Epitope-specific competitive ELISA predicts malaria transmission-blocking vaccine Pfs230D1 activity measured in standard membrane feeding assay
Cristina A. Meehan, Matthew V. Cowles, Robert D. Morrison, Yuyan Yi, Jingwen Gu, Jen C.C. Hume, Mina P. Peyton, Issaka Sagara, Sara A. Healy, Jonathan P. Renn, Patrick E. Duffy
Cristina A. Meehan, Matthew V. Cowles, Robert D. Morrison, Yuyan Yi, Jingwen Gu, Jen C.C. Hume, Mina P. Peyton, Issaka Sagara, Sara A. Healy, Jonathan P. Renn, Patrick E. Duffy
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Research Article Immunology Infectious disease

Epitope-specific competitive ELISA predicts malaria transmission-blocking vaccine Pfs230D1 activity measured in standard membrane feeding assay

Abstract

Functional antibody responses to malaria transmission-blocking vaccines (TBVs) are assessed using the standard membrane feeding assay (SMFA). This assay quantifies the percentage reduction of oocyst levels in mosquitoes fed gametocytes mixed with antisera/antibodies, referred to as transmission-reducing activity (TRA). As TBVs advance to large clinical trials, new scalable assays are needed to characterize vaccine responses. Here, we developed an epitope-specific competitive ELISA platform (P230Compete) for TBV candidate Pfs230D1, based on single-chain variable fragments against epitopes recognized by human monoclonal antibodies with high TRA. We quantified functional epitope-specific antibody responses (F) in phase I Pfs230D1-EPA/AS01 vaccine trial participants, using 171 serum samples collected at 2 postvaccination time points. Five antibody features were examined by P230Compete, including total IgG (reported as ELISA units, EUF), IgG subclasses (IgG1F, IgG3F, IgG4F), and bound complement factor C1q (C1qF). EUF and IgG1F demonstrated strong correlation and excellent prediction of TRA (≥80%) in logistic regression analysis (AUC of 0.81 for both assays after dose 3, and 0.80 and 0.76 after dose 4). Furthermore, combining EUF and IgG1F showed even better predictive performance at each time point. P230Compete offers a promising proxy assay to replace SMFA in late-stage Pfs230D1 trials.

Authors

Cristina A. Meehan, Matthew V. Cowles, Robert D. Morrison, Yuyan Yi, Jingwen Gu, Jen C.C. Hume, Mina P. Peyton, Issaka Sagara, Sara A. Healy, Jonathan P. Renn, Patrick E. Duffy

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Figure 1

P230Compete platform measures antibody displacement from Pfs230D1 functional epitopes.

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P230Compete platform measures antibody displacement from Pfs230D1 functi...
(A) Functional (blue) and nonfunctional (gold) faces of Pfs230D1 depicted. Functional hmAbs (blue) bound to 3 distinct epitope bins on the functional face; nonfunctional hmAbs (gold) bound to the opposing face. (B) scFv-mediated displacement of functional hmAbs (LMIV230-01, 230AS-18, and 230AL-18), each at 0.1 mg/mL by corresponding scFv (scFvLMIV230-01, scFv230AS-18, scFv230AL-18), and each at a saturating concentration of 10 mg/mL. A greater than 90% reduction in OD was demonstrated for all 3 experiments (n = 5 LMIV230-01; n = 3 AS-18; n = 2 AL-18); data shown as mean ± SD. (C) P230Compete protocol: wells coated with 0.1 mg/mL Pfs230D1; after blocking, trial participant sera added with or without scFv; after washing, labeled secondary antibody added to quantify bound IgG or IgG features. Two OD levels were measured: ODSera in the absence of scFv (dark purple) and ODSera+scFv measured in the presence of scFv (light purple). (D) ΔOD = ODSera – ODSera+scFv and reported as IgG1F, IgG3F, IgG4F, and C1qF, or ΔEU = EUSera – EUSera+scFv and reported as EUF. “F” subscript denotes displacement of serum antibody from the Pfs230D1 functional face (blue). (E) A 1:1 mixture of functional (LMIV230-01) and nonfunctional (LMIV230-02) hmAbs was tested alone (circles) or in combination with 10 μg/mL saturating scFvLMIV230-01 (squares) (n = 3). At 0.375 μg/mL total hmAb concentration (blue box), OD decreased from 1.6 (circle, no scFv) to 0.8 (square, with scFv), indicating a ΔOD of 0.8 by competitive inhibition of scFv; data shown as mean ± SD.