![]() Ideally, an effector cell of immunohomeostasis would be natively embedded within the affected tissue(s), poised to locally dampen excessive inflammatory reactions without triggering systemic immunosuppression. To avert life-threatening tissue destruction within an immunologic “battlefield”, immunoreactivity must be balanced by coincident immunoquiescence, thereby re-establishing immunohomeostasis. The most challenging task of the immune system is not so much in mounting a reaction to a given antigen, it is in not reacting so excessively such as to engender fulminant immunopathology. ![]() These findings indicate that MSCs counteract immunopathology in situ, and highlight a role for CD44 engagement in unleashing MSC immunobiologic properties that maintain/establish tissue immunohomeostasis. Mechanistic studies reveal that ligation of HCELL/CD44 on the MSC surface markedly potentiates MSC immunomodulatory activity by inducing MSC secretion of a variety of potent immunoregulatory molecules, including IL-10. Compared to mice receiving HCELL − MSCs, recipients of HCELL + MSCs had increased MSC intercalation within aGvHD-affected site(s), decreased leukocyte infiltrates, lower systemic inflammatory cytokine levels, superior tissue preservation, and markedly improved survival. aGvHD induced the expression of E-selectin within lesional endothelial beds, and tissue-specific recruitment of systemically administered host-derived MSCs was achieved by enforced expression of HCELL, a CD44 glycoform that is a potent E-selectin ligand. ![]() To address this question, we employed a murine model of fulminant immune-mediated inflammation, acute graft-versus-host disease (aGvHD), provoked by donor splenocyte-enriched full MHC-mismatched hematopoietic stem cell transplant. ![]() While studies in vitro provide abundant evidence of their immunomodulatory capacity, it is unknown whether tissue colonization of MSCs is critical to their ability to dampen/counteract evolving immunopathology in vivo. A greater understanding of MSC cell biology is urgently needed because culture-expanded MSCs are increasingly being used in treatment of inflammatory conditions, especially life-threatening immune diseases. Though best known for generating connective tissue and bone, these cells also display immunoregulatory properties. ![]() Mesenchymal stem/stromal cells (MSCs) are distributed within all tissues of the body. ![]()
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