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    How gene therapies are delivered: ex vivo, viral vectors and LNPs

    A gene editor only works if it reaches the right cells. Therapies either edit cells outside the body and return them (ex vivo) or deliver the editor into the patient (in vivo), and in vivo delivery is still the field's main bottleneck.[1][2]

    Editor reviewedStrict sourcingUpdated Gene editing and gene therapyLife sciencesHealth and medicine

    Delivery is the step between a working editor in a dish and a medicine in a patient. A 2024 review concludes that delivery methods are still far from the goals of high efficiency, specificity and scalability.[2]

    Two routes: outside or inside the body

    There are two ways to do it. In ex vivo therapy, doctors take cells out, edit them in a lab and put them back. In in vivo therapy, the editor is infused into the body and must find the right cells by itself. Early CRISPR therapies were ex vivo. Newer ones increasingly work in vivo, which is harder.[1]

    A 2025 review in Frontiers in Genome Editing notes that in vivo approaches suffer from lower delivery efficiency, off-target effects and instability compared with ex vivo editing.[1] Ex vivo editing of human stem cells mostly uses electroporation, which avoids the challenges of in vivo transfection.[3] The trade-off is the procedure around it. Casgevy patients have their own stem cells collected and edited, then undergo myeloablative conditioning (high-dose chemotherapy) before the edited cells are infused.[4]

    Viral vectors

    Some therapies use modified viruses as carriers. The adeno-associated virus (AAV) is small and can carry only about 4.7 kilobases of DNA, which limits how big a payload fits.[5] Lentiviruses insert their genetic cargo into the cell’s own DNA, so it keeps working for a long time.[6] Lyfgenia, a sickle cell gene therapy approved alongside Casgevy, uses a lentiviral vector.[7]

    For editing, persistence cuts both ways. Long-term AAV or lentiviral expression of Cas9 increases the window for off-target cleavage.[5][6] Systemic AAV dosing also carries safety risks. In July 2025 the FDA said three deaths appeared to result from acute liver failure in people treated with Sarepta’s AAV-based gene therapies. It asked the company to suspend Elevidys distribution and placed some trials on hold.[8]

    Lipid nanoparticles

    Lipid nanoparticles (LNPs) are tiny fat bubbles that can carry the editor’s instructions as mRNA, together with the guide RNA.[9] After an infusion, they mostly reach the liver, which is why many in vivo editing trials target liver genes.[9] See lipid-nanoparticle-delivery for the technology’s clinical track record.

    LNP delivery of Cas9 mRNA plus single guide RNA was tested in people in the NTLA-2001 study, published in 2021. It produced a mean 87% serum TTR reduction at 0.3 mg/kg.[10] The same modality underlies CTX310 (ANGPTL3)[11] and the personalized CPS1 base editor.[12] Reliable targeting of tissues other than the liver remains unsolved.[9] Liver safety still needs close monitoring. Intellia’s nex-z Phase 3 trials were paused in 2025 after a Grade 4 liver enzyme elevation.[13]

    The same carrier, two jobs

    Lipid nanoparticles were developed for RNA drugs and vaccines before they carried gene editors. The mRNA COVID-19 vaccines use the same four-component design to deliver mRNA into cells.[14][15] The difference is what the mRNA encodes and how long the effect lasts. A vaccine’s mRNA encodes an antigen and is broken down by normal cellular processes.[16] An editor’s mRNA encodes a protein that changes DNA, so the change remains after the carrier and the mRNA are gone.[9][10] For the vaccine side of the same technology, see how lipid nanoparticles deliver RNA.

    Why delivery shapes the field

    Which tissue a carrier reaches decides which diseases can be treated first. The first approved CRISPR medicine, for blood disorders, edits blood stem cells taken out of the body.[17] Liver diseases are next because LNPs reach the liver.[9] The analysis page on in vivo safety looks at the risks of each route.

    Questions readers ask

    What is the difference between ex vivo and in vivo gene editing?

    Ex vivo editing modifies cells outside the body, as with Casgevy's blood stem cells, before returning them. In vivo editing delivers the editor directly into the patient, which is harder and raises delivery and off-target concerns.[1][4]

    Why do many in vivo editing therapies target the liver?

    Lipid nanoparticles, a non-viral carrier, reach the liver well, while reliably targeting other tissues remains a challenge.[9]

    What limits AAV vectors?

    AAV carries only about 4.7 kilobases of DNA, and long-lasting expression of an editor from AAV may raise off-target risk. AAV gene therapies have also been linked to serious liver injury.[5][8]

    Sources

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

    1. [1]

      Early CRISPR therapies edited cells outside the body (ex vivo); newer approaches deliver the editor into the patient (in vivo), which a 2025 review notes faces lower delivery efficiency, off-target effects and instability. confirmedas of 2026-10-10

    2. [2]

      A 2024 review in Genes & Diseases concludes that delivery methods are still far from the goals of high efficiency, specificity and scalability. confirmedas of 2026-10-10· interpretation

    3. [3]

      For editing human stem cells outside the body, electroporation (using electric pulses to open cell membranes) is still the main choice, because it avoids the challenges of delivery inside the body. confirmedas of 2026-10-10

    4. [4]

      Treatment with Casgevy involves collecting the patient's own stem cells, editing them, giving myeloablative conditioning (high-dose chemotherapy) to clear the bone marrow, and infusing the edited cells back as a one-time treatment. confirmedas of 2026-10-10

    5. [5]

      Adeno-associated virus (AAV) vectors carry a single-stranded DNA genome of about 4.7 kilobases, which limits cargo size, and their long-lasting expression of Cas9 may raise off-target risk. confirmedas of 2026-10-10

    6. [6]

      Lentiviral vectors usually integrate their genome into the host's DNA, prolonging expression; continuous Cas9 expression increases the chance of off-target edits. confirmedas of 2026-10-10

    7. [7]

      On the same day as Casgevy, the FDA approved Lyfgenia, a sickle cell gene therapy that uses a lentiviral vector rather than gene editing; 28 of 32 patients (88%) had complete resolution of vaso-occlusive events in its trial. confirmedas of 2026-10-10

    8. [8]

      In July 2025 the FDA said three deaths appeared to result from acute liver failure in people treated with AAV-vector gene therapies from Sarepta, requested that Sarepta suspend Elevidys distribution, and placed some of its trials on clinical hold. confirmedas of 2026-10-10

    9. [9]

      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

    10. [10]

      In a 2021 NEJM study, NTLA-2001, a lipid nanoparticle carrying Cas9 mRNA and a guide RNA targeting the TTR gene, given by infusion, lowered blood TTR protein by a mean 87% at the 0.3 mg/kg dose, with mainly mild adverse events. confirmedas of 2026-10-10

    11. [11]

      In November 2025 CRISPR Therapeutics reported Phase 1 data, published in NEJM, for CTX310, an LNP-delivered CRISPR therapy that edits the ANGPTL3 gene in liver cells; at the highest dose mean ANGPTL3 fell 73%, triglycerides 55% and LDL cholesterol 49%, with no treatment-related serious adverse events reported. confirmedas of 2026-10-10

    12. [12]

      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

    13. [13]

      On 29 October 2025 the FDA placed clinical holds on Intellia's Phase 3 MAGNITUDE and MAGNITUDE-2 trials of nex-z after a patient dosed in MAGNITUDE had Grade 4 liver transaminase elevations and increased bilirubin. confirmedas of 2026-10-10

    14. [14]

      Lipid nanoparticles used for mRNA delivery usually contain four components, an ionizable lipid, a PEG-linked lipid, cholesterol and a phospholipid (helper lipid). confirmedas of 2023-03-01

    15. [15]

      The first authorized mRNA COVID-19 vaccines, Pfizer-BioNTech's BNT162b2 and Moderna's mRNA-1273, both encode the SARS-CoV-2 spike protein and are formulated in lipid nanoparticles. confirmedas of 2023-03-01

    16. [16]

      mRNA is a non-infectious, non-integrating platform that is degraded by normal cellular processes. confirmedas of 2018-01-12

    17. [17]

      Casgevy's approach edits a patient's blood stem cells outside the body by electroporating them with CRISPR-Cas9 aimed at an enhancer of the BCL11A gene, a gene that represses fetal hemoglobin, so that the cells make more fetal hemoglobin. confirmedas of 2026-10-10

    Revision history (2)
    1. Page created.
    2. Added a section comparing lipid nanoparticle delivery for gene editors with the same carrier in mRNA vaccines, with cross-links.

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

    Cite this page

    "How gene therapies are delivered: ex vivo, viral vectors and LNPs." ContentLora, updated Oct 10, 2026. https://contentlora.com/explain/how-gene-therapy-delivery-works

    Spotted an error? Suggest a correction or emailcorrections@contentlora.com.

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