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Pfizer/BioNTech COVID-19 vax candidate encouraging in preclinical studies

September 9, 2020

Pfizer (NYSE:PFE) and development partner BioNTech SE (NASDAQ:BNTX) announce preliminary results from preclinical studies of COVID-19 nucleoside-modified messenger RNA vaccine candidate BNT162b2.

In a viral infection model, rhesus macaques received two injections of 100 µg BNT162b2 or saline, then challenged 55 days after the second dose with a very high viral inoculum of ~1M plaque forming units of SARS-CoV-2 via intranasal and intratracheal routes. Animals immunized with BNT162b2 experienced reduced viral infection with no viral RNA detected in the lower respiratory tract. Most of the non-immunized animals showed evidence of viral RNA.

BNT162b2 induced potent SARS-CoV-2 neutralizing antibodies and viral antigen-specific CD4+ and CD8+ T cells. After two shots of either 30 µg or 100 µg of BNT162b2 21 days apart, neutralization titers were 962 in the 30 µg group and 1,689 in the 100 µg group. Geometric mean titers persisted to at least day 56 at levels higher than a panel of human convalescent sera.

BNT162b2 vaccination elicited a high frequency of CD4+ T cells that produced IFN-ɣ, IL-2, and TNF-α. Almost no IL-4 producing CD4+ cells were detectable, indicating a TH1-biased response, an immune profile believed to promote vaccine safety. It also elicited spike-specific IFN-ɣ producing CD8+ T cell responses, which is thought to promote an antiviral effect.

In a mouse model, a single immunization of BNT162b2 (0.2, 1.0 or 5.0 µg) generated B cell and T cell immune responses. SARS-CoV-2 pseudovirus neutralizing activity increased steadily to day 28, the last day titers were reported. CD4+ and CD8+ T cells from splenocytes isolated from BNT162b2-immunized mice were strongly positive for IFNγ and IL-2, producing high levels of the TH1 cytokines but minute amounts of TH2 cytokines suggesting a robust, TH1-biased T cell adaptive immune response.

The large-scale in-human Phase 2/3 trial has now enrolled over 25K participants. The companies reiterate that they remain on track to seek regulatory review as early as next month.

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