Persistence of donor-specific class II antigens in allografted human heart two years after transplantation

Effect of Cognate Human CD4+ T Cell and Endothelial Cell Interactions Upon Chemokine Production

BACKGROUND

In vitro studies have shown that cognate recognition of antigen presented by endothelial cells (EC) causes T cell activation, proliferation, and cytokine release and alters the transmigration of T cells. Here we have investigated chemokine induction caused by cognate interactions between human CD4+ T cells and MHC class II-expressing EC.

METHODS

HLA-DR-restricted CD4+ T cells were cocultured with HLA-DR-expressing allogeneic Eahy.926, aortic, or heart microvascular EC. Chemokine mRNA expression was measured by RTPCR, and chemokine protein secreted was measured by a cytokine array system and ELISA. Molecules involved in chemokine secretion were identified using blocking monoclonal antibodies, and cellular sources of chemokines determined by intracellular chemokine staining. Coculture supernatants were also used in chemotaxis assays.

RESULTS

Nine different chemokine mRNA and proteins were expressed because of noncognate interactions between T cells and EC. Cognate interactions induced de novo expression of four chemokines and upregulation of seven chemokines. Levels of CCL3, CCL8, and CXCL10 secreted into supernatants were in the nanomolar range and were chemotactic for T cells and monocytes. Blocking antibodies to HLA-DR and LFA-3 abrogated production of CCL3, CCL8, and CXCL10. Blocking antibodies to interferon-gamma and tumor necrosis factor-alpha inhibited CCL8 and CXCL10 but not CCL3 production. CCL3 and CXCL10 were produced by both T cells and EC.

CONCLUSIONS

Cognate interactions between alloreactive CD4+ T cells and MHC class II-expressing EC results in a specific pattern of chemokine production. These chemokines could play important roles in recruitment of leukocytes into vascularised allografts.

The induction of major histocompatibility complex class II expression is sufficient for the direct activation of human CD4+ T cells by porcine vascular endothelial cells

BACKGROUND

The role played by major histocompatibility complex (MHC) class II-positive vascular endothelial cells in organ graft rejection is unknown but potentially very important. Methods. The MHC class II-negative porcine vascular endothelial cell line PIEC was stably transfected with the human class II transactivator CIITA, in order to induce MHC class II expression without the coinduction of T-cell costimulatory ligands. These PIEC cells were compared with interferon gamma-treated PIEC cells for their capacity to stimulate the proliferation of pure human CD4+ T cells. Results. The CIITA-transfected PIECs were as effective as interferon y-treated PIECs for stimulating unprimed human CD4+ T cells, the peak response with the CIITA-transfected cells in fact occurring earlier (day 3 instead of day 5). Monoclonal antibodies to SLA-DR substantially inhibited the CD4+ T-cell responses in both cases. However, whereas the response to interferon gamma-treated PIEC was partially inhibited by CTLA4-Ig, that to CIITA-transfected PIEC was not. Conclusions. The strong stimulation of CD4+ T cells by the specific induction of MHC class II antigens demonstrates that PIEC cells constitutively express functionally effective levels of costimulatory ligands. This finding strengthens the case that vascular endothelial cells are professional antigen-presenting cells and that MHC class II-positive vascular endothelial cells might play a role in the rejection of organ allografts.

Human T cell responses to human and porcine endothelial cells are highly sensitive to cyclosporin A and FK506 in vitro

BACKGROUND

Human T cells proliferate in response to both human umbilical vein endothelial cells (HUVEC) and porcine aortic endothelial cells (PAEC) via the second signals LFA-3/CD2 and B7-2 (CD86), respectively. Previous studies have shown that stimulation of T cells via CD28 or phorbol myristate acetate (PMA) activation is highly resistant to inhibition by cyclosporine A (CsA) and tacrolimus (FK506), as is the response of T cells to phytohemmaglutinin in the presence of endothelial cells. We have investigated the inhibitory effects of CsA and FK506 on the direct response of human CD4+ T cells to HUVEC and PAEC and the effect of adding B7-1 transfectants.

METHODS

T cell proliferation, interleukin-2 release bioassays and a multiple cytokine bioassay employing the TF-1 cell line were used as indicators of T cell responses to HUVEC and PAEC either in the presence or absence of CsA and FK506. In some experiments, B7-1 transfectants were also added.

RESULTS

Proliferative responses and interleukin-2 release were highly sensitive to CsA, the ID50 being significantly less for HUVEC (6.5 ng/ml) than PAEC (15 ng/ml). The ID50 of CsA for the mixed lymphocyte response (MLR) was similar to PAEC (18.6 ng/ml), all these values being significantly less than the T cell activation by phytohemmaglutinin (PHA) (227 ng/ml). Addition of B7-1 transfectants significantly increased interleukin-2 production by T cells/HUVEC and resistance to CsA was greatly increased to an ID50 of > 1000 ng/ml. In contrast, addition of B7-1 transfectants to T cells/PAEC had no effect either on T cell proliferation, IL-2 production, or CsA resistance. Similar results were obtained with FK506. Using the TF-1 cell line, it was determined that cytokines other than IL-2 are released during CD4+ T cell/EC interactions, with similar sensitivity to CsA and FK506.

CONCLUSIONS

It is concluded that both allogeneic and xenogeneic T cell/endothelial responses should be inhibited by therapeutic levels of CsA in vivo, assuming the absence of trans-stimulation by B7 molecules.

Role of endothelial cells in allograft rejection

The immunological properties of endothelial cells suggest they perform a pivotal role in acute and chronic rejection following solid organ transplantation. Their constitutive expression of MHC class II molecules (which initiate allograft rejection by activating CD4 T cells) and accessory molecules allows them to present foreign antigen by both the direct and indirect route to the recipient's immune system. The costimulatory molecules used by endothelial cells appear to differ from those used by traditional antigen-presenting cells such as B cells and dendritic cells. Release of non-HLA antigens from damaged endothelial cells results in a chronic antibody response--possibly contributing to graft vasculopathy and chronic rejection. Further understanding of the factors that regulate MHC class II and accessory molecule expression on endothelial cells could lead to novel strategies of therapeutic intervention.

Reduction of cellular rejection and increase in longer-term survival after heart transplantation after HLA-DR matching

HLA matching in cardiac transplants is perceived as being logistically difficult. We studied 1135 consecutive primary cardiac allografts between 1980 and 1994 to assess the effect of HLA mismatching on long-term graft survival and cellular rejection episodes within 3 months of transplantation. We found a significant association between HLA-DR mismatching and the number of episodes of rejection (no mismatch 0.80 [SE 0.13], one mismatch 1.22 [0.06], two mismatches 1.42 [0.06], p < 0.05). We found a similar correlation between the total number of biopsy specimens showing evidence of cellular rejection and HLA-DR mismatch. The time between operation and the first rejection episode shortened with increasing HLA-DR mismatch (no mismatch 85.5 [37.3] days, one mismatch 43.1 [8.1], two mismatches 24.1 [2.9], p < 0.05). Furthermore, the proportion of patients with no evidence of rejection correlated with HLA-DR incompatibility. A significant association between improved graft survival and HLA-DR mismatching was found over 1, 5, and 10 years after transplantation (no mismatch 1 year 92%, 5 years 83%, 10 years 76%, one mismatch 1 year 81%, 5 years 73%, 10 years 59%, and two mismatches 78% 1 year, 5 years 70%, and 10 years 52%, p = 0.02). Increased efforts to prospectively HLA match patients has resulted in 25% of patients transplanted between January and May 1995 (n = 13/52) receiving grafts matched for HLA-DR. HLA matching reduces the frequency and severity of acute cardiac allograft rejection and improves graft survival for up to 10 years. Our preliminary results suggest that it is possible to use HLA matching prospectively for our selection of recipients.

The activation antigen CD69 is selectively expressed on CD8+ endomyocardium infiltrating T lymphocytes in human rejecting heart allografts

We analyzed the presence of T-cell subsets (CD4/CD8) and the activation markers CD25 and CD69 in the cellular infiltrates of endomyocardium biopsies taken from transplanted human hearts. The results indicate that CD25 was present within specimens mainly infiltrated by CD4+ cells. In contrast, CD69 was found in infiltrated biopsies by CD8+ cells, as determined by single immunofluorescence. Double immunoenzymatic staining was used to investigate the cellular distribution of the activation markers studied in some representative cases. Thus, CD25 was found on both CD4+ and CD8+ cells while CD69 molecule was selectively expressed on CD8+ T-cell subset. These results suggest that CD69 is a surface molecule relevant to the CD8+ cell-mediated graft rejection events of allografted human hearts.

Alloreactive lymphoid infiltrates in human heart transplants. Loss of class II-directed cytotoxicity more than 3 months after transplantation

From 535 endomyocardial biopsies (87 heart transplant recipients) 283 cell cultures could be generated. All cultures tested contained T lymphocytes and in most cases CD4 was the predominant phenotype at any time posttransplant. A significantly higher proportion of CD8-dominated cultures was found among cultures from biopsies without myocytolysis. In the first 3 months post transplant 57% of cultures showed cytotoxicity against both class I and class II mismatched donor major histocompatibility complex (MHC) antigens, changing to an incidence of 33% at greater than 90 days. This proved to be due to a significant decrease in the number of cultures with human leukocyte antigen class II-directed cytotoxicity. This study shows that early after transplantation a heart transplant is infiltrated with activated donor-specific cytotoxic T cells which recognize a broad spectrum of mismatched donor MHC antigens, and that in time this spectrum becomes more restricted.

Identification of antigen presenting cells in normal and transplanted human heart: importance of endothelial cells

The nature of class II-positive cells in normal and transplanted human heart has been investigated using immunoperoxidase and dual-immunofluorescent techniques. In normal heart approximately 83% of DR expression can be accounted for by EN4+ endothelial cells, most of which express intercellular adhesion molecule 1 constitutively. Few cells bearing the leukocyte common antigen are found in normal heart; most of them are RFD7+ macrophages or T cells. There is a paucity of RFD1+ dendritic cells. In transplanted heart showing signs of rejection, the infiltrate consists of RFD7+, RFD1+, RFD7+, RFD1+ cells and T lymphocytes. The increased class II expression within these biopsies is confined to the infiltrating cells. Dual-immunofluorescence demonstrates that nearly all the RFD1+ cells are from the recipient. In conclusion, in normal heart presentation of allogeneic class II is by the intercellular adhesion molecule-1-positive endothelial cells. After transplantation, there is an influx of recipient cells of the macrophage/dendritic series which are probably able to process allogeneic class II.