NFAT signaling is indispensable for persistent memory responses of MCMV-specific CD8+ T cells

Cytomegalovirus (CMV) induces a uniquely robust and persistent T cell response, where the size of the antigen-specific population does not contract, but rather inflates during viral latency. It has been proposed that intermittent engagements of T cell receptors (TCRs) by viral antigens upon subclinical episodes of virus reactivation feed the inflation of CMV-specific memory cells, but evidence of TCR engagement has remained lacking. Nuclear factor of activated T cells (NFAT) is a family of transcription factors, where NFATc1, NFATc2 and NFATc3 are expressed in mature T lymphocytes, of which NFATc1 and NFATc2 are the dominating family members. In an in vivo model of mouse CMV (MCMV) infection of mice with genetic ablation of NFAT signaling, we show a selective impact of this defect in TCR signaling on the long-term inflation of MCMV-specific CD8 T cell responses, while the initial responses to acute infection remain largely maintained. NFATc1 ablation had an immediate effect, while ablation of both NFATs had the most profound influence. In presence of other lymphocytes, NFAT deficiency in T cells had no effect on virus replication or latency, but in adoptive immunotherapy of RAG2-deficient recipient mice, the lack of both NFAT molecules in solely transplanted CD8+ T cells uncovered their decreased antiviral efficacy. We characterized CD8 responses in absence of either or both NFAT molecules by transcriptome analyses and demonstrate that T cell-intrinsic NFAT is not necessary for CD8 T cell priming, but rather for their maturation towards effector memory and in particular the effector cells, which dominate the pool of inflationary cells. Overall design: Comparative gene expression profiling analysis of RNA-seq data for WT and NFATc1, NFATc2 and NFAT-DKO CD8+ T cells isoalted from MCMV infected animals.