This is a single-arm clinical trial to evaluate the efficacy and safety of quadruple immunotherapy with natural killer (NK) cells, anti-GD2 antibody, cytokines (interleukin-2 (IL-2) and granulocyte-macrophage colony stimulating factor (GM-CSF)) and retinoid X receptor gamma (RXRg) agonist spironolactone for paediatric patients with relapsed or refractory neuroblastoma.

Included patients will receive intravenous infusion of donor NK cells on day 0, and anti-GD2 antibody (dinutuximab) on day -6 to day -2. IL-2 will be given subcutaneously on day -1, day +1, day +3, day +5, day +7, and day +9. Subcutaneous injection of GM-CSF will be started on day 0, given daily till neutrophil count >1000/mm3. Spironolactone will be started orally on day -1, given three times daily till cessation of GM-CSF.

Alternative anti-GD2 antibody (Naxitamab) can be used instead of dinutuximab, to be given on day -5, day -3, day +1 and day +3.

Inclusion Criteria:

• relapsed or refractory neuroblastoma
• Adequate organ function: creatinine clearance ≥40 ml/min/1.73m2, total bilirubin ≤3 times upper limit of normal and ALT ≤500 IU/L, left ventricular shortening fraction ≥25%, and oxygen saturation ≥92% in room air
• Karnofsky or Lansky performance status score ≥50
• Has an appropriate HLA-haploidentical NK-cell donor available

Exclusion Criteria:

• Pregnant or lactating woman
• HIV infection
• Patients for whom conventional treatment is deemed more appropriate
• Patients who are unlikely to benefit, e.g., terminal malignancy with life expectancy <1 month