The promise of gene therapy for the treatment of alpha-1 antitrypsin deficiency

Immunogenicity of Recombinant Adeno-Associated Virus (AAV) Vectors for Gene Transfer

Recombinant adeno-associated viruses (AAVs) have emerged as promising gene delivery vehicles resulting in three US Food and Drug Administration (FDA) and one European Medicines Agency (EMA)-approved AAV-based gene therapies. Despite being a leading platform for therapeutic gene transfer in several clinical trials, host immune responses against the AAV vector and transgene have hampered their widespread application. Multiple factors, including vector design, dose, and route of administration, contribute to the overall immunogenicity of AAVs. The immune responses against the AAV capsid and transgene involve an initial innate sensing. The innate immune response subsequently triggers an adaptive immune response to elicit a robust and specific response against the AAV vector. AAV gene therapy clinical trials and preclinical studies provide important information about the immune-mediated toxicities associated with AAV, yet studies suggest preclinical models fail to precisely predict the outcome of gene delivery in humans. This review discusses the contribution of the innate and adaptive immune response against AAVs, highlighting the challenges and potential strategies to mitigate these responses, thereby enhancing the therapeutic potential of AAV gene therapy.

In Vitro Evaluation of a Novel mRNA-Based Therapeutic Strategy for the Treatment of Patients Suffering from Alpha-1-Antitrypsin Deficiency

In single-gene disorders, like alpha-1-antitrypsin deficiency (AATD), a gene mutation causes missing or dysfunctional protein synthesis. This, in turn, can lead to serious complications for the patient affected. Furthermore, single-gene disorders are associated with severe early-onset conditions and necessitate expensive lifelong care. Until nowadays, therapeutic treatment options are still limited, cost-intensive, or lack effectiveness. For these reasons, we aim to develop a novel mRNA-based therapeutic strategy for the treatment of single-gene disorders, such as AATD, which is based on the induction of de novo synthesis of the functional proteins. Therefore, an alpha-1-antitrypsin (AAT) encoding mRNA was generated by in vitro transcription. After in vitro delivery of the mRNA to different cells, protein expression and functionality, as well as adverse effects and mRNA serum stability, were analyzed. Our results show that the AAT mRNA-transfected cells express the AAT protein in high amounts within the first 24 h. Moreover, the expressed AAT protein is highly functional, since the activity of elastase is significantly inhibited. Our data also show that mRNA concentrations up to 1 μg per 150,000 cells have no adverse effects on cell viability and immune activation. Furthermore, the encapsulated AAT encoding mRNA is stable and functional in human serum for up to 30 min. Overall, the proposed project provides an innovative, highly promising, and safe therapeutic approach and, thus, promises a novel progress in the treatment of single-gene disorders, whereby affected patients could greatly benefit.

α-1-antitrypsin gene delivery reduces inflammation, increases T-regulatory cell population size and prevents islet allograft rejection

Antiinflammatory clinical-grade, plasma-derived human α-1 antitrypsin (hAAT) protects islets from allorejection as well as from autoimmune destruction. hAAT also interferes with disease progression in experimental autoimmune encephalomyelitis (EAE) and in collagen-induced arthritis (CIA) mouse models. hAAT increases IL-1 receptor antagonist expression in human mononuclear cells and T-regulatory (Treg) cell population size in animal models. Clinical-grade hAAT contains plasma impurities, multiple hAAT isoforms and various states of inactive hAAT. We thus wished to establish islet-protective activities and effect on Treg cells of plasmid-derived circulating hAAT in whole animals. Islet function was assessed in mice that received allogeneic islet transplants after mice were given hydrodynamic tail-vein injection with pEF-hAAT, a previously described Epstein-Barr virus (EBV) plasmid construct containing the EBV nuclear antigen 1 (EBNA1) and the family of repeat EBNA1 binding site components (designated "EF") alongside the hAAT gene. Sera collected from hAAT-expressing mice were added to lipopolysaccharide (LPS)-stimulated macrophages to assess macrophage responsiveness. Also, maturation of peritoneal cells from hAAT-expressing mice was evaluated. hAAT-expressing mice accepted islet allografts (n = 11), whereas phosphate-buffered saline-injected animals (n = 11), as well as mice treated with truncated-hAAT-plasmid (n = 6) and untreated animals (n = 20) rapidly rejected islet allografts. In hAAT-expressing animals, local Treg cells were abundant at graft sites, and the IL-1 receptor antagonist was elevated in grafts and circulation. Sera from hAAT-expressing mice, but not control mice, inhibited macrophage responses. Finally, peritoneal cells from hAAT-expressing mice exhibited a semimature phenotype. We conclude that plasmid-derived circulating hAAT protects islet allografts from acute rejection, and human plasma impurities are unrelated to islet protection. Future studies may use this in vivo approach to examine the structure-function characteristics of the protective activities of AAT by manipulation of the hAAT plasmid.

Pulmonary drug delivery: medicines for inhalation

Mankind has inhaled substances for medical and other reasons for thousands of years, notably resulting in the cultural manifestations of tobacco and opium smoking. Over the course of time concepts of pulmonary application, including inhalation devices and drug formulations, have been and still are being continuously developed. State of the art instruments even allow for individualized drug application by adaptation of the inhalation procedure to the breathing pattern of the patient. Pulmonary drug delivery offers promising advantages in comparison to "classical" drug administration via the oral or transcutaneous routes, which is also reflected by an increasing interest and number of marketed products for inhalation therapy. However, the lungs' efficient clearance mechanisms still limit the benefit of many therapeutic concepts. In consequence the objective of current research and development in pulmonary drug delivery is to overcome and to control drug clearance from the intended target site. Here, several of the most auspicious future drug delivery concepts are presented and discussed in order to give the reader an insight into this emerging field of medicine.

Transduction efficiencies of novel AAV vectors in mouse airway epithelium in vivo and human ciliated airway epithelium in vitro

We have characterized the ability of adeno-associated virus (AAV) serotypes 1-9 in addition to nineteen novel vectors isolated from various tissues, to transduce mouse and human ciliated airway epithelium (HAE). Vectors expressing alpha-1-antitrypsin (AAT) and beta-galactosidase were co-instilled into the mouse lung. Of all the vectors tested rh.64R1, AAV5 and AAV6 were the most efficient. The high transduction observed in mouse was reproduced in HAE cell cultures for both rh.64R1 and AAV6 but not for AAV5. Since AAV6 was the most efficient vector in mouse and HAE we also tested the transduction efficiencies of the AAV6 singleton vectors (i.e., AAV6 variants with targeted mutations) in these models. Of these, AAV6.2 transduced mouse airway epithelium and HAE with greater efficiency than all other AAV vectors tested. We demonstrated that AAV6.2 exhibits improved transduction efficiency compared to previously reported AAVs in mouse airways and in culture models of human airway epithelium and that this vector requires further development for preclinical and clinical testing.