Mixed chimerism of thyroid follicle cells after allogeneic bone marrow transplantation. (2003)

Recently, a growing amount of data have been accumulated concerning the plasticity of human adult stem cells that may generate a multilineage engraftment. In this context, there is some evidence of a putative relationship between mixed microchimerism in thyroid follicle cells (1) of presumed fetal origin and autoimmune disease in female patients (2–4). A model to study this issue would include patients in whom bone marrow transplantations (BMTs) with a sex-mismatched constellation were performed. Therefore, a retrospective analysis of thyroid gland tissue derived from four male patients with chronic myelogenous leukemia who underwent allogeneic BMTs was performed. These patients received full unmanipulated grafts (median size 2.3×108/kg nucleated cells) from sex-mismatched human leukocyte antigen-identical (female) family donors following standard procedures that included conditioning regimens (Cy 60 mg/kg/day×2; dose of total body irradiation 4×2.5 Gy 60 cobalt) and graft-versus-host-disease prophylaxis (short-term methotrexate +cyclosporine A). Leukemic relapse occurred in two patients after a posttransplant observation time ranging from 2 to 26 months. Relevant grades of acute graft-versus-host-disease accompanied by lethal infections developed in the other two patients of this series approximately 3 to 12 weeks after BMT. As controls, postmortem tissue samples without evidence of thyroid pathology were obtained from two male and two female patients. During the autopsy, samples of thyroid gland tissue were randomly taken from the right and left lobes and fixed in buffered 5% formalin. For dual-color genotypic evaluation, paraffin-embedded sections were used and processed by a previously described modified fluorescence in situ hybridization (FISH) technique applying x- and y-chromosome probes (5). To neutralize possible artefacts in the autopsy material and to match with the obstacles of a certain plane of section regarding proper signal recognition, only cells were evaluated that displayed two distinctive red and green dots. After FISH, distinctively labeled thyroid epithelial cells lining the walls of the colloid-containing follicles were easily identifiable. In each of the four patients of the control group, 300 follicle cells were counted; however, FISH failed to reveal any sex-mismatched chromosome signals in this cohort. Contrasting this finding in the four patients with a history of BMT, a striking, although quantitatively low, number of thyroid epithelium displayed mixed microchimerism (Table 1). It is noteworthy that this small amount of female donor cells among the host-type (male) thyroid follicle cells was not related to the period of engraftment.Table 1: Mixed chimerism of the thyroid follicle cells in a sex-mismatched (host male, donor female) allogeneic bone marrow transplantation constellation (percentages are listed in brackets)Considering the negative findings in the control group of patients, sensitivity of the FISH technique seems to be reliable and is in keeping with a study reporting the absence of any male cells in thyroid glands without pathologic changes that were derived from women at necropsy (1). On the other hand, in multinodular goiter, chronic thyroiditis, and Grave’s disease, a variable amount of mixed microchimerism was described (1,3,4) and was related to the pathogenesis of disease (6). In this context, it is remarkable that in two patients of our cohort with longstanding engraftments and mixed microchimerism, no thyroid pathology developed after BMT. Moreover, the demonstration of donor-type thyroid follicle cells after successful engraftment indicates that after myeloablative therapy, adult bone marrow-derived stem cells are able not only to reconstitute normal hematopoiesis but also to maintain the capacity to differentiate into other specialized cell compartments. J. Thiele E. Varus C. Wickenhauser H. M. Kvasnicka K. Weirauch K. A. Metz D. W. Bellen