MicroRNA-155 Modulates Acute Graft-versus-Host Disease by Impacting T Cell Expansion, Migration, and Effector Function [TRANSPLANTATION]

MicroRNA-155 (miR-155) is a small noncoding RNA critical for the regulation of inflammation as well as innate and adaptive immune responses. MiR-155 has been shown to be dysregulated in both donor and recipient immune cells during acute graft-versus-host disease (aGVHD). We previously reported that miR-155 is upregulated in donor T cells of mice and humans with aGVHD and that mice receiving miR-155–deficient (miR155^–/–) splenocytes had markedly reduced aGVHD. However, molecular mechanisms by which miR-155 modulates T cell function in aGVHD have not been fully investigated. We identify that miR-155 expression in both donor CD8⁺ T cells and conventional CD4⁺ CD25^– T cells is pivotal for aGVHD pathogenesis. Using murine aGVHD transplant experiments, we show that miR-155 strongly impacts alloreactive T cell expansion through multiple distinct mechanisms, modulating proliferation in CD8⁺ donor T cells and promoting exhaustion in donor CD4⁺ T cells in both the spleen and colon. Additionally, miR-155 drives a proinflammatory Th1 phenotype in donor T cells in these two sites, and miR-155^–/– donor T cells are polarized toward an IL-4–producing Th2 phenotype. We further demonstrate that miR-155 expression in donor T cells regulates CCR5 and CXCR4 chemokine-dependent migration. Notably, we show that miR-155 expression is crucial for donor T cell infiltration into multiple target organs. These findings provide further understanding of the role of miR-155 in modulating aGVHD through T cell expansion, effector cytokine production, and migration.

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