Single-cell and spatial transcriptomics reveals memory CD8+ T cell differentiation fostered by monocytes through TGF-β signaling

Upon antigen recognition, CD8+ T cells undergo a robust expansion and differentiation to give rise to effector and memory CD8+ T cells. The spatial determinants for effector and memory CD8+ T cell fate decision during acute infection is poorly understood. By integrating single-cell RNA sequencing (scRNA-seq) and spatial resolved transcriptomics, we investigated the anatomical locations, cell-cell interactions and molecular mechanisms that contribute to memory CD8+ T cell differentiation. We found naïve CD8+ T cells adopted a divergent differentiation trajectory where they rapidly differentiated into memory precursors (MP) and IFN-responsive cells which represent the entry point of effector T cell lineage.In the spleen, monocytes were largely colocalized with CD8+ MP cells in an antigen stimulation-dependent manner. CD8+ T cells primed with monocytes, compared to DC populations, had significantly increased memory T cell differentiation. Mechanistically, monocytes promoted memory CD8+ T cell differentiation by providing TGF-β signaling. Our study reveals a novel spatial mechanism for memory CD8+ T cell fate decision, shedding lights on the importance of monocytes and TGF-β in fostering memory CD8+ T cell development. The spleen tissues were dissociated into single-cell suspensions from the mice 5 days post-infection (Recipient sample). In the in vivo T cell adoptive transfer model, donor CD8+ 581 T cells (CD45.2+CD8+7AAD-) 582 were sorted and subjected to scRNA-seq (Donor sample).