Rapid mobilization of tissue-resident memory T cells in systemic immune reactions

In a recent paper published in the European Journal of Immunology, scientists from the DRFZ describe  that memory T cells residing in the bone marrow (BM) of healthy individuals can be rapidly mobilized into the blood following a repeat vaccination with the measles-mumps-rubella (MMR) vaccine. These mobilized memory T cells play an important role in the ensuing immune response.

Previous work from the same group had shown that the BM is an important reservoir for long-lived resident memory T cells, even when such cells have disappeared from the blood. This work has now been expanded to answer the question of whether tissue-resident memory T cells just protect their tissue of residency, or can also leave the tissue and participate in a secondary immune reaction after re-encountering their antigen. The researchers found that 0.5 – 2 days after re-vaccination, reactivated memory T cells, specific for the MMR vaccine, left the BM and entered the bloodstream. These reactivated BM memory T cells then became a major component of the immune reaction triggered.

Although this study was based on using the MMR vaccine as an antigen, these results can in all likelihood be extrapolated to other vaccination and infection settings, including COVID-19. These results demonstrate for the first time that BM resting memory T cells not only protect the bone marrow, but also the entire body from severe disease after re-encountering a pathogen.