The significance of donor-specific HLA antibodies in rejection and ductopenia development in ABO compatible liver transplantation

Clinical relevance of human leukocyte antigen antibodies in liver, heart, lung and intestine transplantation

PURPOSE OF REVIEW

Solid phase assays identify human leukocyte antigen (HLA) antibodies with a great sensitivity. Whether to accept or decline an organ if the virtual crossmatch is positive, when to monitor and whether to treat de-novo donor-specific antibody (DSA) posttransplant remain challenging issues for the transplant clinician.

RECENT FINDINGS

Technologies that can differentiate which antibodies pose the greatest risk for antibody-mediated rejection (AMR) are evolving. Complement fixing luminex assays have been used to predict high-risk antibodies, but using these assays alone will miss some preformed antibodies. How these technologies fit into the laboratory's testing algorithm will likely need to be individualized. Posttransplant de-novo DSAs are associated with inferior outcomes. In hearts, similar to renal transplantation, acute rejection is a risk factor for developing de-novo DSA. Further data are needed to determine whether other risk factors are similar to those reported for renal transplants. Antibodies to self-antigens are increasingly recognized posttransplant and how the alloimmune response contributes to altered autoregulation is a current research focus.

SUMMARY

Identification of DSA enables the clinician to make informed decisions regarding whether or not to accept an organ and if augmented immunosuppression is indicated. Monitoring for DSA posttransplant identifies recipients at a greater risk for AMR and can guide management. However, the best approach to dealing with de-novo DSA remains unclear.

Generation of highly effective and stable murine alloreactive Treg cells by combined anti-CD4 mAb, TGF-β, and RA treatment

The transfer of alloreactive regulatory T (aTreg) cells into transplant recipients represents an attractive treatment option to improve long-term graft acceptance. We recently described a protocol for the generation of aTreg cells in mice using a nondepleting anti-CD4 antibody (aCD4). Here, we investigated whether adding TGF-β and retinoic acid (RA) or rapamycin (Rapa) can further improve aTreg-cell generation and function. Murine CD4(+) T cells were cultured with allogeneic B cells in the presence of aCD4 alone, aCD4+TGF-β+RA or aCD4+Rapa. Addition of TGF-β+RA or Rapa resulted in an increase of CD25(+)Foxp3(+)-expressing T cells. Expression of CD40L and production of IFN-γ and IL-17 was abolished in aCD4+TGF-β+RA aTreg cells. Additionally, aCD4+TGF-β+RA aTreg cells showed the highest level of Helios and Neuropilin-1 co-expression. Although CD25(+)Foxp3(+) cells from all culture conditions displayed complete demethylation of the Treg-specific demethylated region, aCD4+TGF-β+RA Treg cells showed the most stable Foxp3 expression upon restimulation. Consequently, aCD4+TGF-β+RA aTreg cells suppressed effector T-cell differentiation more effectively in comparison to aTreg cells harvested from all other cultures, and furthermore inhibited acute graft versus host disease and especially skin transplant rejection. Thus, addition of TGF-β+RA seems to be superior over Rapa in stabilising the phenotype and functional capacity of aTreg cells.

Preformed class II donor-specific antibodies are associated with an increased risk of early rejection after liver transplantation

Preformed donor-specific human leukocyte antigen antibodies (DSAs) are considered a contraindication to the transplantation of most solid organs other than the liver. Conflicting data currently exist on the importance of preformed DSAs in rejection and patient survival after liver transplantation (LT). To evaluate preformed DSAs in LT, we retrospectively analyzed prospectively collected samples from all adult recipients of primary LT without another organ from January 1, 2000 to May 31, 2009 with a pre-LT sample available (95.8% of the patients). Fourteen percent of the patients had preformed class I and/or II DSAs with a mean fluorescence intensity (MFI) ≥ 5000. Preformed class I DSAs with an MFI ≥ 5000 remained persistent in only 5% of patients and were not associated with rejection. Preformed class II DSAs with an MFI of 5000 to 10,000 remained persistent in 23% of patients, and this rate increased to 33% for patients whose MFI was ≥10,000 (P < 0.001). Preformed class II DSAs in multivariable Cox proportional hazards modeling were associated with an increased risk of early rejection [hazard ratio (HR) = 1.58; p = 0.004]. In addition, multivariate modeling showed that in comparison with no DSAs (MFI < 1000), preformed class I and/or II DSAs with an MFI ≥ 5000 were independently correlated with the risk of death (HR = 1.51; p = 0.02).

Liver transplantation with a strongly positive crossmatch: case study and literature review

A positive crossmatch has been associated with increased risk in liver transplantation. To study the clinical significance of preformed donor-specific human leukocyte antigen antibodies (DSAs) in liver transplantation, we reviewed patients who underwent liver transplantation with a strongly positive flow cytometry crossmatch. DSAs were evaluated with a Luminex solid phase assay. The complement-fixing ability of DSAs was tested with a complement component 1q (C1q) assay. Using an assay correlation between complement-dependent cytotoxicity crossmatch, flow cytometry crossmatch, and DSA results, we reviewed the effects of DSAs on the outcomes of our patients as well as reported cases in the literature. Five of 69 liver recipients had a strongly positive crossmatch: 4 had a positive T cell crossmatch [median channel shift (MCS) = 383.5 ± 38.9], and 5 had a positive B cell crossmatch (MCS = 408.8 ± 52.3). The DSAs were class I only in 1 patient, class I and II in 3 patients, and class II only in 1 patient. Cholestasis, acute rejection, or both were observed in 3 of the 4 patients with a positive T cell crossmatch with an MCS approximately greater than 300. The C1q assay was positive for 3 patients. Two had either persistent cholestasis or early acute rejection. One patient who was treated with preemptive intravenous immunoglobulin had an unremarkable outcome despite a positive C1q result. One of the 2 patients with a negative C1q assay experienced persistent cholestasis and early and recurrent acute rejection; the other had an unremarkable outcome. None of the patients died or lost a graft within the first year of transplantation. Our study suggests that human leukocyte antigen antibody screening, flow cytometry crossmatch MCS levels, DSA mean fluorescent intensity levels, and C1q assays may be useful in assessing the risk of antibody-mediated rejection and timely interventions in liver transplantation.

Elevation of CD4+ differentiated memory T cells is associated with acute cellular and antibody-mediated rejection after liver transplantation

BACKGROUND

It is now well known that the outcome after allogeneic transplantation, such as incidence of acute rejections, very much depends on the individual's immune reactivity status. There is also increasing evidence that the presence of preexisting memory T cells can affect antigraft immune responses.

METHODS

In a prospective study, we monitored peripheral CD4 and CD8 central memory, effector memory, and terminal differentiated effector memory (TEMRA) T cells in 55 patients who underwent deceased liver transplantation and received conventional immunosuppressive treatment with or without basiliximab induction. The primary endpoint of the study was acute allograft rejection during a 1-year follow-up period.

RESULTS

We observed significantly increased proportions of CD4 and CD8 TEMRA cells in patients before transplantation compared with healthy controls (P=0.006 and 0.009, respectively). This characteristic was independent of the underlying disease. In patients with no signs of acute rejection, we observed an immediate reduction of CD4 TEMRA cells. In contrast, patients who experienced acute cellular rejection, and especially antibody-mediated rejection, displayed persistent elevated TEMRA cells (P=0.017 and 0.027, respectively). Basiliximab induction therapy did not influence CD4 and CD8 TEMRA numbers.

CONCLUSIONS

Conventional immunosuppressive or basiliximab treatment cannot control the persistence of TEMRA T cells, which may contribute to acute cellular rejection and antibody-mediated rejection after liver transplantation. In the future, specific targeting of TEMRA cells in selected patients may prevent the occurrence of difficult to treat steroid-resistant rejections, thereby leading to improved patient outcome.

Impact of donor-specific antibodies on results of liver transplantation

PURPOSE OF REVIEW

To critically examine the recent literature evaluating the importance of HLA donor-specific antibody (DSA) impact on liver transplant and simultaneous liver-kidney transplant (SLKT) outcomes.

RECENT FINDINGS

Many preformed DSAs, especially of low mean fluorescence intensity (MFI), are absorbed by the liver at transplant. However, patients with post-liver transplant DSA, especially of higher MFI, are at increased risk of acute and chronic rejection. C4d staining, when positive, may be helpful but lacks sensitivity especially in formalin tissue. SLKT recipients may need close follow-up when class II DSA is found, as the liver protects the kidney from hyperacute rejection, but can still cause early renal antibody-mediated rejection, liver allograft rejection, and impair patient, liver allograft, and renal allograft survival.

SUMMARY

Some DSAs are relevant in liver transplant and can lead to acute and chronic allograft rejection. However, before clinical practice patterns can change we must create unified diagnostic criteria, define the pathologic potential of different DSAs, and improve the specificity of current testing.

Tissue biopsy monitoring of operational tolerance in liver allograft recipients

PURPOSE OF REVIEW

Highly selected, long-surviving, liver allograft recipients with normal/near normal liver injury tests can be weaned from immunosuppression. Baseline biopsies document changes before weaning and can help stratify risk of rejection or dysfunction after weaning; biopsies after weaning are used to study mechanisms of operational tolerance and to monitor for subclinical events.

RECENT FINDINGS

Clinicopathological features associated with successful weaning include a lack of sensitization [negative donor-specific antibodies (DSA) and lack of tissue C4d deposits]; 'inexperienced' recipient immune system with limited potential for cross-reactivity (less immunological memory; infant recipients); noninflamed allograft in those with nonviral, nonimmunological original diseases; upregulation of liver genes associated with iron metabolism; allograft colonization with 'immunosuppressive' cells (Treg and γδ-1>γδ-2); and longer time on immunosuppression, which might signal slow clonal deletion or silencing. The differential diagnosis of histopathological findings detected before and after weaning includes emerging infections, typical and atypical cellular rejection, indolent antibody-mediated rejection, 'autoimmunity', and other causes of progressive fibrosis.

SUMMARY

Operationally tolerant liver allograft recipients can be successfully managed with very low, and sometimes no immunosuppression, but challenges exist. Newer approaches to tissue pathology and tissue, serum, and cross-platform analytics are needed to predict successful weaning and to monitor for subclinical events.

De novo donor-specific HLA antibodies decrease patient and graft survival in liver transplant recipients

The role of de novo donor-specific HLA antibodies (DSA) in liver transplantation remains unknown as most of the previous studies have only focused on preformed HLA antibodies. To understand the significance of de novo DSA, we designed a retrospective cohort study of 749 adult liver transplant recipients with pre- and posttransplant serum samples that were analyzed for DSA. We found that 8.1% of patients developed de novo DSA 1 year after transplant; almost all de novo DSAs were against HLA class II antigens, and the majority were against DQ antigens. In multivariable modeling, the use of cyclosporine (as opposed to tacrolimus) and low calcineurin inhibitor levels increased the risk of de novo DSA formation, while a calculated MELD score >15 at transplant and recipient age >60 years old reduced the risk. Multivariable analysis also demonstrated that patients with de novo DSA at 1-year had significantly lower patient and graft survival. In conclusion, we demonstrate that de novo DSA development after liver transplantation is an independent risk factor for patient death and graft loss.

Significance of semiquantitative assessment of preformed donor-specific antibody using luminex single bead assay in living related liver transplantation

Aim. To analyze the risks of preoperatively produced donor-specific antibody (DSA) in liver transplantation. Methods. DSA was assessed using direct complement-dependent cytotoxicity (CDC) and anti-human globulin- (AHG-) CDC tests, as well as the Luminex Single Antigen assay. Among 616 patients undergoing blood type identical or compatible living donor liver transplantation (LDLT), 21 patients were positive for CDC or AHG-CDC tests, and the preserved serum from 18 patients was examined to determine targeted Class I and II antigens. The relationships between the mean fluorescence intensity (MFI) of DSA and the clinical outcomes were analyzed. Results. Patients were divided into 3 groups according to the MFI of anti-Class I DSA: high (11 patients with MFI > 10,000), low (2 patients with MFI < 10,000), and negative (5 patients) MFI groups. Six of 11 patients with high Class-I DSA showed positive Class-II DSA. Hospital death occurred in 7 patients of the high MFI group. High MFI was a significant risk factor for mortality (P = 0.0155). Univariate analysis showed a significant correlation between MFI strength and C4d deposition (P = 0.0498). Conclusions. HLA Class I DSA with MFI > 10,000 had a significant negative effect on the clinical outcome of patients with preformed DSA in LDLT.

Four-year allograft survival in a highly sensitized combined liver-kidney transplant patient despite unsuccessful anti-HLA antibody reduction with rituximab, splenectomy, and bortezomib

Although donor-specific lymphocytotoxic antibodies are regarded as a contraindication for kidney transplantation (KTx), the data available for liver or combined liver or kidney transplantation (cLKTx) are scarce. Here, we report a case of a highly sensitized young man receiving his sixth liver and second kidney graft. Multiple anti-HLA antibodies were present at the time of transplantation. As a result of suspected antibody-mediated graft damage, the patient was treated with rituximab, plasmapheresis, intravenous immunoglobulins, splenectomy, and bortezomib to decrease the antibody production. So far, patient and allograft survival has reached 4 years despite failure to achieve a permanent reduction of anti-HLA antibodies, and particularly nondonor directed antibodies.

Antibody-mediated rejection in the liver allograft

PURPOSE OF REVIEW

There is increasing evidence to suggest that antibody-mediated mechanisms play a role in the pathogenesis of liver allograft rejection. This article will review the pathology of antibody-mediated rejection (AMR) focusing on recent studies which have improved our understanding of the clinicopathological features and diagnostic approaches.

RECENT FINDINGS

Recent studies have investigated the patterns of immunohistochemical staining for C4d as a tissue marker of AMR in posttransplant biopsies, and have correlated these findings with other histopathological changes and with the presence of donor-specific antibodies (DSAs). These studies have highlighted the diagnostic applications and limitations of C4d immunostaining. They have also emphasized the importance of using strict criteria for defining 'pure' AMR in the liver allograft - that is, graft dysfunction associated with compatible histological findings (typically resembling biliary obstruction), the presence of DSAs and diffusely positive staining for C4d.

SUMMARY

Pure AMR is relatively uncommon in ABO-compatible grafts - it should be diagnosed on the basis of strict criteria and requires treatment with antibody-depleting immunosuppression. C4d immunostaining in isolation has limited diagnostic value. However, the presence of diffuse C4d immunostaining (involving endothelium or stroma in >50% of portal tracts or sinusoids) suggests a significant component of antibody-mediated graft damage. In a person with suggestive histological features, this finding should prompt testing for DSAs. Even in the absence of typical histological features of AMR, the combined presence of DSAs and diffuse C4d positivity is associated with more frequent or severe acute and chronic rejection, which may also warrant treatment with antibody-depleting immunosuppression.

Consensus guidelines on the testing and clinical management issues associated with HLA and non-HLA antibodies in transplantation

BACKGROUND

The introduction of solid-phase immunoassay (SPI) technology for the detection and characterization of human leukocyte antigen (HLA) antibodies in transplantation while providing greater sensitivity than was obtainable by complement-dependent lymphocytotoxicity (CDC) assays has resulted in a new paradigm with respect to the interpretation of donor-specific antibodies (DSA). Although the SPI assay performed on the Luminex instrument (hereafter referred to as the Luminex assay), in particular, has permitted the detection of antibodies not detectable by CDC, the clinical significance of these antibodies is incompletely understood. Nevertheless, the detection of these antibodies has led to changes in the clinical management of sensitized patients. In addition, SPI testing raises technical issues that require resolution and careful consideration when interpreting antibody results.

METHODS

With this background, The Transplantation Society convened a group of laboratory and clinical experts in the field of transplantation to prepare a consensus report and make recommendations on the use of this new technology based on both published evidence and expert opinion. Three working groups were formed to address (a) the technical issues with respect to the use of this technology, (b) the interpretation of pretransplantation antibody testing in the context of various clinical settings and organ transplant types (kidney, heart, lung, liver, pancreas, intestinal, and islet cells), and (c) the application of antibody testing in the posttransplantation setting. The three groups were established in November 2011 and convened for a "Consensus Conference on Antibodies in Transplantation" in Rome, Italy, in May 2012. The deliberations of the three groups meeting independently and then together are the bases for this report.

RESULTS

A comprehensive list of recommendations was prepared by each group. A summary of the key recommendations follows. Technical Group: (a) SPI must be used for the detection of pretransplantation HLA antibodies in solid organ transplant recipients and, in particular, the use of the single-antigen bead assay to detect antibodies to HLA loci, such as Cw, DQA, DPA, and DPB, which are not readily detected by other methods. (b) The use of SPI for antibody detection should be supplemented with cell-based assays to examine the correlations between the two types of assays and to establish the likelihood of a positive crossmatch (XM). (c) There must be an awareness of the technical factors that can influence the results and their clinical interpretation when using the Luminex bead technology, such as variation in antigen density and the presence of denatured antigen on the beads. Pretransplantation Group: (a) Risk categories should be established based on the antibody and the XM results obtained. (b) DSA detected by CDC and a positive XM should be avoided due to their strong association with antibody-mediated rejection and graft loss. (c) A renal transplantation can be performed in the absence of a prospective XM if single-antigen bead screening for antibodies to all class I and II HLA loci is negative. This decision, however, needs to be taken in agreement with local clinical programs and the relevant regulatory bodies. (d) The presence of DSA HLA antibodies should be avoided in heart and lung transplantation and considered a risk factor for liver, intestinal, and islet cell transplantation. Posttransplantation Group: (a) High-risk patients (i.e., desensitized or DSA positive/XM negative) should be monitored by measurement of DSA and protocol biopsies in the first 3 months after transplantation. (b) Intermediate-risk patients (history of DSA but currently negative) should be monitored for DSA within the first month. If DSA is present, a biopsy should be performed. (c) Low-risk patients (nonsensitized first transplantation) should be screened for DSA at least once 3 to 12 months after transplantation. If DSA is detected, a biopsy should be performed. In all three categories, the recommendations for subsequent treatment are based on the biopsy results.

CONCLUSIONS

A comprehensive list of recommendations is provided covering the technical and pretransplantation and posttransplantation monitoring of HLA antibodies in solid organ transplantation. The recommendations are intended to provide state-of-the-art guidance in the use and clinical application of recently developed methods for HLA antibody detection when used in conjunction with traditional methods.

Predicting operational tolerance in pediatric living-donor liver transplantation by absence of HLA antibodies

BACKGROUND

The role of anti-human leukocyte antigen (HLA) antibodies in operational tolerance (OT) after pediatric living-donor liver transplantation (LDLT) remains inconclusive. We investigated whether the presence of HLA antibodies impeded the development of OT.

METHODS

We retrospectively examined the prevalence of anti-HLA antibodies in pediatric LDLT recipients before transplantation and at 3 weeks after transplantation and analyzed the significance of those antibodies in relation to later OT. Forty pediatric LDLTs were performed between April 1996 and December 2000 and followed up through July 2011, with sera available for measurement of HLA antibodies. Seventeen patients achieved OT (mean follow-up, 4571.9±544.7 days) and 23 patients did not achieve OT (mean follow-up, 4532.0±425.4 days). Protocol liver biopsy was done for 14 OT patients and 16 non-OT patients. Their sera were tested for anti-HLA class I and II antibodies using the LABScreen single antigen beads test, in which a 1000 mean fluorescence value was considered positive.

RESULTS

The prevalence of antibodies after transplantation in non-OT patients was higher than in OT patients (95.2% vs. 73.3%; P<0.001). The highest mean fluorescence intensity of antibodies was significantly higher in non-OT patients than in OT patients. The prevalence of HLA-B, HLA-C, HLA-DQ, and HLA-DR antibodies was significantly higher in non-OT patients than in OT patients. The highest mean fluorescence intensity of HLA-A, HLA-B, and HLA-DQ observed in non-OT patients was significantly higher than those in OT patients.

CONCLUSIONS

In our study, posttransplantation HLA antibodies were associated with the future absence of OT. A prospective study with more patients is necessary to confirm the predictive value of HLA antibodies for OT.

Class II alloantibody and mortality in simultaneous liver-kidney transplantation

Hyperacute kidney rejection is unusual in crossmatch positive recipients of simultaneous liver-kidney transplants (SLKT). However, recent data suggest that these patients remain at risk for antibody-mediated kidney rejection. To further investigate the risk associated with donor-specific alloantibodies (DSA) in SLKT, we studied 86 consecutive SLKT patients with an available pre-SLKT serum sample. Serum samples were analyzed in a blinded fashion for HLA DSA using single antigen beads (median florescence intensity≥2,000=positive). Post-SLKT samples were analyzed when available (76%). Thirty patients had preformed DSA, and nine developed de novo DSA. Preformed class I DSA did not change the risk of rejection, patient or allograft survival. In contrast, preformed class II DSA was associated with a markedly increased risk of renal antibody mediated rejection (AMR) (p=0.006), liver allograft rejection (p=0.002), patient death (p=0.02), liver allograft loss (p=0.02) and renal allograft loss (p=0.045). Multivariable modeling showed class II DSA (preformed or de novo) to be an independent predictor of patient death (HR=2.2; p=0.043) and liver allograft loss (HR=2.2; p=0.044). These data warrant reconsideration of the approach to DSA in SLKT.

Precision diagnostics in transplantation: from bench to bedside

The Canadian and American Societies of Transplantation held a symposium on February 22, 2012 in Quebec City focused on discovery, validation and translation of new diagnostic tools into clinical transplantation. The symposium focused on antibody testing, transplantation pathology, molecular diagnostics and laboratory support for the incompatible patient. There is an unmet need for more precise diagnostic approaches in transplantation. Significant potential for increasing the diagnostic precision in transplantation was recognized through the integration of conventional histopathology, molecular technologies and sensitive antibody testing into one enhanced diagnostic system.

Meeting report of the International Liver Transplantation Society's 18th annual international congress: Hilton San Francisco Hotel, San Francisco, CA, May 16-19, 2012

From May 16-19, 2012, the International Liver Transplantation Society held its annual congress in San Francisco, CA. More than 1300 registrants attended the meeting, which included a premeeting conference entitled Balancing Risk in Liver Transplantation, focused topic sessions, and a variety of oral and poster presentations. This report is not all-inclusive and focuses on specific research abstracts on key topics in liver transplantation. As always, the new data herein are presented in the context of the published literature to further enhance knowledge in the field.

Progressive graft fibrosis and donor-specific human leukocyte antigen antibodies in pediatric late liver allografts

The role of donor-specific anti-human leukocyte antigen antibodies (DSAs) that develop late after living donor liver transplantation is unknown. Seventy-nine pediatric recipients who had good graft function and underwent protocol liver biopsy more than 5 years after transplantation (median = 11 years, range = 5-20 years) were reviewed. DSAs were determined with the Luminex single-antigen bead assay at the time of the last biopsy, and complement component 4d (C4d) immunostaining was assessed at the times of the last biopsy and the previous biopsy. The donor specificity of antibodies could be identified in 67 patients: DSAs were detected in 32 patients (48%), and they were usually against human leukocyte antigen class II (30 cases) but were rarely against class I (2 cases). These patients had a higher frequency of bridging fibrosis or cirrhosis (28/32 or 88%) than DSA-negative patients (6/35 or 17%, P < 0.001). Fibrosis was likely to be centrilobular-based. DSA-positive patients, in comparison with DSA-negative patients, had higher frequencies of diffuse/focal endothelial C4d staining (P < 0.001) and mild/indeterminate acute rejection [15/32 (47%) versus 5/35 (14%), P = 0.004]. Four DSA-negative patients were off immunosuppression, whereas no patients in the DSA-positive group were (P = 0.048). In conclusion, the high prevalence of graft fibrosis and anti-class II DSAs in late protocol biopsy samples suggests that humoral alloreactivity may contribute to the process of unexplained graft fibrosis late after liver transplantation.

Preformed and de novo donor specific antibodies in visceral transplantation: long-term outcome with special reference to the liver

Despite improvement in early outcome, rejection particularly chronic allograft enteropathy continues to be a major barrier to long-term visceral engraftment. The potential role of donor specific antibodies (DSA) was examined in 194 primary adult recipients. All underwent complement-dependent lymphocytotoxic crossmatch (CDC-XM) with pre- and posttransplant solid phase HLA-DSA assay in 156 (80%). Grafts were ABO-identical with random HLA-match. Liver was included in 71 (37%) allografts. Immunosuppression was tacrolimus-based with antilymphocyte recipient pretreatment in 150 (77%). CDC-XM was positive in 55 (28%). HLA-DSA was detectable before transplant in 49 (31%) recipients with 19 continuing to have circulating antibodies. Another 19 (18%) developed de novo DSA. Ninety percent of patients with preformed DSA harbored HLA Class-I whereas 74% of recipients with de novo antibodies had Class-II. Gender, age, ABO blood-type, cold ischemia, splenectomy and allograft type were significant DSA predictors. Preformed DSA significantly (p < 0.05) increased risk of acute rejection. Persistent and de novo HLA-DSA significantly (p < 0.001) increased risk of chronic rejection and associated graft loss. Inclusion of the liver was a significant predictor of better outcome (p = 0.004, HR = 0.347) with significant clearance of preformed antibodies (p = 0.04, OR = 56) and lower induction of de novo DSA (p = 0.07, OR = 24). Innovative multifaceted anti-DSA strategies are required to further improve long-term survival particularly of liver-free allografts.

Bortezomib for acute antibody-mediated rejection in liver transplantation

Antibody-mediated rejection (AMR) is an uncommon, but challenging type of rejection after solid organ transplantation. We review three cases of AMR in ABO-compatible liver transplant recipients. These cases were characterized by severe acute rejection resistant to steroids and antithymocyte globulin, histologic evidence of plasma cell infiltrates, C4d positivity and high serum anti-HLA donor-specific antibodies. All three patients were treated with bortezomib, a proteasome inhibitor effective in depleting plasma cells. After treatment, all patients had improved or normal liver function tests, resolution of C4d deposition and significant decline in their HLA donor-specific antibodies.

The value of C4d deposit in post liver transplant liver biopsies

BACKGROUND

Presence of C4d in renal and cardiac allografts is a sign of antibody-mediated rejection and is associated with worse outcomes. The value of C4d in liver specimens is controversial. We aimed to determine the association of C4d deposition with acute cellular rejection (ACR), hepatitis C (HCV) recurrence, and clinical outcome after ABO compatible liver transplants (OLT).

METHODS

Using immunohistochemical stain, 70 liver biopsies (44 study and 26 control groups) were evaluated for C4d deposition. Study group included for-cause post OLT biopsies. Staining of endothelial cells was considered positive.

RESULTS

In the study group C4d was positive in 22.7% versus 3.8% in controls (P=0.03), all had portal vein deposits. In 17 biopsies with ACR, 3 had positive C4d (17.6%) versus 7/27 with HCV recurrence (25.9%) (P=0.4). In HCV recurrence, 3/7 biopsies with fibrosing cholestatic hepatitis had positive C4d (42.9%) versus 4/20 without these features (20%) (P=0.24). Out of 10 recipients with positive C4d 4 had poor outcomes versus 3/22 with negative C4d (P=0.12).

CONCLUSIONS

C4d staining was significantly more frequent in post OLT biopsies compared with controls. C4d is not specifically associated with ACR and does not differentiate it from HCV recurrence but is associated with a trend toward poorer outcome.

Donor-specific human leukocyte antigen antibodies of the immunoglobulin G3 subclass are associated with chronic rejection and graft loss after liver transplantation

In a previous study, we found that 92% of patients with chronic rejection had donor-specific human leukocyte antigen antibodies (DSAs), but surprisingly, 61% of comparator patients without rejection also had DSAs. We hypothesized that immunoglobulin G (IgG) subclasses were differentially distributed between the 2 groups. A modified single-antigen bead assay was used to detect the presence of individual IgG subclasses against human leukocyte antigen in 39 chronic rejection patients and 66 comparator patients. DSAs of the IgG1 subclass were most common and were found in 45% of all patients; they were followed by IgG3 DSAs (21%), IgG4 DSAs (14%), and IgG2 DSAs (13%). The percentage of patients with multiple IgG subclasses was significantly higher in the chronic rejection group versus the comparator group (50% versus 14%, P < 0.001). Patients with normal graft function in the presence of DSAs mostly had isolated IgG1, whereas patients with chronic rejection had a combination of IgG subclasses. Patients who developed DSAs of the IgG3 subclass showed an increased risk of graft loss (hazard ratio = 3.35, 95% confidence interval = 1.39-8.05) in comparison with patients with DSAs of other IgG subclasses or without DSAs. Although further study is needed, the determination of the IgG subclass in DSA-positive patients may help us to identify patients with a higher risk of chronic rejection and graft loss.

Long-term hepatic allograft acceptance based on CD40 blockade by ASKP1240 in nonhuman primates

Blockade of the CD40-CD154 costimulatory signal is an attractive strategy for immunosuppression and tolerance induction in organ transplantation. Treatment with anti-CD154 monoclonal antibodies (mAbs) results in potent immunosuppression in nonhuman primates (NHPs). Despite plans for future clinical use, further development of these treatments was halted by complications. As an alternative approach, we have been focusing on the inhibition of the counter receptor, CD40 and have shown that a novel human anti-CD40 mAb, ASKP1240, markedly prolongs renal allograft survival in NHPs, although allografts eventually underwent chronic allograft nephropathy. On the basis of our previous findings that a CD40-CD154 costimulation blockade induces tolerance to hepatic, but not cardiac, allografts in rodents, we tested here our hypothesis that a blockade of CD40 by ASKP1240 allows acceptance of hepatic allografts in NHPs. A 2-week ASKP1240 induction treatment prolonged liver allograft survival in NHPs; however, the graft function deteriorated due to chronic rejection. In contrast, a 6-month ASKP1240 maintenance monotherapy efficiently suppressed both cellular and humoral alloimmune responses and prevented rejection on the hepatic allograft. No serious side effects, including thromboembolic complications, were noted in the ASKP1240-treated monkeys. We conclude that CD40 blockade by ASKP1240 would be a desirable immunosuppressant for clinical liver transplantation.

Prevalence, course and impact of HLA donor-specific antibodies in liver transplantation in the first year

The presence of preformed donor-specific HLA antibodies (DSA) in liver transplant recipients is increasingly recognized; however, the prevalence of DSA and their impact on early allograft function remains unknown. We prospectively followed serum DSA levels of 90 consecutive liver transplant recipients from baseline to 4 months. Twenty recipients (22.2%) had preformed DSA. No antibody-targeting treatments were undertaken. Seven days after transplantation, DSA levels decreased markedly in all but three patients. Day 7 protocol biopsies showed diffuse C4d deposition along the portal stroma, central vein, subendothelial and stromal space in the patients with persistent high DSA levels. The rate of acute cellular rejection was not significantly different in patients with DSA. The transaminase and bilirubin levels remained comparable during the first year despite the presence of DSA. The three patients with persistently high DSA levels continue to have normal allograft function. We conclude that in most cases, DSA disappear after liver transplant, however in rare instances where they persist, there is evidence of complement activation in the liver allograft, without significant clinical impact in the first year.

Sinusoidal C4d deposits in liver allografts indicate an antibody-mediated response: diagnostic considerations in the evaluation of liver allografts

There is a paucity of data concerning the correlation of complement component 4d (C4d) staining in liver allografts and antibody-mediated rejection. Data about the location and character of C4d deposits in native and allograft liver tissues are inconsistent. We performed C4d immunofluorescence (IF) on 141 fresh-frozen liver allograft biopsy samples and native livers, documented the pattern of C4d IF staining, and correlated the findings with the presence of donor-specific alloantibodies (DSAs). A linear/granular sinusoidal pattern of C4d IF was noted in 18 of 28 biopsy samples obtained after transplantation from patients with positive crossmatch and detectable donor-specific alloantibody (pos-XM/DSA) findings. None of the 59 tested biopsy samples from patients with negative crossmatch and detectable donor-specific alloantibody (neg-XM/DSA) findings were C4d-positive (P < 0.001). No significant association was found between pos-XM/DSA and C4d IF staining in other nonsinusoidal liver compartments. To compare the results of sinusoidal C4d staining with IF and 2 immunohistochemistry (IHC) techniques, C4d IHC was performed on 19 liver allograft biopsy samples in which a sinusoidal pattern of C4d IF had been noted. Sinusoidal C4d IHC findings were negative for 17 of the 19 biopsy samples; 2 showed weak and focal staining, and both patients had pos-XM/DSA findings. Portal vein endothelium staining was present in only 1 IF-stained biopsy sample (pos-XM/DSA) but in 11 IHC-stained biopsy samples (2 of the 11 samples had neg-XM/DSA findings). We conclude that sinusoidal C4d deposits detected by IF in frozen tissue samples from liver allograft recipients correlate with the presence of DSAs and an antibody-mediated alloresponse. These observations are similar to findings reported for other solid organ transplants and can provide relevant information for patient management. Further validation of IHC techniques for C4d detection in liver allograft tissue is required.

Re-examination of the lymphocytotoxic crossmatch in liver transplantation: can C4d stains help in monitoring?

C4d-assisted recognition of antibody-mediated rejection (AMR) in formalin-fixed paraffin-embedded tissues (FFPE) from donor-specific antibody-positive (DSA+) renal allograft recipients prompted study of DSA+ liver allograft recipients as measured by lymphocytotoxic crossmatch (XM) and/or Luminex. XM results did not influence patient or allograft survival, or cellular rejection rates, but XM+ recipients received significantly more prophylactic steroids. Endothelial C4d staining strongly correlates with XM+ (<3 weeks posttransplantation) and DSA+ status and cellular rejection, but not with worse Banff grading or treatment response. Diffuse C4d staining, XM+, DSA+ and ABO- incompatibility status, histopathology and clinical-serologic profile helped establish an isolated AMR diagnosis in 5 of 100 (5%) XM+ and one ABO-incompatible, recipients. C4d staining later after transplantation was associated with rejection and nonrejection-related causes of allograft dysfunction in DSA- and DSA+ recipients, some of whom had good outcomes without additional therapy. Liver allograft FFPE C4d staining: (a) can help classify liver allograft dysfunction; (b) substantiates antibody contribution to rejection; (c) probably represents nonalloantibody insults and/or complete absorption in DSA- recipients and (d) alone, is an imperfect AMR marker needing correlation with routine histopathology, clinical and serologic profiles. Further study in late biopsies and other tissue markers of liver AMR with simultaneous DSA measurements are needed.

The role of B cells in solid organ transplantation

The role of antibodies in chronic injury to organ transplants has been suggested for many years, but recently emphasized by new data. We have observed that when immunosuppressive potency decreases either by intentional weaning of maintenance agents or due to homeostatic repopulation after immune cell depletion, the threshold of B cell activation may be lowered. In human transplant recipients the result may be donor-specific antibody, C4d+ injury, and chronic rejection. This scenario has precise parallels in a rhesus monkey renal allograft model in which T cells are depleted with CD3 immunotoxin, or in a CD52-T cell transgenic mouse model using alemtuzumab to deplete T cells. Such animal models may be useful for the testing of therapeutic strategies to prevent DSA. We agree with others who suggest that weaning of immunosuppression may place transplant recipients at risk of chronic antibody-mediated rejection, and that strategies to prevent this scenario are needed if we are to improve long-term graft and patient outcomes in transplantation. We believe that animal models will play a crucial role in defining the pathophysiology of antibody-mediated rejection and in developing effective therapies to prevent graft injury. Two such animal models are described herein.

Significance of complement split product C4d in ABO-compatible liver allograft: diagnosing utility in acute antibody mediated rejection

Diagnosis of liver allograft antibody-mediated rejection (AMR) is difficult and requires a constellation of clinical, laboratory and histologic features that support the disease and exclude other causes. Histologic features of AMR may intermix with those of biliary obstruction, preservation/reperfusion injury, and graft ischemia. Tissue examination for complement degradation product 4d (C4d) has been proved to support this diagnosis in other allografts. For this reason, we conducted a retrospective review of all ABO compatible/identical re-transplanted liver patients with primary focus on identifying AMR as a possible cause of graft failure and to investigate the utility of C4d in liver allograft specimens. We reviewed 193 liver samples obtained from 53 consecutive ABO-compatible re-transplant patients. 142 specimens were stained with C4d. Anti-donor antibody screening and identification was determined by Luminex100 flow cytometry. For the study analysis, patients were stratified into 3 groups according to time to graft failure: group A, patients with graft failure within 0-7 days (n=7), group B within 8-90 days (n=13) and C >90 days (n=33). Two patients (3.7%) met the diagnostic criteria of acute AMR. Both patients experienced rapid decline of graft function with presence of donor specific antibodies (DSA), morphologic evidence of humoral rejection and C4d deposition in liver specimens. C4d-positive staining was identified in different medical liver conditions i.e., acute cellular rejection (52%), chronic ductopenic rejection (50%), recurrent liver disease (48%), preservation injury (18%), and hepatic necrosis (54%). Univariate analysis showed no significant difference of C4d-positive staining among the 3 patients groups, or patients with DSA (P>.05). In conclusion, AMR after ABO-compatible liver transplantation is an uncommon cause of graft failure. Unlike other solid organ allografts, C4d-positive staining is not a rugged indicator of humoral rejection, thus, interpretation should be done with caution to avoid diagnostic dilemmas.

Recurrent hepatitis C and acute allograft rejection: clinicopathologic features with emphasis on the differential diagnosis between these entities

Chronic hepatitis C virus infection is the leading etiology for liver transplantation in the United States. Recurrent hepatitis C occurs nearly universally in these patients and represents a serious posttransplantation complication. Despite the detailed characterization of the histologic features of both recurrent hepatitis C and acute cellular rejection (ACR) over the last decades, the pathologic distinction between these 2 conditions remains one of the greatest diagnostic challenges in liver pathology. An accurate diagnosis, nevertheless, plays an essential role in patient management, as different therapeutic strategies are used for these conditions. In this review, the clinicopathologic features of posttransplantation recurrent hepatitis C and ACR are discussed, with emphasis on distinguishing histopathologic features, morphologic variants, ancillary techniques, and diagnostic pitfalls.