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 stem cell antigen-1 (Sca-1) B cell lymphoma 2 (Bcl-2) 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.