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. 2023 May 23;18(5):e0286117.
doi: 10.1371/journal.pone.0286117. eCollection 2023.

Correlations between three ELISA protocols measurements of RTS,S/AS01-induced anti-CSP IgG antibodies

Robert M Mugo  1   2   3 , Benedict Orindi  1 , Faiz M Shee  2 , Duncan Bellamy  4 , Jedidah Mwacharo  1 , Katie J Ewer  4 , Philip Bejon  1   4 , Francis M Ndungu  1   2   3   4   5
Affiliations

Correlations between three ELISA protocols measurements of RTS,S/AS01-induced anti-CSP IgG antibodies

Robert M Mugo et al. PLoS One. .

Abstract

Background: RTS,S/AS01 induced anti-circumsporozoite protein (CSP) IgG antibodies are associated with the vaccine efficacy. There is currently no international standardisation of the assays used in the measurement of anti-CSP IgG antibody concentrations for use in evaluations of the vaccine's immunogenicity and/or efficacy. Here, we compared the levels of RTS,S/AS01 induced anti-CSP IgG antibodies measured using three different enzyme-Linked ImmunoSorbent Assays (ELISA).

Methods: 196 plasma samples were randomly selected from the 447 samples collected during the RTS,S/AS01 phase IIb trial in 2007 from Kenyan children aged between 5-17 months. The vaccine-induced anti-CSP IgG antibodies were then measured using two independently developed ELISA protocols ('Kilifi-RTS,S' and 'Oxford-R21') and compared to the results from the reference 'Ghent-RTS,S' protocol for the same participants. For each pair of protocols, a deming regression model was fitted. Linear equations were then derived to aid in conversions into equivalent ELISA units. The agreement was assessed using Bland and Altman method.

Findings: The anti-CSP IgG antibodies measured from the three ELISA protocols were in agreement, and were positively and linearly correlated; 'Oxford' and 'Kilifi' r = 0.93 (95% CI 0.91-0.95), 'Oxford' and 'Ghent' r = 0.94 (95% CI: 0.92-0.96), and 'Kilifi' and 'Ghent' r = 0.97 (95% CI: 0.96-0.98), p<0.0001 for all correlations.

Conclusions: With the linearity, agreement and correlations established between the assays, conversion equations can be applied to convert results into equivalent units, enabling comparisons of immunogenicities across different vaccines of the same CSP antigens. This study highlights the need for the international harmonisation of anti-CSP antibody measurements.

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Conflict of interest statement

The authors have declared that no competing interests exist.

Figures

Fig 1
Fig 1. Violin plots showing the log10 EU/mL individual distributions and comparisons between the ‘Oxford’, ‘Kilifi’, and ‘Ghent’ ELISA protocols, the middle line represents the medians.
The upper and lower whiskers represent the highest and lowest values within 1.5 interquartile ranges, with outliers shown as extreme values, n = 196 for each of the protocols.
Fig 2
Fig 2. Scatterplots showing strong positive correlations of the anti-CSP IgG antibodies measurements expressed in log10 EU/mL among the three ELISA assays.
A: ‘Kilifi’ and ‘Oxford’, B: ‘Oxford’ and ‘Ghent’, and C: ‘Ghent’ and ‘Kilifi’ ELISA protocols (n = 196 for all protocols). (bottom right) presents the prediction equations relating to the three assays for the conversion of the arbitrary ELISA units (EU/mL) into inter-assay equivalent units estimated using deming regression model.
Fig 3
Fig 3. Bland-Altman plots for each pair of the assays.
The solid horizontal black line corresponds to the mean difference while the dotted horizontal blue lines correspond to the 95% limits of agreement.
See this image and copyright information in PMC

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