Current Clinical Applications Of In Vivo Gene Therapy With AAVs Part 6

Pompe Disease

Pompe disease is a glycogen storage disorder that leads to glycogen accumulation in muscle and motoneurons.235,236 Lack of acid alpha-glucosidase (GAA) activity in patients with severe/early onset results in a clinical pathology that includes profound weakness hypotonia and cardiorespiratory failure.237 

Pompe disease is a degenerative disease that affects memory, but we should not overemphasize its negative impact on memory. Instead, we should look at this disease positively and seek effective treatments to improve the quality of life of patients.

As we know, memory is a very complex cognitive function that involves complex interactions between multiple areas of the brain and neurons. Pompe disease is mainly caused by the gradual death of neurons in the brain. Therefore, this disease does affect the formation and retention of memory.

However, we must realize that memory does not completely determine a person's identity and quality of life. Although Pompe disease affects patients' cognitive abilities and self-management abilities, they can still have a meaningful life. Social interaction, sports, and artistic creation are all ways to help Pompe disease patients maintain a positive attitude toward life.

In addition, the families and communities of Pompe disease patients should give them full care and support. Care and support are like sunshine, which can help patients believe that they still have value and dignity, and bring warmth and encouragement to their hearts.

In summary, Pompe disease is undoubtedly a frustrating disease, but we should help patients build a positive mindset, improve their quality of life, keep their faith, and embrace life through a positive attitude, careful care, and scientific treatment methods. It can be seen that we need to improve memory, and Cistanche can significantly improve memory because Cistanche can also regulate the balance of neurotransmitters, such as increasing the levels of acetylcholine and growth factors, which are very important for memory and learning. In addition, Cistanche can also improve blood flow and promote oxygen delivery, which can ensure that the brain obtains sufficient nutrition and energy, thereby improving brain vitality and endurance.

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Recently, newborn screening efforts have discovered a significantly higher incidence of up to 1:9,500, making gene therapy a rational solution for presymptomatic treatment. For Pompe disease, four-phase I/II gene therapy studies have achieved approval from the FDA. 

Corti et al.238 and Byrne et al.239 conducted a first-in-human trial injecting AAV1-cytomegalovirus (CMV)-GAA into the diaphragms of nine patients with ventilatory insufficiency to correct the respiratory dysfunction characteristic of early-onset Pompe disease (EOPD). 

The results indicated that the vector was both safe to use and effective at improving ventilatory performance in all subjects.238,240,241 Another clinical trial from the University of Florida is currently being conducted in patients with late-onset Pompe disease (LOPD). 

The study evaluates the ability to repeat the administration of AAV (rAAV9-DES-hGAA) after a period to maintain therapeutic levels of GAA in adult Pompe patients 242 (ClinicalTrials.gov: NCT02240407). 

Preliminary results suggest that pharmacological modulation of the immune system using rituximab and sirolimus, before and at the time of AAV dosing, prevents the formation of antibodies and allows for repeated AAV dosing. With early intervention due to newborn screening, this is an important observation for LSDs affecting the muscle and the liver, where somatic growth may cause a decline in genome copy number. 

The University of Florida team, in collaboration with an NIH Clinical Center team led by Dr. Bönneman, is also conducting a study to evaluate the safety and efficacy of an intravenous dose of AAV-GAA in children with EOPD. 

Patients enrolled in this study will receive the same immunomodulation regimen used in the LOPD study to manage immune responses to AAV and GAA. In addition to the work conducted at the University of Florida, a few other programs have initiated clinical programs to test their own AAV vectors in patients with Pompe disease. 

Spark Therapeutics has been approved to enroll in phase I/II vector-mediated liver gene transfer for GAA in LOPD. This approach relies on the stable expression of GAA in the liver achieved via AAV vector-mediated gene transfer, resulting in cross-correction in peripheral organs with no evident immunogenicity against the transgene (ClinicalTrials.gov: NCT04093349). 

The preclinical data revealed promising results, suggesting sustained plasma levels of GAA.243 10 months postdosing, all GAA knockout (Gaa/) mice showed decreased glycogen accumulation; increased survival; and improved cardiac, respiratory, and muscle function compared to wild-type mice. 

In comparison to ERT, the current standard of care for Pompe disease, SPK-3006 was also more effective at breaking down and clearing excess glycogen build-up in refractory muscle groups typically mute to the effects of ERT (Mendoza, 2018, International Congress of the World Muscle Society, conference).243 

First-in-human clinical studies are currently underway at the University of California Irvine Health (ClinicalTrials.gov: NCT04093349). Asklepios Biopharmaceutical has also been approved to enroll in a phase I/II open-label trial to assess the safety and determine the bioactivity of ACTUS-101 (AAV2/8LSPhGAA) at two dose levels in human subjects with LOPD. 

With the use of a liver-specific promoter, this AAV vector was manufactured to express GAA specifically in the liver accompanied by GAA secretion and receptor-mediated uptake of GAA in the cardiac and skeletal muscle. 

The central hypothesis is that continuous GAA production from a liver depot will provide more benefit than ERT in Pompe disease (ClinicalTrials.gov: NCT03533673). On January 22, 2019, the first patient in the phase I/II clinical study was dosed with ACTUS-101.244

Gaucher Disease

Gaucher disease, the most common of the LSDs, is an autosomal recessive LSD caused by a deficiency in lysosomal enzyme acid beta-glucosidase (glucocerebrosidase). 

Although heterogenous in its presentation based on type, the main clinical effects are hepatosplenomegaly, neurodegeneration, bone disease, and pulmonary complications.245 There have been two ex vivo gene replacement trials to date for Gaucher disease. 

With the use of retroviral transduction of peripheral blood or CD34+ cells, Dunbar and Kohn246 examined the safety of a G1Gc vector that uses the viral long terminal repeat (LTR) promoter to express the human glucocerebrosidase cDNA.247 

The study did result in transient low-level expression of corrected cells, however too low to result in any clinical benefit or increased glucocerebrosidase enzyme activity.248 

In the second, currently active gene-therapy trial, AVROBIO is using an ex vivo lentiviral-based gene-therapy approach designed to result in a stable integration of the desired genes into patient-derived hematopoietic stem cells (ClinicalTrials.gov: NCT04145037). 

Preclinical trials showed positive results in lentiviral vector integration into parent stem cells and effective replication of integrated progeny cells.249

Fabry Disease

Fabry disease is characterized by deficient activity of a-galactosidase A (a-Gal A), resulting in the accumulation of glycolipids (globotriaosylceramide [Gb3] and globotriaosylsphingosine [LysoGb3]) in various tissues. 

Clinical manifestations include progressive kidney failure, heart disease, cerebrovascular disease, skin lesions, and other abnormalities.250,251 Although ERT is the current standard of care for patients with Fabry, it does have its limitations producing increased interest in gene replacement therapies.252,253 Of the five gene replacement studies to date, two of them use an ex vivo approach (AVROBIO and University Health Network, Toronto), whereas two others use an in vivo approach (Sangamo Therapeutics and Freeline Therapeutics). 

AVROBIO's vector (AVR-RD-01) is derived from hemopoietic stem cells to which the gene encoding AGA is added in an ex vivo process using a lentiviral vector. In the ongoing phase I/II clinical trial (ClinicalTrials.gov: NCT03454893), interim data showed all four patients dosed in the phase I portion displayed increased AGA enzyme activity levels above the levels of patients with classical Fabry (ESGCT Annual Meeting abstract, Lausanne, 2018).251,254 Preclinical studies for the University Health Network's lentiviral product also showed promising results.255 

University Health Network's lentiviral a-Gal A transduced stem cell therapy is currently being tested at several Canadian clinical trial sites (ClinicalTrials.gov: NCT02800070) (ASGCT Annual Meeting abstract, San Diego, 2010). 

Another first-in-human phase I/II trial sponsored by Sangamo Therapeutics uses an AAV vector (rAAV2/6) to produce the deficient enzyme at clinically significant levels. ST-920 is an AAV vector encoding the cDNA for human a-Gal A with a liver-specific promoter designed to enable a patient's liver to produce a continuous supply of the a-Gal A enzyme (ClinicalTrials.gov: NCT04046224). 

The constant production is anticipated to reduce Gb3 and LysoGb3.251,256 Similarly, Freeline Therapeutics is using an AAV vector (rAAV8) with a liver-specific promoter to produce sustained high levels of a-Gal A. 

Preliminary data on the starting dose in the dose-escalation study reported a 3- to 4-fold increase in plasma a-Gal A activity by week 4 postdose and was sustained through the data cutoff.251 

On March 10, 2020, the European Commission granted orphan drug designation for FLT190 for the treatment of Fabry disease, based on a positive opinion from the Committee for Orphan Medicinal Products of the European Medicines Agency.257 4D Molecular Therapeutics is also pursuing a gene therapy study that is recently open for enrollment.

MPS Type III (MPS III)-Sanfilippo Syndrome

MPS III, also known as Sanfilippo syndrome, is a progressive disorder characterized by the accumulation of glycosaminoglycan in neural cells.254 MPS III primarily affects the CNS, resulting in neurodegeneration, progressive intellectual disability, and developmental regression. 

As the brain is the most affected organ with MPS III, brain-targeted gene replacement therapies have become increasingly studied for both MPS IIIA and MPS IIIB by different sponsors using similar approaches. LYSOGENE, a biotechnology company from France, used AAVrh.10 to carry the human SGSH and SUMF1 cDNAs for the treatment of MPS II. 

The therapeutic vector AAVrh.10-hMPS3A was administered to four children in a phase I first-in-human trial via intracerebral injections. All four patients were followed for a year postdose. 

The results of the trial proved the method of administration to be safe for direct AAV vector delivery into the CNS. Neurocognitive evaluations suggested a cognitive benefit in the youngest child, whereas a more limited benefit in the three older patients.254,258 uniQure Biopharma B.V., also using intracranial injections, administered a rAAV2/5 vector encoding human a-N-acetylglucosaminidase (NAGLU) in seven children for the treatment of MPS IB. 

Following administration, NAGLU activity in the CNS was found to be increased from baseline with sustained enzyme production by brain cells. All patients displayed improvements in their neurocognitive evaluations with the youngest functioning close to that of a healthy child. 

These results suggest that this approach could prevent or slow cognitive decline in children with MPS IB.259 Additional in vivo and ex vivo phase I/II gene-therapy clinical trials for MPS are listed in Table 1.

NCLs

NCLs are a group of inherited, autosomal, progressive childhood neurodegenerative disorders characterized clinically by dementia, epilepsy, and vision loss through retinal degeneration. 

NCLs are caused by an accumulation of ceroid lipofuscin in the neuronal cells in the brain and the retina. To date, there are 13 forms of NCLs, each having distinct defects in genes encoding proteins in the lysosomal system.260–262 Currently, there are no treatments approved for NCLs. 

To find an efficacious therapy for NCL, novel gene replacement strategies have been explored. Worrall et al.263 developed an AAV serotype 2 vector expressing the human CLN2 cDNA (AAV2CUhCLN2) and administered the vector in the CNS of 10 children with late infantile NCL (LINCL).262 

In comparison to the control subjects, disease progression assessed by CNS imaging was slower, although not statistically significant, showing reduced gray matter and ventricular volume. 

Notably, results from the modified Hamburg scale postdose demonstrated significantly slower functional decline compared to the control group.262,263 Also with the use of an in vivo approach, Cain et al. 

264 developed a scAAV9 vector expressing the hCLN6 gene under the control of a CB hybrid promoter.262 scAAV9.CB.hCLN6 was injected intrathecally into the CSF of 4-year-old NHPs and intracerebroventricularly (i.c.v.) into mice. 

High transgene expression was found throughout the brain and spinal cord of the NHPs with very few lab abnormalities. The i.c.v. injection administered to the mice also exhibited promising results, including prevention of classic CLN6 brain disease pathology, correction of behavioral deficits, and increased survival. 

Taken together, the results indicate the efficacy and safety of scAAV9.CB.hCLN6.262,264 This approach was adopted by Amicus Therapeutics and is currently being studied clinically in patients with Batten disease (ClinicalTrials.- gov: NCT02725580). Additional in vivo phase I/II gene-therapy clinical trials for NCLs are listed in Table 4.

Conclusions

The advent of advanced therapeutics in lysosomal storage disease provides new opportunities for patients and hopefully transformative therapeutic opportunities. 

As the field matures, we hope that additional safe and effective therapeutic options will be widely available. Challenges still exist for establishing a network of qualified providers to administer gene-therapy medicinal products.

ACKNOWLEDGMENTS

This work was supported by US National Institutes of Health grant K08 HL 146991-01 (L.A.G. and by a Canadian Institute of Health Research grant 18059 (J.P.T.)

AUTHOR CONTRIBUTIONS

All authors contributed to the writing of this article.

DECLARATION OF INTERESTS

I received consulting fees for AveXis, Amicus, Neurogene, Affinia Therapeutics, and Novartis. S.J.G. has received royalty and/or consulting income from Asklepios Biopharma, Neurogene, Abeona Therapeutics, Sarepta Therapeutics, Vertex Pharmaceuticals, LYSOGENE, and Amicus Therapeutics. L.A.G. holds intellectual property related to the use of a factor VIII variant protein for gene therapy, has served as a consultant for Pfizer, and is the clinical principal investigator for ongoing hemophilia A and B phase I/II trials sponsored by Spark Therapeutics/Roche and Pfizer, respectively.

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