Early specification of CD8(+) T lymphocyte fates during adaptive immunity revealed by single-cell gene expression analyses

T lymphocytes responding to microbial infection give rise to effector cells that mediate acute host defense and memory cells that provide long-lived immunity, but the fundamental question of when and how these cells arise remains unresolved. Here we combine single-cell gene expression analyses with machine-learning approaches to trace the transcriptional roadmap of individual CD8(+) T lymphocytes throughout the course of an immune response in vivo. Gene expression signatures predictive of eventual fates could be discerned as early as the first T lymphocyte division and may be influenced by asymmetric partitioning of the interleukin-2 receptor during mitosis. These findings underscore the importance of single-cell analyses in understanding fate determination and provide new insights into the specification of divergent lymphocyte fates early during an immune response to microbial infection.