INDIRECT ALLORECOGNITION OF MAJOR HISTOCOMPATIBILITY COMPLEX ALLOPEPTIDES IN HUMAN RENAL-TRANSPLANT RECIPIENTS WITH CHRONIC GRAFT DYSFUNCTION

Background, It has been suggested that T cells primed by processed don or major histocompatibility complex antigen (the ''indirect'' pathway of allorecognition) may be responsible for mediating chronic allograft rejection. The purpose of this study was to develop a clinically usef ul assay to study the occurrence of indirect allorecognition during ch ronic rejection in humans. Methods. A panel of 20 mer peptides corresp onding to the hypervariable regions of HLA-DRB10101, DRB1*1501, and D RB10301 were synthesized. Lymphocytes obtained from renal allograft r ecipients were cocultured with these peptides. Proliferation was assay ed by DNA incorporation of [H-3]thymidine, and positive proliferation was defined by a statistically significant increase in counts per minu te over background with a minimum stimulation index of 2, The precurso r frequency of allopeptide reactive T cells was determined by limiting dilution analysis. Results. Lymphocytes from 82% of patients who were mismatched for at least one of the three DR molecules and had chronic allograft dysfunction specifically proliferated to the mismatched all opeptides (n=11), Proliferation was seen in only 6% of control subject s (2/33, P<0.0001). The proliferative response was low grade and was b est detected on day 7-8 of culture in vitro. The precursor frequency o f peptide-specific T cells was more than 10-fold higher compared with controls (P<0.001). Conclusions. These data demonstrate for the first time that T cells of patients with chronic graft dysfunction are prime d to recognize and respond to specific donor-derived major histocompat ibility complex allopeptides. Our results support the hypothesis that T cells primed via the indirect pathway of allorecognition may be impo rtant mediators of chronic rejection and provide the rationale to deve lop specific therapeutic strategies to prevent or interrupt this proce ss.