Mass General Brigham Gene and Cell Therapy Researchers Present Key Findings at ASGCT

Leaders and investigators from the Mass General Brigham Gene and Cell Therapy Institute, a hub of innovation dedicated to accelerating groundbreaking research, conducting clinical trials and developing FDA-approved treatments in gene and cell therapy, will present at the 2024 American Society of Gene and Cell Therapy (ASGCT) Annual Meeting, held May 7-11, in Baltimore.

ASGCT is the premier event dedicated to gene and cell therapy research, innovation, clinical trials and research discoveries. Presentations from Mass General Brigham investigators include developments and work with RNA therapeutics, gene editing in glioma, neurodegenerative diseases such as molybdenum cofactor deficiency (MoCD), extracellular vesicle-associated adeno-associated viral vectors and more.

“Academic medical centers, such as ours, are uniquely positioned to accelerate gene and cell therapies, with patients in mind and at the center of all our research. That is exactly what these ASGCT presentations are demonstrating,” said Nathan L. Yozwiak, PhD, Head of Research at the Mass General Brigham Gene and Cell Therapy Institute. “I am proud to see such groundbreaking work being presented by our outstanding investigators — and we look forward to continuing to support their work, from preclinical studies to first-in-human trials and beyond.”

The Mass General Brigham Gene and Cell Therapy Institute was established in 2022 to fuel the discovery and development of targeted, transformative treatments that have the potential to cure diseases or halt their progression. The institute unites more than 500 researchers and clinicians dedicated to advancing gene and cell therapy for first-in-human clinical trials, and ultimately, life-saving treatments for patients.

Below are a few highlights from Mass General Brigham presenters at this year’s conference (all times are ET). View all abstracts here.

AAV9-rMOCS1 Gene Therapy, a Bicistronic Gene Delivery, Fully Rescues Neonatally Lethal Mouse Model of Molybdenum Cofactor Deficiency Type A (abstract 35)

Claire Shamber & Patricia Musolino, MD, PhD, Massachusetts General Hospital
Tuesday, May 7, 2:15–2:30 pm, in Ballroom 4

Molybdenum cofactor (MOCO) deficiency (MOCOD) is a devastating genetic, neurodegenerative disease characterized by neonatal intractable seizures and neurological disability that leads to death in the first three years of life. MOCOD affects one in 200,000 newborns globally. MOCOD Type A stems from mutations in the conserved bicistronic MOCS1 gene that produces proteins MOCS1A and B which form a complex in the MOCO pathway. Loss of activity abolishes production of MOCO and inactivates MOCO dependent enzymes. Among these enzyme deficiencies, the loss of sulfite oxidase, which metabolizes toxic sulfite into non-toxic sulfate, is necessary and sufficient to cause the neurodegenerative phenotype of MOCOD. Current available treatments are not well tolerated or fail to prevent disease progression. The team designed an AAV compatible recombinant version of the endogenous human MOCS1 gene. Their designed rMOCS1 construct expressed MOCS1A and MOCS1B and successfully restored sulfite oxidase enzymatic activity in MOCS1 KO HEK293 cells. Mutant and control treated animals showed no apparent toxicity or significant abnormalities in growth, neurological examination or behavior. Thus, the team demonstrated in vivo successful endogenous splicing and protein expression of a bicistronic human gene delivered by a single AAV vector. Single dose systemic AAV-mediated gene delivery of the rMOCS1 construct fully rescued neurological and systemic disease long term. This study serves as a proof of concept for a single dose AAV9 gene therapy with long-lasting effects enabling a first in human study for children suffering from MOCOD Type A.

Engineering of a Nucleic Acid Platform to Augment RNA Mediated Therapy (poster 443)

Debora Mazzetti, MS, Brigham and Women’s Hospital
Wednesday, May 8, 12:00–1:30 pm, in the Exhibit Hall

RNA-mediated interference has been proven over the years to be biologically effective, yet translational benefits in oncology have been lagging. RNA constructs, in particular, non-coding transcripts, have the potential to offer a high degree of customization that make them superior to drugs by achieving focused oncogene multitargeting, a progressively recognized necessity in cancer treatment. Taking advantage of the genetic structure of microRNA genes, the team engineered artificial RNA sequences recognized by the cell microprocessor as bona fide microRNA transcripts. Three sequences of progressive structural complexity were designed and biologically validated in HEK293 cells as a proof of principle. Each showed retained ability to be processed by the cells into desired clusters of microRNAs (CL3 sequence), an additional sponge sequence against oncogenic miR-21 (CL3a21 sequence), and an aptamer directed against NFkB (CL3a21ap65). A functional analysis of the biological effects of the three different sequences was performed in primary, patient-derived, glioblastoma cell lines after lentiviral mediated expression of each sequence. Adding the antimiR21 function to CL3 significantly reduced growth (clonal ability, migration potential and tumorigenicity) in vivo. Cell proliferation demonstrated a substantial decrease of nearly 50%. CL3a21 displayed a reduction of 60% in comparison to CL3 and 80% in comparison to the negative control for migration and invasion properties. Similarly, the clonal potential was significantly reduced in CL3a21 cells. This study provides proof of principle and feasibility for designing artificial RNA constructs based on the genetic scaffolds of microRNAs, offering a significantly augmented capacity for tumor multitargeting by RNA-based interference.

All-in-One Adeno-Associated Virus Delivery for Therapeutic miR-21 Editing by saCas9 In Vivo (abstract 113)

Lisa Nieland & Xandra Breakefield, PhD, Massachusetts General Hospital
Wednesday, May 8, 4:45–5:00 pm, in Ballroom 4

Glioma, the most aggressive tumor of the CNS, has poor patient outcomes with limited effective treatments available. CRISPR-Cas9 technology has opened a new avenue for gene therapy and has been previously used to target non-coding RNAs, including microRNA-21 (miR-21), a microRNA highly expressed in glioma cells responsible for tumor progression. In previous research, the team showed that miR-21 is crucial for tumor growth, and a complete knock out in vitro reduced its tumorigenesis potential. Here, the team designed a single all-in-one recombinant adeno-associated vector (rAAV) containing Staphylococcus aureus Cas9 (saCas9) guided by a single-guide RNA (sgRNA) to target miR-21 coding sequences in the genome in vivo. Utilizing a CRISPR delivery system using AAV-based gene therapy in a glioma mouse model, they showed that the AAV-8 serotype is capable of reaching the tumor cells and that saCas9 is functionally expressed in glioma cells upon AAV-mediated delivery. This resulted in miR21 downregulation in tumor cells leading to reduced tumor growth and improved overall survival. This approach, specifically targeting microRNA coding sequences, can be applied not only in the context of glioma, but for a range of genome editing purposes in vivo. Thus, engineering a single AAV can achieve therapeutic genome editing outcomes. Further, the team expects that successful in vivo delivery of saCas9 can also advance therapeutic gene-editing in humans.

New Biological Insights into Extracellular Vesicle Associated AAV Help Improve Vector Yield and Provides Rational for Intraluminal AAV Packing (abstract 221)

Casey Maguire, PhD, Massachusetts General Hospital
Thursday, May 9, 4:15–4:30 pm, in Room 314–317

Extracellular vesicle-associated adeno-associated virus vectors (EV-AAV) represent a unique population of vectors generated during production in 293 cells, in contrast to conventional nonenveloped AAV capsids. Several studies have provided experimental evidence that EV-AAV provides desirable gene delivery aspects, such as greater resistance to antibody neutralization and transduction of organs and tissues in vivo in mice. Despite these promising data, there is a great deal of characterization of the EV-AAV system that needs to be performed.

To do so, the team used an optimized density gradient to answer some outstanding questions regarding EV-AAV characteristics, as well as using it to assess optimization of the production system. Gradient purification allowed the research team to accurately quantitate EV-AAV and conventional AAV yields in producer cell media. The anti-AAV9 pulldown assay suggests that AAV9 capsids inside EVs are functional at transduction and therefore do not require AAV9 on the EV surface to mediate transgene expression. The antibody neutralization data also suggests that surface-bound AAV9 capsids are not required for antibody evasion by EV-AAV as UP-EV-AAV9 was similarly resistant to IVIg as EV-AAV9. Thus, strategies aimed at increasing AAV packing inside EVs are warranted. The experiments with heterologous expression of MAAP8 suggest that yields of EV-AAV9 can be improved using this approach. In sum, these data provide important information for the further development of the EV-AAV vector system.