Full Analysis Of The MRNA Drug Manufacturing Process: How TFF Technology Solves Purification Challenges
In recent years, mRNA technology has achieved breakthrough progress in the biopharmaceutical field, demonstrating tremendous application potential, particularly in vaccines and gene therapy. The successful development of mRNA vaccines has not only provided new solutions for the prevention and control of infectious diseases, but has also driven advances in cancer immunotherapy and personalized medicine. As a novel class of therapeutic products, large-scale mRNA manufacturing is highly challenging, involving control of RNA stability, removal of residual enzymes and reaction by-products, buffer exchange, and the achievement of high-purity recovery rates, all of which require manufacturing technologies with regulatory-approved solutions.
The manufacturing process of mRNA vaccines or therapeutics is mainly divided into three stages: preparation of plasmid DNA bulk solution, preparation of mRNA bulk solution, and preparation of mRNA–LNP drug product.
mRNA Drug Manufacturing Process Flowchart
Tangential flow filtration (TFF), as a well-established membrane separation technology, is widely applied in mRNA manufacturing due to its high-efficiency molecular sieving capability, controllable buffer exchange, and low shear stress characteristics. Based on membrane module design, common TFF configurations include flat-sheet cassettes and hollow-fiber modules. In addition, pressure-driven membrane separation in TFF can be classified into microfiltration (MF), ultrafiltration (UF), nanofiltration (NF), and reverse osmosis (RO) according to membrane pore size, with progressively increasing selectivity.
TFF plays a critical role across multiple stages of mRNA drug manufacturing, including the preparation of plasmid DNA bulk, mRNA bulk production, and the final formulation of mRNA–LNP drug products. Through appropriate selection of membrane type, molecular weight cut-off (MWCO), and membrane material, TFF enables efficient removal of reaction by-products and low-molecular-weight impurities, while also facilitating buffer exchange and concentration both before and after LNP encapsulation. This significantly enhances RNA purity, stability, and overall process scalability.
In addition, the performance of tangential flow filtration is influenced by system configuration factors such as pump type and tubing design, as well as key process parameters including transmembrane pressure (TMP), shear stress, and filtration flux. These factors must be carefully selected and optimized based on the characteristics of the target product, particularly for stress-sensitive products such as mRNA–LNP, which are highly susceptible to external mechanical forces during processing.
Purification of plasmid DNA
The preparation of plasmid DNA stock solution is fundamentally based on the sequence design of the transcription template. The preparation methods typically involve plasmid DNA amplification, though PCR amplification can also be used. Taking DNA amplification as an example, engineered E. coli is commonly used for fermentation-based amplification. The downstream purification process mainly includes cell collection, lysis and clarification, concentration and buffer exchange, sterile filtration, linearization, and chromatographic purification. In industrial settings, continuous-flow centrifugation is often used for cell collection, but it generates relatively high shear forces. Hollow fiber systems, with their open channels and low shear, are more suitable for handling samples with high solid content, high viscosity, or shear sensitivity, such as plasmid DNA. After collection, the cells are subjected to high-pressure homogenization, ultrasonication, or alkaline lysis, followed by preliminary clarification through depth filtration.
To facilitate subsequent chromatography, tangential flow filtration (TFF) using membrane cassettes or hollow fiber columns with molecular weight cut-offs of 30 kDa, 100 kDa, or 300 kDa is often employed first for concentration and buffer exchange. This reduces the sample volume while simultaneously removing some impurities such as RNA, host cell proteins (HCP), and host cell DNA fragments (HCD). Chromatography serves as the core purification step. Typically, anion exchange chromatography (AEX) is combined with hydrophobic interaction chromatography (HIC) to efficiently remove impurities and enrich highly bioactive supercoiled plasmid DNA, thereby significantly improving plasmid purity.
After purification, the plasmid is subjected to TFF again to concentrate the solution to the target concentration (usually 0.5–2 mg/mL) and to perform dialysis with the final storage buffer. This step removes residual salts and organic solvents from the process, ensuring that the buffer system meets the requirements for downstream in vitro transcription (IVT) reactions.
Purification of in vitro transcribed (IVT) mRNA
In vitro transcription (IVT) and modification are the key processes for the preparation of mRNA stock solutions. During IVT mRNA production, a combination of tangential flow filtration (TFF1) – chromatography – tangential flow filtration (TFF2) is employed. This strategy ensures efficient and high-quality purification of mRNA, providing critical support for vaccine manufacturing.
After the transcription and modification reactions are completed, ultrafiltration/diafiltration using membrane cassettes or hollow fiber columns with molecular weight cut-offs of 30 kDa, 100 kDa, or 300 kDa is typically performed first. This step effectively removes various process-related impurities from the reaction system, such as RNA polymerase, residual DNA fragments, unreacted NTPs, capping enzymes, double-stranded RNA (dsRNA), and small-molecule inhibitors, while simultaneously achieving buffer exchange. After a single tangential flow filtration step, most impurities are effectively removed, and the only detectable residual protein impurity is RNA polymerase.
Subsequently, multiple chromatography techniques are applied for further purification. Commonly used methods include affinity chromatography, size-exclusion chromatography, ion-pair reverse-phase chromatography, and ion-exchange chromatography. Through this combination of ultrafiltration and sequential chromatography, the mRNA achieves a high level of purity.
To meet formulation or storage requirements, the mRNA stock solution is again concentrated or diluted using 30 kDa, 100 kDa, or 300 kDa membrane cassettes or hollow fiber columns to precisely adjust the target concentration and exchange into the final formulation buffer. Finally, sterile-grade filtration is applied to control microbial load, completing the temporary storage and filling of the material.
Exploration of TFF-related process parameters: Relevant studies have shown that a membrane with a molecular weight cut-off (MWCO) of 100 kDa provides the optimal purification efficiency; the transmembrane pressure (TMP) should not exceed 5 psi; and an mRNA concentration of 1 mg/mL ensures a relatively high permeate flux (>25 LMH).
Purification of mRNA-LNP formulations
Lipid nanoparticles (LNPs) are currently the most extensively studied delivery system for mRNA therapeutics. At present, various mRNA-LNP formulations are in different stages of preclinical and clinical development. LNPs are highly sensitive to manufacturing processes. Among the unit operations required for mRNA-LNP production, concentration and buffer exchange via tangential flow filtration (TFF) as well as sterile filtration present significant challenges. These steps must be carefully optimized to ensure process scalability and product quality, while avoiding issues such as membrane fouling and incorrect filter loading.
After mRNA encapsulation, tangential flow filtration (TFF) is used for purification. The purpose of this step is to remove unencapsulated mRNA, free polymers or lipid materials, as well as residual solvents from mRNA and lipids. Since mRNA-LNPs exhibit limited stability at room temperature, optimization of downstream processes, including TFF, is critical to maintaining product quality.
Key optimization directions include: appropriately setting the transmembrane pressure (TMP) and tangential flow rate based on the particle size and stability of mRNA-LNPs to balance filtration efficiency and particle stress; selecting membranes or hollow fiber columns with suitable molecular weight cut-offs (MWCO, e.g., 100 kDa or 300 kDa) to efficiently remove free mRNA, impurities, and exchange buffer while minimizing particle adsorption or damage; and optimizing the concentration and diafiltration volumes to ensure effective buffer exchange into the target formulation and control the final particle concentration and dispersity.
Additionally, critical quality attributes (such as particle size, polydispersity index [PDI], and mRNA encapsulation efficiency) must be closely monitored during the process, and parameters dynamically adjusted based on real-time data to achieve stable, scalable, and efficient purification and formulation of mRNA-LNPs.
In addition, due to the instability of mRNA-LNPs and their components under terminal sterilization methods, a 0.2 µm sterile-grade filter is typically used to remove bacteria and other microbial contaminants.
