A matrikine organizes the dendritic cell–T cell triads that build tertiary lymphoid structures

ABSTRACT Tertiary lymphoid structures (TLS) predict response to checkpoint inhibition, and conventional dendritic cells (cDC) are required to build and maintain them. What renders a niche permissive for their assembly is unknown: chemokines recruit the cellular constituents but do not specify how they organize. Here we show that the organizing signal is a matrix fragment. Proteolysis of the proteoglycan versican (VCAN) releases the matrikine versikine, constitutively in germinal center light zones and inducibly in tumor stroma. Versikine activates CD11b⁺ cDC and expands cDC1 to assemble TLS-archetypal triads, apposed DC:CD4⁺T:CD8⁺T units. Versikine-conditioned DC engage progenitor-exhausted CD8⁺ T cells (Tpex) and Th1-polarized follicular helper CD4⁺ T cells. Excess unproteolyzed VCAN inverts this toward DC–Treg crosstalk and Tpex loss. Versikine supplied as mRNA or recombinant protein sensitizes refractory tumors to PD-L1 blockade. VCAN proteolysis prospectively predicted outcomes after PD-1 blockade in metastatic colorectal cancer. Matrikines organize chemokine-recruited cells into functional immune niches. One-sentence summary Chemokines recruit the cells of lymphoid tissue; a VCAN-matrikine organizes them.