In fact, “approximately 95% of gene therapies today use adeno-associated viruses (AAVs) to deliver a transgene to its target. However, because the AAVs are highly immunogenic, you can’t give a second dose,” Carsten Brunn, Ph.D., president and CEO of Selecta Biosciences, told BioSpace. To further compound matters, Brunn added, “up to 40% of patients have antibodies to AAVs, so they are not eligible for gene therapy.” Their immune systems would clear the therapy before it could take effect.