Role of CD8+ lymphocytes in chronic rejection of transplanted hearts

Background: The contribution of CD8(+) lymphocytes to the pathogenesis of cardiac allograft vasculopathy, or chronic rejection in heart transplants, remains undefined. We used both major histocompatibility complex class I mismatched and major histocompatibility complex class II mismatched models of cardiac allograft vasculopathy to characterize the role of CD8(+) lymphocytes in the development of cardiac allograft vasculopathy. Methods: Donor hearts from B10.A mice were transplanted into B10.BR recipients (major histocompatibility complex class I mismatched). Donor hearts were harvested at 1, 7, 14, and 30 days after transplantation and (1) quantitated morphometrically for lesion development, (2.) stained immunohistochemically, or (3) digested for isolation of graft-infiltrating cells. The cytotoxic phenotype of graft-infiltrating CD8(+) lymphocytes was determined with flow cytometry. Intracellular cytokine staining of CD8(+) and CD4(+) lymphocytes for interleukin 2, interferon gamma, interleukin 4, and interleukin 10 was performed with 2-color flow cytometry. Finally, B6.C-H2(bm12) donor hearts were transplanted into either C57BL/6 wild-type (major histocompatibility complex class II mismatched) or CD8 -/- knockout recipients and examined for the development of cardiac allograft vasculopathy. Results: In the major histocompatibility complex class I mismatched model, CD8(+) lymphocytes were the predominant T-lymphocyte subset that infiltrated the allografts and demonstrated markers of activation. The intracellular cytokine-staining assay demonstrated that CD8(+) lymphocytes were the primary sources of allograft interleukin 2 and interferon gamma. Intimal lesions developed in the allografts by day 14 (12.0% +/- 4.0%) and further increased by day 30 (44.0% +/- 5.0%). In the major histocompatibility complex class II mismatched model, the donor hearts in the CD8 -/- knockout recipients had substantially less severe intimal lesions when compared with the donor hearts in wild-type recipients (19.0% +/- 6.0% vs 50.0% +/- 7.0%, respectively; P < .05). Conclusions: In both major histocompatibility complex class I and II mismatched models, CD8(+) lymphocytes contribute significantly to chronic rejection. The findings of this study suggest that control of chronic rejection requires interventions directed at CD8(+) lymphocytes.