CD4 and CD8 mark helper and cytotoxic T cell lineages, respectively, and serve as coreceptors for MHC-restricted TCR recognition. How coreceptor expression is matched with TCR specificity is central to understanding CD4/CD8 lineage choice, but visualising coreceptor gene activity in individual selection intermediates has been technically challenging. It therefore remains unclear whether the sequence of coreceptor gene expression in selection intermediates follows a stereotypic pattern, or is responsive to signaling. Here we use single cell RNA sequencing (scRNA-seq) to classify mouse thymocyte selection intermediates by coreceptor gene expression. In the unperturbed thymus, Cd4+Cd8a- selection intermediates appear before Cd4-Cd8a+ selection intermediates, but the timing of these subsets is flexible according to the strength of TCR signals. Our data show that selection intermediates discriminate MHC class prior to the loss of coreceptor expression and suggest a model where signal strength informs the timing of coreceptor gene activity and ultimately CD4/CD8 lineage choice.

CNAG CRG Centre for Genomic Regulation Barcelona Spain

Comprehensive Cancer Centre School of Cancer and Pharmaceutical Sciences Faculty of Life Sciences and Medicine King's College London London UK

Department of Immunology Duke University Medical Center Durham NC USA

Laboratory of Adaptive Immunity Institute of Molecular Genetics of the Czech Academy of Sciences Prague Czech Republic

MRC London Institute of Medical Sciences Institute of Clinical Sciences Faculty of Medicine Imperial College London London UK

School of Life Sciences and Biotechnology Shanghai Jiao Tong University Shanghai China

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Unique roles of co-receptor-bound LCK in helper and cytotoxic T cells