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There are two ways to edit someone. You can take cells out, edit them in a facility, check them, and give them back — that is ex vivo, and it is how the approved therapy works. Or you can inject the editing machinery and let it find the cells inside the body — in vivo, which is far easier on the patient but cannot be inspected before it happens.
Ex vivo editing permits controlled conditions, quality control and release testing before administration, but is limited to accessible cell types and generally requires conditioning to enable engraftment. In vivo editing avoids cell manufacturing and conditioning but exposes the whole body to the editor, offers no opportunity to verify the product before it acts, and depends entirely on delivery tropism.
The trade-off in one table
| Ex vivo | In vivo | |
|---|---|---|
| Where editing happens | In a manufacturing facility | Inside the patient |
| Can you check before giving? | Yes — the product is tested and released | No |
| Patient burden | High — apheresis, conditioning chemotherapy, weeks in hospital | Low — an infusion |
| Cell types | Blood and immune cells, mostly | Whatever the delivery vehicle reaches |
| If something goes wrong | The product can be discarded before use | It cannot be withdrawn |
| Cost and complexity | Very high — bespoke manufacturing per patient | Lower — a manufactured product |
The last row is why in vivo is where most of the field is heading, and the row above it is why in vivo safety events are taken so seriously.
Sources
- National Human Genome Research Institute
Talking Glossary of Genomic Terms ↗