RNA Lipid Particles Targeting Pediatric Recurrent Intracranial Malignancies and Other systEmic Solid Tumors

For recurrent pHGG there will be two non-randomized arms assigned at the discretion of the patient and treatment team: * Arm 1-A single neoadjuvant pp65 RNA-LP (DP1) will be administered prior to surgical resection/biopsy, and then two adjuvant DP1. * Arm 2-Surgical resection/biopsy will occur first and all three DP1 will be administered in the adjuvant setting For recurrent OSA there will be three arms based on disease status on enrollment: * Arm 1-Patients with unilateral pulmonary-only metastatic recurrent OSA * Arm 2-Patients with bilateral pulmonary-only metastatic recurrent OSA * Arm 3-Patients with unresectable OSA in any location. The Phase I dose-escalation study for either recurrent/progressive pHGG or recurrent OSA cohort will be performed in 18 subjects using a 3+3 design. Both recurrent pHGG trial arms will be enrolled together as a single cohort for safety, and similarly all recurrent OSA trial arms will be enrolled together as a single cohort for safety during phase I.