1 Detailed Core Content
1.1 Establishment, Characterization and Release Testing of MCB and WCB
Process Overview
- Pre-MCB: Competent E. coli cells are transformed with the target plasmid. Single colonies are isolated via selective culture, expanded, and preserved in glycerol stock cryovials.
- MCB (Master Cell Bank): Derived from pre-MCB expansion. Cell culture is terminated when OD₆₀₀ ≥ 2.0, followed by glycerol supplementation and cryopreservation.
- WCB (Working Cell Bank): Manufactured through scale-up expansion of the MCB and cryopreserved under identical storage conditions.
Impacts of Critical Process Parameters on Quality Attributes
1.Fermentation temperature (32 ± 2°C): Governs cellular growth kinetics. Elevated temperatures may trigger stress protein expression or plasmid loss, compromising plasmid copy number and sequence stability; suboptimal low temperatures suppress volumetric productivity.
2.Cultivation duration: Harvest is performed upon reaching a defined cell density to sustain cell viability. Prolonged cultivation depletes nutrients and accumulates metabolic byproducts, elevating risks of bacteriophage contamination and host DNA/RNA impurities, which impede linearized plasmid purity.
3.Selective pressure (antibiotic concentration): Mandatory for plasmid retention. Deviations from set concentrations drastically increase plasmid loss rates.
1.2 Production and Release Testing of Linearized Plasmid DNA
Process Overview
1.Thaw WCB vials, perform shake flask seed expansion, and inoculate production bioreactors with animal-component-free minimal salt-glucose medium.
2.Harvest biomass post-fermentation and recover plasmid DNA via chemical lysis.
3.Purify circular plasmid through ultrafiltration/diafiltration (UF/DF) and standard chromatographic workflows.
4.Digest purified circular plasmid with restriction endonucleases to generate linearized plasmid.
5.Conduct post-linearization UF/DF buffer exchange, followed by 0.2 μm sterile filtration.
Impacts of Critical Process Parameters on Quality Attributes
1.Fermentation scale and medium composition (animal-component-free minimal glucose-salts formulation): Determine biomass yield and plasmid volumetric titer. High-cell-density fermentation elevates host cell DNA/protein impurity loads, which must be removed via downstream purification. Glucose-limited feeding strategies theoretically reduce organic acid buildup.
2.Chemical lysis conditions (pH, temperature, incubation time): Regulate plasmid release and degradation, directly modulating residual host DNA levels.
3.Chromatographic purification (mobile phase gradient, volumetric flow rate): Optimized separation resolves supercoiled plasmids from open-circular and linear isoforms to achieve high circular plasmid purity.
4.Restriction endonuclease linearization (enzyme dosage, incubation time, temperature): Complete linearization is non-negotiable. Uncut circular template DNA generates aberrant IVT transcripts such as double-stranded RNA (dsRNA) or truncated mRNA, deteriorating RNA purity and integrity.
5.UF/DF and filtration steps (molecular weight cutoff, transmembrane pressure): Govern concentration fold and buffer exchange efficiency.
1.3 Manufacturing and Release Testing of mRNA Drug Substance (DS)
Process Overview
1.In Vitro Transcription (IVT): Reaction system comprises linearized plasmid template, nucleotide triphosphates (ATP, CTP, m1ΨTP, GTP), 5’ cap analog, T7 RNA polymerase, and inorganic pyrophosphatase. Batch feeding is implemented to suppress dsRNA formation and related impurities.
2.DNase I Digestion: Degrades residual template plasmid DNA.
3.mRNA Purification: Captures full-length target mRNA and eliminates dsRNA contaminants.
4.UF/DF: Concentrates mRNA and performs buffer exchange into formulation buffers such as HEPES-EDTA buffer (pH 7.0).
5.Final filtration and bulk filling: Sequential 0.45 μm and 0.2 μm filtration, followed by cryopreservation in EVA bags at −15 °C to −25 °C.
Critical Process Parameters
1.NTP dosing volumes: Limiting ATP or CTP concentrations generate truncated transcripts and reduce RNA integrity; excess NTP concentrations exacerbate dsRNA formation, a high-priority immunogenicity-related CQA. Bolus fed-batch strategies maintain low steady-state NTP concentrations to minimize dsRNA impurities.
2.Reaction temperature (32–40 °C, designated CPP): Modulates enzymatic activity, mRNA productivity and secondary RNA structure formation.
3.Enzyme loadings (T7 RNA polymerase, inorganic pyrophosphatase): T7 polymerase dosage controls transcription velocity and fidelity; pyrophosphatase hydrolyzes inorganic pyrophosphate (PPi) to prevent magnesium ion chelation. Insufficient enzyme dosing leads to incomplete transcription.
4.DNase I incubation parameters (time, temperature, cofactors including CaCl₂ and EDTA): Ensures complete degradation of template DNA (residual host DNA is a core CQA); EDTA chelates divalent cations to terminate nuclease activity.
5.UF/DF operating conditions (transmembrane pressure, diavolume exchange): Removes small-molecule impurities (unreacted NTPs, enzyme fragments). Insufficient diafiltration retains residual impurities; over-diafiltration dilutes mRNA or induces RNA shear degradation.
1.4 Manufacturing and Release Testing of mRNA-LNP Drug Product (DP)
Process Overview
1.LNP formation: Aqueous mRNA DS phase and ethanolic lipid mixture are co-mixed via microfluidic platforms to self-assemble LNPs.
2.Tangential Flow Filtration (TFF): Removes ethanol, concentrates LNPs, and performs buffer exchange to target RNA concentration and formulation buffer.
3.Sterile filtration and aseptic filling.
4.Ultra-low-temperature storage (−90 °C to −60 °C).
Critical Process Parameters and Corresponding Quality Attribute Impacts
1.N/P ratio: The most fundamental CPP. Low N/P ratios reduce mRNA encapsulation efficiency, leaving uncomplexed free mRNA susceptible to degradation and unwanted immunostimulation; excessively high N/P ratios raise cytotoxicity risks and compromise LNP colloidal stability. This parameter governs electrostatic complexation and nanoparticle assembly kinetics, directly determining encapsulation efficiency and intracellular delivery potency.
2.Ethanol-aqueous phase mixing ratio, volumetric flow rates and shear force: Regulate nanoparticle self-assembly kinetics. Rapid controlled mixing generates uniform small LNPs (60–80 nm); slow mixing yields particles with elevated polydispersity index (PDI) or aggregation, altering DLS particle size and PDI (key CQAs) and shelf stability.
3.TFF diavolume and buffer exchange cycles: Stripping ethanol to concentrations complying with ICH Q3C residual solvent limits while concentrating mRNA to target potency. Incomplete ethanol removal introduces toxicity and destabilizes LNPs; over-processing causes LNP disassembly and mRNA leakage.
4.TFF transmembrane pressure and crossflow velocity: Modulate fluid shear stress. Excessive shear ruptures LNP lipid bilayers, releasing encapsulated mRNA and lowering encapsulation efficiency and RNA integrity.
5.Sterile filtration and filling (filter membrane compatibility, operating pressure): Achieve microbial sterility while minimizing LNP retention and particle aggregation on filter media.
Conclusion
