Preformed lymphocytotoxic antibodies: the effects of class, titer and specificity on liver vs. heart allografts

Xenoreactive antibodies in α-granules of human platelets bind pig liver endothelial cells

Pig liver xenotransplantation is limited by a thrombocytopenic coagulopathy that occurs immediately following graft reperfusion. In vitro and ex vivo studies from our lab suggested that the thrombocytopenia may be the result of a species incompatibility in platelet glycosylation. Realization that platelet α-granules contain antibodies caused us to reevaluate whether the thrombocytopenia in liver xenotransplantation could occur because IgM and IgG from inside platelet α-granules bound to pig liver sinusoidal endothelial cells (LSECs). Our in vitro analysis of IgM and IgG from inside α-granules showed that platelets do carry xenoreactive antibodies that can bind to known xenoantigens. This study suggests that thrombocytopenia occurring following liver xenotransplantation could occur because of xenoreactive antibodies tethering human platelets to the pig LSEC enabling the platelet to be phagocytosed. These results suggest genetic engineering strategies aimed at reducing xenoantigens on the surface of pig LSEC will be effective in eliminating the thrombocytopenia that limits survival in liver xenotransplantation.

Suppression of liver transplant rejection by anti-donor MHC antibodies via depletion of donor immunogenic dendritic cells

BACKGROUND

We previously found two distinct passenger dendritic cell (DC) subsets in the rat liver that played a central role in the liver transplant rejection. In addition, a tolerance-inducing protocol, donor-specific transfusion (DST), triggered systemic polytopical production of depleting alloantibodies to donor class I MHC (MHCI) antigen (DST-antibodies).

METHODS

We examined the role of DST-antibodies in the trafficking of graft DC subsets and the alloresponses in a rat model. We also examined an anti-donor class II MHC (MHCII) antibody that recognizes donor DCs more selectively.

RESULTS

Preoperative transfer of DST-antibodies or DST pretreatment eliminated all passenger leukocytes, including both DC subsets and depleted the sessile DCs in the graft to ~20% of control. The CD172a+CD11b/c+ immunogenic subset was almost abolished. The intrahost direct or semi-direct allorecognition pathway was successfully blocked, leading to a significant suppression of the CD8+ T-cell response in the recipient lymphoid organs and the graft with delayed graft rejection. Anti-donor MHCII antibody had similar effects without temporary graft damage. Although DST pretreatment had a priming effect on the proliferative response of recipient regulatory T cells, DST-primed sera and the anti-donor MHCII antibody did not.

CONCLUSION

DST-antibodies and anti-donor MHCII antibodies could suppress the CD8+ T-cell-mediated liver transplant rejection by depleting donor immunogenic DCs, blocking the direct or semi-direct pathways of allorecognition. Donor MHCII-specific antibodies may be applicable as a selective suppressant of anti-donor immunity for clinical liver transplantation without the cellular damage of donor MHCII- graft cells and recipient cells.

Single blood transfusion induces the production of donor-specific alloantibodies and regulatory T cells mainly in the spleen

Donor-specific blood transfusion is known to induce alloresponses and lead to immunosuppression. We examined their underlying mechanisms by employing fully allogeneic rat combinations. Transfused recipients efficiently produced alloantibodies of the IgM and IgG subclasses directed against donor class I MHC. The recipients exhibited active expansion of CD4⁺ T cells and CD4⁺FOXP3⁺ regulatory T cells (T_reg cells), followed by CD45R⁺ B cells and IgM⁺ or IgG subclass⁺ antibody-forming cells mainly in the spleen. From 1.5 days, the resident MHCII⁺CD103⁺ dendritic cells (DCs) in the splenic T-cell area, periarterial lymphocyte sheath, formed clusters with recipient BrdU⁺ or 5-ethynyl-2′-deoxyuridine⁺ cells, from which the proliferative response of CD4⁺ T cells originated peaking at 3–4 days. Transfusion-induced antibodies had donor passenger cell-depleting activity in vitro and in vivo and could suppress acute GvH disease caused by donor T cells. Furthermore, T_reg cells significantly suppressed mixed leukocyte reactions in a donor-specific manner. In conclusion, single blood transfusion efficiently induced a helper T-cell-dependent anti-donor class I MHC antibody-forming cell response with immunoglobulin class switching, and a donor-specific T_reg cell response mainly in the spleen, probably by way of the indirect allorecognition via resident DCs. These antibodies and T_reg cells may be involved, at least partly, in the donor-specific transfusion-induced suppression of allograft rejection.

ABO-compatible liver allograft antibody-mediated rejection: an update

PURPOSE OF REVIEW

Liver allograft antibody-mediated rejection (AMR) studies have lagged behind parallel efforts in kidney and heart because of a comparative inherent hepatic resistance to AMR. Three developments, however, have increased interest: first, solid phase antibody testing enabled more precise antibody characterization; second, increased expectations for long-term, morbidity-free survival; and third, immunosuppression minimization trials.

RECENT FINDINGS

Two overlapping liver allograft AMR phenotypic expressions are beginning to emerge: acute and chronic AMR. Acute AMR usually occurs within the several weeks after transplantation and characterized clinically by donor-specific antibodies (DSA) persistence, allograft dysfunction, thrombocytopenia, and hypocomplementemia. Acute AMR appears histopathologically similar to acute AMR in other organs: diffuse microvascular endothelial cell hypertrophy, C4d deposits, neutrophilic, eosinophilic, and macrophag-mediated microvasculitis/capillaritis, along with liver-specific ductular reaction, centrilobular hepatocyte swelling, and hepatocanalicular cholestasis often combined with T-cell-mediated rejection (TCMR). Chronic AMR is less well defined, but strongly linked to serum class II DSA and associated with late-onset acute TCMR, fibrosis, chronic rejection, and decreased survival. Unlike acute AMR, chronic AMR is a slowly evolving insult with a number of potential manifestations, but most commonly appears as low-grade lymphoplasmacytic portal and perivenular inflammation accompanied by unusual fibrosis patterns and variable microvascular C4d deposition; capillaritis can be more difficult to identify than in acute AMR.

SUMMARY

More precise DSA characterization, increasing expectations for long-term survival, and immunosuppression weaning precipitated a re-emergence of liver allograft AMR interest. Pathophysiological similarities exist between heart, kidney, and liver allografts, but liver-specific considerations may prove critical to our ultimate understanding of all solid organ AMR.

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.

Seeking beyond rejection: an update on the differential diagnosis and a practical approach to liver allograft biopsy interpretation

Pathologic evaluation of liver allograft biopsies plays an integral role in the management of patients after liver transplantation. This review summarizes the clinical context and classical histology of different types of allograft rejection and also the common entities that enter the differential diagnosis of allograft rejection, and provides practical approaches to liver allograft biopsy interpretation. In addition, some of the new developments in the field of liver transplant pathology are updated. The purpose of this review is to provide guidance for pathologists interpreting liver allograft biopsies, particularly those interested in developing expertise in the field of liver transplant pathology.

Significance of C4d staining in ABO-identical/compatible liver transplantation

Complement degradation product C4d has become an important marker of humoral or antibody-mediated rejection in renal and heart allograft biopsies. Although there have been several reports on the detection of C4d in liver allografts, the significance of C4d in liver transplantation and its relationship with humoral rejection are still not clear. We investigated the frequency and pattern of C4d staining in liver allograft biopsies with reference to preoperative lymphocyte crossmatch tests, which detect donor-reactive lymphocyte antibody. Survival rates at 5 years were 77% for crossmatch-negative patients and 53% for crossmatch-positive patients (P=0.009). In crossmatch-negative patients, reproducible positive staining was obtained in 28 of 86 (33%) biopsies taken within 90 days after transplantation and 33 of 96 (34%) biopsies 90 days or after transplantation. Most C4d staining was observed in the portal areas, and no clear correlation was observed between C4d positivity and histological diagnosis. In crossmatch-positive patients, 9 of 11 (82%) biopsies showed positivity for C4d. C4d stained perivenular areas as well as portal areas. Histology of crossmatch-positive patients included acute rejection and cholangitis, but did not include periportal changes that were seen in humoral rejection in ABO-incompatible liver transplantation. In summary, focal C4d deposition was seen in various types of liver allograft injury and had little clinical impact on crossmatch-negative patients, but extensive C4d staining in crossmatch-positive patients may be associated with humoral rejection and poor graft survival.

Susceptibility of liver allografts to high or low concentrations of preformed antibodies as measured by flow cytometry

Liver grafts are more resistant to damage by HLA antibodies than other organ allografts, but it is not clear if the antibodies are associated with graft rejection or graft loss, or if different antibody concentrations have different effects. To explore potential associations between antibody concentrations and outcome, preformed IgG antibodies against donor cells were quantified by flow cytometry in 465 consecutive liver transplant recipients. Antibody-positive patients were classified according to whether they had high or low antibody concentrations and analyzed for possible correlation with graft rejection or graft loss. The results showed that the incidence of rejection was not significantly different between antibody-positive and negative patients. However, patients with high antibody concentrations had a higher incidence of steroid-resistant rejections (31% at 1 year) than patients with low antibody (4%) or no antibody (8%, p < 0.0004). These effects were mainly due to T-cell (HLA class 1) antibodies. The overall incidence of rejection at 1 year was 69% for high antibody patients, 51% for patients with low antibodies and 53% for patients with no antibodies (p not significant). In an apparent paradox, antibody-positive patients underwent fewer early graft losses. Thus, the associations of preformed antibodies and outcome depend, on the one hand, on antibody concentrations, and on the other hand on whether the outcome measured is steroid-sensitive rejection, steroid-resistant rejection or graft survival. These complex interactions may explain the controversial results observed in previous studies.

Tolerance of islet allografts induced by orthotopic liver transplantation

BACKGROUND

The induction of immunological tolerance by orthotopic liver transplantation (OLT) is donor-specific. Moreover, after the acceptance of a liver, other organs are not rejected. The aim of this study is to clarify characteristics of the prolonged islet survival as a result of immunological tolerance which was induced following simultaneous OLT.

MATERIALS AND METHODS

About 2000 islets were isolated from F344 rats. OLT was performed from F344 rats to diabetic LEW rats. Then the islets were transplanted into the transplanted F344 livers of diabetic LEW rats. Survival of the pancreatic islet allografts and deposits of IgM and IgG in the transplanted liver and islets were investigated.

RESULTS

Survival time in the group with OLT (mean survival time: 46.4 +/- 38.2 days) was significantly longer than that without OLT (mean survival time: 8.1 +/- 0.8 days) (P < 0.01). Amount of serum antibody against donor lymphocytes was slightly higher in the group without OLT, and was very high in the group with OLT. Histologically, severe lymphocytic infiltration was observed in the Glisson's sheaths in the group with OLT. Islets were lodged, without lymphocytes inside, in small branches of the portal vein 7 days after transplantation. Immunohistologically, IgM and IgG deposits were found in the Glisson's sheaths and along sinusoids; however, they were not found in the islets.

CONCLUSIONS

Induction of immunological tolerance and long-term survival of islets are possible by simultaneous OLT. The mechanism of this tolerance could be the host's selection of the liver as a target of preferred immunological attack.

IgG, but not IgM, mediates hyperacute rejection in hepatic xenografting

We reported previously that no classical features of hyperacute rejection (HAR) could be found in liver grafts in the guinea-pig (GP)-to-rat model and that recipients died shortly after transplantation of non-immunologic causes. Thus, the GP-to-rat model is not suitable for studying the mechanisms of discordant liver xenograft rejection. In the hamster to rat model, long-term survival of a liver graft is possible, but extremely low levels of xenoreactive natural antibodies are present. To mimic a discordant situation with pre-formed IgM and IgG antibodies, we sensitized rats 1 or 5 weeks before grafting. Specific anti-hamster IgM antibodies were found in recipients sensitized at week -1 but not week -5. Anti-hamster IgG was present in all recipients, albeit considerably higher in animals sensitized 5 weeks before grafting. In these two models, we examined the mechanism of HAR of liver grafts and compared this with heart xenografts. Control heart and liver grafts were rejected 4 and 7 days after transplantation respectively. Liver grafts in recipients sensitized at week -5 showed venous congestion and bleeding after reperfusion, indicating HAR, however this was not observed after sensitization at week -1. This surprising finding was confirmed by histology. Massive extravasation, edema, and acute liver cell degradation were noticed in grafts subjected to HAR. Liver grafts of recipients sensitized at week -1 showed only minimal changes. Heart grafts were rejected hyperacutely in both sensitization models. IgG antibodies could be detected on liver grafts in the group sensitized at week -5 but not in the group sensitized at week -1. Minimal IgM depositions were found on liver grafts of animals sensitized 1 week before grafting. Rejected heart grafts from similar sensitization groups showed identical antibody depositions; only IgM depositions were massive. Complement depositions were found in all groups. These results indicate that IgG, but not IgM, mediates HAR in hepatic xenografting. Such a predominance of IgG over IgM does not exist for heart grafts.

Infiltrating CD45RC- T cells are associated with immunologic unresponsiveness induced by donor class I major histocompatibility complex antigens in rats

It has previously been shown that a single intravenous injection of freshly heparinized donor-specific blood transfusion (DST) before transplantation significantly prolongs the survival of fully allogeneic ACI (RT1a)-to-LEW(RT1(1)) rat hepatic allografts. Additionally, we have shown that pretreatment of LEW rats with PVG.r1 blood, which shares only the RT1.A major histocompatibility complex (MHC) region with ACI, significantly prolongs the survival of ACI hepatic allografts. In this study, we report the cellular identity of hepatic allograft leukocyte infiltrates following transplantation. Fluorescence-activated cell sorting (FACS) analysis revealed that CD4+ T cells infiltrating liver allografts could be divided into two subsets, CD45RC- CD4+ and CD45RC+ CD4+ T cells, and that the ratio of CD45RC- CD4+/CD45RC+ CD4+ T cells was significantly higher in hepatic allografts of recipients pretreated with DST or PVG.r1 blood as compared to untreated allografts. Further, CD8+ T cells that accumulated in the liver grafts could be similarly divided into two subsets, and the ratio of CD45RC- CD8+/CD45RC+ CD8+ T cells was also significantly higher in hepatic allografts of recipients pretreated with DST or PVG.r1 blood. Reverse transcriptase polymerase chain reaction (RT-PCR) analysis revealed that CD45RC- CD4+ T cells harvested from hepatic allografts pretreated with PVG.r1 blood expressed interleukin-4 (IL-4) and interleukin-10 (IL-10), but not interleukin-2 (IL-2) or interferon-gamma (IFN-gamma). In contrast, CD45RC- CD8+ T cells from hepatic allografts pretreated with PVG.r1 blood expressed IL-4, IL-10, and IFN-lambda, but not IL-2. These results indicate that the CD45RC leukocyte common antigen could be used to differentiate CD4+ and CD8+ T cells following pretreatment with DST or PVG.r1 blood. Persistent infiltration of CD45RC- CD4+ and CD45RC- CD8+ T cells, capable of secreting Th2-type cytokines may prevent allograft rejection by causing immunologic unresponsiveness.

Immunoglobulin G lymphocytotoxic antibodies in clinical liver transplantation: studies toward further defining their significance

Twenty-two consecutive liver allograft recipients, who tested positive for immunoglobulin G (IgG) lymphocytotoxicity were subjected to pretransplantation and posttransplantation immunologic monitoring of anti-donor IgG lymphocytotoxic antibody titers, total hemolytic complement activity (CH100), circulating immune complexes (CIC), and platelet counts in an effort to improve our understanding of the preformed antibody state in clinical hepatic transplantation. Ten contemporaneous liver transplant recipients whose crossmatch results were negative and who experienced severe hepatocellular damage early after transplantation were included as controls. Crossmatch test results were negative 1 day after transplantation and during the 1 month follow-up remained negative in 14 of 22 (64%) sensitized recipients, most of whom had relatively low (< or = 1:16) anti-donor IgG antibody titers before transplantation. After transplantation, this group and the control group experienced no thrombocytopenia, no increase of CIC, and a gradual increase in CH100 activity that reached normal levels within 1 week. A strong negative correlation between prothrombin time (PT) and CH100 activity in these groups of patients suggested that changes in CH100 activity (P < .0005) were tightly linked to liver synthetic function. In contrast, the crossmatch test results remained positive after transplantation in 8 of 22 (36%) sensitized recipients, all of whom had relatively high (> 1:32 to 1024) pretransplantation titers of anti-donor IgG antibodies. After transplantation these patients developed a syndrome that was characterized by decreased CH100 activity and increased CIC compared with pretransplantation levels and refractory thrombocytopenia that was associated with a 50% allograft failure rate because of biopsy-proven humoral and acute (cellular) rejection.(ABSTRACT TRUNCATED AT 250 WORDS)

The biological basis of and strategies for clinical xenotransplantation

Recent discoveries have suggested that the exchange of multiple leukocyte lineages between grafts and host and subsequent long-term chimerism in both is the seminal mechanism of the acceptance of organs transplanted from the same (allografts) or different species (xenografts). This insight suggests new strategies which may allow xenotransplantation, the principal obstacle to which has been humoral rejection. We have defined humoral rejection as a family of complement activation syndromes afflicting allografts and xenografts in which there is a strong (but not invariable) association with performed antigraft antibodies, invariable evidence of complement activation, histopathologic stigmas of vascular endothelial damage, and a concomitant local or systemic coagulopathy. The generic descriptive term hyperacute rejection is a misnomer because a slow-motion version of the same "humoral" process can occur with some allografts and is the rule with the so-called concordant species xenotransplantations. The pathway of experience and discovery leading to this conclusion shows clearly that the distinction frequently made between allograft versus xenograft humoral rejection does not actually exist in principle, but only in details and intensity. Breaking down this barrier to xenotransplantation, whether or not it is associated with antibodies, is unrealistic. However, the possibility of avoiding the barrier has been exposed by showing that animal organs can be humanized, with a mixed donor and recipient cell population similar to the chimerism seen in long surviving allografts or even with complete leukocyte replacement. Pilot experiments in rodents suggest that organs from fully xenogeneic chimeras can be made into xenogeneic targets that are no more provocative of complement activation than allografts when they are transplanted into the donor bone marrow species. Although the validity of this concept of organ xenograft preparation is only at the pilot stage of verification, there is reason to suspect that the complement trigger of humoral rejection can be thereby disarmed. If this can be accomplished, independent evidence suggests that cellular rejection can be controlled with conventional T-cell directed immunosuppression, perhaps even with surprising ease. The potential subtle liability of synthetic products of xenogeneic parenchymal cells is not yet known.

Combined liver-kidney transplantation and the effect of preformed lymphocytotoxic antibodies

Thirty-eight sequentially placed liver and kidney allografts were evaluated with respect to patient and graft survival, and the influence of preformed lymphocytotoxic antibodies was analysed. The results suggest that the survival rate of combined liver and kidney transplantation is similar to the survival rate of liver transplantation alone. Sequentially placed kidney allografts may be protected from hyperacute rejection in the presence of donor specific lymphocytotoxic antibodies, but not in all instances. Both patient and kidney allograft survival was lower in positive crossmatch patients (33% and 17% respectively) than in negative crossmatch patients (78% and 75%). High levels of panel reactive antibodies (> 10%) also appeared to have a deleterious effect on survival, although the majority of the patients who failed also had a positive crossmatch. Although performed lymphocytotoxic antibodies are not an absolute contraindication to combined liver-kidney transplantation, they do appear to have a deleterious effect on long-term graft survival. However, more correlation with clinical parameters is needed.

Liver allograft rejection in sensitized recipients. Observations in a clinically relevant small animal model

A sequential analysis of liver allograft rejection in sensitized rats using immunopathological and ultrastructural microscopy is described. Lewis rats were primed with four ACI skin grafts and challenged with an arterialized ACI orthotopic liver allograft 14 to 17 weeks later. The sensitization resulted in a mix of IgG and IgM lymphocytotoxic antibodies at a titer of 1:512 at the time of transplantation. Specificity analysis of pretransplant immune sera revealed a predominance of IgG anti-class I major histocompatibility complex (RT1) antibodies with a minor IgG fraction showing apparent endothelial cell specificity (non-RT1). This level of sensitization was associated with accelerated graft failure in 3 to 5 days from mixed humoral and cellular rejection. Sequential analysis of serial posttransplant graft biopsies revealed diffuse vascular IgG deposition and platelet thrombi in portal veins and periportal sinusoids within 3 minutes after reperfusion. This was followed by endothelial cell hypertrophy and vacuolization, periportal hepatocyte necrosis, arterial spasm, focal large bile duct necrosis, and hilar mast cell infiltration and degranulation. However, the liver allografts did not fail precipitously and hyperacute rejection was not seen. Kupffer cell phagocytosis of the sinusoidal platelets began as early as 30 minutes posttransplant and by 24 hours, the platelet thrombi had decreased. Cholangioles appeared focally at the edge of the limiting plates by 2 to 3 days, apparently in response to earlier periportal hepatocyte damage. A mononuclear portal and perivenular infiltrate became evident at 3 days, and graft failure was attributed to both antibody and cell-mediated rejection (Furuya et al: Preformed lymphocytotoxic antibodies: Hepatology 1992, 16: 1415-1422). The model described resembles observations in crossmatch positive human liver allograft recipients. The mechanisms of hepatic graft resistance to antibody mediated rejection and the possible long term consequences of early damage to the biliary tree are discussed.