The inverse correlation between PARP1 and PD-L1, PAR, and p-STAT3 expression in surgical specimens of ovarian cancer. The inverse correlation between PARP1 and PD-L1, PAR, and p-STAT3 expression in surgical specimens of ovarian cancer. A, Patient tissues were stained with PARP1 and PD-L1. Representative images of IHC staining of PARP1 and PD-L1 in human ovarian cancer tissues (n = 41) are shown. Scale bar, 100 μm. The correlation analysis between PARP1 and PD-L1 was analyzed, and the P value was calculated by the Pearson correlation test (P = 0.0002, r = −0.54784). “−,” negative expression; “+,” low expression; “++,”, medium expression; “+++,” high positive expression. B, Patient tissues were stained with anti-PAR and anti–p-STAT3. Representative images of IHC staining of PAR and p-STAT3 in human ovarian cancer tissues (n = 53) are shown. Scale bar, 100 μm (P < 0.0001, r = −0.8953). C, PARP1-mediated poly(ADP-ribosyl)ation of STAT3 as a key step in inhibiting the transcription of PD-L1. A graphical description of how PARP1 suppresses the transcription of PD-L1 by poly(ADP-ribosyl)ating STAT3. Ling Ding et al. Cancer Immunol Res 2019;7:136-149 ©2019 by American Association for Cancer Research