T FR Cells Inhibit Anti-Tumor Immunity and are Responsive to Immune Checkpoint Blockade

Immune checkpoint blockade (ICB) has shown remarkable clinical success in boosting anti-tumor immunity. However, the breadth of its cellular targets and specific mode of action remain elusive. We find that T follicular regulatory (TFR) cells are present in high numbers in multiple tumors, inhibit anti-tumor immunity and are responsive to ICB. TCR-seq data, trajectory analyses and adoptive transfer studies indicate intratumoral TREG to TFR cell conversion. When compared to TREG cells, TFR cells exhibited enhanced suppressive capacity. In syngeneic tumor models, anti-PD-1 treatment increased the number of tumor-infiltrating TFR cells. Conditional knockout of TFR cells or depletion of TFR cells with anti-CTLA-4 antibody prior to anti-PD-1 treatment, improved tumor control in mice. Notably, in a cohort of melanoma patients, treatment with anti-CTLA-4 followed by anti-PD-1 at progression was associated with better long-term survival outcomes than anti-PD-1 or anti-CTLA-4 monotherapy, anti-PD-1 followed by anti CTLA-4 at progression or concomitant combination therapy.