The Vector
Volume 7, Issue 1: January 2018
Editorial Team
Guohua Yi, PhD - Editor, The Vector
Phillip Doerfler, PhD - Associate Editor, The Vector
Melvin Rincon, MD, PhD - Junior Editor, The Vector
Inside This Issue
President's Message
Breaking Through
Society News
Public Policy
Industry News
President's Message
Dear Colleagues,
2017 continued to be a landmark year for gene therapy with the announcement on December 19, that the FDA approved Luxturna (voretigene neparvovec-rzyl) for the treatment of patients with confirmed biallelic RPE65 mutation-associated retinal dystrophy. Luxturna developed by Spark Therapeutics uses an adeno-associated virus (AAV) vector to deliver the normal human RPE65 gene to retinal cells. This was a particular milestone as Luxturna is not only the first directly administered in vivo gene therapy approved in the United States but also the first approval to target a genetic disease and the first to use AAV. This will likely be the first of many approvals using AAV as there are a number of other AAV products currently in clinical testing in eye gene therapy and in other diseases such as hemophilia. Dr. Kathy High who will deliver the George Stamatoyannopoulos lecture at the upcoming Annual Meeting will provide an overview of the development and future directions of AAV gene therapy strategies to treat genetic diseases.
In the spirit of New Year’s resolutions, ASGCT is developing new initiatives for 2018. The Board of Directors recently passed a budget that will allow for additional funds to be allocated for patient education and supporting our trainee members. In 2017, ASGCT collaborated with the Hemophilia Federation of America for a series of two webinars. This year, the Society will continue this effort with a renewed investment in resources for educating the patient and patient advocate community about gene therapies that are approved or in clinical trials. Additionally, ASGCT plans to fulfill the commitments made in the 2016 strategic plan with regard to supporting and investing in the next generation of gene and cell therapy researchers with input from the Trainee Council. Expanding on current trainee support, the Society will bring the number of Excellence in Research Awards from six at $1,000 each to 15. The Society will add funding and for up to seven fellowships or trainee exchange grants and seven career development grants valued at $25,000 which will correspond to the primary abstract categories to ensure coverage of all areas in our field.
I urge you all to make plans to attend the Annual Meeting in Chicago, IL, May 16-19, 2018. Visit the Annual Meeting website to register and book your stay at the Hilton Chicago. Additionally, the deadline for abstract submission is January 31, at 5pm Central. You will not want to miss out on the opportunity to share your research at the Annual Meeting. Associate Members who are first and presenting authors of an abstract receive free registration. Please also consider submitting a nomination for an ASGCT Award. Nominations for the Outstanding Achievement Award, Outstanding New Investigator Awards, and the Sonia Skarlatos Public Service Award must be submitted by tomorrow, January 19.
Breaking Through
Single-Dose Gene-Replacement Therapy for Spinal Muscular Atrophy
Mendell JR, Al-Zaidy S, Shell R, et al. Single Dose Gene-Replacement Therapy for Spinal Muscular Atrophy. N Engl J Med 2017; 377:1713-22.
Summary written by Jerry R Mendell MD & Brian K Kaspar, PhD
Spinal muscular atrophy type 1 (SMA1) is the most common genetic cause of death in infants resulting from bi-allelic mutations of the survival motor neuron gene (SMN1, telomeric), located on chromosome 5q13.2. The deficient gene product is survival motor neuron (SMN) protein causing SMA1. A centromeric, duplicated homologue is present in humans, referred to as SMN2; a mutation in exon 7 results in an unstable transcript. Occasionally alternative splicing permits expression of low levels of SMN2, but not enough to prevent disease. Overall the disease incidence of SMA1 is about 1 in 6000 live births. The natural history of SMA1 is well described. During infancy there is marked hypotonia, failure to achieve motor milestones, inability to sit without support, poor suck and swallow, and death or the need for mechanical ventilation in 92% of infants by age 2.1
In a gene replacement clinical trial at Nationwide Children’s Hospital, 15 patients with SMA1 received a single dose of intravenous adeno-associated virus serotype 9 (AAV9) carrying SMN encoding the missing SMN protein.2 Three of the patients (Cohort 1) received a low dose of vector (6.7×1013 vg per kilogram of body weight), and 12 (Cohort 2) received a high dose (2.0×1014 vg per kilogram). Vector was delivered over 60 minutes. As a result of serum aminotransferase elevations in Patient 1 (Cohort 1), all remaining patients received oral prednisolone at a dose of 1 mg per kilogram per day for approximately 30 days, starting 24 hours before the administration of gene vector.
The primary outcome for this trial was safety. The secondary outcome was the time until death or the need for ventilatory assistance exceeding 16 hours per day continuously for 14 days in the absence of an acute, reversible illness. Exploratory outcomes included motor-milestone achievements (particularly, sitting unassisted) and CHOP INTEND scores.3, 4
All patients in this trial reached at least 20 months of age and did not require permanent mechanical ventilation compared to only 8% of the patients in a historical cohort.1 All patients in cohorts 1 and 2 had increased CHOP INTEND scores from baseline and maintained these improvements during the study. In Cohort 2 increases were seen as early as 1 month (9.8 points) and 3months (15.4 points) (P<0.001). A total of 11 of 12 patients in cohort 2 were able to sit unassisted for at least 5 seconds, 10 for at least 10 seconds, and 9 for at least 30 seconds. A total of 11 achieved head control, 9 could roll over, and 2 were able to crawl, pull to stand, stand independently, and walk independently. Eleven patients attained the ability to speak. No patients in the historical cohorts had achieved any of these motor milestones and rarely had achieved the ability to speak.5, 6 Maintaining pulmonary and nutritional independence was seen in the majority of subjects in Cohort 2.
Adverse events (AEs) related to AAV gene replacement therapy were uncommon. Serious AEs were limited to elevated serum aminotransferase levels without other liver enzyme abnormalities in two patients; two other patients had elevations that did not reach the cutoff for the definition of SAEs (i.e., remained below 10 times the normal range). Elevations in liver enzymes were attenuated by prednisolone treatment.
In summary, viral vector containing DNA coding for SMN in patients with SMA1 resulted in extended survival, improved motor function, and increased scores on the CHOP INTEND scale to levels that had not previously been observed in this disease. No clinical regression was seen in follow up for up to 2 years. There were very few safety concerns despite delivery of high titers of virus. There was an overall observation that younger and less affected infants with SMA show a better response to gene delivery. This will be an important finding for design of future clinical gene therapy studies.
References
1. Finkel RS, McDermott MP, Kaufmann P, et al. Observational study of spinal muscular atrophy type I and implications for clinical trials. Neurology 2014; 83: 810-7.
2. Mendell JR, Al-Zaidy S, Shell R, et al. Single-Dose Gene-Replacement Therapy for Spinal Muscular Atrophy. N Engl J Med 2017; 377:1713-22.
3. Glanzman AM, Mazzone E, Main M, et al. The Children’s Hospital of Philadelphia
Infant Test of Neuromuscular Disorders (CHOP INTEND): test development and reliability. Neuromuscul Disord 2010;20: 155-61.
4. Glanzman AM, McDermott MP, Montes J, et al. Validation of the Children’s Hospital of Philadelphia Infant Test of Neuromuscular Disorders (CHOP INTEND). Pediatr Phys Ther 2011; 23: 322-6.
5. De Sanctis R, Coratti G, Pasternak A, et al. Developmental milestones in type I spinal muscular atrophy. Neuromuscul Disord 2016; 26: 754-9.
6. Bach JR, Gupta K, Reyna M, Hon A. Spinal muscular atrophy type 1: prolongation of survival by noninvasive respiratory aids. Pediatr Asthma Allergy Immunol 2009; 22: 151-61.
Mapping the Structural Determinants Required for AAVrh.10 Transport across the Blood-Brain Barrier
Albright BH, Storey CM, Murlidharan G, et. al. Mapping the Structural Determinants Required for AAVrh.10 Transport across the Blood-Brain Barrier Mol Ther. 2017 Oct 26. pii: S1525-0016(17)30533-6.
Summary written by Aravind Asokan
The blood brain barrier (BBB) is composed of endothelial cell tight junctions along with associated astrocytic end-feet and pericytes. It functions to prevent large or hydrophilic molecules, as well as the vast majority of all drugs and most microbial pathogens, including small viruses from entering the brain. As a barrier to CNS gene delivery across the vasculature, the BBB limits the dosage of AAV vectors that can enter the brain. For example, when AAV1 is injected intravenously, it is unable to cross the vascular wall and is therefore largely sequestered within the brain microvasculature. Nevertheless, some natural AAV isolates can overcome this obstacle. For instance, earlier work by Guangping Gao’s group and others characterizing the abilities of various AAV serotypes to cross the BBB, has shown that AAVrh.10, along with several other natural isolates, demonstrates the ability to cross the BBB and mediate robust transduction of neurons and glia (along with endothelial cells) globally throughout the brain.
Our goal was to achieve a better understanding of how some AAV serotypes are able to cross the BBB to transduce cells in the CNS while others cannot. We hypothesized that specific structural determinants exist on the AAVrh.10 capsid that enable transvascular transport across the BBB. To test this hypothesis, we adapted a library-based approach. Despite their contrasting phenotypes in regards to crossing the BBB, the capsid genes of AAV1 & AAVrh.10 actually share an ~85% sequence similarity. We took advantage of this and used DNA shuffling to generate a library of AAV1/rh.10 chimeric capsids. We hypothesized that screening variants from this library would allow us to identify the structure-function correlates for BBB traversal.
We generated a panel of a few dozen variant capsid sequences isolated from this library, which displayed substantial sequence diversity at the DNA and amino acid levels. Computational analyses, including sequence alignments, phylogenetic tree construction and homology-based structural modelling were used to further characterize these capsid sequences and to broadly categorize them along a spectrum of more AAV1-like to more AAVrh.10-like. Informed by this data, we selected a subset of structurally diverse variants to screen in vivo for their ability to cross the BBB following systemic administration via tail vein injections in mice. Each vector screened was produced packaging a CBh-scGFP reporter transgene and injected at a dose of 5 x 1011 viral genomes (vg) per mouse. Immunostaining of GFP reporter transgene expression in the cerebral cortex, performed at three weeks post-injection, revealed two variants, AAV1R6 & AAV1R7, which demonstrate the ability to cross the BBB and transduce cells in the CNS, such as neurons and glia, within the brain parenchyma. We also observed that the more AAV1-like chimeras, phenocopy AAV1, showing transduction restricted to the vasculature, and additionally found several intermediate phenotypes.
We then employed a rational, structure-based approach to narrow and functionally map a minimal number of AAVrh.10-derived amino acid residues that enable crossing the BBB and impart CNS tropism. We eliminated any residues that were not exposed on the capsid surface, including several within the AAV capsid protein
VP1/2 unique N-termini, as well as those within the conserved β-strand E on the monomer. We also excluded any residues located within the pore-forming loop at the 5-fold axis of symmetry, as this region is important for capsid assembly and packaging/release of viral genomes, and is not implicated in influencing either tropism or antigenicity. We were able to hone in on a minimal footprint, that hinges on variable region-I (VR-I) on the AAVrh.10 capsid protein that was sufficient for crossing the BBB. We then rationally engineered a new capsid, AAV1RX, by grafting this footprint from AAVrh.10 onto the AAV1 capsid. Structural models of the AAV1RX capsid and its various axes of symmetry, along with stereographic roadmap projection of the topology at the capsid surface, show that these residues are surface-exposed and manifest as clusters near the depression at the 2-fold axis of symmetry and on the shoulders at the base of the protrusions at the three-fold axis of symmetry, a region known to influence tropism and antigenicity.
To validate our engineered AAV1RX capsid, we packaged a CBh-scGFP reporter transgene and it was administered at a dose of 5 x 1011 vg via tail vein injection in mice. Immunostaining at three weeks post injection showed that AAV1RX phenocopies AAV1R6 & AAV1R7, mediating robust neuronal transduction and moderate glial transduction in the absence of endothelial cell transduction across multiple brain regions, including the cortex, hippocampus, thalamus, striatum and amygdala. These trends were additionally corroborated by quantifications of cellular transduction. Furthermore, AAV1RX is also detargeted from the liver with low copy numbers observed for the vector in peripheral tissues, compared to parental capsids.
The engineered AAV1RX variant and the footprint when grafted onto other AAV strains might prove to be useful additions to the clinical AAV arsenal. The ability to cross the BBB, widespread CNS transduction and improved neuronal specificity are favorable characteristics that could facilitate efficient gene transfer, silencing and/or gene editing modalities to treat disorders such as Alzheimer disease, Friedrich’s Ataxia, Spinal muscular atrophy, Huntington’s disease or amyotrophic lateral sclerosis amongst others. Furthermore, the ability to detarget peripheral organs such as the liver could improve the safety profile of such vectors for CNS gene transfer applications using a systemic route of administration. Continued efforts to map structure-function correlates of the AAV tropism and elucidating the mechanism(s) underlying BBB traversal could significantly improve vector design for a range of neurological disorders.
Society News
ASGCT Abstract Deadline Less Than Two Weeks Away!
Make sure to submit your abstract to ASGCT by January 31, 2018 at 5 p.m. CT! Don’t miss the opportunity to present your science at the 21st Annual Meeting in Chicago, IL, May 16-19, 2018. Associate Members who are first and presenting author of an abstract receive free registration to the Annual Meeting! Submit your abstract and learn more by visiting the Annual Meeting website.
Register for the Annual Meeting and Pre-meeting Workshops
Housing for the 21st Annual Meeting is now available at the Chicago Hilton. Book your room today by visiting the Annual Meeting housing website. We encourage you to reserve your room early as the ASGCT housing block will likely sell out.
Registration for the 21st Annual Meeting is now open. Visit ASGCT's Annual Meeting website for group and individual registration rates. Please also consider registering for a pre-meeting workshop taking place on May 15, 2018. Pre-meeting workshop topics include Gene Editing, Commercialization, and CAR T Cell Therapies. Early registration will be available until April 25, 2018.
FACT-ASGCT Webinar: Maintaining Commercial Cell Therapy Products Chain of Custody
On February 14 at 11 a.m. ET, this webinar will discuss the importance of maintaining chain of custody for personalized cellular therapy products in an increasingly complex environment. Presenters will be Dr. Solveig Ericson, Executive Director of the CAR-T Program at Novartis Pharmaceuticals Corporation, Dr. Sarah Nikiforow of the Dana Farber Cancer Institute / Cell Manipulation Core Facility, and Dr. Rayne Rouce of the Baylor College of Medicine, Stem Cell Transplant Program, Texas Children's Hospital and Houston Methodist Hospital. Registration is available now.
Stem Cell Clonality and Genome Stability Retreat
This is the 13th anniversary of the start of the Stem Cell Clonality and Genome Stability Retreat series and each of the previous retreats have been great successes. Our last meeting in the beautiful Florence, Italy was “sold out” and garnered outstanding feedback. This meeting brings together international experts discussing state-of-the-art gene transfer and gene therapy clinical applications, new vector approaches, and insertional & genome biology. This meeting is limited in size to 100 participants to foster an interactive format. Please register here.
Public Policy
FDA Framework for Regenerative Medicine
The FDA announced a comprehensive regenerative medicine policy framework in November, outlined in two finalized guidance documents, and two draft guidance documents. The two draft guidance documents provide important information to spur and streamline the development of innovative regenerative therapies. Of note, the guidance on expedited programs for regenerative medicine therapies indicates that gene therapies, including genetically modified cells, which lead to a durable modification of cells or tissues, are eligible for consideration for the regenerative medicine advanced therapy (RMAT) designation. The draft guidance documents both have 90-day comment periods. The two final guidance documents clarify the FDA’s interpretation of the risk-based criteria for manufacturers to use to determine whether a product is subject to the FDA’s pre-market review.
One-Year Anniversary Congressional Hearings on 21st Century Cures Act
The House Energy & Commerce Subcommittee on Health and the Senate Health, Education, Labor, and Pensions Committee both held hearings in December in which the FDA and NIH provided updates on the implementation of the 21st Century Cures Act. Provisions affecting regenerative medicine that have been implemented include:
- The establishment of an Oncology Center of Excellence at the FDA, which has already led to approvals of two gene therapy products targeting rare cancers.
- The launching of the Regenerative Medicine Innovation Project, which awarded its first research funds in October.
- The FDA’s expediting of reviews of certain regenerative medicine products (see Framework for Regenerative Medicine).
- The formation of the Next Generation Researchers Initiative by the NIH, which aims to increase research awards to early-stage and mid-career investigators, which have declined since 2003.
Despite these accomplishments, NIH Director Francis Collins, MD said that the decline in NIH funding has resulted in the NIH only being able to fund approximately 19 percent of research applications. While the 21st Century Cures Act authorized funding increases to FDA and NIH, the actual funding level is dependent on annual appropriations.
Senate HELP Committee Hearing on Gene Editing
In November, the Senate Committee on Health, Education, Labor, and Pensions (HELP) held a hearing on gene editing technology. They heard testimony from experts in the field about scientific, regulatory, and ethical aspects of the topic. Two of the three invited witnesses at the hearing are members of ASGCT—Matt Porteus, MD, PhD, a member of the ASGCT Board of Directors, and Katrine Bosley. Speakers informed the committee about gene editing technologies, which are in the human clinical trial phase of research with a report of the first in vivo gene editing in the United States released the day after the congressional hearing. All three witnesses indicated that current, robust regulatory mechanisms are in place to ensure the safe use of gene editing for its intended medical purposes.
Tax Legislation Effects on the Field
The final version of the Congressional tax overhaul affects two issues on which ASGCT has issued positions. The Orphan Drug Tax Credit (ODTC) was cut in half, reducing the credit drug developers can claim to 25 percent of the qualified costs of clinical research and drug testing of orphan drugs. The House version of the bill would have completely repealed the tax credit, and the Senate version would have reduced the ODTC rate to 27.5 percent. Because the tax credit provides incentives for the development of therapies for rare diseases, ASGCT supported its retention through a letter to Sen. Hatch, chairman of the Senate Finance Committee and member of the reconciliation committee.
The recently passed tax legislation did not include a tax on tuition waivers for graduate students that the House of Representatives version of the bill had threatened. Graduate students will remain taxed only on the monetary stipends they receive from their academic institutions, rather than additionally counting tuition waivers as income. ASGCT strongly opposed the tax on tuition waivers, which would have been an excessive financial burden to graduate students, who play a crucial role in developing cutting-edge science.
ASGCT a Stakeholder at Cell Therapy Liaison Meeting
The International Society for Cellular Therapy annually holds meetings between the FDA Center for Biologics Evaluation and Research and over 20 invited stakeholder organizations. ASGCT will have two representatives at the Cell Therapy Liaison Meeting on January 30 in Bethesda, MD. These meetings enable the cell therapy community to discuss specific issues of concern with CBER and provide updates on recent developments in field.
ASGCT Responds to CMMI Plan to Test New Pricing and Payment Models
ASGCT submitted a comment in November to a request for information from the Center for Medicare and Medicaid Innovation (CMMI), which requested input on its plans to test models in eight focus areas, including new pricing and payment model designs for prescription drugs. ASGCT comments included a recommendation that CMMI consider testing existing and new payment methodologies for gene and cell therapies to ensure access to care to these durable and potentially curative treatments. Additionally, ASGCT recommended that if outcomes-based testing models for FDA-approved gene therapies are created, CMMI establishes a process to obtain input from experts in the field to contribute to identifying the criteria that will define successful outcomes, as well as the anticipated time frame for such criteria to be attained.
Industry News
ASGCT Celebrates FDA Approval of Luxturna
On December 19, 2017, the FDA approved Voretigene Neparvovec (Luxturna), an innovative one-time gene therapy treatment used to improve vision in patients with established genetic vision loss due to Leber congenital amaurosis or retinitis pigmentosa, both inherited retinal diseases (IRD). As the first AAV viral vector product approved for clinical use in the United States, Luxturna represents a historic landmark, not only in the field of gene therapy, but in the history of medicine.
Read ASGCT's statement