PiggyBac-Engineered T Cells Expressing CD19-Specific CARs that Lack IgG1 Fc Spacers Have Potent Activity against B-ALL Xenografts

Advancements and challenges in developing in vivo CAR T cell therapies for cancer treatment

The Chimeric Antigen Receptor (CAR) T cell therapy has emerged as a ground-breaking immunotherapeutic approach in cancer treatment. To overcome the complexity and high manufacturing cost associated with current ex vivo CAR T cell therapy products, alternative strategies to produce CAR T cells directly in the body have been developed in recent years. These strategies involve the direct infusion of CAR genes via engineered nanocarriers or viral vectors to generate CAR T cells in situ. This review offers a comprehensive overview of recent advancements in the development of T cell-targeted CAR generation in situ. Additionally, it identifies the challenges associated with in vivo CAR T method and potential strategies to overcome these issues.

Evolution of the clinical-stage hyperactive TcBuster transposase as a platform for robust non-viral production of adoptive cellular therapies

Cellular therapies for the treatment of human diseases, such as chimeric antigen receptor (CAR) T and natural killer (NK) cells have shown remarkable clinical efficacy in treating hematological malignancies; however, current methods mainly utilize viral vectors that are limited by their cargo size capacities, high cost, and long timelines for production of clinical reagent. Delivery of genetic cargo via DNA transposon engineering is a more timely and cost-effective approach, yet has been held back by less efficient integration rates. Here, we report the development of a novel hyperactive TcBuster (TcB-M) transposase engineered through structure-guided and in vitro evolution approaches that achieves high-efficiency integration of large, multicistronic CAR-expression cassettes in primary human cells. Our proof-of-principle TcB-M engineering of CAR-NK and CAR-T cells shows low integrated vector copy number, a safe insertion site profile, robust in vitro function, and improves survival in a Burkitt lymphoma xenograft model in vivo. Overall, TcB-M is a versatile, safe, efficient and open-source option for the rapid manufacture and preclinical testing of primary human immune cell therapies through delivery of multicistronic large cargo via transposition.

Cas9-induced targeted integration of large DNA payloads in primary human T cells via homology-mediated end-joining DNA repair

The reliance on viral vectors for the production of genetically engineered immune cells for adoptive cellular therapies remains a translational bottleneck. Here we report a method leveraging the DNA repair pathway homology-mediated end joining, as well as optimized reagent composition and delivery, for the Cas9-induced targeted integration of large DNA payloads into primary human T cells with low toxicity and at efficiencies nearing those of viral vectors (targeted knock-in of 1-6.7 kb payloads at rates of up to 70% at multiple targeted genomic loci and with cell viabilities of over 80%). We used the method to produce T cells with an engineered T-cell receptor or a chimaeric antigen receptor and show that the cells maintained low levels of exhaustion markers and excellent capacities for proliferation and cytokine production and that they elicited potent antitumour cytotoxicity in vitro and in mice. The method is readily adaptable to current good manufacturing practices and scale-up processes, and hence may be used as an alternative to viral vectors for the production of genetically engineered T cells for cancer immunotherapies.

CAR T cell therapies for diffuse midline glioma

Diffuse midline glioma (DMG) is a fatal pediatric cancer of the central nervous system (CNS). The location and infiltrative nature of DMG prevents surgical resection and the benefits of palliative radiotherapy are temporary; median overall survival (OS) is 9-11 months. The tumor immune microenvironment (TIME) is 'cold', and has a dominant immunosuppressive myeloid compartment with low levels of infiltrating lymphocytes and proinflammatory molecules. Because survival statistics have been stagnant for many decades, and therapies targeting the unique biology of DMG are urgently needed, this has prompted the clinical assessment of chimeric antigen receptor (CAR) T cell therapies in this setting. We highlight the current landscape of CAR T cell therapy for DMG, the role the TIME may play in the response, and strategies to overcome treatment obstacles.

Targeting FLT3-specific chimeric antigen receptor T cells for acute lymphoblastic leukemia with KMT2A rearrangement

CD19-specific chimeric antigen receptor T (CAR T) immunotherapy is used to treat B-cell malignancies. However, antigen-escape mediated relapse following CAR T therapy has emerged as a major concern. In some relapsed cases, especially KMT2A rearrangement-positive B-acute lymphoblastic leukemia (KMT2A-r B-ALL), most of the B-cell antigens are lost via lineage conversion to the myeloid phenotype, rendering multi-B-cell-antigen-targeted CAR T cell therapy ineffective. Fms-related tyrosine kinase-3 (FLT3) is highly expressed in KMT2A-r B-ALL; therefore, in this study, we aimed to evaluate the antitumor efficacy of CAR T cells targeting both CD19 and FLT3 in KMT2A-r B-ALL cells. We developed piggyBac transposon-mediated CAR T cells targeting CD19, FLT3, or both (dual) and generated CD19-negative KMT2A-r B-ALL models through CRISPR-induced CD19 gene-knockout (KO). FLT3 CAR T cells showed antitumor efficacy against CD19-KO KMT2A-r B-ALL cells both in vitro and in vivo; dual-targeted CAR T cells showed cytotoxicity against wild-type (WT) and CD19-KO KMT2A-r B-ALL cells, whereas CD19 CAR T cells demonstrated cytotoxicity only against WT KMT2A-r B-ALL cells in vitro. Therefore, targeting FLT3-specific CAR T cells would be a promising strategy for KMT2A-r B-ALL cells even with CD19-negative relapsed cases.

Novel xeno-free and serum-free culturing condition to improve piggyBac transposon-based CD19 chimeric antigen receptor T-cell production and characteristics

BACKGROUND AIMS

Chimeric antigen receptor (CAR) T cell is a novel therapy for relapse and refractory hematologic malignancy. Characteristics of CAR T cells are associated with clinical efficacy and toxicity. The type of serum supplements used during cultivation affects the immunophenotype and function of viral-based CAR T cells. This study explores the effect of serum supplements on nonviral piggyBac transposon CAR T-cell production.

METHODS

PiggyBac CD19 CAR T cells were expanded in cultured conditions containing fetal bovine serum, human AB serum or xeno-free serum replacement. We evaluated the effect of different serum supplements on cell expansion, transduction efficiency, immunophenotypes and antitumor activity.

RESULTS

Xeno-free serum replacement exhibited comparable CAR surface expression, cell expansion and short-term antitumor activity compared with conventional serum supplements. However, CAR T cells cultivated with xeno-free serum replacement exhibited an increased naïve/stem cell memory population and better T-cell expansion after long-term co-culture as well as during the tumor rechallenge assay.

CONCLUSIONS

Our study supports the usage of xeno-free serum replacement as an alternative source of serum supplements for piggyBac-based CAR T-cell expansion.

piggyBac-transposon-mediated CAR-T cells for the treatment of hematological and solid malignancies

Since the introduction of the use of chimeric antigen receptor T-cell therapy (CAR-T therapy) dramatically changed the therapeutic strategy for B cell tumors, various CAR-T cell products have been developed and applied to myeloid and solid tumors. Although viral vectors have been widely used to produce genetically engineered T cells, advances in genetic engineering have led to the development of methods for producing non-viral, gene-modified CAR-T cells. Recent progress has revealed that non-viral CAR-T cells have a significant impact not only on the simplicity of the production process and the accessibility of non-viral vectors but also on the function of the cells themselves. In this review, we focus on piggyBac-transposon-based CAR-T cells among non-viral, gene-modified CAR-T cells and discuss their characteristics, preclinical development, and recent clinical applications.

Switchable targeting of solid tumors by BsCAR T cells

The development of chimeric antigen receptor (CAR) T cell therapy has become a critical milestone in modern oncotherapy. Despite the remarkable in vitro effectiveness, the problem of safety and efficacy of CAR T cell therapy against solid tumors is challenged by the lack of tumor-specific antigens required to avoid on-target off-tumor effects. Spatially separating the cytotoxic function of CAR T cells from tumor antigen recognition provided by protein mediators allows for the precise control of CAR T cell cytotoxicity. Here, the high affinity and capability of the bacterial toxin-antitoxin barnase-barstar system were adopted to guide CAR T cells to solid tumors. The complementary modules based on (1) ankyrin repeat (DARPin)-barnase proteins and (2) barstar-based CAR (BsCAR) were designed to provide switchable targeting to tumor cells. The alteration of the DARPin-barnase switches enabled the targeting of different tumor antigens with a single BsCAR. A gradual increase in cytokine release and tunable BsCAR T cell cytotoxicity was achieved by varying DARPin-barnase loads. Switchable BsCAR T cell therapy was able to eradicate the HER2+ ductal carcinoma in vivo. Guiding BsCAR T cells by DARPin-barnase switches provides a universal approach for a controlled multitargeted adoptive immunotherapy.

The Past, Present, and Future of Non-Viral CAR T Cells

Adoptive transfer of chimeric antigen receptor (CAR) T lymphocytes is a powerful technology that has revolutionized the way we conceive immunotherapy. The impressive clinical results of complete and prolonged response in refractory and relapsed diseases have shifted the landscape of treatment for hematological malignancies, particularly those of lymphoid origin, and opens up new possibilities for the treatment of solid neoplasms. However, the widening use of cell therapy is hampered by the accessibility to viral vectors that are commonly used for T cell transfection. In the era of messenger RNA (mRNA) vaccines and CRISPR/Cas (clustered regularly interspaced short palindromic repeat-CRISPR-associated) precise genome editing, novel and virus-free methods for T cell engineering are emerging as a more versatile, flexible, and sustainable alternative for next-generation CAR T cell manufacturing. Here, we discuss how the use of non-viral vectors can address some of the limitations of the viral methods of gene transfer and allow us to deliver genetic information in a stable, effective and straightforward manner. In particular, we address the main transposon systems such as Sleeping Beauty (SB) and piggyBac (PB), the utilization of mRNA, and innovative approaches of nanotechnology like Lipid-based and Polymer-based DNA nanocarriers and nanovectors. We also describe the most relevant preclinical data that have recently led to the use of non-viral gene therapy in emerging clinical trials, and the related safety and efficacy aspects. We will also provide practical considerations for future trials to enable successful and safe cell therapy with non-viral methods for CAR T cell generation.

Characterizing piggyBat-a transposase for genetic modification of T cells

Chimeric antigen receptor (CAR) T cells targeting CD19 have demonstrated remarkable efficacy in the treatment of B cell malignancies. Current CAR T cell manufacturing protocols are complex and costly due to their reliance on viral vectors. Non-viral systems of genetic modification, such as with transposase and transposon systems, offer a potential streamlined alternative for CAR T cell manufacture and are currently being evaluated in clinical trials. In this study, we utilized the previously described transposase from the little brown bat, designated piggyBat, for production of CD19-specific CAR T cells. PiggyBat demonstrates efficient CAR transgene delivery, with a relatively low variability in integration copy number across a range of manufacturing conditions as well as a similar integration site profile to super-piggyBac transposon and viral vectors. PiggyBat-generated CAR T cells demonstrate CD19-specific cytotoxic efficacy in vitro and in vivo. These data demonstrate that alternative, naturally occurring DNA transposons can be efficiently re-tooled to be exploited in real-world applications.

Evolving Strategies to Eliminate the CD4 T Cells HIV Viral Reservoir via CAR T Cell Immunotherapy

Although the advent of ART has significantly reduced the morbidity and mortality associated with HIV infection, the stable pool of HIV in latently infected cells requires lifelong treatment adherence, with the cessation of ART resulting in rapid reactivation of the virus and productive HIV infection. Therefore, these few cells containing replication-competent HIV, known as the latent HIV reservoir, act as the main barrier to immune clearance and HIV cure. While several strategies involving HIV silencing or its reactivation in latently infected cells for elimination by immune responses have been explored, exciting cell based immune therapies involving genetically engineered T cells expressing synthetic chimeric receptors (CAR T cells) are highly appealing and promising. CAR T cells, in contrast to endogenous cytotoxic T cells, can function independently of MHC to target HIV-infected cells, are efficacious and have demonstrated acceptable safety profiles and long-term persistence in peripheral blood. In this review, we present a comprehensive picture of the current efforts to target the HIV latent reservoir, with a focus on CAR T cell therapies. We highlight the current challenges and advances in this field, while discussing the importance of novel CAR designs in the efforts to find a HIV cure.

Donor T cells for CAR T cell therapy

Adoptive cell therapy using patient-derived chimeric receptor antigen (CAR) T cells redirected against tumor cells has shown remarkable success in treating hematologic cancers. However, wider accessibility of cellular therapies for all patients is needed. Manufacture of patient-derived CAR T cells is limited by prolonged lymphopenia in heavily pre-treated patients and risk of contamination with tumor cells when isolating T cells from patient blood rich in malignant blasts. Donor T cells provide a good source of immune cells for adoptive immunotherapy and can be used to generate universal off-the-shelf CAR T cells that are readily available for administration into patients as required. Genome editing tools such as TALENs and CRISPR-Cas9 and non-gene editing methods such as short hairpin RNA and blockade of protein expression are currently used to enhance CAR T cell safety and efficacy by abrogating non-specific toxicity in the form of graft versus host disease (GVHD) and preventing CAR T cell rejection by the host.

PiggyBac Transposon-Mediated CD19 Chimeric Antigen Receptor-T Cells Derived From CD45RA-Positive Peripheral Blood Mononuclear Cells Possess Potent and Sustained Antileukemic Function

The quality of chimeric antigen receptor (CAR)-T cell products, namely, memory and exhaustion markers, affects the long-term functionality of CAR-T cells. We previously reported that piggyBac (PB) transposon-mediated CD19 CAR-T cells exhibit a memory-rich phenotype that is characterized by the high proportion of CD45RA⁺/C-C chemokine receptor type 7 (CCR7)⁺ T-cell fraction. To further investigate the favorable phenotype of PB-CD19 CAR-T cells, we generated PB-CD19 CAR-T cells from CD45RA⁺ and CD45RA⁻ peripheral blood mononuclear cells (PBMCs) (RA⁺ CAR and RA⁻ CAR, respectively), and compared their phenotypes and antitumor activity. RA⁺ CAR-T cells showed better transient gene transfer efficiency 24 h after transduction and superior expansion capacity after 14 days of culture than those shown by RA⁻ CAR-T cells. RA⁺ CAR-T cells exhibited dominant CD8 expression, decreased expression of the exhaustion marker programmed cell death protein-1 (PD-1) and T-cell senescence marker CD57, and enriched naïve/stem cell memory fraction, which are associated with the longevity of CAR-T cells. Transcriptome analysis showed that canonical exhaustion markers were downregulated in RA⁺ CAR-T, even after antigen stimulation. Although antigen stimulation could increase CAR expression, leading to tonic CAR signaling and exhaustion, the expression of CAR molecules on cell surface after antigen stimulation in RA⁺ CAR-T cells was controlled at a relatively lower level than that in RA⁻ CAR-T cells. In the in vivo stress test, RA⁺ CAR-T cells achieved prolonged tumor control with expansion of CAR-T cells compared with RA⁻ CAR-T cells. CAR-T cells were not detected in the control or RA⁻ CAR-T cells but RA⁺ CAR-T cells were expanded even after 50 days of treatment, as confirmed by sequential bone marrow aspiration. Our results suggest that PB-mediated RA⁺ CAR-T cells exhibit a memory-rich phenotype and superior antitumor function, thus CD45RA⁺ PBMCs might be considered an efficient starting material for PB-CAR-T cell manufacturing. This novel approach will be beneficial for effective treatment of B cell malignancies.

Investigation of product-derived lymphoma following infusion of piggyBac-modified CD19 chimeric antigen receptor T cells

We performed a phase 1 clinical trial to evaluate outcomes in patients receiving donor-derived CD19-specific chimeric antigen receptor (CAR) T cells for B-cell malignancy that relapsed or persisted after matched related allogeneic hemopoietic stem cell transplant. To overcome the cost and transgene-capacity limitations of traditional viral vectors, CAR T cells were produced using the piggyBac transposon system of genetic modification. Following CAR T-cell infusion, 1 patient developed a gradually enlarging retroperitoneal tumor due to a CAR-expressing CD4+ T-cell lymphoma. Screening of other patients led to the detection, in an asymptomatic patient, of a second CAR T-cell tumor in thoracic para-aortic lymph nodes. Analysis of the first lymphoma showed a high transgene copy number, but no insertion into typical oncogenes. There were also structural changes such as altered genomic copy number and point mutations unrelated to the insertion sites. Transcriptome analysis showed transgene promoter-driven upregulation of transcription of surrounding regions despite insulator sequences surrounding the transgene. However, marked global changes in transcription predominantly correlated with gene copy number rather than insertion sites. In both patients, the CAR T-cell-derived lymphoma progressed and 1 patient died. We describe the first 2 cases of malignant lymphoma derived from CAR gene-modified T cells. Although CAR T cells have an enviable record of safety to date, our results emphasize the need for caution and regular follow-up of CAR T recipients, especially when novel methods of gene transfer are used to create genetically modified immune therapies. This trial was registered at www.anzctr.org.au as ACTRN12617001579381.

Advances in chimeric antigen receptor T cells

PURPOSE OF REVIEW

To discuss the important advances in CAR T cell therapy over the past year, focusing on clinical results where available.

RECENT FINDINGS

Approximately 30 years after they were first conceived of and 15 years after the first small-scale single-center clinical trials, the past 3 years represent a major milestone in the development of CAR T cells. In the United States, the Food and Drug Administration (FDA) approved Tisagenlecleucel for the treatment of relapsed/refractory B-ALL and Axicabtagene Ciloleucel, for adults with relapsed/refractory diffuse large B cell lymphoma (R/R DLBCL) in 2017. Tisagenlecleucel received a second indication in adults with R/R DLBCL in 2018. Regulatory approval for CAR T cells was then granted in Europe, Canada, Australia, and Japan. Most recently, in July 2020 the FDA granted regulatory approval to a third CAR T cell product, Brexucabtagene Autoleucel for mantle cell lymphoma. All products target the CD19 antigen but differ in the costimulatory molecule within the CAR construct. Currently, it is unknown whether there are any differences in clinical activity or toxicity between these products.

SUMMARY

The CAR T cell the platform is evolving at a rapid pace and is expected to further improve the therapeutic outcomes of hematological malignancies.

PiggyBac-Generated CAR19-T Cells Plus Lenalidomide Cause Durable Complete Remission of Triple-Hit Refractory/Relapsed DLBCL: A Case Report

MYC/BCL2/BCL6 triple-hit lymphoma (THL) is an uncommon subset of high-grade B-cell lymphoma with aggressive clinical behavior and poor prognosis. TP53 mutation is an independently poor progonistic indicator in patients with THL, hence novel therapeutic strategies are needed for these patients. CD19-directed chimeric antigen receptor(CAR19)-T cell therapy has shown promising efficacy for relapsed/refractory diffuse large B cell lymphoma (RR DLBCL), but the majority of CAR19-T cell products to date have been manufactured using viral vectors. PiggyBac transposon system, with an inclination to memory T cells, offers a more convenient and economical alternative for transgene delivery. We herein report the first case of triple-hit RR DLBCL with TP53 mutation who was treated with piggyBac-generated CAR19-T cells and accompanied by grade 2 cytokine release syndrome. The patient obtained a complete remission (CR) in the 2nd month post-infusion and demanded maintenance therapy. Whether maintenance therapy is favorable and how to administrate it after CAR-T cell infusion remain controversial. Preclinical studies demonstrated that lenalidomide could enhance antitumor activity of CAR19-T cells. Therefore, we pioneered oral lenalidomide after CAR19-T therapy in the patient from the 4th month, and he discontinued after one cycle due to side effects. The patient has still kept sustained CR for over 24 months. Our case have firstly demonstrated the feasibility, preliminary safety and efficacy of piggyBac-produced CAR19-T cell therapy in triple-hit lymphoma. The innovative combination with lenalidomide warrants further investigation. Our findings shed new light on the possible solutions to improve short-term relapse after CAR19-T cell therapy in RR DLBCL. ChiCTR, number ChiCTR1800018111.

Phase I clinical trial of EGFR-specific CAR-T cells generated by the piggyBac transposon system in advanced relapsed/refractory non-small cell lung cancer patients

PURPOSE

This phase I clinical trial is designed to assess the safety and feasibility of the epidermal growth factor receptor (EGFR) chimeric antigen receptor (CAR) T-cell generated by the piggyBac transposon system in advanced relapsed/refractory non-small cell lung cancer (NSCLC) patients. Compared to viral systems, the piggyBac transposon system is a simpler, more economical, and alternative way to introduce chimeric antigen receptor (CAR) transgenes into T cells.

METHODS

This study recruited nine patients with advanced relapsed/refractory EGFR-positive NSCLC for two cycles of the piggyBac-generated EGFR-CAR T cells at dose of 1 × 10⁶ cells/kg or 3 × 10⁶ cells/kg of body weight. The patients were monitored for adverse events, clinical response, and persistence of plasma GFR-CAR T cells.

RESULTS

Infusions of piggyBac-generated EGFR-CAR T cells were well tolerated in all nine patients. The most common adverse events were grade 1 to 3 fever and there were no patients who experienced grade 4 adverse events or serious cytokine release syndrome. After treatment, eight of nine patients showed detectable EGFR-CAR T cells in their peripheral blood. One patient showed a partial response and lasted for more than 13 months, while six had stable disease, and two had progressed disease. The progression-free survival of these nine patients was 7.13 months (95% CI 2.71-17.10 months), while the median overall survival was 15.63 months (95% CI 8.82-22.03 months).

CONCLUSION

This Phase I clinical trial revealed that the non-viral piggyBac transposon system-engineered EGFR-CAR T-cell therapy is feasible and safe in treatment of EGFR-positive advanced relapsed/refractory NSCLC patients. Future study will assess it in more patients or even possibly with a higher dose. Trial registration number NCT03182816.

The Intracellular Domain of CD40 is a Potent Costimulatory Element in Chimeric Antigen Receptors

The costimulatory domains incorporated into second-generation and third-generation chimeric antigen receptors (CARs) strongly influence CAR-T-cell function. Here, we explored second-generation and third-generation CARs harboring the signaling domain of the CD40 receptor as a new costimulatory element in comparison with similar CARs carrying the 4-1BB domain. In CARs of both generations, CD40 was more potent than 4-1BB in triggering the NF-κB signaling pathway. In human T cells from 2 donors, CD40 was comparable to 4-1BB in upregulating costimulatory and activation markers, inducing proinflammatory cytokine secretion and mediating target cell killing. Interestingly, differences in the response pattern of T cells from the 2 donors with respect to CD40 and 4-1BB were evident. We conclude that in human T cells, the CD40 signaling domain is a potent costimulatory element in both second-generation and third-generation CARs.

Development of CAR T-cell lymphoma in two of ten patients effectively treated with piggyBac modified CD19 CAR T-cells

CD19-specific chimeric antigen receptor (CAR19) T-cells effectively induce remission of B-cell malignancy, but the cost and complexity of production using viral vectors is a factor limiting widespread application. Furthermore, the small cargo capacity of viral vectors may hamper future development of more heavily engineered CAR T-cells. We demonstrated the feasibility of generating CAR19 T-cells from HLA-matched donors of sibling allogeneic hematopoietic stem cell transplant (HSCT) patients via a simple and inexpensive method using the high-capacity piggyBac transposon. A cohort of 10 patients with relapsed or refractory B-cell acute lymphoblastic leukemia or aggressive lymphoma following HSCT were the first human subjects to receive piggyBac-generated CAR19 T-cells. Treatment with intra-patient escalating doses of CAR19 T-cells was effective, with all 9 evaluable patients achieving complete remission. At a median follow-up of 18.0 months, 5 patients remained in complete remission of B-cell malignancy. One patient died of viral sepsis. Four patients developed cytokine release syndrome of maximum grade 2, and no neurotoxicity or new graft-versus-host disease occurred. However, two patients developed malignant CAR19 T-cell tumors, one of whom was successfully treated; one patient died of the secondary tumor. The piggyBac system represents a feasible alternative to viral vectors for the generation of effective CAR19 T-cells, but its oncogenic potential in the context of the described production process will need to be addressed before any further clinical use is possible. This trial was registered at www.anzctr.org.au as ACTRN12617001579381.

Mutated GM-CSF-based CAR-T cells targeting CD116/CD131 complexes exhibit enhanced anti-tumor effects against acute myeloid leukaemia

Objectives

As the prognosis of relapsed/refractory (R/R) acute myeloid leukaemia (AML) remains poor, novel treatment strategies are urgently needed. Clinical trials have shown that chimeric antigen receptor (CAR)‐T cells for AML are more challenging than those targeting CD19 in B‐cell malignancies. We recently developed piggyBac‐modified ligand‐based CAR‐T cells that target CD116/CD131 complexes, also known as the GM‐CSF receptor (GMR), for the treatment of juvenile myelomonocytic leukaemia. This study therefore aimed to develop a novel therapeutic method for R/R AML using GMR CAR‐T cells.

Methods

To further improve the efficacy of the original GMR CAR‐T cells, we have developed novel GMR CAR vectors incorporating a mutated GM‐CSF for the antigen‐binding domain and G4S spacer. All GMR CAR‐T cells were generated using a piggyBac‐based gene transfer system. The anti‐tumor effect of GMR CAR‐T cells was tested in mouse AML xenograft models.

Results

Nearly 80% of the AML cells predominant in myelomonocytic leukaemia were found to express CD116. GMR CAR‐T cells exhibited potent cytotoxic activities against CD116⁺ AML cells in vitro. Furthermore, GMR CAR‐T cells incorporating a G4S spacer significantly improved long‐term in vitro and in vivo anti‐tumor effects. By employing a mutated GM‐CSF at residue 21 (E21K), the anti‐tumor effects of GMR CAR‐T cells were also improved especially in long‐term in vitro settings. Although GMR CAR‐T cells exerted cytotoxic effects on normal monocytes, their lethality on normal neutrophils, T cells, B cells and NK cells was minimal.

Conclusions

GMR CAR‐T cell therapy represents a promising strategy for CD116⁺ R/R AML.

Priming Leukemia with 5-Azacytidine Enhances CAR T Cell Therapy

Purpose

Despite the success of chimeric antigen receptor (CAR) T cells in clinical studies, a significant proportion of responding patients eventually relapsed, with the latter correlating with low CAR T cell expansion and persistence.

Methods and Results

Using patient-derived xenograft (PDX) mouse models of CD19⁺ B cell acute lymphoblastic leukemia (B-ALL), we show that priming leukemia-bearing mice with 5-azacytidine (AZA) enhances CAR T cell therapy. AZA given 1 day prior to CAR T cell infusion delayed leukemia growth and promoted CAR T cell expansion and effector function. Priming leukemia cells with AZA increased CAR T cell/target cell conjugation and target cell killing, promoted CAR T cell divisions and expanded IFNγ⁺ effector T cells in co-cultures with CD19⁺ leukemia Nalm-6 and Raji cells. Transcriptome analysis revealed activation of diverse immune pathways in leukemia cells isolated from mice treated with AZA. We propose that epigenetic priming with AZA induces transcriptional changes that sensitize tumor cells to subsequent CAR T cell treatment. Among the candidate genes up-regulated by AZA is TNFSF4 which encodes OX40L, one of the strongest T cell co-stimulatory ligands. OX40L binds OX40, the TNF receptor superfamily member highly specific for activated T cells. TNFSF4 is heterogeneously expressed in a panel of pediatric PDXs, and high TNFSF4 expression correlated with increased CAR T cell numbers identified in co-cultures with individual PDXs. High OX40L expression in Nalm-6 cells increased their susceptibility to CAR T cell killing while OX40L blockade reduced leukemia cell killing.

Conclusion

We propose that treatment with AZA activates OX40L/OX40 co-stimulatory signaling in CAR T cells. Our data suggest that the clinical use of AZA before CAR T cells could be considered.

Autologous antigen-presenting cells efficiently expand piggyBac transposon CAR-T cells with predominant memory phenotype

The quality of chimeric antigen receptor (CAR)-T cell products, including the expression of memory and exhaustion markers, has been shown to influence their long-term functionality. The manufacturing process of CAR-T cells should be optimized to prevent early T cell exhaustion during expansion. Activation of T cells by monoclonal antibodies is a critical step for T cell expansion, which may sometimes induce excess stimulation and exhaustion of T cells. Given that piggyBac transposon (PB)-based gene transfer could circumvent the conventional pre-activation of T cells, we established a manufacturing method of PB-mediated HER2-specific CAR-T cells (PB-HER2-CAR-T cells) that maintains their memory phenotype without early T cell exhaustion. Through stimulation of CAR-transduced T cells with autologous peripheral blood mononuclear cell-derived feeder cells expressing both truncated HER2, CD80, and 4-1BBL proteins, we could effectively propagate memory-rich, PD-1-negative PB-HER2-CAR-T cells. PB-HER2-CAR-T cells demonstrated sustained antitumor efficacy in vitro and debulked the HER2-positive tumors in vivo. Mice treated with PB-HER2-CAR-T cells rejected the second tumor establishment owing to the in vivo expansion of PB-HER2-CAR-T cells. Our simple and effective manufacturing process using PB system and genetically modified donor-derived feeder cells is a promising strategy for the use of PB-CAR-T cell therapy.

Renaissance of armored immune effector cells, CAR-NK cells, brings the higher hope for successful cancer therapy

In recent decades, a new method of cellular immunotherapy was introduced based on engineering and empowering the immune effector cells. In this type of immunotherapy, the immune effector cells are equipped with chimeric antigen receptor (CAR) to specifically target cancer cells. In much of the trials and experiments, CAR-modified T cell immunotherapy has achieved very promising therapeutic results in the treatment of some types of cancers and infectious diseases. However, there are also some considerable drawbacks in the clinical application of CAR-T cells although much effort is in progress to rectify the issues. In some conditions, CAR-T cells initiate over-activated and strong immune responses, therefore, causing unexpected side-effects such as systemic cytokine toxicity (i.e., cytokine release syndrome), neurotoxicity, on-target, off-tumor toxicity, and graft-versus-host disease (GvHD). To overcome these limitations in CAR-T cell immunotherapy, NK cells as an alternative source of immune effector cells have been utilized for CAR-engineering. Natural killer cells are key players of the innate immune system that can destroy virus-infected cells, tumor cells, or other aberrant cells with their efficient recognizing capability. Compared to T cells, CAR-transduced NK cells (CAR-NK) have several advantages, such as safety in clinical use, non-MHC-restricted recognition of tumor cells, and renewable and easy cell sources for their preparation. In this review, we will discuss the recent preclinical and clinical studies, different sources of NK cells, transduction methods, possible limitations and challenges, and clinical considerations.

αPD-1-mesoCAR-T cells partially inhibit the growth of advanced/refractory ovarian cancer in a patient along with daily apatinib

Epithelial ovarian cancer (EOC) is the leading cause of death among gynecological malignancies in China. In particular, advanced/refractory ovarian cancer lacks effective targeted therapies due to the immunosuppressive and proangiogenic tumor microenvironment. Mesothelin (MSLN) has been found to be highly expressive in most EOC. Targeting MSLN by antibodies or chimeric antigen receptor-modified T (CAR-T) cells and immune checkpoint blockades as well as apatinib, an anti-angiogenic drug, have been used in patients with refractory ovarian cancer. Apatinib was reported to promote the infiltration of CD8⁺ T cells in lung cancer. However, the combination therapy of CAR-T secreting anti-PD-1 antibody with apatinib in EOC has not been reported.

CASE PRESENTATION

Here we report a case of refractory EOC in a patient who had relapsed after multiline chemotherapy. The patient received autologous T cells that contained sequences encoding single-chain variable fragments specific for MSLN and full-length antibody for PD-1 (αPD-1). The modified T cells were called αPD-1-mesoCAR-T cells. After infusion, the copy number and PD-1 antibody secretion of the CAR-T cells were increased in the blood. By application of multimodality tumor tracking, MRI of the liver showed shrinkage of metastatic nodules from average diameter of 71.3-39.1 mm at month 2. The patient achieved partial response and survived more than 17 months. IL-6 levels in the patient fluctuated from the baseline to 2-4-folds after treatment, but side effects were mild with only grade 1 hypertension and fatigue.

CONCLUSION

αPD-1-mesoCAR-T cell therapy combined with apatinib demonstrates a potential therapeutic effect on advanced refractory ovarian cancer.

TRIAL REGISTRATION NUMBER

NCT03615313.

Genetic and epigenetic modification of human primary NK cells for enhanced antitumor activity

Cancer immunotherapy using genetically modified immune cells such as those expressing chimeric antigen receptors has shown dramatic outcomes in patients with refractory and relapsed malignancies. Natural killer (NK) cells as a member of the innate immune system, possessing both anticancer (cytotoxic) and proinflammatory (cytokine) responses to cancers and rare off-target toxicities have great potential for a wide range of cancer therapeutic settings. Therefore, improving NK cell antitumor activity through genetic modification is of high interest in the field of cancer immunotherapy. However, gene manipulation in primary NK cells has been challenging because of broad resistance to many genetic modification methods that work well in T cells. Here we review recent successful approaches for genetic and epigenetic modification of NK cells including epigenetic remodeling, transposons, mRNA-mediated gene delivery, lentiviruses, and CRISPR gene targeting.

Optimisation of Tet-On inducible systems for Sleeping Beauty-based chimeric antigen receptor (CAR) applications

Regulated expression of genetic elements that either encode polypeptides or various types of functional RNA is a fundamental goal for gene therapy. Inducible expression may be preferred over constitutive promoters to allow clinician-based control of gene expression. Existing Tet-On systems represent one of the tightest rheostats for control of gene expression in mammals. However, basal expression in absence of tetracycline compromises the widespread application of Tet-controlled systems in gene therapy. We demonstrate that the order of P2A-linked genes of interest was critical for maximal response and tightness of a chimeric antigen receptor (CAR)-based construct. The introduction of G72V mutation in the activation region of the TetR component of the rtTA further improved the fold response. Although the G72V mutation resulted in a removal of a cryptic splice site within rtTA, additional removal of this splice site led to only a modest improvement in the fold-response. Selective removal of key promoter elements (namely the BRE, TATA box, DPE and the four predicted Inr) confirmed the suitability of the minimal CMV promoter and its downstream sequences for supporting inducible expression. The results demonstrate marked improvement of the rtTA based Tet-On system in Sleeping Beauty for applications such as CAR T cell therapy.

T-Cell Receptor-Based Immunotherapy for Hematologic Malignancies

Adoptive immunotherapy with engineered T cells is at the forefront of cancer treatment. T cells can be engineered to express T-cell receptors (TCRs) specific for tumor-associated antigens (TAAs) derived from intracellular or cell surface proteins. T cells engineered with TCRs (TCR-T) allow for targeting diverse types of TAAs, including proteins overexpressed in malignant cells, those with lineage-restricted expression, cancer-testis antigens, and neoantigens created from abnormal, malignancy-restricted proteins. Minor histocompatibility antigens can also serve as TAAs for TCR-T to treat relapsed hematologic malignancies after allogeneic hematopoietic cell transplantation. Moreover, TCR constructs can be modified to improve safety and enhance function and persistence of TCR-T. Transgenic T-cell receptor therapies targeting 3 different TAAs are in early-phase clinical trials for treatment of hematologic malignancies. Preclinical studies of TCR-T specific for many other TAAs are underway and offer great promise as safe and effective therapies for a wide range of cancers.

Recent advances in CAR-T cell engineering

Chimeric antigen receptor T (CAR-T) cell therapy is regarded as an effective solution for relapsed or refractory tumors, particularly for hematological malignancies. Although the initially approved anti-CD19 CAR-T therapy has produced impressive outcomes, setbacks such as high relapse rates and resistance were experienced, driving the need to discover engineered CAR-T cells that are more effective for therapeutic use. Innovations in the structure and manufacturing of CAR-T cells have resulted in significant improvements in efficacy and persistence, particularly with the development of fourth-generation CAR-T cells. Paired with an immune modifier, the use of fourth-generation and next-generation CAR-T cells will not be limited because of cytotoxic effects and will be an efficient tool for overcoming the tumor microenvironment. In this review, we summarize the recent transformations in the ectodomain, transmembrane domain, and endodomain of the CAR structure, which, together with innovative manufacturing technology and improved cell sources, improve the prospects for the future development of CAR-T cell therapy.

Value and affordability of CAR T-cell therapy in the United States

In the United States the increasing number of Food and Drug Administration (FDA)-approved, innovative, and potentially effective commercial cancer therapies pose a significant financial burden on public and private payers. Chimeric antigen receptor (CAR) T cells are prototypical of this challenge. In 2017 and 2018, tisagenlecleucel (Kymriah, Novartis) and axicabtagene ciloleucel (Yescarta, Kite) were approved by the FDA for use after showing groundbreaking results in relapsed/refractory B-cell malignancies. In 2020 and 2021, four further submissions to the FDA are expected for CAR T-cell therapies for indolent and aggressive B-cell malignancies and plasma cell myeloma. Yet, with marketed prices of over $350,000 per infusion for the two FDA-approved therapies and similar price tags expected for the coming products, serious concerns are raised over value and affordability. In this review we summarize recent, peer-reviewed cost-effectiveness studies of tisagenlecleucel and axicabtagene ciloleucel in the United States; discuss key issues concerning the health plan budget impact of CAR T-cell therapy; and review policy, payment and scientific approaches that may improve the value and affordability of CAR T-cell therapy.

Transposon-Based CAR T Cells in Acute Leukemias: Where are We Going?

Chimeric Antigen Receptor (CAR) T-cell therapy has become a new therapeutic reality for refractory and relapsed leukemia patients and is also emerging as a potential therapeutic option in solid tumors. Viral vector-based CAR T-cells initially drove these successful efforts; however, high costs and cumbersome manufacturing processes have limited the widespread clinical implementation of CAR T-cell therapy. Here we will discuss the state of the art of the transposon-based gene transfer and its application in CAR T immunotherapy, specifically focusing on the Sleeping Beauty (SB) transposon system, as a valid cost-effective and safe option as compared to the viral vector-based systems. A general overview of SB transposon system applications will be provided, with an update of major developments, current clinical trials achievements and future perspectives exploiting SB for CAR T-cell engineering. After the first clinical successes achieved in the context of B-cell neoplasms, we are now facing a new era and it is paramount to advance gene transfer technology to fully exploit the potential of CAR T-cells towards next-generation immunotherapy.

Neoantigens in Hematologic Malignancies

T cell cancer neoantigens are created from peptides derived from cancer-specific aberrant proteins, such as mutated and fusion proteins, presented in complex with human leukocyte antigens on the cancer cell surface. Because expression of the aberrant target protein is exclusive to malignant cells, immunotherapy directed against neoantigens should avoid “on-target, off-tumor” toxicity. The efficacy of neoantigen vaccines in melanoma and glioblastoma and of adoptive transfer of neoantigen-specific T cells in epithelial tumors indicates that neoantigens are valid therapeutic targets. Improvements in sequencing technology and innovations in antigen discovery approaches have facilitated the identification of neoantigens. In comparison to many solid tumors, hematologic malignancies have few mutations and thus fewer potential neoantigens. Despite this, neoantigens have been identified in a wide variety of hematologic malignancies. These include mutated nucleophosmin1 and PML-RARA in acute myeloid leukemia, ETV6-RUNX1 fusions and other mutated proteins in acute lymphoblastic leukemia, BCR-ABL1 fusions in chronic myeloid leukemia, driver mutations in myeloproliferative neoplasms, immunoglobulins in lymphomas, and proteins derived from patient-specific mutations in chronic lymphoid leukemias. We will review advances in the field of neoantigen discovery, describe the spectrum of identified neoantigens in hematologic malignancies, and discuss the potential of these neoantigens for clinical translation.

CAR T Cell Generation by piggyBac Transposition from Linear Doggybone DNA Vectors Requires Transposon DNA-Flanking Regions

CD19-specific chimeric antigen receptor (CAR19) T cells, generated using viral vectors, are an efficacious but costly treatment for B cell malignancies. The nonviral piggyBac transposon system provides a simple and inexpensive alternative for CAR19 T cell production. Until now, piggyBac has been plasmid based, facilitating economical vector amplification in bacteria. However, amplified plasmids have several undesirable qualities for clinical translation, including bacterial genetic elements, antibiotic-resistance genes, and the requirement for purification to remove endotoxin. Doggybones (dbDNA) are linear, covalently closed, minimal DNA vectors that can be inexpensively produced enzymatically in vitro at large scale. Importantly, they lack the undesirable features of plasmids. We used dbDNA incorporating piggyBac to generate CAR19 T cells. Initially, expression of functional transposase was evident, but stable CAR expression did not occur. After excluding other causes, additional random DNA flanking the transposon within the dbDNA was introduced, promoting stable CAR expression comparable to that of using plasmid components. Our findings demonstrate that dbDNA incorporating piggyBac can be used to generate CAR T cells and indicate that there is a requirement for DNA flanking the piggyBac transposon to enable effective transposition. dbDNA may further reduce the cost and improve the safety of CAR T cell production with transposon systems.

Massive clonal expansion of medulloblastoma-specific T cells during adoptive cellular therapy

In both human and murine systems, we have developed an adoptive cellular therapy platform against medulloblastoma and glioblastoma that uses dendritic cells pulsed with a tumor RNA transcriptome to expand polyclonal tumor-reactive T cells against a plurality of antigens within heterogeneous brain tumors. We demonstrate that peripheral TCR Vβ repertoire analysis after adoptive cellular therapy reveals that effective response to adoptive cellular therapy is concordant with massive in vivo expansion and persistence of tumor-specific T cell clones within the peripheral blood. In preclinical models of medulloblastoma and glioblastoma, and in a patient with relapsed medulloblastoma receiving adoptive cellular therapy, an early and massive expansion of tumor-reactive lymphocytes, coupled with prolonged persistence in the peripheral blood, is observed during effective therapeutic response to immunotherapy treatment.

Current status and hurdles for CAR-T cell immune therapy

Chimeric antigen receptor T (CAR-T) cells have emerged as novel and promising immune therapies for the treatment of multiple types of cancer in patients with hematological malignancies. There are several key components critical for development and application of CAR-T therapy. First, the design of CAR vectors can considerably affect several aspects of the physiological functions of these T cells. Moreover, despite the wide use of γ-retrovirus and lentivirus in mediating gene transfer into T cells, optimal CAR delivery systems are also being developed and evaluated. In addition, several classes of mouse models have been used to evaluate the efficacies of CAR-T cells; however, each model has its own limitations. Clinically, although surprising complete remission (CR) rates were observed in acute lymphoblastic leukemia (ALL), lymphoma, and multiple myeloma (MM), there is still a lack of specific targets for acute myeloid leukemia (AML). Leukemia relapse remains a major challenge, and its mechanism is presently under investigation. Cytokine release syndrome (CRS) and neurotoxicity are life-threatening adverse effects that need to be carefully treated. Several factors that compromise the activities of anti-solid cancer CAR-T cells have been recognized, and further improvements targeting these factors are the focus of the development of novel CAR-T cells. Overcoming the current hurdles will lead to optimal responses of CAR-T cells, thus paving the way for their wide clinical application.

Use of Chimeric Antigen Receptor T Cell Therapy in Clinical Practice for Relapsed/Refractory Aggressive B Cell Non-Hodgkin Lymphoma: An Expert Panel Opinion from the American Society for Transplantation and Cellular Therapy

Axicabtagene ciloleucel (YESCARTA; Kite Pharma, a Gilead Company, Los Angeles CA) and tisagenlecleucel (KYMRIAH; Novartis Pharmaceuticals Corp., Basel, Switzerland) are two CD19-directed chimeric antigen receptor (CAR) T cell products currently approved by the US Food and Drug Administration; the European Medicines Agency; Health Canada; Ministry of Health, Labor and Welfare (Japan); and Therapeutic Goods Administration (Australia) for treatment of specific subtypes of relapsed/refractory aggressive B cell non-Hodgkin lymphoma (NHL). Although this approval has been transformative in the use of cellular immunotherapy in lymphoma, there are concerns regarding appropriate use of this novel therapy and of short- and long-term toxicities. To address these issues, representatives of the American Society of Transplantation and Cellular Therapy convened to recognize and address key issues surrounding the clinical application of CD19 CAR T cell therapy in B cell lymphomas, in collaboration with worldwide experts. The aim of this article is to provide consensus opinion from experts in the fields of hematopoietic cell transplantation, cellular immunotherapy, and lymphoma regarding key clinical questions pertinent to the use of CD19 CAR T cell products for the treatment of NHL. As the clinical practice using CAR T cells grows worldwide, we anticipate that this guidance will be relevant for hematology/oncology physicians who care for patients with lymphomas.

Modified CAR T cells targeting membrane-proximal epitope of mesothelin enhances the antitumor function against large solid tumor

Mesothelin (MSLN) is an attractive antigen for chimeric antigen receptor (CAR) T therapy and the epitope selection within MSLN is essential. In this study, we constructed two types of CARs targeting either region I of MSLN (meso1 CAR, also known as a membrane-distal region) or region III of MSLN (meso3 CAR, also known as a membrane-proximal region) using a modified piggyBac transposon system. We reported that, compared with meso1 CAR T cells, meso3 CAR T cells express higher levels of CD107α upon activation and produce increased levels of interleukin-2, TNF-α, and IFN-γ against multiple MSLN-expressing cancer cells in vitro. In a real-time cell analyzer system and a three-dimensional spheroid cancer cell model, we also demonstrated that meso3 CAR T cells display an enhanced killing effect compared with that of meso1 CAR T cells. More importantly, in a gastric cancer NSG mice model, meso3 CAR T cells mediated stronger antitumor responses than meso1 CAR T cells did. We further identified that meso3 CAR T cells can effectively inhibit the growth of large ovarian tumors in vivo. Collectively, our study provides evidences that meso3 CAR T-cell therapy performs as a better immunotherapy than meso1 CAR T-cell therapy in treating MSLN-positive solid tumors.

Optimization of manufacturing conditions for chimeric antigen receptor T cells to favor cells with a central memory phenotype

BACKGROUND

Chimeric antigen receptor (CAR)-T cells are genetically engineered to recognize tumor-associated antigens and have potent cytolytic activity against tumors. Adoptive therapy with CAR-T cells has been highly successful in B-cell leukemia and lymphoma. However, in solid tumor settings, CAR-T cells face a particularly hostile tumor microenvironment where multiple immune suppressive factors serve to thwart the anti-cancer immune response. Clinical trials of solid tumor antigen-targeted CAR-T cells have shown limited efficacy, and issues for current CAR-T cell therapies include failures of expansion and persistence, tumor entry, deletion and functional exhaustion.

METHODS

We compared our standard protocol for CAR-T cell manufacturing, currently used to generate CAR-T cells for a phase 1 clinical trial, with two alternative approaches for T-cell activation and expansion. The resulting cultures were analyzed using multicolor flow cytometry, cytokine bead array and xCELLigence cytotoxicity assays.

RESULTS

We have found that by changing the method of activation we can promote generation of CAR-T cells with enhanced CD62L and CCR7 expression, increased interleukin (IL)-2 production and retention of cytolytic activity, albeit with slower kinetics.

DISCUSSION

We propose that these phenotypic characteristics are consistent with a central memory phenotype that will better enable CAR-T cell survival and persistence after activation in vivo, and we aim to test this in a continuation of our current phase 1 clinical trial of CAR-T cells in patients with advanced melanoma.

Biologie, concepts et principes des CAR-T cells

CAR-T CELLS

BIOLOGY, CONCEPTS AND PRINCIPLES: The development of new anti-tumor immunotherapy approaches has recently dramatically increased. Progresses made in molecular biology and the development of various genetic manipulation tools allow the "reprogrammation" of T cells in order to make them express a chimeric receptor including the variable part of an immunoglobulin capable of recognizing a tumor antigen along with the expression of molecules involved in T-lymphocyte activation signaling. Genetically modified T-cells, called "CAR (chimeric antigen receptors) -T cells", have yielded impressive clinical results in the treatment of relapsed or refractory lymphoid hematological malignancies after conventional treatments and are in development in solid tumors. Different generations of CAR-T cells have been developed and technological progress makes it possible to envisage modulations of gene constructs that could further optimize the efficacy and tolerance of CAR-T cells. The first challenge of these approaches concerns the identification of specific tumor antigen targets in order to limit the on-target/off-tumor effects and the loss of expression of the target. Approaches i) targeting several antigens or ii) limiting the duration of expression of CAR in lymphocytes or iii) destroying CAR-T cells by a suicide gene. Interesting approaches are the second objective of improvement concerns the accessibility of CAR-T cells to tumor sites and the control of the immune escape mechanisms of tumor cells to the cytotoxicity of CAR-T cells. This issue is currently under the way of search of innovative strategies that should improve the clinical effectiveness of CAR-T cells, especially in solid tumors. Cet article fait partie du numéro supplément Les cellules CAR-T : une révolution thérapeutique ? réalisé avec le soutien institutionnel des partenaires Gilead : Kite et Celgene.

Hematopoietic Stem Cell Transplantation in the Era of Engineered Cell Therapy

PURPOSE OF REVIEW

Cellular therapy using T cells modified to express chimeric antigen receptors (CAR-T cells) has had striking success in patients that have failed previous treatment for CD19+ B cell non-Hodgkin lymphoma (NHL), chronic lymphocytic leukemia (CLL), or acute lymphoblastic leukemia (ALL). Curative therapy for this group of diseases has previously been limited to allogeneic hematopoietic cell transplantation HCT (alloHCT). The recent results of CAR-T cell therapy raise the question of how best to integrate CAR-T cell therapy and alloHCT in the care of these patients.

RECENT FINDINGS

Within the past 2 years, results from larger trials and increased follow-up of patients treated with CD19 CAR-T cell therapy suggest that some may achieve durable remission without transplant. The balance of efficacy and toxicity for CAR-T cell therapy and alloHCT vary by disease type, disease status at the time of treatment, patient characteristics, and the specific therapy employed. There are early signals that subsequent transplantation of patients who have achieved remission with CAR-T may be a potentially viable (though expensive) strategy.

Integration Mapping of piggyBac-Mediated CD19 Chimeric Antigen Receptor T Cells Analyzed by Novel Tagmentation-Assisted PCR

Insertional mutagenesis is an important risk with all genetically modified cell therapies, including chimeric antigen receptor (CAR)-T cell therapy used for hematological malignancies. Here we describe a new tagmentation-assisted PCR (tag-PCR) system that can determine the integration sites of transgenes without using restriction enzyme digestion (which can potentially bias the detection) and allows library preparation in fewer steps than with other methods. Using this system, we compared the integration sites of CD19-specific CAR genes in final T cell products generated by retrovirus-based and lentivirus-based gene transfer and by the piggyBac transposon system. The piggyBac system demonstrated lower preference than the retroviral system for integration near transcriptional start sites and CpG islands and higher preference than the lentiviral system for integration into genomic safe harbors. Integration into or near proto-oncogenes was similar in all three systems. Tag-PCR mapping is a useful technique for assessing the risk of insertional mutagenesis.