1. Oxford Vaccine Group, Department of Paediatrics, University of Oxford, Oxford OX3 7LE, UK
2. Division of Structural Biology, Wellcome Centre for Human Genetics, University of Oxford, Oxford OX1 2JD, UK
3. Instituto Politécnico Nacional (IPN), Av. Luis Enrique Erro s/n. Unidad Adolfo López Mateos, México City 07738, Mexico