In Vivo Gene Editing in 2026: The Trials Proving We Can Edit Genes Inside the Body

Until recently, editing a person's genes meant doing it the hard way. Doctors would remove cells from the patient's body, shuttle them into a laboratory, reprogram their DNA using CRISPR or another editing tool, run quality checks, and then infuse the modified cells back into the patient. The process worked — spectacularly, in some cases — but it was slow, expensive, and limited to diseases involving cells that could survive the round trip.

Now, for the first time, that paradigm is breaking. In clinical trials across the United States and Europe, doctors are injecting gene editors directly into patients' bloodstreams. No cell extraction. No laboratory detour. Think of it as performing surgery on your genes while they're still inside you, no extraction needed. The editors travel through the blood, find the right organ, enter the target cells, and make a precise cut to the DNA — all inside the living human body.

And it's working. Across multiple diseases, multiple companies, and multiple delivery systems, in vivo gene editing is producing real clinical data in real patients. This article is your comprehensive guide to where those trials stand in 2026.

Ex Vivo vs In Vivo: Why It Matters

To understand why in vivo gene editing is such a milestone, you need to understand the two fundamental approaches to editing genes in people.

The Ex Vivo Model

Ex vivo gene editing — literally, editing "outside the body" — is the approach that brought us the first approved CRISPR therapy. Here is the basic workflow:

Collect cells from the patient (typically blood stem cells or immune cells).
Edit those cells in a laboratory using CRISPR-Cas9 or a similar tool.
Verify the edits were made correctly and that no dangerous off-target changes occurred.
Infuse the edited cells back into the patient.

This is the model behind Casgevy (exagamglogene autotemcel), the landmark CRISPR therapy approved in late 2023 for sickle cell disease and transfusion-dependent beta-thalassemia. It works, but it requires myeloablative conditioning (essentially wiping out the patient's existing bone marrow with chemotherapy), weeks of hospitalization, and specialized transplant centers. The entire process can cost over $2 million per patient.

Ex vivo editing is also inherently limited in scope. It only works for diseases involving cell types that can be extracted, edited, and returned — primarily blood cells and certain immune cells. But what about diseases of the liver? The eyes? The brain? The lungs? You can't remove someone's liver cells, edit them in a dish, and put them back.

The In Vivo Revolution

In vivo gene editing — editing "inside the body" — eliminates the extraction step entirely. Instead, the gene editing components are packaged into a delivery vehicle and administered directly to the patient, typically through an intravenous infusion. The delivery vehicle carries the editors to the target organ, the editors enter the cells, and the DNA is modified in place.

This approach is harder to engineer. You need a delivery system that can protect the editing components in the bloodstream, navigate to the correct organ, enter the right cell type, release the editors inside the cell nucleus, and then disappear without triggering a dangerous immune response. But if you can solve the delivery problem, the payoff is enormous:

Broader disease coverage: You can target organs that are impossible to reach with ex vivo approaches.
Simpler treatment: A single IV infusion instead of weeks of hospitalization.
Lower cost potential: No need for patient-specific cell manufacturing.
Scalability: The same drug product can treat every patient, rather than requiring custom manufacturing for each individual.

The diseases that stand to benefit most from in vivo gene editing are those affecting tissues deep inside the body — the liver, the retina, the central nervous system, the lungs, the kidneys, and skeletal muscle. For patients with these conditions, in vivo editing isn't just a nicer option. It's the only option.

The Delivery Revolution: Lipid Nanoparticles

The story of in vivo gene editing is, in many ways, a story about delivery. The editing tools themselves — CRISPR-Cas9, base editors, prime editors — have been refined for years. The bottleneck has always been getting those tools to the right cells inside a living person.

What Are Lipid Nanoparticles?

Lipid nanoparticles (LNPs) are tiny spheres made of specialized fat molecules that can encapsulate nucleic acids — in this case, messenger RNA (mRNA) encoding the Cas9 protein and the guide RNA that directs it to the target gene. If you received a Moderna or Pfizer-BioNTech COVID-19 vaccine, you've already encountered LNP technology: those vaccines used LNPs to deliver mRNA encoding the SARS-CoV-2 spike protein.

For gene editing, the principle is the same but the payload is different. Instead of delivering mRNA that instructs cells to make a viral protein, LNPs deliver mRNA that instructs cells to make the Cas9 enzyme along with a guide RNA that tells Cas9 exactly where to cut.

How LNPs Deliver Gene Editors

The journey of an LNP-based gene editor through the body follows a predictable path:

Infusion: The LNPs are administered intravenously.
Circulation: In the bloodstream, the LNPs acquire a "protein corona" — a coating of blood proteins, including apolipoprotein E (ApoE), which naturally directs particles toward the liver.
Uptake: Liver cells (hepatocytes) recognize the ApoE-coated LNPs and internalize them through receptor-mediated endocytosis.
Endosomal escape: Inside the cell, the LNPs must escape from the endosome (a membrane-bound compartment) before being degraded. This is one of the most critical and difficult steps.
mRNA release and translation: The freed mRNA is translated by the cell's ribosomes into Cas9 protein.
Editing: Cas9, guided by the co-delivered guide RNA, travels to the nucleus and makes a targeted double-strand break in the DNA.
Clearance: The mRNA and Cas9 protein are transient — they are degraded by the cell within hours to days, limiting the window for off-target editing.

Natural Liver Tropism

One of the most important properties of current LNP formulations is their natural liver tropism — their inherent tendency to accumulate in the liver after intravenous injection. This is why liver diseases have been the first targets for in vivo CRISPR therapy. The liver is, in a sense, the "low-hanging fruit" of in vivo gene editing, not because the diseases are simple, but because the delivery problem is partially solved by biology.

To further enhance liver specificity, some formulations incorporate GalNAc (N-acetylgalactosamine) ligands on the LNP surface. GalNAc binds to the asialoglycoprotein receptor, which is expressed almost exclusively on hepatocytes, providing an additional layer of targeting precision.

Advantages Over AAV

Before LNPs, the leading delivery vehicle for in vivo gene therapy was adeno-associated virus (AAV) — a small, non-pathogenic virus engineered to carry therapeutic genes. AAV has been used successfully in approved gene therapies like Luxturna (for inherited retinal dystrophy) and Zolgensma (for spinal muscular atrophy). But AAV has significant limitations:

Feature	LNPs	AAV
Payload size	Large (can carry full-size Cas9 mRNA + guide RNA)	Small (~4.7 kb packaging limit)
Re-dosability	Can be re-dosed; low immunogenicity	Single dose only; immune response prevents re-dosing
Immune response	Mild, transient	Can trigger significant immune responses
Duration of expression	Transient (ideal for editing — you want the editor to disappear)	Long-lasting expression (good for gene replacement, but means persistent editor if used for editing)
Manufacturing	Chemical synthesis; scalable	Biological production; complex and expensive

The transient nature of LNP-delivered mRNA is actually an advantage for gene editing. You want the Cas9 protein to be present just long enough to make the edit, then vanish. Persistent expression of a gene editor increases the risk of off-target cuts accumulating over time.

Intellia Therapeutics: Leading the In Vivo Charge

No company has done more to advance in vivo CRISPR gene editing than Intellia Therapeutics, a Cambridge, Massachusetts-based biotech co-founded by CRISPR pioneer Jennifer Doudna. Intellia's two lead programs — NTLA-2001 and NTLA-2002 — have produced the most mature clinical data for any in vivo gene editing therapy.

NTLA-2001 for Transthyretin Amyloidosis (hATTR)

In June 2021, Intellia made history. The company presented data showing that a single intravenous infusion of NTLA-2001 could reduce levels of the disease-causing transthyretin (TTR) protein by an average of 87% in patients with hereditary transthyretin amyloidosis (hATTR). It was the first time anyone had demonstrated that CRISPR could edit genes inside the living human body.

The disease: hATTR is caused by mutations in the TTR gene, which encodes the transthyretin protein. Mutant TTR misfolds and accumulates as amyloid deposits in nerves, the heart, and other organs, leading to progressive neuropathy, cardiomyopathy, and death. The disease affects an estimated 50,000 people worldwide.

The therapy: NTLA-2001 uses LNPs to deliver Cas9 mRNA and a guide RNA targeting the TTR gene in liver cells. The goal is simple: knock out TTR production in the liver (which produces approximately 95% of circulating TTR), thereby eliminating the source of amyloid deposits.

Clinical results: By early 2026, more than 25 patients have been dosed across multiple dose cohorts in the ongoing Phase I/II clinical trial. The key findings:

Serum TTR reduction: At the 1.0 mg/kg dose, patients achieved a mean TTR reduction of approximately 93% from baseline, sustained over follow-up periods exceeding two years.
Durability: The editing is permanent. Unlike RNA interference therapies (such as patisiran or vutrisiran) that require repeated dosing, NTLA-2001 is designed as a one-time treatment.
Safety: No serious adverse events attributed to the therapy have been reported. The most common side effects were mild, transient infusion-related reactions and transient elevations in liver enzymes (ALT and AST), which resolved without intervention.
Functional improvement: Patients have shown stabilization or improvement in neuropathy scores and cardiac biomarkers, though the trial was not powered to detect these endpoints.

In a significant regulatory milestone, Intellia has received alignment from the FDA on a biomarker-based accelerated approval pathway — meaning that sustained TTR reduction, rather than years of clinical endpoint data, could serve as the basis for initial approval. This could bring NTLA-2001 to market years earlier than a traditional approval pathway would allow.

NTLA-2002 for Hereditary Angioedema (HAE)

Intellia's second in vivo program targets hereditary angioedema (HAE), a genetic condition characterized by recurrent, unpredictable episodes of severe swelling in the skin, gastrointestinal tract, and airway. Airway attacks can be life-threatening.

The biology: HAE is most commonly caused by deficiency or dysfunction of C1 inhibitor, a protein that regulates several inflammatory pathways, including the kallikrein-kinin system. In the absence of adequate C1 inhibitor, plasma kallikrein (encoded by the KLKB1 gene) becomes overactive, generating excess bradykinin, which drives the swelling attacks.

The therapy: NTLA-2002 uses LNPs to deliver Cas9 mRNA and a guide RNA targeting the KLKB1 gene in the liver. By knocking out kallikrein production, the therapy aims to eliminate the root cause of swelling attacks — effectively providing a functional cure.

Clinical results: In the Phase I/II study (presented at major medical conferences through 2025), NTLA-2002 demonstrated:

Near-complete elimination of attacks: At the 75 mg dose level, patients experienced a mean reduction in monthly attack rate of approximately 95% compared to baseline, with several patients reporting zero attacks during the observation period.
Rapid onset: Reductions in plasma kallikrein activity were observed within weeks of dosing.
Favorable safety: Similar to NTLA-2001, the most common adverse events were mild infusion-related reactions and transient liver enzyme elevations. No dose-limiting toxicities were observed.

NTLA-2002 is now advancing into a pivotal Phase III trial, with data expected to support a regulatory filing. For patients who currently manage HAE with frequent injections of preventive therapies (such as lanadelumab or berotralstat), the prospect of a one-time curative treatment is transformative.

YolTech YOLT-203: Primary Hyperoxaluria Type 1

While Intellia has dominated the headlines, another company has quietly produced one of the most exciting in vivo gene editing datasets of the past year.

YolTech Therapeutics has reported positive clinical data for YOLT-203, an LNP-delivered CRISPR therapy targeting primary hyperoxaluria type 1 (PH1) — a rare metabolic disorder that causes the liver to overproduce oxalate, leading to recurrent kidney stones, kidney damage, and ultimately kidney failure.

The biology: PH1 is caused by mutations in the AGXT gene, which encodes an enzyme normally responsible for preventing the accumulation of glyoxylate in liver cells. Without functional AGXT, glyoxylate is converted to oxalate, which is excreted by the kidneys. Excess oxalate forms calcium oxalate crystals that damage kidney tissue.

The therapeutic strategy: Rather than trying to replace the defective AGXT gene, YOLT-203 takes a "substrate reduction" approach. It uses CRISPR to knock out the HAO1 gene, which encodes glycolate oxidase — the enzyme that produces the glyoxylate that eventually becomes excess oxalate. By eliminating glycolate oxidase, the therapy cuts off the upstream supply of the problematic metabolite. This is the same biological rationale used by Alnylam's RNA interference therapy lumasiran (Oxlumo), but YOLT-203 aims to achieve the effect with a single dose instead of monthly injections.

Clinical results: In early-phase clinical data presented in late 2025 and early 2026:

Oxalate reduction: Patients treated at the highest dose level showed an approximately 70% reduction in urinary oxalate levels from baseline — a clinically meaningful reduction that brings many patients into or near the normal range.
Durability: The reduction has been maintained throughout the follow-up period, consistent with permanent gene editing rather than transient gene silencing.
Safety: The therapy was generally well tolerated, with adverse events consistent with those seen with other LNP-based therapies (mild infusion reactions, transient liver enzyme elevations).

Why this matters: YOLT-203 represents the first positive in vivo gene editing data for a condition that primarily affects the kidneys. While the editing itself occurs in the liver (because HAO1 is expressed in the liver), the therapeutic benefit is measured in the kidneys — making this a proof of concept that liver-targeted editing can treat diseases beyond the liver. For PH1 patients, many of whom face the prospect of combined liver-kidney transplantation, a one-time infusion that normalizes oxalate production would be life-changing.

Casgevy's Next Chapter: Children Ages 5-11

While in vivo gene editing advances, the world's first approved CRISPR therapy continues to evolve — and its next frontier is pediatric patients.

Casgevy (exagamglogene autotemcel), developed by CRISPR Therapeutics and Vertex Pharmaceuticals, was approved in late 2023 in the UK and in early 2024 in the US for sickle cell disease (SCD) and transfusion-dependent beta-thalassemia (TDT) in patients ages 12 and older. Now, the companies are pushing to expand access to younger children.

Phase III Pediatric Expansion

A Phase III clinical trial is currently enrolling children ages 5-11 with severe sickle cell disease or transfusion-dependent beta-thalassemia. This is a significant step for several reasons:

Earlier intervention: Sickle cell disease causes cumulative organ damage from early childhood. Treating children before significant damage accumulates could preserve organ function and quality of life.
Different physiology: Pediatric patients have different pharmacokinetics, body composition, and immune system characteristics compared to adolescents and adults. Safety and dosing must be validated in this population.
Conditioning considerations: The myeloablative conditioning required for Casgevy (using busulfan) carries serious risks including infertility and secondary malignancies. These risks weigh differently in young children with decades of life ahead of them.

Regulatory Timeline

CRISPR Therapeutics and Vertex have indicated that they expect to file for a pediatric label expansion in the first half of 2026, based on safety and efficacy data from the ongoing trial. If approved, Casgevy would become the first CRISPR therapy available to children under 12.

Why Pediatric Trials Matter Beyond Casgevy

The pediatric Casgevy trial is also significant as a bellwether for the broader gene editing field. Regulatory agencies, payers, and the public are watching carefully to see how gene editing therapies perform in children. Positive results could accelerate the development of pediatric in vivo gene editing programs, while safety concerns could slow the entire field.

It is worth noting that Casgevy remains an ex vivo therapy — it is not in vivo gene editing. But its expansion into younger patients reflects the growing confidence in CRISPR-based medicines and sets the stage for future in vivo approaches in pediatric populations.

Beyond the Liver: Emerging In Vivo Targets

The liver has been the proving ground for in vivo gene editing, but it won't be the only target for long. Researchers are actively developing delivery systems to reach other organs, and several programs are already in or approaching clinical trials.

Eye Diseases

The eye is an attractive target for in vivo gene editing because it is a small, enclosed, immune-privileged organ that can be accessed directly through injection.

EDIT-101, developed by Editas Medicine, was one of the earliest in vivo CRISPR programs to enter clinical trials. It targets a mutation in the CEP290 gene that causes Leber congenital amaurosis type 10 (LCA10), a form of inherited childhood blindness. EDIT-101 uses an AAV5 vector (not LNPs) to deliver the CRISPR components directly into the retina via subretinal injection.

While EDIT-101's clinical development has faced challenges — including modest efficacy signals in early dose cohorts and the broader difficulties Editas has experienced as a company — the program demonstrated that in vivo CRISPR editing in the eye is feasible and generally safe. Next-generation ocular gene editing programs are now in development using improved delivery vectors and more potent editing strategies.

Lung Diseases

Reaching the lungs with gene editors has been a long-standing challenge, but inhaled delivery approaches are showing promise in preclinical studies. Several academic groups and biotech companies are developing aerosolized LNP formulations that can be inhaled directly into the airways, potentially enabling gene editing for conditions like cystic fibrosis and alpha-1 antitrypsin deficiency.

Key challenges include:

The mucus barrier in the airways, which traps nanoparticles before they reach the target cells.
The need to edit enough cells to achieve therapeutic benefit in a large organ.
Immune responses in the lung, which is constantly exposed to foreign particles.

No inhaled CRISPR therapy has yet entered clinical trials, but several groups have demonstrated proof of concept in animal models, and IND-enabling studies are underway.

Brain and Central Nervous System

The blood-brain barrier (BBB) remains one of the most formidable obstacles in all of medicine, and in vivo gene editing for neurological diseases is no exception. Standard LNPs do not cross the BBB efficiently, and AAV vectors that can reach the brain (such as AAV9) require very high systemic doses, raising safety concerns.

Current strategies being explored include:

Intrathecal delivery: Injecting gene editors directly into the cerebrospinal fluid, bypassing the BBB.
Engineered AAV capsids: Novel AAV variants selected for enhanced brain penetration at lower doses.
Focused ultrasound: Temporarily opening the BBB using ultrasound to allow nanoparticle delivery to specific brain regions.
Receptor-mediated transcytosis: Engineering LNPs or other nanoparticles to hijack transport receptors on the BBB.

Diseases of interest include Huntington's disease, amyotrophic lateral sclerosis (ALS), and various forms of neurodegeneration caused by toxic gain-of-function mutations that could, in principle, be silenced by gene editing.

Muscle: Duchenne Muscular Dystrophy

Duchenne muscular dystrophy (DMD) is one of the most-discussed targets for in vivo gene editing, but also one of the most challenging. DMD is caused by mutations in the DMD gene (the largest gene in the human genome), and the target tissue — skeletal muscle — constitutes roughly 40% of body mass.

Editing enough muscle cells to restore meaningful dystrophin production requires delivering enormous quantities of gene editors throughout the body. Several academic groups have demonstrated correction of the DMD gene in mouse and dog models of DMD using AAV-delivered CRISPR, but scaling these approaches to humans remains daunting.

The development of compact Cas proteins — smaller versions of Cas9 or alternative CRISPR enzymes like CasMINI and Cas12f — is critical for DMD, because these smaller editors can fit within AAV's limited packaging capacity, enabling single-vector delivery strategies.

Kidney

While YOLT-203 addresses a kidney disease by editing the liver, true direct kidney editing remains an active area of research. The kidney presents unique delivery challenges: it filters enormous volumes of blood but has limited uptake of standard nanoparticles by the cells most commonly affected in kidney diseases (podocytes, tubular epithelial cells).

Approaches in development include:

Engineered LNPs with kidney-targeting ligands.
Retrograde ureteral delivery to access renal tubular cells.
AAV serotypes with enhanced kidney tropism.

No direct kidney gene editing program has yet entered clinical trials, but academic laboratories have published promising preclinical results, and several biotech companies have kidney-focused programs in their pipelines.

The Safety Picture

As in vivo gene editing trials accumulate data, a clearer picture of the safety profile is emerging. So far, the news has been largely reassuring — but important questions remain.

Aggregate Safety Data

Across all in vivo CRISPR trials reported to date (primarily Intellia's NTLA-2001 and NTLA-2002, as well as YOLT-203 and EDIT-101), the aggregate safety data show:

No deaths attributed to gene editing therapy.
No severe (Grade 4 or 5) adverse events attributed to the editing itself.
No evidence of off-target editing causing clinical harm.

This is a remarkably clean safety record for a technology that was, just five years ago, considered too risky for direct human application.

Common Adverse Events

The most frequently reported adverse events in LNP-based in vivo gene editing trials include:

Infusion-related reactions (IRRs): Mild to moderate symptoms during or shortly after the IV infusion, including flushing, chills, nausea, and elevated heart rate. These are managed with premedication (antihistamines, corticosteroids, antipyretics) and typically resolve within hours.
Transient liver enzyme elevations: Increases in ALT and AST, reflecting the liver processing the LNPs. These elevations are generally mild (Grade 1-2), transient (resolving within 1-2 weeks), and have not been associated with clinical liver dysfunction.
Mild cytokine elevations: Some patients show transient increases in inflammatory markers, consistent with innate immune recognition of the LNPs or their mRNA cargo.

Long-Term Monitoring

Because in vivo gene editing produces permanent changes to the DNA, long-term safety monitoring is essential. Key concerns that regulatory agencies are tracking include:

Off-target editing: Although preclinical studies have identified very few off-target sites for the guide RNAs used in current clinical programs, the theoretical risk of unintended mutations — including at tumor suppressor genes — cannot be eliminated until long-term follow-up data are available. Current trials include protocols for long-term monitoring extending 5-15 years post-treatment.
Liver health: Whether transient liver enzyme elevations have any long-term consequences for liver function.
Oncogenicity: Whether DNA double-strand breaks introduced by Cas9 could, in rare cases, lead to chromosomal rearrangements or other changes that increase cancer risk.
Germline editing: All current in vivo therapies target somatic cells (body cells), not reproductive cells. However, regulators require evidence that the editing components do not reach the gonads in meaningful quantities.

In Vivo vs Ex Vivo Safety Comparison

In some respects, in vivo gene editing has a simpler safety profile than ex vivo approaches:

No myeloablative conditioning: Ex vivo therapies like Casgevy require high-dose chemotherapy to make room for the edited cells, which carries risks of infertility, secondary cancers, and infections. In vivo therapies avoid this entirely.
No engraftment failure: Ex vivo therapies require the edited cells to successfully engraft and proliferate. In vivo editing modifies cells already in place.
Transient editor exposure: LNP-delivered mRNA produces Cas9 protein for a limited time, reducing the window for off-target editing. In contrast, AAV-based approaches can produce persistent editor expression.

However, in vivo approaches have their own unique risks:

Biodistribution: The editing components are distributed throughout the body, potentially reaching unintended tissues.
Less quality control: With ex vivo editing, you can characterize the edited cells before returning them to the patient. With in vivo editing, you cannot inspect the edits after they are made.

What's Coming Next

The pace of in vivo gene editing development is accelerating. Here is what the field can expect in the near term.

New Clinical Trials in 2026-2027

Several new in vivo gene editing programs are expected to enter clinical trials within the next 12-18 months:

Intellia's pipeline expansion: Beyond NTLA-2001 and NTLA-2002, Intellia has preclinical programs targeting additional liver diseases, including alpha-1 antitrypsin deficiency (AATD) and hemophilia. The AATD program, which aims to knock out production of the toxic mutant Z-AAT protein, is anticipated to file an IND in 2026.
Verve Therapeutics: Although Verve's lead program (VERVE-102 for heterozygous familial hypercholesterolemia) uses base editing rather than standard CRISPR-Cas9, it represents an important expansion of the in vivo editing paradigm to cardiovascular disease — specifically, permanent reduction of LDL cholesterol through inactivation of the PCSK9 gene in the liver.
New entrants: Multiple biotech companies with novel delivery technologies are advancing in vivo editing programs toward IND-enabling studies.

Non-Liver Targets Entering the Clinic

The next major milestone for the field will be the first clinical trial of in vivo gene editing targeting an organ other than the liver (excluding the eye, which EDIT-101 has already addressed). Leading candidates include:

Inhaled CRISPR for lung diseases.
Intrathecal delivery for neurological conditions.
Muscle-targeted delivery for DMD.

Compact Editors and AAV-Based In Vivo Delivery

The combination of compact CRISPR editors with AAV delivery could open up tissues that LNPs cannot easily reach. Smaller Cas proteins (such as Cas12f variants and engineered mini-Cas9 proteins) can fit within AAV's ~4.7 kb packaging limit as a single-vector system — encoding both the editor and the guide RNA in one AAV particle.

This approach is particularly promising for:

Muscle diseases: Where AAV serotypes with muscle tropism (AAV8, AAV9, AAVrh74) are well characterized.
CNS diseases: Where AAV9 and engineered capsids can cross the blood-brain barrier.
Cardiac diseases: Where AAV-based gene therapy has already been tested in clinical trials.

From Rare Diseases to Common Conditions

Today's in vivo gene editing trials focus on rare genetic diseases — conditions affecting thousands to tens of thousands of patients worldwide. This is appropriate for a new technology: rare diseases offer clear genetic targets, motivated patient populations, and favorable regulatory pathways.

But the long-term potential extends far beyond rare diseases. If in vivo gene editing proves safe and effective over years of follow-up, the technology could eventually be applied to:

Cardiovascular disease: Permanent reduction of LDL cholesterol (Verve's approach), lipoprotein(a), or other risk factors.
Chronic hepatitis B: Disrupting the viral cccDNA reservoir in liver cells.
HIV: Disrupting the CCR5 co-receptor to confer resistance to HIV infection.
Chronic pain: Silencing pain-signaling genes in sensory neurons.

These applications remain years away, but the clinical trials happening today are laying the foundation.

Frequently Asked Questions

What is in vivo gene editing and how does it differ from ex vivo editing?

In vivo gene editing means injecting gene editing tools directly into a patient's bloodstream to modify DNA inside the living body — no cell extraction needed. Ex vivo editing, used by therapies like Casgevy, requires removing cells from the patient, editing them in a laboratory, and transplanting them back. In vivo editing is simpler (a single IV infusion vs. weeks of hospitalization), potentially cheaper, and can reach organs like the liver, brain, and eyes that are impossible to target with ex vivo approaches.

How many in vivo gene editing clinical trials are running in 2026?

Multiple programs are generating clinical data as of 2026. Intellia Therapeutics leads with two programs: NTLA-2001 for hereditary transthyretin amyloidosis (hATTR, 25+ patients dosed) and NTLA-2002 for hereditary angioedema (HAE, now advancing to Phase III). YolTech's YOLT-203 is treating primary hyperoxaluria type 1, and Verve's VERVE-102 is testing base editing for familial hypercholesterolemia. Editas Medicine's EDIT-101 has addressed an inherited eye disease.

Which diseases are being targeted by in vivo gene editing?

Current clinical trials target hereditary transthyretin amyloidosis (Intellia's NTLA-2001, achieving 93% TTR protein reduction), hereditary angioedema (NTLA-2002, 95% reduction in attack rate), primary hyperoxaluria type 1 (YOLT-203, 70% reduction in urinary oxalate), familial hypercholesterolemia (Verve's VERVE-102, up to 69% LDL-C reduction), and Leber congenital amaurosis type 10 (EDIT-101). Future targets include cystic fibrosis, chronic hepatitis B, HIV, and Duchenne muscular dystrophy.

How are gene editors delivered inside the body?

The primary delivery vehicle is lipid nanoparticles (LNPs) — tiny spheres of specialized fat molecules that encapsulate mRNA encoding the Cas9 protein and the guide RNA. After IV infusion, LNPs naturally accumulate in the liver due to ApoE protein coating, and some formulations add GalNAc ligands for enhanced hepatocyte targeting. For eye diseases, AAV vectors are injected directly into the retina. The mRNA and Cas9 protein are transient, degrading within hours to days after making the edit.

Is in vivo gene editing safe based on clinical trial data so far?

The aggregate safety data across all in vivo CRISPR trials to date show no deaths attributed to gene editing, no severe (Grade 4 or 5) adverse events from the editing itself, and no evidence of off-target editing causing clinical harm. The most common side effects are mild infusion-related reactions (flushing, chills, nausea) and transient liver enzyme elevations that resolve within 1-2 weeks. Long-term monitoring extending 5-15 years post-treatment is ongoing to track for potential off-target mutations or oncogenicity.

The Bottom Line

In vivo gene editing has crossed the threshold from theoretical possibility to clinical reality. Multiple programs have now demonstrated that you can inject gene editing tools into a person's bloodstream, have those tools find their way to the liver, enter the correct cells, and permanently modify disease-causing genes — safely and effectively.

The data from Intellia's NTLA-2001 (for hATTR amyloidosis) and NTLA-2002 (for hereditary angioedema), YolTech's YOLT-203 (for primary hyperoxaluria), and the expanding Casgevy pediatric program collectively represent a turning point. We are no longer asking whether in vivo gene editing can work in humans. We are now asking how many diseases it can treat, how quickly it can reach patients, and how safely it can be scaled.

The challenges ahead are real. Reaching organs beyond the liver remains difficult. Long-term safety data are still accumulating. Manufacturing and cost barriers must be addressed before these therapies can reach the patients who need them worldwide. And the ethical questions surrounding permanent, heritable genetic modifications — while not directly raised by somatic cell editing — continue to demand thoughtful societal engagement.

But the trajectory is clear. In vivo gene editing is no longer a promise for someday. It is a medicine being tested, refined, and readied for patients today.

Sources & Further Reading

Gillmore, J.D., et al. "CRISPR-Cas9 In Vivo Gene Editing for Transthyretin Amyloidosis." New England Journal of Medicine, 2021. DOI: 10.1056/NEJMoa2107454
Intellia Therapeutics. NTLA-2001 and NTLA-2002 clinical data presentations. intelliatx.com
Finn, J.D., et al. "A Single Administration of CRISPR/Cas9 Lipid Nanoparticles Achieves Robust and Persistent In Vivo Genome Editing." Cell Reports, 2018.
Hou, X., et al. "Lipid nanoparticles for mRNA delivery." Nature Reviews Materials, 2021.
Maeder, M.L., et al. "Development of a gene-editing approach to restore vision loss in Leber congenital amaurosis type 10." Nature Medicine, 2019.
ClinicalTrials.gov — Active gene editing clinical trials. clinicaltrials.gov
CRISPR Therapeutics / Vertex Pharmaceuticals. Casgevy prescribing information and pediatric trial updates. crisprtx.com
YolTech Therapeutics. YOLT-203 clinical data presentations for primary hyperoxaluria type 1.
Musunuru, K., et al. "In vivo CRISPR base editing of PCSK9 durably lowers cholesterol in primates." Nature, 2021.
Raguram, A., et al. "Therapeutic in vivo delivery of gene editing agents." Cell, 2022.