Base editing is moving from the lab into human patients, and the early results are striking. A single infusion of VERVE-102, an in vivo base-editing therapy that inactivates the PCSK9 gene in the liver, produced a mean 88% reduction in circulating PCSK9 and a 62% reduction in LDL cholesterol at the highest dose, according to interim results published in the New England Journal of Medicine (NEJM, 2026).
Unlike CRISPR's first generation, which cuts both strands of DNA, base editing makes a single-nucleotide change without double-strand breaks. This reduces the risk of off-target insertions or deletions, making it safer for therapeutic use. The approach mimics naturally occurring protective genetic variants (NEJM, 2026).
The first liver biopsy proof
A separate case report from a Phase I/Ia trial showed the first direct histological evidence that base editing can correct a disease-causing mutation in a living human organ. Ten weeks after a single infusion of YOLT-202, a liver biopsy showed 54% (Sanger) and 57% (Illumina) on-target correction of the PI*ZZ variant in a patient with alpha-1 antitrypsin deficiency, with no bystander edits or off-target effects (medRxiv, 2026).
How does base editing work?
Base editors use a modified Cas protein fused to an enzyme that chemically converts one DNA base to another, such as an A to a G or a C to a T. This corrects the underlying genetic defect without cutting both strands. VERVE-102 delivers its machinery as a lipid nanoparticle-encapsulated mRNA and guide RNA, targeting hepatocytes (NEJM, 2026).
The results support the feasibility and safety of gene editing approaches for AATD, correcting the mutation itself rather than just adding a functional copy.
— medRxiv preprint, 2026
What conditions are being targeted?
Base editing is being tested across several conditions. VERVE-102 targets PCSK9 for hypercholesterolemia. A separate trial, BEACON, uses base editing of the HBG1 and HBG2 promoters for sickle cell disease, with 31 patients showing durable expression of fetal hemoglobin and no severe vaso-occlusive crises. Researchers are also exploring base editing for Huntington's disease (PubMed, 2026).
| Therapy | Target | Condition |
|---|---|---|
| VERVE-102 | PCSK9 | Hypercholesterolemia |
| YOLT-202 | SERPINA1 | Alpha-1 antitrypsin deficiency |
| Risto-cel | HBG1/HBG2 | Sickle cell disease |
| VERVE-201 | ANGPTL3 | High cholesterol/triglycerides |
What are the risks?
The trials show mild-to-moderate infusion-related reactions and transient elevations in liver enzymes. In the VERVE-102 trial, no dose-limiting toxicities, deaths, or withdrawals occurred. The studies are small, open-label, and with relatively short follow-up, so longer and larger trials are needed to confirm safety, durability, and clinical benefit (NEJM, 2026).
Sources and further reading
- NEJM — In Vivo Base Editing of PCSK9 with VERVE-102 for Hypercholesterolemia
- medRxiv — Liver biopsy confirms correction of SERPINA1 after in vivo base editing
- PubMed — Base Editing of HBG1 and HBG2 Promoters for Sickle Cell Disease
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Bottom line
The trials show mild-to-moderate infusion-related reactions and transient elevations in liver enzymes. In the VERVE-102 trial, no dose-limiting toxicities, deaths, or withdrawals occurred. The studies are small, open-label, and with relatively short follow-up, so longer and larger trials are needed to confirm safety, durability, and clinical benefit (NEJM, 2026).
What we still don't know
This is a fast-moving story. We update the post as new facts land — and we'll flag it when we do.
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