CAR T cells. Flow cytometry is a convenient and commonly used method in monitoring CAR T cell kinetics, but its performance remains to be validated. By using a commercial anti-idiotype antibody that detects unique epitopes on the most popular CAR19 construct, we evaluated important performance parameters, including specificity, lower limit of detection, lower limit of quantification, and precision of flow cytometry in the detection and quantification of CAR19 T cells. Consistency between the results generated by flow cytometry and droplet digital PCR was then investigated in 188 pairs of clinical data and in cell line experiments. Rabbit anti-mouse FMC63 monoclonal antibody possesses high specificity in the detection of CAR19 positive cells by FCM with a cut-off value of 0.05%. The results produced by flow cytometry and ddPCR were well correlated in the clinical samples and in cell lines, but the correlation deteriorated as the abundance of CAR19 positive cells decreased. This was especially evident with less than 0.5% of lymphocytes in clinical data, possibly due to reduced precision (indicated by intra- and inter-assay coefficients of variability) of both droplet digital PCR and flow cytometry. We demonstrated that flow cytometry using anti-idiotype antibody is a reliable and robust approach in the detection and quantification of CAR19 T cells in vivo and has good consistency with droplet digital PCR in monitoring CAR19 T cell kinetics.

Safety and Efficacy of Humanized Versus Murinized CD19 and CD22 CAR T-Cell Cocktail Therapy for Refractory/Relapsed B-Cell Lymphoma

CD19 chimeric antigen receptor T-cell (CAR-T) therapy is efficacious for refractory/relapsed (R/R) B-cell hematological malignancies, yet relapse due to CD19 antigen escape remains a challenge. Our trial explored simultaneous targeting of multiple B-cell antigens as a therapeutic approach that may reduce the risk of relapse. We tested the safety and efficacy of CAR19/22 T-cell cocktail therapy including murinized and humanized products among patients with R/R aggressive B-cell lymphoma. In the group that received the humanized product, 11/12 (91.7%) patients achieved an objective response, including 9/12 (75%) complete responses (CRs) by day 28. The overall response rate and CR rate in the murinized group was 92.9% (13/14) and 42.9% (6/14), respectively. Nine of 12 (75%) patients in the humanized group maintained CR at month 3 following infusion, compared to 5/14 patients (35.7%) in the murinized group. Progression-free survival (PFS) was more favorable in the humanized compared to the murinized group. Most patients had mild cytokine release syndrome (CRS) (grade 1-2) in both groups. This study demonstrates that CAR19/22 T-cell cocktail therapy is safe and effective for R/R B-cell lymphoma and that patients treated with a humanized CAR-T exhibited better efficacy compared to patients treated with a murinized CAR-T therapy.

DLK1-directed chimeric antigen receptor T-cell therapy for hepatocellular carcinoma

BACKGROUND

Delta-like homologue 1 (DLK1), a transmembrane protein, is highly expressed in hepatocellular carcinoma (HCC). We explored whether DLK1-directed chimeric antigen receptor (CAR) T cells can specifically eliminate DLK1-positive HCC cells and serve as a therapeutic strategy for HCC immunotherapy.

METHODS

We first characterized a homemade anti-human DLK1 monoclonal antibody, sequenced the single-chain Fragment variable (scFv) and integrated it into the second-generation CAR lentiviral vector, and then developed the DLK1-directed CAR-T cells. The cytotoxic activities of DLK1-directed CAR-T cells against different HCC cells were evaluated in vitro and in vivo.

RESULTS

The genetically modified human T cells with the DLK1-directed CARs produced cytotoxic activity against DLK1-positive HCC cells. Additionally, the DLK1-directed CARs enhanced T cell proliferation and activation in a DLK1-dependent manner. Interestingly, the DLK1-targeted CAR-T cells significantly inhibited both subcutaneous and peritoneal xenograft tumours derived from human liver cancer cell lines HepG2 or Huh-7.

CONCLUSION

DLK1-directed CAR-T cells specifically suppresses DLK1-positive HCC cells in vitro and in vivo. This study provides a novel transmembrane antigen DLK1 as a potential therapeutic target appropriate for CAR-T cell therapy, which may be further developed as a clinical therapeutic strategy for HCC immunotherapy.

Impact of cryopreservation on CAR T production and clinical response

Adoptive cell therapy with chimeric antigen receptor (CAR) T cells has become an efficient treatment option for patients with hematological malignancies. FDA approved CAR T products are manufactured in centralized facilities from fresh or frozen leukapheresis and the cryopreserved CAR T infusion product is shipped back to the patient. An increasing number of clinical centers produce CAR T cells on-site, which enables the use of fresh and cryopreserved PBMCs and CAR T cells. Here we determined the effect of cryopreservation on PBMCs and CD19 CAR T cells in a cohort of 118 patients treated with fresh CAR T cells and in several patients head-to-head. Cryopreserved PBMCs, obtained from leukapheresis products, contained less erythrocytes and T cells, but were sufficient to produce CAR T cells for therapy. There was no correlation between the recovery of PBMCs and the transduction efficacy, the number of CAR T cells obtained by the end of the manufacturing process, the in vitro reactivity, or the response rate to CAR T therapy. We could show that CAR T cells cryopreserved during the manufacturing process, stored and resumed expansion at a later time point, yielded sufficient cell numbers for treatment and led to complete remissions. Phenotype analysis including T cell subtypes, chemokine receptor and co-inhibitory/stimulatory molecules, revealed that fresh CAR T cells expressed significantly more TIM-3 and contained less effector T cells in comparison to their frozen counterparts. In addition, fresh CAR T infusion products demonstrated increased in vitro anti-tumor reactivity, however cryopreserved CAR T cells still showed high anti-tumor potency and specificity. The recovery of cryopreserved CAR T cells was similar in responding and non-responding patients. Although fresh CAR T infusion products exhibit higher anti-tumor reactivity, the use of frozen PBMCs as staring material and frozen CAR T infusion products seems a viable option, as frozen products still exhibit high in vitro potency and cryopreservation did not seem to affect the clinical outcome.

Development of STEAP1 targeting chimeric antigen receptor for adoptive cell therapy against cancer

Chimeric antigen receptors (CARs) that retarget T cells against CD19 show clinical efficacy against B cell malignancies. Here, we describe the development of a CAR against the six-transmembrane epithelial antigen of prostate-1 (STEAP1), which is expressed in ∼90% of prostate cancers, and subgroups of other malignancies. STEAP1 is an attractive target, as it is associated with tumor invasiveness and progression and only expressed at low levels in normal tissues, apart from the non-vital prostate gland. We identified the antibody coding sequences from a hybridoma and designed a CAR that is efficiently expressed in primary T cells. The T cells acquired the desired anti-STEAP1 specificity, with a polyfunctional response including production of multiple cytokines, proliferation, and the killing of cancer cells. The response was observed for both CD4⁺ and CD8⁺ T cells, and against all STEAP1⁺ target cell lines tested. We evaluated the in vivo CAR T activity in both subcutaneous and metastatic xenograft mouse models of prostate cancer. Here, the CAR T cells infiltrated tumors and significantly inhibited tumor growth and extended survival in a STEAP1-dependent manner. We conclude that the STEAP1 CAR exhibits potent in vitro and in vivo functionality and can be further developed toward potential clinical use.

Selective B cell depletion upon intravenous infusion of replication-incompetent anti-CD19 CAR lentivirus

Anti-CD19 chimeric antigen receptor (CAR)-T therapy for B cell malignancies has shown clinical success, but a major limitation is the logistical complexity and high cost of manufacturing autologous cell products. If engineered for improved safety, direct infusion of viral gene transfer vectors to initiate in vivo CAR-T transduction, expansion, and anti-tumor activity could provide an alternative, universal approach. To explore this approach we administered approximately 20 million replication-incompetent vesicular stomatitis virus G protein (VSV-G) lentiviral particles carrying an anti-CD19CAR-2A-GFP transgene comprising either an FMC63 (human) or 1D3 (murine) anti-CD19 binding domain, or a GFP-only control transgene, to wild-type C57BL/6 mice by tail vein infusion. The dynamics of immune cell subsets isolated from peripheral blood were monitored at weekly intervals. We saw emergence of a persistent CAR-transduced CD3⁺ T cell population beginning week 3-4 that reaching a maximum of 13.5% ± 0.58% (mean ± SD) and 7.8% ± 0.76% of the peripheral blood CD3⁺ T cell population in mice infused with ID3-CAR or FMC63-CAR lentivector, respectively, followed by a rapid decline in each case of the B cell content of peripheral blood. Complete B cell aplasia was apparent by week 5 and was sustained until the end of the protocol (week 8). No significant CAR-positive populations were observed within other immune cell subsets or other tissues. These results indicate that direct intravenous infusion of conventional VSV-G-pseudotyped lentiviral particles carrying a CD19 CAR transgene can transduce T cells that then fully ablate endogenous B cells in wild-type mice.

Parallel CD19/CD20 CAR-Activated T-Cells Are More Effective for Refractory B-Cell Lymphoma In Vitro and In Vivo

Anti-CD19 chimeric antigen receptor (CAR) T-cells are an effective treatment for refractory B-cell lymphoma, but CD19 deletion is prone to relapse. We conducted this study to find more effective dual CAR19/20 T-cells to target B-cell lymphoma and prevent antigen loss leading to recurrence. In this study, we transduced CD19 and CD20 CARs into human T cells in parallel and compared parallel dual CAR19/20, single CAR, and tandem CAR19/20 in vitro and in vivo. After transduction with the corresponding vectors, CD19 and CD20 CARs were dually expressed in human T cells. It was observed that parallel CAR19/20 T-cells contained a substantial proportion of naive subpopulations and were able to proliferate in vitro. Treatment with parallel CAR19/20, single CAR, or tandem CAR19/20 T-cells sustainably induced complete lysis of leukemia cells in a 5 : 1 ratio. Compared with single or tandem CAR T-cell-transplanted mice, parallel CAR19/20 T-cell-transplanted mice exhibited smaller tumor volume, more stable body weight, and longer survival. This suggests that parallel CAR19/20 has superior antilymphoma activity in vivo. In addition, parallel CAR19/20 T-cells were also able to kill patients' lymphoma cells in vitro. Therefore, it can be considered that parallel CAR19/20 is equally effective against single CAR and tandem CAR19/20 in vitro but more effective against lymphoma cells in vivo. This is a promising treatment to prevent the recurrence of antigen loss following CD19-targeted therapy in B lymphoma.

CAR T-Cell Targeting of Macrophage Colony-Stimulating Factor Receptor

Macrophage colony-stimulating factor receptor (M-CSFR) is found in cells of the mononuclear phagocyte lineage and is aberrantly expressed in a range of tumours, in addition to tumour-associated macrophages. Consequently, a variety of cancer therapies directed against M-CSFR are under development. We set out to engineer chimeric antigen receptors (CARs) that employ the natural ligands of this receptor, namely M-CSF or interleukin (IL)-34, to achieve specificity for M-CSFR-expressing target cells. Both M-CSF and IL-34 bind to overlapping regions of M-CSFR, although affinity of IL-34 is significantly greater than that of M-CSF. Matched second- and third-generation CARs targeted using M-CSF or IL-34 were expressed in human T-cells using the SFG retroviral vector. We found that both M-CSF- and IL-34-containing CARs enable T-cells to mediate selective destruction of tumour cells that express enforced or endogenous M-CSFR, accompanied by production of both IL-2 and interferon (IFN)-γ. Although they contain an additional co-stimulatory module, third-generation CARs did not outperform second-generation CARs. M-CSF-containing CARs mediated enhanced cytokine production and cytolytic activity compared to IL-34-containing CARs. These data demonstrate the feasibility of targeting M-CSFR using ligand-based CARs and raise the possibility that the low picomolar affinity of IL-34 for M-CSFR is detrimental to CAR function.

The establishment of polypeptide PSMA-targeted chimeric antigen receptor-engineered natural killer cells for castration-resistant prostate cancer and the induction of ferroptosis-related cell death

Background

The mortality of castration‐resistant prostate cancer (CRPC) is high due to lack of an effective treatment. Chimeric antigen receptor (CAR)‐based therapy is a promising immunotherapeutic strategy. Here, we aimed to design a novel CAR‐natural killer (NK) cells with a clinically significant tumoricidal effect on CRPC.

Methods

We constructed novel CAR‐NK92MI cells with a CD244‐based recombinant lentiviral vector. Different intracellular segments (CD244, NKG2D, or CD3ζ) were screened to identify the best candidate according to cell lysis assay and CD107a expression levels. To enhance the affinity of the CAR to the tumor antigen, we compared an antibody specific for prostate‐specific membrane antigen (anti‐PSMA) with PSMA‐targeted polypeptide (p‐PSMA), which was screened by phage display combinatorial library. Then, CAR‐NK92MI cells with both a high affinity for PSMA and a strong tumoricidal capacity were generated. In addition, we verified their tumor‐killing effect in vitro and in vivo. The release of cytokine by NK92MI cells was compared with that by CAR‐NK92MI cells through flow cytometry and enzyme‐linked immunosorbent assay. Moreover, ferroptosis‐related cell death was explored as a possible underlying mechanism.

Results

Three different CAR intracellular regions CAR1 (CD244), CAR2 (CD244, NKG2D) and CAR3 (CD244, NKG2D, and CD3ζ) were constructed. CAR2 was chosen to confer a stronger tumoricidal ability on CAR‐NK92MI cells. Compared with anti‐PSMA, p‐PSMA exhibited enhanced affinity for the tumor antigen. Thus, p‐PSMA‐CAR‐NK92MI cells, which expressed CAR with a polypeptide‐based antigen‐binding region, an intracellular CD244 and a NKG2D costimulatory domain, were generated. They could selectively and successfully kill PSMA⁺ target cells and exhibited specific lysis rate of 73.19% for PSMA‐positive C4‐2 cells and 33.04% for PSMA‐negative PC3 cells. Additionally, p‐PSMA‐CAR‐NK92MI cells had significantly higher concentrations of IFN‐γ, TNF‐α and granzyme B than NK92MI cells. In a CRPC cancer xenograft model, p‐PSMA‐CAR‐NK92MI cells significantly inhibited tumor growth and exerted a more consistent killing effect than NK92MI cells. Moreover, ferroptosis is a potential mechanism through which CAR‐NK92MI cells attack cancer cells, and is triggered by IFN‐γ.

Conclusions

p‐PSMA‐CAR‐NK92MI cells can effectively kill CRPC^PSMA+ cells in vitro and in vivo. This strategy may provide additional treatment options for patients with CRPC.

Engineering of an Avidity-Optimized CD19-Specific Parallel Chimeric Antigen Receptor That Delivers Dual CD28 and 4-1BB Co-Stimulation

Co-stimulation is critical to the function of chimeric antigen receptor (CAR) T-cells. Previously, we demonstrated that dual co-stimulation can be effectively harnessed by a parallel (p)CAR architecture in which a CD28-containing second generation CAR is co-expressed with a 4-1BB containing chimeric co-stimulatory receptor (CCR). When compared to linear CARs, pCAR-engineered T-cells elicit superior anti-tumor activity in a range of pre-clinical models. Since CD19 is the best validated clinical target for cellular immunotherapy, we evaluated a panel of CD19-specific CAR and pCAR T-cells in this study. First, we generated a panel of single chain antibody fragments (scFvs) by alanine scanning mutagenesis of the CD19-specific FMC63 scFv (V_H domain) and these were incorporated into second generation CD28+CD3ζ CARs. The resulting panel of CAR T-cells demonstrated a broad range of CD19 binding ability and avidity for CD19-expressing tumor cells. Each scFv-modified CAR was then converted into a pCAR by co-expression of an FMC63 scFv-targeted CCR with a 4-1BB endodomain. When compared to second generation CARs that contained an unmodified or mutated FMC63 scFv, each pCAR demonstrated a significant enhancement of tumor re-stimulation potential and IL-2 release, reduced exhaustion marker expression and enhanced therapeutic efficacy in mice with established Nalm-6 leukemic xenografts. These data reinforce the evidence that the pCAR platform delivers enhanced anti-tumor activity through effective provision of dual co-stimulation. Greatest anti-tumor activity was noted for intermediate avidity CAR T-cells and derived pCARs, raising the possibility that effector to target cell avidity is an important determinant of efficacy.

3D-organoid culture supports differentiation of human CAR+ iPSCs into highly functional CAR T cells

Unlimited generation of chimeric antigen receptor (CAR) T cells from human-induced pluripotent stem cells (iPSCs) is an attractive approach for "off-the-shelf" CAR T cell immunotherapy. Approaches to efficiently differentiate iPSCs into canonical αβ T cell lineages, while maintaining CAR expression and functionality, however, have been challenging. We report that iPSCs reprogramed from CD62L⁺ naive and memory T cells followed by CD19-CAR engineering and 3D-organoid system differentiation confers products with conventional CD8αβ-positive CAR T cell characteristics. Expanded iPSC CD19-CAR T cells showed comparable antigen-specific activation, degranulation, cytotoxicity, and cytokine secretion compared with conventional CD19-CAR T cells and maintained homogeneous expression of the TCR derived from the initial clone. iPSC CD19-CAR T cells also mediated potent antitumor activity in vivo, prolonging survival of mice with CD19⁺ human tumor xenografts. Our study establishes feasible methodologies to generate highly functional CAR T cells from iPSCs to support the development of "off-the-shelf" manufacturing strategies.

A Targeted Catalytic Nanobody (T-CAN) with Asparaginolytic Activity

Simple Summary

The therapy of Acute Lymphoblastic Leukemia (ALL) is based on Escherichia coli (E. coli) L-asparaginase, which is a very effective drug in most cases. However, its side effects sometimes prevent its usage or impose its interruption. The main issues derive from its bacterial origin, which elicits a strong immune response in the patient, and from its generalized action on all body compartments. In this work, we describe how we generated a fully active and miniaturized form of L-asparaginase starting from a camel single domain antibody, a class of antibodies known to have a very limited immunogenicity in humans. We also targeted it onto tumor cells by attaching it to an antibody fragment directed onto the CD19 B-cell surface receptor, expressed on ALL cells. We named this new molecule “Targeted Catalytic Nanobody” (T-CAN). The T-CAN is active and successfully binds to CD19 expressing cells in vitro. Thanks to its reduced immunogenic potential, it represents a new tool which deserves further development.

Abstract

E. coli L-asparaginase is an amidohydrolase (EC 3.5.1.1) which has been successfully used for the treatment of Acute Lymphoblastic Leukemia for over 50 years. Despite its efficacy, its side effects, and especially its intrinsic immunogenicity, hamper its usage in a significant subset of cases, thus limiting therapeutic options. Innovative solutions to improve on these drawbacks have been attempted, but none of them have been truly successful so far. In this work, we fully replaced the enzyme scaffold, generating an active, miniaturized form of L-asparaginase by protein engineering of a camel single domain antibody, a class of antibodies known to have a limited immunogenicity in humans. We then targeted it onto tumor cells by an antibody scFv fragment directed onto the CD19 B-cell surface receptor expressed on ALL cells. We named this new type of nanobody-based antibody-drug conjugate “Targeted Catalytic Nanobody” (T-CAN). The new molecule retains the catalytic activity and the binding capability of the original modules and successfully targets CD19 expressing cells in vitro. Thanks to its theoretically reduced immunogenic potential compared to the original molecule, the T-CAN can represent a novel approach to tackle current limitations in L-asparaginase usage.

A comparison of chimeric antigen receptors containing CD28 versus 4-1BB costimulatory domains

Chimeric antigen receptors (CARs) are engineered proteins designed to target T cells to cancer cells. To effectively activate the T cells in which they are expressed, CARs must contain a costimulatory domain. The CAR T cell products approved for the treatment of B cell lymphomas and/or acute lymphoblastic leukaemia or multiple myeloma incorporate either a CD28-derived or a 4-1BB-derived costimulatory domain. Almost all other clinically tested CARs also use costimulatory domains from CD28 or 4-1BB. In preclinical experiments, cytokine release is usually greater with CARs containing CD28 versus 4-1BB costimulatory domains; however, constructs with either domain confer similar anticancer activity in mouse models. T cell products expressing CARs with either CD28 or 4-1BB costimulatory domains have been highly efficacious in patients with relapsed haematological malignancies, with anti-CD19 products having similar activity regardless of the source of the costimulatory domain. In large-cohort clinical trials, the rates of neurological toxicities have been higher with CD28-costimulated CARs, although this finding is probably the result of a combination of factors rather than due to CD28 signalling alone. Future preclinical and clinical research should aim to compare different costimulatory domains while controlling for confounding variables. Herein, we provide an overview of T cell costimulation by CD28 and 4-1BB and, using the available preclinical and clinical data, compare the efficacy and toxicity profiles associated with CARs containing either costimulatory domain.

Antigen-Specific Stimulation and Expansion of CAR-T Cells Using Membrane Vesicles as Target Cell Surrogates

Development of CAR-T therapy led to immediate success in the treatment of B cell leukemia. Manufacturing of therapy-competent functional CAR-T cells needs robust protocols for ex vivo/in vitro expansion of modified T-cells. This step is challenging, especially if non-viral low-efficiency delivery protocols are used to generate CAR-T cells. Modern protocols for CAR-T cell expansion are imperfect since non-specific stimulation results in rapid outgrowth of CAR-negative T cells, and removal of feeder cells from mixed cultures necessitates additional purification steps. To develop a specific and improved protocol for CAR-T cell expansion, cell-derived membrane vesicles are taken advantage of, and the simple structural demands of the CAR-antigen interaction. This novel approach is to make antigenic microcytospheres from common cell lines stably expressing surface-bound CAR antigens, and then use them for stimulation and expansion of CAR-T cells. The data presented in this article clearly demonstrate that this protocol produced antigen-specific vesicles with the capacity to induce stronger stimulation, proliferation, and functional activity of CAR-T cells than is possible with existing protocols. It is predicted that this new methodology will significantly advance the ability to obtain improved populations of functional CAR-T cells for therapy.

Conditional control of chimeric antigen receptor T-cell activity through a destabilizing domain switch and its chemical ligand

BACKGROUND AIMS

Despite the impressive efficacy of chimeric antigen receptor (CAR) T-cell therapy, adverse effects, including cytokine release syndrome and neurotoxicity, impede its therapeutic application, thus making the modulation of CAR T-cell activity a priority. The destabilizing domain mutated from Escherichia coli dihydrofolate reductase (DHFR) is inherently unstable and degraded by proteasomes unless it is stabilized by its chemical ligand trimethoprim (TMP), a Food and Drug Administration-approved drug. Here the authors reveal a strategy to modulate CAR T-cell activity at the protein level by employing DHFR and TMP as a chemical switch system.

METHODS

First, the system was demonstrated to work in human primary T cells. To introduce the system to CAR T cells, DHFR was genetically fused to the carboxyl terminal of a third-generation CAR molecule targeting CD19 (CD19-CAR), constructing the CD19-CAR-DHFR fusion.

RESULTS

The CD19-CAR-DHFR molecule level was shown to be modulated by TMP. Importantly, the incorporation of DHFR had no impact on the recognition specificity and normal function of the CAR molecule. Little adverse effect on cell proliferation and apoptosis was detected. It was proved that TMP could regulate cytokine secretion and the in vitro cytotoxicity of CD19-CAR-DHFR T cells. Furthermore, the in vivo anti-tumor efficacy was demonstrated to be controllable through the manipulation of TMP administration. The approach to control CD19-CAR also succeeded in 19-BBZ(71), another CD19-targeting CAR with a different structure.

CONCLUSIONS

The proposed approach based on DHFR and TMP provides a facile strategy to bring CAR T-cell therapy under conditional user control, and the strategy may have the potential to be transplantable.