PARP inhibitors accumulate B7-H3 on fibroblasts via blocking autophagic flux to potentiate immune evasion in ovarian cancer

Besides targeting tumor cells via canonical synthetic lethality, poly(ADP-ribose) polymerase inhibitors (PARPis) can remodel tumor immune microenvironment (TIME), which then affects PARPis' anti-tumor capabilities. However, exact function of PARPis on TIME remains insufficiently explored. Here, by leveraging paired samples during neoadjuvant PARPi Niraparib treatment derived from a prospective clinical trial, we discovered that the expression of immune checkpoint ligand B7-H3 was induced by PARPis in cancer-associated fibroblasts (CAFs) of ovarian cancer. Depletion of B7-H3 in CAFs by using host <i>cd276</i> (coding B7-H3) knockout mice or B7-H3 deficient fibroblast cells both boosted T cell functions and enhanced the anti-tumor capacities of PARPis in immunocompetent mouse models. Besides, increased B7-H3 on CAFs also attenuated the anti-tumor potentials of T cells in co-culture system. Mechanistically, PARPis blocked autophagic flux by inhibiting <i>PIP4K2A</i> expression, a critical regulator of autophagosome and lysosome fusion, and therefore dampening the lysosomal degradation of B7-H3. Importantly, neutralizing B7-H3 antibodies had synergistic effects with PARPis and achieved superior therapeutic efficacy than PARPis plus PD-1 blockade in a syngeneic mouse ovarian cancer model. Collectively, this study revealed an autophagy-mediated pathway by which PARPis contribute to immune evasion via enhanced B7-H3 accumulation on CAFs, highlighting the complexity of the regulation of PARPis on TIME and the potential application of combining PARPis with B7-H3 blockade in the treatment of ovarian cancer.