Base editing

01Overview and value chain

Markers: [EC: ATMP Regulation (EC No 1394/2007) | OECD: Bio-Pharmaceuticals | Regulator: FDA (USA), EMA (EU), NMPA (China)]

Base editing makes a single-nucleotide change with no double-strand break (DSB) and no indel risk: a chimeric protein fuses catalytically dead Cas9 (dCas9) or nickase nCas9 to a DNA deaminase. Cytidine editors (CBE) convert C· G to T· A; adenine editors (ABE) convert A· T to G· C. The absence of DSB rules out the large chromosomal rearrangements and karyotype chaos of classic Cas9. First ABE clinical trials showed up to 90% correction with minimal off-targets — for sickle-cell disease, beta-thalassemia, progeria.

Key platforms of base editing:

1. Cytidine editors (CBE): C· G to T· A (APOBEC/AID deaminases).
2. Adenine editors (ABE): A· T to G· C (TadA*8e, k_cat > 10 s⁻¹).
3. Nickase nCas9 (D10A): a single-strand nick on the unedited strand drives repair.
4. RNP/LNP delivery: pre-formed ribonucleoproteins or mRNA in lipid nanoparticles.

Sectoral value chain

[gRNA design + deaminase choice] ──> [CBE/ABE expression + purification] ──> [mRNA/RNP + LNP formulation]
                                                                                       │
                                                                              (cell delivery)
                                                                                       │
                                                                                       ▼
[QC: accuracy + off-target] <─── [deep sequencing] <─── [targeted deamination]

Value chain levels

Cross-cutting technologies of the sector:

• Narrow window (narrow-window): mutant deaminases active over 1–2 nt — no bystander editing.
• RNP delivery: pre-formed RNPs for short activity and minimal off-targets.
• CBE+ABE tandems: dual editors for several base changes at once.

02US

The US holds the key patents (David Liu lab, Harvard/Broad) and leads in the clinic.

Beam Therapeutics, Prime Medicine, FDA deep-sequencing oversight

• Beam Therapeutics: key ABE/CBE patents, BEAM-101 (sickle-cell disease).
• Prime Medicine: hybrid Prime+Base platforms for neurodegeneration.
• FDA: detailed deep sequencing of target loci post-therapy; delivery biosafety oversight.

03CN

China is one of the leaders by number of Base Editing clinical trials.

EdiGene, Wenzhou Medical University, NMPA orphan-disease fast-track

• EdiGene: domestic editors, haematology clinical trials.
• Wenzhou Medical University: high-precision BE for inherited blindness; prenatal editing.
• NMPA: subsidies and simplified phase-1 protocols for orphan diseases.

04EU

The EU leads in deaminase-nCas9 structural biology and ex-vivo virus-free delivery.

Max Planck, DKFZ/DE-DK-FR, EMA long-term safety

• Max Planck Institute: nCas9-deaminase crystallography, thermostable deaminases.
• DE/DK/FR labs: virus-free editor delivery into blood stem cells ex vivo.
• EMA: long-term culture of edited cells before transplantation.

05Leading companies and research institutes

06Tech stack and innovations

The stack rests on evolved deaminases, nCas9 nickase and analytics.

1. TadA*8e (ABE deaminase):
   • a super-fast evolved tRNA deaminase on single-stranded DNA, k_cat > 10 s⁻¹.
2. Nickase nCas9 (D10A):
   • a single-strand nick on the unedited strand drives repair off the edited strand.
3. Analytics:
   • Illumina MiSeq + Oxford Nanopore GridION (long-deletion detection); Benchling for sgRNA design.

07Value chains and production pipelines

RNP production and QC pipeline for base editors (cGMP)

┌───────────────────────────┐      ┌───────────────────────────┐
│ 1. ABE/CBE expression     │ ───> │ 2. Purification (Ni-NTA,IEX)│
└───────────────────────────┘      └───────────────────────────┘
                                                 │
                                                 ▼
┌───────────────────────────┐      ┌───────────────────────────┐
│ 4. RNP assembly (1:1.2)   │ <─── │ 3. sgRNA synthesis        │
└───────────────────────────┘      └───────────────────────────┘
              │
              ▼
┌───────────────────────────┐      ┌───────────────────────────┐
│ 5. CD34+ electroporation  │ ───> │ 6. Amplicon-seq QC        │
└───────────────────────────┘      └───────────────────────────┘

Stage 1: Protein expression

An E. coli producer over-expresses the chimeric protein (e.g. nCas9-TadA*8e for ABE) in a fermenter.

Stage 2: Protein purification

Lysis, Ni-NTA metal-affinity + ion-exchange chromatography to >98% purity.

Stage 3: sgRNA synthesis

Chemical synthesis of the guide RNA with modifications on OligoPilot.

Stage 4: RNP assembly

ABE/CBE protein and sgRNA are mixed at 1{:}1.2 at room temperature for self-assembly.

Stage 5: Ex-vivo electroporation

RNPs are electroporated into autologous CD34^+ stem cells on MaxCyte GTx.

Stage 6: Genome QC

Amplicon-seq verifies the target change and the absence of indels/off-targets before transplantation.