Thread by @vipintukur

Developing an #mRNA vaccine is a sure-shot way to success? No! Despite the spectacular performance of #Pfizer & #Moderna vaccines, we also have a #CureVac fiasco. We need to dig in much deeper into the intricacies of developing a highly efficacious mRNA vaccine 1/

https://twitter.com/vipintukur/status/1405322405862535169

There is more than low dose & impact of VOCs behind #CureVac’s failure. And here we once again need to salute the sheer brilliance of @kkariko . Will do a little thread to explain, why! 2/

No doubt, the #CureVac used a much lower #RNA dose. Dose is lower (12 (CureVac) vs 30 (#Pfizer) vs 100 ug (#Moderna)) but no idea how that translates to protein. Need to know how much of a role the lower dose played in the lower efficacy 3/

#CureVac also employed ‘2P’ substitution to fix spike protein in prefusion conformation. 4/

However, the one key difference was they used unmodified #mRNA unlike other two mRNA vaccines. The idea was that the natural, unmodified RNA's higher reactogenicity would correlate with immunogenicity and allow the same protection at a lower dose. Apparently, it does not 5/

Animal study of #CureVac induced high NAbs. But Phase 1 induced #NAbs that were ~equal to convalescent compared to several times higher for the #Moderna & #Pfizer doses. It tells us that the problem is with the RNA, the lipids, or both 6/

nature.com/articles/s4154…

Now, the main reason...is #CureVac used #uridine instead of #m1Ψ (1-methyl-pseudouridine) in their unmodified mRNA... & likely to accidentally hit #TLR before the #Ribosome that way & wind-up w/ translational shutdown via phosphorylation of IFN2α after induction of ISGs.. 7/

So, probably their product induced too much type-I #IFNs when trying to translate #mRNA. Their immunogenicity data missed checking for IFN induction? 8/

Here, I need to insert some sort of explanation regarding the '#Uridine' & '#Pseudouridine'. The normal RNA characters are A,C,G and U. U is also known as ‘T’ in DNA 9/

#mRNA molecules are single-stranded slithers of genetic code formed of #nucleosides which instruct the human cells to produce certain proteins. However, for years there was a stumbling block: mRNA caused an inflammatory reaction when injected 10/

Another problem was that #synthetic mRNA was notoriously vulnerable to the body’s natural defenses, meaning it would likely be destroyed before reaching its target cells 11/

It wasn't until 2004 that @kkariko and her colleague
@DrewWeissman found that, by using a slightly altered #nucleoside in the mRNA string, the potentially fatal problem could be overcome 12/

https://twitter.com/vipintukur/status/1336526524061679616?s=20

So, in the #Pfizer & #Moderna vaccines, every U has been replaced by 1-methyl-3 pseudouridylyl (Ψ). The really clever bit is that although this replacement placates (Calms) our immune system, it is accepted as a normal U by relevant parts of the cell 13/
cell.com/action/showPdf…

This was a master stroke by @kkariko & @DrewWeissman to use m1Ψ instead of uridine to ‘dodge’ the immune system. And may be the main reason for the success of Pfizer & Moderna vaccines but failure of CureVac 14/

ncbi.nlm.nih.gov/pmc/articles/P…

This is the reason why she is considered as a front runner for #Noble prize in Medicine or Chemistry. CureVac incident has made her claims stronger. It was sheer brilliance, hard work & perseverance that paid off in long run 15/

Those of you wish to go for further details on the issue of Uridine vs Pseudouridine trick, an interesting blog shall be quite useful 👇 16/

berthub.eu/articles/posts…

Some explanation: #Uridine is detected by TLRs, interferons are activated, and this prevents protein translation/expression. Less expression, less spike, less Antibodies, right? And #m1Ψ dodges the innate immune system & go unnoticed

Some of the tweets are based on the discussion by the #coronavirologist
@wanderer_jasnah 👇 17/

https://twitter.com/wanderer_jasnah/status/1405270761124683776?s=21

So, what are the takeaways?

For a successful #mRNA vaccine, you need:
➡️ A proper dose (to modulate adequate immune response & limit excessive innate activation)
➡️ Use ‘Synthetic’/’Modified’ mRNA (Ψ substituting U to avoid innate immune sensors)
➡️ Stabilize 'spike' (2P) 18/

➡️ Proper purification & delivery systems (encapsulated into LNPs- protect RNA against potential digestion by ribonuclease)
➡️ Thermostability
➡️ To reduce doses & longer duration of immune responses, you may need ‘self-amplifying” RNA vaccine
#Gennova 19/end