Developing gene therapy to treat blindness caused by Stargardt Disease
Lead Research Organisation:
University of Oxford
Department Name: Clinical Neurosciences
Abstract
Stargardt disease leads to blindness in young people due to loss of the light sensing cells known as photoreceptors that line the retina at the back of the eye. Stargardt disease is caused by the deficiency of a protein known as ABCA4 which stands for "ATP Binding Cassette subtype A4". This protein is very important for recycling the visual pigments necessary for the light-sensitive photoreceptors. When there is a deficiency of ABCA4, the light-sensitive pigments accumulate in the retina which leads to toxic damage and eventual cell death. Stargardt disease usually presents in childhood and there then follows a period of several years of progressive loss of sight and blindness in many cases. There is therefore a window of opportunity of several years after diagnosis in which to intervene with some form of treatment to prevent sight loss.
Gene therapy is a new technique which has been shown to be highly effective at reintroducing defective genes into the retina. Gene therapy was first used in this manner in 2007 in three clinical trials to treat inheriuted blindess caused by defiency of anothe gene known as RPE65. More recently we have started a new gene therapy treatment in Oxford to treat a photoreceptor disease known as choroideraemia and several patients have been treated so far without adverse effects. In these gene therapy trials we are using a small viral particle known as adeno associated virus, or AAV. This viral particle is one of the smallest lifeforms known and it is not associated with any disease in humans. The virus survives by remaining dormant and undetected by the immune system. We have taken advantage of AAV by removing the viral genes and replacing them with the gene that is missing for the particular retinal disease. The ability of the virus to evade the immune system is very helpful because the lack of inflammation means that the virus does not damage the retina when injected into the eye. The AAV particle is however too small to carry many genes that are missing in certain types of retinal degeneration. Unfortunately the ABCA4 gene, which would need to be replaced to cure Stargardt disease, is just too large to fit into AAV.
The purpose of this project is to solve this problem by exploring a new property which has recently been identified in relation to AAV. It has recently been discovered that a large gene can be broken into two segments each of which is carried by an AAV particle and these particles are able to recombine the gene back into full length after infecting nerve cells. In this project we aim to perform a series of experiments whereby we optimise the process of recombining two fragments of the ABCA4 gene in order to deliver its successfully into photoreceptors. We will validate the function of the gene in a genetically engineered mouse, which is also deficient of the same gene and has features similar to Stargardt disease on retinal examination. If we can correct or even improve the deficiency of ABCA4 using our new vector then we would have the ideal background information to support a new clinical trial.
Gene therapy is a new technique which has been shown to be highly effective at reintroducing defective genes into the retina. Gene therapy was first used in this manner in 2007 in three clinical trials to treat inheriuted blindess caused by defiency of anothe gene known as RPE65. More recently we have started a new gene therapy treatment in Oxford to treat a photoreceptor disease known as choroideraemia and several patients have been treated so far without adverse effects. In these gene therapy trials we are using a small viral particle known as adeno associated virus, or AAV. This viral particle is one of the smallest lifeforms known and it is not associated with any disease in humans. The virus survives by remaining dormant and undetected by the immune system. We have taken advantage of AAV by removing the viral genes and replacing them with the gene that is missing for the particular retinal disease. The ability of the virus to evade the immune system is very helpful because the lack of inflammation means that the virus does not damage the retina when injected into the eye. The AAV particle is however too small to carry many genes that are missing in certain types of retinal degeneration. Unfortunately the ABCA4 gene, which would need to be replaced to cure Stargardt disease, is just too large to fit into AAV.
The purpose of this project is to solve this problem by exploring a new property which has recently been identified in relation to AAV. It has recently been discovered that a large gene can be broken into two segments each of which is carried by an AAV particle and these particles are able to recombine the gene back into full length after infecting nerve cells. In this project we aim to perform a series of experiments whereby we optimise the process of recombining two fragments of the ABCA4 gene in order to deliver its successfully into photoreceptors. We will validate the function of the gene in a genetically engineered mouse, which is also deficient of the same gene and has features similar to Stargardt disease on retinal examination. If we can correct or even improve the deficiency of ABCA4 using our new vector then we would have the ideal background information to support a new clinical trial.
Technical Summary
ABCA4 is a protein expressed in photoreceptor cells which is vital for normal photoreceptor function. Mutations in ABCA4 are the commonest cause of monogenic inherited retinal degeneration and usually present in childhood. Although gene therapy with AAV vectors has been shown to be safe and effective at photoreceptor gene replacement, the ABCA4 coding sequence at 6.7 KB is known to be too large to be packaged effectively into standard AAV vectors. We have recently developed an AAV transgene sequence which includes the full length ABCA4 and various regulatory elements to enhance gene expression. We have developed a method of packaging this transgene in two parts into AAV5 and AAV8 capsid serotypes. Through a complex method of intracellular DNA recombination, transduction with these vectors leads to effective expression of ABCA4 protein in human cells in vitro. We wish to take these vectors along a developmental pathway that would result in a Phase 1 clinical trial to treat Stargardt disease. We have a considerable amount of experience with the processes required by GTAC and the MHRA in gaining clinical trial approval for AAV gene
therapy First in Man studies. The method of delivery of the ABCA4 transgene is technically challenging and several steps are now required to optimise vector efficiency and the targeting of photoreceptors. We propose to test several compounds which may improve the efficiency of recombination within photoreceptors and would therefore reduce the total vector dose administered to each patient. We will also confirm functional activity of the ABCA4 protein in the knockout mouse in our laboratory. Whilst lentiviruses provide an alternative way of delivering large genes, these vectors have additional safety concerns for human use, such as the risk of insertional mutagenesis and also an increased risk of immune reactions. AAV vectors in contrast have been shown to be safe and effective for human retinal gene delivery.
therapy First in Man studies. The method of delivery of the ABCA4 transgene is technically challenging and several steps are now required to optimise vector efficiency and the targeting of photoreceptors. We propose to test several compounds which may improve the efficiency of recombination within photoreceptors and would therefore reduce the total vector dose administered to each patient. We will also confirm functional activity of the ABCA4 protein in the knockout mouse in our laboratory. Whilst lentiviruses provide an alternative way of delivering large genes, these vectors have additional safety concerns for human use, such as the risk of insertional mutagenesis and also an increased risk of immune reactions. AAV vectors in contrast have been shown to be safe and effective for human retinal gene delivery.
Planned Impact
Ultimately patients affected by retinal degenerations associated with deficiency of the ABCA4 gene have the most to gain from this research. This will include children with Stargardt disease, which is the commonest recessive inherited macular degeneration affecting the younger age group. It will also be of benefit to those with cone dystrophy which is a rarer variant of ABCA4 deficiency and also some patients with classical retinitis pigmentosa which can be caused by more profound absence of the ABCA4 gene. Beyond this, patients who have retinal degeneration caused by deficiencies of larger genes such as some types of Usher syndrome could also benefit from the technology, although it would need to be redesigned around a different gene. On an even wider basis, any patients with retinal degeneration which would include age-related macular degeneration, the overall commonest cause of blindness in the developed world, would benefit from any technology which aims to develop a single injection gene therapy treatment, as this could be used to deliver any type of gene. The development of retinal gene therapy using AAV has great potential in the future treatment of many currently incurable diseases that lead to blindness. The technical objectives of the proposed research include identifying an optimal means of recombining to viral particles to deliver a large gene and this may also have implications for developing new treatments for other genetic diseases such as muscular dystrophy and cystic fibrosis, which also depend on successful delivery of larger genes.
Organisations
People |
ORCID iD |
Robert MacLaren (Principal Investigator) |
Publications
Charbel Issa P
(2013)
Fundus autofluorescence in the Abca4(-/-) mouse model of Stargardt disease--correlation with accumulation of A2E, retinal function, and histology.
in Investigative ophthalmology & visual science
McClements ME
(2013)
Gene therapy for retinal disease.
in Translational research : the journal of laboratory and clinical medicine
Müller PL
(2015)
Monoallelic ABCA4 Mutations Appear Insufficient to Cause Retinopathy: A Quantitative Autofluorescence Study.
in Investigative ophthalmology & visual science
Lipinski DM
(2015)
CNTF Gene Therapy Confers Lifelong Neuroprotection in a Mouse Model of Human Retinitis Pigmentosa.
in Molecular therapy : the journal of the American Society of Gene Therapy
Charbel Issa P
(2015)
Rescue of the Stargardt phenotype in Abca4 knockout mice through inhibition of vitamin A dimerization.
in Proceedings of the National Academy of Sciences of the United States of America
McClements ME
(2016)
A fragmented adeno-associated viral dual vector strategy for treatment of diseases caused by mutations in large genes leads to expression of hybrid transcripts.
in Journal of genetic syndromes & gene therapy
Patrício MI
(2017)
Inclusion of the Woodchuck Hepatitis Virus Posttranscriptional Regulatory Element Enhances AAV2-Driven Transduction of Mouse and Human Retina.
in Molecular therapy. Nucleic acids
Hickey DG
(2017)
Tropism of engineered and evolved recombinant AAV serotypes in the rd1 mouse and ex vivo primate retina.
in Gene therapy
McClements ME
(2017)
Adeno-associated Virus (AAV) Dual Vector Strategies for Gene Therapy Encoding Large Transgenes.
in The Yale journal of biology and medicine
Yusuf IH
(2018)
A splice-site variant in FLVCR1 produces retinitis pigmentosa without posterior column ataxia.
in Ophthalmic genetics
McClements ME
(2019)
An AAV Dual Vector Strategy Ameliorates the Stargardt Phenotype in Adult Abca4-/- Mice.
in Human gene therapy
Hughes CP
(2019)
AAV2/8 Anti-angiogenic Gene Therapy Using Single-Chain Antibodies Inhibits Murine Choroidal Neovascularization.
in Molecular therapy. Methods & clinical development
Cehajic-Kapetanovic J
(2019)
Electrophysiological verification of enhanced S-cone syndrome caused by a novel c.755T>C NR2E3 missense variant.
in Ophthalmic genetics
McClements ME
(2020)
Assessment of AAV Dual Vector Safety in theAbca4-/- Mouse Model of Stargardt Disease.
in Translational vision science & technology
Piotter E
(2021)
Therapy Approaches for Stargardt Disease.
in Biomolecules
Description | Developing gene therapy for Best disease |
Amount | £100,000 (GBP) |
Funding ID | 1391/92 |
Organisation | Fight for Sight |
Sector | Charity/Non Profit |
Country | United Kingdom |
Start | 10/2013 |
End | 09/2016 |
Description | Developing novel optogenetic tools for the treatment of retinal degenerations |
Amount | $50,000 (USD) |
Organisation | Bayer |
Sector | Private |
Country | Germany |
Start | 12/2018 |
End | 11/2019 |
Description | Developing rhodopsin gene therapy to treat dominant retinitis pigmentosa |
Amount | £296,000 (GBP) |
Funding ID | MR/N00101X/1 |
Organisation | Medical Research Council (MRC) |
Sector | Public |
Country | United Kingdom |
Start | 10/2015 |
End | 09/2018 |
Description | Development and preclinical validation of gene therapy candidates for the treatment of geographic atrophy and age-related macular degeneration |
Amount | £38,000 (GBP) |
Organisation | Gyroscope Therapeutics |
Sector | Private |
Country | United Kingdom |
Start | 05/2016 |
End | 04/2017 |
Description | Development and validation of accurate and reproducible assays for measuring potency of NSR-REP1 and NSR-RPGR vectors |
Amount | £418,000 (GBP) |
Organisation | Biogen |
Sector | Private |
Country | United Kingdom |
Start | 02/2020 |
End | 01/2022 |
Description | Development of AAV CRISPR retinal gene therapy for targeted knockdown in vivo using novel Cas9 variants |
Amount | £60,000 (GBP) |
Organisation | University of Oxford |
Sector | Academic/University |
Country | United Kingdom |
Start | 10/2019 |
End | 09/2020 |
Description | Development of AAV gene therapy for blindness caused by cone-rod dystrophy |
Amount | £319,000 (GBP) |
Funding ID | MR/R000735/1 |
Organisation | Medical Research Council (MRC) |
Sector | Public |
Country | United Kingdom |
Start | 10/2017 |
End | 09/2020 |
Description | Development of CRISPR gene therapy for dominantly inherited retinal diseases |
Amount | £60,000 (GBP) |
Organisation | The Royal College of Surgeons of Edinburgh |
Sector | Charity/Non Profit |
Country | United Kingdom |
Start | 10/2018 |
End | 09/2019 |
Description | Development of a CRISPR gene therapy system for treating inherited retinal degenerations |
Amount | £60,000 (GBP) |
Organisation | The Royal College of Surgeons of Edinburgh |
Sector | Charity/Non Profit |
Country | United Kingdom |
Start | 10/2017 |
End | 09/2018 |
Description | Development of a minicircle gene therapy system for expanding treatment options of inherited retinal diseases |
Amount | £60,000 (GBP) |
Organisation | University of Oxford |
Sector | Academic/University |
Country | United Kingdom |
Start | 10/2019 |
End | 09/2020 |
Description | Development of potency and functionality assays for AAV2.REP1 |
Amount | £214,000 (GBP) |
Organisation | NightstaRx Ltd |
Sector | Private |
Country | United Kingdom |
Start | 10/2014 |
End | 09/2019 |
Description | Gene therapies for age-related macular degeneration and uveitis |
Amount | £1,232,122 (GBP) |
Funding ID | 216593/Z/19/Z |
Organisation | Wellcome Trust |
Sector | Charity/Non Profit |
Country | United Kingdom |
Start | 09/2019 |
End | 08/2025 |
Description | In vivo testing of CRISPR gene therapy vectors for dominantly inherited retinal diseases |
Amount | £60,000 (GBP) |
Organisation | The Royal College of Surgeons of Edinburgh |
Sector | Charity/Non Profit |
Country | United Kingdom |
Start | 10/2019 |
End | 09/2020 |
Description | Investigating ways of inhibiting innate immune responses to retinal gene therapy |
Amount | £100,000 (GBP) |
Funding ID | 5039/40 |
Organisation | Fight for Sight |
Sector | Charity/Non Profit |
Country | United Kingdom |
Start | 10/2017 |
End | 09/2020 |
Description | Optimising gene therapy treatments for dominant retinitis pigmentosa |
Amount | £50,000 (GBP) |
Organisation | The Royal College of Surgeons of Edinburgh |
Sector | Charity/Non Profit |
Country | United Kingdom |
Start | 10/2015 |
End | 09/2016 |
Description | Optimising gene therapy treatments to improve patient safety |
Amount | £50,000 (GBP) |
Organisation | The Royal College of Surgeons of Edinburgh |
Sector | Charity/Non Profit |
Country | United Kingdom |
Start | 10/2016 |
End | 09/2017 |
Description | Photoreceptor function following gene therapy for Choroideremia |
Amount | $50,000 (USD) |
Organisation | Bayer |
Sector | Private |
Country | Germany |
Start | 12/2014 |
End | 11/2015 |
Description | Project Grant: Gene therapy for choroideremia - a Phase II clinical trial |
Amount | £1,660,000 (GBP) |
Funding ID | EME/12/66/35 |
Organisation | Medical Research Council (MRC) |
Sector | Public |
Country | United Kingdom |
Start | 08/2015 |
End | 07/2021 |
Description | Translating retinal gene therapy treatments into clinical trials |
Amount | £540,000 (GBP) |
Organisation | NightstaRx Ltd |
Sector | Private |
Country | United Kingdom |
Start | 02/2016 |
End | 01/2020 |
Title | COMPOSITIONS AND METHODS FOR THE TREATMENT OF STARGARDT DISEASE |
Description | The present disclosure provides an adeno-associated viral (AAV) vector system for expressing a human ABCA4 protein in a target cell, the AAV vector system comprising a first AAV vector comprising a first nucleic acid sequence and a second AAV vector comprising a second nucleic acid sequence; wherein the first nucleic acid sequence comprises a 5' end portion of an ABCA4 coding sequence (CDS) and the second nucleic acid sequence comprises a 3' end portion of an ABCA4 CDS, and the 5' end portion and the 3' end portion together encompass the entire ABCA4 CDS; wherein the first nucleic acid sequence comprises a sequence of contiguous nucleotides corresponding to nucleotides 105 to 3597 of SEQ ID NO: 1; wherein the second nucleic acid sequence comprises a sequence of contiguous nucleotides corresponding to nucleotides 3806 to 6926 of SEQ ID NO: 1; wherein the first nucleic acid sequence and the second nucleic acid sequence each comprise a region of sequence overlap with the other; and wherein the region of sequence overlap comprises at least about 20 contiguous nucleotides of a nucleic acid sequence corresponding to nucleotides 3598 to 3805 of SEQ ID NO: 1. Also provided are uses of AAV vector systems in the prevention or treatment of disease. |
IP Reference | WO2019195726 |
Protection | Patent granted |
Year Protection Granted | 2019 |
Licensed | Yes |
Impact | The AAV.ABCA4 dual vector has been licensed by the University of Oxford to Nightstar Therapeutics (now part of Biogen Inc.). |
Title | DUAL OVERLAPPING ADENO-ASSOCIATED VIRAL VECTOR SYSTEM FOR EXPRESSING ABC4A |
Description | The present invention provides an adeno-associated viral (AAV) vector system for expressing a human ABCA4 protein in a target cell, the AAV vector system comprising a first AAV vector comprising a first nucleic acid sequence and a second AAV vector comprising a second nucleic acid sequence; wherein the first nucleic acid sequence comprises a 5' end portion of an ABCA4 coding sequence (CDS) and the second nucleic acid sequence comprises a 3' end portion of an ABCA4 CDS, and the 5' end portion and the 3' end portion together encompass the entire ABCA4 CDS; wherein the first nucleic acid sequence comprises a sequence of contiguous nucleotides corresponding to nucleotides 105 to 3597 of SEQ ID NO: 1; wherein the second nucleic acid sequence comprises a sequence of contiguous nucleotides corresponding to nucleotides 3806 to 6926 of SEQ ID NO: 1; wherein the first nucleic acid sequence and the second nucleic acid sequence each comprise a region of sequence overlap with the other; and wherein the region of sequence overlap comprises at least about 20 contiguous nucleotides of a nucleic acid sequence corresponding to nucleotides 3598 to 3805 of SEQ ID NO: 1. Also provided are uses of AAV vector systems in the prevention or treatment of disease. |
IP Reference | WO2017216560 |
Protection | Patent granted |
Year Protection Granted | 2017 |
Licensed | Yes |
Impact | The AAV.ABCA4 dual vector has been licensed by the University of Oxford to Nightstar Therapeutics (now part of Biogen Inc.). |
Description | Lecture given to peers and members of the House of Commons Joint Scientific Committee, London |
Form Of Engagement Activity | A talk or presentation |
Part Of Official Scheme? | No |
Geographic Reach | National |
Primary Audience | Policymakers/politicians |
Results and Impact | Lecture on gene therapy for retinal disease. |
Year(s) Of Engagement Activity | 2014 |
Description | Media coverage |
Form Of Engagement Activity | A press release, press conference or response to a media enquiry/interview |
Part Of Official Scheme? | No |
Geographic Reach | International |
Primary Audience | Media (as a channel to the public) |
Results and Impact | Extensive media coverage of our research work in retinal gene therapy, electronic retinal implants and intraocular robotic surgery - see link: www.ndcn.ox.ac.uk/research/clinical-ophthalmology-research-group/public/media Public communication |
Year(s) Of Engagement Activity | 2011,2012,2013,2014,2015,2016,2017,2018,2019,2020,2021,2022 |
URL | http://www.ndcn.ox.ac.uk/research/clinical-ophthalmology-research-group/public/media |
Description | NIHR Oxford Biomedical Research Centre public lectures, symposia and open days |
Form Of Engagement Activity | Participation in an open day or visit at my research institution |
Part Of Official Scheme? | No |
Geographic Reach | Regional |
Primary Audience | Public/other audiences |
Results and Impact | NIHR Oxford Biomedical Research Centre public lectures, symposia and open days for the benefit of the general public, patients and carers. A number of email enquiries from patients regarding treatment potential. |
Year(s) Of Engagement Activity | 2010,2011,2012,2013,2014,2015,2016,2017,2018,2019,2020,2022 |