Dr. Melissa Moore, Chief Scientific Officer, Moderna Therapeutics, Inc.
One of the most exciting keynotes of the week was delivered by Dr. Melissa Moore, Chief Scientific Officer, Moderna Therapeutics, Inc., revealing the latest uses of messenger RNA in drug and vaccine development.
Dr. Melissa Moore, Chief Scientific Officer, Moderna Therapeutics, Inc., started her presentation by saying that, at Moderna, it all starts with an idea for a new therapeutic protein and its unique aminoacid sequence.
This is then back-translated using Moderna’s proprietary computer algorithm, which has been refined over the years to pick the best mRNA sequence for delivery.
For mRNA vaccine development, four essential steps are needed: (1) efficient methods to make large quantities of individual mRNAs at high purity; (2) ability to avoid the innate immune sensors that defend against RNA viruses; (3) efficient delivery methods; and (4) knowledge of how to engineer the best mRNA sequence for a particular purpose.
To achieve the first point, the Clinical train at Moderna manufactures larger batches of 5-75g+ mRNAs. These are currently being scaled up with manufacturing collaborators, with the objective of making 10x Kilograms of mRNAs in the near future.
Dr. Moore then explained that, to achieve the second point of avoiding the innate immune sensors, two type of receptors need to be eluded: Toll-like receptors (TLR), and RIG-I/MDA-5-like receptors. To avoid TLRs, Moderna mRNAs are engineered to replace all U’s with Pseudiuridines, which are natural occurring nucleotides that exist in ribosomal RNA and tRNA in our bodies and do not affect base-pairing.
To escape the RIG-I/MDA-5-like receptors, Moderna avoids the creation of double-stranded RNA (dsRNA) with state-of-the-art HPLC purification. This technique has just been published in Science Advances (June 2020). At this point, Moderna’s researchers have decided to go a step further, and reengineered T7 RNA polymerase not to produce dsRNA at all. A publication will soon come out, according to Dr. Moore; but for now, a recording of the last Annual Science Day presentation is available at Moderna’s website (June 2nd, 2020).
For the third step of an efficient mRNA delivery, most Routes of Administration (ROAs) require encapsulation with Lipid nanoparticles (LNPs, 80-100nm). At Moderna, each encased particle contains 2-6 molecules of mRNA; phospholipid cholesterol; a PEG lipid that keeps the lipid nanoparticles from aggregating; and, an ionizable lipid, that at low pH, interacts with the mRNA. Two peer-revied articles are currently available on these techniques (Sabis et al, Mol Ther, 2018; Hassett et al, Mol Ther Nuc Acids, 2019). Dr. Moore further described that mRNAs can also be nakedly injected into the heart (VEGFA) and tumours.
Finally, Dr. Moore said that in order to make a good mRNA-drug, there needs to be translation initiation fidelity, high translation efficiency, a functional mRNA half-life, and hit the correct cell type using off-logic gates (e.g., microRNAs target sites in the 3’prime UTR causing the mRNA to be degraded in case it hits an undesired cell type). All of these factors are currently being researched and developed at Moderna.
The first question in the live Q&A related to the role of RNA structure on protein translation. Dr. Moore remitted to a Moderna publication (Mauger et al, PNAS 2019), in which by fitting detailed kinetic expression data to mathematical models, they showed that secondary structure can increase mRNA half-life independent of codon usage. She further explained that higher secondary structure seems to avoid ribosomal collision and RNA degradation. Dr. Moore was then asked about computational methods used, to which she replied that they use these models to understand to the nanosecond how LNPs form and stabilize; and also, machine-learning to comprehend how different composites and structures change LNPs.
There were many questions from the audience related to the immune responses against mRNA therapeutics. Dr. Moore said that there are no adjuvants in the vaccine formulation, although the LNPs might be immunostimulatory. Responding to a following question regarding RNA stability, Dr. Moore ensured that the COVID-19 vaccine will be stable for 18 months at -200C, and then stable in the refrigerator for up to a week. In relation to the CMV vaccine, this one is presented in a lyophilized state, stable for 18 months (-200C).
The audience was curious about how naked-RNA delivery to the heart functions. Dr. Moore said that when injected in the skeletal muscle, LNPs tend to go to draining lymph nodes; although, this is not an issue in the heart muscle. The other reason for naked-RNA delivery to the heart, is that VEGFA-mRNA needs to have a very precise-localized delivery, so that no blood vessels can grow where they might create problems.
The next question related to endosomal escape and its necessity for a functional mRNA-drug. Dr. Moore said that in comparison to the competitor LNPs in the field, Moderna’s LNPs can deliver 30% mRNA into cells vs. 1-2%. They still can’t really understand the mechanism, but Moderna LNPs seem to be more efficient.
The last question regarded purity control strategy, to which Dr. Moore said that Moderna uses quality-by-design principles and multi-layer design strategy to deliver very pure mRNAs.
