Chimeric Antigen Receptor Expression Level Research Articles

HER2 and HLA-A*02 dual CAR-T cells utilize LOH in a NOT logic gate to address on-target off-tumor toxicity

BackgroundOne of the major challenges in chimeric antigen receptor (CAR)-T cell therapy for solid tumors is the potential for on-target off-tumor toxicity due to the expression of CAR tumor antigens...

Physiological lentiviral vectors for the generation of improved CAR-T cells

Anti-CD19 chimeric antigen receptor (CAR)-T cells have achieved impressive outcomes for the treatment of relapsed and refractory B-lineage neoplasms. However, important limitations still remain due to severe adverse events (i.e., cytokine release syndrome and neuroinflammation) and relapse of 40%–50% of the treated patients. Most CAR-T cells are generated using retroviral vectors with strong promoters that lead to high CAR expression levels, tonic signaling, premature exhaustion, and overstimulation, reducing efficacy and increasing side effects. Here, we show that lentiviral vectors (LVs) expressing the transgene through a WAS gene promoter (AW-LVs) closely mimic the T cell receptor (TCR)/CD3 expression kinetic upon stimulation. These AW-LVs can generate improved CAR-T cells as a consequence of their moderate and TCR-like expression profile. Compared with CAR-T cells generated with human elongation factor α (EF1α)-driven-LVs, AW-CAR-T cells exhibited lower tonic signaling, higher proportion of naive and stem cell memory T cells, less exhausted phenotype, and milder secretion of tumor necrosis factor alpha (TNF-α) and interferon (IFN)-ɣ after efficient destruction of CD19+ lymphoma cells, both in vitro and in vivo. Moreover, we also showed their improved efficiency using an in vitro CD19+ pancreatic tumor model. We finally demonstrated the feasibility of large-scale manufacturing of AW-CAR-T cells in guanosine monophosphate (GMP)-like conditions. Based on these data, we propose the use of AW-LVs for the generation of improved CAR-T products.

3D-organoid culture supports differentiation of human CAR+ iPSCs into highly functional CAR Tcells.

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

Optimization of Third Generation Chimeric Antigen Receptor T Cells Targeting ROR1 for Hematological Malignancies

Background: Chimeric Antigen Receptor (CAR) T cell therapy is arguably one of the most significant breakthroughs in cancer treatment. There are currently five FDA-approved products that are commercially available. However, despite their success, these CAR T-cell therapies cannot induce long-term durable responses in approximately 50% of leukemia or lymphoma-treated patients. Similarly, the results of CAR T-cells in solid tumors have been somewhat disappointing. Therefore, there is an urgent need to design and develop novel CAR T cells with improved efficacy in hematologic malignancies and solid tumors. ROR1 is a carcinoembryonic antigen expressed in different cancers and is associated with tumor stemness, proliferation, metastatic transformation, and treatment resistance. In this project, we optimize an anti-ROR1 CAR using a humanized single-chain variable fragment (scFv) with second (2G) or third-generation (3G) costimulatory domains.Methods: Several optimization steps in silico were performed using a selected scFv binding domain that targets ROR1. Those included codon optimizations, positional arrangement of heavy-light chains, evaluation of the ideal length of linkers based on tridimensional modeling of the docking between the antibody-like paratope with the target antigen (Figure 1A). After this initial scFv optimization process, we constructed a lentiviral vector that encodes CARs using the selected scFv linked to a transmembrane domain CD28 and different signaling endodomains for 2G and 3G variants (CD28, 41BB, ICOS, OX40), each linked to the T cell receptor CD3z domain. The cytotoxic activity of these constructs was evaluated using an in vitro rechallenge luciferase assay in ROR1 expressing JeKo-1 cells and ROR1(negative) controls.Results: The 2G 41BB-z construct with V H-V L scFv orientation and a long linker (V H-L-V L) showed optimal cytotoxicity with a CAR expression level in T cells of 36% (Range 28-49% for other constructs, Figure 1B-C). The V H-L-V L 41BB-z construct was evaluated comparatively using a rechallenge cytotoxic assay with 3G constructs that expressed CD28, ICOS, or OX40 signaling domains using JeKo-1 and ROR1(negative) target cells as controls. All the tested constructs showed specific ROR1 medicated cytotoxicity. CD28-41BB-z and ICOS-41BB-z showed the lowest cytotoxicity levels during the Day 1 of the repetitive rechallenge. However, the cytotoxicity levels of those constructs gradually increased during the 7 days of rechallenge and were closed to the levels induced by the 2G- 41BB-z construct (>80% of cytotoxicity). There were no significant differences in CAR T cells subsets generated by the different constructs during the 7 days of rechallenge with a predominance of effector memory phenotype (CCR7-, CD45RA-) and no difference in PD1 expression.Conclusions: Our results demonstrate that optimization of the CAR constructs enhances T-cell effector function and cytotoxicity against ROR1+ target cells. In previous studies, 3G CARs have shown longer persistence of the transduced T cells in peripheral blood, sustained and regulated cellular activation, improved solid tumor infiltration, and positive modulation of the tumor microenvironment. Our preclinical in vitro optimization demonstrates strategies to generate 3G constructs with a progressive and modulated cytotoxic profile that may confer benefits when tested in vivo in terms of enhanced persistence and lower adverse events profile. Additional experiments in vivo will be presented during the meeting to corroborate our findings. [Display omitted] DisclosuresNo relevant conflicts of interest to declare.

Bispecific CD19-CD20 and CD19-CD22 CAR-T Cells with Glycogen Synthase Kinase (GSK)-3β Inhibitor TWS119 Treatment Have Superior Therapeutic Effects on Mantle Cell Lymphoma

Introduction: Chimeric antigen receptor (CAR) - expressing T cells have shown breakthrough clinical successes to hematological malignancies such as diffuse large B cell lymphoma. Intensive development on CAR-T cell therapies are being developed in many common lymphomas. However, the development of CAR-T cell therapies in mantle cell lymphoma (MCL), a rare lymphoma has lagged behind. So far only CD19 CAR-T has been applied to MCL treatment, and MCL frequent relapse from prior CD19 CAR-T therapy with CD19 antigen loss. Bispecific CAR-T cells target two tumor antigens at once could reduce the risk of relapse. In addition, immune checkpoint blockade such as GSK3β and PD-1inhibition has been successfully used to enhance CAR-T cell therapies. Therefore, we attempt to develop a dual CAR for mantle cell lymphoma with checkpoint blockade.Methods: CD19-CD20 and CD19-CD22 bispecific CAR-T constructs were generated by subcloning the fragments in-frame into the pSFG retroviral vector. The BiCAR-T cells were cultured with/without a small molecule GSK3β inhibitor TWS119. Then, we performed a serial of experiments using CARs. 1, We assayed the CAR expression and cell expansion rates in vitro. 2, We assessed the tumor-killing capacity in vitro using MCL cell lines and primary MCL patient samples. 3, We performed phenotypic analyses by determination of proteins expression profiles of exhaustion markers and stem cell markers by flow cytometry. 4, We examined in vivo antitumor efficacy using preclinical models of MCL cell line-derived xenograft (CDX) .Results: Firstly, we found CD19-CD20 and CD19-CD22 bispecific CAR-T cells showed similar CAR expression levels (55%-72% CAR+ ) and similar expansion rate as single CD19 or CD20 CAR. Secondly, bispecific CAR- T cells potently and specifically lysed tumor cells in vitro, and showed the better killing of MCL tumor than CD19 or CD20 single CAR after challenge with MCL cell lines in vitro. Finally, we also confirmed these effects in CDX mice models derived from MCL cell line, Jeko-1 in vivo. CD19-CD20 and CD19-CD22 bispecific CAR successfully eliminated MCL tumor, showed better antitumor efficacy, and prolonged mouse survival than single CAR treated groups (P < 0.001). We also found that CD19-CD20 and CD19-CD22 bispecific-CAR T cells treated with TWS119 express significantly fewer exhaustion markers, such as PD-1 (P < 0.001), and LAG3 (P < 0.001), and showed better antitumor efficacy than the nontreated control group and single CAR groups in vivo. Furthermore, CAR-T cells expressing bispecific CD19-CD20 and CD19-CD22 CAR with TWS119 treatment had superior anti-MCL activity in vitro. In total, significantly better anti-MCL effects were observed for CD19-CD20 and CD19-CD22 bispecific CARs than single CAR. Their anti-MCL functions were further improved by TWS119 treatment.Conclusion: Altogether, these findings suggest that bispecific CD19-CD20 and CD19-CD22 CAR-T cells are potent for treating MCL relapse and drug resistant patients. In addition, bispecific CD19-CD20 and CD19-CD22 CAR-T cells with TWS119 treatment will further bring up the full power of CARs. These data support the therapeutic potential of bispecific CARs in patients with MCL. DisclosuresWang: Newbridge Pharmaceuticals: Honoraria; Moffit Cancer Center: Honoraria; BGICS: Honoraria; Bayer Healthcare: Consultancy; Hebei Cancer Prevention Federation: Honoraria; Clinical Care Options: Honoraria; Lilly: Research Funding; Miltenyi Biomedicine GmbH: Consultancy, Honoraria; Kite Pharma: Consultancy, Honoraria, Research Funding; Mumbai Hematology Group: Honoraria; Epizyme: Consultancy, Honoraria; Dava Oncology: Honoraria; Chinese Medical Association: Honoraria; The First Afflicted Hospital of Zhejiang University: Honoraria; Molecular Templates: Research Funding; Imedex: Honoraria; Physicians Education Resources (PER): Honoraria; VelosBio: Consultancy, Research Funding; InnoCare: Consultancy, Research Funding; Genentech: Consultancy; DTRM Biopharma (Cayman) Limited: Consultancy; CStone: Consultancy; Scripps: Honoraria; OMI: Honoraria; Janssen: Consultancy, Honoraria, Research Funding; Pharmacyclics: Consultancy, Research Funding; Celgene: Research Funding; Oncternal: Consultancy, Research Funding; Loxo Oncology: Consultancy, Research Funding; BioInvent: Research Funding; Juno: Consultancy, Research Funding; CAHON: Honoraria; BeiGene: Consultancy, Honoraria, Research Funding; AstraZeneca: Consultancy, Honoraria, Research Funding; Anticancer Association: Honoraria; Acerta Pharma: Consultancy, Honoraria, Research Funding.

Promoter’s Choice Drive CAR-T Efficiency

The development and the functionality of Chimeric Antigen Receptor (CAR) therapy is highly linked to the stability and expression level of the receptor, for which the choice of the promoter is key. Although EF1α is a reference promoter to induce strong antigen binding and long-term CAR expression, we investigated the impact of this one and other constitutive promoters (MSCV, PGK, β2m and CMV) on a CAR123 construct in the Blastic Plasmocytoid Dendritic Cell Neoplasm (BPDCN). Our results indicate that lentiviral vector titer is affected by transgene nature and promoter activity. Interestingly, by moderating the expression level of CAR123 at the cell surface, its recognition capacity and selectivity were improved. We observed that in early stages after transduction, CAR123 expression level did not affect lymphocyte’s phenotype and its cytotoxic capacity against BPDCN cell line. However, following long-term culture and decrease of cell-surface CAR expression, a hallmark of transition from activation to memory state of T-cells was observed, and only T-cells transduced with CAR-EF1α or -β2m promoters were still functional. We identified β2m as a promising promoter. Though it shows lower antigen-binding CAR-T cell and antigen recognition rates compared to EF1α, β2m promoter still present interesting CAR expression levels, stability, and binding capacity

Predicting the Efficacy and Safety of TACTICs (Tumor Angiogenesis-Specific CAR-T Cells Impacting Cancers) Therapy for Soft Tissue Sarcoma Patients.

Simple SummarySarcomas have few effective treatment options due to the rarity and diversity and have a high risk of recurrence and metastasis. Therefore, the development of new therapeutics that can meet their medical needs is required. Our adoptive immunotherapy strategy using T cells to express the chimeric antigen receptor (CAR) against vascular endothelial growth factor receptor 2 (VEGFR2), which is highly expressed on tumor vascular endothelial cells, has the potential to be a novel treatment against diverse sarcomas with abundant vascular invasion. Here, we optimized the manufacturing and transportation of anti-VEGFR2 CAR-mRNA-transfected T cells and collected information that allowed the extrapolation of their efficacy and safety potential for sarcoma patients. Our results support the development of a “first in humans” study to evaluate the potential of our anti-VEGFR2 CAR-T cell therapy as a new treatment option for sarcoma patients.Soft tissue sarcomas (STSs) are heterogeneous and aggressive malignancies with few effective therapies available. We have developed T cells expressing a vascular endothelial growth factor receptor 2 (VEGFR2)-specific chimeric antigen receptor (CAR) to establish a tumor angiogenesis-specific CAR-T cells impacting cancers (TACTICs) therapy. In this study, we optimized the manufacturing and transportation of mRNA-transfected anti-VEGFR2 CAR-T cells and collected information that allowed the extrapolation of the efficacy and safety potential of TACTICs therapy for STS patients. Although 5-methoxyuridines versus uridines did not improve CAR-mRNA stability in T cells, the utilization of CleanCap as a 5′ cap-structure extended the CAR expression level, increasing VEGFR2-specific cytotoxicity. Furthermore, 4 °C preservation conditions did not affect the viability/cytotoxicity of CAR-T cells, contrarily to a freeze-thaw approach. Importantly, immunohistochemistry showed that most of the STS patients’ specimens expressed VEGFR2, suggesting a great potential of our TACTICs approach. However, VEGFR2 expression was also detected in normal tissues, stressing the importance of the application of a strict monitoring schedule to detect (and respond to) the occurrence of adverse effects in clinics. Overall, our results support the development of a “first in humans” study to evaluate the potential of our TACTICs therapy as a new treatment option for STSs.

Hinge and Transmembrane Domains of Chimeric Antigen Receptor Regulate Receptor Expression and Signaling Threshold.

Chimeric antigen receptor (CAR)-T cells have demonstrated significant clinical potential; however, their strong antitumor activity may cause severe adverse effects. To ensure efficacy and safe CAR-T cell therapy, it is important to understand CAR’s structure–activity relationship. To clarify the role of hinge and transmembrane domains in CAR and CAR-T cell function, we generated different chimeras and analyzed their expression levels and antigen-specific activity on CAR-T cells. First, we created a basic CAR with hinge, transmembrane, and signal transduction domains derived from CD3ζ, then we generated six CAR variants whose hinge or hinge/transmembrane domains originated from CD4, CD8α, and CD28. CAR expression level and stability on the T cell were greatly affected by transmembrane rather than hinge domain. Antigen-specific functions of most CAR-T cells depended on their CAR expression levels. However, CARs with a CD8α- or CD28-derived hinge domain showed significant differences in CAR-T cell function, despite their equal expression levels. These results suggest that CAR signaling intensity into T cells was affected not only by CAR expression level, but also by the hinge domain. Our discoveries indicate that the hinge domain regulates the CAR signaling threshold and the transmembrane domain regulates the amount of CAR signaling via control of CAR expression level.

Impact of scFv structure in chimeric antigen receptor on receptor expression efficiency and antigen recognition properties

Gene-modifying T cells expressing chimeric antigen receptor (CAR) with an extracellular domain consisting of single chain variable fragment (scFv) and an intracellular domain with a T cell activation motif, are promising cancer immuno-medicines that can exert long term potent antitumor activity. However, CAR-T cells have a high risk of causing fatal side effects. Thus, more effective and safer CAR-T cells are urgently needed. Although antigen specificity and reactivity of CAR-T cells are defined by CAR expression level and affinity, information on optimizing the scFv structure that defines CAR avidity is lacking. Here, we investigated the impacts of scFv substitution and structural modification in CAR on receptor expression and antigen recognition properties. Four CARs with distinct scFvs targeting the same antigen were unexpectedly separated into a CAR expressed on T cells and bound to the antigen, CARs that did not show antigen-binding because of cell surface aggregation, and a rarely expressed CAR. Among the scFv structural modifications of CARs, changes in the Fv order and linker did not noticeably affect CAR expression or antigen-binding. In contrast, complementarity-determining region (CDR)-grafting to the stable framework region in Fv dramatically improved the surface expression level of non-producible CAR. These results revealed that CAR expression efficiency and stability on T cells are influenced by the Fv structure. Therefore, stabilization of the Fv structure by CDR-grafting may be an effective means for expressing scFvs, which have excellent antigen specificity and appropriate affinity but low structural stability, as a CAR on T cells.

Calibrated CAR Activation Potential Directs Alternative T Cell Fates and Therapeutic Potency

Immunotherapy with second-generation chimeric antigen receptor (CAR) T cells has achieved great clinical success against hematological malignancies. CD19-specific CARs incorporating CD28 and CD3z signaling domains have demonstrated remarkable potency resulting in the frequent induction of complete remissions and were recently approved by the US FDA for use in some refractory B cell malignancies. We previously demonstrated that CD28-based CARs program strong effector functions, but impart a relatively limited T cell lifespan. Increasing functional T cell persistence is therefore likely to further enhance the therapeutic success of 1928z CAR T cells.We hypothesized that excessive signal strength arising from redundancy of combined CD3z and CD28 signals might foster terminal T cell differentiation and exhaustion. We therefore proceeded to titrate the activation potential of CD28-based CARs and assess the impact thereof on the function, longevity and therapeutic potency of CAR T cells.We analyzed the contribution of individual immunoreceptor tyrosine-based activation motifs (ITAMs) to the phenotype and function of 1928z CAR T cells. ITAM-mutated CAR T cells demonstrated similar expression levels in retrovirally transduced primary T cells and directed comparable short-term cytotoxicity and proliferation capacity in vitro. However, remarkable differences in their therapeutic potency emerged when T cells expressing different mutant CARs were tested in the pre-B acute lymphoblastic leukemia NALM6 mouse model. The CAR “stress test” model revealed that a CAR containing a single functional ITAM - depending on its position - outperformed wild-type 1928z CARs, achieving rapid and durable tumor eradication even at low T cell doses, by delaying T cell differentiation and exhaustion. CAR T cells retrieved from the bone marrow of treated mice demonstrated that inactivation of two ITAM domains augmented CAR persistence at the tumor sites with a higher percentage of central memory cells and a decreased proportion of terminally differentiated effector cells. Deletion mutants further revealed the importance of ITAM location within second-generation CAR T cells.These findings were rigorously tested by directing the mutant CAR cDNAs to the T-cell receptor α constant (TRAC) locus using CRISPR/Cas9 technology, thereby ruling out potentially confounding effects arising from different CAR expression levels. TRAC-1928z mutants demonstrated superior antitumor efficacy compared to conventional TRAC-1928z CARs and prevented terminal T cell differentiation and exhaustion.Genome-wide transcriptional profiles of TRAC-edited naïve peripheral blood T cells further demonstrated that CARs encoding different ITAMs direct T cells to different fates. While TRAC-1928z CARs demonstrated similarity to transcriptional profiles of effector cells, reducing the number of ITAMs to one ITAM preserved a less-differentiated T cell state and promoted greater T cell persistence. We identified one 1928z mutant CAR, which improved therapeutic potency and induced a transcriptional profile similar to that of stem cell memory T cells (TSCM). Another 1928z mutant CAR with further reduction of the activation potential resulted in a naïve-like phenotype with great proliferation potential and persistence, but greatly diminished anti-tumor efficacy.In conclusion, we demonstrate that the number and position of ITAMs in 1928z CAR T cells influence functional, phenotypic and transcriptional programs resulting in profound effects on therapeutic potency. Balancing T cell differentiation and acquisition of effector functions is essential to optimize therapeutic potency of CAR T cells and can be intrinsically regulated by defined mutations in the CD3z chain of 1928z CAR T cells.Improved therapeutic potency of CAR T cells can thus be achieved by calibrating activation strength, thus retaining memory functions and preventing exhaustion, without compromising effector functions. Importantly, we were able to identify a novel CAR design which programs a favorable balance of effector and memory signatures, inducing increased persistence of highly functional CARs with the replicative capacity of long-lived memory cells and potent effector functions. Clinical studies evaluating the new CAR design are in preparation. DisclosuresSadelain:Juno Therapeutics: Consultancy, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties, Research Funding; Fate Therapeutics Inc.: Research Funding.

CAR-Modified Th1/Tc1-Polarized T-Rapa Cells Dissociate Inflammatory Cytokine Secretion from Anti-Tumor Cytotoxicity

▪Introduction: Despite some striking clinical success thus far, chimeric antigen receptor (CAR) engineered cells have the potential to cause severe side effects. Neurotoxicity and cytokine release syndrome (CRS), the latter characterized by increased levels of cytokines such as IL-6, IFN-γ, and MCP-1, are common adverse events associated with CAR therapy. Lymphodepleting preconditioning regimens are associated with improved clinical responses to CAR therapy, yet lymphodepletion has also been identified as a risk factor for CRS. Understanding and management of these toxicities has improved significantly, however these conditions are challenging to treat and can be life-threatening. The ability to limit or prevent initiation of CRS would greatly improve the safety of CAR therapy.Previous clinical trials have shown that T-Rapa cells (patient T cells that have been grown exvivo in rapamycin) can be successfully infused back into autologous recipients after a low-dose conditioning regimen. After infusion, these T-Rapa cells have potent effector functions and demonstrate long-term persistence. Here we determine that T-Rapa cells, engineered by lentivirus-mediated gene transfer to express an anti-CD19 CAR, are just as effective at killing tumor cells as similarly-engineered pan T cells but produce dramatically less IFN-γ, for example.Methods: Human CD3+ cells were treated with rapamycin in the presence of IFN-α and IL-2 to produce T-Rapa cells with a Th1/Tc1 phenotype. An anti-CD19-41BB-CD3ζ CAR construct was subcloned into a lentiviral vector backbone containing an IRES-eGFP element. Vector was prepared and used to transduce T or T-Rapa cells. Transgene expression was assessed by FACS for eGFP and Protein L staining for the CAR. CAR-T cells were then expanded using CD3/CD28 beads in the presence of IL-2. The expanded cells were used in assays including FACS assessment of T cell phenotype, co-culture assays, and 51Cr release assays in comparison with non-rapamycin treated CAR T cells and non-transduced controls.Results: Following transduction and expansion, similar eGFP and CAR expression levels were found in T and T-Rapa cells transduced at the same MOI. CAR-T and CAR-T-Rapa cells developed from multiple independent T cell donors exhibited similar phenotypes at days 5 and 14 post-thaw, as determined by analyses of T-cell subset and exhaustion markers including CD45RO, CD127, CCR7, CD95, CD25, CXCR3, CTLA-4, PD-1, LAG-3, and TIM-3. Both CAR-T and CAR-T-Rapa cells exhibited comparable levels of cytotoxicity against CD19+ Raji, SUP-B15 and RS4;11 cancer cell lines after coculture for 4 hours in a 51Cr release assay. Further, both T and T-Rapa CAR cells produced similar amounts of IL-2 following a 24-hour coculture with CD19+ Raji, SUP-B15 and RS4;11 cancer cell lines, as measured by ELISA. Interestingly, CAR-T-Rapa cells produced significantly less IFN- γ that CAR-T cells after 24 hours of coculture with CD19+ tumor cells. This observation was consistent for CAR-T and CAR-T-Rapa cells assessed at both day 5 and day 14 post-thaw.Conclusions: T-Rapa cells can be successfully transduced with a CAR vector, and show comparable T cell subset, exhaustion phenotype, and cytotoxicity to CAR-T cells that have not been treated with rapamycin. In spite of these similarities, when challenged with CD19+ tumor cells, CAR-T-Rapa cells produced less IFN-γ than CAR-T cells. Decreased production of IFN- γ may reduce the risk and severity of CRS, improving the safety of CAR therapy. Additional cytokine production studies, as well as in vivo studies, are underway to further characterize T-Rapa cells as a novel CAR effector cell type. DisclosuresFelizardo:Rapa Therapeutics: Employment, Patents & Royalties. Zhu:Rapa Therapeutics: Employment, Patents & Royalties. Fowler:Rapa Therapeutics: Employment, Equity Ownership, Patents & Royalties. Medin:Rapa Therapeutics: Membership on an entity's Board of Directors or advisory committees, Patents & Royalties.

Marrow-Infiltrating Lymphocytes (MILs) Provide a Robust Platform for CAR-T Cell Therapy

▪Adoptive cellular immunotherapy (ACT) using chimeric-antigen receptor (CAR)-modified T cells has shown unprecedented initial response rates in patients with advanced B cell malignancies and is emerging as a powerful tool for cancer treatment. However, there remains room for improvement in initial response rates, and relapse occurs in a significant fraction of those patients that do respond. Reasons for failure to respond are being elucidated. At least two mechanism of relapse - lack of persistence of infused CAR-T cells and the loss of antigen-expression by tumor cells - are well documented.We have developed a novel platform for ACT called Marrow-infiltrating Lymphocytes (MILs). MILs are a population of polyclonal T cells expanded from the bone marrow (BM) with distinct properties that set them apart from T cells expanded from peripheral blood lymphocytes (PBLs). MILs are enriched with memory T cells and contain tumor antigen-specific T cells that are typically not detected in PBLs. MILs are being developed for several tumor types, including both hematological and solid tumors.Distinguishing features of MILs compared to PBLs include their memory phenotype, inherent tumor antigen-specificity, and ability to persist long-term. As such, we hypothesized that MILs would provide a robust platform for CAR-T cell therapy with the potential to boost initial response rates and reduce the risk of relapse. Herein, data is presented demonstrating superior anti-tumor activity of CAR-modified MILs (CAR-MILs) compared to CAR-T cells generated from patient-matched PBLs (CAR-PBLs).We designed a 2nd generation 4-1BB-CD3z CD38 CAR using an scFv derived from Daratumumab. The CD38 CAR was linked to GFP by a T2a cleavage peptide so that GFP could be used as a marker of CAR expression. The CD38 CAR was expressed in a lentiviral construct and demonstrated equal transduction efficiencies and CAR expression levels in MILs and PBLs. The CAR modified MILs demonstrated superior antigen specific killing compared to PBLs against the 8226 myeloma (MM) cell line but not its isogenic CD38 knocked out line. More importantly, CAR-MILs retained their inherent tumor antigen-specificity and capacity to respond through their endogenous tumor antigen-specific T cell receptors - a property that PBL-CARs did not appear to possess. Tumor antigen-specific T cells were quantified by co-culturing MILs with autologous antigen-presenting cells pulsed with allogeneic multiple myeloma cell line lysates as a source of antigen and measuring IFNγ-production as a read-out. An equal or greater number of tumor antigen-specific IFNγ-producing T cells were measured in CD38 CAR-MILs compared to matched unmodified MILs.Finally, we compared the in vitro cytolytic potential of CD38 CAR-MILs to matched CD38 CAR-PBLs. Co-culture killing assays were performed at decreasing CAR-T effector: target (E:T) ratios. At high E:T ratios, CAR-MILs and CAR-PBLs lysed comparable percentages of CD38+ targets with similar kinetics. However, at lower E:T ratios, CAR-MILs killed a greater percentage of CD38+ targets with faster kinetics compared to CAR-PBLs.In conclusion, we have demonstrated 1) the feasibility of producing CAR-modified MILs, 2) that CAR-MILs retain their inherent tumor antigen-specificity and functional capacity - something that was lacking with CAR-PBLs, and 3) that CAR-MILs kill more efficiently in vitro than matched CAR-PBLs. These data suggest that CAR-MILs may provide both better antigen specific killing but more importantly by targeting the endogenous antigenic repertoire, they could also prevent or minimize the risk of relapse via antigen escape variants and thus increase the overall efficacy of adoptive CAR T cell therapy. DisclosuresLutz:WIndMIL Therapeutics: Employment, Patents & Royalties. Rudraraju:WIndMIL Therapeutics: Employment. DeOliveira:WIndMIL Therapeutics: Employment. Jana:WIndMIL Therapeutics: Employment. Weiss:WIndMIL Therapeutics: Employment. Borrello:WIndMIL Therapeutics: Consultancy, Equity Ownership, Membership on an entity's Board of Directors or advisory committees, Patents & Royalties, Research Funding. Noonan:WIndMIL Therapeutics: Employment, Equity Ownership, Patents & Royalties.

Comparative analysis and optimization of protocols for producing recombinant lentivirus carrying the anti-Her2 chimeric antigen receptor gene.

The production of anti-Her2 chimeric antigen receptor (CAR) T cells needs to be optimized to make it a reliable therapy. Three types of lentiviral vectors expressing anti-Her2 CAR together with packaging plasmids were co-transfected into 293T-17 cells. The vector with the best packaging efficiency was selected, and the packaging cell culture system and packaging plasmid system were optimized. Centrifugation speed was optimized for the concentration of lentivirus stock. The various purification methods used included membrane filtration, centrifugation with a sucrose cushion and the novelly-designed instantaneous high-speed centrifugation. The recombinant lentiviruses were transduced into human peripheral T cells with an optimized multiplicity of infection (MOI). CAR expression levels by three vectors and the efficacy of CAR-T cells were compared. When co-transfected, packaging cells in suspension were better than the commonly used adherent culture condition, with the packaging system psPAX2/pMD2.G being better than pCMV-dR8.91/pVSV-G. The optimal centrifugation speed for concentration was 20 000g, rather than the generally used ultra-speed. Importantly, adding instantaneous centrifugation for purification significantly increased human peripheral T cell viability (from 13.25% to 62.80%), which is a technical breakthrough for CAR-T cell preparation. The best MOI value for transducing human peripheral T cells was 40. pLVX-EF1a-CAR-IRES-ZsGreen1 expressed the highest level of CAR in human peripheral T cells and the cytotoxicity of CAR-T cells reached 63.56%. We optimized the preparation of recombinant lentivirus that can express third-generation anti-Her2 CAR in T cells, which should lay the foundation for improving the efficacy of CAR-T cells with respect to killing target cells.

Driving CARs on the uneven road of antigen heterogeneity in solid tumors

Uniform and strong expression of CD19, a cell surface antigen, on cells of B-cell lineage is unique to hematologic malignancies. Tumor-associated antigen (TAA) targets in solid tumors exhibit heterogeneity with regards to intensity and distribution, posing a challenge for chimeric antigen receptor (CAR) T-cell therapy. Novel CAR designs, such as dual TAA-targeted CARs, tandem CARs, and switchable CARs, in conjunction with inhibitory CARs, are being investigated as means to overcome antigen heterogeneity. In addition to heterogeneity in cancer-cell antigen expression, the key determinants for antitumor responses are CAR expression levels and affinity in T cells. Herein, we review CAR T-cell therapy clinical trials for patients with lung or pancreatic cancers, and provide detailed translational strategies to overcome antigen heterogeneity.

T Cell Maturation Stage Prior to and During GMP Processing Informs on CAR T Cell Expansion in Patients.

Autologous T cells were genetically modified to express a chimeric antigen receptor (CAR) directed toward carboxy-anhydrase-IX (CAIX) and used to treat patients with CAIX-positive metastatic renal cell carcinoma. In this study, we questioned whether the T cell maturation stage in the pre-infusion product affected CAIX CAR expression and function in vitro as well as in vivo CAR T cell numbers and expansion. During the 14 days expansion of CAR T cells prior to administration, we observed shifts from a predominant CD4 to a CD8 T cell phenotype and from a significant fraction of naïve to central effector T cells. Surface expression of the CAR was equally distributed among different T cell subsets and T cell maturation stages. During T cell culture days 14–18 (which covered patient treatment days 1–5), T cells demonstrated a decline in CAR expression level per cell irrespective of T cell maturation stage, although the proportion of CAR-positive T cells and CAR-mediated T cell effector functions remained similar for both CD4 and CD8 T cell populations. Notably, patients with a higher fraction of naïve CD8 T cells at baseline (prior to genetic modification) or central effector CD8 T cells at 2 weeks of CAR T cell culture demonstrated a higher fold expansion and absolute numbers of circulating CAR T cells at 1 month after start of therapy. We conclude that the T cell maturation stage prior to and during CAR T cell expansion culture is related to in vivo CAR T cell expansion.

Balance of Anti-CD123 Chimeric Antigen Receptor (CAR) Binding Affinity and Density for the Treatment of Acute Myeloid Leukemia

Chimeric Antigen Receptors (CARs)-redirected T lymphocytes are a promising novel immunotherapeutic approach, nowadays object of accurate preclinical evaluation also for the treatment of Acute Myeloid Leukemia (AML). In this context, we recently developed a CAR against CD123 (IL-3 receptor α subunit), a tumor associated antigen over-expressed on AML blasts and leukemic stem cells. However, the potential recognition by anti-CD123 CAR-T cells of low CD123 positive healthy tissues, i.e. endothelium and monocytes, through the known "on-target-off-organ" effect, warrants careful preclinical investigation for a safe employment of this approach in the clinic. Therefore, in search for an optimization of this strategy, we evaluated the effect of several variables implicated in the CAR design, known to modulate CAR T-cell functional profiles in a context-dependent manner, such as CAR binding affinity, CAR expression and target antigen density.Computational structural biology tools have been exploited to design rational mutations in the anti-CD123 CAR antigen binding domain that altered CAR expression and CAR binding affinity. To this aim, Cytokine-Induced Killer (CIK) effector cells have been genetically modified with four Chimeric Affinity Mutants (CAMs), represented by CAM-H1 (High Affinity 1), CAM-H2, which maintain the same binding affinity of the wild type (wt) anti-CD123 CAR (10-9 M), CAM-M (Medium affinity) and CAM-L (Low affinity), displaying a 10- and 100-fold affinity reduction, respectively.The functional characterization of CAM-CIK cells revealed both their specificity and effectiveness in early cytotoxic responses against both the high CD123+ THP-1 AML cell line and primary AML cells, reaching more than 70% of killing activity as the wt CAR-CIK cells. However, in this context, among all the variables analyzed, a CAR expression level up to ≈40% proved to be necessary for inducing effective later effector functions towards a high CD123+target, such as proliferation and cytokine production. To mimic the CD123 expression on leukemic and healthy tissues, a panel of cell lines with different surface levels of CD123 was introduced. In particular, a number of ≈1600 CD123 molecules was sufficient to induce a good cytotoxic response by all the CARs tested, with the CAM-L being the less powerful against both the AML U937 cell line and healthy TIME endothelial cell line, sharing the same target antigen density, and allowing for the identification of ≈1600 CD123 molecules as the "lytic threshold" in our setting. At the same time, this antigen density was not enough to determine a good proliferative capability for all the CAR-CIK cells tested, which instead occurred with leukemic cells expressing ≈5000 or more CD123 molecules. Cytokine release induced by all CAM-CIK cells was instead directly proportional to target antigen density, starting from ≈1600 molecules/cell, indicating that both these "activation thresholds" depend on different target antigen densities for being respectively triggered. As a matter of fact, a proportional CAR down-modulation in response to increasing target antigen densities was observed, implying this mechanism as one of the principal determinant for CAR-CIK cell related functional outcomes, independently of CAR binding affinity. Furthermore, with the aim of evaluating the response of CAM-CIK cells against the endothelium in a more physiological context, we set up a co-culture of Matrigel-embedded endothelial cells and CIK cells. The same and limited impairment of vessel formation was observed, with no differences encountered between un-manipulated and CAR-redirected CIK cells, implying that anti-CD123 CAR CIK cells are not activated more than the un-manipulated counterpart towards this target, independently of CAR binding affinity.In conclusion, we were able to define both "lytic" and "activation" antigen thresholds (Figure 1), showing that whereas the early T-cell cytotoxic activity is not affected either by CAR expression or CAR affinity tuning, later effector functions are impaired by low CAR expression. Moreover, a promising balance in the efficacy and safety profiles of CAR-CIK cells was observed in the lowest affinity mutant in response to targets with low CD123 densities. Overall, the full dissection of all these variables offers additional knowledge for the proper design of a suitable anti-CD123 CAR for the treatment of AML. [Display omitted] DisclosuresBiondi:Cellgene: Other: Advisory Board; BMS: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees, Other: Advisory Board.

A Novel Strategy of Switching on/Off CD19CAR Expression Under Tetracycline-Based System

Introduction: Genetic modification of T cells with chimeric antigen receptor (CAR) has emerged with astonishing treatment outcomes for B cell malignancies. Clinical trials of CAR-T therapy demonstrated toxicities such as hypogammaglobulinemia due to B cell aplasia or hemophagocytic syndrome after overactivation of CAR-T cells. These toxicities are considered as major drawbacks for broader application of CAR-T therapy. To overcome these serious adverse events, further modification of CAR-T technology to control CAR expression arbitrary is needed. Therefore we aimed to develop inducible CAR expressing T cells based on tetracycline-regulation system.Methods: We developed a novel inducible CD19CAR system by infusing anti-CD19-CD3z-CD28-tEGFR into pRetroX-TetOne vector (Tet-19CAR). By using Tet-19CAR transduced SUPT1 (T cell line), expression and disappearance kinetics of CAR were determined. We also retrovirally transduced Tet-19CAR into human CD8+ T cells, and achieved more than 90% purity of CAR positive T cells after a selection with anti-EGFR mAb. These CAR-T cells were again expanded with anti-CD3/28 beads and used in 51 Cr release assay, coculture assay, cytokine release assay and T cell proliferation assay. Regarding coculture assay, CD19 transduced K562-CD19 (K562-CD19) was labeled with 0.1 nM CFSE and plated with CAR-T cells at a ratio of 1:1 without IL-2 supplementation and incubated for 96 hours. Finally we examined this system in NOG mice. We injected 0.5 x 106 Raji-ffluc (fire-fly luciferase) followed by 5.0 x 106 CAR-T cells from the tail vein, then we evaluated the tumor flux by in vivo imaging system on days 7, 14, 21, and 30.Results: With more than 100 ng/mL of Doxycycline (Dox), CD19CAR was successfully expressed on both of SUPT1 and CD8+ T cells. For maximum and minimum expression, 24 and 72 hours were needed after addition and discontinuation of Dox, respectively. To determine the cytotoxicity of Tet-19CAR-T cells according to presence or absence of Dox, we performed 51 Cr release assay and coculture assay against K562-CD19. In the presence of Dox, Tet-19CAR showed an equivalent lytic activity to conventional CD19CAR-T cells (c19CAR). In contrast, Tet-19CAR without Dox exhibited significantly lower cytotoxicity against CD19+ target cells. (Dox (-) Tet-19CAR, Dox (+) Tet-19CAR and c19CAR: 14.0±4.0%, 38.0±4.0% and 37.0±2.0% at an E:T ratio = 10:1, respectively). In the coculture assay, Tet-19CAR with Dox eradiated K562-CD19, while they failed to suppress the target cells without Dox.In the intracellular IFN-g assay against K562-CD19, a similar proportion of responder was IFN-g + in Tet-19CAR with Dox and c19CAR. On the other hand, a significantly low proportion of IFN-g + cells were observed in Tet-19CAR without Dox. (Dox (-) Tet-19CAR, 1.0%±0%, Dox (+) Tet-19CAR, 19.1%±6.0% and c19CAR 21.5%±4.0%, respectively)Similar to intracellular IFN-g assay, ELISA revealed that Tet-19CAR with Dox and c19CAR produced IL-2 and IFN-g equally well. However, Tet-19CAR without Dox hardly did. [IL-2 (ng/ml): Dox (-) Tet-19CAR, 1.00±0.060, Dox (+) Tet-19CAR, 9.25±0.30 and c19CAR 8.75±0.68; IFN-g (ng/ml): 2.32±1.24, 57.96±6.95 and 62.42±5.95] (Fig).We next analyzed CAR-T cell proliferation upon stimulation with K562-CD19 over 96 hours. Tet-19CAR with Dox showed 6-7 fold expansion, whereas Tet-19CAR without Dox failed to proliferate.Regarding in vivo model, the mice treated with c19CAR or Tet-19CAR with Dox showed significantly low tumor flux but the mice treated with Tet-19CAR without Dox showed higher tumor burden at day 21 of CAR-T cell infusion [Photons/sec: Dox (-) Tet-19CAR, 2.5 x 1010, Dox (+) Tet-19CAR, 6.4 x 108 and c19CAR, 8.4 x 108 ].Conclusions: We generated tetracycline-inducible CAR-T cells and successfully controlled the CAR expression with Dox administration. Tet-19CAR without Dox still demonstrated some CD19CAR expression and subsequent cytotoxicity against CD19 positive cells. Nonetheless the CAR expression level of Tet-19CAR without Dox was lower than the threshold for exhibiting positive responses in the function assays such as cytokine production and proliferation. This phenomenon was also confirmed in the xenograft model. To regulate CAR expression more precisely and pursue clinical translations in combinations with other CARs, further efforts are needed to reduce any leaky CAR expression by modification of the system. [Display omitted] DisclosuresKiyoi:Pfizer Inc.: Research Funding; Eisai Co., Ltd.: Research Funding; Yakult Honsha Co.,Ltd.: Research Funding; Alexion Pharmaceuticals: Research Funding; MSD K.K.: Research Funding; Takeda Pharmaceutical Co., Ltd.: Research Funding; Taisho Toyama Pharmaceutical Co., Ltd.: Research Funding; Teijin Ltd.: Research Funding; Astellas Pharma Inc.: Consultancy, Research Funding; Japan Blood Products Organization: Research Funding; Nippon Shinyaku Co., Ltd.: Research Funding; FUJIFILM RI Pharma Co.,Ltd.: Research Funding; Nippon Boehringer Ingelheim Co., Ltd.: Research Funding; FUJIFILM Corporation: Patents & Royalties, Research Funding; Zenyaku Kogyo Co., Ltd.: Research Funding; Sumitomo Dainippon Pharma Co., Ltd.: Research Funding; Kyowa Hakko Kirin Co., Ltd.: Consultancy, Research Funding; Bristol-Myers Squibb: Research Funding; Chugai Pharmaceutical Co., Ltd.: Research Funding; Novartis Pharma K.K.: Research Funding; Mochida Pharmaceutical Co., Ltd.: Research Funding.