We found that malignant T-cells and CAFs contribute to each other bidirectionally in ATLL, with CAFs promoting the clonal expansion of CD4 T-cells mediated by FGF7-FGFR1 signaling, and proliferating CD4 T-cells contributing to the growth of CAFs via PDGFA-PDGFRA/PDGFRB signaling. Here, PDGFA is linked to adult T-cell leukemia/lymphoma.