Frequency analysis of cytotoxic T lymphocyte precursors--possible relevance to HLA-matched unrelated donor bone marrow transplantation.

HLA-matched unrelated donor (MUD) bone marrow transplants and transplants between HLA mismatched family members are associated with an increased incidence and severity of graft-versus-host disease (GVHD) in comparison with HLA-identical sibling transplants. A limiting dilution analysis system was set up to measure the frequency of alloreactive cytotoxic T lymphocyte precursors (CTL-p) in normal individuals and in potential donor/patient pairs selected for bone marrow transplantation. The donor/recipient pairs were divided into four groups depending on their degree of HLA disparity. A distinct range of CTL-p frequencies was obtained for each group and these showed a hierarchy of response related to the degree of HLA disparity between donors and recipients in that particular group. This assay system may be of value in selecting potential matched unrelated and mismatched family donor/patient pairs for those at lower risk of GVHD.