What question did this study set out to answer?

To identify the immunological mechanisms and administration parameters underlying immune tolerance and prolonged transgene persistence following muscle-directed AAV1 gene transfer.

January 14, 2020Molecular TherapyOpen Access

Muscle-Directed Delivery of an AAV1 Vector Leads to Capsid-Specific T Cell Exhaustion in Nonhuman Primates and Humans

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Why the study?

Intramuscular rAAV delivery can trigger immune responses, but IM rAAV1 in humans has also induced tolerance; the underlying mechanisms and parameters responsible for this tolerance were not fully understood.

Does muscle-directed delivery of rAAV1 induce capsid-specific T cell exhaustion in nonhuman primates and humans?

Key Points

To identify the immunological mechanisms and administration parameters underlying immune tolerance and prolonged transgene persistence following muscle-directed AAV1 gene transfer.
Tested three muscle-targeted delivery routes (intramuscular injection, venous limb perfusion, and intra-arterial push-and-dwell) in rhesus monkeys, assessing tissue infiltrates at days 21 and 60.
Evaluated the longevity and functional phenotype of capsid-specific T cells, including reversibility via immune checkpoint blockade, in human muscle samples collected at least 5 years after vector administration.
All three muscle-directed delivery methods in nonhuman primates were well tolerated, established persistent transgene expression, and induced local infiltration of regulatory T cells and exhausted T cells at days 21 and 60.
Human tissue analyses demonstrated that capsid-specific exhausted T cells persist for at least 5 years post-injection, with cellular exhaustion being effectively reversed through checkpoint pathway inhibition.

Structured PICO

Does muscle-directed delivery of rAAV1 induce capsid-specific T cell exhaustion in nonhuman primates and humans?

Population

Rhesus monkeys and human samples

Intervention

Muscle-directed administration of rAAV1 via intramuscular delivery, venous limb perfusion, or intra-arterial push and dwell method

Outcome

Presence of Tregs and exhausted T cell infiltrates in situ and functionality of capsid-specific exhausted T cellssurrogate

Persisting transgene expression after muscle-directed AAV gene transfer is mediated by Tregs and exhausted T cells, providing insights into immune tolerance mechanisms.

Implication

May guide tolerogenic AAV strategies for muscle gene therapy; leaves open confirmation in human trials.

Abstract

With the US Food and Drug Administration (FDA) and European Medicines Agency (EMA) approvals for Zolgensma, Luxturna, and Glybera, recombinant adeno-associated viruses (rAAVs) are considered efficient tools for gene transfer. However, studies in animals and humans demonstrate that intramuscular (IM) AAV delivery can trigger immune responses to AAV capsids and/or transgenes. IM delivery of rAAV1 in humans has also been described to induce tolerance to rAAV characterized by the presence of capsid-specific regulatory T cells (Tregs) in periphery. To understand mechanisms responsible for tolerance and parameters involved, we tested 3 muscle-directed administration routes in rhesus monkeys: IM delivery, venous limb perfusion, and the intra-arterial push and dwell method. These 3 methods were well tolerated and led to transgene expression. Interestingly, gene transfer in muscle led to Tregs and exhausted T cell infiltrates in situ at both day 21 and day 60 post-injection. In human samples, an in-depth analysis of the functionality of these cells demonstrates that capsid-specific exhausted T cells are detected after at least 5 years post-vector delivery and that the exhaustion can be reversed by blocking the checkpoint pathway. Overall, our study shows that persisting transgene expression after gene transfer in muscle is mediated by Tregs and exhausted T cells.