A PHASE 1/2 STUDY ASSESSING SAFETY AND PHARMACOKINETICS OF CEMIPLIMAB IN PEDIATRIC PATIENTS WITH RELAPSED OR REFRACTORY SOLID OR CENTRAL-NERVOUS-SYSTEM TUMORS AND SAFETY AND EFFICACY OF CEMIPLIMAB IN COMBINATION WITH RADIOTHERAPY IN PATIENTS WITH NEWLY DIAGNOSED DIFFUSE INTRINSIC PONTINE GLIOMA, NEWLY DIAGNOSED HIGH-GRADE GLIOMA, OR RECURRENT HIGH-GRADE GLIOMA