Inclusion Criteria:

          -  Neuroblastoma (NB)

          -  Documented high-risk disease

          -  Receipt of Standard of Care (SoC) frontline induction/consolidation therapy (including
             surgery, chemotherapy, ASCT, MIBG, radiotherapy, immunotherapy, or retinoids)

          -  Active disease despite previous aggressive multi-drug chemotherapy

          -  One of the following:

               -  Measurable tumor on MRI, (CT) scan obtained within 3 weeks prior to randomization
                  that is MIBG-avid or demonstrates increased FDG uptake on PET scan

               -  MIBG (Metaiodobenzylguanidine) scan obtained within 3 weeks prior to
                  randomization with positive uptake at a minimum of one site. This site must
                  represent disease recurrence after completion of therapy, progressive disease on
                  therapy, or refractory disease during induction

               -  Soft tissue disease that is not MIBG avid or does not demonstrate increased FDG
                  uptake on PET scan, but the presence of viable NB is documented by new biopsy

          -  Life expectancy of at least 6 months, as judged by the Investigator

          -  Written informed consent

        Exclusion Criteria:

          -  Myelodysplastic syndrome or any malignancy other than NB

          -  Any systemic anti-cancer therapy within 3 weeks

          -  Autologous stem cell transplant (ASCT) or stem cell infusion within 6 weeks prior to
             randomization or ongoing toxicity due to the ASCT/stem cell infusion at the discretion
             of the investigator

          -  Therapeutic 131I-MIBG within 6 weeks prior to randomization

          -  Radiotherapy (RT) within 4 weeks prior to randomization at any lesion site that will
             be identified as a target lesion to measure tumor response

          -  Prior treatment with anti-GD2 if the patient experienced Progressive Disease (PD)
             while on anti-GD2 treatment

          -  Receipt of second line chemotherapy after designation of primary refractory disease or
             first relapse or PD

          -  NB in Bone Marrow (BM) only

          -  NB in the Central Nervous System (CNS) or leptomeningeal disease within 6 months prior
             to randomization

          -  Performance status of < 50% as per the Lansky scale (patients less than 16 years of
             age) or Karnofsky scale (for patients aged 16 years or older)

          -  Left ventricular ejection fraction < 50% by echocardiography

          -  Inadequate pulmonary function

          -  Diarrhea Grade ≥ 2

          -  Treatment with long-acting myeloid growth factor within 14 days or short-acting
             myeloid growth factor within 7 days prior to first dose of GM-CSF

          -  Receipt of immunosuppressive treatment (local steroids excluded) within 4 weeks prior
             to randomization

          -  Life threatening infection(s)

          -  Uncontrolled seizure disorders despite anticonvulsant therapy (defined as a seizure
             event within 3 months prior to randomization)

          -  Treatment with enzyme-inducing anticonvulsants including phenytoin, phenobarbital, or
             carbamazepine for at least 7 days prior to randomization

          -  Concomitant use with St John's wort

          -  Allogeneic hematopoietic stem cell transplantation (allo-SCT) or
             donor-lymphocyte-infusion (defined as any kind of active allogenic lymphocyte
             suspension)

          -  Treatment with Hematopoietic Progenitor Cell (HPC) boost or "top-up" of allogenic stem
             cells (lymphocyte-depleted) within 2 months prior to randomization

          -  History of allergy or known hypersensitivity to GM-CSF, yeast-derived products, or any
             component of GM-CSF or naxitamab

          -  History of anaphylactic reactions CTCAE Grade 4 related to prior anti-GD2 antibody
             therapy

          -  Unacceptable hematological status, unacceptable liver or kidney function prior to
             first dosing

          -  Platelet count <75,000/µL

          -  Inability to comply with protocol

          -  Significant intercurrent illness (any ongoing serious medical problem unrelated to
             cancer or its treatment) that is not covered by the detailed exclusion criteria and
             that is expected to interfere with the action of trial agents or to significantly
             increase the severity of the toxicities experienced from trial treatment

          -  Females of childbearing potential who are pregnant, breast feeding, intend to become
             pregnant, or are not using adequate contraceptive methods or males who are not using
             adequate contraceptive methods