Samuel Lyons

Introduction: Crohn’s disease (CD) is a chronic inflammatory disease of the bowel resulting from dysregulated immune responses toward microbial antigens like muramyl-dipeptide (MDP), a frequent member of healthy intestinal flora¹. Studies have demonstrated a connection between this immune response and unbalanced populations of Treg, Th1, and Th17 cells in the intestinal mucosa. Decreased Tregs coupled with increased levels of Th1 and Th17 cells are believed to increase levels of pro-inflammatory cytokines in the gut, leading to profound inflammation and sequalae^2-4. A serious complication of CD is the development of perianal fistulas, which occurs in one-third of CD individuals¹. These fistulas cause significant morbidity and have been notoriously difficult to treat until recent mesenchymal stem cell (MSC) therapies emerged over the last decade⁵. With the growing interest in MSC therapies for fistulizing CD, a cohesive understanding of the mechanisms involved is still missing⁶. By investigating the biochemical mechanisms MSCs exert on tissue from CD patients, an opportunity exists to better understand their future applications in inflammatory disease and tissue repair. Methods: T-cell lineages were surgically isolated from inflamed and non-inflamed colonic mucosa of CD patients and healthy controls. Tissue specimens were grown with MDP in the presence or absence of donor MSC’s. The rate of T-cell apoptosis was measured by flow cytometry with APOPTESTTM-FITC. T-cell phenotypes were assessed were using immunostaining with fluorochrome conjugated antibodies. Cytokine profiles were examined using the Plex Array kit to measure IFN-γ, TNF-α, IL-6, IL-8, and IL-10, an ELISA kit for TGF-β, and two immunoassays to measure levels of IL-17A and IL-21⁷. Results: When cultured with MSCs, inflamed and non-inflamed mucosa of CD patients exhibited a statistically significant increase in apoptosis while the control specimen exhibited no significant change in apoptotic rate. T-cell lines from CD mucosa exhibited a significant decrease in activated CD4+CD25+ T-cells and an increase in the CD3+CD69+ phenotype when cultured with MSCs. Levels of the pro-inflammatory cytokines TNF-α, IFN-γ, IL-17A, and IL-21 were decreased in CD mucosa cultured with MSCs, while levels of TGF-β and IL-6 increased⁷. Conclusions: MSCs possess a strong capacity to modulate the host immune response and redirect aberrant systems back toward healthy states. With MSCs currently demonstrating impressive outcomes in the treatment of fistulizing CD, the potential to expand how and where we use mesenchymal stem cells in the treatment of inflammation and injury requires a stronger understanding of their mechanisms in treatment today.

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