LRRC15(+) myofibroblasts dictate the stromal setpoint to suppress tumour immunity

Recent single-cell studies of cancer in both mice and humans have identified the emergence of a myofibroblast population specifically marked by the highly restricted leucine-rich-repeat-containing protein 15 (LRRC15)(1–3). However, the molecular signals that underlie the development of LRRC15(+) cancer-associated fibroblasts (CAFs) and their direct impact on anti-tumour immunity are uncharacterized. Here in mouse models of pancreatic cancer, we provide in vivo genetic evidence that TGFβ receptor type 2 signalling in healthy dermatopontin(+) universal fibroblasts is essential for the development of cancer-associated LRRC15(+) myofibroblasts. This axis also predominantly drives fibroblast lineage diversity in human cancers. Using newly developed Lrrc15–diphtheria toxin receptor knock-in mice to selectively deplete LRRC15(+) CAFs, we show that depletion of this population markedly reduces the total tumour fibroblast content. Moreover, the CAF composition is recalibrated towards universal fibroblasts. This relieves direct suppression of tumour-infiltrating CD8(+) T cells to enhance their effector function and augments tumour regression in response to anti-PDL1 immune checkpoint blockade. Collectively, these findings demonstrate that TGFβ-dependent LRRC15(+) CAFs dictate the tumour-fibroblast setpoint to promote tumour growth. These cells also directly suppress CD8(+) T cell function and limit responsiveness to checkpoint blockade. Development of treatments that restore the homeostatic fibroblast setpoint by reducing the population of pro-disease LRRC15(+) myofibroblasts may improve patient survival and response to immunotherapy.