YAP/TAZ Blockade Plus Immunotherapy Breaks Immune Exclusion in Bile Duct Cancer

Cholangiocarcinoma (CCA), or bile duct cancer, carries a grim prognosis and is notoriously resistant to immunotherapy. A central reason is that its tumor microenvironment is 'immune excluded'—T cells cannot penetrate the tumor mass. This study identifies YAP and TAZ, mechanosensing transcriptional coactivators of the Hippo pathway, as master drivers of that exclusion.

Using doxycycline-inducible shRNA mouse models that allow whole-body or cell-type-specific knockdown of YAP and TAZ, the researchers first established that continuous, ubiquitous depletion of both proteins is highly toxic, causing multi-organ damage—hepatic inflammation and necrosis, cardiomyocyte degeneration, and renal tubular injury—within about one month. Intermittent 'pulsed' dosing, however, avoided these toxicities and preserved a viable therapeutic window.

In a hydrodynamic tail vein injection model of CCA driven by activated Notch (NICD) and myristoylated AKT, just two weekly pulses of doxycycline-induced YAP/TAZ knockdown nearly doubled median survival in mice with advanced-stage tumors, significantly reducing liver-to-body weight ratios and tumor burden. Cell-type-specific depletion experiments showed that YAP/TAZ suppression in tumor cells—not cancer-associated fibroblasts—was responsible for the survival benefit.

Single-cell RNA sequencing revealed the mechanism: YAP/TAZ depletion triggered a roughly 2-fold increase in intratumoral T and NK cells, with CD8+ cytotoxic T cells appearing in clusters inside the tumor rather than being confined to the margin. A key downstream target identified was Tgfb2, whose YAP/TAZ-driven expression promotes extracellular matrix remodeling and tissue stiffening that physically and chemically excludes immune cells. Intercellular communication analysis (CellChat) confirmed enhanced tumor–T cell interactions after YAP/TAZ loss. Importantly, CD8+ T cell depletion abolished most of the survival benefit, confirming that immune re-engagement was mechanistically critical.

However, infiltrating T cells rapidly upregulated exhaustion markers upon entering the immunosuppressive TME—where macrophages and other cells still expressed PD-L1 and IL-10. This pointed to a rational combination: pulsed YAP/TAZ inhibition to open the door for T cells, followed by immune checkpoint blockade (anti-PD-1/PD-L1) to prevent or reverse exhaustion. This combination reshaped the TME, sustained T cell activation, and sensitized tumors that were otherwise non-responsive to immunotherapy alone. Notably, PD-L1 expression on tumor cells was unchanged by YAP/TAZ depletion in this CCA model, suggesting the mechanism differs from YAP/TAZ effects reported in other cancer types.

The translational signature derived from shYAP/TAZ T cells was predictive of outcomes in human CCA data from TCGA, strengthening clinical relevance. The study positions the YAP/TAZ–TGF-β2–ECM axis as a targetable immune-exclusion program and offers a blueprint for combining TEAD/YAP/TAZ inhibitors (several of which are in clinical trials) with checkpoint immunotherapy in fibrotic, immune-cold cancers.