Stem cells have significant promise for regenerative medicine, but they first require an understanding of molecular or environmental cues that can regulate their proliferation and differentiation. However, precise control over stem cell fates is still a challenge, and their improper differentiation or extensive proliferation can possibly elicit deleterious consequences. In addition, multiple in vitro manipulations of human embryonic stem cells have been recently reported to undergo genetic abnormalities that resemble alterations observed in human cancers. To circumvent these challenges associated with current stem cell therapies, gene delivery of transcription factors or regulatory molecules have been proposed as powerful means to regulate stem cell functions. Critical issues, however, still remain to develop efficient gene delivering vectors and systems.

Adeno-associated viral (AAV) vectors, which are being broadly explored in clinical trials, have significant promise as therapeutic vectors due to their safety and delivery efficiency. Unfortunately, no natural AAV variants have been found with optimal properties for infecting stem cells. Due to the significant advantages of the vector, however, engineering AAV vectors to overcome rate limiting steps (i.e., cellular binding, intracellular trafficking, viral unpackaging, etc.) in stem cell transduction can have a high impact in stem cell therapy. We are pursuing two approaches to overcome these challenges. First, we have developed a high throughput approach to generate de novo AAV vectors with novel and enhanced properties for stem cell infection. Specifically, we have applied molecular evolution to create AAV vectors with novel stem cell tropism. Second, we have genetically engineered an AAV variant capable of binding to immobilized metal surfaces with high affinity. This AAV vector-bound system can bring virus into close proximity with the cell surface, while extending the residence time of the virus. Therefore, this system can possibly overcome one potential rate limiting step for stem cell infection (i.e., low binding), such that it can significantly enhance gene delivery efficiency to stem cells. We will describe the enhancement of AAV-mediated gene delivery to both adult neural and mouse embryonic stem cells using the proposed approaches. These novel approaches have strong potential to provide powerful tools that will aid numerous investigations of stem cell biology and therapy.