Evaluation of a standardised Vi poly-l-lysine ELISA for serology of Vi capsular polysaccharide antibodies

Peter Rigsby,Emma Beamish,Alastair Logan,Elizabeth Jones,Sean C Elias,Krisztina Hitri,Ravipratapnarayan Mishra,Melita A Gordon,Jason Hockley,Akshay Goel,Eleanor Atkinson,Firdausi Qadri,Marcela F Pasetti,Maurice Mbewe,Jae Seung Yang,Andrew J Pollard,Sjoerd Rijpkema,D Raju ,James Meiring ,Novilia Sjafri Bachtıar

doi:10.1016/j.biologicals.2020.05.002

Abstract

Typhoid vaccines based on protein-conjugated capsular Vi polysaccharide (TCVs) prevent typhoid in infants and young children. Analysis of the serum anti-Vi IgG response following immunisation against typhoid confirms the immunogenicity of TCVs and forms an important part of the pathway to licensing. Comparative studies could expedite the licencing process, and the availability of a standardised ELISA method alongside the 1st International Standard (IS) 16/138 for anti-typhoid capsular Vi polysaccharide IgG (human) will facilitate this process. To this end, a non-commercial ELISA based on a coat of Vi and poly-l-lysine (Vi-PLL ELISA) was evaluated by 10 laboratories. Eight serum samples, including IS 16/138, were tested in the standardised Vi-PLL ELISA (n = 10), a commercial Vi ELISA (n = 3) and a biotinylated Vi ELISA (n = 1). Valid estimates of potencies relative to IS 16/138 were obtained for all samples in the Vi-PLL ELISA and the commercial ELISA, with good repeatability and reproducibility evident from the study results and concordant estimates obtained by the two ELISA methods. The study demonstrates that the Vi-PLL ELISA can be used in clinical trial studies to determine the immunogenicity of TCVs.

Highlights

Typhoid fever is caused by an infection with Salmonella enterica subspecies enterica serovar Typhi (S. typhi)
The intralaboratory variability for each sample is shown in Table 4 and cases where the Geometric Coefficient of Variation (GCV) value exceeds 25% are highlighted
A summary of the causes of assay invalidity when applying the criteria described above is given in. If these criteria are used to define a good assay performance, the capsular Vi polysaccharide (Vi)-PLL ELISA of laboratories 1, 2, 6, 8, 9, the VaccZyme ELISA of laboratories 1 and 6, and the biotinylated Vi ELISA of laboratory 6 were all considered to have been performed to a good standard

Summary

Introduction

Typhoid fever is caused by an infection with Salmonella enterica subspecies enterica serovar Typhi (S. typhi). Conjugation of Vi to a carrier protein such as a bacterial toxoid remedied these shortcomings: a prototype typhoid conjugate vaccine (TCV) consisting of Vi conjugated to recombinant Pseudomonas aeruginosa exoprotein A was proven to be immunogenic and induced a booster response in young children, was safe and efficacious in pre-school age children and infants and induced a long lasting anti-Vi IgG response [7,8,9] The success of this TCV prompted the World Health Organization (WHO) to draft the WHO guideline on the quality, safety and efficacy of TCVs, which provides a framework to evaluate TCVs, compare clinical trial studies and analyse the safety, consistency and potency of TCVs by physicochemical assays and immunoassays [10,11]

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