Cell and Gene Therapy Answers: Understanding gene editing and its possible applications

How is gene editing used in cell and gene therapy and how is it different than conventional gene replacement therapy?

Gene editing and gene replacement therapy are both techniques used to treat genetic diseases, but they work in different ways.

Gene editing

Gene editing enables scientists to make precise changes to a person's genes. This is achieved by inserting, deleting or replacing specific pieces of DNA within the human genome. The most commonly used gene editing tool is CRISPR, which utilizes a protein called Cas9 to cut DNA at a specific location. Once the DNA is cut, it can be repaired in a way that introduces the desired genotype. This can be achieved by non-homologous end joining (NHEJ), or homology-directed repair (HDR), so the Cas9 allows for gene knockout or replacement at the target DNA sequences.

In addition, engineered forms of Cas9 that lack nucleus activity are utilized for sequence-directed base   editing and this technique can change the individual DNA nucleotide without introducing double-strand DNA breaks (DSBs).

Gene replacement therapy

Gene replacement therapy involves replacing a defective gene with a healthy copy of the same gene. This is often done with monogenic disease, where a single copy of the gene can help alleviate the symptoms of the disease. Viral vectors or other delivery systems are effective approaches to transfer those therapeutic gene into the target cells. Once delivered, the healthy gene begins to produce the functional protein. But unlike in the gene editing approach, the delivered DNA remains separate from the human genome as an episome.

Gene editing vs. gene replacement therapy

The key difference between gene editing and the conventional gene replacement therapy lies in the level of the precision and the control over the genetic changes. Gene editing allows for precise modification to specific locations within the genome, whereas gene replacement therapy involves adding an entire functional gene. Gene editing offers the potential for more targeted and efficient correction of gene defects and the ability to edit genes directly at the DNA level.

What are emerging applications for gene editing?

The field of gene editing is rapidly evolving, with various technologies like CRISPR paving the way for exciting new applications.

The first CRISPR-based gene editing therapy was approved in 2023. It was a nonviral ex vivo CRISPR/Cas9 gene editing cell therapy for patients suffering from sickle cell diseases. This marked a significant milestone for CRISPR-based gene editing therapy in clinical setting. 

Other clinical studies we see involve cancer immunotherapies. Several trials are using CRISPR to engineer immune cells—for example, T-cells or NK cells—to recognize and attack cancer cells more effectively. This holds promise for targeting various cancers, especially those resistant to traditional therapies.

And some  of the gene editing therapies are targeted to inborn errors of metabolism. For example, CRISPR/Cas9 gene editing therapy can correct faulty genes responsible for rare metabolic disorders like phenylketonuria (PKU), and this enables more targeted and potentially lifelong treatment options.

And in some clinical trials, CRISPR/Cas9 or other gene editing technologies are being used to treat hemophilia. This technology can insert a functional copy of clotting factor genes into patients’ liver cells, aiming for a one-time treatment for hemophilia A or hemophilia B.

What are key considerations in utilizing gene editing as therapies?

Platform

Currently, CRISPR/Cas9 is the most popular, ease-of-use platform. But other platforms like Zinc finger nucleases, transcription activator-like effector nucleases (TALENS) and the meganucleases exist. You have to consider the platform, the different technology and each of their advantages and limitations.

Delivery

Efficiently delivering the editing machinery, like a Cas9 protein,
messenger RNA or guide RNA, to the target cell is critical. Viral vectors (adeno-associated virus and lentivirus), nanoparticles, and even physical methods like electroporations have been explored, each of these with its own set of pros and cons.

Specificity 

In gene editing, we have to ensure precise change at the intended location in the genome. It is crucial to optimize editing tools and the delivery methods to minimize unintended edits, thereby avoiding unforeseen consequences.
One of the major concerns is the potential for off-target effects, where the gene editing machinery introduces unintended changes to the genome. To mitigate these off-target effects requires careful design of  guide RNA and thorough screening of some of the target genes to identify and minimize off-target sites.

Target selection

Some of the considerations beyond technology are the target selections. Selecting the appropriate target gene is crucial for the success of gene editing therapies. The target gene should play a key role in the disease pathology, and its modification should result in a therapeutic benefit. The target sites within the gene should be carefully chosen to minimize off-target effects and maximize the specificity.

Moreover, different genetic disorders require various approaches. For example, a single gene mutation may be corrected, while some complex diseases with multiple contributing factors might require more holistic gene editing strategies. 
Long-term monitoring

And the long-term follow-up is also a big issue. Long-term monitoring of the patient is necessary, considering potential unintended consequences that may arise over time. Factors such as efficacy and the durability of gene editing therapy, the stability of edited  cells and the potential immune response over time need to be carefully evaluated. To understand and mitigate risk, a patient receiving gene-editing therapy may be monitored for an extended period.

Gene editing is a powerful tool with immense potential. However, it is crucial to carefully consider the platform, applications, regulatory issues and even the ethical and social aspects to ensure it is responsible and sustainable development as a therapeutic approach. Collaborations between scientists, physicians, regulatory agencies and the stakeholders are also necessary for the continued development of safe and effective treatments.

What opportunities lie ahead for the future of gene editing?

The future of gene editing is incredibly promising as it offers the opportunity to tackle significant healthcare challenges. However, we must proceed carefully and responsibly, considering safety and the associated risk factors, as gene editing technology continues to advance.

Cancer therapies

Gene editing technology is being utilized to develop innovative  cancer therapies such as allogeneic CAR T-cell therapy, and the gene editing of cancer cells themselves. Gene editing has the potential to lead to more favorable outcomes for patients by enhancing the specificity and efficacy of cancer treatments.

Infectious diseases

Gene editing has the potential to fight against infectious disease by targeting pathogens directly or engineering resistance in host organisms. For example, CRISPR-based technologies could be utilized to develop antiviral treatment to stop the transmission of COVID-19. And some scientists are also using gene editing to treat HIV. So we’re observing some promising data in the area of infectious disease treatment.

Regenerative medicine

Gene editing holds promise for regenerative medicine applications, such as tissue engineering and organ transplantations. By editing stem cells or other types of cells, scientists aim to develop therapies for repairing damaged tissues or organs, thereby
treating conditions such as heart disease, neurodegenerative disorders and spinal cord injuries. 
As we observe more novel ideas emerging from gene editing, along with studies aimed at treating various diseases, it’s clear that gene editing holds a promising future for enhancing healthcare and disease treatment.