AAV-DJ Virus-Like Particles (Empty Capsids)

After systemic administration, AAV vectors transduce tissues and cells depending on their capsid serotype. Over the past few years, research has been directed toward enhancing the ability of vectors to target different cells and tissues. This has often been coupled with attempts to reduce the potential for inactivation by neutralizing antibodies (NAbs), which pose a significant barrier to the transduction capacity of AAV in vivo. Improvements in transduction specificity and the ability to evade NAbs have been addressed by rational capsid engineering and evolutionary approaches. Evolutionary approaches use repertoires of capsids generated by random mutagenesis, capsid serotype shuffling, or peptide library insertion. By transducing target cells in vitro or in vivo, AAV variants with the desired tropism can be enriched. Addition of NAbs to the selection process, usually in the form of mixed human intravenous immunoglobulin (IVIg), facilitates the selection of NAb-evading AAVs.

A notable example is the development of AAV-DJ, an AAV2/8/9 chimera generated by altering the capsids of eight serotypes and selecting in vitro with hepatocytes, combined with negative selection using IVIg. AAV-DJ has been shown to be more efficient at transducing hepatocytes and non-hepatocyte cell lines in vitro than other wild-type AAV serotypes and also operates efficiently in vivo. The versatility of this engineered serotype has been demonstrated through many examples, such as gene delivery to fetal porcine fibroblasts, genome editing in human keratinocytes, and transduction of hepatic ductal organoids. Additionally, in vivo applications of AAV-DJ in animal models include transduction of mouse taste cells, HIV-1 proviral excision in HIV-1 Tg26 transgenic mice, generation of animal models for studying the pathogenesis of Huntington's disease, and gene therapy approaches for treating femoral fractures or acute myocardial ischemia. These examples highlight the broad tropism of AAV-DJ, which goes beyond the initially intended liver-specific transduction but may be advantageous for applications requiring transduction of a variety of cell types and tissues.