Evaluation of rAAVrh74 gene therapy vector seroprevalence by measurement of total binding antibodies in patients with Duchenne muscular dystrophy.

Background: Adeno-associated virus (AAV) vectors are a promising platform for in vivo transfer of transgenes designed to treat diseases. Pre-existing humoral immunity to these vectors can potentially impact the safety and efficacy of gene therapies. Consequently, individuals with pre-existing antibodies to the specific AAV serotypes used may be excluded from clinical trials and treatments. Recombinant AAV serotype rh74 (rAAVrh74), a vector originally isolated from rhesus monkeys and potentially less immunogenic than other serotypes isolated from humans (e.g. AAV2, AAV5, and AAV9), efficiently transduces muscle and is being investigated for use in gene therapy for Duchenne muscular dystrophy (DMD). Objective: To evaluate prevalence of total binding antibodies (neutralizing and non-neutralizing) against rAAVrh74 in patients with DMD. Methods: Eligible individuals (N = 107) were ⩾ 4 to < 18 years old with genetically confirmed DMD and were excluded from the study if they lived with a person who had known exposure to rAAVrh74 or other gene transfer therapy, or if they received prior treatment with gene transfer therapy. A single blood sample was obtained from each participant, and anti-rAAVrh74 total binding antibodies were measured by enzyme-linked immunosorbent assay. Total binding antibody level < 1:400 was defined as not elevated or seronegative. Primary endpoint was the percentage of subjects with elevated total antibody titers to rAAVrh74. Results: A large preponderance (86.1%) of patients with DMD in this data set was seronegative for anti-rAAVrh74 total binding antibodies. These patients would potentially meet the antibody status eligibility criterion for entry into rAAVrh74-based gene therapy clinical trials. Conclusion: Measuring total binding antibodies is a more comprehensive approach to assess pre-existing immune response versus measuring neutralizing antibodies alone. The low seroprevalence of total binding antibodies against rAAVrh74 shown here supports the broad applicability of rAAVrh74-based gene transfer therapy for patients with DMD and potentially other neuromuscular diseases.

MDA5 and MAVS mediate type I interferon responses to coxsackie B virus.

Coxsackie B viruses (CVB) are enteroviruses that have been associated with a variety of human diseases, including myocarditis. In the present study, we found that MDA5 and its adaptor molecule MAVS are critical for type I interferon responses to CVB, since the absence of either MAVS or MDA5 leads to deficient type I interferon production and early mortality in mice infected with CVB. Pancreatic and hepatic necrosis were observed on histopathological examination of MAVS and MDA5 knockout mice infected with CVB. Inflammatory cytokine production in response to systemic CVB infection was independent of MAVS. Surprisingly, virus titers were not elevated in MAVS-deficient mice, despite significant reductions in type I interferon levels. These data highlight the importance of type I interferon in host defense and provide insight on the mechanisms of innate immune responses following coxsackievirus infection.

Clinical development on the frontier: gene therapy for duchenne muscular dystrophy.

Introduction: The development of adeno-associated virus (AAV) vectors as safe vehicles for in vivo delivery of therapeutic genes has been a major milestone in the advancement of gene therapy, enabling a promising strategy for ameliorating a wide range of diseases, including Duchenne muscular dystrophy (DMD).Areas covered: Based on experience with the development of a gene transfer therapy agent for DMD, we discuss ways in which gene therapy for rare disease challenges traditional clinical development paradigms, and recommend a step-wise approach for design and evaluation to support broader applicability of gene therapy.Expert opinion: The gene therapy development approach should intentionally design the therapeutic construct and the clinical study to systematically evaluate agent delivery, safety, and efficacy. Rigorous preclinical work is essential for establishing an effective gene delivery platform and determining the efficacious dose. Clinical studies should thoroughly evaluate transduction, on-target transgene expression at the tissue and cellular level, and functional efficacy.

Cutting Edge: Antibody-mediated TLR7-dependent recognition of viral RNA.

TLR7 recognizes the genome of ssRNA viruses such as Coxsackievirus B. Because TLR7 is expressed in intracellular compartments, viral RNA must be internalized before its recognition by TLR7. In this study, we define plasmacytoid dendritic cells (pDC) as peripheral blood mononuclear immune cells that respond to Coxsackievirus. pDC activation by Coxsackievirus B requires the presence of specific antiviral Abs. We show that Fc receptors mediate the recognition of virus-Ab complexes and that TLR7 is required for human and murine pDC production of cytokines. These data define a pathway by which intracellular TLR7 senses viral RNA and indicate a role for TLRs in association with Abs in sustaining virus-specific responses.

The erythrocyte viral trap: transgenic expression of viral receptor on erythrocytes attenuates coxsackievirus B infection.

Viruses rely on attachment to specific cell surface receptors to infect host cells. Selective expression of viral receptors has the potential to attenuate infection of susceptible tissues by redirecting virus to cells that cannot support viral replication. We propose that erythrocytes are an ideal instrument for this strategy, because they are present in vast numbers, permeate every organ, and cannot serve as hosts for viral propagation. To test this hypothesis, we generated a transgenic mouse, termed globin transcription factor 1 (GATA1)-coxsackie and adenovirus receptor (CAR), that expressed the CAR on erythrocytes. Coxsackievirus group B (CVB) adhered to the surface of CAR-expressing erythrocytes and was rendered noninfectious. Upon infection with CVB, GATA1-CAR mice had diminished viremia and reduced viral replication in heart, brain, and liver. Furthermore, when faced with a CVB challenge that was lethal to WT littermates, the survival of GATA1-CAR mice was prolonged, and their ultimate mortality was reduced. The GATA1-CAR mouse model presented here demonstrates that erythrocyte expression of CAR limits CVB pathogenesis. Erythrocytes also may be coated with a variety of receptors by nontransgenic methods, making this a very flexible model for the treatment of infectious diseases in humans.

Coxsackievirus and adenovirus receptor is essential for cardiomyocyte development.

The coxsackievirus and adenovirus receptor (CAR) is a transmembrane protein that is known to be a site of viral attachment and entry, but its physiologic functions are undefined. CAR expression is maximal in neonates and wanes rapidly after birth in organs such as heart, muscle, and brain, suggesting that CAR plays a role in the development of these tissues. Here, we show that CAR deficiency resulted in an embryonic lethal condition associated with cardiac defects. Specifically, commencing approximately 10.5 days postconception (dpc), CAR-/- cardiomyocytes exhibited regional apoptosis evidenced by both histopathologic features of cell death and positive staining for the apoptotic marker cleaved caspase 3. CAR-/- fetuses invariably suffered from degeneration of the myocardial wall and thoracic hemorrhaging, leading to death by 11.5 dpc. These findings are consistent with the view that CAR provides positive survival signals to cardiomyocytes that are essential for normal heart development.