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BACKGROUND: After solid organ transplantation, the endothelium is the first allorecognition checkpoint of the recipient's immune system. A major player at this interface is the platelet endothelial cell adhesion molecule-1 (PECAM-1), which is an immunoglobulin-like glycoprotein, involved in white blood cell migration, cellular adhesion, and signal transduction.

STUDY DESIGN AND METHODS: The potential of preventing allorecognition at this interface was explored by knocking down PECAM-1 expression using RNA interference. Lentiviral-based vectors encoding short-hairpin RNA sequences specific for PECAM-1 transcripts were used for the transduction of monocytic and endothelial cell lines.

RESULTS: Expression of PECAM-1 decreased by up to 80% at mRNA and protein levels on monocytic and endothelial cell lines. Antigen-binding capacity assays likewise showed up to 80% reduction of PECAM-1 expression on cell surfaces. In allogeneic T-cell stimulation assays, T cells stimulated with PECAM-1–silenced monocytes had granzyme B mRNA levels up to 85% lower than those in T cells stimulated with monocytes expressing nonspecific shRNA. Also, T-cell cytotoxicity showed to decrease significantly against PECAM-1–silenced monocytes versus those nonsilenced for PECAM-1. Moreover, the former T cells did not secrete interferon-γ and exhibited reduced proliferation.

CONCLUSION: These findings suggest that permanent silencing of PECAM-1 expression is feasible and contributes to efficiently inhibiting the cytotoxic T-cell response to allogeneic target cells. Thus, targeting both the immunologic synapse at the regulatory interface and the lymphocyte migration might provide a new strategy to overcome allogeneic transplant rejection.