As thousands of attendees excitedly logged on to the opening session of ASGCT 2021, the 24th annual meeting of the American Society of Gene and Cell Therapy, they were met with a 404 error message on their computer screens. The website was having serious issues that delayed the meeting’s start. Some delegates griped on twitter, while others pined for in-person conferences. As the problem persisted, the organizers issued one groveling apology after another, ultimately conceding there had been a “catastrophic cascading failure.”

But the field of gene therapy is nothing if not resilient. Mirroring the field it represents, the meeting’s organizers made adjustments and got back to work. In gene therapy, it seems, no obstacle is too big to keep it from moving forward.

The gene and cell therapy field has the distinction of being both mature and venturesome, reflecting its deep experience and innovative spirit. The field’s unique qualities were much in evidence in a presentation by Terence R. Flotte, MD, dean of the University of Massachusetts Medical School, editor-in-chief of Human Gene Therapy, and this year’s ASGCT secretary.

His talk, “AAVs—What We Know 56 Years after Discovery,” began with a walk through the history of adeno-associated virus (AAV) biology. Then he posed a pointed question: What do we still need to know in 2021 regarding AAVs? Finally, he suggested where new knowledge would be most useful: uncovering ways to precisely target recombinant AAV (rAAV) delivery, scaling rAAV manufacturing, reducing both innate and adaptive immune responses, and determining how the host will respond to “newer” AAVs.

Essentially, Flotte issued a call to arms. Will the field respond? It would appear so. AAV development has never been hotter. The ranks of AAV-oriented companies are bursting with new recruits, and the market for AAV vector–based gene therapy is poised to grow exponentially.

It would be fair to say that ASGCT 2021 showed that the field of gene and therapy is preparing to go on the march. The meeting was packed with talks on gene editing, delivery systems, rare diseases, patient advocacy, and much more. From our reviewing stand—a refreshed browser—GEN bore witness to a four-day-long parade of exciting new developments.

Timing is everything

Shortly before the conference, news broke of the publication of a landmark gene therapy study. The study, led by Donald B. Kohn, MD, professor at the UCLA Broad Stem Cell Research Center, reported the success of an experimental gene therapy for a rare immunodeficiency. A tweet from Fyodor Urnov, PhD, professor and scientific director of technology and translation at the Innovative Genomics Institute, hailed Kohn’s work as the “single most remarkable achievement of the gene therapy field since it started in 1989.”

child treated with gene therapy at UCLA
Two- and three-year outcomes were recently reported for 50 children treated with a gene therapy for a rare immunodeficiency disease. Treatment was successful in all but 2 of the 50 children, and both of those children were able to return to current standard-of-care therapies,” said Donald Kohn, MD, a researcher based at UCLA. Kohn, the rightmost figure in this photograph, co-led the outcome study.

The study appeared in the New England Journal of Medicine, in a paper entitled, “Autologous Ex Vivo Lentiviral Gene Therapy for Adenosine Deaminase Deficiency.” It described the two- to three-year outcomes of 50 children who were treated for severe combined immunodeficiency due to adenosine deaminase deficiency (ADA-SCID) between 2012 and 2017. The patients’ hematopoietic stem and progenitor cells (HSPCs) were transduced ex vivo with a lentiviral vector encoding human ADA. Overall survival was 100% in all studies up to 24 and 36 months.

Urnov pointed out that the work is the culmination of more than 50 years of research in bone marrow transplantation and 40 years of research in gene transfer. While the concept is the same as it has been for decades, Urnov said now the pieces “have come together to make it actually work.”

Most speakers would be thrilled to talk about their hot-off-the-press NEJM paper. But Kohn’s talk at ASGCT detailed interim results from a different gene therapy study—this one done in collaboration with Rocket Pharmaceuticals—for pediatric patients with severe leukocyte adhesion deficiency 1 (LAD-1). In this immune deficiency, patients suffer from recurrent and fatal infections due to the loss of leukocyte adhesion, leading to an inability for neutrophils to migrate to sites of infection.

The lentiviral-based trial, which is evaluating the safety and efficacy of RP-L201-0318 (NCT03812263), has enrolled five patients so far, aged 5 months to 9 years. The patients’ cells are transduced with a lentiviral vector carrying the ITGB2 gene encoding CD18. Although it is early days, the therapy has led to CD18 expression in the patients’ neutrophils and improvements in both rate of infections and wound healing.

More than one way to edit a gene

Gene therapy and genome editing are becoming increasingly intertwined. Not surprisingly, the companies working on delivering genome edits to correct disease genes delivered some compelling talks.

David Liu, PhD, professor of chemistry at Harvard University and the Broad Institute, presented unpublished results on his team’s progress in using base editing for the treatment of sickle-cell disease (SCD). Base editing—a method for engineering precise base substitutions in DNA without introducing double-strand breaks (as occurs using CRISPR)—offers the potential to directly repair the SCD point mutation, converting the mutant nucleotide to a benign, naturally occurring polymorphism, Hb Makassar.

Last month, researchers at Beam Therapeutics (Liu is a co-founder) reported in The CRISPR Journal success in using a base editor to target the SCD variant in erythroid cells. Since then, Liu’s team has gone further.

Using a different base editor, the team modified SCD cells and transplanted them into immunodeficient mice. After confirming that the base editing did not result in any clinically relevant off-target events, the team then injected base-edited HSPCs from SCD patients into mice.

Using a variety of criteria (including a sharp reduction in Hb S levels and expression of the Hb Makassar variant; a five-fold reduced sickling in reticulocytes from edited HSPCs; and restoration of splenic mass and physiology), the team concluded that it was observing, in Liu’s words, “durable base editing” of SCD at levels comfortably exceeding the 20% editing threshold that would suffice to rescue key blood parameters.

“Even just five years ago,” Liu related, “the idea of using an engineered molecular machine to correct a specific base pair ex vivo and in vivo in animals to alleviate the consequences of genetic disease really seemed like science fiction.”

No more heart disease in monkeys

Verve Therapeutics has prioritized using adenine base editors (ABEs) because they are “potent and specific,” says Andrew Bellinger, MD, PhD, Verve’s chief scientific officer. Bellinger spoke about the company’s work to “disrupt the care of cardiovascular disease through single-course gene editing medicines.” More specifically, the company has been developing a genome editing approach to treat the genetic form of atherosclerotic cardiovascular disease (ASCVD) known as familial hypercholesterolemia. The approach, which involves editing the PCSK9 gene, has been evaluated in nonhuman primates.

Verve Therapeutics’ Verve-101 consists of a lipid nanoparticle that encapsulates a gRNA and an mRNA that encodes a PCSK9-gene-specific adenosine-to-guanosine base editor. A single spelling change disables the gene, which has been implicated in the accumulation of LDL cholesterol and the development of cardiovascular disease. Having achieved long-term reductions in LDL cholesterol levels in cells and animal models, Verve-101 is poised to enter human trials.

In 2006, researchers showed that people who have natural PCSK9 deficiency have very low levels of “bad” cholesterol, that is, low-density lipoprotein (LDL) cholesterol. This finding suggested to Verve that shutting down the PCSK9 gene would help people at high risk for cardiovascular disease. Verve developed VERVE-101, an ABE gene therapy product that relies on nonviral lipid nanoparticle (LNP) delivery and shuts down PCSK9 in the liver.

So far, Verve has achieved high efficiency base editing in monkeys, a “first-in-world demonstration,” Bellinger asserted. Shutting down the PCSK9 gene in the liver resulted in an 89% reduction of blood PCSK9 levels and a 59% drop in blood LDL cholesterol two weeks after treatment.

The monkeys have been followed for 10 months, and the levels remained the same over time. Because the liver turns over in that time, this indicates that the new liver cells likely carry the edit that was introduced. Bellinger anticipates that his colleagues have made a lifetime edit in the monkeys, and naturally hopes for the same in patients.

When asked about the potential for germline editing, Bellinger answered that Verve’s researchers “don’t see any editing in testes or ovaries,” which they believe is “probably sufficient” evidence. But they do continue testing for the possibility by collecting sperm. It is a priority, he noted, but not something that the company expects to be a problem.

Verve’s work evaluating dosing and potency gives Bellinger “a lot of confidence” that the levels will translate to patients. The company is currently in the middle of a toxicology program and hopes to take this platform into the clinic next year.

Multiple ways to achieve “one and done”

Laura Sepp-Lorenzino, PhD, chief scientific officer at Intellia Therapeutics, presented the development of its CRISPR-Cas9 genome editing therapy to treat transthyretin amyloidosis (ATTR) with polyneuropathy, caused by mutations in the TTR gene. The Intelllia platform, she said, delivers CRISPR-Cas9 with the goal to develop a curative therapy after a single dose, taking a “one and done” approach.

Intellia Therapeutics lab
Intellia Therapeutics is developing CRISPR-Cas9 technology for in vivo and ex vivo therapies. The former are intended for genetic diseases; the latter, for cancers and autoimmune diseases. At ASGCT 2021, the company presented updated preclinical data on CRISPR-Cas9-mediated targeted gene insertion to treat alpha-1 antitrypsin deficiency.

Sepp-Lorenzino showed that a more than a 95% reduction in serum TTR protein was achieved after a single dose of the CRISPR-Cas gene editor. This candidate, NTLA-2001, is in Phase I clinical development and represents the “very first in vivo CRISPR drug given systemically.” The first patient was dosed last year. The company expects to report data from this trial later this year.

Experimental treatments for many other diseases are in the pipeline. In one of these projects, in vivo gene editing of bone marrow is showing promise as a way to treat SCD. Encouraging findings cited by Sepp-Lorenzino include data from studies with mouse models. One advantage to performing the editing in vivo, she noted, is avoiding the complexities in morbidity and mortality that are associated with ex vivo approaches.

Like Verve, Intellia is using LNPs. These delivery vehicles are taken up by hepatocytes in the liver when infused into patients. Sepp-Lorenzino said that Intellia prefers LNPs over viral vectors because they are well tolerated, offer large cargo capacity, have low immunogenicity, allow for redosing, can be scaled with synthetic manufacturing, and are clinically proven to deliver to the liver.

Another company that is using in vivo genome editing to treat ATTR is Precision BioSciences, a company that is collaborating with the group of James Wilson, MD, at the University of Pennsylvania. Precision’s proprietary ARCUS genome editing platform makes highly specific cuts in cellular DNA. The work presented at ASGCT demonstrated that high levels of genomic editing were achieved, resulting in substantial and persistent serum TTR reductions.

Zinc fingers, meet the brain

Amy Pooler, PhD, Sangamo
Amy Pooler, PhD, Sangamo

Sangamo Therapeutics, known for using (non-CRISPR based) zinc finger protein transcription factors (ZFP-TFs) in its approach to genomic medicine, presented posters with preclinical data from two of its neurological disease programs. “With genomic medicines,” notes Amy Pooler, PhD, vice president and head of neuroscience at Sangamo, “we may finally be able to better treat some debilitating diseases and deliver long-lasting therapies.” The majority of current treatments in this area, she notes, aim to treat the symptoms of neurological disease, rather than modify the disease itself—something that she says their zinc finger technology may have the potential to do.

The first program, a joint effort by Sangamo and Biogen, uses ZFP-TFs to repress the human alpha-synuclein gene for the treatment of Parkinson’s disease. The second program targets the most frequent genetic cause of amyotrophic lateral sclerosis—the expansion of the hexanucleotide GGGGCC in the C9ORF72 gene. Partnering with Pfizer, the team at Sangamo is targeting this area of the genome, through selective repression of repeat expansion–containing sense and antisense transcripts, for the potential treatment of amyotrophic lateral sclerosis.

Sangamo Therapeutics research
Sangamo Therapeutics is conducting research and development across four distinct but complementary technology platforms: gene therapy, cell therapy, in vivo genome editing, and in vivo genome regulation. The company uses both adeno-associated virus and mRNA to deliver its therapeutics.

Assorted extras

At the ASGCT 2021 conference, many presentations discussed delivery options. Viral vectors and LNPs figured prominently. In a session entitled, “Novel Viral Gene Transfer Vectors and Applications,” additional possibilities were discussed, including functionalities of herpes simplex virus vectors, single-cycle measles virus vectors, and novel poxvirus vectors.

There were also talks on gene therapy for inborn errors of metabolism, immuno-oncology, immunological barriers to gene therapy, development challenges and opportunities in low and middle income groups, racial justice in the gene therapy field, vaccine development, stem cell gene therapy, and much more. As Urnov tweeted, the ASGCT meeting web site may have crashed, “but the field is thriving.”

All about the patients

Jenn McNary, patient advocate
Jenn McNary, patient advocate

Ask any researcher working in gene therapy what motivates them to persist in a complicated field full of challenges. They will answer, “The patients.” But sometimes the relationship between companies and patients needs fostering. Few people know this better than Jenn McNary, a consultant, speaker, and patient advocate. McNary offered advice on how to improve the work that patients and companies are doing—together.

A mother of four, three of whom have rare diseases, McNary expressed her wish that people would develop a better understanding of what matters to patients. To illustrate what she meant, she said that in discussions about Duchenne muscular dystrophy, a disease that affects two of her sons, people are usually focused on restoring the ability to walk. But what matters to her sons is increased independence—a metric difficult to measure in a clinical trial.

The session moderator, John Tisdale, MD, senior investigator at the National Heart, Lung, and Blood Institute, said that McNary’s “eye-opening” talk laid out “nearly every aspect of what we should be thinking about.” Asked what was the biggest obstacle that needed to be overcome, McNary answered: talking to patients. Communication is improving, and many patient advocacy groups are working to ensure that patient perspectives are woven into the science. Still, conversations with patients about the value of a therapy need to happen at the beginning of the process.

McNary ended by saying, “There is a lot to look forward to.” For now, we’ll look forward to next year’s meeting, scheduled to be an in-person event at the cavernous convention center in Washington, DC. Until then, we’ll dream of meeting badges around our necks, drinks with friends old and new, strong coffee, and even stronger Wi-Fi.