Immunological Aspects of Recombinant Adeno-Associated Virus Delivery to the Mammalian Brain

Abstract

Recombinant adeno-associated viruses (rAAV) are highly efficient vectors for gene delivery into the central nervous system (CNS). However, host inflammatory and immune responses may play a critical role in limiting the use of rAAV vectors for gene therapy and functional genomic studies in vivo. Here, we evaluated the effect of repeated injections of five rAAV vectors expressing different genetic sequences (coding or noncoding) in a range of combinations into the rat brain. Specifically, we wished to determine whether a specific immune or inflammatory response appeared in response to the vector and/or the transgene protein after repeated injections under conditions of mannitol coinjection. We show that readministration of the same rAAV to the CNS is possible if the interval between the first and second injection is more than 4 weeks. Furthermore, our data demonstrate that rAAV vectors carrying different genetic sequences can be administered at intervals of 2 weeks. Our data therefore suggest that the AAV capsid structure is altered by the vector genetic sequence, such that secondary structures of the single-stranded genome have an impact on the antigenicity of the virus. This study provides guidelines for more rational design of gene transfer studies in the rodent brain and, in addition, suggests the use of repeated administration of rAAV as a viable form of therapy for the treatment of chronic diseases.

Enhanced expression of glutamate decarboxylase 65 improves symptoms of rat parkinsonian models

“…Re-expression could be activated as long as 15 months after initial injection and expression, indicating that the transgene is retained within the brain. The study of Mastakov et al 19 demonstrated that repeated administration of rAAV was efficient, induced no host immune response, and resulted in no decrease in transgene expression when the interval between injections was 3 months.…”

Recombinant AAV serotype 1 transduction efficiency and tropism in the murine brain

“…In addition to the expanded tropism, rAAV5 mediated a more widely dispersed pattern of transduction. Mastakov et al, 15 also reported that rAAV5, as compared to rAAV2, mediated more widespread transgene gene expression within the CNS following direct intracerebral injection. The results of these studies suggest that intraparenchymal diffusion and the ability to transduce non-neuronal cells are a function of the different binding specificities of each vector.…”

“…However, as a therapeutic agent in many neurologic disorders, this vector is limited by a small region of transduction following intracerebral administration 9,10 and inefficient transduction of glial and ependymal cells. 1,2,11,12 Coadministration of this vector with heparin [13][14][15] or mannitol 10 alone or in combination with convection-enhanced delivery techniques 13,14 has been shown to increase the region of transduction. Also, it might be possible to redirect rAAV2 tropism to non-neuronal cells through genetic modification of the capsid [16][17][18] and the use of bispecific antibodies.…”

Immune responses to gene therapy vectors: influence on vector function and effector mechanisms

“…Other studies, in contrast, have established that this humoral response has no influence on the efficiency of infection with the vector administered within the muscle 33 or lungs. 34 Similarly, the development of anti-AAV antibodies is minimal or nonexistent after administration of AAV into the brain 35,36 or retina. 37 However, these studies were conducted in animals, which do not have pre-existing anti-AAV immunity, in contrast to humans.…”