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J Thorac Cardiovasc Surg 1999;117:565-571
© 1999 Mosby, Inc.
CARDIOTHORACIC TRANSPLANTATION |
From the Division of Cardiothoracic Surgery,a,c Department of Surgery and Pathology,b and the Pulmonary and Critical Care Divisiond/Department of Medicine, Washington University School of Medicine, Barnes Hospital, St Louis, Mo.
This work was supported by National Institutes of Health grant HL56643 (T.M.).
Received for publication Aug 3, 1998. Revisions requested Sept 17, 1998. Revisions received Oct 12, 1998. Accepted for publication Oct 12, 1998. Address for reprints: Sudhir Sundaresan, MD, Northwestern University Medical School, 251 East Chicago Ave, Suite 1030, Chicago, IL 60611.
| Abstract |
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| Introduction |
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| Patients and methods |
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Immunosuppression
The immunosuppression regimen has been described elsewhere in greater detail.
8 In brief, the induction regimen consisted of cyclosporine (INN: ciclosporin), azathioprine, and antithymocyte globulin (since 1992) followed by a maintenance regimen of cyclosporine, azathioprine, and prednisone. Steroids were given in the following manner: methylprednisolone 1 g intravenously before reperfusion, then 0.5 mg/kg intravenously daily, and convert to oral prednisone 0.5 mg/kg daily, tapered gradually to approximately 15 mg orally daily at 1 year.
Follow-up bronchoscopy after transplantation
Recipient follow-up included interval chest radiographs, arterial blood gases, pulmonary function testing, and fiberoptic bronchoscopy. BAL and transbronchial lung biopsy (TBLB) were performed (by fiberoptic bronchoscopy) routinely at 1, 3, 6, and 12 months after transplantation then annually thereafter. Additional BAL and TBLB were carried out when there was clinical suspicion of rejection or infection. The bronchoscopic procedure has been previously described.
8 Lavage fluid was submitted for routine clinical tests, and a small leftover aliquot was provided for this study.
Pathologic diagnosis
TBLB tissue was fixed in formaldehyde solution and stained with hematoxylin and eosin to allow histologic analysis.
Diagnosis of acute rejection. Pathologic findings from TBLB were used to confirm the presence and grade of acute rejection. In brief, the grade of rejection was histologically classified according to the working formulation for the standardization of terminology in heart and lung allograft rejection set forth by the Lung Rejection Study Group
9 and graded from A0 to A4.
Diagnosis of cytomegalovirus infection. Cytomegalovirus pneumonitis was identified histologically by characteristic intracellular inclusions on the hematoxylin and eosin stain or by a positive immunoperoxidase stain.
Cell-mediated lymphocytolysis assay
BAL lymphocyte preparation. Lymphocytes were isolated from BAL fluid and used as effector cells in standard cell-mediated lymphocytolysis (CML) assays. BAL fluid was filtered through 4 layers of surgical gauze and centrifuged at 300g for 12 minutes. The sediments were washed twice in phosphate-buffered saline solution and resuspended in 5 mL of culture medium consisting of RPMI-1640 (Gibco BRL, Gaithersburg, Md), 15% heat-inactivated human serum (MLC Normal Serum Male Non AB plasma; RJO Biologicals Inc, Kansas City, Mo), 5 mmol/L L-glutamine, 25 mmol/L HEPES buffer, and 100 µg/mL streptomycin and 100 U/mL penicillin. Macrophages were removed by magnet sedimentation after a brief incubation with carbonyl iron. The remaining lymphocytes were purified by Ficoll-Hypaque density gradient sedimentation. In general, the volume of BAL obtained from the patient was about 100 mL (range, 60-110 mL). The lymphocyte yield was typically about 1.0 to 2.0 x 106 cells per 100 mL of BAL (range, 0.2-7.1 x 106 cells).
Target cell lines. The cell lines used included BEAS-2B (an immortalized airway epithelial cell line, which was provided by Dr Curtis Harris
10; VAVY, EAG254, and EBZ369 (Epstein Barr virus-transformed B-lymphoblastoid cell lines); and the natural killersensitive cell line, K562.
11 The HLA phenotypes of BEAS-2B and the lymphoblastoid cell lines were determined by the HLA laboratory at Barnes-Jewish Hospital (Table I). For this study, HLA-A and B were considered representative of class I, and HLA-DR was considered representative of class II. These cell lines were selected on the basis of their HLA phenotypes, specifically because they expressed common HLA class I antigens. For example, considering only the HLA-A locus, our 3 lymphoblastoid cell lines expressed HLA-A1, A2, A3, and A24 (Table I
). By including the BEAS-2B target, HLA-A28 was also expressed. The predicted frequencies of these 5 alleles in the white population are 28.6%, 45.8%, 20.6%, 16.8%, and 8.8%, respectively.
12 We therefore thought it likely that these targets would share some mismatched (or "sensitizing") donor HLA class I antigens in a substantial number of the experiments.
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Determination of target lysis. CTL analysis was performed with a standard chromium-51 release assay, as previously described.
13 In brief, 0.5 x 106 cells serving as targets were labeled with 125 µCi of51Cr (ICN, Costa Mesa, Calif) for 60 minutes at 37°C. After extensive washing, 2500 targets in 0.1 mL culture medium were transferred to wells of 96-well U-bottomed plates. BAL lymphocytes in 0.1 mL culture medium were co-cultured with51Cr-labeled target cells for 4 hours at 37°C. The yield of lymphocytes from BAL fluid usually gave an effector-to-target ratio between 10:1 and 20:1 (range, 6:1-40:1). After a 4-hour incubation, culture supernatants were harvested and counted with a gamma counter (Pharmacia LKB Biotechnology, Uppsala, Sweden).
Data analysis
Pathologic diagnosis. In each CML assay, the pathologic diagnosis was determined from the TBLB obtained simultaneously. We sought the following histologic states, as they defined the 3 study groups: quiescent (REJ; ie, implying no rejection or cytomegalovirus infection); acute rejection alone (REJ+; ie, without concomitant cytomegalovirus infection); and cytomegalovirus infection alone (cytomegalovirus+; ie, without concomitant acute rejection).
Mean lysis values and statistical comparisons. Mean (± SEM) values of target lysis were compared for each target (BEAS-2B, lymphoblastoid cell lines, K562) between the following groups: quiescent versus acute rejection; quiescent versus cytomegalovirus infection; and acute rejection versus cytomegalovirus infection. T test with Dunn-Sidak adjusted probabilities and analysis of variance with Tukey's multiple comparisons test were used to determine whether there were significant differences between mean values.
Subgrouping of lysis data for the comparison of quiescent versus acute rejection. For comparison between quiescent versus acute rejection, the mean values for target lysis were subgrouped as Cl I+ or Cl II+ and Cl, respectively, to determine the effect of MHC restriction on the lysis. This was accomplished as follows: each CML assay yielded a lysis value for the 5 targets. For those targets with MHC expression (BEAS-2B and the 3 lymphoblastoid cell lines), the target could be categorized as Cl I+ or Cl II+, if it shared a mismatched class I or II antigen with that recipient's donor, or as Cl, if it lacked entirely any mismatched donor class I or II antigens.
Mean values for K562 lysis cannot be subgrouped this way because this cell line lacks MHC expression. For the comparison between the cytomegalovirus+ versus quiescent and cytomegalovirus+ versus REJ+ groups, the mean values for target lysis were subgrouped as Cl+, if they shared a mismatched class I or II antigen with that recipient's donor. Class I and II were not separated because of the small numbers of CML assays conducted on cytomegalovirus+ recipients (Fig 1).
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| Results |
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Pathologic status and distribution of Cl I+, Cl II+, and Cl targets
Pathologic status of the recipients is summarized in Table II. There were 18 patients in the quiescent group (no rejection or cytomegalovirus infection); 20 patients in the REJ+ group (acute rejection without cytomegalovirus infection); and 6 patients in the cytomegalovirus+ group (cytomegalovirus infection without rejection). In 15 of the 18 assays (83%) in the quiescent group at least 1 target of those tested shared mismatched donor class I or II antigens. In 17 of the 20 assays (85%) in the acute rejection group, at least 1 target shared mismatched donor class I or II antigens. Finally, in 7 of the 7 assays (100%) in the cytomegalovirus+ group, at least 1 target shared mismatched donor class I or II antigens.
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Relationship between CTL activity, acute rejection, and MHC class I and II antigens
Mean percent lysis (± SEM) of BEAS-2B, lymphoblastoid cell lines, and K562 targets was compared between the acute rejection (REJ+) versus quiescent (no rejection [REJ]) groups (Fig 3).For the BEAS-2B target, mean lysis was significantly greater during rejection compared with no rejection when the target expressed donor class I alloantigens (11.1% ± 1.9% [n = 9] vs 2.1% ± 1.2% [n = 4]; P = .007). A difference was noted between rejection and no-rejection groups when the BEAS-2B target expressed class II donor alloantigens (15.3% ± 3.9% [n = 7] vs 5.0% ± 1.8% [n = 7]; P = .09) and even when BEAS-2B did not share any donor class I or II allo-antigens (13.6% ± 4.5% [n = 8] vs 2.3% ± 0.7% [n = 7]; P = .09). When Cl I+ lymphoblastoid cell lines targets were tested even when they expressed donor alloantigens the lysis during rejection was not significantly greater than the no-rejection group (8.2% ± 2.5% [n = 24] vs 3.0% ± 0.9% [n = 21]; P = .18 ). Mean lysis did not differ between rejection and no-rejection groups for any of the other targets including Cl II+ lymphoblastoid cell lines (P = .30), Cl lymphoblastoid cell lines targets (P = .58), or K562 targets (P = .30).
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Relationship between cytotoxicity and cytomegalovirus infection
To determine whether cytomegalovirus infection had any effect on donor-specific responses, we looked at target lysis in patient samples identified as cytomegalovirus positive. For this analysis we compared the lysis of targets that expressed donor mismatched MHC class I and II antigens together (Cl+). When the mean percent lysis of the BEAS-2B, lymphoblastoid cell lines, and K562 targets were compared with the use of a 3-way analysis of variance between the quiescent versus cytomegalovirus+ versus acute rejection, a significant difference in mean lysis was noted only between the acute rejection group and the cytomegalovirus+ group when the airway epithelial cell expressing donor mismatched MHC class I or II antigens was used as a target (12.8% ± 2.6% [n = 12] vs 5.68% ± 1.0% [n = 5]; P = .012).
| Discussion |
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Unlike the previously mentioned studies that have focused on the proliferative response of graft-derived lymphocytes to donor antigens, our study attempted to evaluate the immune status of the graft through demonstration of donor antigenspecific cytotoxicity with CML assays with BAL lymphocytes, specifically examining the activity against an airway epithelial cell. Our demonstration of increased lysis of donor class Irelevant targets during rejection strongly suggests the presence of allospecific CTL in lung allografts during rejection. Recognizing the importance of the role of CTLs in acute cellular allograft rejection, our study would appear to most directly demonstrate ongoing rejection in vivo that is targeted to the epithelium.
A unique feature of our study was that we used an airway epithelial cell line, BEAS-2B, as a target in the panel. There was significantly greater lysis of BEAS-2B during acute rejection compared with the "quiescent" state. However, unlike the lymphoblastoid cell line targets, against which the slight increase in cytotoxicity during rejection was confined to donor class Irelevant targets, an increased lysis of BEAS-2B occurred regardless of whether or not BEAS-2B shared any class I or II antigens with the donor. But, the increased lysis reached significant levels (P = .007) only when the BEAS-2B target expressed the donor class I alloantigen. Hadley and colleagues
15 previously reported on clones of human CTL that exhibit class I allospecificity in a kidney tissuerestricted manner, with an in vitro mixed leukocyte-kidney culture system. The basis for the tissue specificity displayed by those clones was shown to be tissue-specific peptides presented in the context of allo-class I.
16 Our finding of elevated CTL activity against BEAS-2B during rejection raises the possibility that the CTL recognizes a unique bronchial epithelial antigen presented in the context of MHC class I. This hypothesis can be tested only when cloned T cells are available. We are currently conducting further investigation to answer this question.
Cytomegalovirus infection and acute rejection can share similar clinical presentations in patients with lung transplants. Previous investigators have used proliferative assays to identify cytomegalovirus infection in lung allografts. These investigators have made correlations between cytomegalovirus infection and BAL lymphocyte proliferation in response to cytomegalovirus antigens,
17 donor-specific MHC antigens,
2 and even autologous (recipient) MHC antigens.
14 Our study showed no difference in target lysis between the cytomegalovirus+ and histologically normal groups whereas there was a significant difference between target lysis, BEAS-2B sharing donor-mismatched class I or II antigens, in the cytomegalovirus+ and acute rejection group. Notwithstanding the proliferative responses of cytomegalovirus-primed BAL lymphocytes described by other investigators,
2,5,17 the CML assay system we describe appears to distinguish reliably between acute rejection and cytomegalovirus infection only when airway epithelial cell was used as a target.
We included K562 as a target in the panel to evaluate the potential contribution of natural killer cells to lung allograft rejection in vivo. Our data show that although natural killer cell activity was evident in the BAL cell population, it is unlikely that it plays an important role in pulmonary allograft rejection, because there was no significant difference in natural killer activity between acute rejection, cytomegalovirus infection, and normal activity. It is possible that the use of cyclosporine masked the importance of these natural killer cells by virtue of its potent inhibitory effects on interleukin-2 release. Further work would be necessary to clarify this observation.
In summary, donor class Idirected CTL activity is present in BAL lymphocytes from patients with lung transplants who are undergoing acute rejection. The activity is most apparent when the airway epithelial cell is used as a target. These results suggest that a major component of the immune response to lung allograft is directed against the lung epithelium. These results may have direct implications on the possible development of chronic responses in these patients. Destruction of the epithelium is a major pathologic feature in patients with bronchiolitis obliterans syndrome. Our results suggest that these changes may be immune mediated.
| Acknowledgments |
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| References |
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