Tumor tertiary lymphoid structures (TLS) are almost universally associated with better outcomes in cancer patients. Combinations of anti-angiogenic and immune therapies promote immune cell infiltration and TLS formation in tumors. However, the cellular and molecular factors that initiate TLS formation and positioning are unclear.

Using a genetic model of microsatellite stable colorectal cancer, we show that anti-angiogenic immune therapy induces TLS formation near crypt regions in the absence of high endothelial venules.

Mechanistically, TLS neogenesis results from the coordinated reprogramming of pericryptal fibroblasts, which instigate B cell chemoattraction through CXCL13, and endothelial cells, in which anti-angiogenic treatment down-regulates Notch signaling in arterial endothelial cells, enabling pericryptal arterial vessels to function as focal points for swarming B cells. We further show that blocking angiogenic signaling in combination with a CD40 agonistic antibody targeted to tumor-associated fibroblasts (FAP-aCD40) induces TLS formation specifically in tumors without systemic toxicity.

These results highlight a cooperative cross-talk between fibroblasts and arterial endothelial cells in the tumor crypt niche that orchestrates TLS formation and can be therapeutically harnessed in poorly immunogenic colorectal cancers.