Frequency analysis of cytotoxic T lymphocyte precursors in search for donors in bone marrow transplantation.

The usefulness of cytotoxic T lymphocytes precursors (CTLp) frequency analysis in the search for donors in bone marrow transplantation was studied. The frequency of anti-recipient CTLp was approached by limiting dilution assay in HLA matched unrelated, HLA partially matched related and HLA genotypically identical donors. The majority of patients examined were affected with different hematological malignancies. Alloreactive CTLp recognizing non-HLA gene products were not detected in pretransplant examination of two pairs of HLA identical siblings. However, an increased incidence of allospecific CTLp was identified in HLA matched MLC negative unrelated pairs. Thus, CTLp assay allowed to uncover the residual Class I incompatibilities that remained hidden in standard serotyping. In two matched unrelated pairs with high pretransplant CTLp frequency the severe acute graft-versus-host disease (GVHD) developed after bone marrow transplantation. Examination of other relatives in patients lacking an HLA identical sibling showed the importance of Class I incompatibility for CTLp generation as well. The lack of correlation between CTLp frequency and HLA-D disparity could suggest that Class II antigens do not participate in CTLp induction. With one exception we had good correlation between MLC and DNA analysis of Class II antigens demonstrating that MLC gives interpretable results even in unrelated pairs. Our results demonstrate the significance of CTLp frequency assay in detection of residual Class I incompatibilities in matched unrelated pairs and in assessment of Class I compatibility in related pairs. For that it should be used in the final selection of BMT donors.