Quadruple gene-engineered natural killer cells enable multi-antigen targeting for durable antitumor activity against multiple myeloma

Allogeneic natural killer (NK) cell adoptive transfer is a promising treatment for several cancers but is less effective for the treatment of multiple myeloma. In this study, we report on quadruple gene-engineered induced pluripotent stem cell (iPSC)-derived NK cells designed for mass production from a renewable source and for dual targeting against multiple myeloma through the introduction of an NK cell-optimized chimeric antigen receptor (CAR) specific for B cell maturation antigen (BCMA) and a high affinity, non-cleavable CD16 to augment antibody-dependent cellular cytotoxicity when combined with therapeutic anti-CD38 antibodies. Additionally, these cells express a membrane-bound interleukin-15 fusion molecule to enhance function and persistence along with knock out of CD38 to prevent antibody-mediated fratricide and enhance NK cell metabolic fitness. In various preclinical models, including xenogeneic adoptive transfer models, quadruple gene-engineered NK cells consistently demonstrate durable antitumor activity independent of exogenous cytokine support. Results presented here support clinical translation of this off-the-shelf strategy for effective treatment of multiple myeloma.

Abstract 5513: Chimeric CD3 fusion receptors expressed on iPSC-derived universal TCR-less CAR-T and -NK cells synergize with bispecific engagers to enhance antitumor activity and limit antigen escape

Despite success in hematologic malignancies, chimeric antigen receptor (CAR) T cells have been less effective in solid tumors, in part because of the heterogeneous expression of the CAR-specific target antigen (1° Ag) found within the tumor mass. In combination with a CAR, bispecific T cell engagers (BiTEs) can target additional tumor antigens (2° Ag) while engaging CD3 signaling molecules on T cells, providing a unique way to address tumor heterogeneity, mitigate antigen escape and further potentiate durable effector function. However, in generating off-the-shelf universal CAR-T and NK cells, a combination strategy is not feasible as neither modified cell product is compatible to specifically engage with a BiTE. In developing allogeneic CAR-T cells, the T cell receptor (TCR) surface expression must be eliminated to prevent graft versus host disease, but the absence of surface TCR expression leads to loss of surface CD3 expression and BiTE compatibility. Similarly, NK cells naturally lack TCR expression and have no surface CD3 molecules for BiTE engagement.

Here we discuss the development of a novel chimeric CD3ε fusion receptor (CD3-CFR) with a modified transmembrane and endodomain enabling surface expression in TCR-less T or NK cells, allowing for a novel combinatorial solution between universal CAR-T or NK cells with BiTEs in an allogeneic setting.

CD3-CFR signal transduction was initially investigated in TRAC knockout NFAT reporter (T-KO) Jurkat cells engineered with CD3-CFR and co-cultured with EpCAM+ target cells. When soluble EpCAM-BiTE was added to the co-culture, the observed 6.9-fold increase in NFAT activity indicated successful engagement associated with the interaction of CD3-CFR, target cells and the BiTE. CD3-CFR T-KO Jurkat cells were further modified to secrete the EpCAM-BiTE and showed increased NFAT activity, demonstrating the feasibility of self-secreting BiTE-mediated targeting through CD3-CFR signaling.

We next engineered CD3-CFR expressing iPSC-derived CAR-T (iT) cells to show preserved T cell differentiation kinetics and maintained CAR activity against 1° Ag positive targets (>90% cytolysis). Importantly, while CAR-iT cells showed only background lysis of 1° Ag negative tumor cells, CD3-CFR+ CAR-iT cells were able to lyse ~99% of 1° Ag negative tumor cells with the addition of soluble EpCAM-BiTE targeting the 2° Ag. When CD3-CFR+ CAR-iT cells were further engineered to secrete the EpCAM-BiTE, CD3-CFR+ BiTE+ CAR-iT cells demonstrated superior killing of heterogenous tumors compared to CD3-CFR+ BiTE- CAR-iT cells (70% vs. 5% cytolysis). Taken together these data demonstrate for the first time that CD3 expression and BiTE engagement can be combined in a universal iPSC-derived CAR-iT cell product to overcome antigen heterogeneity and enhance efficacy in solid tumor settings.

Citation Format: Eigen Peralta, Dan Lu, Mark Landon, Hui-Yi Chu, Amit Mehta, Philip Chu, Alec Witty, Tom Lee, Bahram Valamehr. Chimeric CD3 fusion receptors expressed on iPSC-derived universal TCR-less CAR-T and -NK cells synergize with bispecific engagers to enhance antitumor activity and limit antigen escape [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5513.

Abstract 2756: Multiplexed-engineered, iPSC-derived T cells expressing three unique targeting modalities address tumor heterogeneity and antigen escape

Adoptive T-cell therapy with chimeric antigen receptor (CAR) has shown promising results in cancer treatment, however, antigen escape and tumor heterogeneity are major causes for disease relapse. While CARs are known to trigger an effective immune response through surface antigen recognition many solid tumor cancer antigens are intracellular and presented by MHC molecules recognized by T cell receptors (TCRs). In addition, many therapeutic antibodies have shown clinical efficacy in solid tumor settings. However, antibody-dependent cellular cytotoxicity (ADCC) is mediated by the CD16 Fc receptor naturally expressed on NK cells although its application in T cells is yet not fully appreciated. Utilizing our proprietary induced pluripotent stem cell (iPSC) platform to engineer multiple modalities into a clonal iPSC line, which can serve as the starting cell source for mass production of off-the-shelf, iPSC-derived CAR-T cells (CAR-iT cells), we aimed to study the combination of these three targeting modalities, CAR, TCR, and CD16, to determine whether challenges associated with the treatment of solid tumors, which are heterogeneous and challenging to treat, may be overcome.To test the base line activity of CAR-iT cells in the solid tumor setting, we selected our anti-MICA/B CAR, previously shown to effectively target stress ligands found on transformed cells, to demonstrate effective anti-tumor activity against multiple solid tumor cell lines (72 hrs cytotoxicity: A2058 = 99%; 786-O = 98%; versus non-specific CAR-iT cells: A258 = 13%; 786-O = 17%). To test compatibility of TCR in our iT cell platform, we engineered MR1-TCR in iT cells to show increased cytokine release and degranulation upon stimulated with MR1 positive lung carcinoma epithelial cells line A549 (fold change compared to un-stimulated: IFNg = 210, p = 0.0032; TNFa = 76.9, p = 0.0005; CD107ab = 115.0, p=0.0013). Notably, with the engineering of tumor antigen specific TCR in TCR-less CAR-iT cells, CD3 complex can be re-established to provide an opportunity to combine with bispecific T cell engagers. Lastly, combining CAR-iT cells with MR1-TCR and hnCD16 uniquely demonstrated synergistic tumor growth inhibition and validated our approach to target multiple antigens at once for an effective anti-tumor response (A549 cytotoxicity: tumor only = 3.68±2.04%; effector+TCR = 41.31±2.27%; effector+TCR+ADCC = 90.28±1.87%). In summary, using the unique approach to engineer iPSCs at the clonal level to create a distinct population of engineered iT cells, we successfully demonstrated the compatibility between CAR, TCR, and hnCD16 to mitigate tumor heterogeneity. This approach is an ideal strategy to create off-the-shelf cellular immunotherapy for a promising therapeutic approach to combat heterogeneous and difficult to treat solid tumors, including those that are resistant due to antigen escape.

Citation Format: Chia-Wei Chang, Bi-Huei Yang, Eason Lin, Soheila Shirinbak, Wen-I Yeh, Mochtar Pribadi, Helen Chu, Alma Gutierrez, Earl Avramis, Jason ORourke, Tom Lee, Alec Witty, Eigen Peralta, Martin Hosking, Bahram Valamehr. Multiplexed-engineered, iPSC-derived T cells expressing three unique targeting modalities address tumor heterogeneity and antigen escape [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2756.

138 Synthetic re-direction of TGFβ receptors as a novel strategy to enhance the anti-tumor activity of CAR-T cells in solid tumors

Background

Transforming growth factor beta (TGFβ) is an immuno-suppressive cytokine present in the tumor microenvironment (TME) that creates considerable challenges for the treatment of solid tumors. Small molecule inhibitors targeting TGFβ exist, but the pleiotropic nature of TGFβ signaling suggests that a more targeted approach is preferential, especially in the context of cellular therapy. We hypothesized that primary T cells and iPSC-derived chimeric antigen receptor-T cells (CAR-iT cells) would benefit not only from blockade of TGFβ signaling, but also from re-direction of the signaling event toward specific cytokine pathways that activate cell function. Here we discuss novel synthetic TGFβ redirector constructs that overcome TME limitations and enhance CAR-iT cell function for improved efficacy in treating solid tumors.

Methods

To identify activation pathways for redirection of TGFβ signaling, we screened a panel of cytokines for their effect on the anti-tumor activity of CAR-iT cells. We then developed synthetic redirector receptors where a TGFBR2 ectodomain was fused to the top selected cytokine receptor endodomains. Redirection of TGFβ signaling was confirmed by phospho-flow of key signaling proteins. Anti-tumor activity of CAR-iT cells expressing these synthetic redirector constructs was tested in serial restimulation assays in the absence of cytokine support and in the presence of recombinant TGFβ (rTGFβ).

Results

A dose-dependent decrease in CAR-iT cell cytolytic capacity in the presence of rTGFβ was observed, with the activity of CAR-iT cells rescued in the presence of unique cytokines. We designed and tested synthetic TGFβ redirector constructs and demonstrated a rTGFβ-dependent increase in pSTAT5 positive cells (2.8-fold over control). The serial stimulation assay was then used to test CAR-iT cells engineered with synthetic TGFβ redirector receptors. After three rounds of restimulation, an increase in tumor cell numbers for non-engineered and dominant negative TGFBR2 CAR-iT cell controls was observed (41-fold and 32-fold increase over base input, respectively). In contrast, the synthetic TGFβ redirector receptor improved the ability of CAR-iT cells to control tumor cell growth with remarkable efficiency, limiting tumor growth to only 1.5-fold over three rounds of restimulation.

Conclusions

These studies demonstrate that a novel synthetic construct comprised of fusion of cytokine endodomains to a TGFBR2 ectodomain can be deployed to hijack the immuno-suppressive signal of TGFβ often found in the TME and activate CAR-iT cells for enhanced anti-tumor activity in solid tumors. Additional studies are underway to assess the temporal expression and activity of these synthetic redirector receptors in various preclinical models which will be further discussed.

120 Chemokine receptor engineering enhances trafficking and homing of primary and iPSC-derived CAR-T cells to solid tumors

Background

Chimeric antigen receptor (CAR)-T cells for solid tumors have shown modest effectiveness as compared to hematologic malignancies, a consequence of antigen heterogeneity, the immuno-suppressive tumor microenvironment (TME), limited cell persistence, and perhaps most notably, the trafficking of the CAR-T cell to the tumor itself. Early detection of CAR-T cells within a solid tumor has been associated with better outcomes across several clinical trials in diverse tumor settings, suggesting that strategies focused on enhancing CAR-T cell homing to and infiltration into the tumor can yield therapeutic benefit.

Methods

Here, we demonstrate that following irradiation or exposure to common chemotherapy drugs, selected tumor cell lines (breast, ovarian, and prostate) specifically upregulate several chemokines, notably the CXCR2 ligand, interleukin (IL)-8, up to 4-fold over baseline control (e.g. 24ng/ml increased to 79ng/ml for SKOV3; 2.9ng/ml increased to 12.5ng/ml for MDA-MB-231). To leverage the upregulation of IL-8 as a mechanism of directing CAR-T cells to the tumor site, we initially engineered primary CAR-T cells to express CXCR2 and demonstrated functional migration, in a dose-dependent manner, to recombinant IL-8 in an in vitro transwell chemotaxis assay; maximal migration of approximately 2-fold over baseline was observed with 10ng/ml of rhIL-8. Similarly, supernatant from pre-conditioned tumor lines also elicited functional enhancements in migration (up to 4-fold specific migration). In addition, ovarian tumors were sub-optimally treated with paclitaxel in vivo, which promoted infiltration of CXCR2+ CAR-T cells and demonstrated enhanced tumor control.

Results

We then incorporated these findings into our off-the-shelf, iPSC-derived CAR-T cell product platform. Induced pluripotent stem cells (iPSCs) were precisely engineered to co-express CAR and CXCR2 and subsequently differentiated to T cells to generate iPSC-derived CAR-T cells (CAR-iT cells). Like their primary CAR-T cell counterparts, functional chemotaxis of CXCR2+ CAR-iT cells was also observed in response to recombinant IL-8 and preconditioned tumor media. Importantly, CXCR2 expression did not limit CAR-dependent cytolytic function and the specificity of CAR-iT cells, underscoring the compatibility of this approach. Further in vitro and in vivo studies are ongoing and will be presented.

Conclusions

Collectively, these data demonstrate that rational engineering of unique chemokine receptors to deliver the ideal chemokine/chemokine receptor match between tumors and effector cells can be leveraged to enhance tumor targeting and trafficking of CAR-iT cells for more effective treatment of solid tumors.

Ethics Approval

These studies were approved by Fate Therapeutics Institutional Animal Care and Use Committee and were carried out in accordance with the National Institutes of Health’s Guide for the Care and Use of Laboratory Animals.

Abstract 332: Chimeric fusion receptors provide a CD3-mediated activation signal to off-the-shelf iPSC-derived TCR-less CAR-T cells for enhanced efficacy

T cells require a combination of signals to properly activate and exhibit their full potential; signal 1 from the T cell receptor (TCR), signal 2 from costimulatory receptors and signal 3 from cytokine receptors can shape the function of T cells. Second generation chimeric antigen receptor (CAR) T-cells targeting CD19 have shown success in hematologic malignancies, in part because signals 1 and 2 are provided by the CAR endodomain. As previously reported, we have developed an off-the-shelf iPSC-derived CAR19 T (CAR19-iT) cell product where the CAR is inserted into the T cell receptor alpha constant (TRAC) locus for enhanced efficacy and disruption of surface TCR expression. While the TCR-less CAR19-iT cells are ideal for allogeneic CAR-T cell therapies, as a consequence, they lack CD3 surface expression and the means by which to mediate CD3 signaling.

To further improve CAR-iT cell performance and facilitate combinatorial strategies with T cell engagers such as bispecific T cell engagers (BiTEs), we designed chimeric fusion receptors (CFRs) comprising an ectodomain of CD3 or CD28, a transmembrane domain of CD28, and various endodomains that provide combinations of signals 1, 2, and 3. In addition to providing co-stimulatory signaling, the CFR designs can be controlled via agonistic antibodies or BiTEs to initiate signal transduction for precision control of the cell product. Furthermore, a series of CFRs with various CD3 endodomains were also developed to augment costimulatory signaling and the ER retention and endocytosis motifs found in CD3 endodomains were mutated to prevent downregulation of the CFRs from the cell surface of TCR-less cells.

Selected CFRs were engineered into TRAC knockout Jurkat cells expressing a luciferase based NFAT reporter gene. After 48 hours, surface expression of the CFRs was confirmed by flow cytometry. Signal transduction via the CFRs was evaluated following exposure to agonistic antibodies or BiTEs. Measurement of the luciferase activity showed comparable levels to activated wildtype reporter cells. After construct validation, the CFRs were introduced into TCR-less CAR19-iT cells and co-cultured overnight with Nalm6 target cells in the presence of agonistic antibodies. Compared to control CAR19-iT cells, the armed CFR-CAR19 iT cells demonstrated superior killing of target cells. These results support the notion that enhancing signal 1 can increase CAR-T cell efficacy with current studies underway to investigate CFRs with endodomains that provide additional signal 2 or 3. We expect these constructs to further enhance CAR-iT cell persistence and engagement with BiTEs for activation and multi-antigen targeting. Collectively, the data suggest that TRC-less CAR-iT cells can be further armed with CFRs containing appropriate endodomains to provide superior antitumor function in a regulated manner.

Citation Format: Eigen Peralta, Dan Lu, Mark Landon, Helen Chu, Shohreh Sikaroodi, Emily Carron, Natalie Navarrete, Alec Witty, Tom Lee, Anhco Nguyen, Bahram Valamehr. Chimeric fusion receptors provide a CD3-mediated activation signal to off-the-shelf iPSC-derived TCR-less CAR-T cells for enhanced efficacy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 332.

Abstract 3245: FT819 path to IND: First-of-kind off-the-shelf CAR19 T-cell for B cell malignancies

Genetic engineering of T cells using a chimeric antigen receptor targeting CD19 antigen (CAR19) is now a well-established treatment of B cell malignancies. While cellular immunotherapies are entering front line treatment, substantial limitations currently hamper the broad application of adoptive T cell therapies in diverse patient population including dysfunctional starting material, lack of product consistency and purity post genetic engineering and inefficient quantity produced for true on-demand availability. FT819 is a first-of-kind off-the-shelf CAR19-T cell product generated from a renewable pluripotent stem cells for large-scale clinical manufacturing. We previously reported the engineering and characterization of the FT819 clonal master cell bank (MCB) derived from a single cell comprising targeted integration of a novel CD19 1XX CAR into the T-cell receptor (TCR) α constant locus to provide optimally regulated CAR expression and elimination of graft versus host (GvH) response. Here we preview the nonclinical study for the original investigational new drug application of FT819. Derived in a manufacturing process analogous to pharmaceutical drug product development, pilot runs from the MCB demonstrated FT819 can be consistently and uniformly manufactured in cGMP compliance, cryopreserved at clinical scale to support off-the-shelf clinical application with greater than 1e5 fold increase in cellular yield from the starting MCB and can be thawed and directly used for facilitated treatment. Repeatedly, FT819 displayed a uniform product profile of ≥95% CAR+, TCR-, CD45+, CD7+ and CD3+ [intracellular] with majority of CD8 T cells expressing CD8β. FT819 global gene expression profile displayed high similarity to primary CAR19-T cells confirming its identity as a T lymphocyte. Functional assessment demonstrated that FT819 possesses potent antigen specific cytolytic activity against leukemia and lymphoma cell lines (p=0.0004). Additional specificity studies demonstrated on-target, off-tumor cytolysis of CD19+ B cells in mixed lymphocyte reaction assay (85% lysis of CD19+ B cells versus < 2% lysis of T cells). Inability of FT819 to produce a GvH response was confirmed in a co-culture assay with anti-TCR crosslinking antibodies. Disseminated leukemia xenograft mouse studies demonstrated the ability of directly thawed and infused FT819 to control tumor growth (p=0.0003 at day 21). In a systemic administered leukemia model FT819 also showed sustained localization in the bone marrow up to 45 days post injection. Ongoing in vivo studies will assess long-term survival and avoidance of GvH disease. Collectively, these studies demonstrate that FT819 is a potent, consistent and uniform CAR19 T cell product and can be effectively and safely used off-the-shelf in the treatment of B cell malignancies with an original Phase 1 clinical trial planned in 2020.

Citation Format: Mili Mandal, Raedun Clarke, Sjoukje van der Stegen, Chia-Wei Chang, Yi-Shin Lai, Alec Witty, Mushtaq Husain, Cheng-Jang Wu, Bi-Huei Yang, Chad Dufaud, Gloria Hsia, Helena Shaked, Laurel Stokely, Helen Chu, Mochtar Pribadi, Gilberto Hernandez, Jason ORourke, Alma Gutierrez, Ramzey Abujarour, Tom Lee, Jolanta Stefanski, Juan Zhen, Meilan Wu, Isabelle Riviere, Michel Sadelain, Bahram Valamehr. FT819 path to IND: First-of-kind off-the-shelf CAR19 T-cell for B cell malignancies [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3245.

Functional arrays of human pluripotent stem cell-derived cardiac microtissues

To accelerate the cardiac drug discovery pipeline, we set out to develop a platform that would be capable of quantifying tissue-level functions such as contractile force and be amenable to standard multiwell-plate manipulations. We report a 96-well-based array of 3D human pluripotent stem cell (hPSC)-derived cardiac microtissues - termed Cardiac MicroRings (CaMiRi) - in custom 3D-print-molded multiwell plates capable of contractile force measurement. Within each well, two elastomeric microcantilevers are situated above a circumferential ramp. The wells are seeded with cell-laden collagen, which, in response to the gradual slope of the circumferential ramp, self-organizes around tip-gated microcantilevers to form contracting CaMiRi. The contractile force exerted by the CaMiRi is measured and calculated using the deflection of the cantilevers. Platform responses were robust and comparable across wells, and we used it to determine an optimal tissue formulation. We validated the contractile force response of CaMiRi using selected cardiotropic compounds with known effects. Additionally, we developed automated protocols for CaMiRi seeding, image acquisition, and analysis to enable the measurement of contractile force with increased throughput. The unique tissue fabrication properties of the platform, and the consequent effects on tissue function, were demonstrated upon adding hPSC-derived epicardial cells to the system. This platform represents an open-source contractile force screening system useful for drug screening and tissue engineering applications.

Abstract LB-073: Generation of novel single cell-derived engineered master pluripotent cell line as a renewable source for off-the-shelf TCR-less CAR T cells in support of first-of-kind clinical trial

Adoptive transfer of autologous T cells expressing chimeric antigen receptor (CAR) has shown great promise in the treatment of blood malignancies. Challenges for the application of current CAR T cell therapies to broader and more diverse patient populations include inherent variability, cost of manufacture, and the requirement for precise genetic engineering to generate a highly homogenous and consistent CAR T cell product. We have previously reported pre-clinical data supporting the development of FT819, a first-of-kind off-the-shelf CAR T cell product candidate. FT819 is generated from a renewable clonal master human induced pluripotent stem cell (hiPSC) line derived from a single cell engineered to contain bi-allelic disruption of the T cell receptor (TCR) and a novel CD19 CAR targeted into the T cell receptor α constant (TRAC) locus to provide antigen specificity and enhanced efficacy while eliminating the possibility of graft versus host disease. For the manufacture of a clinical-grade FT819 clonal master hiPSC line, we sourced peripheral blood mononuclear cells from a fully consented and eligible donor with protocol overseen by an independent Institutional Review Board. Sourced T cells were enriched (>98%) through positive selection for TCRαβ, and cryopreserved cells were confirmed to have stable genome by karyotyping. Using our proprietary non-integrating cellular reprogramming platform, αβ T cells were reprogrammed into hiPSCs. Concurrently with the reprogramming process, reprogrammed cells received nuclease and donor template to mediate targeting of CD19 CAR into the TRAC locus with bi-allelic knockout of the TCR. To generate clonal lines, engineered cells were sorted by flow cytometry for various markers and single cells were seeded into individual wells of feeder-free 96-well plates. hiPSC clones were screened for bi-allelic integration of CAR into the TRAC locus by amplifying the genomic DNA flanking the homologous recombination site and confirmed by a SNP phasing assay. Clones were further screened for random integration of donor template by quantitative PCR (qPCR), and the CAR copy number was confirmed by droplet digital PCR. Out of 545 hiPSC clones screened, 27 clones (5%) had bi-allelic TRAC targeting with no detectable random integration. Maintenance of pluripotency was confirmed in 19 out of the 27 engineered hiPSC clones (70%). Seventeen clones were further tested and were confirmed to be footprint-free of transgenic reprogramming factors. Of the 18 clones tested for genomic stability, 12 clones had normal karyotypes (67%). Validated, TRAC-targeted hiPSC clones were cryopreserved (~150 vials per clone) and are currently being assessed for off-target editing, differentiation propensity into highly-functional T cells, genomic stability, clone identity, sterility and lack of mycoplasma detection. In summary, using our novel iPSC technology platform for reprogramming, single cell engineering and multiplex high-throughput screening of hiPSCs, we have generated clinical-grade clonal master hiPSC lines in support of our first-of-kind clinical trials evaluating FT819 allogenic off-the-shelf hiPSC-derived TCR-less TRAC-CAR19 T cells for the treatment of blood malignancies.

Citation Format: Ramzey Abujarour, Yi-Shin Lai, Mochtar Pribadi, Tom Lee, Megan Robinson, Chelsea Ruller, Sjoukje Van der Stegen, Xiuyan Wang, Jolanta Stefanski, Juan Zhen, Jason Dinella, Greg Bonello, Janel Huffman, Helen Chu, Raedun Clarke, Alec Witty, Amanda Medcalf, Jaeger Davis, Stacey Moreno, Pieter Lindenbergh, Isabelle Riviere, Michel Sadelain, Bahram Valamehr. Generation of novel single cell-derived engineered master pluripotent cell line as a renewable source for off-the-shelf TCR-less CAR T cells in support of first-of-kind clinical trial [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr LB-073.

Cloche is a bHLH-PAS transcription factor that drives haemato-vascular specification

Vascular and haematopoietic cells organize into specialized tissues during early embryogenesis to supply essential nutrients to all organs and thus play critical roles in development and disease. At the top of the haemato-vascular specification cascade lies cloche, a gene that when mutated in zebrafish leads to the striking phenotype of loss of most endothelial and haematopoietic cells and a significant increase in cardiomyocyte numbers. Although this mutant has been analysed extensively to investigate mesoderm diversification and differentiation and continues to be broadly used as a unique avascular model, the isolation of the cloche gene has been challenging due to its telomeric location. Here we used a deletion allele of cloche to identify several new cloche candidate genes within this genomic region, and systematically genome-edited each candidate. Through this comprehensive interrogation, we succeeded in isolating the cloche gene and discovered that it encodes a PAS-domain-containing bHLH transcription factor, and that it is expressed in a highly specific spatiotemporal pattern starting during late gastrulation. Gain-of-function experiments show that it can potently induce endothelial gene expression. Epistasis experiments reveal that it functions upstream of etv2 and tal1, the earliest expressed endothelial and haematopoietic transcription factor genes identified to date. A mammalian cloche orthologue can also rescue blood vessel formation in zebrafish cloche mutants, indicating a highly conserved role in vertebrate vasculogenesis and haematopoiesis. The identification of this master regulator of endothelial and haematopoietic fate enhances our understanding of early mesoderm diversification and may lead to improved protocols for the generation of endothelial and haematopoietic cells in vivo and in vitro.

Parthenogenetic stem cells for tissue-engineered heart repair

Uniparental parthenotes are considered an unwanted byproduct of in vitro fertilization. In utero parthenote development is severely compromised by defective organogenesis and in particular by defective cardiogenesis. Although developmentally compromised, apparently pluripotent stem cells can be derived from parthenogenetic blastocysts. Here we hypothesized that nonembryonic parthenogenetic stem cells (PSCs) can be directed toward the cardiac lineage and applied to tissue-engineered heart repair. We first confirmed similar fundamental properties in murine PSCs and embryonic stem cells (ESCs), despite notable differences in genetic (allelic variability) and epigenetic (differential imprinting) characteristics. Haploidentity of major histocompatibility complexes (MHCs) in PSCs is particularly attractive for allogeneic cell-based therapies. Accordingly, we confirmed acceptance of PSCs in MHC-matched allotransplantation. Cardiomyocyte derivation from PSCs and ESCs was equally effective. The use of cardiomyocyte-restricted GFP enabled cell sorting and documentation of advanced structural and functional maturation in vitro and in vivo. This included seamless electrical integration of PSC-derived cardiomyocytes into recipient myocardium. Finally, we enriched cardiomyocytes to facilitate engineering of force-generating myocardium and demonstrated the utility of this technique in enhancing regional myocardial function after myocardial infarction. Collectively, our data demonstrate pluripotency, with unrestricted cardiogenicity in PSCs, and introduce this unique cell type as an attractive source for tissue-engineered heart repair.