Missed a big detail last night in the Pfizer/BioNTech announcement. They're actually going forward into Phase II/III trials with the BNT162b2 mRNA vaccine candidate, not the BNT162b1 mRNA vaccine candidate, which had been the focus of all the press and papers to date. The differences are in what parts of the SARS-CoV-2 spike protein and other proteins are encoded into the chimp adenovirus vector. Derek Lowe explains it nicely in today's In the Pipeline, below. Sorry for missing that last night. I don't think it really makes a huge difference, since both, supposedly had similar responses in humans, with the b1 version having a slightly better T-cell response and lower levels of side effects. Hopefully, they've made the right choice.
https://blogs.sciencemag.org/pipeli.../pfizer-and-biontech-pick-a-vaccine-candidate
It comes down to the antigen(s) being coded for. The b1 candidate, the one we’ve been hearing about, codes for the coronavirus Spike protein’s receptor-binding domain (RBD), and this was constructed as a trimer, three RBDs attached to a “foldon” protein core. Meanwhile, the b2 candidate codes for what they say is an “optimized full-length Spike” protein instead, not just the receptor-binding domain. Pfizer’s press release says that both the b1 and b2 candidates “induced favorable viral antigen specific CD4+ and CD8+T cell responses, high levels of neutralizing antibody in various animal species, and beneficial protective effects in a primate SARS-CoV-2 challenge model“. But they made the choice for the b2 variety partly because it seemed to be better tolerated on injection, and also because it led to a wider variety of T-cell responses. These include both CD4+ and CD8+ T-cells, and these were raised not only to recognize the RBD region, but also other regions of the Spike protein that weren’t contained at all in the b1 candidate. And they’re quite right – that could well be beneficial, and the better tolerability is a bonus. The release says that the neutralizing antibody response was similar between the two candidates.
I saw that too. I thought they were going ahead with both, but apparently read that wrong. Thanks for explaining.