Cytotoxic T Lymphocyte Responses to Transgene Product, Not Adeno-Associated Viral Capsid Protein, Limit Transgene Expression in Mice

Abstract

The use of adeno-associated viral (AAV) vectors for gene replacement therapy is currently being explored in several clinical indications. However, reports have suggested that input capsid proteins from AAV-2 vector particles may result in the stimulation of cytotoxic T lymphocyte (CTL) responses that can result in a loss of transduced cells. To explore the impact of anti-AAV CTLs on AAV-mediated transgene expression, both immunocompetent C57BL=6 mice and B cell-deficient mMT mice were immunized against the AAV2 capsid protein (Cap) and were injected intravenously with an AAV-2 vector encoding a-galactosidase (a-Gal). C57BL=6 mice, which developed both CTL and neutralizing antibody responses against Cap, failed to show any detectable a-Gal expression. In contrast, serum a-Gal levels comparable to those of naive mice were observed in mMT mice despite the presence of robust CTL activity against Cap, indicating that preexisting Cap-specific CTLs did not have any effect on the magnitude and duration of transgene expression. The same strategy was used to assess the impact of CTLs against the a-Gal transgene product on AAV-mediated gene delivery and persistence of transgene expression. Preimmunization of mMT mice with an Ad=a-Gal vector induced a robust CTL response to a-Gal. When these mice were injected with AAV2=a-Gal vector, initial levels of a-Gal expression were reduced by more than 1 log and became undetectable by 2 weeks postinjection. Overall, our results indicate that CTLs against the transgene product as opposed to AAV capsid protein are more likely to interfere with AAV transgene expression.

Using drug-excipient interactions for siRNA delivery

“…These will therefore not be covered in this review. Adeno-associated viral vectors (AAV) on the other hand have been shown to induce less immunogenic response and are currently under evaluation for gene therapy in several clinical trials and might have a potential as a siRNA delivery vehicle [11]. However, the toxicity issues remain to be resolved before moving this drug forward [12].…”

An Immune-Competent Murine Model to Study Elimination of AAV-Transduced Hepatocytes by Capsid-Specific CD8+ T Cells

“… 18 Until recently, efforts directed toward mimicking the immunological response against AAV capsid in mouse models had been unsuccessful. 19 , 20 , 21 , 22 , 23 , 24 Studies conducted in mice with an AAV capsid engineered to express the CD8 + epitope for ovalbumin (ova) induced activated ova-specific CD8 + T cells, confirming that input AAV capsid was processed and presented in mice. 25 Therefore, we hypothesized that previous attempts may have lacked specific and sufficient activation signals during capsid antigen exposure.…”

“…Although an absence of Cap-CD8 responses in mice was anticipated because of no prior exposure to wild-type AAV, 17 nonhuman primates are naturally infected with AAV and also failed to predict this outcome 18 . Until recently, efforts directed toward mimicking the immunological response against AAV capsid in mouse models had been unsuccessful 19, 20, 21, 22, 23, 24. Studies conducted in mice with an AAV capsid engineered to express the CD8 + epitope for ovalbumin (ova) induced activated ova-specific CD8 + T cells, confirming that input AAV capsid was processed and presented in mice 25 .…”

Gene Therapy for the Nervous System: Challenges and New Strategies

“…One of the most effective and powerful of these mechanisms is the innate and adaptive immune response. Innate immune cells, such as macrophage and liver sinusoidal endothelial cells, can internalize and degrade virus vectors [29]; preexisting antibodies against the wild type virus (from which the vector is derived) can eliminate vector from circulation; and cytotoxic T cells directed against viral antigens [30] or the transgene product [31] can eliminate transgene-expressing cells.…”