Surface CD6 regulates T cell adhesion and migration through direct ligand interaction and stabilization of VLA4

Abstract

Abstract The CD6-ALCAM pathway is an important regulator of T cell activity and trafficking. However, its precise role in modulating T-cell adhesion and migration during inflammation is unclear. To investigate its role in adhesion and transendothelial migration, we used itolizumab, an anti-CD6 mAb that can induce cleavage of CD6 from the T cell surface when in the presence of monocytes. PBMCs were stimulated overnight or left unstimulated prior to treatment with itolizumab to generate CD6low T cells. Cells were then tested in standard adhesion and migration assays. The CD6 low T cells had ~ 50% decreased adherence to HUVEC cells compared to the control T cells (CD6high); similar results were observed by blocking ALCAM on HUVEC. Modulating CD6 on T cells or blocking ALCAM on the HUVEC also translated to a ~3-fold decrease in migration of Teff cells. Loss of CD6 was associated with reduced protein levels of VLA4, but not of other integrins, under both stimulated (~70%) and non-stimulated conditions (~40%). Antibody blockade of CD6 without cleavage did not affect VLA4 levels, but still decreased migration of unstimulated T cells though less so than in stimulated T cells, where VLA4 reduction is required to modulate migration. Our data demonstrate that CD6 contributes to cell adhesion/migration both through direct ligand interactions with ALCAM, and through the stabilization of cell membrane VLA4 and that these functions can be abrogated by modulation of cell surface levels of CD6.