Are Tγ cells of myelomonocytic lineage

To evaluate the cell lineage from which Tγ cells derive by means other than cell membrane markers, the rare situation of human chimerism was studied. In patients with severe combined immunodeficiency who have been successfully treated by bone marrow transplantation, the occurrence of split take has been well documented: whereas myelomonocytic hemopoietic cell lines remain of host origin, the T lymphoid compartment is of donor origin, and the B lymphoid compartment may be either of host or of donor origin. We have studied the Tγ cells of two patients successfully treated by bone marrow transplantation from donors of the opposite sex with respect to the sex chromosome pattern, the binding of OKM1 and OKT3 monoclonal antibody and the killer (K) and natural killer (NK) cell activities. All Tγ cells of both patients were found to be of donor origin. These Tγ cells contained two serologically distinct subpopulations, one OKM1+, OKT3+, the other OKM1+, OKT3−, as was also found in normal persons. However, the ratio between these two subpopulations is 1. Furthermore, the patients' Tγ cells displayed strongly reduced K and NK activities (< 5% of normal). It was concluded that at least part of the OKM1+, OKT3− and the OKM1+, OKT3− Tγ cells are derived from other than the myelomonocytic lineage, presumably from the lymphocytic lineage. The origin of the K- and NK-active Tγ cells, however, cannot be conclusively determined from these experiments. The findings also imply that the antigen detected by OKM1 should no longer be regarded as exclusively present on myelomonocytic cells.