Assessing T cell differentiation at the single-cell level

This thesis describes the development and use of a novel technology for single-cell fate mapping, called cellular barcoding. With this technology, unique and heritable genetic tags (barcodes) are introduced into na_ve T cells. Using cellular barcoding, we investigated I) how different antigen-specific CD8+ T cell clones contribute to the formation of effector and memory T cell subsets II) at what point during in vivo CD8+ T cell differentiation fate decisions take place and III) to what extent the clonal expansion of individual antigen-specific CD8+ T cells shapes the overall response magnitude. Our experiments demonstrate that most if not all effector and memory T cells are progeny of the same na_ve T cells and that the decision to develop into either subset is taken after the first cell division. Furthermore, we show that the overall T cell response magnitude is primarily controlled by the extent of clonal expansion, as the efficiency by which na_ve T cells are recruited into the response is remarkably constants. Quantification of barcode abundances revealed that individual antigen-specific T cells produce highly variable numbers of daughter cells, and that this strong disparity in output is established during the first phase of infection.UBL - phd migration 201