Available Configurations & Antibody Expression
Fusion BioLabs offers the Human IgG1 (QL: T250Q/M428L) Fc Engineering Expression Vector (AFV-28) as a single Fc-engineered heavy-chain vector or an Fc Engineering Set/Pair with a compatible human kappa (κ) or lambda (λ) light-chain expression vector.
For complete Fc-engineered IgG antibody expression, the heavy-chain expression vector must be co-transfected with a compatible light-chain expression vector containing the corresponding antibody VL sequence.
The Fc Engineering Set/Pair includes two separate plasmids (5.0 µg each), supplied individually in TE buffer.
Important: Antibody-specific VH and VL sequences must be cloned into the corresponding vectors unless explicitly supplied with pre-inserted variable regions. Purified antibody is not included.
Compatible light-chain expression vectors are also available separately in the Fusion BioLabs Antibody Expression Vector product category.
Fc Engineering Overview
The Human IgG1 (QL) — QL Fc Variant incorporates dual-site engineering to enhance FcRn binding and extend serum half-life. It increases FcRn affinity through complementary mutations in the CH2 (T250Q) and CH3 (M428L) domains, delivering a 1.5–3× extended serum half-life (depending on species) while fully preserving normal FcγR and C1q interactions.
Functional Profile
| Property | Effect |
|---|---|
| FcγR binding | Normal |
| ADCC | Normal |
| CDC | Normal |
| FcRn binding | Increased ↑ |
| Serum half-life | Extended ↑ |
| PK profile | Long-acting |
Mechanism of Action
The QL Fc variant introduces two complementary FcRn-enhancing mutations:
- T250Q (CH2 domain): Increases FcRn affinity at acidic pH and enhances recycling efficiency.
- M428L (CH3 domain): Strengthens FcRn interaction at the CH3 interface and improves endosomal rescue from degradation.
Together, these mutations provide robust half-life extension while preserving normal FcγR and C1q interactions.
Phenotypic Effects
- Increased FcRn binding affinity.
- Extended serum half-life (1.5–3× depending on species).
- Maintains normal ADCC and CDC.
- Preserves structural integrity and antigen binding.
- Suitable for long-acting therapeutic antibodies.
Applications
- Long-acting therapeutic antibodies.
- PK/PD optimization.
- FcRn mechanistic studies.
- Antibodies requiring preserved effector function with extended duration.
- Preclinical development of extended-half-life biologics.
Sequence Map & Feature Annotation
Human IgG1 (T250Q/M428L)
Insert Architecture: VH – CH1 – hinge – CH2(T250Q) – CH3(M428L)
- VH: Variable heavy domain
- CH1: Constant heavy 1
- Hinge: Native IgG1 hinge
- CH2(T250Q): FcRn-enhancing mutation
- CH3(M428L): FcRn-enhancing mutation
Comparison within Fusion BioLabs FcRn / PK-Modulated Fc Variant Family
| Variant | Mechanism | Strength (PK Extension) | Primary Application & Notes |
|---|---|---|---|
| human IgG1 (WT) (Wild-Type) |
Native FcRn binding | ★★☆☆☆ | Baseline Control. Standard physiological baseline (∼21-day half-life in humans). |
| human IgG1 (N434A) N434A |
Single-point FcRn-enhanced | ★★★☆☆ | Single-point mutation providing a moderate 1.5–2× PK boost with low immunogenicity risk and easy manufacturing integration. |
| human IgG1 (LA) M428L / N434A |
FcRn-enhanced | ★★★★☆ | Strong PK Extension. Dual mutation combining M428L and N434A; enhances acidic FcRn binding with minimal neutral binding. |
| human IgG1 (LS) M428L / N434S |
FcRn-enhanced | ★★★★★ | Very Strong PK Extension. Extends human serum half-life up to 3–5× (>70–90 days; e.g., tixagevimab/ cilgavimab). |
| human IgG1 (YTE) M252Y / S254T / T256E |
FcRn-enhanced | ★★★★★ | Benchmark PK Extension. Industry-standard benchmark delivering ∼3–4× PK boost in humans (e.g., nirsevimab / Beyfortus®). |
| human IgG1 (QL) T250Q / M428L |
FcRn-enhanced | ★★★★☆ | Moderate-to-Strong PK Extension. Increases acidic FcRn affinity with favorable intellectual property freedom to operate. |
| human IgG1 (YTE + KF) M252Y/S254T/T256E + H433K/N434F |
Hyper-FcRn-enhanced / FcRn Blocker | ★★★★★ | FcRn Antagonist / Autoimmune Control. Binds tightly across pH 6.0 and 7.4 to block FcRn recycling and clear endogenous IgGs. |
| human IgG1 (V308P) V308P |
Controlled/Accelerated Clearance | ★★☆☆☆ | Tunable Fast-Clearance Variant. Modulates FcRn dissociation kinetics to yield accelerated clearance (2–5-day half-life); ideal for ADCs and immuno-PET imaging to limit non-target toxicity. |
| human IgG1 (I253A) I253A |
FcRn-null / Abrogated | ★☆☆☆☆ | Ultra-Fast Clearance Control. Complete knockout of the core FcRn binding triad; rapidly cleared within hours. |
Storage & Handling
- Store plasmid at −20°C.
- Avoid repeated freeze–thaw cycles.
- Use sterile technique when handling.
- Suitable for transient or stable mammalian expression.
References
- Hinton PR, Johlfs MG, Xiong JM, Hanestad K, Ong KC, Bullock C, Keller S, Tang MT, Tso JY, Vásquez M, Tsurushita N. Engineered human IgG antibodies with longer serum half-lives in primates. J Biol Chem. 2004;279(8):6213-6216.
- Hinton PR, Xiong JM, Johlfs MG, Tang MT, Keller S, Tsurushita N. An engineered human IgG1 antibody with longer serum half-life. J Immunol. 2006;176(1):346-356.
- Datta-Mannan A, Witcher DR, Lu J, Wroblewski VJ. Influence of improved FcRn binding on the subcutaneous bioavailability of monoclonal antibodies in cynomolgus monkeys. MAbs. 2012; 4(2):267-273.
