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

Deciphering the Contribution of γδ T Cells to Outcomes in Transplantation

γδ T cells are a subpopulation of lymphocytes expressing heterodimeric T-cell receptors composed of γ and δ chains. They are morphologically and functionally heterogeneous, innate yet also adaptive in behavior, and exhibit diverse activities spanning immunosurveillance, immunomodulation, and direct cytotoxicity. The specific responses of γδ T cells to allografts are yet to be fully elucidated with evidence of both detrimental and tolerogenic roles in different settings. Here we present an overview of γδ T-cell literature, consider ways in which their functional heterogeneity contributes to the outcomes after transplantation, and reflect on methods to harness their beneficial properties.

Characteristics of Vδ1(+) and Vδ2(+) γδ T cell subsets in acute liver allograft rejection

BACKGROUND

To investigate the characteristics of γδ T cells as well as the Vδ1(+) and Vδ2(+) subsets in the peripheral blood in liver allograft recipients.

METHODS

Sixty-three liver transplant recipients were enrolled in this study: 26 cases with acute allograft rejection (Gr-AR), and 37 cases with stable allograft liver function (Gr-SF). The frequencies of γδ T cells, the Vδ1(+) and Vδ2(+) subsets, and interleukin (IL)-10-producing Vδ1(+) γδ T cells in the peripheral blood were analyzed by flow cytometry. The relationship between liver function parameters and the Vδ1(+)/Vδ2(+) ratio was analyzed.

RESULTS

The frequency of the Vδ1(+) subset and the Vδ1(+)/Vδ2(+) ratio in Gr-SF was significantly higher than that in Gr-AR; in contrast, the frequency of the Vδ2(+) subset in Gr-SF was markedly lower than that in Gr-AR. In addition, there was no significant difference in the frequency of γδ T cells between the Gr-AR and Gr-SF groups. Moreover, there was a significant negative correlation between the Vδ1(+)/Vδ2(+) ratio with the levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) in Gr-AR.

CONCLUSIONS

Vδ1(+) γδ T cells may have a potential role in maintaining stable graft liver function, and Vδ2(+) γδ T cells may be associated with liver allograft rejection. The Vδ1(+)/Vδ2(+) ratio could serve as a prognostic marker for acute rejection after liver transplantation.

FoxP3+ T Cells Can Be Expanded From Rejecting Cardiac Allografts

A specific subset of T cells, the FoxP3+ regulatory T cells, control effector T-cell responses to self and foreign antigens. In transplant patients, we and others have shown that high intragraft FOXP3 mRNA levels are associated with acute rejection, suggesting that immune regulation is dependent on immune activation. To study whether transplanted grafts harbor FoxP3+ T cells and to functionally analyze them, graft infiltrating lymphocytes (GILs) must be propagated from the transplanted tissue. In the present study, we analyzed whether FoxP3+ T cells can be grown from endomyocardial biopsies (EMBs; n = 5) from patients after heart transplantation during acute cellular rejection. After 18 to 21 days of culture, 0.5 to 1.0 x 10(6) GILs were cultured from the EMBs. Of these GILs, 10.6% (median; range, 1.6%-17.1%) stained positive for FoxP3. Thus Foxp3+ T cells can be grown from EMBs, providing the tools to functionally characterize these cells in depth in forthcoming studies.

Calcineurin Inhibitor Withdrawal in Stable Kidney Transplant Patients Decreases the Donor-Specific Cytotoxic T Lymphocyte Precursor Frequency

BACKGROUND

In a prospective study, calcineurin inhibitors (CNI) were withdrawn in patients two years after kidney transplantation. We questioned whether stopping CNI had an effect on the donor-specific reactivity, as CNI might hinder immune responses leading to graft acceptance.

METHODS

We measured the donor-specific cytotoxic T lymphocyte (CTL) precursor frequency (CTLpf) in 54 patients before and after withdrawal of CNI. In addition, the T-cell reactivity of PBMC to donor and third-party antigens was tested in MLR, and in IFNgamma-Elispot. Reactivity to tetanus toxoid (TET) was studied as well.

RESULTS

Donor-specific CTLpf significantly decreased after CNI withdrawal (P=0.0001). In contrast, no difference was observed in third-party reactive CTLpf, donor and third-party reactive MLR and IFNgamma-Elispot. Proliferative responses and the number of IFNgamma-producing cells to TET also decreased after CNI withdrawal. The decrease in CTLpf correlated with the time between the two blood samples (before and after stopping CNI, P=0.05). This decrease was caused by stopping CNI, because there was no correlation between CTLpf and the duration of the CNI treatment after transplantation. Moreover, the percentage of regulatory T cells in the peripheral blood increased after CNI withdrawal.

CONCLUSIONS

We report here that after withdrawal of CNI the donor-specific CTLpf decreases. We hypothesize that CNI suppress regulatory mechanisms that have the potential to down-regulate donor-specific CTL responses and reactivity to TET.

Analyses of peripheral blood mononuclear cells in operational tolerance after pediatric living donor liver transplantation

Operational tolerance (graft acceptance in an immunosuppression (IS)-free environment) after living-donor liver transplantation (LDLT) could occur by our elective protocol in some patients. There is, nevertheless, no reliable parameter to monitor patients who may discontinue IS without a risk of rejection. To identify such parameters, we systemically phenotyped peripheral blood mononuclear cells from operationally tolerant patients. An increase was observed in the frequency of CD4+CD25high+ cells, B cells and Vdelta1/Vdelta2 gammadeltaT-cells ratio in operationally tolerant patients (Gr-tol; n = 12), compared with those from age-matched volunteers (Gr-vol; n = 24) or patients on IS (Gr-IS; n = 19). The frequency of NK cells was decreased in Gr-tol, compared with those in Gr-IS or Gr-vol. The frequency of NKT cells was decreased after LDLT, compared with that in Gr-vol. Although the contribution of those subsets to the tolerant state remains elusive, the results may provide important clues for reliable indicators of tolerance after LDLT.

Phenotype of endomyocardial biopsy-derived T-lymphocyte cultures and chronic rejection after heart transplantation

Chronic rejection (CR) is a major problem in long-term survival in heart transplantation. We analysed whether the occurrence of CR correlates with the incidence of acute rejections (AR) or with characteristics of endomyocardial biopsy-derived cell cultures. CR was diagnosed by annual angiography and defined as all coronary vascular changes. One year after transplantation 24 of the 63 patients had CR (38%). The incidence of AR in CR+ and CR- patients was comparable. The patients in both groups had similar individual median percentages of EMB-yielding cell cultures. During the first year the CR- patients had more cultures in which at least 60% of the cells were CD4+ T cells (50% vs 37%, P = 0.05), due to a stronger CD4 predominance in the first 6 months. In the second year the CD4 predominance in the patients diagnosed as CR+ after 1 year tended to be higher (P = 0.08). The patients had comparable percentages of cultures predominated by CD8+ T cells, gammadelta T cells or NK cells, irrespective of the time interval. These results might indicate that CD4+ T lymphocytes play a dual role in the aetiology of CR.

Monitoring of cardiac graft recipients: comparison of in vivo activated, committed T lymphocytes in peripheral blood and in the graft

The proliferative and cytotoxic capacity of peripheral blood lymphocytes (PBL) and the cytotoxic activity of lymphocytes propagated from endomyocardial biopsies (EMB) towards donor cells was used to identify in vivo activated, committed T cells. A series of 39 PBL samples and 38 EMB simultaneously taken from 20 patients after heart transplantation was cultured in interleukin 2 (IL-2) conditioned medium. The cytotoxic capacity of these cultures against donor cells was tested in a 4-h chromium-51 release assay. From a comparable patient group, 224 samples were evaluated for donor reactivity by a primed lymphocyte test (PLT). Analysis showed that PBL cultures hardly ever contained committed cytotoxic T lymphocytes (cCTL, 2/39) or committed proliferative T lymphocytes (cPTL, 1/224). In contrast, significantly more EMB cultures (17/38, P < 0.001, chi2 test) demonstrated donor-directed cytotoxicity. This was especially found during rejection (11/17 vs 6/21 without rejection, P = 0.05). These results show that after heart transplantation, committed cells are mainly found in the graft.

Long-term survival of heart grafts in the presence of donor-specific cytotoxic T-cell precursors (CTLp) in the peripheral blood

To monitor their immunological status we determined donor and third-party-specific cytotoxic T-cell precursor frequencies (CTLpf) in the peripheral blood of 15 heart transplant recipients. PBL samples were obtained at different time points before and after transplantation. Donor-specific CTLpf and third-party-specific CTLpf were within the same range for all samples (1-1489/10(6) cells). The donor-specific CTLpf were not different between patients who had never had an acute rejection (AR) and patients who had an acute rejection as diagnosed by endomyocardial biopsy (EMB). No difference was observed between donor-specific CTLpf of samples taken on the day of transplantation and those obtained between 3 months and 3 years after transplantation. There was also no relationship between the donor-specific CTLpf in the PBL and the culturing success of lymphocytes from EMB taken at the same time. CTLpf were in the same range both when cultures could be propagated from the graft and when no cells grew out. We conclude that long-term graft survival is possible in the presence of CTLpf in peripheral blood.

Discrepancy between mRNA expression and production of IL-2 and IL-4 by cultured graft infiltrating cells propagated from endomyocardial biopsies

We studied whether acute rejection correlated with the cytokine production pattern and mRNA expression of interleukin-2 (IL-2) and interleukin-4 (IL-4) in lymphocyte cultures derived from endomyocardial biopsies (EMB) that were stimulated with B cell lines of donor origin. Unstimulated biopsy cultures neither expressed mRNA nor produced IL-2 or IL-4. All stimulated biopsy cultures contained mRNA transcripts for IL-2 and IL-4. In contrast, we found different IL-2 and IL-4 production patterns. Within the first 90 days after heart transplantation (HTx), higher levels of IL-4 were measured in cultures derived from EMB with myocytolysis than in cultures from EMB without signs of myocytolysis. More than 90 days after HTx, this phenomenon was reversed and more IL-4 was produced in cultures derived from EMB without myocytolysis. These differences were not detected for IL-2 production.

The frequency and avidity of committed cytotoxic T lymphocytes (cCTL) for donor HLA class I and class II antigens and their relation with graft vascular disease

Cellular immune processes may trigger the development of graft vascular disease (GVD). CD4 and CD8 cytotoxic T lymphocytes that infiltrate the allograft could play a role in the development of GVD. We studied the presence of in vivo primed or committed CTL (cCTL) and their avidity for donor HLA class I and class II antigens in graft-infiltrating lymphocyte cultures propagated from endomyocardial biopsies derived from patients with and without signs of GVD. The fraction of cCTL with high avidity for HLA class I or class II antigens was estimated by the addition of anti-CD8 or anti-CD4 MoAbs to the cytotoxic phase of the limiting dilution analysis. In the first year after transplantation no difference in the frequency of donor-specific class I cCTL between patients with and without GVD was found. Addition of anti-CD8 MoAb revealed that most cultures predominantly consisted of cCTL with low avidity for donor HLA class I antigens, irrespective of the development of GVD at 1 year after transplantation. However, in patients who did not develop GVD, the frequency of cCTL with donor HLA class II specificity was significantly higher than in patients who did develop GVD. The avidity for donor HLA class II antigens was comparable in both groups. A high frequency of donor-specific cCTL for HLA class II antigens seems to be a protective factor against the development of GVD. These cCTL might be cytotoxic for cells involved in GVD development, e.g. activated endothelium and smooth muscle cells of donor origin.

Kinetics of IL-2 and IL-4 mRNA and protein production by graft-infiltrating lymphocytes responsible for rejection after clinical heart transplantation

During cardiac rejection we studied the kinetics of IL-2 and IL-4 mRNA and subsequent protein production by in vivo primed graft-infiltrating lymphocytes (GIL), using semiquantitative RT-PCR and ELISA. Following in vitro stimulation with either donor or third-party antigens, mRNA expression of IL-2 and IL-4 were already detectable 1-2 h after stimulation, while their protein production could be measured from 4 h onwards at least until 48 h. At both the mRNA and protein level, we measured a donor-specific signal for IL-2 and for IL-4 production (p = 0.02), while the relative donor-specific IL-2 mRNA level was significantly higher than the relative IL-4 mRNA level (p = 0.002). These observations suggest that after in vitro challenge with donor antigens, GIL obtained from rejecting cardiac allografts predominantly produce IL-2 mRNA and protein.

Apoptosis of mononuclear cell infiltrates in cardiac allograft biopsy specimens questions studies of biopsy-cultured cells

During acute rejection, CD4 and CD8 T cells infiltrate the myocardium and cause myocyte death and dropout. CD4 and CD8 cells use a number of cytotoxic mechanisms, including fas-fas ligand interactions, which lead to apoptotic death. Since fas is expressed on myocytes, we investigated endomyocardial biopsy specimens from cardiac transplant patients to determine whether apoptosis is one of the mechanisms of cell death in acute rejection. Serial sections of individual endomyocardial biopsy specimens from patients histologically diagnosed as having grade 3A rejection (n=22 biopsy specimens), biopsy specimens showing a typical "Quilty effect" (n=10), and specimens with concurrent grade 3A rejection and the Quilty effect (n=6) were evaluated using the C-terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) technique for frequency of apoptosis in myocytes and mononuclear cell infiltrates. None of the examined sections showed detectable evidence of apoptotic myocytes, even within regions clearly showing myocyte damage. Of interest was our consistent finding that 85-98% of mononuclear cell infiltrates within biopsy specimens scored as having grade 3A rejection had undergone apoptosis. In marked contrast, 9 of the 10 specimens with Quilty lesions showed <5% apoptotic mononuclear cells in the endomyocardial infiltrates. Of further interest was our finding of 85-98% apoptotic mononuclear cell infiltrates within Quilty lesions associated with biopsy specimens scored as having grade 3A rejection. The frequency of apoptotic cells determined by the TUNEL technique was confirmed by histological examination of the morphology of the cells and with a technique that involves detection of c-jun. These results prompt a note of caution in the interpretation of data on the phenotype, cytokine profile, Vbeta T cell receptor repertoire, and donor specificity of mononuclear cells cultured and propagated from such cardiac biopsy specimens. The possible reasons for apoptosis of graft-infiltrating mononuclear cells are discussed.

Progressive accumulation of CTL with high avidity for donor antigens during the development of acute cardiac rejection

To study the importance of cytotoxic T lymphocytes (CTL) with high avidity for donor antigens (Ag) in the development of acute cardiac allograft rejection, their appearance within the graft in relation to rejection was analyzed. For this study, donor directed CTL propagated from sequentially taken endomyocardial biopsies (EMB) were enumerated by limiting dilution analysis (LDA). Subsequentially, the fraction of these CTL having high avidity for donor Ag was determined by addition of a CD8 monoclonal antibody (mAb) to the cytotoxic phase of the LDA. Analysis of 37 EMB cultures obtained from 11 heart transplant (HTx) patients before, during, or after they experienced rejection, revealed the kinetics of donor specific CTL in relation to rejection for HTx patients in general. For 5 individual recipients, a more detailed analysis was performed. The kinetics found for individual patients confirmed the pattern found for the total group of HTx recipients tested. Frequencies of donor specific precursor CTL (pCTL) as well as of in vivo primed donor reactive CTL (committed CTL or cCTL) increased towards rejection and decreased after successful rejection therapy. More than 2 weeks before rejection was diagnosed, only a small fraction of the graft infiltrating donor specific pCTL and cCTL had high avidity for donor Ag (median = 35% and 11%, respectively). Within 2 weeks preceding rejection, this fraction increased gradually (median = 52% and 55%, respectively) and became dominant during rejection (median = 87% and 78%, respectively). After successful rejection therapy, a decrease to basal levels (median = 18% and 24%, respectively) was observed. Conclusively, intragraft accumulation of high avidity, donor specific pCTL and cCTL may cause transplant rejection.

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.

Phenotypic analysis of lymphocytes infiltrating human cardiac allografts during acute rejection and the development of graft vascular disease

Acute rejection (AR) and graft vascular disease (GDV) are processes mediated, at least in part, by cellular processes. Therefore, we cultured graft-infiltrating lymphocytes (GIL) from endomyocardial biopsies (EMB) taken during the first year after transplantation, determined their phenotypic composition, and correlated it to AR and GVD. We observed more often GIL growth from EMB with AR than from non-rejection EMB (P = 0.02), but no difference was found between patients with and without GVD 1 year after transplantation. CD4+ cells were always more numerous than CD8+ cells, and no difference in phenotypic composition was found between AR and non-rejection EMB nor between EMB derived from patients with or without signs of GVD. In conclusion, AR is correlated with cell growth of EMB, but the development of GVD is not associated with AR, GIL growth from EMB, or their phenotypic composition.

Rejection of cartilage formed by transplanted allogeneic chondrocytes: evaluation with monoclonal antibodies

Cellular infiltrates participating in rejection of cartilage formed by transplanted allogeneic rat epiphyseal chondrocytes were evaluated immunohistochemically using a panel of different monoclonal antibodies. One week after transplantation, the grafts were surrounded by numerous class II MHC+ (OX6+, OX17+), CD4+ (W3/25+), and W3/13+ cells as well as some ED1+ monocytes/macrophages. Only a few T (OX19+) and B (HIS14+) cells were present. The number of class II MHC+ cells and ED1+ monocytes/macrophages did not change significantly in the course of rejection whereas the number of CD4+ and W3/13+ cells gradually decreased. On the other hand, there was a significant increase in the number of CD8+ (OX8+) cells. CD8+ cells accumulated close to the transplants and some of them penetrated cartilage matrix suggesting that they might be involved in chondrocyte killing. After 3 months, cartilage was almost completely destroyed and the intensity of infiltrations was markedly decreased. Fibrous connective tissue predominated, however, some class II+ as well as few ED1+, CD4+ and CD8+ cells were still present adjacent to the cartilage remnants. At the time of transplantation, chondrocytes were endowed with RT1.D class II antigen (OX17+), but they did not react with OX6 mAb (monoclonal antibody) recognizing the RT1.B class II molecule. However, after 1 week, some chondrocytes reacted with OX6 mAb and the number of RT1.B positive chondrocytes increased in the course of cartilage rejection.

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.

Characteristics of graft-infiltrating lymphocytes after human heart transplantation. HLA mismatches and the cellular immune response within the transplanted heart

The influence of HLA mismatches between donor and recipient on the phenotypes, function, and specificity of T-lymphocyte cultures derived from endomyocardial biopsies was studied in 118 heart transplant recipients. In case of HLA-DR mismatches, the majority of the EMB-derived cultures were dominated by CD4+ T cells while, in patients with HLA-A and -B mismatches but without DR mismatches, CD8+ T cells comprised the predominant T-cell subset. Cytotoxicity against donor antigens was observed in 75% of the cultures. A significantly (p < 0.005) lower proportion of the cultures showed cytotoxicity against HLA-A antigens (36%) when compared with HLA-B (53%) or HLA-DR (49%). An HLA-A2 mismatch elicited a cytotoxic response that was comparable to that found against HLA-B and -DR antigens: 62% of the cultures from HLA-A2 mismatched donor-recipient combinations was reactive against A2. A higher number of A, B, or DR mismatches resulted in a higher number of cytotoxic cultures directed against these antigens. A higher number of HLA-B and -DR mismatches was associated with a lower freedom from rejection. Our data indicate that, despite the use of adequate immunosuppressive therapy, the degree of HLA matching plays a crucial role in the immune response against a transplanted heart, resulting in a significant effect on freedom from rejection.

Prophylactic therapy with OKT3 does not affect donor specific reactivity of peripheral blood lymphocytes from heart transplant recipients

To avoid the nephrotoxic effect of high-dose cyclosporin A (CsA) immediately posttransplant, heart transplant recipients received as prophylactic therapy intravenous OKT3 for seven days instead of intravenous CsA. Patients receiving OKT3 were compared with patients receiving CsA with respect to specific proliferation and cytotoxicity of their peripheral blood mononuclear cells (PMNC) against donor antigens, at different times within three months post-transplant. No effect of the initial immunosuppressive therapy was observed on these parameters. Acute rejection did not induce a consistent effect on the relative proliferation. PMNC from patients who experienced one or more rejection episodes showed a decrease in donor specific relative proliferative response in time after transplantation, while nonrejectors did not or only slightly, independent of the initial immunosuppressive protocol. Within the group of patients not receiving OKT3, this effect of rejection reached significance. In conclusion, no effect of prophylactic OKT3 therapy compared with prophylactic CsA therapy was observed on donor reactivity of PMNC in vitro during the subsequent three to four months post-transplant.

Cytomegalovirus infection and allospecific cytotoxic activity of graft-infiltrating cells after heart transplantation

We have investigated whether cytomegalovirus (CMV) infection has an effect on donor directed cytotoxicity of graft-infiltrating cells in human heart transplants. Our study group consisted of 89 heart transplant recipients. Thirty-eight (43%) showed signs of CMV infection; in 28 of them, cytolytic activity of biopsy derived cultures could be tested during the infection. Eight patients had a primary and 20 a secondary infection. We found that during CMV infection, both primary and secondary, a significantly higher proportion of the biopsy-derived cultures showed cytotoxicity against donor HLA antigens (chi 2 test; P < 0.01 in comparison with 51 patients without infection). This was most evident in patients with both infection and acute rejection episodes when compared to patients with only one of these complications. This suggests that one process amplifies the other with regard to the up-regulation of alloreactivity within the transplanted heart. In secondary infections, only an increase of donor class I-directed cytotoxicity was found, while in primary infections cytotoxicity against donor class I and II antigens was increased (P < 0.005 vs. secondary infection).

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

The in vitro cytotoxic reactivity of allograft infiltrating cells cultured from endomyocardial biopsies was tested against endothelial cells (EC) isolated from the own donor heart. EC derived from pieces of atrium were found to be proper targets for graft infiltrating cytotoxic T cells from four patients. The specificity of this cytotoxicity was further analysed by cold target inhibition studies and blocking with anti-CD3, anti-CD4 or anti-CD8 monoclonal antibodies. The experiments revealed that, besides a clearly HLA directed recognition, a more heterogeneous, multispecific response can be found, which might be partially explained by the activity of EC specific T cell clones. We conclude that this system provides a valuable approach to investigate the reactivity of graft infiltrating cells against EC in relation to the clinical course of the transplantation.

Acute rejection in heart transplant patients is associated with the presence of committed donor-specific cytotoxic lymphocytes in the graft but not in the blood

In vivo-activated, committed donor-specific cytotoxic lymphocytes (cCTL) can be propagated and expanded from endomyocardial biopsies (EMB) in IL-2-enriched medium especially during an acute rejection episode. We report here our efforts to detect these cCTL by the same technique in peripheral blood at the moment of rejection and when no rejection was diagnosed. During or just before rejection, significantly less frequent (P less than 0.01) donor reactive cCTL were found in PBL samples (two out of 20) than in the simultaneously taken EMB samples (13 out of 19). Donor B-LCL and/or third-party B-LCL were lysed by 15 PBL samples. Inhibition studies revealed that this lysis was due to LAK-like cytotoxicity. The results show that peripheral blood does not reflect intra-graft events, which is probably the reason for the irreproducible results of diagnosis of rejection by monitoring immunological parameters in the peripheral blood.

Lysis of heart endothelial cells from donor origin by cardiac graft infiltrating cells

Endothelial cells may be involved in the acute rejection of allografts. In the present study, graft infiltrating lymphoid cell lines were propagated from a heart graft at the time of histological diagnosis of rejection. The cell lines containing CD8+ cells lysed donor-derived BLCL and endothelial cells (EC) but not third party BLCL or random EC, suggesting that HLA antigens were recognized. The cell lines containing CD4+ cells only did not lyse any target cells. The lysis of EC without preincubation with gamma interferon (gIFN) indicated that the HLA antigens recognized were class I antigens. These results suggested that lysis of donor EC may be one of the mechanisms involved in rejection.

The influence of HLA-mismatches on phenotypic and functional characteristics of graft infiltrating lymphocytes after heart transplantation

We studied the influence of HLA mismatches on T lymphocyte cultures that were derived from endomyocardial biopsies (EMB) from 118 heart transplant recipients. From patients with DR mismatches, the majority of the EMB-derived cultures were dominated by CD4, while in patients without DR mismatches, CD8 was the predominant T cell subset. The majority (75%) of the cultures were cytotoxic against donor antigens. A significantly (P < 0.005) lower proportion of the cultures showed cytotoxicity (36%) against HLA-A antigens when compared to HLA-B (53%) or HLA-DR (49%). A dose effect phenomenon was detected for all HLA antigens, including HLA-A: a higher number of A, B or DR mismatches resulted in a higher number of cytotoxic cultures directed against these antigens. B and DR matching had the greatest influence on 6 month freedom from rejection. Both our experimental and clinical data indicated that HLA matching played a role in the immune response against a transplanted heart.

Donor directed cytotoxicity of cardiac graft infiltrating cells during cytomegalovirus infection

We investigated whether cytomegalovirus (CMV) infection had an effect on donor directed cytotoxicity of cardiac graft infiltrating cells. The group we studied comprised 89 heart transplant recipients. Thirty eight showed signs of CMV infection, and in 27 of them cytolytic activity of biopsy-derived cultures could be tested during the infection. Fifty-one patients had never had CMV infection, and they were used as the control group. Eight patients had a primary, and 19 a secondary infection. We found that during CMV infection, both primary and secondary, a significantly higher proportion of the biopsy-derived cultures showed cytotoxicity against donor antigens (P < 0.01 when compared to the control group). In secondary infections, this was only due to an increase in donor class I directed cytotoxicity, while in primary infections a significant increase of class II directed cytotoxicity was also found (P < 0.005 when compared to secondary infection).