Successful Interference with Cellular Immune Responses to Immunogenic Proteins Encoded by Recombinant Viral Vectors

Abstract

Vectors derived from the adeno-associated virus (AAV) have been successfully used for the long-term expression of therapeutic genes in animal models and patients. One of the major advantages of these vectors is the absence of deleterious immune responses following gene transfer. However, AAV vectors, when used in vaccination studies, can result in efficient humoral and cellular responses against the transgene product. It is therefore important to understand the factors which influence the establishment of these immune responses in order to design safe and efficient procedures for AAV-based gene therapies. We have compared T-cell activation against a strongly immunogenic protein, the influenza virus hemagglutinin (HA), which is synthesized in skeletal muscle following gene transfer with an adenovirus (Ad) or an AAV vector. In both cases, cellular immune responses resulted in the elimination of transduced muscle fibers within 4 weeks. However, the kinetics of CD4 ؉ T-cell activation were markedly delayed when AAV vectors were used. Upon recombinant Ad (rAd) gene transfer, T cells were activated both by direct transduction of dendritic cells and by crosspresentation of the transgene product, while upon rAAV gene transfer T cells were only activated by the latter mechanism. These results suggested that activation of the immune system by the transgene product following rAAV-mediated gene transfer might be easier to control than that following rAd-mediated gene transfer. Therefore, we tested protocols aimed at interfering with either antigen presentation by blocking the CD40/ CD40L pathway or with the T-cell response by inducing transgene-specific tolerance. Long-term expression of the AAV-HA was achieved in both cases, whereas immune responses against Ad-HA could not be prevented. These data clearly underline the importance of understanding the mechanisms by which vector-encoded proteins are recognized by the immune system in order to specifically interfere with them and to achieve safe and stable gene transfer in clinical trials.

Major role of local immune responses in antibody formation to factor IX in AAV gene transfer

“…26 Others published similar data for muscle transduction with an AAV vector expressing influenza virus hemagglutinin. 24 Data from this current study provide an explanation for our previous observations in hemophilia B dogs, which suggested an increased risk of inhibitor formation in animals that received high doses per site of i.m. injection of AAV vector expressing canine F.IX.…”

“…However, this did not result in an inflammatory response, likely because of inefficient CD8 + T-cell activation. 9,14,23,24 It is thought that because of unproductive transduction of dendritic cells and lack of innate immunity to the AAV vector, there is inefficient MHC class I presentation of F.IX peptides to CD8 + T cells by professional antigen presenting cells (APCs). [23][24][25] However, lack of inflammation during the first month after gene transfer and shift toward Th2 immunity did not prevent subsequent activation of CD8 + T cells and inflammation at later time points (Figure 3).…”

“…9,14,23,24 It is thought that because of unproductive transduction of dendritic cells and lack of innate immunity to the AAV vector, there is inefficient MHC class I presentation of F.IX peptides to CD8 + T cells by professional antigen presenting cells (APCs). [23][24][25] However, lack of inflammation during the first month after gene transfer and shift toward Th2 immunity did not prevent subsequent activation of CD8 + T cells and inflammation at later time points (Figure 3). Consistent with this interpretation, we found that a local immune response to ovalbumin transgene product caused activation of ovalbumin-specific CD4 + T cells at first (day 5) exclusively in draining LN, but not in the spleen or nondraining LN.…”

Induction of long-term cardiac allograft survival by heme oxygenase-1 gene transfer

“…injection. 16,17 This hypothesis is strengthened by the detection of transduced cells in the spleen after the i.g., i.m. and i.v.…”

Liver gene therapy: advances and hurdles

“…36 However, after AAVmediated gene transfer, presentation of transgene epitopes by MHC class I molecules of antigen-presenting cells (cross-presentation) may occur, resulting in the induction of immune response. 37,38 …”