Intestinal mucosal mononuclear cell chimaerism after sex-mismatched allogeneic bone marrow transplantation.

The contribution of haemopoietic cell chimaerism to the pathogenesis of GVHD after BMT is unclear. This report raises the possibility that donor lymphocyte-recipient macrophage chimaerism may occur shortly after allogeneic marrow engraftment and hence might contribute to the development of GVHD. Immunohistological studies of intestinal mucosa in an allogeneic BMT patient, who did not engraft, revealed an almost complete absence of lymphocytes 30 days after transplant, but preservation of mucosal macrophage numbers. Subsequently, combined immunohistology-Y chromosome in situ hybridization studies were performed in two female BMT recipients of male donor marrow. These studies revealed that between 25 and 40% of macrophages and between 25 and 40% of T lymphocytes were of donor origin during the first 6 months after transplant. In conclusion, whilst the immunohistological studies of intestinal mucosa from a patient who failed to engraft suggest that donor lymphocyte-recipient macrophage ('split') chimaerism may occur shortly after marrow engraftment, the subsequent in situ hybridization studies revealed 'mixed' chimaerism in the two sex-mismatched BMT recipients.