Circulating donor-specific cytotoxic T lymphocytes with high avidity for donor human leukocyte antigens in pediatric and adult cardiac allograft valved conduit recipients

Objective: Specific immunological responses may be involved in the process of cryopreserved allograft valved conduit (AVC) degeneration, which is more frequently seen in young recipients. Rejection of heart and corneal allogr afts is preceded by an increase in the fraction of cytotoxic T lymphocytes (CTL) with high avidity for donor human leukocyte antigens (HLA) circulatin g in both peripheral blood and the affected graft. These donor-specific hig h-avidity CTLs are regarded as the destructive cells capable of causing gra ft damage. To monitor the precursors of these cells (CTLp) in young and adu lt AVC recipients, in vitro quantitative tests were performed on sequential ly taken blood samples to quantitate CTLp frequencies and their avidity for donor antigens. Method: Six children and nine adults who received a cryopr eserved AVC in the period between 1994 and 1997 were included in the study. From these patients, two to six blood samples were obtained up to 3 years after valve implantation. The number of circulating CTLp present within the peripheral blood mononuclear cell (PBMC) population was determined by limi ting dilution analysis (LDA). The fraction of CTLp with high avidity for do nor HLA class I was determined by addition of CD8 monoclonal antibodies (mA b) during the cytotoxic phase of the assay. Third-party stimulator cells we re used to verify the donor-specificity of the response. Results: The numbe r of donor-specific CTLp increased significantly in the period 6-12 months after AVC implantation, while third-party-specific CTLp frequencies were no t affected. Additionally, we found a significant increase of the high-avidi ty fraction of CTLp directed against donor antigens as early as during the first 6 months after AVC implantation. The fraction of high-avidity CTLp re mained significantly higher post- compared with pre-implantation, even afte r 12 months. We observed no significant difference in the kinetics of CTLp frequencies between pediatric and adult AVC recipients. Conclusion: Implant ation of cryopreserved human AVC induces an increase in the total number of circulating CTLp directed against donor HLA class I in both adults and chi ldren. The shift towards more destructive high-avidity CTLp in the peripher al blood indicates their potential damaging effect towards the heart valve allograft. (C) 2000 Elsevier Science B.V. All rights reserved.