Alloreactive T cell responses between HLA-identical siblings. Detection of anti-minor histocompatibility T cell clones induced in vivo.

Cytotoxic T cell (CTL) clones were isolated from the peripheral blood of a patient 13 days following marrow transplantation from her HLA-identical brother. Nineteen of the clones were specifically reactive with host--but not donor--cells, but one clone was reactive with donor but not host cells. Family studies using the 19 clones showed reactivity patterns consistent with three non-HLA, minor histocompatibility antigens (minor-HA). The frequency of reactivity on a large panel of unrelated cells indicated a relatively limited degree of polymorphism. Each of the clones was restricted in its activity by a class I epitope common to HLA-B7, B27, and B40. These data demonstrate that by clonal analysis it is possible to identify in vivo antidonor and antihost alloreactive CTL clones directed against HLA determinants following marrow transplantation.