In contrast, B7-H3 is highly expressed on many different pediatric solid tumors, including rhabdomyosarcoma (95% of tumors stained), Ewing sarcoma (89%), Wilms tumor (100%), neuroblastoma (82%), ganglioneuroblastoma and ganglioneuroma (53%), medulloblastoma (96%), glioblastoma multiforme (84%), and diffuse intrinsic pontine glioma (100%).
To see whether CAR T therapy might have better efficacy than checkpoint inhibitors in this population, the investigators created a B7-H3 CAR using the B7-H3 tumor–specific monoclonal antibody MGA271, which has been shown to be safe in both adults and children in early clinical trials.
In human tumor xenograft models of osteosarcoma, all mice who received a single dose of the B7-H3 CAR survived at least 70 days after tumor engraftment, whereas all control mice, who received the CD19 CAR, died by day 60 (P = .0067). Similarly, in a model of Ewing sarcoma, all mice treated with B7-H3 survived at least 100 days, whereas all controls were dead by day 50 (P = .0015).
The B7-H3 construct also showed good activity against a model of medulloblastoma, showing that it was capable of crossing the blood-brain barrier.