CD4(+) TSCMs in the Bone Marrow Assist in Maturation of Antibodies against Influenza in Mice

The bone marrow (BM) is not only a reservoir of hematopoietic stem cells but a repository of immunological memory cells. Further characterizing BM-resident memory T cells would be helpful to reveal the complicated relationship between the BM and immunological memory. In this study, we identified CD122(high) stem cell antigen-1 (Sca-1) (high) B cell lymphoma 2 (Bcl-2) (high) CD4(+) stem cell-like memory T cells (TSCMs) as a distinct memory T cell subset, which preferentially reside in the BM, where they respond vigorously to blood-borne antigens. Interestingly, the natural CD4(+) TSCMs homing to the BM colocalized with VCAM-1(+) IL-15(+) IL-7(+) CXCL-12(+) stromal cells. Furthermore, compared to spleen-resident CD4(+) TSCMs, BM-resident TSCMs induced the production of high-affinity antibodies against influenza by B lymphocytes more efficiently. Taken together, these observations indicate that the BM provides an appropriate microenvironment for the survival of CD4(+) TSCMs, which broadens our knowledge regarding the memory maintenance of antigen-specific CD4(+) T lymphocytes.