Regulation Of Transgene Expression Research Articles

Development of a tightly regulated copper-inducible transient gene expression system in Nicotiana benthamiana incorporating a suicide exon and Cre recombinase.

Chemical-inducible gene expression systems are commonly used to regulate gene expression for functional genomics in various plant species. However, a convenient system that can tightly regulate transgene expression in Nicotiana benthamiana is still lacking. In this study, we developed a tightly regulated copper-inducible system that can control transgene expression and conduct cell death assays in N. benthamiana. We tested several chemical-inducible systems using Agrobacterium-mediated transient expression and found that the copper-inducible system exhibited the least concerns regarding leakiness in N. benthamiana. Although the copper-inducible system can control the expression of some tested reporters, it is not sufficiently tight to regulate certain tested hypersensitive cell death responses. Using the MoClo-based synthetic biology approach, we incorporated the suicide exon HyP5SM/OsL5 and Cre/LoxP as additional regulatory elements to enhance the tightness of the regulation. This new design allowed us to tightly control the hypersensitive cell death induced by several tested leucine-rich repeat-containing proteins and their matching avirulence factors, and it can be easily applied to regulate the expression of other transgenes in transient expression assays. Our findings offer new approaches for both fundamental and translational studies in plant functional genomics.

Model-guided design of microRNA-based gene circuits supports precise dosage of transgenic cargoes into diverse primary cells.

To realize the potential of engineered cells in therapeutic applications, transgenes must be expressed within the window of therapeutic efficacy. Differences in copy number and other sources of extrinsic noise generate variance in transgene expression and limit the performance of synthetic gene circuits. In a therapeutic context, supraphysiological expression of transgenes can compromise engineered phenotypes and lead to toxicity. To ensure a narrow range of transgene expression, we design and characterize Co mpact m icroRNA- M ediated A ttenuator of N oise and D osage ( ComMAND ), a single-transcript, microRNA-based incoherent feedforward loop. We tune the ComMAND output profile, and we model the system to explore additional tuning strategies. By comparing ComMAND to two-gene implementations, we highlight the precise control afforded by the single-transcript architecture, particularly at relatively low copy numbers. We show that ComMAND tightly regulates transgene expression from lentiviruses and precisely controls expression in primary human T cells, primary rat neurons, primary mouse embryonic fibroblasts, and human induced pluripotent stem cells. Finally, ComMAND effectively sets levels of the clinically relevant transgenes FMRP1 and FXN within a narrow window. Together, ComMAND is a compact tool well-suited to precisely specify expression of therapeutic cargoes.

Transcription Factor Binding Site in Promoter Determines the Pattern of Plasmid-Based Transgene Expression In Vivo.

Understanding the regulation of transgene expression is critical for the success of plasmid-based gene therapy and vaccine development. In this study, we used two sets of plasmid vectors containing secreted embryonic alkaline phosphatase or the mouse IL-10 gene as a reporter and investigated the role of promoter elements in regulating transgene expression in vivo. We demonstrated in mice that hydrodynamic transfer of plasmids with the CMV promoter resulted in a high level of reporter gene expression that declined rapidly over time. In contrast, when plasmids with albumin promoters were used, a lower but sustained gene expression pattern was observed. We also found that plasmids containing a shorter CMV promoter sequence with fewer transcription factor binding sites showed a decrease in the peak level of gene expression without changing the overall pattern of reporter gene expression. The replacement of regulatory elements in the CMV promoter with a single regulatory element of the albumin promoter changed the pattern of transient gene expression seen in the CMV promoter to a pattern of sustained gene expression identical to that of a full albumin promoter. ChIP analyses demonstrated an elevated binding of acetylated histones and TATA box-binding protein to the promoter carrying regulatory elements of the albumin promoter. These results suggest that the strength of a promoter is determined by the number of appropriate transcription factor binding sites, while gene expression persistence is determined by the presence of regulatory elements capable of recruiting epigenetic modifying complexes that make the promoter accessible for transcription. This study provides important insights into the mechanisms underlying gene expression regulation in vivo, which can be used to improve plasmid-based gene therapy and vaccine development.

Improved gene therapy for spinal muscular atrophy in mice using codon-optimized hSMN1 transgene and hSMN1 gene-derived promotor

Physiological regulation of transgene expression is a major challenge in gene therapy. Onasemnogene abeparvovec (Zolgensma®) is an approved adeno-associated virus (AAV) vector gene therapy for infants with spinal muscular atrophy (SMA), however, adverse events have been observed in both animals and patients following treatment. The construct contains a native human survival motor neuron 1 (hSMN1) transgene driven by a strong, cytomegalovirus enhancer/chicken β-actin (CMVen/CB) promoter providing high, ubiquitous tissue expression of SMN. We developed a second-generation AAV9 gene therapy expressing a codon-optimized hSMN1 transgene driven by a promoter derived from the native hSMN1 gene. This vector restored SMN expression close to physiological levels in the central nervous system and major systemic organs of a severe SMA mouse model. In a head-to-head comparison between the second-generation vector and a benchmark vector, identical in design to onasemnogene abeparvovec, the 2nd-generation vector showed better safety and improved efficacy in SMA mouse model.

Engineered poly(A)-surrogates for translational regulation and therapeutic biocomputation in mammalian cells

Here, we present a gene regulation strategy enabling programmable control over eukaryotic translational initiation. By excising the natural poly-adenylation (poly-A) signal of target genes and replacing it with a synthetic control region harboring RNA-binding protein (RBP)-specific aptamers, cap-dependent translation is rendered exclusively dependent on synthetic translation initiation factors (STIFs) containing different RBPs engineered to conditionally associate with different eIF4F-binding proteins (eIFBPs). This modular design framework facilitates the engineering of various gene switches and intracellular sensors responding to many user-defined trigger signals of interest, demonstrating tightly controlled, rapid and reversible regulation of transgene expression in mammalian cells as well as compatibility with various clinically applicable delivery routes of in vivo gene therapy. Therapeutic efficacy was demonstrated in two animal models. To exemplify disease treatments that require on-demand drug secretion, we show that a custom-designed gene switch triggered by the FDA-approved drug grazoprevir can effectively control insulin expression and restore glucose homeostasis in diabetic mice. For diseases that require instantaneous sense-and-response treatment programs, we create highly specific sensors for various subcellularly (mis)localized protein markers (such as cancer-related fusion proteins) and show that translation-based protein sensors can be used either alone or in combination with other cell-state classification strategies to create therapeutic biocomputers driving self-sufficient elimination of tumor cells in mice. This design strategy demonstrates unprecedented flexibility for translational regulation and could form the basis for a novel class of programmable gene therapies in vivo.

An Adapted GeneSwitch Toolkit for Comparable Cellular and Animal Models: A Proof of Concept in Modeling Charcot-Marie-Tooth Neuropathy.

Investigating the impact of disease-causing mutations, their affected pathways, and/or potential therapeutic strategies using disease modeling often requires the generation of different in vivo and in cellulo models. To date, several approaches have been established to induce transgene expression in a controlled manner in different model systems. Several rounds of subcloning are, however, required, depending on the model organism used, thus bringing labor-intensive experiments into the technical approach and analysis comparison. The GeneSwitch™ technology is an adapted version of the classical UAS-GAL4 inducible system, allowing the spatial and temporal modulation of transgene expression. It consists of three components: a plasmid encoding for the chimeric regulatory pSwitch protein, Mifepristone as an inducer, and an inducible plasmid. While the pSwitch-containing first plasmid can be used both in vivo and in cellulo, the inducible second plasmid can only be used in cellulo. This requires a specific subcloning strategy of the inducible plasmid tailored to the model organism used. To avoid this step and unify gene expression in the transgenic models generated, we replaced the backbone vector with standard pUAS-attB plasmid for both plasmids containing either the chimeric GeneSwitch™ cDNA sequence or the transgene cDNA sequence. We optimized this adapted system to regulate transgene expression in several mammalian cell lines. Moreover, we took advantage of this new system to generate unified cellular and fruit fly models for YARS1-induced Charco-Marie-Tooth neuropathy (CMT). These new models displayed the expected CMT-like phenotypes. In the N2a neuroblastoma cells expressing YARS1 transgenes, we observed the typical "teardrop" distribution of the synthetase that was perturbed when expressing the YARS1CMT mutation. In flies, the ubiquitous expression of YARS1CMT induced dose-dependent developmental lethality and pan-neuronal expression caused locomotor deficit, while expression of the wild-type allele was harmless. Our proof-of-concept disease modeling studies support the efficacy of the adapted transgenesis system as a powerful tool allowing the design of studies with optimal data comparability.

Temporal regulation of transgene expression controlled by amino acid availability in human T cells.

T cell therapy strategies, from allogeneic stem cell transplantation toward genetically-modified T cells infusion, develop powerful anti-tumor effects but are often accompanied by side effects and their efficacy remains sometimes to be improved. It therefore appears important to provide a flexible and easily reversible gene expression regulation system to control T cells activity. We developed a gene expression regulation technology that exploits the physiological GCN2-ATF4 pathway's ability to induce gene expression in T cells in response to one essential amino acid deficiency. We first demonstrated the functionality of NUTRIREG in human T cells by transient expression of reporter genes. We then validated that NUTRIREG can be used in human T cells to transiently express a therapeutic gene such as IL-10. Overall, our results represent a solid basis for the promising use of NUTRIREG to regulate transgene expression in human T cells in a reversible way, and more generally for numerous preventive or curative therapeutic possibilities in cellular immunotherapy strategies.

AAV-based in vivo gene therapy for neurological disorders.

Recent advancements in gene supplementation therapy are expanding the options for the treatment of neurological disorders. Among the available delivery vehicles, adeno-associated virus (AAV) is often the favoured vector. However, the results have been variable, with some trials dramatically altering the course of disease whereas others have shown negligible efficacy or even unforeseen toxicity. Unlike traditional drug development with small molecules, therapeutic profiles of AAV gene therapies are dependent on both the AAV capsid and the therapeutic transgene. In this rapidly evolving field, numerous clinical trials of gene supplementation for neurological disorders are ongoing. Knowledge is growing about factors that impact the translation of preclinical studies to humans, including the administration route, timing of treatment, immune responses and limitations of available model systems. The field is also developing potential solutions to mitigate adverse effects, including AAV capsid engineering and designs to regulate transgene expression. At the same time, preclinical research is addressing new frontiers of gene supplementation for neurological disorders, with a focus on mitochondrial and neurodevelopmental disorders. In this Review, we describe the current state of AAV-mediated neurological gene supplementation therapy, including critical factors for optimizing the safety and efficacy of treatments, as well as unmet needs in this field.

Evolution of molecular switches for regulation of transgene expression by clinically licensed gluconate.

Synthetic biology holds great promise to improve the safety and efficacy of future gene and engineered cell therapies by providing new means of endogenous or exogenous control of the embedded therapeutic programs. Here, we focused on gluconate as a clinically licensed small-molecule inducer and engineered gluconate-sensitive molecular switches to regulate transgene expression in human cell cultures and in mice. Several switch designs were assembled based on the gluconate-responsive transcriptional repressor GntR from Escherichia coli. Initially we assembled OFF- and ON-type switches by rewiring the native gluconate-dependent binding of GntR to target DNA sequences in mammalian cells. Then, we utilized the ability of GntR to dimerize in the presence of gluconate to activate gene expression from a split transcriptional activator. By means of random mutagenesis of GntR combined with phenotypic screening, we identified variants that significantly enhanced the functionality of the genetic devices, enabling the construction of robust two-input logic gates. We also demonstrated the potential utility of the synthetic switch in two in vivo settings, one employing implantation of alginate-encapsulated engineered cells and the other involving modification of host cells by DNA delivery. Then, as proof-of-concept, the gluconate-actuated genetic switch was connected to insulin secretion, and the components encoding gluconate-induced insulin production were introduced intotype-1 diabetic miceas naked DNA via hydrodynamic tail vein injection. Normoglycemia was restored, thereby showcasing the suitability of oral gluconate to regulate in situ production of a therapeutic protein.

Abstract A067: Cellular cartography reveals transcriptional specificity and spatial organization of diverse luminal epithelial cells in the murine prostate

Abstract Introduction Prostate cancer (PCa) is the second most frequent malignancy in men. Genetically engineered PCa mouse models (GEMMs) do not faithfully recapitulate human PCa progression. Reasons include architectural differences between the multi-lobulated mouse prostate and the human organ, choice of gene promoter (such as probasin, Pbsn) used to regulate transgene expression in GEMMs and lobular differences in susceptibility to castration. Imaging studies showed that androgen deprivation (first line therapy for metastatic PCa) by castration leads to dramatic regression of ventral prostate (VP) by up to 70%. Hence delineating cell type equivalents between the human and mouse prostates and mapping their distribution across the distinct lobes will provide fundamental knowledge to improve GEMMs, to effectively model human PCa. Methods We performed single-cell RNA sequencing (scRNA-seq) of C57BL6 and FVB mice prostates (n=10) to delineate cell type composition. We also conducted sc multi-omics (10X Multiome gene expression+ ATAC) and spatial transcriptomics (10X Visium) of prostates from mice that were unperturbed or castrated (C57BL6) to study transcriptional module (TM) alterations and spatial gene expression among the luminal epithelial (LE) cell types upon castration. Results Analyses of scRNA-seq data from 9,439 cells identified 22 different cell types from epithelial, stromal, and immune compartments and includes 9 different LE cell types that are under-studied. The lack of a standard nomenclature describing murine prostate LE cells in previous scRNA-seq studies poses a challenge for integrative analysis. We resolved this by integrating 4 independent scRNA-seq studies with our data to arrive at unified nomenclature and simultaneously validate our findings by statistical analysis. Multi-omics data analysis revealed LE cells TM differences, suggesting that LE cell diversity is developmentally triggered. Spatial transcriptomics and matched RNA in situ hybridization captured the lobe specific distribution patterns of LE cell types. For e.g., Pbsn+ LE cells were predominantly found across the AP, dorsal and lateral prostate, while Spink1+LE cells containing stemness associated genes (e.g.Tacstd2) were enriched in the VP. Analysis of the castration model revealed susceptibility differences to androgen deprivation among LE populations. Multi-omics analysis also showed a reduction in both chromatin accessibility and transcription of androgen regulated genes upon castration. Finally, cell type enrichment analysis suggests LE cells of the mouse AP and VP as equivalents of human LE and putative cell lineage signatures were enriched in PCa profiles, possibly stratifying PCa patient population. Conclusion A comprehensive mouse prostate cell atlas was built from two mouse strains. We provide a practical reference for the transcriptional and spatial profiles of each epithelial population. LE cells from AP and VP were most sensitive to castration and best represent human LE and the cell type specific genes identified here can guide future GEMM development. Citation Format: Hanbyul Cho, Yuping Zhang, Jean Tien, Jie Luo, June E. Wilke, Saravana M. Dhanasekaran, Rahul Mannan, Lisha Wang, Fengyun Su, Rui Wang, Evan T. Keller, Xuhong Cao, Sethu Pitchaya, Arul M. Chinnaiyan. Cellular cartography reveals transcriptional specificity and spatial organization of diverse luminal epithelial cells in the murine prostate [abstract]. In: Proceedings of the AACR Special Conference: Advances in Prostate Cancer Research; 2023 Mar 15-18; Denver, Colorado. Philadelphia (PA): AACR; Cancer Res 2023;83(11 Suppl):Abstract nr A067.

OPTO-BLUE: An Integrated Bidirectional Optogenetic Lentiviral Platform for Controlled Light-Induced Gene Expression.

Regulated systems for transgene expression are useful tools in basic research and a promising platform in biomedicine due to their regulated transgene expression by an inducer. The emergence of optogenetics expression systems enabled the construction of light-switchable systems, enhancing the spatial and temporal resolution of a transgene. The LightOn system is an optogenetic tool that regulates the expression of a gene of interest using blue light as an inducer. This system is based on a photosensitive protein (GAVPO), which dimerizes and binds to the UASG sequence in response to blue light, triggering the expression of a downstream transgene. Previously, we adapted the LightOn system to a dual lentiviral vector system for neurons. Here, we continue the optimization and assemble all components of the LightOn system into a single lentiviral plasmid, the OPTO-BLUE system. For functional validation, we used enhanced green fluorescent protein (EGFP) as an expression reporter (OPTO-BLUE-EGFP) and evaluated the efficiency of EGFP expression by transfection and transduction in HEK293-T cells exposed to continuous blue-light illumination. Altogether, these results prove that the optimized OPTO-BLUE system allows the light-controlled expression of a reporter protein according to a specific time and light intensity. Likewise, this system should provide an important molecular tool to modulate gene expression of any protein by blue light.

Controlling therapeutic protein expression via inhalation of a butter flavor molecule.

Precise control of the delivery of therapeutic proteins is critical for gene- and cell-based therapies, and expression should only be switched on in the presence of a specific trigger signal of appropriate magnitude. Focusing on the advantages of delivering the trigger by inhalation, we have developed a mammalian synthetic gene switch that enables regulation of transgene expression by exposure to the semi-volatile small molecule acetoin, a widely used, FDA-approved food flavor additive. The gene switch capitalizes on the bacterial regulatory protein AcoR fused to a mammalian transactivation domain, which binds to promoter regions with specific DNA sequences in the presence of acetoin and dose-dependently activates expression of downstream transgenes. Wild-type mice implanted with alginate-encapsulated cells transgenic for the acetoin gene switch showed a dose-dependent increase in blood levels of reporter protein in response to either administration of acetoin solution via oral gavage or longer exposure to acetoin aerosol generated by a commercial portable inhaler. Intake of typical acetoin-containing foods, such as butter, lychees and cheese, did not activate transgene expression. As a proof of concept, we show that blood glucose levels were normalized by acetoin aerosol inhalation in type-I diabetic mice implanted with acetoin-responsive insulin-producing cells. Delivery of trigger molecules using portable inhalers may facilitate regular administration of therapeutic proteins via next-generation cell-based therapies to treat chronic diseases for which frequent dosing is required.

An optimized Tet-On system for conditional control of gene expression in sea urchins.

Sea urchins and other echinoderms are important experimental models for studying developmental processes. The lack of approaches for conditional gene perturbation, however, has made it challenging to investigate the late developmental functions of genes that have essential roles during early embryogenesis and genes that have diverse functions in multiple tissues. The doxycycline-controlled Tet-On system is a widely used molecular tool for temporally and spatially regulated transgene expression. Here, we optimized the Tet-On system to conditionally induce gene expression in sea urchin embryos. Using this approach, we explored the roles the MAPK signaling plays in skeletogenesis by expressing genes that perturb the pathway specifically in primary mesenchyme cells during later stages of development. We demonstrated the wide utility of the Tet-On system by applying it to a second sea urchin species and in cell types other than the primary mesenchyme cells. Our work provides a robust and flexible platform for the spatiotemporal regulation of gene expression in sea urchins, which will considerably enhance the utility of this prominent model system.

Regulation of Transgene Expression by the Natural Sweetener Xylose.

Next-generation gene and engineered-cell therapies benefit from incorporating synthetic gene networks that can precisely regulate the therapeutic output in response to externally administered signal inputs that are safe, readily bioavailable and pleasant to take. To enable such therapeutic control, a mammalian gene switch is designed to be responsive to the natural sweetener xylose and its functionality is assessed in mouse studies. The gene switch consists of the bacterial transcription regulator XylR fused to a mammalian transactivator, which binds to an optimized promoter in the presence of xylose, thereby allowing dose-dependent transgene expression. The sensitivity of SWEET (sweetener-inducible expression of transgene) is improved by coexpressing a xylose transporter. Mice implanted with encapsulated SWEET-engineered cells show increased blood levels of cargo protein when taking xylose-sweetened water or coffee, or highly concentrated apple extract, while they do not respond to intake of a usual amount of carrots, which contain xylose. In a proof-of-concept therapeutic application study, type-1 diabetic mice engineered with insulin-expressing SWEET show lowered glycemia and increased insulin levels when administered this fairly diabetic-compliant sweetener, compared to untreated mice. A SWEET-based therapy appears to have the potential to integrate seamlessly into patients' life-style and food habits in the move toward personalized medicine.

Cytosolic dsRNA sensors as regulators of transgene expression from AAV vectors in human iPSC-derived cardiomyocytes

Abstract Background Adeno-associated viral vectors (AAVs) are safe and efficient tools for delivery of therapeutic genes in numerous applications. Although they elicit only limited immune response in host cells, a recent study has demonstrated an association between decreasing transgene expression in the liver and induction of the immune response to cytoplasmic dsRNA. While AAVs are DNA vectors, it appears that their unique genome structure allows the generation of dsRNA in transduced cells. Since the expression cassette is flanked by inverted terminal repeats (ITRs), which can function as bidirectional promoters, assembly of sense and antisense transcripts can potentially result in formation of dsRNA structures, especially in cells exhibiting high transgene expression. Purpose In this study, we explored the mechanism of dsRNA recognition in cardiomyocytes, to unravel its role in the regulation of transgene expression from AAV vectors. Methods For this purpose, we utilised human iPSC-derived cardiomyocytes transduced with self-complementary AAV6 or AAV9 vectors encoding GFP. Since we focused on the long-term effects of transgene expression, all the analyses were performed 7–9 days after AAV transduction. Results We confirmed that ITR serves as a functional promoter in the cells, capable of maintaining approximately half of the fluorescence signal compared to the CMV promoter. Long-term transgene expression was associated with elevated expression of dsRNA sensors (MDA5, RIG-I, LGP2 and TLR3) and the appearance of small foci of dsRNA in the perinuclear region. Unlike an artificial ligand for dsRNA sensors, poly (I:C), dsRNA in AAV-transduced cells did not interact with the LGP2 protein. To induce dsRNA recognition, we stimulated the cells with IFNβ for 1 week, starting from day 1 after transduction. We found that transgene expression is significantly hampered in such conditions. Furthermore, IFNβ induced the direct interaction of dsRNA with the OAS1 protein in transduced cells. During viral infections, OAS1 and its effector nuclease RNAse L promote the degradation of mRNA to restrict the production of viral proteins. Since RNAse L is not specific for particular transcripts, we hypothesize that activation of the OAS1 pathway in transduced cells is responsible for downregulation of transgene expression. While IFNβ induced OAS1-dsRNA recognition, we did not observe such an event in cells transduced with AAV and maintained under standard conditions. In turn, AAV transduction resulted in a reduction in OAS1 expression at the mRNA and protein level, suggesting a possible reason for tolerance to dsRNA in transduced cardiomyocytes. Conclusions Our data present a novel mechanism of regulation of transgene expression in AAV-transduced cells involving OAS1–RNAse L pathway and provide deeper insight into the general signal transduction routes activated in response to cytosolic dsRNA in human iPSC-derived cardiomyocytes. Funding Acknowledgement Type of funding sources: Public grant(s) – National budget only. Main funding source(s): National Science Centre - PRELUDUM grant 2019/33/N/NZ1/03066Jagiellonian University, Faculty of Biochemistry, Biophysics and Biotechnology - grant for young scientists MNS 6/2020

OS05.6.A Modification of the tumor microenvironment in patients with glioblastoma using autologous, genetically modified, hematopoietic stem cell-based therapy: the TEM-GBM STUDY (NCT03866109)

Abstract Background Bone marrow-derived macrophages account for substantial GBM tumor volume and contribute to the local inflammatory tumor microenvironment, disease progression and treatment response. Material and Methods We have developed a genetically modified, autologous hematopoietic stem cell-based platform designed to deliver Interferon-alpha (IFNa), thanks to a transcriptional and post-transcriptional control mechanism mediated by miRNA target sequences, specifically into the tumor microenvironment via Tie-2 expressing monocytes (Temferon). Results As of Feb 2022, 3 escalating doses of Temferon (from 0.5 to 2.0x106/kg) were tested across 15 patients with newly diagnosed, unmethylated MGMT glioblastoma (GBM) assigned to 5 cohorts. The duration of follow-up from surgery is 6 - 28 mo (2 - 25 mo after Temferon). To date, no dose limiting toxicities have been identified. As expected, one month after the administration of the highest tested dose, the hematopoietic system of Temferon-treated patients was composed of up to 30% of CD14+ genetically modified cells, as determined by the presence of vector genomes in the DNA in peripheral blood and bone marrow cells. Temferon-derived progeny persisted, albeit at lower levels, up to 18 months (longest time of analysis). Despite the substantial proportion of engineered cells, very low median concentrations of IFNα were detected in the plasma (D+30, 5.9; D+90, 8.8pg/mL) and in the CSF (D+30, 1.5; D+90, 2.4pg/mL), indicating tight regulation of transgene expression. SAEs were mostly attributed to conditioning chemotherapy (e.g. infections) or disease progression (e.g. seizures). 1 SUSAR (persistent GGT elevation) has occurred. Median OS is 15 mo from surgery (range 6.1-28.4 mo; 10.8 mo post Temferon). Of the 15 pts treated so far, 4 pts belonging to low dose cohorts underwent 2nd surgery. Homing of transduced cells from BM to the tumor site was demonstrated by the presence of gene-marked cells in the specimens collected from 3 of the 4 analyzed pts. Single-cell RNA seq performed on CD45+ cells purified from the TME of Temferon-treated pts compared to recurrent tumors belonging to GBM pts treated as per the current standard of care, highlighted a Temferon signature defined by the induction of markers of IFNa responses and macrophage repolarization. Potential long-term benefit with Temferon was identified in a patient from cohort 3, who had disease progression at D+120 with two distant enhancing lesions, and increased tumor necrosis. One year following Temferon, with no 2nd line therapy added, there was approximately 40% reduction in enhancing tumor volume compared to D+180 with a stable clinical and imaging picture thereafter. Conclusion The results provide initial evidence of Temferon’s potential to modulate the TME of GBM patients, and anecdotal evidence for long lasting effects of Temferon in prevention of disease progression.

284MO Targeting the tumor microenvironment of glioblastoma multiforme using a macrophage-based treatment for the local delivery of immune-therapeutic payload: The TEM-GBM study (NCT03866109)

Bone marrow-derived macrophages account for a substantial Glioblastoma (GBM) tumor volume and contribute to the local inflammatory tumor microenvironment (TME), disease progression & treatment response. We have developed a genetically modified, autologous hematopoietic stem cell-based platform designed to deliver IFNa, specifically into the TME via Tie-2 expressing monocytes (Temferon). TEM-GBM is an open-label, phase I/IIa dose-escalation study evaluating safety and efficacy of Temferon in up to 21 newly diagnosed, unmeth-MGMT GBM patients. The patients will be assigned to 7 cohorts and will receive a single increasing dose of Temferon. As of April 2022, 4 doses of Temferon (0.5-3.0x106/kg) were tested across 16 patients assigned to 6 cohorts. Follow-up from surgery is 6–28mo (2–25mo after Temferon). To date, no DLTs have been identified. Temferon-derived progeny as defined by gene-marked cells were found within the hematopoietic system within 2-weeks of Temferon administration and persisted, albeit at lower levels, up to 18mo (longest time of analysis). Very low concentrations of IFNα were detected in plasma and CSF, indicating tight regulation of transgene expression. SAEs were mostly attributed to conditioning chemotherapy (infections) or disease progression (PD) (seizures). 1SUSAR (persistent GGT elevation) occurred. Median OS is 15mo from surgery. Transduced cells were detected in the 2nd surgery specimens of 3 out 4 pts belonging to low dose cohorts. Single-cell RNA seq of the TME highlighted a Temferon signature associated with the induction IFNa responsive genes and macrophage repolarization. Potential long-term benefit with Temferon was identified in a patient from C3, who had PD at D+120 with 2-distant enhancing lesions, and increased tumor necrosis. 1y following Temferon, with no 2nd-line therapy added, there was approximately 40% reduction in enhancing tumor volume compared to D+180 with a stable clinical and imaging picture thereafter. The results provide initial evidence of Temferon’s potential to modulate GBM TME, and anecdotal evidence for long lasting effects of Temferon in prevention of PD.

CLRM-08 TARGETING IMMUNE-PAYLOAD TO THE GLIOBLASTOMA TUMOR MICROENVIRONMENT USING A MACROPHAGE-BASED TREATMENT RELYING ON AUTOLOGOUS, GENETICALLY MODIFIED, HEMATOPOIETIC STEM CELL-BASED THERAPY: THE TEM-GBM STUDY (NCT03866109)

We developed an autologous hematopoietic stem cell-based platform designed to deliver IFNa, by a transcriptional and post-transcriptional control mechanism mediated by miRNA target sequences, specifically into the tumor microenvironment (TME) via Tie-2 expressing monocytes (Temferon). As of Feb 2022, 3 escalating doses of Temferon (0.5-2.0x106/kg) were tested across 15 newly diagnosed, unmethylated MGMT GBM patients assigned to 5 cohorts. Follow-up from surgery is 6–28mo (2–25mo after Temferon). To date, no DLTs have been identified. As expected, 1mo after the administration of the highest tested dose, the hematopoietic system of Temferon-treated patients was composed of up to 30% of CD14+ modified cells. Temferon-derived progeny persisted, albeit at lower levels, up to 18mo (longest time of analysis). Despite the substantial proportion of engineered cells, very low concentrations of IFNα were detected in the plasma and in the CSF, indicating tight regulation of transgene expression. SAEs were mostly attributed to conditioning chemotherapy (infections) or disease progression (seizures). 1SUSAR (persistent GGT elevation) occurred. Median OS is 15mo from surgery. Homing of transduced cells to the tumor was demonstrated by the presence of gene-marked cells in the 2nd surgery specimens of 3 out 4 pts belonging to low dose cohorts. Single-cell RNA seq of the TME highlighted a Temferon signature associated with the induction IFNa responsive genes and macrophage repolarization. Potential long-term benefit with Temferon was identified in a patient from cohort 3, who had PD at D+120 with two distant enhancing lesions, and increased tumor necrosis. 1y following Temferon, with no 2nd-line therapy added, there was approximately 40% reduction in enhancing tumor volume compared to D+180 with a stable clinical and imaging picture thereafter. The results provide initial evidence of Temferon’s potential to modulate the TME of GBM patients, and anecdotal evidence for long lasting effects of Temferon in prevention of disease progression.

A Novel Cre/lox71-Based System for Inducible Expression of Recombinant Proteins and Genome Editing.

In this study, we developed a novel Cre/lox71-based system for the controlled transient expression of target genes. We used the bacteriophage P1 Cre recombinase, which harbors a short, highly specific DNA-binding site and does not have endogenous binding sites within mouse or human genomes. Fusing the catalytically inactive form of Cre recombinase and the VP64 transactivation domain (VP16 tetramer), we constructed the artificial transcription factor Cre-VP64. This transcription factor binds to the lox71 sites within the promoter region of the target gene and, therefore, upregulates its expression. We tested the Cre-VP64/lox71 system for the controlled expression of several genes, including growth factors and the genome editor CRISPR/Cas9, and obtained superior efficiency in the regulation of transgene expression, achieving a high expression level upon induction together with low basal activity. This system or its modified forms can be suggested as a novel effective tool for the transitory controlled expression of target genes for functional genomic studies, as well as for gene therapy approaches.

A single promoter-TALE system for tissue-specific and tuneable expression of multiple genes in rice.

SummaryIn biological discovery and engineering research, there is a need to spatially and/or temporally regulate transgene expression. However, the limited availability of promoter sequences that are uniquely active in specific tissue‐types and/or at specific times often precludes co‐expression of multiple transgenes in precisely controlled developmental contexts. Here, we developed a system for use in rice that comprises synthetic designer transcription activator‐like effectors (dTALEs) and cognate synthetic TALE‐activated promoters (STAPs). The system allows multiple transgenes to be expressed from different STAPs, with the spatial and temporal context determined by a single promoter that drives expression of the dTALE. We show that two different systems—dTALE1‐STAP1 and dTALE2‐STAP2—can activate STAP‐driven reporter gene expression in stable transgenic rice lines, with transgene transcript levels dependent on both dTALE and STAP sequence identities. The relative strength of individual STAP sequences is consistent between dTALE1 and dTALE2 systems but differs between cell‐types, requiring empirical evaluation in each case. dTALE expression leads to off‐target activation of endogenous genes but the number of genes affected is substantially less than the number impacted by the somaclonal variation that occurs during the regeneration of transformed plants. With the potential to design fully orthogonal dTALEs for any genome of interest, the dTALE‐STAP system thus provides a powerful approach to fine‐tune the expression of multiple transgenes, and to simultaneously introduce different synthetic circuits into distinct developmental contexts.