Early differences in TCR signal strength modulate effector and memory differentiation of CD4+ T cells responding to viral infection.

Abstract

Abstract Heterogeneity in TCR-dependent activation signals influences both effector differentiation and memory formation of CD4+ T cells. Our previous studies found that the formation of CD4+ memory T cells specific for lymphocytic choriomeningitis virus (LCMV) was associated with the selection of TCRs with sustained antigen binding properties. The goal of the current study was to define early TCR-dependent activation events that promote memory differentiation. We found that early in vitro and in vivo activation of distinct T cell clones specific for the same LCMV antigen demonstrated highly variable NFAT transcriptional activity and expression of early activation markers such as CD25. Clones with enhanced memory potential had reduced NFAT activity in vitro and rapid down-regulation of CD25 in vivo. We further observed decreased CD3ζ and Zap-70 phosphorylation, as well as a decrease in NFAT-dependent gene transcription, in virus-specific CD4+ T cells that displayed decreased CD25 surface expression early after LCMV infection. Adoptive transfer of CD25hi or CD25lo effector T cells (d3 or d5 post-infection) into infection-matched hosts revealed that the vast majority of both Th1-like and Tfh-like memory cells derived from CD25lo effector cells. RNASeq analysis further confirmed enrichment of genes associated with enhanced memory development within CD25lo effector cells, including Tcf-1 and OCA-B, but decreased expression of genes associated with enhanced effector activity. We conclude that differences in TCR signal strength account for clonal differences in CD4+ memory T cell differentiation, with weaker early TCR signals permitting long-term memory formation without terminal effector differentiation.