Tracking the in vivo history and fate of IL-2 producing CD8 T cells during memory differentiation

Abstract

Abstract IL-2 is a key driver of T cell responses critical for the conversion of resting antigen specific T cells into glycolytic powerhouses that undergo massive expansion and elicit cytolytic function to clear infections. Recent studies have used ex vivo antigen challenge combined with somatic IL-2 deletion to show that both paracrine and autocrine IL-2 signals are indispensable for the formation of highly functional memory CD8 T cells. Despite this critical role of autocrine IL-2 for memory T cell fate, the in vivo history and fate of autocrine IL-2 producing CD8 T cells remains unknown. We generated a mouse model in which autocrine IL-2 production leads to transcription of TdTomato, leading to an indelibly marked T cell. Following acute infection, a proportion of antigen specific CD8 T cells made autocrine IL-2, however, more than half of the T cell response had no history of IL-2 production. Furthermore, contrary to their ex vivo functionality, memory precursor and terminal effector T cells had similar history of in vivo IL-2 production. Despite autocrine IL-2 production being a benchmark of highly functional memory T cells, we observed no increase in the ex vivo polyfunctionality of T cells that produced in vivo IL-2 during infection. Finally, while strong TCR engagement is critical for the recruitment of robust T cell responses, we saw that in vivo autocrine IL-2 production is more effectively elicited by lower affinity TCR signals. Thus, we see that while proportion of T cells rely on autocrine IL-2 during infection, the ability of a CD8 T cell to recruit autocrine IL-2 function heavily depends on the avidity of the TCR to the peptide-MHC complex. Together these data provide the first insights into the in vivo function of IL-2 in antigen specific CD8 T cells.