IMMU-11. Evaluation of CAR-T cells targeting CD276 in medulloblastoma

Abstract Brain tumors are the most frequent category of solid tumors in children and have the highest mortality rate among all pediatric cancers. Although diagnosis and treatment have improved prognosis over the past decades for some childhood brain tumors, others remain lethal and current treatments are highly toxic to the developing brain, resulting in severe sequelae and considerably affecting the patient’s quality of life. Thus, new therapeutic options with reduced secondary effects are urgently needed. From this perspective, immunotherapies have gained a lot of attention due to their effectiveness in targeting tumor cells specifically. Chimeric-antigen receptor (CAR) T-cells recognize the target antigen on the surface of. CD276 is an immune checkpoint molecule that is expressed in a variety of solid tumor entities, including pediatric brain tumors. We analyzed the CD276 expression in our Patient-Derived-Xenograft (PDX) biobank of brain tumors and found that CD276 is ubiquitously expressed (ATRT, MB, EPN, GBM, ETMR, etc). Flow cytometry of MB PDX (n=4) confirmed CD276 expression of 97-99% of tumor cells, indicating that CD276 might be a good antigen target for CAR-T cell therapy of MBG3 and MBSHH. We found that second generation CAR-T cells targeting CD276 antigen significantly decreased tumor burden of the most aggressive MB subgroups (G3 and SHH-TP53mut PDX models) in NSG mice. We further treated NSG mice carrying a high tumor burden of the aggressive SHH-TP53mut PDX BT084 with second (CD28) and third generation (CD28-41BB) CD276-CAR-T cells. While both 2nd and 3rd generation improved the survival rates compared with CD19-CAR-T control cells, we found no difference in survival between the CD276 CAR-T generations, with no severe secondary effect during treatment. In conclusion, CD276 is a good antigen target for medulloblastoma, and warrants further evaluation for the treatment of medulloblastoma patients at relapse or as a maintenance therapy after standard treatment.