The transcription factor AFF3 maintains naïve CD8 T cell quiescence restraining premature cell activation allowing for optimal T cell response to viral infection.

Quiescent naïve CD8 T cells are poised to rapidly proliferate upon activation to eliminate infected and cancerous cells. The mechanisms that control naïve CD8 T cell quiescence are incompletely understood. We identified the transcription factor AF4/FMR2 Family Member 3 (Aff3) as a novel regulator of CD8 T cell quiescence to prevent premature activation and differentiation. To determine the role of AFF3 in CD8 T cells we designed a T cell specific conditional AFF3 knockout (KO) mouse model. Total RNA-sequencing data comparing WT and KO CD8 T cells show that the largest differences in gene expression occur between naïve and CD8 T cells activated for a few hours. These differences primarily involve pathways linked to TCR signaling and metabolism. Although at baseline naïve CD8 AFF3 KO T cells do not develop an antigen-experienced phenotype, they trend towards having higher basal respiration rates and spare respiratory capacity establishing that AFF3 regulates T cell metabolism even prior to their activation. In co-adoptive transfer experiments, KO cells are present at a higher frequency at 5 days post infection (dpi) but at a lower frequency at 8 dpi compared to the WT cells following acute LCMV infection, indicating an accumulation defect. When naïve CD8 T cells are stimulated ex vivo, KO cells activate and enter the cell cycle more rapidly but fail to sustain proliferation compared to WT. Additionally, as the KO and WT mice age the disruption in expansion begins to diminish and the cells are more similar phenotypically. In both aged and young recipient mice the young WT CD8 T cells consistently expand more than the young KO, aged KO, and aged WT cells. In addition, we found that the mRNA expression of AFF3 decreases in the T cells as early as 6 months of age. This suggest reduced expression of AFF3 may have an important role in the loss of quiescence of CD8 T cells that can occur during aging. Together, our data suggest that AFF3 is important to maintain naïve CD8 T cell quiescence leading to optimal accumulation and function of CD8 T cells in viral infection.