Gene Therapy vs Gene Editing
Gene therapy and gene editing are fundamentally different approaches to treating genetic diseases. Gene therapy delivers a functional copy of a gene (gene addition), while gene editing directly modifies the patient's own DNA. By early 2026, there are 30+ FDA-approved gene/cell therapies but only one gene editing therapy (Casgevy). However, the gene therapy business model faces a crisis — bluebird bio, with three approved therapies, is going private for less than $30M due to commercial failure. Meanwhile, gene editing companies like Intellia and Beam are advancing rapidly toward potential approvals.
Last updated: March 29, 2026
Gene Therapy (Gene Addition)
Delivers a functional copy of a gene into cells using viral vectors (AAV, lentivirus) to compensate for a defective one. The original mutation remains — it's supplemented, not fixed.
Gene Editing
Directly modifies the patient's own DNA to correct mutations, delete harmful sequences, or insert new genetic material at precise locations. Includes CRISPR-Cas9, base editing, and prime editing.
Key Specifications
| Feature | Gene Therapy (Gene Addition) | Gene Editing |
|---|---|---|
| Mechanism | Add functional gene copy via viral vector | Modify existing DNA (cut, base convert, or prime edit) |
| Permanence | Variable — some wane over years (Roctavian) | Permanent (edits DNA directly) |
| Delivery | AAV (most common), lentivirus, retrovirus | Ex vivo (cells removed/edited/returned) or in vivo (LNP to liver) |
| Precision | Low (gene-level, not base-level) | Very high (single-base with base editing) |
| Re-dosing | Not possible (anti-vector immunity) | Not needed (permanent edit) |
| FDA approvals | 30+ cell & gene therapies (including CAR-T) | 1 — Casgevy (ex vivo CRISPR, Dec 2023) |
| Cost range | $850K (Luxturna) to $4.25M (Lenmeldy) | $2.2M (Casgevy) — potentially lower for in vivo |
| History | First AAV therapy approved 2017 (Luxturna) | — |
| 2025 commercial outlook | Mixed — Zolgensma $297M/Q2 but declining; Elevidys $898M/FY but safety issues | — |
| Key risk | Business model — many commercially unviable despite clinical success | — |
| In vivo frontier | — | Intellia lonvo-z Phase 3 complete, BLA target H2 2026 |
| Clinical trials | — | 100+ CRISPR trials + ~10 base editing trials |
| Next milestones | — | Beam BEAM-101 BLA (2026), Intellia lonvo-z BLA (H2 2026) |
Gene Therapy (Gene Addition)
Advantages
- 30+ FDA-approved cell and gene therapies with extensive clinical data (since 2017)
- Multiple delivery vectors well-characterized: AAV, lentivirus, retrovirus
- Zolgensma (SMA) has generated $6.4B+ cumulative revenue — proven commercial model for some indications
- Elevidys (DMD) achieved $898M in FY2025 revenue despite safety concerns
- Works for diseases where gene editing isn't practical (e.g., large gene replacement)
- New intrathecal delivery routes expanding addressable patient populations (Itvisma for SMA 2+)
Limitations
- Pricing crisis: therapies cost $850K–$4.25M per patient, with many commercially failing
- bluebird bio collapse: 3 approved therapies but going private for <$30M due to <$84M total 2024 revenue
- Cannot re-dose due to anti-vector immune response — single-shot with potentially waning efficacy
- Roctavian (hemophilia A) withdrawn from Europe due to poor uptake and reimbursement challenges
- AAV safety concerns: hepatotoxicity, TMA, deaths in high-dose trials (Audentes AT132)
- BioMarin's Roctavian showed declining Factor VIII levels after 2+ years in some patients
- Insertional mutagenesis risk with integrating vectors (lentivirus, retrovirus)
Gene Editing
Advantages
- Permanently fixes the root cause at the DNA level — no gene silencing over time
- Casgevy (CRISPR) FDA-approved Dec 2023: $2.2M, ~165 patients, $116M revenue in 2025
- In vivo CRISPR validated in humans: Intellia's nex-z showed 93% TTR knockdown sustained 3+ years
- Intellia's lonvo-z Phase 3 enrollment COMPLETED (Sept 2025) — potential first in vivo CRISPR approval by 2027
- Base editing achieving clinical genetic correction (Beam BEAM-302, March 2025)
- One-time treatment — no re-dosing needed for permanent DNA edits
- Multiple editing modalities: CRISPR, base, prime, epigenetic, RNA editing
Limitations
- Only 1 FDA-approved gene editing therapy vs 30+ gene therapies — less clinical track record
- Casgevy's complex ex vivo process: 6-9 months from cell collection to infusion, myeloablative conditioning required
- Off-target edits remain a concern (though improving with high-fidelity variants)
- In vivo delivery currently limited to liver via LNP — brain, muscle, lung remain challenges
- Ethical debates around germline editing persist (moratorium on clinical germline editing)
- Intellia's MAGNITUDE trial for ATTR-CM had FDA clinical hold (now lifted) — safety bar is high
The Verdict
Gene therapy has a 30+ product head start but faces an existential business model crisis — the collapse of bluebird bio (3 approved therapies, going private for <$30M) illustrates that clinical success doesn't guarantee commercial viability at $2-4M per patient. Gene editing is the future: Casgevy is commercially ramping ($116M in 2025), in vivo CRISPR is approaching approval (Intellia's lonvo-z Phase 3 complete, BLA target H2 2026), and base editing achieved its first clinical genetic correction. For gene addition-treatable diseases, established gene therapies work but face pricing headwinds. For precision corrections, gene editing is increasingly the better approach — and the one-time IV infusion model (in vivo editing) could solve the access and cost problems that plague ex vivo approaches.
Sources & References
- [1]FDA approved cell & gene therapy products
- [2]bluebird bio going private — Carlyle/SK acquisition
- [3]Casgevy commercial update (CRSP Q3 2025)
- [4]Intellia lonvo-z HAELO Phase 3 enrollment complete
- [5]Sarepta Elevidys sales and safety
- [6]BioMarin Roctavian EU withdrawal
- [7]Gene therapy pricing analysis (CSRxP)