Lentiviral and adeno-associated vectors efficiently transduce mouse T lymphocytes when targeted to murine CD8

Preclinical studies on gene delivery into mouse lymphocytes are often hampered by insufficient activity of lentiviral (LV) and adeno-associated vectors (AAVs) as well as missing tools for cell type selectivity when considering in vivo gene therapy. Here, we selected designed ankyrin repeat proteins (DARPins) binding to murine CD8. The top-performing DARPin was displayed as targeting ligand on both vector systems. When used on engineered measles virus (MV) glycoproteins, the resulting mCD8-LV transduced CD8+ mouse lymphocytes with near-absolute (>99%) selectivity. Despite its lower functional titer, mCD8-LV achieved 4-fold higher gene delivery to CD8+ cells than conventional VSV-LV when added to whole mouse blood. Addition of mCD8-LV encoding a chimeric antigen receptor (CAR) specific for mouse CD19 to splenocytes resulted in elimination of B lymphocytes and lymphoma cells. For display on AAV, the DARPin was inserted into the GH2-GH3 loop of the AAV2 capsid protein VP1, resulting in a DARPin-targeted AAV we termed DART-AAV. Stocks of mCD8-AAV contained similar genome copies as AAV2 but were >20-fold more active in gene delivery in mouse splenocytes, while exhibiting >99% specificity for CD8+ cells. These results suggest that receptor targeting can overcome blocks in transduction of mouse splenocytes.

Directed evolution of a family of AAV capsid variants enabling potent muscle-directed gene delivery across species

Replacing or editing disease-causing mutations holds great promise for treating many human diseases. Yet, delivering therapeutic genetic modifiers to specific cells in vivo has been challenging, particularly in large, anatomically distributed tissues such as skeletal muscle. Here, we establish an in vivo strategy to evolve and stringently select capsid variants of adeno-associated viruses (AAVs) that enable potent delivery to desired tissues. Using this method, we identify a class of RGD motif-containing capsids that transduces muscle with superior efficiency and selectivity after intravenous injection in mice and non-human primates. We demonstrate substantially enhanced potency and therapeutic efficacy of these engineered vectors compared to naturally occurring AAV capsids in two mouse models of genetic muscle disease. The top capsid variants from our selection approach show conserved potency for delivery across a variety of inbred mouse strains, and in cynomolgus macaques and human primary myotubes, with transduction dependent on target cell expressed integrin heterodimers.

Engineered Capsids for Efficient Gene Delivery to the Retina and Cornea

Adeno-associated viral (AAV) vectors represent an ideal vehicle for human gene transfer. One advantage to the AAV vector system is the availability of multiple naturally occurring serotypes that provide selective tropisms for various target cells. Strategies to enhance the properties of the natural AAV isolates have been developed and can be divided into two approaches, rational design or directed evolution. The rational design approach utilizes knowledge of AAV capsids to make targeted changes to the capsid to alter transduction efficiency or specificity, while the directed evolution approach does not require a priori knowledge of capsid structure and includes random mutagenesis, capsid shuffling, or random peptide insertion. In this study, we describe the generation of novel variants for both AAV2 and AAV5 using a rational design approach and knowledge of AAV receptor binding, surface charge, and AAV capsid protein posttranslational modifications. The novel AAV2 and AAV5 variants demonstrate improved transduction properties in both the mouse retina and cornea. The translational fidelity of the novel AAV2 variant was confirmed in the context of the nonhuman primate (NHP) retina, whereas a NHP tissue explant model was established to allow the rapid assessment of translational fidelity between species for the AAV5 variants. The capsid-modified AAV2 and AAV5 variants described in this study have novel attributes that will add to the efficacy and specificity of their potential use in gene therapy for a range of human ocular diseases.