Adeno-Associated Viral Gene Therapy for Retinal Disorders - Gene Delivery and Therapy for Neurological Disorders - page 206

acuity [ 15 ], and increased light sensitivity was found in seven out
of nine patients.
Further publications from these centers along with a fourth
center in Israel [ 17 ] have now detailed a total of 31 patients of age
range 8-30 that have been treated. Jacobson et al. [ 18 ] provide up
to 3 years follow-up data from 15 patients and show no systemic
toxicity or signifi cant immune reactions but some adverse events
related to ocular surgery. There was a signifi cant improvement in
the full-fi eld sensitivity testing in study eyes compared to control
eyes. Three patients have also had vector administration to their
second eye, 1.7-3.3 years after the initial treatment, with a subse-
quent follow-up reported after 6 months [ 19 ]. No detectable
T-cell or neutralizing antibody response was found to the vector or
transgene product. In terms of function, all “second” eyes showed
improvement in full-fi eld sensitivity testing, pupillometry, and
functional MRI, suggesting that eventually treatment of both eyes
may be safe and effi cacious.
Clinical trial results have recently been published of phase 1/2
trial treating a further retinal degeneration called choroideremia,
an X-linked recessive condition in which there are mutations in the
CHM gene encoding Rab escort protein-1 (REP1). In this trial, an
AAV2 vector expressing REP1 under the control of a CBA pro-
moter was delivered subretinally in six patients. There were no
adverse effects (related to both surgery and vector administration),
and in two patients, visual acuity improvements were reported
[ 20 ]. A further clinical trial to treat retinitis pigmentosa due to
MERTK mutations is underway (NCT01482195), the results of
which are awaited.
Gene therapy for retinal disease has so far proven to be safe and
effi cacious. There are numerous further retinal degenerations that
may be treated using gene therapy for which new vectors will need
to be developed and tested.
In this chapter, we will discuss features of AAV vector design to
be considered when targeting retinal cells for gene therapy, proto-
cols for vector production, and methods of testing vectors in vitro
and in vivo.

2 Strategies for Vector Design

AAVs are single-stranded DNA parvoviruses that are not associated
with pathogenicity in humans. Their 4.7 kb genome consists of
two coding sequences, rep and cap, on either side of which lies a
palindromic region known as an inverted terminal repeat (ITR) of
145 bp [ 21 ], required for replication, packaging, and insertion
into the host genome [ 22 ]. The latter process occurs into a specifi c
site on human chromosome 19 (AAV2) [ 23 ], but the majority of
the wild-type AAV DNA exists as circular double-stranded episomes