Tumour assembloids recapitulate tumour-CAF-T cell crosstalk in renal cancer

Dynamic interactions between tumours and their microenvironment are crucial for cancer progression and therapeutic outcomes^1,2. However, our understanding of these relationships remains limited by the constrained capacity of current human model systems to manipulate diverse cellular components and to interrogate complex tumour-stroma crosstalk. Here we generated combinatorial, mix-and-match tumour assembloids by conditionally reconstituting multiple components of human renal cell carcinoma, including cancer cells, cancer-associated fibroblasts (CAFs) and tumour-infiltrating immune cells. Using genetically engineered renal cell carcinoma assembloids with humanized mouse models, we uncovered mechanisms by which CAFs coordinate interactions between tumour cells and CD8⁺ T cells to maintain non-cell-autonomous CD8⁺ T cell stemness and drive responsiveness to anti-PD-1 therapy. These interactions operate through a tumour-CAF-T cell signalling axis in which tumour-derived WNT induces CAF expression of activin A, which enhances CD8⁺ T cell stemness and sensitivity to PD-1 blockade. In non-responders, we also identified a subset of WNT-unresponsive CAFs that do not produce activin A, which leads to impaired CD8⁺ T cell stemness and resistance to therapy. Together, these findings establish a tumour-CAF-T cell axis as a key determinant of heterogeneous responses to immune checkpoint inhibitors. Moreover, tumour assembloids provide a versatile platform for mechanistic dissection of the tumour microenvironment and evaluation of personalized immunotherapy strategies.