PITTSBURGH – Call it the CAR of the future – an investigational chimeric antigen receptor–T cell construct targeted against an antigen highly expressed on pediatric solid tumors has shown promising efficacy in preclinical studies.
Investigators found that the antigen, labeled B7-H3, was expressed on 84% of microarrays of pediatric solid tumors. More importantly, a single dose of CAR targeted to B7-H3 caused complete regression of osteosarcoma and Ewing sarcoma xenografts and improved survival over an untransduced, CD19-targeted CAR in mice, Robbie Majzner, MD, reported at the annual meeting of the American Society of Pediatric Hematology/Oncology.
Dr. Majzner was the recipient of an ASPHO young investigator award for his team’s research into developing a CAR T that could be as effective against solid tumors as other CAR Ts have been against hematologic malignancies such as acute lymphoblastic leukemia.
Solid tumors are more challenging to target than leukemias or lymphomas because of the small number of antigens expressed on most pediatric tumors, he said.
“Over 95% of tumors have a very low rate of mutations, which means that they have very few neoantigens which the immune system can recognize in order to attack,” he said.
In the Children’s Oncology Group, single-agent immunotherapy with the anti–programmed death protein 1 (PD-1) inhibitor nivolumab (Opdivo) showed no evidence of efficacy against either Ewing sarcoma, osteosarcoma, rhabdomyosarcoma, or measurable neuroblastoma. PD–ligand 1 was found to be expressed in only a few of the 43 tumors studied, suggesting that checkpoint inhibitor therapy is unlikely to work in these solid tumors, he said.