The phase I single arm trial assesses escalating doses of iv hu3F8 (days 1, 3, 5) in the presence of sc GM-CSF (day -4 through 5). These 3 doses of hu3F8 and 10 days of GM-CSF constitute a treatment cycle. The expansion phase II single arm trial assesses the anti-NB activity of hu3F8+GM-CSF.in 3 groups of patients: Group 1 patients have primary refractory disease (no prior relapse but incomplete response to treatment) in BM as documented by histology and/or 123I-MIBG scan. Group 2 patients are in ≥2nd CR and at high risk for another relapse. Group 3 patients have secondary refractory disease (prior relapse and incomplete response to retrieval therapy) in BM as documented by histology and/or 123I-MIBG scan. Ph II: Groups 1 & 3 pts can continue to get cycles every 1-2 months for up to 24 months from study enrollment or until they receive 5 cycles after a major response (CR or PR) is achieved.

Group 1 patients have primary refractory disease (no prior relapse but incomplete response to treatment) in BM as documented by histology and/or 123^I-MIBG scan. Group 2 patients are in >2nd CR/VGPR and at high risk for another relapse. Group 3 patients have secondary refractory disease (prior relapse and incomplete response to retrieval therapy) in BM as documented by histology and/or 123^I-MIBG scan. GM-CSF can be omitted if patients have a history of an allergy to GM-CSF or develop an allergic reaction to GM-CSF after initiating therapy while on the protocol.

Ph I: 1 cycle consists of treatment with hu3F8 for 3 days (day 1, 3 & 5). GM-CSF starts 5 days in advance of each hu3F8 cycle at 250 mcg/m^2/day (day -4 to day 0), & at 500 mcg/m^2/day x 5 days (day 1 to day 5). Hu3F8 cycles are 5 days. Ph II pts may receive treatment on a modified schedule of 3 doses of IV hu3F8 over a maximum of 10 days, as needed. With modified schedules of hu3F8, GM-CSF will be administered at 250 mcg/m2/day x5 days before the 1st dose of hu3F8, as with the standard schedule, but then GM-CSF at 500 mcg/m2/day will be administered on day of the 1st dose of hu3F8, on the day before and on the day of the 2nd dose of hu3F8, and on the day before and on the day of the 3rd dose of hu3F8. Cycles are repeated at 2-4 week intervals between 1st days of hu3F8, through 4 cycles. Pts who complete 4 cycles of treatment w/o complications or disease progression have the option of continuing treatment for up to 24 months from their 1st dose of hu3F8.

hu3F8 when combined with GM-CSF. DLT is defined after 1 cycle. Seventeen dosage levels of hu3F8 will be tested with three to six patients at each dosage level.

of the humanized anti GD2 antibody hu3F8 when combined with Granulocyte-Macrophage Colony Stimulating Factor (GM-CSF) in patients with high risk neuroblastoma. All observed adverse events, regardless of treatment group or suspected causal relationship to study drug will be recorded. Adverse events will be identified and graded using the Common Toxicity Criteria Version 4.0

(Phase I) when combined with GM-CSF. Pharmacokinetics will be measured by serial blood sampling following the first two iv doses of hu3F8 as listed in Table 3. Serum hu3F8 will be measured pre-infusion and at time pre- (within an hour before hu3F8), 5 min, 3h, 6-8h, 24h, 48h, 72h, 96, 120h, 168h 216h and 264h after the first infusion of hu3F8 during cycle1 and, whenever possible, peak hu3F8 level at pre- and ~5 minutes post-infusion will also be measured for each dose of hu3F8 in subsequent cycles .