To enable discovery of serum antibodies indicative of disease and simultaneously develop reagents suitable for diagnosis, in vitro directed evolution was applied to identify consensus peptides recognized by patients' serum antibodies. Bacterial cell-displayed peptide libraries were quantitatively screened for binders to serum antibodies from patients with celiac disease (CD), using cellsorting instrumentation to identify two distinct consensus epitope families specific to CD patients (PEQ and/ F Q consensus epitope identified a celiac-specific epitope, distinct from the two CD hallmark antigens tissue transglutaminase-2 and deamidated gliadin, exhibiting 71% sensitivity and 99% specificity (n = 231). Expansion of the first-generation PEQ consensus epitope via in vitro evolution yielded octapeptides QPEQAFPE and PFPEQxFP that identified ω-and γ-gliadins, and their deamidated forms, as immunodominant B-cell epitopes in wheat and related cereal proteins. The evolved octapeptides, but not first-generation peptides, discriminated one-way blinded CD and non-CD sera (n = 78) with exceptional accuracy, yielding 100% sensitivity and 98% specificity. Because this method, termed antibody diagnostics via evolution of peptides, does not require prior knowledge of pathobiology, it may be broadly useful for de novo discovery of antibody biomarkers and reagents for their detection.

Antigen discovery and mapping strategies that enable the precise identification of serum antibody-binding epitopes in human diseases will be invaluable for translational diagnostics and therapeutic development. Protein and peptide library display screening techniques have shown utility for the discovery of antigens associated with disease onset and progression. Here, we describe a screening methodology using bacterial peptide library display to identify consensus families of disease-specific binding motifs to multiple pools of human serum antibodies. The sensitivity and specificity of identified disease-specific peptide motifs are then optimized using in vitro evolution techniques.

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