Immunological tolerance in an HLA non-identical chimeric twin

Blood group chimeric twins offer a unique opportunity to study immunologica l tolerance in humans. Although this condition is not as rare as previously considered, derailed immunological studies of blood group chimeras are lac king. We describe here a case of secondary chimerism in a dizygotic twin of opposite gender. The karyotypes of the cultured fibroblast confirmed the s ex of each twin, all cells in the boy were 46, XY and all cells in the girl were 46, XX. Molecular HLA typing on fibro-blasts revealed HLA-DR, DQ and DP disparities between the two siblings. Mixed lymphocyte culture (MLC) rev ealed a mutual absence of alloreactivity. (C) American Society for Histocom patibility and Immunogenetics, 2000. Published by Elsevier Science Inc.