A framework to identify antigen-expanded T Cell Receptor (TCR) clusters within complex repertoires
Common approaches for monitoring T cell responses are limited in their multiplexity and sensitivity. In contrast, deep sequencing of the T Cell Receptor (TCR) repertoire offers a global view whose theoretical sensitivity is limited only by the depth of available sampling. However, assignment of antigen specificities within TCR repertoires has become a bottleneck. Here, we combine antigen-driven expansion, deep TCR sequencing and a novel analysis framework to show that homologous Clusters of Expanded TCRs (CETs) can be confidently identified without cell isolation, and assigned to antigen against a background of non-specific clones. We show that clonotypes within each CET respond to the same epitope, and that protein antigens stimulate multiple CETs reactive to constituent peptides. Finally, we demonstrate the personalized assignment of antigen-specificity to rare clones within fully-diverse unexpanded repertoires. The method presented here may be used to monitor T cell responses to vaccination and immunotherapy with high fidelity.