Intraparenchymal delivery of adeno-associated virus vectors for the gene therapy of neurological diseases

ABSTRACT

Introduction

In gene therapy with adeno-associated virus (AAV) vectors for diseases of the central nervous system, the vectors can be administered into blood vessels, cerebrospinal fluid space, or the brain parenchyma. When gene transfer to a large area of the brain is required, the first two methods are used, but for diseases in which local gene transfer is expected to be effective, vectors are administered directly into the brain parenchyma.

Areas covered

Strategies for intraparenchymal vector delivery in gene therapy for Parkinson’s disease, aromatic l-amino acid decarboxylase (AADC) deficiency, and epilepsy are reviewed.

Expert opinion

Stereotactic intraparenchymal injection of AAV vectors allows precise gene delivery to the target site. Although more surgically invasive than intravascular or intrathecal administration, intraparenchymal vector delivery has the advantage of a lower vector dose, and preexisting neutralizing antibodies have little effect on the transduction efficacy. This approach improves motor function in AADC deficiency and led to regulatory approval of an AAV vector for the disease in the EU. Although further validation through clinical studies is needed, direct infusion of viral vectors into the brain parenchyma is expected to be a novel treatment for Parkinson’s disease and drug-resistant epilepsy.

KEYWORDS:

• AAV vector
• Aromatic l-amino acid decarboxylase
• epilepsy
• Parkinson’s disease
• stereotactic surgery

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Article highlights

• Adeno-associated virus (AAV) vectors are the most used and play a central role in in vivo gene therapy for neurological diseases.

• Direct injection of AAV vectors into the brain parenchyma through stereotactic surgery is useful for gene therapy of localized lesions.

• Therapeutic genes introduced into neurons are expressed for long periods of time without causing side effects.

• Gene transfer of aromatic l-amino acid (AADC) alleviates motor symptoms of AADC deficiency, and this approach is also applied to Parkinson’s disease.

• Several gene therapy strategies have been developed to suppress neuronal hyperexcitability in drug-resistant epilepsy.

Declaration of interests

Shin-ichi Muramatsu owns equity in a company, Gene Therapy Research Institution, a company that commercializes the use of AAV vectors for gene therapy applications. To the extent that the work in this manuscript may increase the value of these commercial holdings, Muramatsu has a conflict of interest. The authors have no other relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.

Author contributions

All authors were involved in the conception of the article, all reviewed and revised the article for important intellectual content, and all authors approved the final submission.

Reviewer disclosures

Peer reviewers on this manuscript have no relevant financial or other relationships to disclose.

The structure of the AAV2 vector, which is commonly applied for intracerebral administration, is depicted. The vector comprises 4.7 kb of single-stranded DNA genome within a 25 nm diameter capsid. The genome carries an expression cassette consisting of a promoter, cDNA of the therapeutic gene, and polyadenylation signal sequence between inverted terminal repeats (ITR) at both ends. AAV2 vectors preferentially transduce neurons, and a ubiquitous promoter, such as cytomegalovirus (CMV) immediate-early promoter or neuron-specific promoter, is employed in most protocols. Other types of AAV vectors are used for gene transfer to astrocytes. sgRNA, single guide RNA; CAS, CRISPR-associated system gene.

Clinically applied AAV vectors are indicated. AAV2 vectors that harbor cytomegalovirus (CMV) immediate-early promoter is used for Parkinson’s disease and AADC deficiency.

An AAV9 vector that expresses microRNA under human synapsin 1 promoter was applied in gene therapy for refractory mesial temporal lobe epilepsy.

AADC, aromatic l-amino acid decarboxylase; GAD, glutamic acid decarboxylase; GCH, guanosine 5’-triphosphate cyclohydrolase I; TH, tyrosine hydroxylase; miGRIK2, a miRNA targeting GRIK2 that encodes the glutamate ionotropic receptor kainate type subunit 2 (GluK2).

Table 2a. Molecular targets in gene therapy for epilepsy: advanced to clinical trial

AAV, adeno-associated virus; GRIK2, kainate receptor subunit GluK2; KA, kainic acid; KCNA1, voltage-gated potassium channel Kv1.1; MTLE, mesial temporal lobe epilepsy; N/A, not applicable; NCT#, ClinicalTrials.gov ID; PIL, pilocarpine; PTZ, pentylenetetrazole; SCN1A, voltage-gated sodium channel Na_V1.1

i.a., intraamygdalar; i.c.v., intracerebroventricular; i.ctx. intracortical; i.h., intrahippocampal; i.p., intraperitoneal; s.c., subcutaneous

Table 2b. Molecular targets in gene therapy for epilepsy: preclinical stage

Additional information

Funding

This paper was supported by AMED (Grant Numbers JP23bk0104166, JP24ek0109733, and JP23bm1323001) and JSPS KAKENHI (Grant Number 23KJ1866). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.