Inclusion Criteria:  Inclusion criteria for all participants:  Life expectancy of greater than or equal to 12 weeks, in the opinion of the Investigator Diagnosis of GBM based on the Consortium to Inform Molecular and Practical Approaches to Central Nervous System Tumor Taxonomy (cIMPACT) NOW 6 criteria Participants must have confirmed EGFRvIII-expression Karnofsky Performance Status (KPS) Score of >=70%. Adequate organ functions prior to start of study treatment Willingness to abide by contraceptive measures for the duration of the study.  Inclusion criteria for Part I and Part II only:  Participants whose tumors have an unmethylated O6-methylguanine-DNA methyltransferase (MGMT) promotor status based on local assessment Participants must have completed standard of care therapy for newly diagnosed disease, including surgical resection and adjuvant radiotherapy with or without concomitant temozolomide.  Inclusion criteria for Part III and Part IV only:  Documented first or second recurrence of GBM At least one measurable GBM lesion as per RANO criteria prior to initiation of study treatment.  Exclusion Criteria:  Exclusion criteria for all participants:  Participants with infratentorial tumors and tumors primarily located in or close to critical structures (e.g., brain stem). Presence of extracranial metastatic or leptomeningeal disease Known hypersensitivity to immunoglobulins or to any other component of the investigational medicinal product formulation Active bleeding or pathological condition that carries a high risk of bleeding, including inherited and acquired coagulopathies Participants unable to undergo an MRI with contrast.  Exclusion criteria for Part I and Part II only:  Recurrent malignant gliomas Any prior anti-tumor treatment for GBM: tumor resection, adjuvant radiotherapy with or without concomitant temozolomide must be the only tumor-directed treatment that the participant has received for GBM.  Exclusion criteria for Part III and Part IV only:  More than two recurrences of GBM Prior anti-EGFRvIII-targeting agents (including vaccines), anti-angiogenic therapy, and/ or gene therapy for the treatment of GBM and gliomas.