Disclosure of potential conflict of interest: M. Gattorno has received consultancy fees, research support, and lecture fees from Novartis and SOBI. C. Rodríguez-Gallego and C. Hinze have received lecture fees from Novartis. J. A. Bernstein has received consultancy fees from McKesson, research support from the National Institutes of Health (NIH) and CIRM, and lecture fees from the University of Minnesota. J. A. Church has received research support from Pfizer and BioProducts Laboratory. R. Skinner has provided expert testimony for the Medical Defence Union and the NHS Health Service and has received research support from Newcastle upon Tyne Hospitals NHS Foundation Trust, Malawi-Royal Victoria Infirmary, the Children's Cancer Fund, and Children with Cancer UK. The rest of the authors declare that they have no relevant conflicts of interest.