Humoral theory of transplantation

Significance of Donor-Specific Antibodies in Acute Rejection

Significant advances in recent years in the diagnosis of antibody-mediated graft rejection have led to the re-evaluation of humoral alloreactivity in organ transplantation. By introducing the "C4d-test" into the work-up of transplant biopsies, donor-specific antibodies were claimed to be directly involved in about 30% of acute rejection episodes. The diagnostic criteria for antibody-mediated rejections of renal grafts are now incorporated in the "Banff classification" as refined at a recent consensus conference. Capillary C4d is not always concordant with circulating anti-HLA-antibodies, even if these are assayed with improved techniques. Antibody absorption within the graft and antigens other than HLA, therefore, have to be considered. Effective therapy of humoral rejection is now available. Serial assessment of humoral alloreactivity also in the posttransplantation period is now mandatory to identify at-risk patients.

Diagnostic value of C4d in renal biopsies

PURPOSE OF REVIEW

Capillary C4d is now an established marker of antibody-mediated rejection in graft biopsies. The technique is widely used to further define the clinical relevance of humoral alloreactivity in various patient subgroups. These include highly sensitized patients, recipients with late graft failure and also some with 'stable' graft function.

RECENT FINDINGS

The C4d technique compares favourably with other techniques that are explored, for example detection of C3d. Capillary C4d can be associated with any graft pathology, including transplant glomerulopathy. C4d is related to circulating alloantibodies but not autoantibodies, and is probably not derived from local sources. Presensitization and de-novo sensitization are important scenarios of humoral alloreactivity that require refined analysis and treatment.

SUMMARY

Detection of C4d in graft biopsies has emerged as an important tool that could substantiate the clinical significance of antibody-mediated rejections. The comprehensive analysis of humoral alloreactivity in the posttransplantation period is still ongoing and will hopefully result in improved patient care and better long-term graft survival.

Impact of HLA Antibodies on Transplant Glomerulopathy

The influence of humoral rejection on the development of chronic allograft nephropathy (CAN) is controversial, especially in relation to transplant glomerulopathy. The aim of our study was to analyse the influence of anti-HLA antibodies on the development of transplant glomerulopathy (cg0, cg1, cg2, and cg3; Banff'97). We selected all renal transplants patients from 1975 to 2003 who had a functioning graft for at least 6 months and a clinically indicated graft biopsy with CAN and chronic glomerular changes (case group). We studied the presence of anti-HLA antibodies (Ab) in the last serum taken while the graft was functioning and divided them into three groups according to the severity of glomerular lesions. We also selected 52 contemporary and comparable cases without transplant glomerulopathy (control group). A total of 77 case had transplant glomerulopathy: 39 cg1, 29 cg2, and 9 cg3. Pretransplant Ab titers and number of previous blood transfusions were higher among the subgroup with the most severe glomerulopathy. Patients who developed posttransplant anti-HLA Ab more frequently showed transplant glomerulopathy. Serum creatinine and proteinuria were higher among cases with chronic glomerulopathy, and more grafts were lost in that group. Thus, the presence of HLA-Ab is a key factor in the development of transplant glomerulopathy and chronic allograft rejection.

Predictive Value of HLA Antibodies and Serum Creatinine in Chronic Rejection: Results of a 2-year Prospective Trial

In this large collaborative study, 2,231 transplanted patients with functioning kidneys were tested for HLA antibodies, then examined 2 years later for graft survival. Among 478 patients with antibodies, 15.1% failed in 2 years, compared to 6.8% failure in 1,753 patients without antibodies (P=0.00000002). Cytotoxicity testing correlated better with outcome than flow cytometry or ELISA testing on HLA coated beads, possibly because it detected non-HLA antigens. When the patients were further broken down into those with serum creatinine at the time of testing of 0.5-1.9, 4.4% of antibody patients failed at 2 years, compared to 4.3% of patients without antibodies. This 0.1% difference increased among patients with serum creatinine values of 2.0-2.9 to 17.9%, and among those with 3.0-3.9 to 16.3%. We conclude that HLA antibodies posttransplantation is predictive of subsequent graft failure, and its predictive value can be enhanced among patients with higher serum creatinine values.

Humoral theory of transplantation: further evidence

In the two and a half years following our initial paper on the humoral theory of transplantation, many publications have emerged in support of the hypothesis, with no studies in opposition. It is accepted that the role of antibodies is incontrovertible in hyperacute rejection, although what fraction of acute rejection is humoral remains to be determined. A recent large-scale prospective trial showing that transplant patients with antibodies have twice the failure rate as those without antibodies suggests that chronic rejection is also caused by antibodies. Together with serum creatinine, HLA antibodies are, therefore, the best predictor of graft function in kidney patients.

Ultra-late antibody-mediated rejection 30 years after a living-related renal allograft

Antibody-mediated renal allograft rejection has become increasingly recognized and more clearly defined through the use of flow cytometry cross-matching and the deposition of C4d in renal allograft biopsies. All of the cases reported thus far have developed an antibody within 10 years of transplantation, and many lacked HLA and/or donor specificity. The present patient developed an anti-HLA donor-specific antibody between the 22nd and 30th year after a living-related renal transplant. At the 30th year post-transplantation, she experienced a rise in the serum creatinine from 0.7 to 1.9 mg/dL associated with transplant biopsy C4d deposition in peritubular capillaries and glomeruli. After the replacement of azathioprine with mycophenolate mofetil, and six apheresis treatments followed by two infusions of IVIG, the renal function stabilized at 1.9 mg/dL, 33 years after transplantation. Antibody-mediated rejection must be considered as a possible cause or renal allograft dysfunction at all time periods after transplantation.

The Impact of Mycophenolate Mofetil on Long-Term Outcomes in Kidney Transplantation

Mycophenolate mofetil (MMF) has been used in kidney and pancreas transplantation for almost 10 years. In the pivotal phase III trials, MMF use was accompanied by a dramatic reduction of rejection rates in kidney transplantation; however, the impact on graft and patient was undetermined. Analyses of the United States Renal Data System and the Scientific Registry of Transplant Recipients databases later provided a valuable measure of the impact of MMF in improving outcomes. In this review, we provide a synopsis of the prospective studies, including but not limited to the pivotal MMF approval trials, and analyses of the national transplant registries relevant to the long-term impact of MMF in kidney transplantation. Indeed, a substantial body of evidence has shown MMF treatment improves patient survival, graft survival, and death-censored graft survival in kidney transplantation. The beneficial effects of MMF have been particularly notable in high-risk recipients such as African Americans. In coming years, these benefits will require reevaluation in the context of the growing use of novel protocols combining MMF with tacrolimus or sirolimus.

Anti-HLA antibodies in kidney transplanted patients

Anti-human leukocyte antibodies (HLA) play a central role in graft survival, particularly in kidney transplantation. The presence of preformed donor specific anti-HLA antibodies is always excluded before transplantation by performing crossmatches using current and historic recipient serum samples. Several recent studies have observed a correlation between HLA antibodies and graft rejection. It has been suggested that these antibodies should be monitored routinely after kidney transplant to predict graft failure. Here in report the results of a study of on serum samples from 111 kidney transplant recipients that were monitored for anti-HLA antibodies using flow cytometry. Anti-HLA antibodies were only detected in four pre-immunized patients and showed the same HLA specificity that was present before the transplantation (in two cases against previous graft antigens). Furthermore, only two patients with functioning grafts developed anti-HLA antibodies, at 1 month and 1 year after the transplantation. However, they were not donor specific, but probably related to posttransplant transfusions. In our study, none of the patients who suffered an adverse event during the first year (including two with histologically documented acute rejection) developed anti-HLA antibodies. These results are probably related to the use of mycophenolate mofetil, which may reduce the incidence of HLA antibodies. We cannot exclude the possibility that antibodies produced by some patients may not be detectable because they are attached to the graft.

Serial ten-year follow-up of HLA and MICA antibody production prior to kidney graft failure

The role of HLA antibodies in chronic allograft rejection was examined utilizing a unique resource of sera collected annually and stored over a 12-year period from patients with rejected or retained grafts. In patients selected for not having preformed HLA antibodies, 679 postoperative serial serum samples from 39 patients who rejected their grafts and 26 with functioning grafts were tested for HLA Class I and Class II antibodies by flow cytometry and for MICA antibodies by cytotoxicity on recombinant cell lines. HLA antibodies were found in 72% of patients who rejected grafts, compared to 46% with functioning transplants (p<0.05). In addition, the incidence of IgG HLA plus MICA antibodies was higher (77%) among those with failed transplants than those with functioning transplants (42%) (p<0.01). Finally, if patients with IgM anti-HLA antibodies were included, 95% of the 39 patients who rejected their grafts had HLA or MICA antibodies, compared to 58% with functioning grafts (p<0.01). Patients who rejected transplants had HLA and MICA antibodies more frequently than those with functioning grafts. These antibodies found in the peripheral circulation, were not necessarily donor-specific, but their association with failure is consistent with a causality hypothesis.

Expansion of Humoral Donor-Specific Alloreactivity After Renal Transplantation Correlates With Impaired Graft Outcome

IgG human leukocyte antigen (HLA) antibodies were investigated retrospectively after transplantation in 264 primary renal graft recipients. All patients who developed de novo donor-specific antibodies (DSA) and non-DSA (NDSA) (n = 40, 15.1%) were divided into two groups. Group A consisted of patients (n = 20) with stable good graft function (GGF), and group B consisted of patients (n = 20) who developed rejection and/or graft failure (R/GF). DSA were detected in 23 patients (57.5%). Expansion of humoral alloreactivity with the presence of DSA to more than one graft mismatched antigens and coexistence of HLA class I and II DSA were significantly correlated only with R/GF (p = 0.01). Limitation of alloreactivity to one graft-mismatched antigen was detected mainly in patients with GGF. HLA-DQ DSA alone was found only in patients with GGF (p = 0.1). No significant differences were found between the two patient groups with NDSA. Expansion of the humoral alloreactivity to more than one graft molecule in renal transplant recipients identifies patients at high risk of rejection or graft failure. Limitation of humoral alloreactivity to one graft antigen perhaps associates the presence of regulatory mechanisms with GGF only in specific cases.

Biliary epithelial cell antibodies induce expression of toll-like receptors 2 and 3: a mechanism for post-liver transplantation cholangitis?

Studies to determine the role of preformed antibodies to biliary epithelial cells (BECs) in liver transplant rejections have been initiated. However, the clinical importance of these antibodies in the posttransplantation period still remains to be elucidated. Reactivity to BECs isolated from a normal healthy liver was investigated in sera of 56 patients before and after liver transplantation (LTX) using flow cytometry. Functional capacity of BEC antibodies was determined by the ability to induce expression of Toll-like receptors (TLRs) on BECs. Cytokine and chemokine production induced by BEC antibodies was determined by enzyme-linked immunosorbent assay. In all, 7 patients (13%) had BEC antibodies only pre-LTX, 14 (25%) only after LTX, 18 (32%) both before and after LTX, and 17 (30%) had no detectable antibodies. Presence of preformed BEC antibodies correlated with acute rejections (P < 0.03). Deposition of immunoglobulins in bile ducts was detected in biopsies of patients during rejections. Significantly higher numbers of patients with post-LTX antibodies (9 of 32) developed cholangitis, compared with 0 of 17 without antibodies (P < 0.02). Specificity studies indicated that these antibodies were both non-HLA- and HLA-specific. Normal BECs expressed mRNA but not the proteins for the TLRs. However, treatment with F(ab')2 fragments of BEC antibodies induced protein expression of TLRs 2 and 3 and significantly high production of interleukin (IL)-6, monocyte chemoattractant protein (MCP)-1, macrophage inflammatory protein (MIP)-1alpha, epithelial neutrophil activating peptide (ENA)-78, and IL-8. In conclusion, BEC antibodies via induction of TLR2 and TLR3 expression, as well as inflammatory cytokine and chemokine production may induce epithelial cell inflammatory responses to bacterial components and contribute to posttransplantation cholangitis.

Human Leukocyte Antigen Antibodies for Monitoring Transplant Patients

Human leukocyte antigen (HLA) antibody-mediated hyperacute rejection has dramatically decreased since the clinical introduction of crossmatch technology. However, the role of HLA antibody in acute and chronic rejection remains unclear. In this article, we cite publications to show the correlation between HLA antibody and allograft rejection. Potential pathological mechanisms of antibody-mediated rejection are also proposed and the rationale of commonly used HLA antibody detection techniques are introduced. The advantages and disadvantages of these technologies are further discussed in detail. We conclude that owing to the recent availability of improved antibody detection methods, a causal relationship between HLA antibodies and allograft rejection is now considered to exist.

Frequency and Clinical Implications of Development of Donor-Specific and Non–Donor-Specific HLA Antibodies after Kidney Transplantation

The involvement of immunologic and nonimmunologic events in long-term kidney allograft failure is difficult to assess. The development of HLA antibodies after transplantation is the witness of ongoing reactivity against the transplant, and several studies have suggested that the presence of HLA antibodies correlates with poor graft survival. However, they have not discriminated between donor-specific (DS) and non-specific (NDS) antibodies. A total of 1229 recipients of a kidney graft, transplanted between 1972 and 2002, who had over a 5-yr period a prospective annual screening for HLA antibodies with a combination of ELISA, complement-dependent cytotoxicity, and flow cytometry tests were investigated; in 543 of them, the screening was complete from transplantation to the fifth year postgrafting. Correlations were established between the presence and the specificity of the antibodies and clinical parameters. A total of 5.5% of the patients had DS, 11.3% had NDS, and 83% had no HLA antibodies after transplantation. NDS antibodies appeared earlier (1 to 5 yr posttransplantation) than DS antibodies (5 to 10 yr). In multivariate analysis, HLA-DR matching, pretransplantation immunization, and acute rejection were significantly associated with the development of both DS and NDS antibodies and also of DS versus NDS antibodies. The presence of either DS or NDS antibodies significantly correlated with lower graft survival, poor transplant function, and proteinuria. Screening of HLA antibodies posttransplantation could be a good tool for the follow-up of patients who receive a kidney transplant and allow immunosuppression to be tailored.

Strategies for minimizing immunosuppression in kidney transplantation

Immunosuppression remains the cause of most morbidity following organ transplantation. However, its use is also responsible for the outstanding graft and patient survival rates commonplace in modern transplantation. Thus, the predominant challenge for transplant clinicians is to provide a level of immunosuppression that prevents graft rejection while preserving immunocompetence against environmental pathogens. This review will outline several strategies for minimizing or tailoring the use of immunosuppressive drugs. The arguments for various strategies will be based on clinical trial data rather than animal studies. A distinction will be made between conventional immunosuppressive drug reduction based on over-immunosuppression, and newer induction methods specifically designed to lessen the need for chronic immunosuppression. Based on the available data we suggest that most patients can be transplanted with less immunosuppression than is currently standard.

Clinical Relevance of Low Levels of Preformed Alloantibodies Detected by Flow Cytometry in the First Year Post–Kidney Transplantation

OBJECTIVE

To determine the prevalence of transplants performed with a false-negative cytotoxicity cross-match and to analyze the clinical relevance of alloantibodies (Ab) detected only by flow cytometry (flow).

METHODS

We studied 66 patients undergoing kidney transplantation from a cadaveric donor. All patients had a simultaneous negative T+AHG+DTT and B+DTT. Pretransplant sera were retrospectively analyzed by flow cytometry according to an Emory University protocol: (1) T+ and B-: Ab anti-class I; (2) T- and B+: anti-class II; (3) T+B+: anti-class I + II. Chi-square, Fisher exact, Student t test, and Kaplan Meier analyses were employed with significance assigned at P < or = .05.

RESULTS

The overall incidence of false-negative cytotoxicity was 33.3% (22/66), namely, 6.1% (n = 4) anti-class I; 9.1% (n = 6) anti-class II; and 18.2% (n = 12) anti-class I + II. Primary nonfunctioning grafts occurred in 6.8% (3/44) and 13.6% (3/22) negative and positive flow patients (two anti-class I + II and one class II; P = .39). The incidence of graft loss in the first year was respectively, 13.6% (6/44) and 18.2% (4/22; two anti-class II and two anti-class I + II; P = .72). Compared to flow-negative grafts, creatinine levels were significantly higher among flow-positive patients at 8 and 12 weeks. One-year graft survivals were 86.4% among negative versus 81.8% for the positive group (P = .67).

CONCLUSIONS

We observed that 33% of kidney transplant recipients had low levels of alloantibodies detected only by flow. This single factor was associated with the worst graft function in the first trimester with a suggestion of a higher risk for non-functioning graft.

Soluble CD30 and HLA antibodies as potential risk factors for kidney transplant rejection

Recent literary data suggest that high pre- and post-transplant serum levels of the soluble CD30 (sCD30) molecule may be a risk factor for acute rejection and worse prognosis of the transplanted kidney. The aim of our study was to correlate the concentrations of sCD30 and the presence of HLA antibodies as defined by flow cytometry and ELISA with the clinical course and graft prognosis after transplantation. One hundred and seventeen kidney transplant patients were included into the study. The incidence of rejection episodes, graft function and graft survival for up to 1 year post-transplant were evaluated. Soluble CD30 levels before transplantation were virtually the same in patients who experienced rejection and in non-rejecting patients. In both patient groups, a significant decrease of sCD30 was detected 2 weeks after transplantation (104.4 U/ml before vs. 37.0 U/ml post-transplant, P < 0.001). However, there was a substantial difference in the level of decrease of sCD30 between rejecting and non-rejecting patients. Patients without rejection had lower sCD30 values (31.2 U/ml post-transplant) compared to patients who experienced rejection episodes (62.9 U/ml), P < 0.04. Multifactorial analysis showed that antibodies to HLA class II antigens and elevated concentrations of sCD30 shortly after transplantation were associated with increased risk for acute rejection in the first post-transplant year. Measurement of soluble CD30 after transplantation, taken into consideration with the presence of HLA class II antibodies, might be helpful for evaluating the potential risk for acute rejection.

Impact of ELISA-Detected Anti-HLA Antibodies on Pediatric Cardiac Allograft Outcome

In this study, we determine whether the presence of enzyme-linked immunosorbent assay (ELISA) detected anti-human leukocyte antigen (HLA) antibodies correlates with acute and chronic rejection in pediatric heart transplantation (Tx). Forty-five patients, who had serial ELISA pre- and posttransplantation, were studied. Age at Tx was 8.2 +/- 7.2 years. Acute rejection (AR) was defined as International Society for Heart and Lung Transplantation Grade > or =3a. Patients were defined as rejectors (22 cases) if they had recurrent AR or steroid-resistant AR within the first year post-Tx; the other cases (23) were defined as nonrejectors. Overall, 219 samples were analyzed. Twenty-two of the 45 had pre- or post-Tx anti-HLA antibodies: 77% in rejectors (17/22) and only 22% in nonrejectors (5/23), p = 0.0002. Pre-Tx HLA antibodies were present in 12 cases (27%). Presensitization was more frequent in rejectors (11/22, 50%) than in nonrejectors (1/23, 4%, p = 0.0005). Nineteen cases retained (9 cases) or developed (10 cases) anti-HLA antibodies post-Tx: 14 in rejectors (63.6%) and 5 in nonrejectors (21.7%), p = 0.003. Four of eight cases with coronary artery disease (50%) had preformed anti-HLA antibodies compared with 8 of 37 without coronary artery disease (25.6%) (p = 0.09). Preformed, persistent, and de novo ELISA-detected anti-HLA antibodies were correlated with first-year acute rejection profile.

Single-Antigen-Expressing Cell Lines Are Excellent Tools for Detecting Human Leukocyte Antigen-C???Reactive Antibodies in Kidney Transplant Recipients

BACKGROUND

Human leukocyte antigen (HLA)-C is expressed on nucleated cells and platelets in lower levels than HLA-A,B, and its antigens are in linkage disequilibrium with HLA-B antigens. Therefore, HLA-C antibody detection is difficult. The authors questioned whether HLA-C could serve as a target in clinical kidney transplantation using a newly developed assay.

METHODS

Flow cytometry was performed with sera from patients (n=34) awaiting a kidney retransplant using nine cell lines expressing a single HLA-C antigen (single-antigen lines [SAL]).

RESULTS

The SAL were validated with HLA-C-specific alloantisera and human monoclonal antibodies against HLA-A, -B, and -C. The results were in agreement with the specificities previously reported. Exceptions, because of new HLA-C specificities used here, could be explained by epitope sharing between the antigens. With respect to patient sera, 15 of the 34 patients tested (44%) showed serum reactivity toward one or more HLA-C SAL.

CONCLUSIONS

In contrast to peripheral blood lymphocytes, SAL are excellent targets for detecting HLA-C-reactive alloantibodies by flow cytometry. This preliminary analysis revealed that HLA-C-reactive antibodies are frequently present in sera of retransplant patients, serving as possible targets in clinical transplantation.

Prevalence and significance of anti-HLA and donor-specific antibodies long-term after renal transplantation

Post-transplant circulating anti-human leukocyte antigens (HLA)-antibodies and C4d in allograft biopsies may be important in chronic rejection in renal transplant recipients (RTR). We determined the prevalence and significance of anti-HLA-antibodies and donor-specific antibodies (DSA). Sera were collected from 251 RTR >6 months post-transplant. Sera were tested using enzyme-linked immunosorbent assay (ELISA) screening for anti-HLA antibodies. Positive sera were retested with ELISA-specific panel for antibody specificity. A 11.2% of patients had anti-HLA antibodies and 4.4% had DSA. Anti-HLA antibodies were significantly associated with pretransplant sensitization, acute rejection and in multivariate analysis, higher serum creatinine (2.15 +/- 0.98 vs. 1.57 +/- 0.69 mg/dl in negative anti-HLA antibodies group). Allograft biopsies performed in a subset of patients with anti-HLA antibodies revealed that 66% had C4d in peritubular capillaries (0% in patients without antibodies). Anti-HLA antibodies were associated with a worse allograft function and in situ evidence of anti-donor humoral alloreactivity. Long-term RTR with an increase in creatinine could be screened for anti-HLA antibodies and C4d in biopsy.

Humoral Theory of Transplantation: Mechanism, Prevention, and Treatment

We discuss the potential mechanisms of antibody-induced primary endothelium injury, which includes complement-dependent pathway (membrane attack complex formation, recruitment of inflammatory cells, and complement-complement receptor-mediated phagocytosis) and complement independent pathway antibody-dependent cell cytotoxicity. Secondary to endothelium injury, the following pathological reactions are found to be responsible for progressive tissue injury and final graft function loss: platelet activation and thrombosis, pathological smooth muscle and endothelial cell proliferation, and humoral and/or cellular infiltrate-mediated parenchyma damage after endothelium injury. We also introduce three categories of therapeutic strategy in the prevention and treatment of antibody-mediated rejection: (1) inhibition and depletion of antibody producing cells (immunosuppressants, antilymphocyte antibodies, splenectomy); (2) removal or blockage of preexisting or newly developed antibodies (immunoadsorption, plasmapheresis/plasma exchange, intravenous immunoglobulin); and (3) impediment or postponement of antibody-mediated primary and secondary tissue injury (anticoagulation, glucosteroids). In conclusion, because alloantibodies have destructive effect on allografts, alloantibody monitoring becomes extremely important. It will help clinicians to determine a patient's humoral responses against allograft and will therefore direct clinicians to optimize and/or minimize immunosuppressive drug therapy.

Anti-HLA class II antibodies in kidney retransplant patients

The relevance of anti-HLA class II antibodies for kidney graft survival is still controversial. In part, this can be attributed to difficulties to detect and differentiate anti-HLA class II antibodies. Anti-HLA class II IgG antibody screening was performed by enzyme-linked immunosorbent assay. Subsequently, all anti-HLA class II-positive sera were subjected to the determination and specification using color-coded microspheres coated with purified HLA antigens. In a cohort of 934 patients awaiting kidney transplantation, 41 sera (4.4%) were positive for IgG anti-HLA class II antibodies. The presence was confirmed in 90.2% sera by retesting. Subsequently, all anti-HLA class II-positive patients (n = 27) who in the past had undergone a kidney transplantation with an HLA-DR and/or -DQ-mismatched graft were selected. In 25 of 27 sera (92.6%), the alloantibody specificities corresponded to the known previous transplant mismatches on a broad antigen level. In 20 of 27 sera (74.1%), anticlass I antibodies were detected as well. Anti-HLA-DP antibodies were seen in 24 of the 27 sera of this cohort. In the majority of the cases, the reactivities with different DPB1 alleles could be explained by involvement of a single, specific DPB1 epitope. Donor-specific anti-HLA-DR and -DQ antibodies were seen in the majority of cases with graft failure following HLA class II alloantigen exposure in prior kidney transplantations. In addition, HLA-DP may serve as a transplantation antigen in kidney transplantation, leading to a humoral response.

Humoral sensitization against rejected grafts: specific antibodies to graft immunogenic amino acid triplets

Humoral sensitization against immunogenic amino acid (aa) triplets expressed on a rejected graft was analyzed in 83 retransplant candidates. All patients had lost a graft with HLA-A,-B mismatches. The alloantibodies were detected by a complement-dependent cytotoxicity (CDC) technique and an ELISA method in parallel; they were classified as HLA graft-specific (GS) and non-GS antibodies. The aa triplet specificity of the antibodies was assessed using the HLAMatchmaker algorithm. HLA class I antibodies were detected in 74 of 78 (94%) cases, including GS reactivity in 55 (74.3%) and non-GS in 72 (97.2%), either alone (n = 19) or in parallel with GS antibodies (n = 53). For all HLA-GS-antibody-reactive patients, we defined the specificity against immunogenic aa triplets on the previous graft. Moreover, antibodies specific to graft aa triplets were observed within the non-GS antibodies among 19 of 19 and 28 of 53 cases, respectively. Therefore, aa triplet-specific antibodies against the rejected graft were present in all 74 cases with HLA class I antibodies. Antibodies against aa triplets expressed on all HLA class I-mismatched graft antigens were present in 73% of cases. The high extent of humoral alloreactivity against a rejected graft supports the decision to avoid repeated exposure to immunogenic aa triplet mismatches on a second graft. An accurate analysis for performed antibodies in these cases may be beneficial to select the most suitable second donor.

Development of Posttransplant Antidonor HLA Antibodies Is Associated with Acute Humoral Rejection and Early Graft Dysfunction

BACKGROUND

The goal of this study was to determine whether the production of posttransplant antibodies directed against donor HLA mismatches (donor specific antibody; DSA) is associated with renal allograft rejection and early graft dysfunction.

METHODS

Forty-nine adult renal allograft recipients with increased risk of rejection were enrolled during the period of October 2001 through May 2003 and were prospectively monitored for the development of anti-HLA antibodies.

RESULTS

Of 49 patients, eight (16.3 %) patients were diagnosed with acute humoral rejection (AHR) and 11/49 (22.4%) patients were diagnosed with acute cellular rejection (ACR). A strong association between pretransplant HLA sensitization and AHR was found (P=0.005). Of the eight patients diagnosed with AHR, the majority developed DSA before or concomitant with episodes of rejection (P<0.001). Only 3 of 41 patients (7.3%) without AHR developed DSA. The pathogenic role of alloantibodies was further substantiated by analyzing their association with graft function as measured by serum creatinine levels. The average serum creatinine after the third month posttransplantation in DSA producers was 2.24+/-1.01 mg/dL, while in non-DSA patients the average serum creatinine was 1.41+/-0.37 mg/dL (P<0.01).

CONCLUSION

This study reveals a strong association between the production of DSA, AHR, and early graft dysfunction. Our findings indicate that prospective monitoring for anti-HLA antibodies following transplantation is a useful test for the diagnosis and classification of AHR for identifying patients at risk of early graft dysfunction.

Vimentin Antibodies: A Non-HLA Antibody as a Potential Risk Factor in Renal Transplantation

Chronic allograft rejection is the major problem encountered in solid organ transplantation and is the end point of several complex processes. A number of recent studies show both alloimmune and autoimmune responses may have roles to play. The importance of HLA antibodies in transplantation is well documented, but despite the introduction of very sensitive HLA screening assays, antibody-mediated allograft rejection still occurs without detectable HLA antibodies. The target for antibody-mediated allograft rejection in these circumstances remains elusive, perhaps due to the variety of potential targets presented on endothelial cells. Recent studies identifying C4d and immunoglobulin deposits in patients undergoing late allograft loss provide evidence that chronic rejection involves humoral as well as cellular components. Several endothelial cell antigens that might be important in chronic rejection have been suggested, including MHC class I chain-related genes; Lewis; and the intermediate filament protein, vimentin. Vimentin is an ideal candidate antigen for antibody-mediated rejection as it is found in endothelial cells and is exposed to the immune system following surgery or by chronic allograft rejection due to endothelial cell breakdown, where the development of antibodies may cause further damage. We have developed a flow cytometric assay for the detection of antibodies to vimentin and have investigated whether HLA or vimentin antibodies are present in renal transplant recipients undergoing chronic rejection.

Serum analysis after transplant nephrectomy reveals restricted antibody specificity patterns against structurally defined HLA class I mismatches

This study deals with HLA-mismatched kidney transplants that have been removed following rejection. Sera from 27 patients were screened for HLA-specific antibodies by direct complement-dependent lymphocytotoxicity with HLA-typed cell panels. Circulating donor-specific antibodies were detected in 3 cases (11%) before and in 26 cases (97%) after allograft nephrectomy. These findings demonstrate the production of donor-specific antibodies in patients with rejected transplants, but in most cases, they were undetectable before nephrectomy, because the graft had adsorbed them. With an HLAMatchmaker-based serum analysis program, we observed restricted antibody specificity patterns against amino acid triplet-defined epitopes on donor HLA-A,B antigens. Many donor triplets were non-reactive while others were apparently recognized by antibodies. In some patients, the donor triplet specific antibodies persisted for a long time whereas in many other patients, they became undetectable after a few months. The characterization of the antibody specificity profiles of post-allograft nephrectomy sera is clinically useful in defining criteria of HLA mismatch acceptability for sensitized patients awaiting another transplant. It provides also opportunities for determining the relative immunogenicity of mismatched triplets.

Donor-Specific Antibodies in Allograft Rejection: Clinical and Experimental Data

The ability of donor-specific major histocompatibility complex alloantibodies to destroy a transplanted organ within minutes, the so-called hyperacute rejection phenomenon, has been known for a long time. It is a clear demonstration of the possible cytotoxic effect of antibodies. Apart from this particular situation, the role of antibodies in inducing acute or chronic allograft rejection remains controversial. Many clinical data have shown that transplant recipients capable of developing class I or class II anti-HLA antibodies experienced shorter survival periods than those who were not. This fact, in accordance with experimental data, only demonstrates that high antibody responders reject a transplant more easily than low responders. More interestingly, there is now increasing evidence that posttransplant appearance of donor-specific alloantibodies, and probably of alloreactive-induced autoantibodies, is strongly correlated with reduced graft survival rate, especially from chronic rejection. We demonstrated that donor-specific HLA antibodies can be found in more than 70% of transplanted kidneys with chronic allograft nephropathy, and that the intragraft presence of such antibodies is significantly correlated with high numbers of plasma cells on early biopsies and C4d deposits, a recognized marker of humoral rejection. It is likely that non-HLA antibodies also play a deleterious role in organ transplant outcome, particularly the heterogeneous group of anti-endothelial cells antibodies, anti-MIC antibodies, autoantibodies and some others with no recognized target. Convincing experimental data, especially using B cell and T cell deficient mice, strongly suggest that B cells and donor-specific antibodies are required for fully developed chronic allograft rejection. The role of antibodies in inducing the cascade of cytokines and growth factors leading to tissue lesions is of increasing interest since it is now possible to control B cell proliferation and antibody production.

Basic mechanisms of humoral rejection

Humoral rejection is among the most vexing problems afflicting organ transplants. Triggered by antibodies predominantly against donor human leukocyte (HLA), humoral rejection can now be understood through consideration of basic mechanisms of immunity to foreign antigens and impact of humoral immunity on blood vessels. Basic considerations may also shed light on mechanisms by which various treatments have recently brought about vastly improved outcomes.

HLA-specific antibodies are risk factors for lymphocytic bronchiolitis and chronic lung allograft dysfunction

Bronchiolitis obliterans syndrome (BOS) represents a major limitation in lung transplantation. While acute rejection is widely considered the most important risk factor for BOS, the impact of HLA-specific antibodies is less understood. Of 51 lung recipients who were prospectively tested during a 4.2 +/- 1.6-year period, 14 patients developed HLA-specific antibodies. A multi-factorial analysis was performed to correlate the prevalence of BOS with HLA antibodies, persistent-recurrent acute rejection (ACR-PR), lymphocytic bronchiolitis, and HLA-A, -B, and -DR mismatches. HLA-specific antibodies were associated with ACR-PR (10/14 vs. 11/37 with no antibodies, p < 0.05), lymphocytic bronchiolitis (8/14 vs. 10/37, p < 0.05), and BOS (10/14, vs. 9/37, p < 0.005). Other risk factors for BOS were: lymphocytic bronchiolitis (13/18 vs. 6/33 with no lymphocytic bronchiolitis, p < 0.0001), ACR-PR (12/21 vs. 7/30 with no ACR-PR, p < 0.05), and the number of HLA-DR mismatches (1.7 +/- 0.48 in BOS vs. 1.2 +/- 0.63 without BOS, p < 0.05). The presence of antibodies exhibited a cumulative effect on BOS when it was associated with either lymphocytic bronchiolitis or ACR-PR. The complex relationship between the development of HLA antibodies and acute and chronic lung allograft rejection determines the importance of post-transplant screening for HLA-specific antibodies as a prognostic element for lung allograft outcome.

Donor-specific sensitization by cadaveric venous allografts used for arterial reconstruction in peripheral arterial occlusive vascular disease

The use of allogeneic venous grafts from postmortal organ donors allows for the reconstruction of critically affected arteries in patients with peripheral occlusive vascular disease. We were interested to determine the prevalence and specificity of anti-HLA antibodies in patients after allogeneic vein transplantation. Anti-HLA class I and II alloantibodies were analyzed by flowcytometric analysis using color-coded microbeads coated with HLA antigens including recombinant single antigens. Nine out of 10 patients involving 12 venous allografts were positive for anti-HLA alloantibodies. All antibody-positive patients carried both anti-HLA class I and II alloantibodies. Anti-donor HLA specificity of the anti-HLA alloantibodies was seen in seven out of nine patients for anti-class I antibodies and in eight out of nine patients for anti-HLA class II antibodies. A high rate of donor-specific allosensitization was seen after allogeneic venous transplantation. In conclusion, allosensitization not only includes a humoral response against the constitutively expressed class I antigens but also extends to class II antigens.

Correlation between human leukocyte antigen antibody production and serum creatinine in patients receiving sirolimus monotherapy after Campath-1H induction

BACKGROUND

In this study, we determined whether Campath-1H induction followed by sirolimus monotherapy inhibited alloantibody production in renal transplantation. Second, we evaluated the correlation between human leukocyte antigen (HLA) antibody production and serum creatinine levels.

METHODS

Sera were taken 1 to 24 months after transplantation from 24 patients treated with Campath-1H and sirolimus and tested for serum creatinine and HLA-specific antibody by using flow cytometry and enzyme-linked immunosorbent assay.

RESULTS

Ten (42%) of the 24 patients treated with Campath-1H and sirolimus produced HLA antibodies. Six of these 10 developed both donor-specific antibodies (DSAs) and non-donor-specific antibodies (NDSAs), whereas only NDSAs were detected in the other four patients. In patients with biopsy-diagnosed humoral rejection (C4d+), serum levels of both DSA and NDSA significantly correlated with patient serum creatinine levels. Rejection treatment successfully reduced both DSAs and NDSAs and reversed humoral rejection.

CONCLUSIONS

The numeric relationship between serum creatinine and DSA levels suggests a causal relationship between alloantibody and transplant rejection.

HLA class I signal transduction is dependent on Rho GTPase and ROK

Chronic rejection is the major limitation to long-term allograft survival. HLA class I signaling pathways have been implicated in this process because ligation of class I molecules by anti-HLA antibodies (Ab) initiates intracellular signals in smooth muscle cells (SMC) and endothelial cells (EC) that synergize with growth factor receptors to elicit cell survival and proliferation. Anti-HLA Ab mediate cell proliferation and survival through a focal adhesion kinase dependent pathway that requires the integrity of the actin cytoskeleton. In this study, we investigated the role of Rho and Rho-kinase (ROK) in class I signal transduction. We show that class I ligation results in activation of Rho and increased stress fiber formation. In addition, inhibitors of Rho GTPase and ROK block HLA class I-mediated tyrosyl phosphorylation of paxillin and FAK, central elements of the focal adhesion signaling complex. These results suggest that HLA class I-induced signaling in EC is dependent on Rho GTPase and ROK.

Detection and specification of noncomplement binding anti-HLA alloantibodies

The aim of the study was to investigate the distribution of human leukocyte antigen (HLA) -specific immunoglobulin (Ig) isotypes/subclasses in alloimmunized patients awaiting a kidney retransplant. Sera from 102 patients were analyzed for the presence of anti-HLA-A, anti-HLA-B alloantibodies by complement-dependent cytotoxicity test with the addition of dithiothreitol (CDC+DTT). Furthermore, anti-HLA class I and class II alloantibodies were determined using a commercial solid-phase (enzyme-linked immunosorbent assay [ELISA]) system. The respective isotypes/subclasses were defined by replacing the IgG1-4 secondary antibody with IgG1-, IgG2-, IgG3-, IgG4-, IgA1-, IgA2-, and IgM-specific antibodies. The HLA specificities of the noncomplement-binding IgG2 and IgG4 antibodies were determined and compared with the mismatches from the failed transplants. Thirty-eight of 102 (37%) sera were positive in the class I CDC+DTT, in contrast to 41 of 102 (40%) detected by class I ELISA and 47 of 102 (46%) by class II ELISA. Seventeen of 102 (17%) positive reaction were observed for the IgM-isotype, whereas none were detected for the IgA-isotype. Twenty-five of 102 (25 %) sera contained noncomplement-binding IgG2 and/or IgG4 antibodies; in the majority of the cases, 22 of 25 (88%) were directed against the organ donor antigen. These data show that donor-specific, noncomplement-binding IgG2 and IgG4 alloantibodies exist with high prevalence in HLA-immunized retransplant candidates. Therefore, a thorough antibody screening workup, including CDC with or without DTT and ELISA screening should be performed for patients before they reenter the waiting list. Defining the Ig isotypes and subclasses can be helpful to explain inconsistent results.

Anti-HLA antibodies in heart transplantation

We have analyzed the relationship between the development of transplant-related coronary artery disease (TRCAD) and the following potential risk factors: (a). number of HLA mismatches between recipient and donor; (b). production of anti-HLA antibodies; (c). growth of lymphocytes infiltrating the graft; and (d). frequency of biopsy proven episodes of acute rejection. The study population consisted of 285 adult heart allograft recipients who were monitored over a period of two years or more. The results demonstrate a significant correlation between TRCAD, generation of anti-HLA class II antibodies and potential of lymphocytes infiltrating the graft to proliferate ex-vivo in medium containing IL-2. Humoral and cellular immune responses to HLA-DR antigens expressed by the graft seem to underlie the development of TRCAD.

Weak humoral posttransplant alloresponse after a well-HLA-matched cadaveric kidney transplantation

BACKGROUND

Screening of donor-specific antibodies or alloantibodies after kidney transplantation has not been performed routinely. The aim of this study was to evaluate the humoral antidonor and alloresponse of immunologically low-risk recipients of cadaveric renal allografts during the first posttransplant year.

METHODS

Alloresponse against the donor was analyzed by means of T-cell immunoglobulin (Ig)G and IgM and B cell IgG flow cytometric crossmatch (FCXM) tests with sera from days 0, 21, 90, and 365 posttransplant. In addition, panel reactive anti-human leukocyte antigen (HLA) class I and class II antibodies (PRA I and PRA II) were analyzed using flow cytometric methods. The recipients were treated either with a low initial cyclosporine regimen with single-bolus antithymocyte globulin (ATG) or basiliximab induction or conventional cyclosporine triple therapy.

RESULTS

No significant posttransplant anti-HLA class I or class II sensitization was found in the recipients as a whole. Recipients receiving a single-bolus ATG showed significantly higher proportion of PRA I positivity in the day 21 sample compared with the other groups. Flow cytometric donor-specific T- and B-cell IgG alloresponses remained low, but the proportion of T-cell IgM crossmatch-positive recipients increased during the study. Positive T-cell IgM FCXM was found to be associated with acute rejection episodes and cytomegalovirus (CMV) infections.

CONCLUSIONS

In immunologically low-risk kidney-graft recipients, positive T-cell IgM FCXM at transplantation was found to be a risk factor for rejection episodes. Conversion of T-cell IgM FCXM to positive was found to be associated with CMV infections.

Acute humoral rejection of human lung allografts and elevation of C4d in bronchoalveolar lavage fluid

Antibody-mediated rejection is well established for renal allografts but remains controversial for lung allografts. Cardinal features of antibody-mediated rejection in renal allografts include antibodies to donor human leukocyte antigen (HLA) and evidence for antibody action, such as complement activation demonstrated by C4d deposition. We report a lung allograft recipient with circulating antibodies to donor HLA who failed treatment for acute cellular rejection but responded to therapy for humoral rejection. To address the second criteria for antibody-mediated rejection, we determined whether complement activation could be detected by measuring C4d in bronchoalveolar lavage fluid (BALF) by ELISA. Airway allergen challenge of asthmatics activates the complement pathway; therefore, we used BALF from asthmatics pre- and post-allergen challenge to measure C4d. These controls demonstrated that ELISA could detect increases in C4d after allergen challenge. BALF from the index patient had elevated C4d concomitant with graft dysfunction and anti-donor HLA in the absence of infection. Analysis of BALF from 25 additional lung allograft recipients showed that C4d concentrations >100 ng/mL were correlated with anti-HLA antibodies (p = 0.006), but were also observed with infection and in asyptomatic patients. The findings support the occurrence of anti-HLA-mediated lung allograft rejection and suggest that C4d measurement in BALF may be useful in diagnosis.

Immune regulation and graft survival in kidney transplant recipients are both enhanced by human leukocyte antigen matching

We hypothesized that donor/recipient sharing of the human leukocyte antigen (HLA) involved in allopeptide presentation to the T regulatory cell increases the incidence of immune regulation, thus contributing to long-term graft survival. Peripheral blood mononuclear cells (PBMC) were obtained from 40 living related donor (LRD) and 31 cadaver renal transplant recipients. The trans vivo delayed type hypersensitivity (DTH) assay was used to assign patients to regulator, nonregulator, and sensitized categories. In a large cohort (n=1934 patients), primary graft survival and rejection episodes were analyzed using a log rank test for comparison with the DTH results. The highest incidence of regulated anti-donor DTH was observed in the LRD HLA-identical group (6/6; 100%) followed by the LRD HLA 1 haplotype matched group (18/27; 67%). Within the cadaver population, two DR-matched recipients had a higher frequency of regulated anti-donor DTH (6/11; 55%) than 1 & 0 DR-matched recipients (3/18; 17%). In a multivariate model, matching for HLA-DR alone, or for DR plus DQ was significantly (p=0.045, p=0.041) correlated with DTH regulation. The better HLA-matched groups showed the highest incidence of DTH regulation and, in a larger retrospective analysis, displayed better graft survival and freedom from acute rejection (p<0.0001). HLA matching, and HLA-DR matching in particular, correlates with the incidence of immune regulation after kidney transplantation.

Mycophenolate mofetil in solid-organ transplantation

This review focuses on the use of mycophenolate mofetil (MMF) as an immunosuppressive agent in solid-organ transplantation. MMF, a non-competitive inhibitor of inosine monophosphate dehydrogenase, blocks de novo purine synthesis in T and B lymphocytes, resulting in the selective inhibition of proliferation of these cells in response to antigenic stimuli. MMF may also promote apoptosis of these cells. The immunosuppressive ability of MMF is thought to derive mainly from the inhibition of inosine monophosphate dehydrogenase. The other effects of MMF include suppression of antibody synthesis by B lymphocytes, inhibition of proliferation of smooth muscle cells in culture and impaired glycosylation of adhesion molecules. MMF may exhibit anti-inflammatory effects resulting from decreased activity of the inducible form of nitric oxide synthase, a consequence of depletion of tetrahydrobiopterin, which leads to decreased generation of peroxynitrite, a pro-inflammatory molecule. The pharmacokinetics, pharmacodynamics and principles underlying therapeutic drug monitoring of MMF are reviewed. The results of the pivotal clinical trials of MMF in kidney and heart transplantation are discussed and a summary of the major studies demonstrating a positive effect of MMF on renal transplantation outcomes is presented. The use of MMF in the context of ABO-incompatible renal transplantation, renal transplantation in highly sensitised and cross-match positive recipients, humoral rejection of renal allografts, chronic allograft nephropathy and steroid/calcineurin inhibitor minimisation in renal transplantation are also discussed.