IL-4, IL-15, and Type I Interferon Orchestrate the Shaping of the Heterogeneity of Virtual Memory CD8 T Cells.

The development of virtual memory CD8 T cells is dependent on IL-4, type I interferon, and IL-15. However, it remains unclear whether these cytokines individually contribute to the generation of specific subsets of virtual memory CD8 T cells. In this study, virtual memory CD8 T cells were categorized into four subsets based on Ly6C and Sca-1 expression, and their development was examined using knock-out mice lacking IFNAR1, IL-4, or IL-15Rα. Notably, both Ly6C Sca-1 and Ly6C Sca-1 subsets were significantly reduced in the spleen of IFNAR1 knock-out mice, while the proportion of Ly6C Sca-1 VM CD8 T cells was reduced in IL-4-deficient mice. In IL-15Rα knock-out mice, both the Ly6C Sca-1 and Ly6C Sca-1 subsets were significantly reduced. Bulk RNA sequencing analysis revealed distinct gene expression patterns in naïve cells, true memory cells, and the four virtual memory cell subsets. Specifically, Ly6C subsets were enriched with IL-15 signal-related genes, whereas Ly6C subsets and true memory cells were enriched for cell cycle-related genes. Functionally, the Ly6C and/or Sca-1 subsets exhibited higher production of IFN-γ and TNF-α compared with the Ly6C Sca-1 subsets. Overall, this study demonstrates the heterogeneity of virtual memory CD8 T cells and highlights the cytokine-dependent nature of their development.