Advances and challenges in human AAV-mediated gene transfer: Immunological insights from a mouse model of human glycosylation

Successful gene transfer for monogenic human disease can potentially provide a singularly administered, lifelong cure. Yet concerns remain over the safety and efficacy of gene transfer. Adeno-associated virus (AAV) is a commonly used gene transfer vector that is predominantly non-integrating, can transduce and persist in non-dividing cells, and is relatively non-inflammatory. AAV\u27s have seen extensive pre-clinical success in animal models of Hemophilia B, with recent efficacy in the clinic. In both muscle-directed and liver-directed gene transfer of Factor IX (F.IX), multi-year expression of F.IX from AAV was observed in mice, dogs, and non-human primates. However, muscle-directed transfer to Hemophilia B human subjects resulted in sub therapeutic circulating F.IX, and liver-directed transfer led to transient therapeutic F.IX plasma levels that were eliminated by a hepatocyte-clearing CD8 T cell response directed against the AAV capsid. Thus the challenge of maintaining long-term, clinically meaningful levels of F.IX from an AAV vector in human subjects remains. The second chapter of this dissertation details a follow up study on the initial muscle-directed, AAV-F.IX trial. We now show 10-year F.IX expression in the muscle of a trial subject. This is the longest expression yet demonstrated in humans from a parenterally administered gene therapy vector. While therapeutic levels were never achieved in this trial, the persistence of gene expression over a decade after vector administration is an important finding for the field of gene transfer. Interestingly, AAV-F.IX delivery to the liver did result in efficacious levels of F.IX, but in the first human trial in liver, levels fell to baseline by two months post- delivery. The CD8 T cell response directed against the AAV capsid in these patients was not predicted in any pre-clinical animal studies. The third chapter of this dissertation investigates a uniquely human glycosylation mutation in the Cmah gene that potentially rendered humans more immunologically reactive. When modeled in mice, this mutation leads to enhanced T cell proliferation and activation in vitro, and to more robust T cell responses to viral challenges in vivo. The goal of these investigations is to highlight the long-term potential of AAV-mediated gene transfer, while attempting to delineate the uniquely human immune mechanisms that that influence duration of expression and that were not predicted by extensive studies in other species

Advances and challenges in human AAV-mediated gene transfer: Immunological insights from a mouse model of human glycosylation

Successful gene transfer for monogenic human disease can potentially provide a singularly administered, lifelong cure. Yet concerns remain over the safety and efficacy of gene transfer. Adeno-associated virus (AAV) is a commonly used gene transfer vector that is predominantly non-integrating, can transduce and persist in non-dividing cells, and is relatively non-inflammatory. AAV\u27s have seen extensive pre-clinical success in animal models of Hemophilia B, with recent efficacy in the clinic. In both muscle-directed and liver-directed gene transfer of Factor IX (F.IX), multi-year expression of F.IX from AAV was observed in mice, dogs, and non-human primates. However, muscle-directed transfer to Hemophilia B human subjects resulted in sub therapeutic circulating F.IX, and liver-directed transfer led to transient therapeutic F.IX plasma levels that were eliminated by a hepatocyte-clearing CD8 T cell response directed against the AAV capsid. Thus the challenge of maintaining long-term, clinically meaningful levels of F.IX from an AAV vector in human subjects remains. The second chapter of this dissertation details a follow up study on the initial muscle-directed, AAV-F.IX trial. We now show 10-year F.IX expression in the muscle of a trial subject. This is the longest expression yet demonstrated in humans from a parenterally administered gene therapy vector. While therapeutic levels were never achieved in this trial, the persistence of gene expression over a decade after vector administration is an important finding for the field of gene transfer. Interestingly, AAV-F.IX delivery to the liver did result in efficacious levels of F.IX, but in the first human trial in liver, levels fell to baseline by two months post- delivery. The CD8 T cell response directed against the AAV capsid in these patients was not predicted in any pre-clinical animal studies. The third chapter of this dissertation investigates a uniquely human glycosylation mutation in the Cmah gene that potentially rendered humans more immunologically reactive. When modeled in mice, this mutation leads to enhanced T cell proliferation and activation in vitro, and to more robust T cell responses to viral challenges in vivo. The goal of these investigations is to highlight the long-term potential of AAV-mediated gene transfer, while attempting to delineate the uniquely human immune mechanisms that that influence duration of expression and that were not predicted by extensive studies in other species

Key Diagnostic Finding in a Condition with Variable Clinical Presentations

This is an interesting case series on a very common genetic condition which are often diagnosed late as clinical signs are inconspicuous. We would like to highlight the principal clinical examination finding which led to diagnosis