Immunological Instability of Persistent Adenovirus Vectors in the Brain: Peripheral Exposure to Vector Leads to Renewed Inflammation, Reduced Gene Expression, and Demyelination

Abstract

Nonreplicating adenovirus vectors are being developed as vehicles for the delivery of therapeutic genes in vivo. Whereas in many organs an antiviral T cell response eliminates the vector and damages local tissue, when adenovirus vectors are injected into the brain the subsequent immune attack can be ineffective, allowing the vector to persist. In the present study, E1-deleted human adenovirus vectors were injected into the caudate nucleus of rats. Two months later, expression of protein from the vector was still evident and little inflammation was seen. A subcutaneous injection of adenovirus vector at this time, however, led within 2 weeks to severe mononuclear inflammation and microglial activation in the caudate. This caused local demyelination and a decrease in detectable protein expression from the vector. Interestingly, intense microglial activation and numerous lymphocytes and monocytes were also seen in brain areas containing neurons capable of retrogradely transporting the adenovirus vector from the caudate. Control experiments established that this inflammation in distant brain areas was not a nonspecific consequence of degeneration. These experiments demonstrate that although adenovirus vectors can persist in the brain without causing chronic inflammation, they remain the potential target of a damaging cell-mediated immune response brought about by a subsequent peripheral exposure to vector. The finding of lymphocytes in brain areas that project to the caudate further shows that viral antigens that are retrogradely transported by neurons can also be the target of a T cell attack.

Inflammation and adaptive immune responses to adenoviral vectors injected into the brain: peculiarities, mechanisms, and consequences

“…[17][18][19] Cytokine 20 and cellular 21 inflammatory reactions are elicited upon injection of first-generation adenoviral vectors. This is reflected in a release of the cytokines IL-1, IL-6, TNFa, and the stimulation of a fever response, 20 when adenovirus is injected into the third ventricle.…”

“…Thus, the adenoviral capsid on its own may cause, through direct interactions at the membrane of target cells, stimulation of pro-inflammatory signalling cascades resulting in cytokine release. 17,19,21,[29][30][31] Peak influx is around 3-7 days postviral vector injection. Adenoviral vectorinduced inflammation is dose dependent, with cellular influx first detected at doses of 1 Â 10 6 infectious units (iu).…”

“…41,42,47 Systemic immunization of animals following the injection of adenovirus or herpesvirus vectors into the brain leads to inflammation, and elimination of transgene expression. [17][18][19]21,29,[31][32][33]30,62 In particular, first-generation adenoviral-vectormediated expression in the brain is stable in the absence of systemic priming. In its presence, transgene expression is eliminated within 1-2 months, depending on various factors including the nature of the transgene and its levels of expression.…”

In vivo transgene expression from an adenoviral vector is altered following a 6-OHDA lesion of the dopamine system

“…In spite of the supposed immune privilege of the brain, inflammation was also reported following intracerebral injection of first generation viruses. As well as local activation of astrocytes and microglia there was also expression of major histocompatibility antigens T cell activation [6,7,24,31].…”

“…Similar studies using adeno-associated viruses also report sparing of dopamine neurones from the toxin [6,13,22,24,31]. AAV delivery of the dopamine synthetic genes tyrosine hydroxylase (TH), aromatic amino-decarboxylase (AADC) and GTP cyclohydrolase 1(GCH1) has also been successful [2,7,19,32]. Lentiviral vectors have been used for direct delivery of GDNF or the GDNF-related protein, neublastin, into the brain and have proved protective against the effects of a 6-OHDA lesion in rats [18,20], and in primates [21,23,29].…”