Tumour DDR1 promotes collagen fibre alignment to instigate immune exclusion

Immune exclusion predicts poor patient outcomes in multiple malignancies, including triple-negative breast cancer (TNBC) 1 . The extracellular matrix (ECM) contributes to immune exclusion 2 . However, strategies to reduce ECM abundance are largely ineffective or generate undesired outcomes 3 , 4 . Here we show that discoidin domain receptor 1 (DDR1), a collagen receptor with tyrosine kinase activity 5 , instigates immune exclusion by promoting collagen fibre alignment. Ablation of Ddr1 in tumours promotes the intratumoral penetration of T cells and obliterates tumour growth in mouse models of TNBC. Supporting this finding, in human TNBC the expression of DDR1 negatively correlates with the intratumoral abundance of anti-tumour T cells. The DDR1 extracellular domain (DDR1-ECD), but not its intracellular kinase domain, is required for immune exclusion. Membrane-untethered DDR1-ECD is sufficient to rescue the growth of Ddr1 -knockout tumours in immunocompetent hosts. Mechanistically, the binding of DDR1-ECD to collagen enforces aligned collagen fibres and obstructs immune infiltration. ECD-neutralizing antibodies disrupt collagen fibre alignment, mitigate immune exclusion and inhibit tumour growth in immunocompetent hosts. Together, our findings identify a mechanism for immune exclusion and suggest an immunotherapeutic target for increasing immune accessibility through reconfiguration of the tumour ECM. In mouse models of triple-negative breast cancer, the extracellular domain of the collagen receptor DDR1 has a role in tumour defence against the immune system, by aligning collagen fibres to obstruct immune infiltration.