Induction of immune tolerance to FIX following muscular AAV gene transfer is AAV-dose/FIX-level dependent

Muscle-Directed Delivery of an AAV1 Vector Leads to Capsid-Specific T Cell Exhaustion in Nonhuman Primates and Humans

With the US Food and Drug Administration (FDA) and European Medicines Agency (EMA) approvals for Zolgensma, Luxturna, and Glybera, recombinant adeno-associated viruses (rAAVs) are considered efficient tools for gene transfer. However, studies in animals and humans demonstrate that intramuscular (IM) AAV delivery can trigger immune responses to AAV capsids and/or transgenes. IM delivery of rAAV1 in humans has also been described to induce tolerance to rAAV characterized by the presence of capsid-specific regulatory T cells (Tregs) in periphery. To understand mechanisms responsible for tolerance and parameters involved, we tested 3 muscle-directed administration routes in rhesus monkeys: IM delivery, venous limb perfusion, and the intra-arterial push and dwell method. These 3 methods were well tolerated and led to transgene expression. Interestingly, gene transfer in muscle led to Tregs and exhausted T cell infiltrates in situ at both day 21 and day 60 post-injection. In human samples, an in-depth analysis of the functionality of these cells demonstrates that capsid-specific exhausted T cells are detected after at least 5 years post-vector delivery and that the exhaustion can be reversed by blocking the checkpoint pathway. Overall, our study shows that persisting transgene expression after gene transfer in muscle is mediated by Tregs and exhausted T cells.

Lessons learned from lung and liver in-vivo gene therapy: implications for the future

INTRODUCTION

Ex-vivo gene therapy has had significant clinical impact over the last couple of years and in-vivo gene therapy products are being approved for clinical use. Gene therapy and gene editing approaches have huge potential to treat genetic disease and chronic illness.

AREAS COVERED

This article provides a review of in-vivo approaches for gene therapy in the lung and liver, exploiting non-viral and viral vectors with varying serotypes and pseudotypes to target-specific cells. Antibody responses inhibiting viral vectors continue to constrain effective repeat administration. Lessons learned from ex-vivo gene therapy and genome editing are also discussed.

EXPERT OPINION

The fields of lung and liver in-vivo gene therapy are thriving and a comparison highlights obstacles and opportunities for both. Overcoming immunological issues associated with repeated administration of viral vectors remains a key challenge. The addition of targeted small molecules in combination with viral vectors may offer one solution. A substantial bottleneck to the widespread adoption of in-vivo gene therapy is how to ensure sufficient capacity for clinical-grade vector production. In the future, the exploitation of gene editing approaches for in-vivo disease treatment may facilitate the resurgence of non-viral gene transfer approaches, which tend to be eclipsed by more efficient viral vectors.

A Retrospective Study of the Cytokine Profile Changes in Mice with FVIII Inhibitor Development After Adeno-Associated Virus-Mediated Gene Therapy in a Hemophilia A Mouse Model

The development of inhibitory autoantibodies to the infused clotting factor VIII (FVIII) is a major complication for severe hemophilia A management. Novel therapy options for hemophilia have significantly progressed in the last decade, and a gene therapy cure for hemophilia is becoming a reality. However, mechanistic studies of FVIII autoantibodies (FVIII inhibitors) have lagged behind and remain a challenge for both protein replacement and gene therapy. FVIII inhibitor formation is assumed to be a classical T cell-dependent immune response in which cytokines/chemokines play an important role. The study of cytokine profile changes during FVIII inhibitor development may be helpful to understand the mechanism of inhibitor development and to explore potential novel approaches that will minimize the risk. After FVIII^-/- mice were treated with intravenous administration of an adeno-associated virus 8 vector encoding human FVIII, FVIII expression peaked at week 2 (W2), and FVIII inhibitor was thoroughly developed at week 8 (W8). W8 plasma that showed positive FVIII inhibitor, and W2 samples with negative FVIII inhibitor (anti-FVIII[+]), were subjected to multiplex cytokines measurement. W8 and W2 samples were both negative for FVIII inhibitor (anti-FVIII[-]) as the control. In comparison to mice in the anti-FVIII(-) group, mice in the anti-FVIII(+) group exhibited significantly elevated pro-inflammatory cytokines of interleukin (IL)-1, IL-6, IL-12p40, monocyte chemoattractant protein-1, macrophage inflammatory protein (MIP)-1, MIP-2, and tumor necrosis factor alpha (TNF-α), especially at higher titers. The anti-inflammatory cytokine of transforming growth factor beta (TGF-β) was decreased at W2 in both groups. Multivariate analysis of the risk factors for FVIII inhibitor development showed peak FVIII activity at W2. IL-6 and TNF-α at W8 were positively correlated with inhibitor formation, and negatively correlated with the age starting gene therapy. Collectively, the elevated monocyte derived pro-inflammatory cytokines/chemokines, together with the decreased anti-inflammatory cytokine of TGF-β at an early time point, may contribute to the persistent inflammatory environment in favor of an immune response toward FVIII inhibitor development.

Liver transplant tolerance and its application to the clinic: can we exploit the high dose effect?

The tolerogenic properties of the liver have long been recognised, especially in regard to transplantation. Spontaneous acceptance of liver grafts occurs in a number of experimental models and also in a proportion of clinical transplant recipients. Liver graft acceptance results from donor antigen-specific tolerance, demonstrated by the extension of tolerance to other grafts of donor origin. A number of factors have been proposed to be involved in liver transplant tolerance induction, including the release of soluble major histocompatibility (MHC) molecules from the liver, its complement of immunosuppressive donor leucocytes, and the ability of hepatocytes to directly interact with and destroy antigen-specific T cells. The large tissue mass of the liver has also been suggested to act as a cytokine sink, with the potential to exhaust the immune response. In this review, we outline the growing body of evidence, from experimental models and clinical transplantation, which supports a role for large tissue mass and high antigen dose in the induction of tolerance. We also discuss a novel gene therapy approach to exploit this dose effect and induce antigen-specific tolerance robust enough to overcome a primed T cell memory response.

Role of antigen-specific regulatory CD4+CD25+ T cells in tolerance induction after neonatal IP administration of AAV-hF.IX

Neonatal AAV8-mediated Factor IX (F.IX) gene delivery was applied as a model for exploring mechanisms of tolerance induction during immune ontogeny. Intraperitoneal delivery of AAV8/ Factor IX (hF.IX) during weeks 1–4 of life, over a 20-fold dose range, directed stable hF.IX expression, correction of coagulopathy in F.IX-null hemophilia B mice, and induction of tolerance to hF.IX; however, only primary injection at 1–2 days of life enabled increasing AAV8-mediated hF.IX expression after re-administration, due to the absence of anti-viral capsid antibodies. Adoptive splenocyte transfer from tolerized mice demonstrated induction of CD4⁺CD25⁺ T regulatory (T_reg) populations that specifically suppressed anti-hF.IX antibody responses, but not responses to third party antigen. Induction of hF.IX antibodies was only observed in tolerized mice after in vivo CD4⁺CD25⁺ cell depletion and hF.IX challenge. Thus, primary injection of AAV during a critical period in the first week of life does not elicit antiviral responses, enabling re-administration of AAV and augmentation of hF.IX levels. Expansion of hF.IX-specific CD4⁺CD25⁺ T_regs has a major role in tolerance induction early in immune ontogeny. Neonatal gene transfer provides a useful approach for defining the ontogeny of immune responses and may suggest approaches for inducing tolerance in the context of genetic therapies.

Oral vaccination with adeno-associated virus vectors expressing the Neu oncogene inhibits the growth of murine breast cancer

Recombinant adeno-associated viruses (AAV) have been used for therapeutic gene transfer. These vectors offer a number of advantages including resistance to the effects of pH, a broad cellular tropism, efficient gene transfer, persistence of gene expression, and little toxicity. AAV vectors; however, at high doses can induce humoral and cellular immune responses. While potentially problematic for replacement gene therapy, this effect may be advantageous for antitumor vaccination. We examined the activity of an oral and intramuscular antitumor vaccination using AAV serotypes 5 and 6 expressing a truncated neu oncogene in a neu-positive murine TUBO breast cancer model. Mice receiving a single oral administration of AAV5-neu or AAV6-neu demonstrated improved survival. Oral vaccination significantly improved survivals compared with intramuscular vaccination. Mice vaccinated with AAV6-neu survived longer than those treated with AAV5-neu. Vaccination with AAV5-neu or AAV6-neu induced both humoral and cellular immune responses against the NEU antigen. These responses were more robust in the mice undergoing oral vaccination compared with mice receiving the intramuscular vaccination. Protection from tumor was long lasting with 80% of the animals treated with oral AAV6-neu surviving a re-challenge with TUBO cells at 120 and 320 days post-vaccination. Further evaluation of AAV-based vectors as tumor vaccines is warranted.

Muscle-directed anti-Aβ single-chain antibody delivery via AAV1 reduces cerebral Aβ load in an Alzheimer's disease mouse model

We previously reported that anti-amyloid-beta (Aβ) single-chain antibody (scFv59) brain delivery via recombinant adeno-associated virus (rAAV) was effective in reducing cerebral Aβ load in an Alzheimer's disease (AD) mouse model without inducing inflammation. Here, we investigated the prophylactic effects and mechanism of a muscle-directed gene therapy modality in an AD mouse model. We injected rAAV serotype 1 encoding scFv59 into the right thigh muscles of 3-month-old mice. Nine months later, high levels of scFv59 expression were confirmed in the thigh muscles by both immunoblotting and immunohistochemistry. As controls, model mice were similarly injected with rAAV1 encoding antihuman immunodeficiency virus Gag antibody (scFvGag). AAV1-mediated scFv59 gene delivery was effective in decreasing Aβ deposits in the brain. Compared with the scFvGag group, levels of Aβ in cerebrospinal fluid (CSF) decreased significantly while Aβ in serum tended to increase in the scFv59 group. AAV1-mediated scFv59 gene delivery may alter the equilibrium of Aβ between the blood and brain, resulting in an increased efflux of Aβ from the brain owing to antibody-mediated sequestration/clearance of peripheral Aβ. Our results suggest that muscle-directed scFv59 delivery via rAAV1 may be a prophylactic option for AD and that levels of CSF Aβ may be used to evaluate the efficacy of anti-Aβ immunotherapy.

MicroRNA-150-regulated vectors allow lymphocyte-sparing transgene expression in hematopoietic gene therapy

Endogenous microRNA (miRNA) expression can be exploited for cell type-specific transgene expression as the addition of miRNA target sequences to transgenic cDNA allows for transgene downregulation specifically in cells expressing the respective miRNAs. Here, we have investigated the potential of miRNA-150 target sequences to specifically suppress gene expression in lymphocytes and thereby prevent transgene-induced lymphotoxicity. Abundance of miRNA-150 expression specifically in differentiated B and T cells was confirmed by quantitative reverse transcriptase PCR. Mono- and bicistronic lentiviral vectors were used to investigate the effect of miRNA-150 target sequences on transgene expression in the lymphohematopoietic system. After in vitro studies demonstrated effective downregulation of transgene expression in murine B220(+) B and CD3(+) T cells, the concept was further verified in a murine transplant model. Again, marked suppression of transgene activity was observed in B220(+) B and CD4(+) or CD8(+) T cells whereas expression in CD11b(+) myeloid cells, lin(-) and lin(-)/Sca1(+) progenitors, or lin(-)/Sca1(+)/c-kit(+) stem cells remained almost unaffected. No toxicity of miRNA-150 targeting in transduced lymphohematopoietic cells was noted. Thus, our results demonstrate the suitability of miRNA-150 targeting to specifically suppress transgene expression in lymphocytes and further support the concept of miRNA targeting for cell type-specific transgene expression in gene therapy approaches.

Muscle-directed gene therapy for hemophilia B with more efficient and less immunogenic AAV vectors

BACKGROUND

Adeno-associated viral vector (AAV)-mediated and muscle-directed gene therapy is a safe and non-invasive approach to treatment of hemophilia B and other genetic diseases. However, low efficiency of transduction, inhibitor formation and high prevalence of pre-existing immunity to the AAV capsid in humans remain as main challenges for AAV2-based vectors using this strategy. Vectors packaged with AAV7, 8 and 9 serotypes have improved gene transfer efficiencies and may provide potential alternatives to overcome these problems.

OBJECTIVE

To compare the long-term expression of canine factor IX (cFIX) levels and anti-cFIX antibody responses following intramuscular injection of vectors packaged with AAV1, 2, 5, 7, 8 and 9 capsid in immunocompetent hemophilia B mice.

RESULTS

Highest expression was detected in mice injected with AAV2/8 vector (28% of normal), followed by AAV2/9 (15%) and AAV2/7 (10%). cFIX expression by AAV2/1 only ranged from 0 to 5% of normal levels. High incidences of anti-cFIX inhibitor (IgG) were detected in mice injected with AAV2 and 2/5 vectors, followed by AAV2/1. None of the mice treated with AAV2/7, 2/8 and 2/9 developed inhibitors or capsid T cells.

CONCLUSIONS

AAV7, 8 and 9 are more efficient and safer vectors for muscle-directed gene therapy with high levels of transgene expression and absence of inhibitor formation. The absence of antibody response to transgene by AAV7, 8 and 9 is independent of vector dose but may be due to the fact that these three serotypes are associated with high level distribution to, and transduction of, hepatocytes following i.m. injection.

Inhibition and promotion of tumor growth with adeno-associated virus carcinoembryonic antigen vaccine and Toll-like receptor agonists

Carcinoembryonic antigen (CEA) is a cancer vaccines target. Several feature of recombinant adeno-associated virus (rAAV) are attractive for vaccine applications. Combining other viral vector vaccines with Toll like receptor (TLR) agonists enhances antitumor immunity. Wild-type and CEA transgenic (Tg) mice were immunized with rAAV expressing CEA, the TLR9 agonist, ODN1826, and the TLR7 agonist, imiquimod. Mice were challenged with MC38 colon tumor cells and MC38 cells expressing CEA. rAAV-CEA immunization combined with ODN1826 or imiquimod enhanced CEA-specific T-helper-1 immunity and protected against tumor challenge in wild-type but not in CEA-Tg mice. In contrast, immunization with rAAV-CEA in CEA-Tg mice could abrogate the antitumor effects of ODN1826 and promote tumor growth. Compared to wild-type, CEA-Tg mice were characterized by a greater myeloid suppressor cell and T-helper 2 response to TLR agonists and to syngeneic tumors. Depleting PDCA1+ plasmacytoid dendritic cells and Gr1+ myeloid cells increased anti-CEA immune responses in CEA-Tg mice to rAAV-CEA-ODN1826 immunization; depleting CD25+ T cells did not. There are differences in the response of wild-type and CEA-Tg mice to rAAV-CEA, TLR agonists, and syngeneic tumor. In CEA-Tg mice tumor growth can be promoted with rAAV-CEA and TLR agonists. Dendritic and myeloid cells play a regulatory role.

Immune tolerance induction in haemophilia: evidence and the way forward

Given the inhibitor-associated morbidity resulting from limited effective treatment options, antibody eradication is the ultimate goal of inhibitor management. The only clinically proven strategy for achieving antigen-specific tolerance to factor VIII is immune tolerance induction (ITI). First reported over 30 years ago, much of our current knowledge about ITI in haemophilia A and B was derived from small cohort studies and retrospective national and international ITI registries. More recently, prospective randomised ITI trials have been designed and initiated to answer outstanding questions related to the optimisation of current therapeutic strategy in haemophilia A. However, due to the low incidence of inhibitor development in haemophilia B compared to haemophilia A, there are few comparable data from which to develop a useful evidence-based approach to the prevention and eradication of FIX inhibitors. The lack of an effective strategy is particularly problematic given the even greater morbidity associated with the almost unique occurrence of allergic and anaphylactic reactions that often herald FIX antibody development, and further complicates attempts to eradicate FIX inhibitors. Ultimately, successful inhibitor prevention and eradication strategies for both diseases will emerge from the clinical translation of our evolving knowledge of immune stimulation and tolerance. This paper will discuss our current understanding of immune tolerance outcome and outcome predictors for haemophilia A and B; it will also review the current consensus recommendations for ITI, as well as the emerging scientific body of immunological knowledge that may significantly impact the therapeutic and preventative strategies of the future.

Regulation of the activity of an adeno-associated virus vector cancer vaccine administered with synthetic Toll-like receptor agonists

Recombinant adeno-associated virus (rAAV) is being tested as a vaccine vector, but the cellular immune responses elicited in animal tumor models have not been completely protective. The adjuvant effects of the TLR7 agonist, imiquimod, and the TLR9 agonist, ODN1826, were tested with rAAV expressing the melanoma antigen, Trp2. Mice immunized with rAAV-TRP2 and either TLR agonist alone generated T-helper-1 antitumor immune responses. Antitumor activity in all experiments was still incomplete. Furthermore, antitumor activity was not achieved when the combination of ODN1826 and imiquimod was used as adjuvant. In vitro, the combination increased IL-10 production by dendritic cells. In vivo, the combination reduced T-helper-1 response and dendritic cell activation and increased myeloid suppressor cells; regulatory T cells were not significantly modulated. Depletion of myeloid derived suppressor cells enhanced the antitumor activity of immunization with rAAV-TRP2 and the imiquimod-ODN1826 combination; depletion of regulatory T cells did not. TLR7 and TLR9 agonists can be used to enhance the immune response to rAAV immunogens, but antagonism can be observed when combined. Suppressor mechanisms, including those mediated by myeloid cells, may negatively regulate the antitumor immune response.

Safety of AAV factor IX peripheral transvenular gene delivery to muscle in hemophilia B dogs

Muscle represents an attractive target tissue for adeno-associated virus (AAV) vector-mediated gene transfer for hemophilia B (HB). Experience with direct intramuscular (i.m.) administration of AAV vectors in humans showed that the approach is safe but fails to achieve therapeutic efficacy. Here, we present a careful evaluation of the safety profile (vector, transgene, and administration procedure) of peripheral transvenular administration of AAV-canine factor IX (cFIX) vectors to the muscle of HB dogs. Vector administration resulted in sustained therapeutic levels of cFIX expression. Although all animals developed a robust antibody response to the AAV capsid, no T-cell responses to the capsid antigen were detected by interferon (IFN)-gamma enzyme-linked immunosorbent spot (ELISpot). Interleukin (IL)-10 ELISpot screening of lymphocytes showed reactivity to cFIX-derived peptides, and restimulation of T cells in vitro in the presence of the identified cFIX epitopes resulted in the expansion of CD4(+)FoxP3(+)IL-10(+) T-cells. Vector administration was not associated with systemic inflammation, and vector spread to nontarget tissues was minimal. At the local level, limited levels of cell infiltrates were detected when the vector was administered intravascularly. In summary, this study in a large animal model of HB demonstrates that therapeutic levels of gene transfer can be safely achieved using a novel route of intravascular gene transfer to muscle.

Gel-mediated delivery of AAV1 vectors corrects ventilatory function in Pompe mice with established disease

Pompe disease is a muscular dystrophy that results in respiratory insufficiency. We characterized the outcomes of targeted delivery of recombinant adeno-associated virus serotype 1 (rAAV2/1) vector to diaphragms of Pompe mice with varying stages of disease progression. We observed significant improvement in diaphragm contractile strength in mice treated at 3 months of age that is sustained at least for 1 year and enhanced contractile strength in mice treated at 9 and 21 months of age, measured 3 months post-treatment. Ventilatory parameters including tidal volume/inspiratory time ratio, minute ventilation/expired CO2 ratio, and peak inspiratory airflow were significantly improved in mice treated at 3 months and tested at 6 months. Despite early improvement, mice treated at 3 months and tested at 1 year had diminished normoxic ventilation, potentially due to attenuation of correction over time or progressive degeneration of nontargeted accessory tissues. However, for all rAAV2/1-treated mice (treated at 3, 9, and 21 months, assayed 3 months later; treated at 3 months, assayed at 1 year), minute ventilation and peak inspiratory flows were significantly improved during respiratory challenge. These results demonstrate that gel-mediated delivery of rAAV2/1 vectors can significantly augment ventilatory function at initial and late phases of disease in a model of muscular dystrophy.

Regulatory T cells and immune tolerance to coagulation factor IX in the context of intramuscular AAV1 gene transfer

Regulatory T cells play a major role in induction and maintenance of immune tolerance and immunological homeostasis. A variety of strategies have been attempted to induce regulatory T cells for control of unwanted, adverse immunity in autoimmune diseases, transplantation as well as gene transfer. We recently reported efficient induction of immune tolerance to coagulation factor IX (FIX) following intramuscular AAV1 gene transfer. In the current study, we performed a systematic and comprehensive examination of the role and function of regulatory T cells in induction and maintenance of FIX tolerance in the context of intramuscular AAV1 gene transfer. We observed no significant upregulation of regulatory T cells in the FIX-tolerant mice. In addition, adoptive transfer of splenocytes from FIX-tolerant mice did not suppress anti-hFIX immunity in recipient mice. Both in vitro and in vivo depletion of regulatory T cells failed to reverse FIX tolerance. These observations revealed that regulatory T cells do not play a significant role in the maintenance/protection of the established FIX tolerance. Our results provide critical insight into the role and function of regulatory T cells in induction and maintenance/protection of immune tolerance in gene transfer, complementing the current paradigm of immune tolerance mechanism.

Induction of immune tolerance to FIX by intramuscular AAV gene transfer is independent of the activation status of dendritic cells

The nature of viral vectors is suggested to be a significant contributor to undesirable immune responses subsequent to gene transfer. Such viral vectors, recognized as danger signals by the host immune system, activate dendritic cells (DCs), causing unwanted antivector and/or transgene product immunity. We recently reported efficient induction of immune tolerance to coagulation factor IX (FIX) by direct intramuscular injection of adeno-associated virus (AAV)-FIX. AAV vectors are nonpathogenic and elicit minimal inflammatory response. We hypothesized that the nonpathogenic nature of AAV plays a critical role in induction of tolerance after AAV gene transfer. We observed inefficient recruitment and activation of DCs subsequent to intramuscular injection of AAV. To further validate our hypothesis, we examined immune responses to FIX after intramuscular injection of AAV with simultaneous activation of DCs. We were able to achieve phenotypic and functional activation of DCs after administration of lipopolysaccharide and anti-CD40 antibody. However, we observed efficient induction of FIX tolerance irrespective of DC activation in mice with different genetic and major histocompatibility complex backgrounds. Furthermore, activation of DCs did not exaggerate the immune response induced after intramuscular injection of AAV serotype 2 vector. Our results demonstrate that induction of FIX tolerance after AAV gene transfer is independent of DC activation status.