Not Just Passing Through: Bone Marrow as a Home for Diverse Resident T Cells

Recent studies add to our understanding of T cell residency in the human bone marrow (BM). In the May 2025 issue of EJI, Schneider Revueltas et al. demonstrate that CD69^- CD4⁺ and CD8+ memory T cells, presumed to be recirculating, have a distinct transcriptional cluster profile and a distinct TCR repertoire from their blood counterparts. These findings are in line with CD69^- memory T cells taking up residence in the BM, similar to their CD69⁺ counterparts. In parallel, Pulvirenti et al. identify a subset of CD69⁺EOMES⁺GzmK⁺ Tr1-like cells in the BM maintained by IL-15. Together, these studies refine our understanding of the BM as a heterogeneous immune niche and suggest a broader definition of resident cells within this tissue.