4D Molecular Therapeutics LLC is using libraries of capsid-mutated adeno-associated virus vectors as a starting point for directed evolution of new vectors to overcome challenges in delivering gene therapy.

AAV vectors have emerged as a preferred strategy for gene therapy because they can effectively deliver therapeutic amounts of protein and are generally considered safe. The only approved gene therapy, uniQure N.V.'s Glybera alipogene tiparvovec, uses an AAV vector to deliver the missing gene in lipoprotein lipase deficiency (LPLD).