Adeno-Associated Virus Vector Design-Moving the Adeno-Associated Virus to a Bioengineered Therapeutic Nanoparticle

Although the number of market-approved gene therapies is still low, this new class of therapeutics has become an integral part of modern medicine. The success and safety of gene therapy depend on the vectors used to deliver the therapeutic material. Adeno-associated virus (AAV) vectors have emerged as the most frequently used delivery system for in vivo gene therapy. This success was achieved with first-generation vectors, using capsids derived from natural AAV serotypes. Their broad tropism, the high seroprevalence for many of the AAV serotypes in the human population, and the high vector doses needed to transduce a sufficient number of therapy-relevant target cells are challenges that are addressed by engineering the capsid and the vector genome, improving the efficacy of these biological nanoparticles.

Onasemnogene abeparvovec-xioi: a gene replacement strategy for the treatment of infants diagnosed with spinal muscular atrophy

In May of 2019, the adeno-associated virus (AAV)-based gene therapy onasemnogene abeparvovec-xioi (Zolgensma) became the second Food and Drug Administration (FDA)-approved gene therapy with designated use for infants diagnosed with spinal muscular atrophy (SMA). The decision came nearly 10 years after results of the first preclinical models were initially reported. While the journey was an arduous one, the approval was an indication of the remarkable success of the first in-human clinical trials. According to the traditional classification system of autosomal recessive SMA, of which there are multiple types with phenotypic variability, SMA type 1 is the most common and most severe and represents 45% of the SMA patient population. Children with SMA type 1 cannot lift their heads without assistance and do not live past their second birthday. With Zolgensma, the first treated children with SMA type 1 have reached 5 years of age and some of them achieved the ability to sit unassisted or even walk. In this article, we review the work that led to FDA approval with emphasis on the development of preclinical and clinical studies.

An ex vivo Approach to Assess Mitochondrial ROS by Flow Cytometry in AAV-tagged Astrocytes in Adult Mice

Mitochondrial reactive oxygen species (mROS) are naturally produced signalling molecules extremely relevant for understanding both health- and disease-associated biological processes. The study of mROS in the brain is currently underway to decipher their physiopathological roles and contributions in neurological diseases. Recent advances in this field have highlighted the importance of studying mROS signalling and redox biology at the cellular level. Neurons are especially sensitive to the harmful effects of excess mROS while astrocytic mROS have been shown to play a relevant physiological role in cerebral homeostasis and behaviour. However, given the complexity of the brain, investigating mROS formation in a specific cell-type in adult animals is methodologically challenging. Here we propose an approach to specifically assess mROS abundance in astrocytes that combines i) a targeting strategy based on the use of adeno-associated virus (AAV) vectors expressing the green fluorescent protein (GFP) under an astrocyte (glial fibrillary acidic protein or GFAP) promoter, along with, ii) a robust and widely extended protocol for the measurement of mROS by flow cytometry using commercial probes. The significance of this work is that it allows the selective study of astrocytic mROS abundance by means of easily accessible technology.

Gene Therapy for Hemophilia

The best currently available treatments for hemophilia A and B (factor VIII or factor IX deficiency, respectively) require frequent intravenous infusion of highly expensive proteins that have short half-lives. Factor levels follow a saw-tooth pattern that is seldom in the normal range and falls so low that breakthrough bleeding occurs. Most hemophiliacs worldwide do not have access to even this level of care. In stark contrast, gene therapy holds out the hope of a cure by inducing continuous endogenous expression of factor VIII or factor IX following transfer of a functional gene to replace the hemophilic patient's own defective gene.