ICOS and neoplasm: Not only is it a pharmacodynamic biomarker to assess the response to anti-CTLA-4 treatment, but ICOS can also be targeted in combination with CTLA-4 blockade for enhanced tumor rejection, substantiated by evidence from ICOS/ICOSL pathway–deficient mice showing a weakened antitumor response compared to wild-type mice after anti-CTLA-4 treatment (Fu et al., 2011).