AAV8 Gene Therapy for Crigler-Najjar Syndrome in Macaques Elicited Transgene T Cell Responses That Are Resident to the Liver

Abstract

Systemic delivery of adeno-associated viral (AAV) vectors has been evaluated for the treatment of several liver diseases, including homozygous familial hypercholesterolemia, ornithine transcarbamylase deficiency, and hemophilia. Here, we evaluated this approach for the treatment of Crigler-Najjar syndrome. We administered wild-type rhesus macaques with 1.0 × 1013 or 2.5 × 1013 genome copies/kg of an AAV serotype 8 vector expressing a codon-optimized version of human uridine diphosphate glucuronosyl transferase 1A1 (UGT1A1) from a liver-specific promoter. We extensively studied vector biodistribution, transgene expression, and immune responses following vector administration. All rhesus macaques survived until their scheduled necropsy at day 56 and showed no clinical abnormalities during the course of the study. Macaques administered with either vector dose developed a T cell response to the AAV capsid and/or transgene. We mapped the immunodominant epitope in the human UGT1A1 sequence, and we found no correlation between peripheral and tissue-resident lymphocyte responses. Upon further investigation, we characterized CD107a+, granzyme B+, CD4+, and CD8+ transgene-specific cellular responses that were restricted to tissue-resident T cells. This study highlights the importance of studying immune responses at the vector transduction site and the limited usefulness of blood as a surrogate to evaluate tissue-restricted T cell responses.

Human Immune Responses to Adeno-Associated Virus (AAV) Vectors

“…The potential development of an immune response against the transgene is dependent on several variables, including the tissue targeted with gene transfer, the host genetic background, and the extent of the residual expression of the donated gene. Gene transfer in a context of missense mutations and residual endogenous expression of the full length protein is unlikely to induce anti-transgene immune responses, although some preclinical studies suggest that even single amino acid variations can be recognized by the host immune system (84). Conversely, gene transfer in the context of stop mutations with no residual protein expression, is potentially more likely to result in antitransgene immunity due to the absence of central tolerance against the transgene product itself.…”

Loss of transgene expression limits liver gene therapy in primates

“…The goal of our studies was to define the mechanisms that limit efficient and durable transgene expression following liver gene therapy with AAV vectors. Previous studies with complete preclinical and clinical datasets suggest that nonhuman primates (NHPs) are better suited for evaluating key aspects of vector performance than other animal models [1][2][3][4] . We conducted initial studies in rhesus macaques using macaque-derived β-choriogonadotropic hormone (rh-β-CG) as the transgene.…”

Immune Response Mechanisms against AAV Vectors in Animal Models

“…53,54,138 A recent study evaluating a clinical AAV8 vector expressing human UGUT1A1 in NHPs reported a mainly transgene product T cell response and found that peripheral transgene product T cell responses did not always correlate with the local T cell response in the liver. 139 Insulin gene therapy with an AAV8 vector in nonobese diabetic (NOD) mice found that immune suppression was needed to maintain insulin expression, suggesting that liver tolerance alone was not sufficient to overcome established autoimmunity. 140 However, it should be noted that NOD mice have a genetic predisposition for autoimmunity and that the target level of insulin required for therapeutic benefit may be below the threshold need for tolerance induction.…”