Thread by @KristaGFreeman

Virtual conferencing = pipette-free-hands = finally a chance to tweet about our new paper!

Introducing BaDAS and DEaDAS, mycobacteriophage-based COVID-19 vaccine candidates - recently published in @Micro_MDPI
mdpi.com/1371530

My first ever tweetorial below...

Early in the pandemic we in the @GHatfull lab, stuck at home, started a journal club to keep our science skills sharp. I presented @JeremyJBarr's seminal work on the enrichment of phages with exposed Ig-like domains on mucosal surfaces: pnas.org/content/110/26…

The resulting conversation, coupled with the worldwide lockdown, inspired @GHatfull to revisit an old idea: could Ig-like domains on mycobacteriophage capsids be replaced with foreign (SARS-CoV-2) antigens to make a phage-based vaccine? I wanted to find out!

We decided to try it on phage Bxb1. Bxb1 doesn't actually have Ig-like domains, but it DOES display non-essential domains of unknown function on its surface... here's a sneak preview of my cryo-EM structure showing those domains sticking out of the capsid floor:

So in May 2020, @kswetzel1 and I got cracking. We were soon back in the lab, awash with synthetic DNA substrates. We spent the next month madly picking plaques and running gels as we attempted to engineer recombinant phages with CRISPY-BRED.
nature.com/articles/s4159…

After some setbacks (see unsuccessful constructs below) we found a strategy that worked: instead of replacing the native displayed domain, build off of it. Using this approach we displayed epitope-rich 30-amino acid peptides of the Receptor Binding Motif on the Bxb1 capsid.

Thus, BaDAS: Bacteriophage Displaying Antigens of SARS-CoV-2

But we didn't stop there! @kswetzel1 incorporated a mammalian expression cassette encoding the Receptor Binding Domain into the BaDAS genome, giving a vaccine class:
DNA Encoded and Displayed Antigens of SARS-CoV-2

The next step was prepping phage for mouse studies. Amplifying mycobacteriophages in liquid culture is challenging, and supply chain issues made disposable petri dishes precious... so I put on my phage pharmer hat and used giant cafeteria trays instead.

We handed off our phage vaccine candidates to the Williams lab (@Jgecko77) who immunized mice, harvested serum and delivered our first positive ELISA and Western blot data!

I was very excited by the preliminary results and decided to try my hand at ELISAs and Westerns. Much to my surprise, it seems I awakened an immunology enthusiast that was sleeping inside me all these years...

Hundreds of ELISAs and dozens of blots later, we concluded that some of our candidates (especially BaDAS-1) could induce a respectable anti-Spike antibody response... though this paled in comparison to the anti-phage response.

So immunization with our phage-based vaccine candidates can produce Spike-binding antibodies... but are they protective? The McElroy lab (@fablabpitt) tested this with live virus neutralization assays. Unfortunately, none of the antibodies were neutralizing.

So that is where our story ends... for now! Luckily, professional vaccinologists have been more successful and their efforts will hopefully see the world through this pandemic. We still believe this platform has potential, and I am working on ways to improve it for the future.

It's worth noting that we weren't the only phage enthusiasts trying to make a COVID vaccine. There are several other studies reporting varying levels of success. A great example is this tour de force effort from the Rao lab:
science.org/doi/10.1126/sc…

Big thanks to all the co-authors on this project. It was a thrilling ride and a great experience of scientific teamwork. Thanks also to @MotherOfPhage and @ReefViruses for serving as Guest Editors for this special issue of Microorganisms.