Nature review: Gene editing therapy is in full swing.

Text . . . On 15 May
, the Nature Reviews Drug Discovery published an article entitled "Gene-editing takes pipeline off". In this paper, the author takes stock and analyzes the research and development pipeline of gene editing therapy. Globally, clinical trials related to genomic editing techniques, including CRISPR-Cas9, zinc finger nuclease (ZFNs) and transcription-activated factor-like effect nuclease (TALENs), are driving the development of a number of therapeutic areas, including eye diseases and tumors.
In the past year and a half alone, at least 11 gene editing research and development projects have entered clinical development in the United States and the European Union, six of which use CRISPR-Cas-based editing tools.
" is an exciting time. Professor Jennifer Doudna of the University of California, Berkeley, one of the pioneers of CRISPR-Cas technology. After years of imagining how this emerging technology could change the treatment of diseases, key clinical research data is finally coming out.
Although most gene-editing therapies have so far focused on monogene rare diseases and tumor immunotherapy, researchers have begun to expand their reach.
"Like other new technologies, drug developers will first apply CRISPR technology to rare or extremely serious diseases with no other treatment options." The results of the first studies have had a significant impact on whether the technology can be applied more widely. Professor Doudna explains.
of course, other gene-editing techniques cannot be ignored (Figure 1). Progress has also been made in the development of zinc-based nucleases (ZFNs), transcriptionactivated sub-factor nucleases (TALENs) and large-scale nucleases (meganucleases).. Leaders in gene therapy, such as Bluebird bio and Spark Therapeutics, have been laying an important foundation for the development of this area by exploring delivery vectors and setting targets for adaptation or action. Pioneers of tumor immunocellular therapy, such as Novartis, Kite Pharma, and pioneers in the field of oligonucleotides such as Ionis Pharmaceuticals and Alnylam Pharmaceuticals, are also driving the development of gene editing therapies. John Evans, CEO of Beam Therapeutics, a
CRISPR base-based editing company, believes that the entire gene editing space is making strides and will accelerate across the board in the future.
in vitro gene editing is a relatively low risk starting point for the pioneers of exploring gene editing, which is re-injected as a therapeutic drug after the editing of cells collected in the patient's body. first,
, it is easier to introduce a gene editing system into cells in a laboratory environment than to allow the gene editing system directly into the body's cells. Because in vitro gene editing can use electro-perforation technology to enable gene editing tools to cross the cell membrane into specific cell types, while relative in vivo gene editing requires screening and optimization of vectors that can deliver gene editing systems.
in vitro editing also has security benefits. On the one hand, in vitro gene editing therapy has a lower risk of off-targeting and off-tissue editing (cells that occur in vitro by detection can be removed). When used to edit autologous cells in vitro, the gene editing system is also less likely to trigger an immune response. In addition, the researchers were able to quantify editing efficiency and carefully control the dose before re-delivering the cells back into the patient."
sickle cell disease and beta-thalassemia are both hereditary red blood cell diseases caused by hemoglobin (responsible for transporting oxygen in the body) with dysfunction or insufficient levels. All the first in vitro gene editing projects focused on both diseases (Table 1).. However, the first applications of gene editing techniques were not intended to directly correct the mutations that cause these diseases, but rather to regulate the compensatory expression of fetal hemoglobin. Fetal hemoglobin is usually only expressed for two to four months after birth, but its special expression in adulthood can play a protective role against sickle cell disease and beta-thalassemia.
Sangamo Therapeutics is a leader in gene therapy, and like most companies involved in in vitro gene editing therapy, its DEVELOPMENT of ST-400 and BIVV003 enhances fetal hemoglobin by editing BCL11A. The BCL11A code usually turns off the zinc finger transcription factor for the expression of fetal hemoglobin. Mutants in BCL11A can raise fetal hemoglobin levels.
Sangamo began clinical trials of more than one drug in May 2018, and according to Clinical Trials.gov, the initial completion of the trial is expected later this year.
in addition, CRISPR Therapeutics and Vertex Pharmaceuticals, the CRISPR-Cas-based candidate drug CTX001, entered clinical studies in February 2019 for the treatment of similar diseases. Last year, the two companies reported preliminary safety and efficacy data from two patients and announced that the trial would be completed by early 2021.
, however, the competition for haemoglobinopathy could be fierce. In addition to the recent success of small molecule and antibody therapy for sickle cell disease, Bluebird bio's one-off in vitro gene therapy betibeglogene autotemcel was approved in the European Union in 2019. The therapy treats beta-thalassemia by introducing functional globulin genes into red blood cells through a slow virus vector. In two summary trials that supported regulatory approval, nearly 80 percent of patients with beta-thalassemia no longer need ed'blood transfusions for at least 12 months after treatment. Bluebird bio has started rolling NDA applications in the United States, and development for sickle cell disease is continuing.
T cells also offer attractive opportunities for in vitro gene editing.
Sangamo tested the therapy in 2010. Before tumor immunotherapy became popular, Sangamo found a way to regulate T cells to fight infectious diseases, and its in vitro editing project SB-728 used ZFN to destroy the expression of CCR5 receptors in collected T cells. Because HIV enters T cells with CCR5 receptors, Sangamo believes this method protects T-cells from HIV infection. In 2014, lead researcher Professor Carl June of the University of Pennsylvania (one of the pioneers of CAR-T cell therapy) and colleagues reported in the New England Journal of Medicine that Sangamo's gene editing tool was able to modify CCR5 and was safe, demonstrating the feasibility of using ZFN to prepare modified T cells.
, although the SB-728 has not continued since. However, the potential of engineered T cells in tumor immunology has gradually become apparent (Table 2).. Novartis's 2017 FDA-approved CAR-T therapy tisagenlecleucel (originally developed by Professor Carl June and his colleagues) identifies how reprogramming T cells can be used to target cancer cells.
in this therapy, the researchers modified the collected T cells in vitro with a slow viral vector that encodes CD19 to identify the chimeric antigen receptor (CAR). After re-injecting these cells carrying CD19 CAR into the patient' body, CD19 CAR can identify and destroy cancer cells that express CD19. This treatment has long-term long-lasting remission effects on B-cell acute lymphoblastic leukemia and diffuse large B-cell lymphoma.
however, there are some problems with the way these CARs are added to T cells. On the one hand, the persistent expression of endogenous receptors in engineered T cells reduces its effectiveness in killing cancer cells. Second, T-cells are also constrained and balanced by other signals, leading to dysfunction and depletion. Many researchers are trying to solve these problems, and gene editing technology provides a way forward.
2019, Professor June brings another milestone study. He and his collaborators treated the first patient in the United States using CRISPR engineered candidate therapy NYCE T cells. The team first used CRISPR-Cas9 to knock out two genes that encode the endogenous T-cell receptor (TCR) and the gene that encodeped PD1, and then used a slow virus vector to insert a TCR transgen that identifies the cancer antigen NY-ESO-1. (CARs can only identify antigens expressed on the surface of cancer cells, while TCR can identify a wider range of antigens.)
February, the first part of the results, published in Science, showed the safety and feasibility of the treatment in three patients. Efficacy data are still being collected.
in addition, advanced editing techniques may be key to off-the-shelf allogeneic cell therapy, which is less difficult to produce than somatic cell therapy.
currently has a diverse range of projects in the invivia gene editing therapy pipeline. (Table 3).. Sangamo's SB-913 is used to treat a rare genetic disease, type II mucosacized storage disease (MPS II). Sangamo seeks to outdo other invivigenetic products such as Spark's voretigene neparvovec and Avexis's onasemgene abeparvovec. Previous projects have shown that adnosyd-related viruses (AAVs) can be used in the body to deliver new genes to the nucleus, but these gms are rarely integrated into the genome. Sangamo hopes to demonstrate the feasibility of inserting functional versions of missing genes directly into cell chromosome DNA through SB-913 therapy, and the company hopes to regulate protein expression by controlling genetically modified shears with a strong promoter.
SB-913 began clinical trials in November 2017. However, in February 2019, the company explicitly accepted SB-913 treatment for patients who did not receive sufficient benefits.
in addition to inserting genes, companies based on CRISPR technology are also exploring using the editing tool to remove DNA.
for example, Editas Medicine (co-founded by Zhang Feng) and Allergan developed EDIT-101 using CRISPR-Cas9 to cut a part of the mutation CEP290 in patients with Leber congenital black-skinned 10 (LCA10) blindness, forcing the body to produce functional proteins to restore vision. It is also a landmark study.
this attempt, Editas is following in the footsteps of gene therapy pioneer Spark Therapeutics, which first received FDA approval in 2017 to treat LCA2 congenital blindness with voretigene neparvovec. Spark avoided complications that hindered gene therapy by choosing ophthalmology. Because the eyes have immune privileges, the risk of immune response to foreign vectors and the introduction of genetically modified organisms is low. And the limited circulation from the eye to the rest of the body reduces the risk of off-tissue editing. In addition, the edited cells are no longer updated, increasing the likelihood of long-term effects.
Doudna, the co-founder of Editas, hopes that the development of the CRISPR-Cas9 system will take advantage of these advantages.
other leading invivite candidate therapy also uses the CRISPR-Cas system to cut DNA.
theritin (TTR) is a transporter protein that can be folded and aggregated incorrectly when it mutates, leading to TTR-mediated amyloid degeneration. Intellia's leading candidate therapy, NTLA-2001, uses CRISPR-Cas to knock out the TTR gene. Intellia and its partner Regeneron hope to provide lifelong treatment to patients by reducing the expression of TTR.
in fact, the forerunners of antisense therapy and RNA interference (RNAi) have proven the potential of targeting TTR. In 2018, the FDA approved Alnylam's drug patisiran for hereditary TTR-mediated amyloid degeneration, the first approved RNAi therapy (which is used to silence mRNAs with oligonucleotides in tTR). In addition, EU regulators have approved Akcea Therapeutics and Ionis's inotersen, an anantino-oligarchic nucleotide that can achieve similar results under the same environment.
Intellia can focus on demonstrating the benefits of CRISPR-Cas9. For example, does the gene editing pathway result in lower TTR levels? Can gene-editing therapy be safer? Can single-dose treatment be more effective?
many of the most advanced invivitive therapies focus on rare genetic diseases, and genes expressed in the liver, muscles and central nervous system are highly prioritized therapeutic targets, partly related to the transport characteristics of AAV vectors. In addition, gene editing has also been applied to the treatment of a number of infectious diseases.
gene editing is also being used in viruses. For example, The CRISPR-Cas9 candidate for ExcisbioTherapeutics is about to enter clinical development, removing integrated HIV DNA from the patient's genome, and patients infected with HIV may no longer need antiretroviral therapy. The first clinical trial will begin later this year. Precision Biosciences and its partner Gilead are expected to submit in 2021 an indhus tintation of hepatitis B virus therapy based on a wide range of nucleases. Researchers are also thinking about how to use DNA cutting to treat COVID-19.
with the results of gene editing trials being revealed, some key clinical findings may have significant implications for the development of gene-editing therapy.