Tumor effusion samples

Tumor effusion fluids were collected from patients with cancer (see table S1 for details) presenting with malignant effusions at the University Hospital Basel after obtaining written informed consent. After collection, the cellular components of the malignant effusions were separated by centrifugation, and the cells and fluids were frozen at −80°C until further use. Where indicated in the legends, total effusion cells were cultured or analyzed, and CD4⁺ T cells were identified by staining with CD4–fluorescein isothiocyanate (FITC) (clone RPA-T4, BD Biosciences).