No abstract

dCircumsporozoite protein (CSP) of Plasmodium falciparum is a protective human malaria vaccine candidate. There is an urgent need for models that can rapidly down-select novel CSP-based vaccine candidates. In the present study, the mouse-mosquito transmission cycle of a transgenic Plasmodium berghei malaria parasite stably expressing a functional full-length P. falciparum CSP was optimized to consistently produce infective sporozoites for protection studies. A minimal sporozoite challenge dose was established, and protection was defined as the absence of blood-stage parasites 14 days after intravenous challenge. The specificity of protection was confirmed by vaccinating mice with multiple CSP constructs of differing lengths and compositions. Constructs that induced high NANP repeat-specific antibody titers in enzyme-linked immunosorbent assays were protective, and the degree of protection was dependent on the antigen dose. There was a positive correlation between antibody avidity and protection. The antibodies in the protected mice recognized the native CSP on the parasites and showed sporozoite invasion inhibitory activity. Passive transfer of anti-CSP antibodies into naive mice also induced protection. Thus, we have demonstrated the utility of a mouse efficacy model to down-select human CSP-based vaccine formulations.

The COVID-19 pandemic continues to be a public health threat with emerging variants of SARS-CoV-2. Nirmatrelvir (PF-07321332) is a reversible, covalent inhibitor targeting the main protease (Mpro) of SARS-CoV-2 and the active protease inhibitor in PAXLOVID (nirmatrelvir tablets and ritonavir tablets). One of the predominant SARS-CoV-2 variants emerging is the B.1.1.529 Omicron harboring a mutation at amino acid position 132 in the Mpro changing a proline to a histidine (P132H). In vitro biochemical enzymatic assay characterization of the enzyme kinetics of the Omicron Mpro (P132H) demonstrate that it is catalytically comparable to wildtype and that nirmatrelvir has similar potency against both wildtype and Omicron (P132H) Mpro with Ki of 0.933nM (wildtype) and 0.635nM (P132H) each, respectively. This observation is reinforced by our structural determination of nirmatrelvir bound to the omicron Mpro at 1.63Å resolution. These in vitro data suggest that PAXLOVID has the potential to maintain plasma concentrations of nirmatrelvir many-fold times higher than the amount required to stop the SARS-CoV-2 variant Omicron from replicating in cells.

HighlightsHighly purified flagellins obtained from liquid bacterial fermentation supernatants.Purification accomplished in four process steps to clarify, bind, wash, polish.Ion-exchange membranes exhibit improved flagellin retention compared to resins.Purified flagellins retain epitope conformation, innate immune biological activity.