GPC3 and Wilms tumor: Carcinoembryonic antigen glypican-3 (GPC3), a hepatic heparan sulfate proteoglycan expressed in many pediatric tumors such as hepatoblastoma, yolk-sac tumors, and Wilms’ tumors, has also been piloted as a target for vaccination.112,113 A phase I study of 18 pediatric patients with GPC3-expressing solid tumors found that vaccination with a single MHC-I matched GPC3-peptide formulated in a water-in-oil emulsion improved or maintained clinical status (CR + PR + SD) in 67% of patients,114 despite using a suboptimal emulsion formulation, as discussed above.