Thread by @vipintukur

‘#Spike protein’ is the major target of #NAbs in infected/vaccinated people. The prefusion conformation of the Spike represents the most relevant target because Abs can successfully interfere w/ infection only if they prevent binding to target cells or prevent fusion itself 1/

https://twitter.com/EricTopol/status/1405950829417222145

Various approaches are adopted to express ‘#Spike’ protein in vivo, such as nucleic acid structures & virus vectors. Alternatively, other vaccine platforms like recombinant protein particles & inactivated vaccines can directly deliver this protein 2/

Most structural studies of the wild-type spike protein exhibited one #RBD in the 'open' conformation. By contrast, 2 or 3 RBDs were observed in the open conformation in the more infective #D614G mutant--the RBD #conformation plays a vital role in the infectivity of SARSCoV2 3/

Spike is not standing up on a top of a virus surface (because there is no virus), but free floating. This is a problem as spike protein would collapse into diff shape that isn’t like the virus spike anymore. The vaccine would not work well in this way 4/

So, it is critical to stabilize 'Spike' in prefusion conformation to present #RBD in an 'open' form to immune system & avoid folding of RBD. Potent, high avidity non-binding Abs can be formed if RBD remains in an open form 5/

For example, subunit vaccines that can elicit S-specific #NAbs should present lower #ADE risks (especially against S stabilized in the prefusion conformation, to reduce the presentation of non-neutralizing epitopes). These design should reduce potential ADE ass with non-NAbs 6/

Researchers now know which genetic modifications would stabilize the spike in its “prefusion” configuration—important for a robust and safe antibody response 7/

They changed nucleotides in such a way that new sequence now coded for 2 Proline AA in front of CH that would stabilize the spike in its “prefusion” conformation: the '2P' substitution 8/

This ‘key’ 2 proline (P) substitutions (genetic mutation) in vaccine design is critical for vaccine success. This #2P substitution was incorporated into the #mRNA vaccine & few other vaccines designs 9/

Few vaccine developers like Australian, University of Queensland (#UQ) have used a “molecular clamp”, a small 80-AA fragment of an HIV protein (red), technology to stabilize spike. Unfortunately, that HIV fragment also generated Abs that could confuse HIV diagnostic tests 10/

This led the UQ to abandon their vaccine development plan though there was nothing wrong with the vaccine 11/

Now, many vaccine developers (I am aware of five) have incorporated this '2P' substitution in the vaccines. And #CureVac was also one of them, yet it failed. #JNJ also have this but it performed not so well as #SputnikV which doesn't have this substitution 12/

So, what does it inform? Stabilizing the Spike in its 'prefusion conformation' is one critical aspect of vaccine development. There are other issues also that may help a vaccine succeeds 13/

This @NEJM study points toward key advantages of having a spike from #D614G strain. They describe G614 spike as a "formidable" antigen 14/

nejm.org/doi/pdf/10.105…

A recent study in @CellCellPress indicate that vaccines based on #B117 may broadly protect against all current variants including beta, gamma & delta 15/

cell.com/cell/fulltext/…

This observation provides new insight for vaccine policy with future vaccines in non-immune populations. So, why not utilize #B117 Spike for next generation vaccines? It should be far more formidable against all VOCs than based on D614G!!

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cell.com/cell/fulltext/…