Pooled-peptide epitope mapping strategies are efficient and highly sensitive: An evaluation of methods for identifying human T cell epitope specificities in large-scale HIV vaccine efficacy trials

Andrew Fiore-Gartland, Bryce A. Manso, David P. Friedrich, Erin E. Gabriel, Greg Finak, Zoe Moodie, Tomer Hertz, Stephen C. De Rosa, Nicole Frahm, Peter B. Gilbert, M. Juliana McElrath

Research output: Contribution to journalArticlepeer-review

27 Scopus citations

Abstract

The interferon gamma, enzyme-linked immunospot (IFN-γ ELISpot) assay is widely used to identify viral antigen-specific T cells is frequently employed to quantify T cell responses in HIV vaccine studies. It can be used to define T cell epitope specificities using panels of peptide antigens, but with sample and cost constraints there is a critical need to improve the efficiency of epitope mapping for large and variable pathogens. We evaluated two epitope mapping strategies, based on group testing, for their ability to identify vaccineinduced T-cells from participants in the Step HIV-1 vaccine efficacy trial, and compared the findings to an approach of assaying each peptide individually. The group testing strategies reduced the number of assays required by >7-fold without significantly altering the accuracy of T-cell breadth estimates. Assays of small pools containing 7-30 peptides were highly sensitive and effective at detecting single positive peptides as well as summating responses to multiple peptides. Also, assays with a single 15-mer peptide, containing an identified epitope, did not always elicit a response providing validation that 15-mer peptides are not optimal antigens for detecting CD8+ T cells. Our findings further validate pooling-based epitope mapping strategies, which are critical for characterizing vaccineinduced T-cell responses and more broadly for informing iterative vaccine design. We also show ways to improve their application with computational peptide:MHC binding predictors that can accurately identify the optimal epitope within a 15-mer peptide and within a pool of 15-mer peptides.

Original languageEnglish
Article numbere0147812
JournalPLoS ONE
Volume11
Issue number2
DOIs
StatePublished - 1 Feb 2016

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