Recently, the pretransplant estimation of alloreactive cytotoxic T lymphocyte precursors (CTLp) frequency in unrelated HLA matched donor/recipient pairs is considered as one of criteria in the selection of donors for bone marrow transplantation.
A limiting — dilution system was established to measure the frequency of alloreactive cytotoxic T lymphocyte precursors in humans. Here we demonstrate strong variations in the frequency of CTLp in different combinations of unrelated individuals. The frequency variation in HLA mismatched unrelated and siblings ranged from 1:10869 to 1: 78740. The strongly positive values of CTLp frequencies were also observed in three of four HLA matched MLC negative unrelated combinations. In comparison CTLp frequencies in HLA identical siblings have ranged from 1: 322580 to 1: 11721170. These results show that
1. the cytotoxic T cell clones generated in the cultures of cells of two donors are specifically activated by alloantigens of major histocompatibility system HLA. The products of non-HLA loci are not involved in the process, and
2. in combinations of unrelated individuals the conventional methods of HLA matching are not sufficient. The frequency of CTLp estimation appears to be the method disclosing the difference in major histocompatibility system in unrelated pairs compatible by conventional typing.
The high frequency of alloreactive CTLp was retrospectively found in one case of allogeneic bone marrow transplantation between HLA matched unrelated individuals.