Regulatory T-cell-derived interleukin-15 shapes cytotoxic T cell memory.

It is well known that regulatory T-cells (Tregs) are required to prevent autoimmunity, but they may also have some less-well understood immune-stimulatory effects. In particular, in CD8 + T-cell responses Tregs select high affinity clones upon priming and promote memory by inhibiting inflammation-dependent generation of short-lived effector cells. In the current issue of the European Journal of Immunology [Eur. J. Immunol. 2023. 53: XXXX-XXXX], Madi et al. report the surprising finding that human and murine FOXP3+ Tregs are a physiological relevant source of Interleukin-15, a homeostatic cytokine that promotes antigen-independent maintenance of CD8+ memory T-cells. In mice that lack IL-15 selectively in FOXP3+Tregs the authors show that the composition of the CD8+ T-cell memory pool is altered in the absence of Treg-derived IL-15, since a subset of terminally effector memory cells is drastically reduced. Otherwise Treg-derived IL-15 is dispensable for anti-viral immune responses and the generation of anti-viral CD8+ memory T-cells. These findings add to our understanding of the multifaceted role of Tregs in immune responses, and how IL-15 derived from different cellular sources maintains anti-viral T-cell memory. This article is protected by copyright. All rights reserved.