GSE178245
Myeloid Niches Sustain Antitumor T Cells and License PD-1 Blockade via CD28 Costimulation
The local mechanisms regulating exhaustion of tumor-infiltrating lymphocytes (TILs) and responsiveness to PD-1 blockade remain partly elucidated. In human ovarian cancer we show that tumor-reactive intraepithelial (ie)CD8+ TILs engaged by antigen are polyfunctional and upregulate PD-1, which restrains their effectiveness. PD-1+ TILs exhibit a continuum of TCR-engaged/exhausted states with variable effector fitness related to CD28 costimulation, which they receive in intraepithelial niches involving myeloid antigen-presenting cells (mAPC). Following PD-1 blockade, activation of TILs requires CD28 costimulation mediated in situ by tumor mAPCs, which is locally enhanced by CTLA-4 blockade. CD40 ligand also amplifies TIL responses in situ, especially in tumors in which mAPCs are not activated. Thus, dysfunctional and exhausted TILs, in a state of TCR engagement but without proper CD28 costimulation by mAPCs in situ, are unlikely to fully benefit from PD-1 blockade. Overall design: scRNA-seq of CD8+ TILs from 17 ovarian tumor-digest cultures.