Megakaryocyte chimerism after allogeneic stem cell transplantation in children

The aim of this study was to investigate the extent and the clinical implications of mixed chimerism in megakaryocytes after stem cell transplantation (SCT). Polymerase chain reaction analyzing allele length polymorphisms was used to determine the origin of immunomagnetically isolated megakaryocytes and leukocyte subpopulations after SCT in 13 children. Eleven were unselected consecutive cases while two were included due to known leukocyte mixed chimerism. Recipient DNA was detected in the megakaryocytes in six out of the 11 cases at levels between 1 and 100%. Coinciding mixed chimerism in the leukocyte populations was detected in two of the 11 cases. Of the two selected cases with known leukocyte mixed chimerism, two boys with aplastic anemia and Wiskott-Aldrich syndrome had 1-5 and 70% recipient megakaryocytes, respectively. Although the four relapses or deaths, within the 13 months of observation, were restricted to patients with multilineage or isolated megakaryocyte (n = 1) mixed chimerism, it was not possible to link any other apparent clinical problems, except a prolonged thrombocytopenia in one case, to the mixed chimerism in this limited study group.