AAV vector transduction restriction and attenuated toxicity in hESCs via a rationally designed inverted terminal repeat

Abstract

Adeno-associated virus (AAV) inverted terminal repeats (ITRs) induce p53-dependent apoptosis in human embryonic stem cells (hESCs). To interrogate this phenomenon, a synthetic ITR (SynITR), harboring substitutions in putative p53 binding sites was generated and evaluated for vector production and gene delivery. Replication of SynITR flanked transgenic genome was similar compared to wild type (wt) ITR, with a modest increase in vector titers. Packaged in the AAV2 capsid, wtITR and SynITR vectors demonstrated similar transduction efficiencies of human cells without toxicity. Following AAV2-wtITR vector infection of hESCs, rapid apoptosis was observed as reported. In contrast, infection by AAV2 vectors packaged with SynITRs attenuated the wtITR-induced hESC toxicity. While hESC particle entry and the abundance of double stranded circular episomes was similar for the ITR contexts, reporter expression was inhibited from transduced SynITR genomes. Mechanistically, infection of hESCs induced γH2AX in an ITR-independent manner, however, canonical activation of p53α was uncoupled using AAV-SynITR. Further investigations in hESCs revealed additional novel findings: (i) p53β is uniquely and constitutively active and (ii) AAV vector infection, independent of the ITR sequence, induces activation of p53ψ. The data herein reveal an ITR-dependent AAV vector transduction restriction specific to hESCs and manipulation of the DNA damage response via ITR engineering.