Systemic Vector Administration Research Articles

Absence of functional deficits in rats following systemic administration of an AAV9 vector despite moderate peripheral nerve and dorsal root ganglia findings: A clinically silent peripheral neuropathy

Adeno-associated virus (AAV)-based vectors are commonly used for delivering transgenes in gene therapy studies, but they are also known to cause dorsal root ganglia (DRG) and peripheral nerve toxicities in animals. However, the functional implications of these pathologic findings and their time course remain unclear. At 2, 4, 6, and 8 weeks following a single dose of an AAV9 vector carrying human frataxin transgene in rats, non-standard functional assessments, including von Frey filament, electrophysiology, and Rotarod tests, were conducted longitudinally to measure allodynia, nerve conduction velocity, and coordination, respectively. Additionally, DRGs, peripheral nerves, brain and spinal cord were evaluated histologically and circulating neurofilament light chain (NfL) was quantified at 1, 2, 4, and 8 weeks, respectively. At 2 and 4 weeks after dosing, minimal-to-moderate nerve fiber degeneration and neuronal degeneration were observed in the DRGs in some of the AAV9 vector-dosed animals. At 8 weeks, nerve fiber degeneration was observed in DRGs, with or without neuronal degeneration, and in sciatic nerves of all AAV9 vector-dosed animals. NfL values were higher in AAV9 vector-treated animals at weeks 4 and 8 compared with controls. However, there were no significant differences in the three functional endpoints evaluated between the AAV9 vector- and vehicle-dosed animals, or in a longitudinal comparison between baseline (predose), 4, and 8 week values in the AAV9 vector-dose animals. These findings demonstrate that there is no detectable functional consequence to the minimal-to-moderate neurodegeneration observed with our AAV9 vector treatment in rats, suggesting a functional tolerance or reserve for loss of DRG neurons after systemic administration of AAV9 vector.

Oncolytic herpes simplex viruses designed for targeted treatment of EGFR-bearing tumors

Oncolytic herpes simplex viruses (oHSVs) have emerged as leading cancer therapeutic agents. Effective oHSV virotherapy may ultimately require both intratumoral and systemic vector administration to target the primary tumor and distant metastases. An attractive approach to enhancing oHSV tumor specificity is engineering the virus envelope glycoproteins for selective recognition of and infection via tumor-specific cell surface proteins. We previously demonstrated that oHSVs could be retargeted to EGFR-expressing cells by the incorporation of a single-chain antibody (scFv) at the N terminus of glycoprotein D (gD). Here, we compared retargeted oHSVs generated by the insertion of scFv, affibody molecule, or VHH antibody ligands at different positions within the N terminus of gD. When compared to the scFv-directed oHSVs, VHH and affibody molecules mediated enhanced EGFR-specific tumor cell entry, spread and cell killing invitro, and enabled long-term tumor-specific virus replication following intravenous delivery invivo. Moreover, oHSVs retargeted via a VHH ligand reduced tumor growth upon intravenous injection and achieved complete tumor destruction after intratumoral injection. Systemic oHSV delivery is important for the treatment of metastatic disease, and our enhancements in targeted oHSV design are a critical step in creating an effective tumor-specific oHSVs for safe administration via the bloodstream.

Abstract A024: Systemic administration of CD3-redirected lentiviral vector efficiently targets CD19-CAR delivery to human T cells in vivo

Abstract In recent years, there has been a significant increase in interest regarding the generation of CAR-T cells directly within patients using a simple vector injection containing the CAR transgene. This promising technology has the potential to streamline the procedure and decrease its overall cost. To ensure effective in vivo delivery, these vectors must demonstrate resistance to neutralization by human serum, the ability to specifically target and transduce desired cells, and must support their subsequent expansion. Lentiviral vectors (LV) pseudotyped with VSV G-protein (G-WT) have a broad tropism, targeting various cell types through their affinity for the ubiquitously expressed LDL receptor (LDLR). G-WT LV have proven effective in generating therapeutic CAR-T cells ex vivo, however, requiring proper purification and activation of T cells beforehand. To address challenges related to their in vivo delivery, we utilized rational engineering to redesign the G protein, resulting in a modified version termed G-CD3. This redesigned G protein incorporates a CD3-specific single-chain antibody, allowing for targeted recognition of T cells while avoiding LDLR recognition. Upon testing the newly designed G-CD3 LV, we demonstrated its specificity in targeting and infecting both un-activated and activated T cells in peripheral blood monocytic cell cultures. In addition, the G-CD3 LV powerfully activates T cells, evident from their increased CD25 expression, and the infection is not hindered by the presence of human serum (25%). In further experiments, we successfully demonstrated that G-CD3-LV can infect T cells in fresh whole blood. In vivo evaluation of G-CD3-LV efficiency was performed in humanized NSG mice with more than 40 % of human CD45+ cells by intravenous (IV) or intraperitoneal (IP) LV delivery using LV encoding anti-CD19 CAR and GFP transgenes. Both IV and IP delivery of G-CD3-LV led to in vivo CAR T cell generation. However, CAR-T blood levels were higher after IP administration, reaching 13-17% of total circulating human CD45+ cells at the peak on day 21. Anti CD19-CAR-T cell generation coincided with the disappearance of endogenous CD19+ B cells, demonstrating functional in vivo CAR-T generation. Tissue analysis at day 39 after LV injection showed the presence of anti-CD19 CAR-T cells accompanied by the absence or dramatic reduction in CD19+ B cells in spleen, bone marrow and liver. In contrast, no CAR-T cell generation was detected at any time point in the mice injected with G-WT-LV, regardless of whether the virus was administered IV or IP. Taken together these data highlight the potential applicability of newly designed retargeted LV for in vivo gene delivery, offering promising prospects for future human gene therapy applications. Citation Format: Karina Krotova, Gopal Naik Nenavath, Nandakumar Packiriswamy, Rianna Vandergaast, Christopher Ziegler, Melissa Moy, Riya Narjari, Luke Schnebeck, Zachary Larson, Kyle Gromer, Chia-Hsuan Chin, Samantha Reiter, Miguel Muñoz Alía, Kah-Whye Peng, Stephen Russell. Systemic administration of CD3-redirected lentiviral vector efficiently targets CD19-CAR delivery to human T cells in vivo [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Tumor Immunology and Immunotherapy; 2023 Oct 1-4; Toronto, Ontario, Canada. Philadelphia (PA): AACR; Cancer Immunol Res 2023;11(12 Suppl):Abstract nr A024.

Affilin-based retargeting of adenoviral vectors to the epidermal growth factor receptor

IntroductionTreatment of head and neck squamous cell carcinomas (HNSCC) by oncolytic adenoviral vectors holds promise as an efficient anti-cancer therapy. The epidermal growth factor receptor (EGFR) represents an attractive target receptor since it is frequently overexpressed in many types of HNSCC. MethodsTo achieve EGFR-specific targeting by human adenovirus type 5 (HAdV-5) based vectors, the EGFR affinity ligand Affilin was covalently attached in a position specific manner either to the fiber or the hexon protein of the vector capsid. In vitro and in vivo studies investigated EGFR-specific cancer cell transduction, susceptibility to natural sequestration mechanisms, pharmacokinetics and biodistribution profiles of Affilin-decorated vectors. ResultsAffilin-decorated vectors showed strongly enhanced and EGFR-specific cancer cell transduction in vitro and less susceptibility to known sequestration mechanisms of HAdV-5 particles. However, in vivo neither systemic nor intratumoral vector administration resulted in an improved transduction of EGFR-positive tumors. Comprehensive analyses indicated hampered EGFR-targeting by Affilin-decorated vectors was caused by rapid vector particle consumption due to binding to the murine EGFR, insufficient tumor vascularization and poor target accessibility for Affilin in the solid tumor caused by a pronounced tumor stroma. ConclusionIn vitro studies yielded proof-of-concept results demonstrating that covalent attachment of a receptor-specific Affilin to the adenoviral capsid provides an effective and versatile tool to address cancer-specific target receptors by adenoviral vectors. Regarding EGFR as the vector target, off-target tissue transduction and low receptor accessibility within the tumor tissue prevented efficient tumor transduction by Affilin-decorated vectors, rendering EGFR a difficult-to-target receptor for adenoviral vectors.

Global brain delivery of neuroligin 2 gene ameliorates seizures in a mouse model of epilepsy.

Despite the increasing availability of effective drugs, around one-third of patients with epilepsy are still resistant to pharmacotherapy. Gene therapy has been suggested as a plausible approach to achieve seizure control, in particular for patients with focal epilepsy. Because seizures develop across wide spans of the brain in many forms of epilepsy, global delivery of the vectors is necessary to tackle such generalized seizures. Neuroligin 2 (NL2) is a postsynaptic cell adhesion molecule that induces or strengthens inhibitory synaptic function by specifically combining with neurexin 1. In the present study, we applied an adeno-associated virus (AAV) type 9 vector expressing NL2 to modulate neuronal excitability in broad areas of the brain in epileptic (EL) mice, a model of polygene epilepsy. We administered the AAV vector expressing Flag-tagged NL2 under the synapsin I promoter (AAV-NL2) via cardiac injection 6 weeks after birth. Significant reductions in the duration, strength and frequency of seizure were observed during a 14-week observation period in NL2-treated EL mice compared to untreated or AAV-green fluorescent protein-treated EL mice. No behavioral abnormality was observed in NL2-treated EL mice in an open-field test. Immunohistochemical examination at 14 weeks after AAV-NL2 injection revealed the expression of exogenous NL2 in broad areas of the brain, including the hippocampus and, in these areas, NL2 co-localized with postsynaptic inhibitory molecule gephyrin. Global brain delivery of NL2 by systemic administration of AAV vector may provide a non-invasive therapeutic approach for generalized epilepsy.

Selective Microvascular Tissue Transfection Using Minicircle DNA for Systemic Delivery of Human Coagulation Factor IX in a Rat Model Using a Therapeutic Flap.

Gene therapy is a promising treatment for protein deficiency disorders such as hemophilia B. However, low tissue selectivity and efficacy are limitations of systemic vector delivery. The authors hypothesized that selective transfection of rat superficial inferior epigastric artery flaps could provide systemic delivery of coagulation factor IX, preventing the need for systemic vector administration. Minicircle DNA containing green fluorescent protein, firefly luciferase, and human coagulation factor IX was created. Vector constructs were validated by transfecting adipose-derived stromal cells isolated from Wistar rat superficial inferior epigastric artery flaps and evaluating transgene expression by fluorescence microscopy, bioluminescence, and enzyme-linked immunosorbent assay. Minicircle DNA luciferase (10 and 30 μg) was injected into murine (wild-type, C57/BL/6) inguinal fat pads (n = 3) and followed by in vivo bioluminescence imaging for 60 days. Wistar rat superficial inferior epigastric artery flaps were transfected with minicircle DNA human coagulation factor IX (n = 9) with plasma and tissue transgene expression measured by enzyme-linked immunosorbent assay at 2 and 4 weeks. Transfected adipose-derived stromal cells expressed green fluorescent protein for 30 days, luciferase for 43 days, and human coagulation factor IX (21.9 ± 1.2 ng/ml) for 28 days in vitro. In vivo murine studies demonstrated dose-dependence between minicircle DNA delivery and protein expression. Ex vivo rat superficial inferior epigastric artery flap transfection with minicircle DNA human coagulation factor IX showed systemic transgene expression at 2 (266.6 ± 23.4 ng/ml) and 4 weeks (290.1 ± 17.1 ng/ml) compared to control tissue (p < 0.0001). Rat superficial inferior epigastric artery flap transfection using minicircle DNA human coagulation factor IX resulted in systemic transgene detection, suggesting that selective flap or angiosome-based tissue transfection may be explored as a treatment for systemic protein deficiency disorders such as hemophilia B.

Macrophage Depletion via Clodronate Pretreatment Reduces Transgene Expression from AAV Vectors In Vivo

Adeno-associated virus is a popular gene delivery vehicle for gene therapy studies. A potential roadblock to widespread clinical adoption is the high vector doses required for efficient transduction in vivo, and the potential for subsequent immune responses that may limit prolonged transgene expression. We hypothesized that the depletion of macrophages via systemic delivery of liposome-encapsulated clodronate would improve transgene expression if given prior to systemic AAV vector administration, as has been shown to be the case with adenoviral vectors. Contrary to our expectations, clodronate liposome pretreatment resulted in significantly reduced transgene expression in the liver and heart, but permitted moderate transduction of the white pulp of the spleen. There was a remarkable localization of transgene expression from the red pulp to the center of the white pulp in clodronate-treated mice compared to untreated mice. Similarly, a greater proportion of transgene expression could be observed in the medulla located in the center of the lymph node in mice treated with clodronate-containing liposomes as compared to untreated mice where transgene expression was localized primarily to the cortex. These results underscore the highly significant role that the immune system plays in influencing the distribution and relative numbers of transduced cells in the context of AAV-mediated gene delivery.

BMPER Ameliorates Renal Fibrosis by Inhibiting Tubular Dedifferentiation and Fibroblast Activation.

Tubulointerstitial fibrosis is both a pathological manifestation of chronic kidney disease and a driving force for the progression of kidney disease. A previous study has shown that bone morphogenetic protein-binding endothelial cell precursor-derived regulator (BMPER) is involved in lung fibrogenesis. However, the role of BMPER in renal fibrosis remains unknown. In the present study, the expression of BMPER was examined by real-time PCR, Western blot and immunohistochemical staining. The in vitro effects of BMPER on tubular dedifferentiation and fibroblast activation were analyzed in cultured HK-2 and NRK-49F cells. The in vivo effects of BMPER were dissected in unilateral ureteral obstruction (UUO) mice by delivery of BMPER gene via systemic administration of plasmid vector. We reported that the expression of BMPER decreased in the kidneys of UUO mice and HK-2 cells. TGF-β1 increased inhibitor of differentiation-1 (Id-1) and induced epithelial mesenchymal transition in HK-2 cells, and knockdown of BMPER aggravated Id-1 up-regulation, E-cadherin loss, and tubular dedifferentiation. On the contrary, exogenous BMPER inhibited Id-1 up-regulation, prevented E-cadherin loss and tubular dedifferentiation after TGF-β1 exposure. In addition, exogenous BMPER suppressed fibroblast activation by hindering Erk1/2 phosphorylation. Knockdown of low-density lipoprotein receptor-related protein 1 abolished the inhibitory effect of BMPER on Erk1/2 phosphorylation and fibroblast activation. Moreover, delivery of BMPER gene improved renal tubular damage and interstitial fibrosis in UUO mice. Therefore, BMPER inhibits TGF-β1-induced tubular dedifferentiation and fibroblast activation and may hold therapeutic potential for tubulointerstitial fibrosis.

Abstract 4784: Combination of sorafenib with liver cancer-targeted gene therapy exerts synergistic efficacy against hepatocellular carcinoma

Abstract Hepatocellular carcinoma (HCC) is one of the leading causes of cancer-related death worldwide. Sorafenib, a multikinase inhibitor, is the first-line target therapy for patients with advanced HCC, but the response rate is low. Thus, development of more effective therapeutics for HCC is needed. Previously we have established a HCC-targeted BikDD gene therapy vector driven by a liver cancer-specific α-fetoprotein promoter/enhancer and transcriptional amplification module. Systemic administration of liposome-loaded HCC-targeted BikDD gene therapy vector effectively suppressed tumor growth and prolonged survival in multiple orthotopic HCC mouse models with no toxicity. Here, we further investigated whether combination of sorafenib with gene therapy could enhance anti-HCC activity. The results showed that combination of BikDD gene therapy with HCC targeted therapeutic agent sorafenib synergistically killed a panel of liver cancer cells but not normal cells in vitro by WST-1 assays and analysis of combination index according to the Chou and Talalay method. Moreover, a low dose of sorafenib combined with BikDD gene therapy augmented tumor inhibition and better mice survival compared with separate treatment alone in xenograft and syngeneic orthotopic HCC mouse models. These results suggest that sorafenib combined with HCC-targeted gene therapy may improve the therapeutic efficacy and may be a potential alternative therapeutics for HCC. Citation Format: Huei-Yue Dai, Long-Yuan Li. Combination of sorafenib with liver cancer-targeted gene therapy exerts synergistic efficacy against hepatocellular carcinoma [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 4784.

Optimization of Dexamethasone Administration for Maintaining Global Transduction Efficacy of Adeno-Associated Virus Serotype 9.

Glucocorticoids have been commonly used in clinic for their anti-inflammatory and immunosuppressive effects, and it has been proposed that they be used to prevent liver toxicity when systemic administration of adeno-associated virus (AAV) vectors is needed in patients with central nervous system diseases and muscular disorders. Glucocorticoids also enable modulation of vascular permeability. First, this study investigated the impact of dexamethasone on AAV vascular permeability after systemic injection. When a low dose of AAV9 was injected into mice treated with dexamethasone, global transduction and vector biodistribution were not significantly different in most tissues, other than the liver and the heart, when compared to control mice. When AAV9 vectors were used at a high dose, both the transgene expression and the AAV vector genome copy number were significantly decreased in the majority of murine tissues. However, no effect on global transduction was observed when dexamethasone was administered 2 h after AAV vector injection. The study on the kinetics of AAV virus clearance demonstrated that dexamethasone slowed down the clearance of AAV9 in the blood after systemic application. The mechanism study showed that dexamethasone inhibited the enhancement of AAV9 vascular permeability mediated by serum proteins. The findings indicate that dexamethasone is able to inhibit the vascular permeability of AAV and compromise the therapeutic effect after systemic administration of AAV vector. In conclusion, this study provides valuable information for the design of future clinical studies when glucocorticoids are needed to be compatible with the systemic administration of AAV vectors in patients with central nervous system and muscular diseases.

Vaspin protects against LPS‑induced ARDS by inhibiting inflammation, apoptosis and reactive oxygen species generation in pulmonary endothelial cells via the Akt/GSK‑3β pathway.

Acute respiratory distress syndrome (ARDS) is characterized by uncontrolled extravasation of protein-rich fluids, which is caused by disruption and dysfunction of the barrier of pulmonary endothelial cells (ECs). Visceral adipose tissue-derived serine protease inhibitor (vaspin) is a novel adipokine with pleiotropic properties, which has been reported to exert beneficial effects against obesity-associated systemic vascular diseases; however, its effects on ARDS remain unknown. In the present study, mice were subjected to systemic administration of adenoviral vector expressing vaspin (Ad-vaspin) to examine its effects on lipopolysaccharide (LPS)-induced ARDS in vivo. Histological analysis was then conducted, and cytokine [tumor necrosis factor (TNF)-α, interleukin (IL)-6 and IL-10] levels, and intercellular cell adhesion molecule-1 (ICAM-1) and adherens junctions (AJs) expression were detected. In addition, human pulmonary microvascular ECs (HPMECs) were treated with recombinant human (rh)-vaspin to further investigate its molecular basis and underlying mechanism. The mRNA expression levels of inflammatory cytokines (TNF-α and IL-6) and endothelial-specific adhesion markers [vascular cell adhesion molecule-1 and E-selectin], activation of nuclear factor-κB, and cell viability and apoptosis were then examined. Furthermore, the expression of AJs and organization of the cytoskeleton, as well as expression and activity of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and generation of reactive oxygen species (ROS) were determined. The results indicated that Ad-vaspin protected against LPS-induced ARDS by alleviating the pulmonary inflammatory response and pulmonary EC barrier dysfunction in mice, which was accompanied by activation of the protein kinase B (Akt)/glycogen synthase kinase (GSK)-3β pathway. In addition, pretreatment of HPMECs with rh-vaspin attenuated inflammation, apoptosis and ROS generation without alterations in AJs and cytoskeletal organization following LPS insult, which was accompanied by activation of the Akt/GSK3β pathway. In conclusion, the present study demonstrated that vaspin protects against LPS-induced ARDS by reversing EC barrier dysfunction via the suppression of inflammation, apoptosis and ROS production in pulmonary ECs, at least partially via activation of the Akt/GSK3β pathway. These findings provide evidence of a causal link between vaspin and EC dysfunction in ARDS, and suggest a potential therapeutic intervention for patients with ARDS.

Intramuscular administration of AAV overcomes pre-existing neutralizing antibodies in rhesus macaques

The seroprevalence of neutralizing antibodies (NAbs) to adeno-associated viral (AAV) vector capsids may preclude a percentage of the population from receiving gene therapy, particularly following systemic vector administration. We hypothesized that the use of intramuscular (IM) administration of AAV vectors might circumvent this issue. IM injections were used to administer AAV8 vectors expressing either secreted or non-secreted transgenes into mice and the influence of NAbs supplied by pre-administration of pooled human IgG on transgene expression was evaluated. We then studied the impact of naturally occurring pre-existing AAV8 NAbs on expression of a secreted transgene following IM vector delivery in rhesus macaques. Finally, we evaluated the ability to readminister AAV vectors via IM injections in rhesus macaques. In mice, the presence of AAV8 NAbs had no effect on gene expression in the injected skeletal muscle. However, liver transgene expression following hepatic distribution of the vector was ablated. In rhesus macaques, naturally occurring pre-existing AAV8 NAb titers of ⩽1:160 had no effect on expression levels of a secreted transgene after IM delivery of the vector. Additionally, readministration of AAV vectors was possible by IM injection into the previously injected muscle groups, with no effect on transgene expression by the original vector. Therefore, the presence of pre-existing NAbs in the human population should not preclude subjects from receiving gene therapy by IM administration of the vector so long as sufficient levels of secreted transgene expression can be produced without the involvement of liver.

Omentin protects against LPS-induced ARDS through suppressing pulmonary inflammation and promoting endothelial barrier via an Akt/eNOS-dependent mechanism.

Acute respiratory distress syndrome (ARDS) is characterized by increased pulmonary inflammation and endothelial barrier permeability. Omentin has been shown to benefit obesity-related systemic vascular diseases; however, its effects on ARDS are unknown. In the present study, the level of circulating omentin in patients with ARDS was assessed to appraise its clinical significance in ARDS. Mice were subjected to systemic administration of adenoviral vector expressing omentin (Ad-omentin) and one-shot treatment of recombinant human omentin (rh-omentin) to examine omentin's effects on lipopolysaccharide (LPS)-induced ARDS. Pulmonary endothelial cells (ECs) were treated with rh-omentin to further investigate its underlying mechanism. We found that a decreased level of circulating omentin negatively correlated with white blood cells and procalcitonin in patients with ARDS. Ad-omentin protected against LPS-induced ARDS by alleviating the pulmonary inflammatory response and endothelial barrier injury in mice, accompanied by Akt/eNOS pathway activation. Treatment of pulmonary ECs with rh-omentin attenuated inflammatory response and restored adherens junctions (AJs), and cytoskeleton organization promoted endothelial barrier after LPS insult. Moreover, the omentin-mediated enhancement of EC survival and differentiation was blocked by the Akt/eNOS pathway inactivation. Therapeutic rh-omentin treatment also effectively protected against LPS-induced ARDS via the Akt/eNOS pathway. Collectively, these data indicated that omentin protects against LPS-induced ARDS by suppressing inflammation and promoting the pulmonary endothelial barrier, at least partially, through an Akt/eNOS-dependent mechanism. Therapeutic strategies aiming to restore omentin levels may be valuable for the prevention or treatment of ARDS.

Pulmonary Targeting of Adeno-associated Viral Vectors by Next-generation Sequencing-guided Screening of Random Capsid Displayed Peptide Libraries.

Vectors mediating strong, durable, and tissue-specific transgene expression are mandatory for safe and effective gene therapy. In settings requiring systemic vector administration, the availability of suited vectors is extremely limited. Here, we present a strategy to select vectors with true specificity for a target tissue from random peptide libraries displayed on adeno-associated virus (AAV) by screening the library under circulation conditions in a murine model. Guiding the in vivo screening by next-generation sequencing, we were able to monitor the selection kinetics and to determine the right time point to discontinue the screening process. The establishment of different rating scores enabled us to identify the most specifically enriched AAV capsid candidates. As proof of concept, a capsid variant was selected that specifically and very efficiently delivers genes to the endothelium of the pulmonary vasculature after intravenous administration. This technical approach of selecting target-specific vectors in vivo is applicable to any given tissue of interest and therefore has broad implications in translational research and medicine.

255. A Method for Developing More Potent AAV Capsids by Prolonging the Vector Half-Lives in the Blood Circulation

Adeno-associated virus (AAV) has been used successfully as a vector for in vivo gene therapy. Many different serotypes are under investigation, but AAV9 vectors especially show robust in vivo transduction by systemic administration via the periphery. Although the mechanism of this robustness is not yet completely understood, the superior ability to cross the endothelial cell barriers including the blood-brain barrier has been presumed to play a key role in efficient systemic gene delivery by AAV9. In this regard, our laboratory has accumulated provocative evidence that AAV permeability across the endothelium is not substantially different among many AAV strains (serotypes and mutants) per se, but that AAV9's in vivo robustness following intravascular administration is due to its distinctively delayed blood clearance. Given that many AAV strains transduce cells better than AAV9 when directly injected into the parenchyma, it should be reasonable to hypothesize that prolonging the half-life of an AAV could substantially increase in vivo transduction efficiency following systemic administration. Here, we show that substitution of a small subset of amino acids in the C-terminal half of the viral capsid can substantially prolong the half-life of AAV1 in the blood and confer a superior in vivo transduction efficiency that is better than that of AAV9 following systemic vector administration. Based on the results from our preliminary AAV1 and AAV9 capsid domain swapping study and a capsid amino acid sequence alignment study, we identified 7 capsid segments comprising 5 to 23 amino acids that might contribute to the persistent circulation of AAV9 in the blood. Each of these 7 segments can be replicated in the AAV1 capsid, which shows a rapid blood clearance rate, by substituting 3 to 11 amino acids of the AAV1 capsid with those of the AAV9 capsid. In the study, we created a panel of 27=128 AAV1-derived strains that carry these segment(s) in any possible combinations (note: one of the 128 is the same as the wild-type AAV1 capsid). We then determined blood clearance rates of all the 128 AAV1-derived strains and AAV9 following intravenous injection into mice using the AAV Barcode-Seq approach. The results show that 42 mutants that showed a >30-fold increase in persistence in the blood at 24 hours post-injection compared to the parental wild-type AAV1 all shared either of the following segment combinations, xxx9xx9 or xxxxx99 (note: each letter represents a segment and × can be either AAV1 or AAV9). This indicates that the 7th segment plays an indispensable role but requires either of the 4th and 6th segments for substantially prolonging the half-life. A preliminary tissue transduction analysis in mice revealed that these AAV1-derived mutants with a long half-life showed enhanced in vivo gene delivery compared to AAV9. In a separate study, we also identified a 16 amino acid-long segment in the N-terminal half of the AAV9 capsids that is essential for maintaining high levels of circulating viral particles in the blood at 72 hours post-injection. We are currently investigating whether this amino acid motif, when combined with the above-described xxx9xx9 or xxxxx99 motifs, could further enhance persistence of AAV1-derived mutants and augment in vivo transduction, using another set of 24 AAV1-derived composite mutant capsids in mice. In summary, the study establishes proof-of-principle of a new approach to create more portent AAV vectors by modulating the vector half-life. This approach will be particularly useful for developing novel AAV capsids that can transduce the brain tissues more efficiently by systemic vector administration.

257. Selection of Next Generation AAV Gene Therapy Vectors for Specific and Precise Gene Delivery

The ultimate goal in human gene therapy is the specific and exclusive modification of the desired target cells upon systemic vector administration. Especially vectors derived from adeno-associated virus (AAV) are among the most promising gene transfer systems for in vivo application and have received broad attention due to substantial clinical benefit. However, AAV specificity for a particular target cell or tissue has been hampered by the broad tropism of different AAV serotypes. Over the last several years, new approaches have been initiated to create and select for more effective and selective recombinant AAV vectors by genetically modifying the capsid protein. These methods include random and/or rationale amino acid substitutions, creation of chimeric capsid variant libraries and various selection screens, and/or peptide insertion. A different approach involves the incorporation of highly specific binding molecules (DARPins) into the AAV capsid. DARPins are derived from ankyrin-repeat proteins that have been developed as alternative to antibody-based scaffolds, which are selected by high-throughput screens from DARPin libraries. At present, the bottleneck remains the cumbersome selection of DARPin molecules and the low number of functional DARPin capsid chimeras, which are able to assemble into a functional vector and still bind their intended extracellular target. Thus after months of screening and analysis the majority of the pre-selected DARPins are found not to be suitable for AAV targeting approaches. Here we describe a novel reliable and faster selection approach. First we eliminate the cumbersome and often misleading prokaryotic selection steps. To do this, we incorporate an entire DARPin library into the AAV capsid as VP2-fusion protein, generating either replication deficient or competent AAV library systems allowing for direct screening on therapeutically relevant cell types in vitro or in vivo. Our studies show that replicating deficient and replicating AAV libraries can be generated with high diversity up to 5×107 and high functional titers retaining their infectivity. We have generated a DARPin-capsid library in AAV-DJ (serotype with diverse cellular tropism) and AAV-LK03 (human selective serotype) and after only two selection rounds, found up to 10% of selected DARPins sharing identical repeat motifs responsible for target receptor binding in the pancreas and the liver. We are currently making vectors from these chimeric capsids and will determine their target specificity both in vivo and in vitro. This new approach takes only six days per selection cycle, allowing discovery of novel DARPin molecules and selection for targeted vectors in substantially reduced time. This approach expands the potential diversity in creating and defining novel rAAV vectors with medically relevant transduction properties. Such viral vectors will not only open the door for an array of new approaches to treat acquired human diseases but also push the development of new AAV-based gene therapy vectors to the next level.

540. Identification of a 16 Amino Acid-Long Motif in the N-Terminal Half of the AAV9 Capsid Essential for Persistence in the Blood for an Extended Period of up to 3 Days

The distinctively prolonged half-life in the blood circulation is one of the key features of AAV9 vectors and is presumed to play an important role in efficient gene delivery to various target organs following systemic vector administration. We have so far analyzed blood clearance rates of nearly one thousand different AAV strains (serotypes and capsid-engineered mutants) in mice following intravenous vector injection, and have discovered that the wild-type AAV9 and many AAV9-derived capsid mutants are particularly unique in that they can persist in the blood circulation at significant levels when measured at 72 hours post-injection. Although non AAV9-derived capsid mutants exist that show a blood vector concentration at a level equivalent to or higher than that of the wild-type AAV9 at 24 hours post-injection, their blood vector concentrations surprisingly and without exception become substantially lower than the wild-type AAV9 concentration at 72 hours post-injection. In AAV vector development, long half-life should be an attractive feature of new vectors; however, the paucity of knowledge of the capsid amino acid sequences responsible for vector persistence in the blood has made it difficult to design novel AAV capsids with a prolonged half-life. Here we report the identification of a 16 amino acid-long motif in the N-terminal half of the AAV9 capsid essential for the vector persistence in the blood for an extended period of up to 3 days, which is the pharmacokinetic profile unique to AAV9. In our previous study, we performed double alanine scanning of the entire C-terminal half of the AAV9 capsids (amino acid positions 356 to 736), and identified approximately 40 amino acids that showed loss of vector persistence in the blood only at the 72-hour time point when mutated to alanine. Many of these amino acids are not unique to AAV9 or are scattered within the capsid amino acid sequence. In the present study, we performed double alanine scanning of the entire N-terminal half of the AAV9 capsids (amino acid positions 4 to 355), and determined their blood clearance rates in mice by the AAV Barcode-Seq approach. Among these 175 double alanine mutants, 52 mutants did not produce viral particles at levels required for the analysis; therefore, the pharmacokinetic data could be collected only from 123 of the 175 mutants. This analysis revealed 7 double alanine mutants that span a stretch of 16 consecutive amino acids and form a group that is clearly distinctive from the other 116 mutants (note: one mutant within this amino acid stretch could not be assessed due to the inability to produce viral particles). That is, the 116 mutants showed the same pharmacokinetic profile as that of the wild-type AAV9 while the distinctive 7 mutants persisted in the blood for only up to 24 hours post-injection at levels similar or superior to the wild-type AAV9 and showed substantially lower concentrations at 72 hours post-injection. Interestingly, this motif contains one of the most variable regions across different serotypes and the amino acid sequence of the identified motif is unique only to AAV9 and other Clade F AAV serotypes. We are currently investigating whether swapping this motif of AAV9 with other serotypes’ could result in loss of persistence at 72 hours post-injection or whether replication of this motif in other non-AAV9 capsids could bestow long-term persistence. In summary, our study suggests that the 16 amino acid-long motif in the N-terminal half of the capsid that is unique to the Clade F AAV serotypes plays an essential role in maintaining the persistence of circulating viral particles in the blood for an extended period of several days.

503. Adeno-Associated Virus Vector (AAV) Microdystrophin Gene Therapy Prolongs Survival and Restores Muscle Function in the Canine Model of Duchenne Muscular Dystrophy (DMD)

Duchenne Muscular Dystrophy (DMD) is a X-linked inherited muscle-wasting disease primarily affecting young boys with a prevalence of 1:5,000. The disease is caused by loss-of-function mutations in the gene encoding for the Dystrophin protein and is characterized by systemic, progressive, irreversible and severe loss of muscle function. Among vector systems that allow efficient in vivo gene transfer, recombinant Adeno-Associated Virus vectors (rAAV) hold great promise and allow very efficient transduction of skeletal and cardiac muscles. However, full-length dystrophin cDNA exceeds the packaging capacity for a single rAAV gene-delivery cassette. Therefore, truncated versions namely micro-dystrophins have been designed and optimized to contain few clinically important regions of the dystrophin protein. We have tested a rAAV2/8 vector encoding a sequence optimised canine micro-dystrophin transgene, driven by a muscle-synthetic Spc512 promoter (rAAV2/8-Spc512-µDys) in a total of 12 Golden Retriever Muscular Dystrophy (GRMD) dogs, the canine model of DMD. Isolated limb perfusion studies using a single administration of vector induced high levels of micro-dystrophin expression in the treated limb (up to 90% dystrophin positive fibres) with significant normalisation of histological, NMR imaging and spectroscopy parameters and muscle strength, without deleterious immune responses. Similarly, single-dose intravascular delivery of the same rAAV2/8-Spc512-µDys, in absence of immunosuppression, led to long-term transduction of distant muscle groups and extended lifespan (up to 2 years). Profound improvement of multiple clinical features was observed, including gait and respiratory parameters and no toxicity or deleterious humoral and/or cell-mediated immune responses were observed. This study demonstrates the safety and long term efficacy of rAAV2/8-Spc5.12-µDys gene therapy in a relevant large-animal models of DMD and paves the way towards human clinical gene therapy using systemic peripheral vein administration of vector, and applicable to all DMD patients regardless of their genotype.

Exclusive Transduction of Human CD4+ T Cells upon Systemic Delivery of CD4-Targeted Lentiviral Vectors.

Playing a central role in both innate and adaptive immunity, CD4(+) T cells are a key target for genetic modifications in basic research and immunotherapy. In this article, we describe novel lentiviral vectors (CD4-LV) that have been rendered selective for human or simian CD4(+) cells by surface engineering. When applied to PBMCs, CD4-LV transduced CD4(+) but not CD4(-) cells. Notably, also unstimulated T cells were stably genetically modified. Upon systemic or intrasplenic administration into mice reconstituted with human PBMCs or hematopoietic stem cells, reporter gene expression was predominantly detected in lymphoid organs. Evaluation of GFP expression in organ-derived cells and blood by flow cytometry demonstrated exclusive gene transfer into CD4(+) human lymphocytes. In bone marrow and spleen, memory T cells were preferentially hit. Toward therapeutic applications, we also show that CD4-LV can be used for HIV gene therapy, as well as for tumor therapy, by delivering chimeric Ag receptors. The potential for in vivo delivery of the FOXP3 gene was also demonstrated, making CD4-LV a powerful tool for inducible regulatory T cell generation. In summary, our work demonstrates the exclusive gene transfer into a T cell subset upon systemic vector administration opening an avenue toward novel strategies in immunotherapy.

Intravenous AAV9 efficiently transduces myenteric neurons in neonate and juvenile mice.

Gene therapies for neurological diseases with autonomic or gastrointestinal involvement may require global gene expression. Gastrointestinal complications are often associated with Parkinson's disease and autism. Lewy bodies, a pathological hallmark of Parkinson's brains, are routinely identified in the neurons of the enteric nervous system (ENS) following colon biopsies from patients. The ENS is the intrinsic nervous system of the gut, and is responsible for coordinating the secretory and motor functions of the gastrointestinal tract. ENS dysfunction can cause severe patient discomfort, malnourishment, or even death as in intestinal pseudo-obstruction (Ogilvie syndrome). Importantly, ENS transduction following systemic vector administration has not been thoroughly evaluated. Here we show that systemic injection of AAV9 into neonate or juvenile mice results in transduction of 25–57% of ENS myenteric neurons. Transgene expression was prominent in choline acetyltransferase positive cells, but not within vasoactive intestinal peptide or neuronal nitric oxide synthase cells, suggesting a bias for cells involved in excitatory signaling. AAV9 transduction in enteric glia is very low compared to CNS astrocytes. Enteric glial transduction was enhanced by using a glial specific promoter. Furthermore, we show that AAV8 results in comparable transduction in neonatal mice to AAV9 though AAV1, 5, and 6 are less efficient. These data demonstrate that systemic AAV9 has high affinity for peripheral neural tissue and is useful for future therapeutic development and basic studies of the ENS.