SARS-CoV-2 RBD-Tetanus Toxoid Conjugate Vaccine Induces a Strong Neutralizing Immunity in Preclinical Studies.

Controlling the global COVID-19 pandemic depends, among other measures, on developing preventive vaccines at an unprecedented pace. Vaccines approved for use and those in development intend to elicit neutralizing antibodies to block viral sites binding to the host's cellular receptors. Virus infection is mediated by the spike glycoprotein trimer on the virion surface via its receptor binding domain (RBD). Antibody response to this domain is an important outcome of immunization and correlates well with viral neutralization. Here, we show that macromolecular constructs with recombinant RBD conjugated to tetanus toxoid (TT) induce a potent immune response in laboratory animals. Some advantages of immunization with RBD-TT conjugates include a predominant IgG immune response due to affinity maturation and long-term specific B-memory cells. These result demonstrate the potential of the conjugate COVID-19 vaccine candidates and enable their advance to clinical evaluation under the name SOBERANA02, paving the way for other antiviral conjugate vaccines.

Quantitative assessment of C-polysaccharide in capsular polysaccharides of Streptococcus pneumoniae by 31PNMR.

Capsular polysaccharides of Streptococcus pneumoniae are key components of commercially available anti-pneumococcal vaccines; meanwhile C-polysaccharide is considered an impurity. World Health Organization recommends a strict control over the presence of this biomolecule due to the possibility of introducing an undesired response. An alternative way for assessing this impurity is focused on detect the phosphocholine residues by means of quantitative 1H-NMR. This could be tricky due to the amounts of this substituent may vary generating two C-polysaccharides forms. In this work we propose an improved quantitative NMR methodology based on 31P-NMR for the quantification of C-polysaccharide on capsular polysaccharide preparations. The technique also focuses on phosphocholine but, conversely to above-mentioned methods, allows to discriminate between phosphocholine linked in different positions. The methodology was run on samples of eleven vaccine serotypes, including seven with phosphate groups. From a rational acceptance criterion of 10 wt%, the method allows to quantified from 30 µg of the impurity in 3 mg of total polysaccharide (1 wt%) with a signal/noise ratio of 16:1. Repeatability and intermediate precision evaluation showed a relative standard deviation of 3.33 % and 8.34 % respectively. Additionally, the method provides information about structural identity of phosphate contained in capsular polysaccharides and C-polysaccharide species. This constitutes a new contribution from the NMR that highlights the power of these techniques for assessing imperative parameters in carbohydrate-based vaccines.

NMR line-fitting quantification of polysaccharide N-acylurea-based modification in glycoconjugates of Salmonella Typhi Vi polysaccharide.

The polysaccharides modification via carbodiimide reaction is one of the most applied methods for obtaining conjugated vaccines against Salmonella enterica. However, N-acylurea carbodiimide adduct generated in the process is a critical impurity in carbohydrate-based vaccines. A quantitative NMR method was developed for assessing the N-acylurea carbodiimide adduct impurity. The procedure was based on line-fitting facilities for processing the NMR signals on complex spectra. The method showed good linearity, accuracy and precision under inter-operator variation (relative standard deviation <5%). Copyright © 2017 John Wiley & Sons, Ltd.