Monoclonal Antibody Purification Process
The industry platform process for IgG purification — Protein A capture, ion exchange polishing, viral clearance, and UF/DF formulation
Process Overview
The mAb platform process is the most standardized downstream process in biopharmaceuticals. Over 90% of approved monoclonal antibodies use a variant of this 5–6 step sequence. Starting from CHO cell culture harvest (~1–5 g/L IgG in ~10 L to 20,000 L bioreactors), the process achieves >99.5% purity with overall yields of 70–85%.
Process Steps
1
Clarification
Harvest Clarification
Remove CHO cells and cell debris from bioreactor harvest. Two-stage: centrifugation (disc-stack, 5,000–12,000 ×g) followed by depth filtration (0.2–0.5 μm). Alternatively, single-stage with high-capacity depth filters for smaller scales.
Yield: >98%
Removes: Cells, debris
2
Affinity Chromatography
Protein A Capture
The workhorse of mAb purification. Protein A ligand binds the Fc region of IgG with high specificity. Load clarified harvest at pH 7.0–7.4, wash to remove host cell proteins (HCP) and DNA, elute at low pH (3.0–3.5). Single step achieves >95% purity from crude harvest.
Yield: 90–95%
Purity: >95%
Resin cost is dominant
3
Viral Inactivation
Low pH Viral Inactivation
Hold the Protein A eluate at pH 3.5–3.8 for 30–60 minutes to inactivate enveloped viruses. This leverages the already-low elution pH. Neutralize to pH 5–6 afterward. Required by regulatory agencies for patient safety.
Yield: >99%
LRV: ≥4 log
Cost: Minimal
4
Ion Exchange Chromatography
CEX / AEX Polishing
Cation Exchange (CEX): Bind-and-elute mode at pH 5.0. IgG (pI ~8.5) is positively charged and binds. Elute with NaCl gradient. Removes aggregates, charge variants, leached Protein A.
Anion Exchange (AEX): Flow-through mode at pH 7–8. IgG passes through while DNA, endotoxins, and acidic HCP bind. Often used after CEX for additional polishing.
Yield: 85–95%
Purity: >99%
5
Viral Filtration
Nanofiltration (20 nm)
Pass through 20 nm parvovirus-retentive filter. Removes non-enveloped viruses that survive low pH treatment. IgG (150 kDa, ~10 nm hydrodynamic radius) passes through; viruses (>20 nm) are retained. Second independent viral clearance step required by regulators.
6
UF/DF Formulation
Ultrafiltration / Diafiltration
Final concentration and buffer exchange into formulation buffer (typically histidine or phosphate buffer with polysorbate 80). 30 kDa MWCO TFF system. Concentrate IgG to 10–150 mg/mL depending on product. 6–10 diavolumes for complete buffer exchange.
Yield: >95%
Final: 10–150 mg/mL
Cost Considerations
| Step | Key Cost Driver | Relative Cost |
|---|
| Clarification | Centrifuge + depth filters | Low–Medium |
| Protein A | Resin (most expensive single item) | High |
| Viral Inactivation | Hold tanks + pH control | Low |
| Ion Exchange | Column hardware + resin | Medium |
| Viral Filtration | Single-use nanofilters | Low–Medium |
| UF/DF | TFF cassettes + system | Medium |
Protein A resin is the single largest cost driver in mAb downstream processing. Newer alternatives (multimodal chromatography, continuous processing) aim to reduce this dependence. Use
untangle.bio to model costs at your specific scale.
Target Molecule: IgG
| Molecular Weight | 150,000 Da (150 kDa) |
| Isoelectric Point (pI) | 8.5 (basic protein) |
| Charge at pH 7 | +5 (cationic) |
| Solubility | 150 g/L |
| Density | 1.38 g/cm³ |
| Diffusion Coefficient | 4.0 × 10-7 cm²/s |
| Structure | Y-shaped, 2 heavy + 2 light chains, Fc + 2 Fab regions |
View full IgG molecule page →
Frequently Asked Questions
Why is Protein A chromatography used for almost all mAbs?
Protein A binds the Fc region of IgG with extremely high specificity and affinity (Kd ~10 nM). This means it works for virtually any IgG regardless of the variable region. A single Protein A step goes from crude harvest (~5% IgG) to >95% purity—no other technique achieves this in one step.
Can I skip Protein A to reduce cost?
Yes, but it requires more polishing steps. Alternative capture methods include cation exchange (CEX) at low pH, mixed-mode chromatography, or precipitation. These typically require 2–3 additional steps to reach equivalent purity. The tradeoff: lower resin cost but higher complexity and lower overall yield.
What are the regulatory requirements for viral clearance?
ICH Q5A requires at least two orthogonal viral clearance steps with documented log reduction values (LRV). The standard approach: (1) low pH inactivation (enveloped viruses, ≥4 LRV) + (2) nanofiltration (non-enveloped viruses, ≥4 LRV). Total viral clearance should exceed 12–16 log10 across all steps.
What is the typical processing time for mAb DSP?
2–4 days for a single batch. Protein A is the bottleneck (4–8 hours including load/wash/elute/CIP). Each chromatography step: 4–8 hours. UF/DF: 2–4 hours. Total hands-on time has been significantly reduced by automation and continuous processing.
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