by van de Garde MDB, van Westen E, Poelen MCM, Rots NY, van Els CACM
Published in Infection and Immunity, 25 March 2019.
CD4+ T-cell mechanisms are implied in protection against pneumococcal colonization; however, their target antigens and function are not well defined. In contrast to high-throughput protein arrays for serology, basic antigen tools for CD4+ T-cell studies are lacking. Here researchers evaluate the potential of a bioinformatics tool in silico prediction of immunogenicity as a method to reveal domains of pneumococcal proteins targeted by human CD4+ T-cells.
For hundred pneumococcal proteins CD4+ T-cell immunogenicity was predicted based on HLA-DRB1 binding motifs. Then, for twenty potentially CD4+ T-cell-immunogenic proteins epitope regions were verified by testing synthetic peptides in T-cell assays using PBMCs from healthy adults. Peptide pools of 19 out of 20 proteins evoked T-cell responses. Most frequent responses (detectable in ≥20% of donors tested) were found to SP_0117 (PspA), SP_0468 (putative sortase), SP_0546 (BlpZ), SP_1650 (PsaA), SP_1923 (Ply), SP_2048 (Conserved Hypothetical Protein), SP_2216 (PscB), and SPR_0907 (PhtD). Responding donors had diverging recognition patterns and profiles of signature cytokines (IFNγ, TNFα, IL-13 and/or IL-17A) against single epitope regions. Natural HLA-DR restricted presentation and recognition of a predicted SP_1923-derived epitope was validated through the isolation of a CD4+ T-cell clone producing IFNγ, TNFα and IL-17A in response to the synthetic peptide, whole protein, and heat-inactivated pneumococcus.
This proof of principle for a bioinformatics tool to identify pneumococcal protein-epitopes targeted by human CD4+ T-cells, provides a peptide-based strategy to study cell-mediated immune mechanisms to the pneumococcal proteome, advancing the development of immunomonitoring assays and targeted vaccine approaches.
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