Background

It has been suggested that T cells primed by processed donor 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 useful assay to study the occurrence of indirect allorecognition during chronic rejection in humans.

Methods

A panel of 20 mer peptides corresponding to the hypervariable regions of HLA-DRB1* 0101, DRB1* 1501, and DRB1* 0301 were synthesized. Lymphocytes obtained from renal allograft recipients were cocultured with these peptides. Proliferation was assayed by DNA incorporation of [3 H] thymidine, and positive proliferation was defined by a statistically significant increase in counts per minute over background with a minimum stimulation index of 2. The precursor 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 allopeptides (n= 11). Proliferation was seen in only 6% of control subjects (2/33, P< 0.0001). The proliferative response was low grade and was best detected on day 7-8 of culture in vitro. The precursor frequency of 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 primed to recognize and respond to specific donor-derived major histocompatibility complex allopeptides. Our results support the hypothesis that T cells primed via the indirect pathway of allorecognition may be important mediators of chronic rejection and provide the rationale to develop specific therapeutic strategies to prevent or interrupt this process.