Prenatal AAV9-GFP administration in fetal lambs results in transduction of female germ cells and maternal exposure to virus

Prenatal somatic cell gene therapy (PSCGT) could potentially treat severe, early-onset genetic disorders such as spinal muscular atrophy (SMA) or muscular dystrophy. Given the FDA-approval of adeno-associated virus serotype 9 (AAV9) vectors in infants with SMA, we tested the safety and biodistribution of AAV9-GFP (clinical-grade and dose) in fetal lambs to understand safety and efficacy after umbilical vein (UV) or intracranial (IC) injection on embryonic day 75 (E75). UV-injection led to widespread biodistribution of vector genomes in all examined lamb tissues and in maternal uteruses at harvest (E96 or E140; term=E150). There was robust GFP expression in brain, spinal cord, dorsal root ganglia (DRGs), without DRG toxicity and excellent transduction of diaphragm and quadriceps muscles. However, we found evidence of systemic toxicity (fetal growth restriction) and maternal exposure to the viral vector (transient elevation of total bilirubin and a trend towards elevation in anti-AAV9 antibodies). There were no antibodies against GFP in ewes or lambs. Analysis of fetal gonads demonstrated GFP expression in female (but not male) germ cells, with low levels of integration-specific reads, without integration in select protooncogenes. These results suggest potential therapeutic benefit of AAV9 PSCGT for neuromuscular disorders but warrant caution for exposure of female germ cells.