News came out on July 13, 2023, that the “FDA backs new $82M mRNA manufacturing center at MIT” to build a continuous mRNA manufacturing platform.
To me, who has been working on both continuous bioprocessing and mRNA, this is a very exciting moment, as this thought has been with me for some time now. Continuous bioprocess offers quite some potential benefits compared to traditional batch-mode manufacturing, including but not limited to higher efficiency, cost reduction, consistent product quality, etc. This technology has mainly been explored in the biologics world (especially among monoclonal antibodies) due to the longer history of the drug modality and more mature platform processes, which make the continuous process easier to be implemented. But even in the biologics world, though many companies claimed that they have the capability of producing in a continuous format, very few of them can really achieve end-to-end continuous manufacturing.
Below, I summarized a few of my thoughts on challenges and potential feasibility of continuous manufacturing of mRNA.
- A truly continuous upstream process will be a bottleneck for this platform.
The upstream process for mAbs and mRNA is very different. We use cell culture to produce the mAbs of interest, and once produced, a large portion of them will be secreted into the cell culture. That is what makes the perfusion bioreactor possible. With products outside of cells, we can use a filter device, e.g., ATF, to sieve products and send cells back to the culture for the next round of mAb production. There is a distinct size difference in cells and mAbs.
However, for mRNA upstream production, rather than using cell culture, in vitro enzymatic reaction is used, and plasmid DNA is used as the template to produce mRNA, which is larger, but not to any significant extent. Therefore, it would be challenging to separate the two of them based on their sizing difference. Apart from pDNA, there are many smaller components, such as different enzymes, NTPs, salts, etc., that will be going to the permeate side of the ATF device together with mRNA, which will need to be replenished continuously.
Researchers are now looking into solid-phase IVT in which the template plasmids are conjugated onto the solid beads and therefore can be easily removed from the produced mRNA by mass convection. ThermoFisher already has some products marketed as the DynabeadsTM. The idea is really good. But this technology is only applicable for large-scale mRNA production with the same sequence. Otherwise, if the mRNA sequence is different, then multiple batches of solid beads with different templates will be needed, which greatly increases the COGs due to customization of many different beads. Or if the amount of mRNA needed is not that large, then it is also hard to justify the high cost of customized beads as well.
- DNase and proteinase can be used as continuous steps.
Before any chromatography and TFF, DNase and proteinase can be added to break down the large pDNA and enzyme molecules. Many companies have already been applying this to their platforms. And it is not hard to make the two steps continuous. They just need a mixing device with appropriate temperature control, and incubation time. There are two ways I know that can achieve this goal. One is with an incubation chamber, and the other is with a column that is not chemistry-modified on the beads.
- Continuous Ultrafiltration/Diafiltration (UF/DF) will be easy to implement.
With more than one player in the single-pass TFF field, it is a piece of cake to make the TFF process fit into the complete continuous process. Both Pall and MilliporeSigma already have solutions for this.
For the continuous DF for drug substance (DS) formulation, there are also options out there, either with a fully continuous DF process using Inline Diafiltration device from Pall (more buffer consumption though), or other semi-continuous DF systems that are utilizing two or more feed vessels (similar concept with multi-column chromatography).
- mRNA formulated into LNP is already a continuous process.
By nature, this process is continuous. Just need to be mindful of the pH control if to do inline pH adjustment with acid. After LNP production, purification of it is essentially the same process as with mRNA by using TFF devices for UF/DF.
- PAT will be an important part of the continuous manufacturing.
One big advantage that can be explored is in-process PAT control which has been an important topic in mAb production for a long time. Continuous monitoring and real-time process feedback are essential to assure target specifications are met consistently. Recent improvements in analytical tools, such as biosensors, Raman spectroscopy, fiber optics, nanoparticle sizer, etc. is enabling real-time control through PAT. Applying the same technologies to mRNA continuous manufacturing will be straightforward.
Overall, many of the technologies aiming for continuous bioprocessing of mAbs can be easily transferred into mRNA manufacturing. However, there are still many challenges to be solved and it will take time. Even for mAbs, although we’ve been talking about continuous for years, there are still very few companies that can really achieve it. And it will be the same for mRNA as well. But we cannot deny the fact that this is a trend, and it will be something that will come true one day.