Induction of T-Cell Infiltration and Programmed Death Ligand 2 Expression by Adeno-Associated Virus in Rhesus Macaque Skeletal Muscle and Modulation by Prednisone

Use of adeno-associated virus (AAV) to transduce genes into skeletal muscles can be associated with T-cell responses to viral capsid and/or to transgenic protein. Intramuscular mononuclear cell infiltrates primarily consisting of CD8+ T cells and also containing FOXP3+ regulatory T cells were present in rhesus macaque skeletal muscle treated with rAAVrh74.MCK.GALGT2 by vascular delivery. Administration of oral prednisone prior to AAV gene delivery and throughout the study reduced such infiltrates by 60% at 24 weeks post AAV delivery compared with AAV-treated animals not receiving prednisone, regardless of the presence of pre-existing AAV serum antibodies at the time of treatment. The majority of CD8+ T cells in AAV-treated muscles expressed activated caspase 3 and programmed cell death protein 1 (PD1), suggesting ongoing programmed cell death. AAV-transduced skeletal muscles also had elevated expression of programmed death ligand 2 (PDL2) on skeletal myofibers, and this increase in expression extended to muscles where transgene was not overexpressed. These data demonstrate that prednisone can reduce the extent of intramuscular T-cell infiltrates in AAV-treated muscles, which may aid in achieving long-term transgene expression, as may the induction of PDL2 expression on skeletal myofibers to promote PD1-mediated programmed T-cell death.