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    Base editing

    Also known as base editor, adenine base editing, cytosine base editing, ABE, CBE

    Base editing is a gene-editing method, first reported in 2016, that converts one DNA base into another without cutting through both DNA strands.[1] By 2026 it had treated a child with a therapy designed for his own mutation and reached a pivotal trial for alpha-1 antitrypsin deficiency.[2][3]

    Editor reviewedStrict sourcingUpdated Gene editing and gene therapyLife sciencesHealth and medicine
    Key facts

    Base editing was designed to fix single-letter DNA errors more cleanly than cutting. Beam Therapeutics, one of the companies developing it, describes it as designed to make precise, predictable and efficient single-base changes at targeted sites.[4]

    How it works

    The 2016 Nature paper showed direct, irreversible conversion of one target base into another in a programmable way, without double-strand DNA backbone cleavage. Unwanted insertions or deletions were typically 1% or fewer.[1] Like crispr-cas9, a base editor uses a guide RNA to find its target. Unlike Cas9 nuclease therapies, it does not rely on a double-strand break.[5][1] prime-editing, reported three years later, can make all 12 types of single-base change as well as small insertions and deletions.[6]

    Clinical milestones

    • Personalized therapy (2025). Children’s Hospital of Philadelphia and Penn Medicine designed and manufactured a base editor for one infant’s CPS1 variant in about six months. They delivered it to the liver with lipid nanoparticles.[2] The NEJM report described no serious adverse events, plus improved protein tolerance in the following weeks.[7] See personalized-gene-editing.
    • Alpha-1 antitrypsin deficiency. Beam reports that BEAM-302 raised total and functional AAT, reduced mutant Z-AAT and produced corrected M-AAT, with a well-tolerated profile at single doses up to 75 mg.[8] The first patient in its global pivotal cohort was dosed in July 2026.[3]
    • Sickle cell disease. Beam plans a BLA for risto-cel (formerly BEAM-101), a base-edited cell therapy, as early as year-end 2026.[9]
    • Cardiovascular. In June 2025 Eli Lilly agreed to acquire Verve Therapeutics. Verve’s VERVE-102 is designed to permanently turn off the PCSK9 gene in the liver.[10] Lilly completed the deal in July 2025 for $10.50 per share in cash plus a contingent value right of up to $3.00 per share.[11]
    • Phenylketonuria. In June 2026 the FDA cleared Beam’s application to test BEAM-304, a base editor that initially targets the R408W mutation.[12]

    BEAM-302 in detail

    BEAM-302 is the most advanced in vivo base editor, and its data so far are company-reported. In September 2026 Beam said 38 patients had been dosed as of 17 August 2026. In the 60 mg lung-disease cohort, steady-state total AAT averaged 14.4 micromolar, up from 5.0 at baseline and above the 11 micromolar level regarded as protective. Circulating mutant Z-AAT fell by 84%.[13]

    Beam reported that single doses were well tolerated as of a 24 June 2026 cutoff. The most common drug-related adverse events were mild-to-moderate infusion-related reactions, in 41% of patients, and mostly Grade 1 liver enzyme rises. One patient with existing liver disease had a transient Grade 3 enzyme rise without a bilirubin increase, which resolved without treatment.[14] After FDA feedback, Beam says it is pursuing accelerated approval based on AAT levels measured over 12 months at 60 mg, with about 50 more patients in a pivotal expansion.[15]

    Beam also completed dosing of adults and adolescents in its BEACON trial of risto-cel in sickle cell disease in August 2026, with updated data expected by year-end.[16] Prime Medicine’s PM647 prime editor for the same AATD mutation was cleared for trials in September 2026.[17] In July 2026 an arbitration tribunal ruled that PM647 falls within Prime Medicine’s field under its 2019 agreement with Beam (company-reported).[18] See prime-editing.

    Open questions

    The editors are still delivered mostly by lipid nanoparticles that favour the liver.[19] No base-editing therapy had been approved as of October 2026, and the planned risto-cel filing could be the first test.[9] Regulators are also working out how to judge one-off personalized editors. The FDA’s February 2026 draft guidance on a “plausible mechanism” framework addresses that.[20] In April 2026 the agency also proposed next-generation sequencing methods for checking unintended edits in nonclinical safety studies.[21]

    Questions readers ask

    How is base editing different from CRISPR-Cas9 cutting?

    Standard Cas9 makes a double-stranded break. A base editor converts one DNA base into another without cutting both strands, and the original experiments showed typically 1% or fewer unwanted insertions or deletions.[5][1]

    Has base editing been used in patients?

    Yes. In 2025 an infant with severe CPS1 deficiency received a personalized base-editing therapy delivered by lipid nanoparticles, and Beam's BEAM-302 for alpha-1 antitrypsin deficiency entered a pivotal cohort in July 2026.[2][3]

    Is any base-editing therapy approved?

    Not as of October 2026. Beam plans to file for approval of risto-cel, a base-edited cell therapy for sickle cell disease, as early as year-end 2026.[9]

    Sources

    Each numbered claim is a statement we checked against the sources listed with it. Status shows how well established it is.

    1. [1]

      Base editing, reported in Nature in 2016, converts one DNA base into another in a programmable way without cutting both DNA strands, with typically 1% or fewer unwanted insertions or deletions in the original experiments. confirmedas of 2026-10-10

    2. [2]

      In 2025 a team at Children's Hospital of Philadelphia and Penn Medicine designed and manufactured, within about six months, a personalized base-editing therapy delivered by lipid nanoparticles to the liver for an infant with severe CPS1 deficiency, a rare urea-cycle disorder. confirmedas of 2026-10-10

    3. [3]

      In July 2026 Beam dosed the first patient in the global pivotal cohort of its BEAM-302 trial in AATD-associated lung disease. confirmedas of 2026-10-10

    4. [4]

      Beam Therapeutics describes base editing as a technology designed to make precise, predictable and efficient single-base changes at targeted genomic sequences. confirmedas of 2026-10-10

    5. [5]

      A 2012 Science paper by Jinek, Doudna, Charpentier and colleagues showed that a two-RNA structure directs the Cas9 protein to make double-stranded breaks in target DNA, and highlighted its potential for RNA-programmable genome editing. confirmedas of 2026-10-10

    6. [6]

      Prime editing, reported in Nature in 2019, pairs an impaired Cas9 with an engineered reverse transcriptase and a prime editing guide RNA (pegRNA) that both finds the target and encodes the edit, allowing insertions, deletions and all 12 kinds of single-base change without double-strand breaks or donor DNA. confirmedas of 2026-10-10

    7. [7]

      The case was reported in NEJM in May 2025; CPS1 deficiency has an estimated 50% mortality in early infancy, and in the seven weeks after the first infusion the infant tolerated more dietary protein and half the starting dose of a nitrogen-scavenger medicine, with no serious adverse events. confirmedas of 2026-10-10

    8. [8]

      Beam reports that BEAM-302, an in vivo base-editing therapy for alpha-1 antitrypsin deficiency (AATD), raised total and functional AAT, lowered mutant Z-AAT and produced corrected M-AAT, with a well-tolerated safety profile at single doses up to 75 mg. confirmedas of 2026-10-10

    9. [9]

      Beam plans to submit a Biologics License Application for risto-cel (formerly BEAM-101), a base-edited cell therapy for sickle cell disease, as early as year-end 2026. reportedas of 2026-08-04· forecast

    10. [10]

      On 17 June 2025 Eli Lilly agreed to acquire Verve Therapeutics for $10.50 per share in cash plus a contingent value right of up to $3.00 per share; Verve's lead program VERVE-102 is designed to permanently turn off the PCSK9 gene in the liver to lower cholesterol. confirmedas of 2026-10-10

    11. [11]

      Eli Lilly completed its acquisition of Verve Therapeutics in July 2025 for $10.50 per share in cash, about $549.4 million net of cash acquired, plus a contingent value right of up to $3.00 per share worth up to roughly $300 million; the acquired in-process research and development related primarily to VERVE-102. confirmedas of 2025-10-30

    12. [12]

      In June 2026 the FDA cleared Beam's investigational new drug application for BEAM-304, a base editor for phenylketonuria that initially targets the R408W mutation, and the company began clinical start-up activities for a Phase 1/2 trial. confirmedas of 2026-08-04

    13. [13]

      At the European Respiratory Society Congress in September 2026 Beam reported that 38 patients had been dosed with BEAM-302 as of 17 August 2026, and that in the 60 mg lung-disease cohort steady-state total AAT averaged 14.4 micromolar against 5.0 micromolar at baseline, above the 11 micromolar protective threshold, with an 84% reduction in circulating mutant Z-AAT. confirmedas of 2026-09-08

    14. [14]

      Beam reported that as of the 24 June 2026 data cutoff single-dose BEAM-302 was well tolerated, with mild-to-moderate infusion-related reactions in 41% of patients as the most common drug-related adverse events, mostly Grade 1 liver enzyme elevations, and one patient with underlying AATD-related liver disease who had transient Grade 3 ALT/AST elevations without bilirubin increases that needed no treatment. confirmedas of 2026-09-08

    15. [15]

      Beam says that after FDA feedback it is pursuing an accelerated approval pathway for BEAM-302 based on a primary endpoint of AAT biomarkers measured over 12 months at a 60 mg dose, and expects to enroll about 50 additional patients with AATD-associated lung disease in a pivotal expansion of its Phase 1/2 trial. confirmedas of 2026-09-08

    16. [16]

      Beam reported in August 2026 that dosing was complete for all adult and adolescent patients in the Phase 1/2 BEACON trial of risto-cel in sickle cell disease, with updated data expected by year-end 2026. confirmedas of 2026-08-04

    17. [17]

      On 24 September 2026 Prime Medicine said the FDA had cleared its investigational new drug application for PM647, an in vivo prime editor designed to correct the E342K (Pi*Z) mutation in SERPINA1; the global single-arm Phase 1/2 study will start with adults who have lung-only AATD and then add a cohort with significant liver disease, with initial clinical data expected in 2027. confirmedas of 2026-09-24

    18. [18]

      In July 2026 Prime Medicine announced a binding arbitration ruling under its 2019 collaboration agreement with Beam Therapeutics: the tribunal declared that PM647 is within Prime Medicine's defined field, that Prime Medicine did not breach the agreement and that it owes no monetary damages. confirmedas of 2026-08-06

    19. [19]

      Lipid nanoparticles can carry Cas9 mRNA and guide RNA into tissues, but reliably targeting tissues other than the liver remains a challenge. confirmedas of 2026-10-10

    20. [20]

      On 25 February 2026 the FDA published draft guidance on a "plausible mechanism" framework for generating evidence of effectiveness and safety for individualized therapies that target specific genetic conditions with a known biological cause; comments closed on 27 April 2026. confirmedas of 2026-10-10

    21. [21]

      On 15 April 2026 the FDA published draft guidance recommending next-generation sequencing methods for the nonclinical safety assessment of genome editing in human gene therapy products, with comments due by 14 July 2026. confirmedas of 2026-10-10

    Revision history (2)
    1. Page created.
    2. Added BEAM-302 efficacy and safety data, the accelerated approval path, BEAM-304, the Verve deal closing and FDA sequencing guidance.

    Created Oct 10, 2026. Last reviewed by an editor on Oct 10, 2026. Next scheduled review: Jan 10, 2027.

    Cite this page

    "Base editing." ContentLora, updated Oct 10, 2026. https://contentlora.com/wiki/base-editing

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