Donor heart endothelial cells as targets for graft infiltrating lymphocytes after clinical cardiac transplantation

Immune-mediated vascular injury and dysfunction in transplant arteriosclerosis

Solid organ transplantation is the only treatment for end-stage organ failure but this life-saving procedure is limited by immune-mediated rejection of most grafts. Blood vessels within transplanted organs are targeted by the immune system and the resultant vascular damage is a main contributor to acute and chronic graft failure. The vasculature is a unique tissue with specific immunological properties. This review discusses the interactions of the immune system with blood vessels in transplanted organs and how these interactions lead to the development of transplant arteriosclerosis, a leading cause of heart transplant failure.

Alloreactivity of virus-specific T cells: possible implication of graft-versus-host disease and graft-versus-leukemia effects

Immune reconstitution of functional virus-specific T cells after allogeneic hematopoietic stem cell transplantation (HSCT) has been intensively investigated. However, the possible role of crossreactivity of these virus-specific T cells against allogeneic targets is still unclear. Theoretically, as in the field of organ transplantation, virus-specific T cells possess crossreactivity potential after allogeneic HSCT. Such crossreactivity is assumed to play a role in graft-versus-host disease and graft-versus-leukemia effects. In this article, we aim to give a comprehensive overview of current understanding about crossreactivity of virus-specific T cells.

Antibodies eluted from acutely rejected renal allografts bind to and activate human endothelial cells

This study was designed to investigate how antiendothelial antibodies (EAbs) are involved in acute irreversible renal graft rejection. Eluates from 25 renal allografts, lost by irreversible rejection (n = 22) and by renal vein thrombosis (controls n = 3), were tested against a panel of cultured human umbilical vein endothelial cells (HUVEC). All patients were under immunosuppression at the time of nephrectomy. EAbs binding and membrane expression of adhesion molecules ELAM-1 and VCAM-1 were analyzed by flow cytometry (FACS) and by semiquantitative RT-PCR for mRNAs coding for those molecules. The absence of anti-HLA antibodies against the donor was ascertained at transplant, and before and after nephrectomy by the negativity of specific crossmatches performed using the most sensitive techniques. EAbs eluted from eight rejected kidneys bound to HUVEC. They did not induce any cytotoxicity, but their incubation with HUVEC (4 h at 37 degrees C; 2.5 mg/ml) led to upregulation of mRNAs coding for VCAM-1 (35- to 60-fold increases) and ICAM-1 (8- to 12-fold increases) as compared with control EAbs. Membrane expression of adhesion molecules was also strikingly increased, with 80% of the cells expressing VCAM-1 and 65% expressing ELAM-1 upon incubation. EAbs were detected in eight out of nine (88.8%) eluates from kidneys lost from acute vascular rejection, but in none of the 13 (0.0%) kidneys lost from other types of rejection (p < 0.0001). We conclude that EAbs, capable of activating human endothelial cells, can be recovered from acutely rejected kidneys and may play a direct role in the pathogenesis of acute rejection.

Human heart endothelial-cell-restricted allorecognition

We studied the reactivity of cardiac graft-infiltrating cells, cultured from endomyocardial biopsy specimens, toward heart endothelial cells (Hec). In two cases, Hec derived from the specific donor heart or Hec compatible with the donor were lysed, but not the syngeneic B cell line. A vessel-derived endothelial cell line was not lysed. Panel studies suggest that the epitopes recognized are, in one case, a Hec-specific peptide presented in the context of HLA-Bw41 and, in the other case, a Hec-specific peptide presented by a subtype of HLA-B44. In conclusion, we showed that cardiac graft-infiltrating cells cultured from endomyocardial biopsy specimens can exhibit cytotoxic reactivity specifically directed against HLA-peptide complexes on Hec.

Donor-specific cellular immune response against human cardiac valve allografts

We studied the presence of donor-specific T lymphocytes in explanted human cardiac valve allografts in vivo. From five of seven explants we propagated lymphocyte cultures in an interleukin-2 conditioned medium. Phenotyping revealed the presence of T-cell receptors in more than 95% of the lymphocytes obtained in each culture. Donor-specific cytotoxicity was demonstrated in three patients with known HLA status of the donor. Cytotoxicity was directed against only HLA class I in one patient, and against class I and/or class II in the others. These results indicate that donor-specific cellular reactivity can be induced by transplantation of human cardiac valve allografts.

Stimulation of immune-competent cells in vitro by human cardiac valve-derived endothelial cells

Both fresh and cryopreserved human cardiac valve allografts are transplanted without matching donor and recipient for blood group or human leukocyte antigens (HLA) and without the usual immunosuppressive therapy that follows organ transplantation. Calcification occurs in almost all transplanted valves, and in children acute valve failure is frequently seen. We hypothesized that failure of the human valve allografts could have an immunologic basis. This hypothesis was tested in a functional way by performing lymphocyte stimulation assays using fresh and cryopreserved valve pieces and endothelial cells derived from valve leaflets as stimulator. Human peripheral blood lymphocytes, both matched and mismatched for HLA antigens, were used as responder cells. The results were expressed as the stimulation index. Fresh valve pieces induced a significantly higher stimulation index (median, 9; range, 4 to 117) compared with the cryopreserved pieces (median, 2; range, 0 to 9; p = 0.002 by Wilcoxon test). The stimulation index was significantly reduced when lymphocytes matched for HLA-DR with the valve pieces were used (median, 1; range, 0 to 5) as compared with the HLA-DR-mismatched combination (median, 4; range, 2 to 117; p = 0.006, Wilcoxon test). Valve leaflet-derived endothelial cells were able to induce a median stimulation index of 8 (range, 3 to 15) when incubated with lymphocytes mismatched for HLA-A, -B, and -DR. In conclusion, stimulation of immune-competent cells in vitro is induced by both fresh and cryopreserved human valve pieces and by endothelial cells derived from fresh valve leaflets. The immune response can be reduced by using cryopreserved valves or by matching valve donor and responder lymphocytes for HLA-DR.(ABSTRACT TRUNCATED AT 250 WORDS)

The development of transplant coronary artery disease after cardiac transplantation is correlated with a predominance of CD8+ T lymphocytes in endomyocardial biopsy derived T cell cultures

Long-term survival of heart transplant recipients is limited by the development of transplant coronary artery disease (TCAD). We analysed whether the development of TCAD is correlated with the incidence of acute rejection episodes, with the formation of anti-HLA antibodies or with the composition and function of T lymphocyte cultures derived from endomyocardial biopsies. TCAD was assessed by visual analysis of annually performed coronary angiograms and defined as the presence of all vascular changes, including minor wall irregularities. One year after transplantation, 31 of the 77 patients studied had TCAD (40%). The median age and mean number of HLA mismatches in patients with or without TCAD were highly comparable. The patient groups did not differ in incidence of acute rejection episodes, nor in percentage of endomyocardial biopsies yielding T cell cultures. At 1 year after transplantation, lymphocyte cultures from 18/31 TCAD+ patients (58%) and 27/46 TCAD- patients (57%) were analysed. The TCAD+ patients had, compared with the TCAD- patients, a higher median percentage of CD8+ T cells (71% versus 25%, P = 0.06) and a lower median percentage of CD4+ T cells (4% versus 40%, P = 0.04). Similar differences were found in a longitudinal analysis of the culture results of endomyocardial biopsies (EMBs) obtained during the first year. The cytotoxic reactivity of the cultures against donor HLA class I or class II antigens was comparable in the two groups, although a difference in recognition of heart specific antigens remains possible. The fact that EMB-derived cultures from TCAD+ and TCAD- patients differed in T cell phenotype populations gives some support to the hypothesis that cellular immunological processes are involved in the development of TCAD. However, while the median values differed, the overlap of the percentages of CD8+ cells in cultures from TCAD- and TCAD+ patients shows that other factors besides CD8+ T cells also play a role.