Noninvasive monitoring of human cardiac allograft rejection

Is cytoimmunological monitoring a safe follow-up method for heart transplantation patients?

THE AIM OF THE STUDY

The aim of the study is to show the effects of cytoimmunological monitoring and its role in the patient's follow-up period after heart transplantation.

MATERIAL AND METHODS

Between 2002 and 2009, 8 patients underwent heart transplantation at Gulhane Military Medical Academy Hospital. Seven patients were male. The average age was 43 ± 12 years. Donor hearts were implanted orthotopically in all patients. The patients were then subjected to cytoimmunological monitoring and endomyocardial biopsy. 431 laboratory blood tests were carried out for all patients to analyze their cytoimmunological profiles and diagnose a possible infection or rejection.

RESULTS

The total and average follow-up periods were 17.5 patient years and 30 ± 36 months (1-120 months), respectively. The first patient had two rejection episodes in 3 months. A viral infection was diagnosed in the third patient, who had painful muscle spasms in both lower limbs and the CD4/CD8 ratio was below 0.4. In the fourth patient, the CD4/CD8 ratio suddenly increased and a urinary infection was diagnosed. Only one patient passed away in the early period (less than 30 days). Four patients died because of an infection or hemodynamic deterioration within three months.

CONCLUSIONS

Cytoimmunological monitoring is a simple and effective technique of evaluating the patient's immunological profile. It may provide an adjunctive laboratory test and may decrease the number of endomyocardial biopsies.

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.

Immunologic monitoring

The development of reliable in vitro assays that could allow the quantitation and characterization of anti-donor alloimmune responses has always been a goal in clinical transplantation, both to predict presensitization to the transplanted tissue and to be able to identify rejection without resorting to more invasive tests. With recent development in our understanding of transplantation biology and therapeutics, there is a real expectation that these tests may be used to identify tolerance as much as to predict rejection. The traditional limiting dilution assays still have a contribution to make and are being complemented by an array of tools, such as ELISpot, flow cytometry-based techniques, and microarray analysis. The assays that have been informative, to date, are discussed in this review. This information will lead, at least, to a better understanding of how and when the rejection process occurs. More interestingly, the objective is to apply this information to evaluate tolerance-inducing strategies or to identify patients that have become tolerant to their graft and can be weaned of immunosuppression. Of course sensitive, accurate and specific immunologic monitoring has applications well beyond the field of transplantation.

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.

T helper frequencies in peripheral blood reflect donor-directed reactivity in the graft after clinical heart transplantation

We describe the usefulness of a fast (48-h) limiting dilution assay (LDA) for the enumeration of human alloreactive helper T lymphocytes (HTL) in the peripheral blood, in relation to histologically defined rejection grades after heart transplantation. HTL frequencies (HTLf) in pretransplant samples varied from patient to patient, ranging from 106 to 625 HTL/106 peripheral blood mononuclear cells (PBMC). In the first week after heart transplantation (HTx), when immunosuppression was instituted, HTLf were significant lower (range 30-190 HTL/106). The level of HTL in the first week after HTx when rejection grade was 0 or 1A (ISHLT score) was considered to be the baseline frequency. This frequency did not correlate with the number of subsequent rejection episodes. During rejection (grade 3), donor-specific HTLf were increased above their baseline frequencies (P = 0.01). Expressed as percentage of baseline frequencies, HTLf increased significantly during acute rejection (AR) compared with 1-2 weeks before rejection (P = 0.003). The increase was specific, since viral infections did not result in a rise of donor-specific HTL, while also HTLf specific for third party HLA antigens were not elevated during rejection. Monitoring HTLf in peripheral blood with a shortened (48-h) assay may serve as a non-invasive method for detecting intragraft immunological reactivity. Demonstrating absence of donor-specific reactivity may limit the number of invasive endomyocardial biopsy (EMB) procedures and allow tapering of immunosuppressive treatment.

Kinetics of circulating cytotoxic T lymphocyte precursors that have a high avidity for donor antigens: correlation with the rejection status of the human cardiac allograft

Studies on graft infiltrating cells demonstrated that accumulation of cytotoxic T lymphocytes (CTL) with high avidity for donor antigens (Ag) coincided with acute cardiac rejection. In the present study, we analyse whether such high-avidity CTL are present within the peripheral blood of cardiac transplant recipients and whether their kinetics correspond with the rejection status of the allograft. Using limiting dilution analysis (LDA), donor-specific CTL were enumerated in serial blood samples of seven patients. From each patient, 7-11 samples were obtained during the first year after transplantation and up to three samples were obtained at a later date. Enumerated donor-specific CTL were divided into CTL with high or low avidity for donor Ag, depending on their sensitivity to CD8-blocking. In contrast to the situation in the graft, the donor-specific CTL present within the peripheral blood were CTL precursors (pCTL) and not fully mature CTL (cCTL). The number of donor-specific pCTL among peripheral blood cells fluctuated irrespective of the rejection grade of the allograft, indicating that the frequency of circulating donor-specific CTL does not reflect the immunological status of the allograft. During acute cardiac rejection, 66% (median) of the circulating donor-specific pCTL had a high avidity for donor Ag. This percentage significantly exceeded pre- and postrejection values obtained during the first year post-transplantation (median, 39% and 37%, respectively). The disparity in avidity increased even further more than 1 year after transplantation, when stable engraftment was achieved. Among donor-specific pCTL in peripheral blood, those with a high avidity were absent (median, 0%). Hence the avidity of circulating donor-specific CTL might inform us about the immune status of the cardiac allograft.

Clinical significance of selective decline of donor-reactive IL-2-producing T lymphocytes after renal transplantation

Limiting dilution analysis technique was used to enumerate the circulating precursor frequency of donor and third-party-reactive helper T lymphocytes (HTLpf) in 28 renal allograft recipients before (pre-tx) and at three intervals (T1: 60-90 days, T2: 120-180 days, T3: 360-1620 days) after transplantation (post-tx). Two patterns of responses were identified, in group 1 (n = 12), a five to 31-fold reduction of donor-reactive HTLpf (ranging from 1/19231-1/62500) occurred within 90-1620 days post-tx, while in group 2(n = 16), no significant changes of donor-reactive HTLpf were seen. In both groups, the third-party-reactive HTLpf in most of these patients remained largely unchanged throughout the study period. The number of HLA-DR mismatches, total number of rejection episodes, serum creatinine levels, and biopsy findings at T3 were compared in both groups using Fisher's exact probability, and the Mann-Whitney test. We found that 11 patients (92%) in group 1 were HLA-DR compatible with donors, while nine (56%) patients in group 2 were HLA-DR compatible with donors, p = 0.04. In group 1 eight rejection episodes occurred in five (41.6%) patients during the study period, compared to 33 in 13 (81%) patients in group 2, p = 0.03. Group 1 had a significantly lower serum creatinine level (at T3); median: 136 vs 165 mumol/l for group 2, p = 0.03. Biopsy indicated no rejection (at T3) in eight (66%) patients in group 1 as compared to three (18%) patients in group 2, p = 0.03. Taken together, these results indicate that the frequency of circulating HTLpf correlate with the clinical status of the graft. Therefore monitoring of HTLpf in the peripheral blood could be useful in predicting graft outcome and selecting patients for reducing immunosuppression.

Noninvasive diagnosis of cardiac allograft rejection in an orthotopic canine model

BACKGROUND

A decline in the R wave voltage obtained from surface electrocardiograms once correlated with cardiac allograft rejection. With cyclosporine therapy, however, these electrocardiographic findings became inconsistent, occurring only during severe rejection episodes. Despite cyclosporine use, intramyocardial unipolar peak-to-peak amplitudes obtained from plunge electrodes are reported to be highly sensitive and specific for diagnosing rejection. These reports are based on heterotopic grafts, which atrophy over time, making long-term voltage changes during rejection difficult to interpret. The purpose of this study was to use analysis of unipolar peak-to-peak amplitudes as a prospective monitoring tool for diagnosing orthotopic cardiac allograft rejection.

METHODS

Ten adult mongrel dogs underwent orthotopic heart transplantation with the attachment of four intramyocardial leads. The unipolar peak-to-peak amplitudes were measured daily and compared with endomyocardial biopsy results.

RESULTS

We found that intramyocardial unipolar peak-to-peak amplitude analysis had a sensitivity and a specificity of 100% for diagnosing rejection. We also found that as the number of myocardial leads increased, the sensitivity of detecting rejection also increased.

CONCLUSIONS

We conclude that unipolar peak-to-peak amplitude analysis is an accurate noninvasive means for early detection of cardiac allograft rejection in an orthotopic model. Its success should allow less frequent, more selective use of endomyocardial biopsy.

Noninvasive diagnosis of cardiac allograft rejection: the effect of procainamide

The surface electrocardiogram (ECG) has been used as a noninvasive technique for the diagnosis of cardiac allograft rejection. Alteration in conduction, R-wave amplitude, and rhythm have been associated with rejection. These ECG findings are modulated by the myocyte sodium channel, but are inconsistent and occur only during severe rejection episodes. The purpose of this study was to (1) characterize changes in cardiac electrophysiology during allograft rejection using the highly sensitive intramyocardial electrocardiogram and (2) determine whether pharmacological sodium channel blockade with procainamide enhances subtle ECG changes. Nine mongrel dogs underwent heterotopic heart transplantation in which four intramyocardial leads (one anteriorly and posteriorly on each ventricle) were attached. Leads exited to a subcutaneously placed ECG block which was transcutaneously accessed posttransplant to record direct intramyocardial electrocardiograms. Six animals were treated with procainamide, while three were not and served as controls. Daily measurements included the QRS, QT, and QTc intervals and the R-wave amplitude. Endomyocardial biopsies were performed weekly and also when significant decline in ECG amplitude occurred. Detailed ECG interval analysis failed to establish any correlation between conduction and rejection, even in the procainamide-treated group. Intramyocardial amplitude analysis, however, had a sensitivity of 100% and a specificity of 86% for the diagnosis of rejection. The results indicate that intramyocardial ECG interval analysis is not predictive of rejection even when prolonging conduction with procainamide. Amplitude analysis, however, remains an accurate noninvasive means for the early detection of cardiac allograft rejection and should allow more selective use of endomyocardial biopsy.

Changes in the mononuclear cell subpopulations of rat cardiac transplant recipients administered FK506 for the treatment of ongoing rejection

The inhibitory effect of ongoing rejection and the changes that occurred in mononuclear cell subpopulations were compared between four groups of rats treated with FK506 or steroids. Group 1 was given no immunosuppressive drugs, group 2 was given FK506 from the day of grafting, group 3 was commenced on FK506 on the 4th day after grafting, and group 4 was commenced on methylprednisolone (MP) on the 4th day after grafting. The graft survival times in groups 2 and 3 were significantly longer than those in groups 1 and 4, and there were fewer CD3+ and CD4+ T lymphocytes in the peripheral blood in the groups treated with immunosuppressive drugs than in group 1. In group 4, the levels in both the peripheral blood and thymus were significantly lower than those in the groups treated with FK506 despite the fact that graft rejection occurred soon after the discontinuation of steroid administration. Moreover, the levels of interleukin-2 receptors and macrophages in groups 2, 3, and 4 were significantly lower than that in group 1 postoperatively; however, the number of macrophages in groups 2 and 3 was significantly lower than that in group 4 on the 10th day after transplantation. The findings of this study demonstrated that FK506, even if administered after rejection has begun, might inhibit the subsequent extensive allograft rejection more specifically and effectively than steroids, and that the measurement of a marker for macrophages in the peripheral blood could be useful for the detection of rejection following allograft transplantation in rats.

Limiting dilution analysis: quantification of IL-2 producing allospecific lymphocytes after renal and cardiac transplantation

A rapid and robust limiting dilution assay was developed to measure the frequency of donor-reactive, IL-2 (interleukin 2) producing, helper T lymphocytes in the peripheral T cell population of organ allograft recipients. The IL-2 bioassay was performed using two methodologies to assess the response of CTLL-2 indicator cells. The first depended on spectrophotometric detection of bioreduced XTT whilst the second involved measurement of [3H]thymidine incorporation. The radioisotopic method was slightly more sensitive but both assays could be used for analysis of limiting dilution culture supernatants after primary incubation of recipient lymphocytes with donor splenic cells for 48 hours. All the assays produced results which conformed to single hit kinetics, indicating that IL-2 was production was dependent on a single limiting cell type. The frequency of allospecific helper lymphocytes in the peripheral T cell population of normal volunteers did not vary significantly during a 28-day period. It was found that immunosuppressed allograft recipients had a significantly reduced proportion of T cells in their peripheral blood mononuclear cell population. However, it was possible to measure the frequency of donor-reactive helper cells in the T cell population of transplant patients. These frequency values were very low in two renal allograft recipients who were HLA-DR matched to their donor organs. Three of four HLA-DR mismatched cardiac recipients showed a significant decrease in the frequency of their donor-reactive helper lymphocytes during the period of monitoring. The fourth patient, who received antilymphocyte antibodies for the first three days after transplantation, showed significant fluctuations in the frequency of these cells. The four cardiac recipients showed little histopathological evidence of acute graft rejection with only one patient experiencing a brief episode of moderate rejection; this patient showed a high frequency of donor-reactive helper cells when assayed immediately after this episode but the frequency subsequently declined.

Clinical significance of in vitro donor-specific hyporesponsiveness in renal allograft recipients as demonstrated by the MLR

A longitudinal study was carried out on 19 recipients of cadaveric renal allografts, monitoring their anti-donor and anti-third party responses in the mixed lymphocyte reaction (MLR) at the time of transplantation and at 3, 6, and 12 months post-transplant. Two patterns of responses were identified: in the first (n = 11), patients showed, or later developed, donor-specific hyporesponsiveness, and in the second (n = 8), patients had persistent antidonor and anti-third party responses. After 1 year, the serum creatinine, number of episodes of acute rejection and biopsy findings were compared in both groups. In the first group, the mean serum creatinine was 136.4 mmol/l, the total number of acute rejection episodes was three and in nine of the ten available biopsies, there were minimal cellular infiltrates and normal appearance of the glomeruli, tubules and blood vessels. In the second group, the mean serum creatinine was 163 mmol/l, the total number of acute rejection episodes was 12 and in five of the seven biopsies available, evidence of ongoing rejection was obtained. The difference in mean serum creatinine was not statistically significant (P > 0.05), but the difference in the numbers of acute rejection episodes was (P < 0.05). It is concluded that in some renal allograft recipients, a state of donor-specific hyporesponsiveness develops, and this state may be associated with better graft outcome at 1 year. These data may be useful in selecting patients for reduced immunosuppressive therapy.

Soluble CD8 and CD25 in serum of patients after heart transplantation

To evaluate the diagnostic value of serum cytokine levels and cytokine receptor levels in the diagnosis of acute rejection after heart transplantation, we measured soluble CD8 and soluble CD25 in the serum of heart transplant recipients. The results were compared with endomyocardial biopsy (EMB) histopathology, lymphocyte activation by morphologic inspection of peripheral blood cells (cytoimmunologic monitoring), clinically manifested infections, and the maintenance immunosuppressive therapy. Significantly increased levels were observed in cases of lymphocyte activation in cytoimmunologic monitoring indicative of either rejection or infection. In clinically documented cytomegalovirus (CMV), bacterial, and Pneumocystis carinii infections, increased levels of soluble CD25 were observed. Soluble CD8 was only increased in a single case of P. carinii infection. A statistically significant correlation was calculated between the levels of soluble CD8 and whole blood cyclosporin A level. Considering chemotherapy, the levels of soluble CD8 showed an inverse correlation with the daily dosage of azathioprine. In conclusion, the levels of soluble CD8 and CD25 are associated with lymphocyte activation in peripheral blood, but do not differentiate between lymphocyte activation indicative of rejection or infection. No relationship was observed between levels of soluble CD8 and CD25, and EMB histopathology. Therefore, the assessment of these two cell products has no diagnostic potential for monitoring acute rejection after heart transplantation.

Development of immunological assays to monitor pulmonary allograft rejection

BACKGROUND

At present the diagnosis of pulmonary allograft rejection is made after examination of transbronchial biopsy specimens; this method is highly invasive. A study was performed to determine whether immunological parameters measured in peripheral blood or bronchoalveolar lavage samples correlate with the histological diagnosis of rejection.

METHODS

Left unilateral pulmonary allotransplantation was performed between dogs. The animals were immunosuppressed with cyclosporin A after transplantation but the dose of this drug was gradually reduced to allow controlled rejection to take place. Rejection was diagnosed histologically. Four immunological parameters were investigated: measurement of lavage derived T cell proliferation in response to limited culture with interleukin 2; measurement of changes in the frequency of donor reactive cytotoxic T lymphocytes; assay of the level of donor cell binding IgG antibody in recipient plasma; and measurement of the antibody dependent cell mediated cytotoxic response to donor cells after labelling with recipient plasma.

RESULTS

Assays based on measurement of the function of T cells produced significant results at a time later than the histological diagnosis of severe rejection. The level of donor reactive IgG antibody increased at a time that corresponded closely with the diagnosis of severe rejection. This IgG did not activate the antibody dependent cell mediated cytotoxic effector mechanism to a significant extent.

CONCLUSIONS

Measurement of parameters of donor specific immunoreactivity can yield data which are indicative of severe pulmonary allograft rejection. These methods make use of samples which can be obtained by minimally invasive methods. Measurement of the plasma level of donor reactive IgG antibody appears to be the most useful assay. However, each of the in vitro assays used during this series of experiments was less sensitive to the onset of rejection than was routine histological examination.

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.