The difference in one sentence
Ex vivo means the cells come out, get edited in a facility, get checked, and go back — which is safer in one important way, because you can inspect the product first, and much harder on the patient, because it requires chemotherapy and weeks in hospital. In vivo means an infusion. Easier for the patient, and nothing can be checked before it happens.
| Aspect | Ex vivo | In vivo |
|---|---|---|
| Where editing happens | In a manufacturing facility | Inside the patient's body |
| Can the product be checked first? | Yes — tested and released before use | No |
| Patient burden | High — apheresis, conditioning chemotherapy, weeks in hospital | Low — an infusion |
| Which cells can be reached | Blood and immune cells, mostly | Whatever the delivery vehicle reaches |
| If something goes wrong | The product can be discarded before administration | It cannot be withdrawn |
| Cost and complexity | Very high — a bespoke product per patient | Lower — a manufactured medicine |
| Approved example | Casgevy | None yet |
Sources
- New England Journal of Medicine (Gillmore et al.) · 2021
CRISPR-Cas9 in vivo gene editing for transthyretin amyloidosis ↗