Gene-based medicines are moving from scientific aspiration to clinical reality. Over the past several decades, scientists have moved beyond simply identifying genes linked to inherited disease, and now they are developing therapeutic strategies to directly intervene at the genetic level. Two major categories of genetic intervention have emerged: gene therapy and gene editing. While these approaches are often mentioned in the same breath, they represent fundamentally different philosophies of how to correct genetic disease.
Gene therapy, the older and more clinically established modality, centers on delivering a functional copy of a gene to compensate for one that is missing or defective. Gene editing, by contrast, involves altering the DNA itself—correcting or disabling targeted sequences directly within the genome. Both approaches hold transformative potential, but they come with distinct advantages, limitations, safety considerations, regulatory structures, and clinical trajectories.
Today, with the first approved gene editing therapy now authorized in multiple regions and dozens of new genetic medicines advancing through clinical pipelines, understanding the differences between these approaches is increasingly important—not only for researchers, but also for clinicians, patients, and policymakers. What follows is a comparative look at how gene editing and gene therapy work, what differentiates them in clinical application, where they are succeeding, and where challenges remain as these fields continue to evolve.
What is gene therapy?
Gene therapy traditionally refers to the delivery of a working copy of a gene to patients who lack it or who carry a mutated version that fails to produce a functional protein. To achieve this, most therapies rely on viral vectors, particularly adeno-associated viruses (AAVs (Mendell et al., 2021)) or lentiviral vectors, which are engineered to carry therapeutic genetic material.
The first approved in vivo gene therapy in the United States, Luxturna, treats an inherited retinal disease caused by mutations in the RPE65 gene. By delivering a functional copy of RPE65 to retinal cells, the therapy restores the production of a protein essential for the visual cycle. Similarly, Zolgensma, an AAV-based therapy for spinal muscular atrophy, delivers a functional copy of the SMN1 gene to motor neurons.
Gene therapy’s greatest strength lies in its ability to restore gene expression without altering the patient’s native DNA sequence. This can be especially valuable in disorders where the absence of a protein is the primary driver of disease progression. However, this replacement strategy also introduces several complexities. Gene therapies delivered via viral vectors may produce variable expression levels, immune responses to vector components, or unintended integration of genetic material at off-target genomic sites. In many cases, the therapeutic gene is not integrated into the genome, meaning that gene expression may diminish over time as treated cells divide.
What is gene editing?
Gene editing, led by the advent of CRISPR-Cas systems, takes a fundamentally different approach. Rather than supplementing the genome, gene editing technologies directly rewrite DNA sequences. CRISPR-Cas9 (Jinek et al., 2012), prime editing, and base editing platforms enable researchers to cut, correct, or replace specific nucleotides with unprecedented precision.
For example, the recently approved therapy Casgevy uses CRISPR to edit blood stem cells ex vivo to increase fetal hemoglobin production. By disrupting a regulatory element of the BCL11A gene in hematopoietic stem cells, the therapy reactivates a fetal developmental program that compensates for the defective hemoglobin responsible for sickle cell (Frangoul et al., 2021) disease.
Because gene editing modifies the DNA itself, the therapeutic effect can be long-lasting or potentially permanent, especially in cells that are slow-dividing or capable of self-renewal, such as stem cells. However, permanence cuts both ways. Any unintended edits become permanent genetic changes, raising concerns about off-target effects, genotoxicity, and downstream impacts that may not be immediately observable.
A clinical comparison: Durability, mechanism, and timing
| Feature | Gene Therapy | Gene Editing |
|---|---|---|
| Goal | Introduce a functional gene | Modify endogenous DNA sequence |
| Durability | Often temporary or variable | Durable, potentially permanent |
| Delivery | Typically viral vectors | Viral, LNPs, or ex vivo modification |
| Regulatory Complexity | Well-established pathways | Emerging and evolving regulatory oversight |
| Example Therapies | Luxturna, Zolgensma | Casgevy, investigational base editing therapies |
Gene therapy can be fast-acting because it restores protein expression almost immediately. However, durability remains an ongoing challenge—especially in dividing cells where non-integrated transgenes may be lost over time. Gene editing therapies require more extensive preparation, particularly in ex vivo workflows where cells must be harvested, modified, and reinfused. But the trade-off can be long-term correction, potentially reducing or eliminating the need for repeated treatment.
Delivery and immune response considerations
Delivery remains a central limiting factor for both modalities. AAV vectors, used widely in gene therapy, can trigger immune responses that limit redosing opportunities. Meanwhile, gene editing approaches may require either viral delivery or lipid nanoparticle (LNP) systems similar to those used in mRNA vaccines.
Some gene editing approaches are shifting toward in vivo delivery using LNPs to reach tissues such as the liver—helping sidestep some limitations of viral vectors. However, LNPs have their own challenges, particularly in achieving cell-type specificity and maintaining sufficient editing efficiency.
Case comparison: Sickle cell disease
The difference between the two approaches is particularly clear in sickle cell disease (SCD).
Gene therapy trials for SCD have focused on delivering a functional copy of the β-globin gene or increasing fetal hemoglobin through gene addition strategies. These approaches can improve symptoms but may provide variable benefit depending on engraftment levels.
Casgevy, the recently approved gene editing therapy for SCD, modifies hematopoietic stem cells to reactivate fetal hemoglobin. Because the edit occurs in the genome, the therapeutic effect is expected to be stable for the lifetime of the treated stem cells, providing a potentially durable solution.
Safety and regulatory oversight
As gene editing moves further into the clinic, regulators are refining criteria for assessing long-term risks. Editing therapies require rigorous tracking of off-target modifications, clonal expansions, and potential oncogenic events. Gene therapies face their own safety considerations, including vector-mediated insertional mutagenesis and immune complications.
Despite these differences, both fields share a long-term monitoring burden. Patients receiving genetic medicines are often followed for 15 years or longer, reflecting the lasting physiological implications of these interventions.
Looking ahead
As gene editing technologies expand to include base editors, prime editors, and CRISPR systems with improved specificity, the line between gene therapy and gene editing may blur. Meanwhile, advances in vector engineering, improved promoter design, and non-viral delivery platforms are helping gene therapies achieve more reliable and sustained expression.
Ultimately, gene therapy and gene editing are not competing technologies—they are complementary strategies. Gene therapy may be preferable when protein replacement is sufficient, while gene editing offers deeper intervention when the genomic defect itself must be corrected.
Going forward, the most successful treatments may integrate aspects of both approaches. Just as monoclonal antibodies and small molecules co-exist across therapeutic landscapes, gene editing and gene therapy will likely co-evolve, offering clinicians a broader set of tools to tailor treatment to each patient’s biological and clinical needs.
Freequestly asked questions (FAQs)
1. How does gene editing differ from gene therapy?
Gene therapy adds a functional copy of a gene to compensate for a faulty one, while gene editing directly modifies the existing DNA sequence. Gene editing may offer more durable and precise corrections, but gene therapy remains effective and clinically established for many conditions.
2. Which approach is safer?
Safety depends on the disease context, delivery method, and patient factors. Gene therapy carries risks related to immune response and off-target gene integration. Gene editing can introduce unintended genomic changes, though newer tools and monitoring strategies are reducing this risk. Regulators currently require long-term follow-up for both modalities.
3. Are gene editing therapies permanent?
In many cases, yes—especially when edited cells can self-renew, such as hematopoietic stem cells. However, durability depends on cell turnover and tissue type. Gene therapy may also be long-lasting, but its effects can diminish over time if the delivered gene is not stably expressed.
4. How do clinicians choose between gene therapy and gene editing?
Choice is guided by disease mechanism, target tissue, delivery feasibility, durability requirements, cost, and regulatory considerations. Gene therapy may be preferred for conditions caused by missing or nonfunctional proteins, while gene editing is advantageous when correcting a specific mutation or regulating gene expression is essential.
This article was created with the assistance of Generative AI and has undergone editorial review before publishing.
