A tumor-specific mechanism of Treg enrichment mediated by the integrin αvβ8.

Regulatory T cells (Tregs) that promote tumor immune evasion are enriched in certain tumors and correlate with poor prognosis. However, mechanisms for Treg enrichment remain incompletely understood. We described a mechanism for Treg enrichment in mouse and human tumors mediated by the αvβ8 integrin. Tumor cell αvβ8 bound to latent transforming growth factor-β (L-TGF-β) presented on the surface of T cells, resulting in TGF-β activation and immunosuppressive Treg differentiation in vitro. In vivo, tumor cell αvβ8 expression correlated with Treg enrichment, immunosuppressive Treg gene expression, and increased tumor growth, which was reduced in mice by αvβ8 inhibition or Treg depletion. Structural modeling and cell-based studies suggested a highly geometrically constrained complex forming between αvβ8-expressing tumor cells and L-TGF-β-expressing T cells, facilitating TGF-β activation, independent of release and diffusion, and providing limited access to TGF-β inhibitors. These findings suggest a highly localized tumor-specific mechanism for Treg enrichment.