What in vivo CRISPR has already done in humans — and how well it worked
The strongest human evidence comes from two phase 1 trials targeting the liver, both published in the New England Journal of Medicine. In hereditary angioedema (a rare genetic disease causing severe swelling attacks), a single infusion of NTLA-2002 reduced the number of attacks per month by an average of 95% across all dose groups [1]. In the highest-dose group (75 mg), the disease-causing protein (kallikrein) dropped by 95% from baseline [1]. These are not subtle improvements — patients went from regular, unpredictable attacks to near-complete freedom from them.
For transthyretin amyloidosis (a fatal disease where misfolded protein builds up in nerves and heart), the same technology — NTLA-2001 — cut the target protein (TTR) by 87% at the higher dose (0.3 mg/kg) after a single infusion [2]. The lower dose still achieved a 52% reduction [2]. Both studies reported only mild side effects, with no serious adverse events [1][2]. These results are remarkable because they show that a one-time treatment can permanently edit a gene inside the body and produce a durable, dose-dependent effect.
The big caveats: tiny trials, liver-only delivery, and a long road ahead
The main reason to temper the hype is the size of the human evidence. The angioedema trial had only 10 patients total [1]; the amyloidosis trial had just 6 [2]. Both were phase 1 dose-escalation studies designed to test safety, not to prove efficacy. While the results are stunning, they come from a handful of people, and larger trials are needed to confirm they hold up across a broader population.
A second major limitation is delivery. Both approved human trials use lipid nanoparticles (LNPs) to carry the CRISPR components, and LNPs naturally accumulate in the liver [3]. That means in vivo CRISPR today can only reliably edit liver cells. For diseases of the heart, brain, muscles, or blood, researchers are still working on ways to target those tissues — and a 2024 review notes that 'the complete attainment of the inherent capabilities of in vivo therapy in humans is yet to be accomplished' [4]. A 2025 review of LNP delivery confirms that non-liver targeting is still an active engineering challenge [3].
Finally, even within the liver, not every disease target has been tested in humans. A landmark 2021 primate study showed that base editing of PCSK9 (a cholesterol gene) in monkeys lowered LDL cholesterol by about 60% for at least 8 months [5]. That is promising for heart disease, but it has not yet been tried in humans. So while the hype about 'once-and-done' cures for heart disease is grounded in animal data, the human evidence for that specific application is still zero.
Who benefits right now — and who has to wait
Right now, the people who benefit are those with rare, monogenic liver diseases where a single gene edit can stop the disease process. Hereditary angioedema and transthyretin amyloidosis are textbook examples, and the early data suggest the benefit is life-changing [1][2]. If you have one of these conditions, the hype is justified — these therapies are on track to become approved treatments.
For everyone else — people with common conditions like high cholesterol, heart disease, cancer, or genetic disorders affecting other organs — the evidence is not there yet. The PCSK9 primate study is a strong proof of concept [5], but it has not been replicated in humans. Cancer applications face the additional challenge of selectively editing tumor cells without harming healthy ones, which a 2024 review calls a 'crucial' hurdle [4]. The hype about in vivo CRISPR curing everything is premature; the reality is that it works spectacularly in a few narrow cases, and the rest is still in the lab.
About These Sources
This answer is built on 5 peer-reviewed studies — published from 2021 to 2025, 3 from 2024 or later, 4 in Q1 journals, collectively cited 2,282 times — selected as the most relevant from 5 studies that passed quality screening, drawn from 64 papers retrieved from a database of over 500 million.
Sources used in this answer
CRISPR-Cas9 In Vivo Gene Editing of
In a phase 1 trial of 10 patients with hereditary angioedema, a single dose of NTLA-2002 reduced swelling attacks by 95% on average and lowered the disease protein by up to 95%, with no serious adverse events.
CRISPR-Cas9 In Vivo Gene Editing for Transthyretin Amyloidosis
In a phase 1 trial of 6 patients with transthyretin amyloidosis, a single dose of NTLA-2001 reduced the target protein by up to 87% at 28 days, with only mild side effects.
Lipid Nanoparticles for Delivery of CRISPR Gene Editing Components
A 2025 review of lipid nanoparticle delivery for CRISPR confirms that LNPs are effective for liver targeting but that non-liver delivery remains an active engineering challenge.
Revolutionizing in vivo therapy with CRISPR/Cas genome editing: breakthroughs, opportunities and challenges
A 2024 review of in vivo CRISPR therapies states that full realization of in vivo therapy in humans has not yet been accomplished, with selective targeting of defective cells a key remaining hurdle.
In vivo CRISPR base editing of PCSK9 durably lowers cholesterol in primates
In a nonhuman primate study, a single infusion of CRISPR base editors targeting PCSK9 in the liver lowered LDL cholesterol by about 60% for at least 8 months, but this has not been tested in humans.