1 Department of paediatrics, Stellenbosch University, Stellenbosch, South Africa.
2 Department of Paediatrics, University of Cape Town, Cape Town 7935, South Africa.
3 Department of Immunology, SAMRC Extramural Unit for Stem Research and Therapy, Institute for Cellular and Molecular Medicine, University of Pretoria, Pretoria, South Africa.
4 Department of Paediatrics, University of Cape Town, Cape Town 7935, South Africa. Electronic address: alan.horn@uct.ac.za.