Direct exposure of mouse spermatozoa to very high concentrations of a serotype-2 adeno-associated virus gene therapy vector fails to lead to germ cell transduction

In a clinical safety trial involving an adeno-associated virus (AAV) gene therapy vector encoding human factor IX, intrahepatic administration of the vector was associated with the finding of vector DNA in semen that persisted for several weeks. Uncertainty remains as to the route by which the vector reached semen, but the finding raised the prospect that mature sperm could be exposed to the vector and sustain integration of vector DNA. To provocatively test for the ability of AAV vectors to transduce mature sperm, we exposed mouse sperm to concentrations of the same vector used in clinical studies at concentrations ranging from 840 to 3400 particles per sperm cell, performed in vitro fertilization and embryo transfer, and evaluated newborn pups by Southern analysis for the presence of vector sequences. Of 102 pups analyzed, none showed evidence of vector DNA integration. We conclude from these studies that exposure of mature sperm to AAV gene therapy vectors is highly unlikely to lead to germline transduction.