The significance of the anti-class I antibody response. I. Clinical and pathologic features of anti-class I-mediated rejection

Acute humoral renal allograft rejection

In kidney transplantation, it is well established that donor-specific antibodies can cause substantial graft injury. Hyperacute rejection, now virtually eliminated by routine pretransplant cytotoxic crossmatch testing, represents the prototype of humoral rejection. However, there is now increasing evidence that alloantibody-mediated immune reactions may also cause acute rejection. Acute humoral rejection, which is frequently associated with severe graft dysfunction and immunologic graft loss, represents a particular diagnostic and therapeutic challenge. Reliable detection of antibody-mediated graft injury is required to govern the application of antihumoral therapeutic strategies. This review focuses on new approaches in the diagnosis and treatment of acute humoral rejection. Special attention is given to a novel diagnostic marker, the complement split product C4d.

C4d deposition in acute rejection: an independent long-term prognostic factor

Peritubular capillary deposition of C4d has been demonstrated to be associated with both acute humoral and vascular rejection and increased graft loss. Whether it is an independent predictor of long-term graft survival rates is uncertain. The biopsies (n = 126) from all patients (n = 93) with a tissue diagnosis of acute rejection that were performed between July 1, 1995, and December 31, 1997, were classified according to Cooperative Clinical Trials in Transplantation (CCTT) criteria. Fresh frozen tissue was immunostained for C4d. There were 58 patients with CCTT type I (interstitial) rejection and 35 with CCTT type II (vascular) rejection. For 34 patients, at least one biopsy exhibited peritubular C4d deposition (C4d+ group). The C4d+ group had proportionately more female patients (P = 0.003), more patients with high (>30%) panel-reactive antibody levels (P = 0.024), more patients with resistance to conventional antirejection therapy (P = 0.010), and fewer patients with postrejection hypertension (P = 0.021) and exhibited a greater rate of graft loss (38 versus 7%, P = 0.001). Peritubular C4d deposition was associated with significantly lower graft survival rates in the CCTT type I rejection group (P = 0.003) and the CCTT type II rejection group (P = 0.003). Multivariate analyses demonstrated that peritubular C4d deposition (P = 0.0002), donor age (P = 0.0002), cold ischemic time (P = 0.0211), and HLA matches (P = 0.0460) were significant independent determinants of graft survival rates. Peritubular C4d deposition is a significant predictor of graft survival rates and is independent of histologic rejection type and a variety of clinical prognostic factors.

C4d-positive acute humoral renal allograft rejection: effective treatment by immunoadsorption

There is increasing evidence for an important pathogenetic role of alloantibodies in acute renal allograft rejection. Acute humoral rejection (AHR) has been reported to be associated with a poor transplant survival. Although treatment modalities for cellular rejection are fairly well established, the optimal treatment for AHR remains undefined. Ten of 352 kidney allograft recipients transplanted at the authors' institution between November 1998 and September 2000 were diagnosed as having AHR, supported by severe graft dysfunction, C4d deposits in peritubular capillaries (PTC), and accumulation of granulocytes in PTC. AHR was diagnosed 18.9 +/- 17.5 d posttransplantation. All patients were subjected to immunoadsorption (IA) with protein A (median number of treatment sessions, 9; range, 3 to 17). Seven recipients with additional signs of cellular rejection (according to the Banff classification) received also antithymocyte globulin. In nine of ten patients, AHR was associated with an increase in panel reactive antibody reactivity. A pathogenetic role of alloantibodies was further supported by a positive posttransplant cytotoxic crossmatch in all tested recipients (n = 4). In nine of ten recipients, renal function recovered after initiation of anti-humoral therapy. One patient lost his graft shortly after initiation of specific therapy. Another recipient with partial reversal of AHR returned to dialysis 8 mo after transplantation. Mean serum creatinine in functioning grafts was 2.2 +/- 1.2 mg/dl after the last IA session (n = 9) and 1.5 +/- 0.5 mg/dl after a follow-up of 14.2 +/- 7.1 mo (n = 8). In conclusion, this study suggests that AHR, characterized by severe graft dysfunction, C4d staining, and peritubular granulocytes, can be effectively treated by timely IA. In the majority of patients, IA treatment can restore excellent graft function over a prolonged time period.

Managing the highly sensitized transplant recipient and B cell tolerance

The detection of anti-donor-HLA antibodies in a renal allograft recipient's serum, either at the time of or after transplantation, is usually associated with specific antibody-mediated clinical syndromes. These can be divided temporally into three categories: hyperacute rejection, acute humoral rejection and chronic humoral rejection. With the identification of new immunosuppressive drug combinations, more-effective control of alloantibody production has been recently achieved in humans. Thus, prevention and/or treatment of antibody-mediated allograft injury are now possible. Ultimately, the induction of mixed hematopoietic chimerism may allow us to overcome the problem of allosensitization and accept an allograft without chronic immunosuppression.

Effect of Bw4 and Bw6 epitope mismatches on antibody production, acute and chronic rejection, and graft survival in renal allografts

BACKGROUND

Highly sensitized patients often have antibodies directed against the HLA Bw4 and Bw6 epitopes. Because of the high frequency of these epitopes, when present, these antibodies result in a high incidence of positive cross-matches. We sought to determine whether antibodies specific for Bw4 or Bw6 affected renal allograft outcome.

METHODS

The effect of mismatches for the HLA class I public epitopes, Bw4 and Bw6, was examined in 72 recipients of one haplotype matched recipients of living, related donor renal allografts selected to control for degree of HLA mismatch. Analysis of the production of HLA-specific antibody was performed for 180 recipients of failed cadaveric allografts by complement-dependent cytotoxicity tests and by an enzyme-linked immunoadsorbent assay (ELISA).

RESULTS

No significant difference was observed in the incidence of acute rejection, number of rejection episodes or 1-year allograft survival among Bw4/6 matched versus mismatched recipients of one haplotype matched allografts. Additionally, no significant difference in the development of chronic allograft nephropathy was noted among 56 recipients followed long-term (> or =3 years). In the recipients of failed cadaveric transplants, Bw4/6 mismatching was associated with the frequency and magnitude of production of HLA-specific antibody. However, the panel reactive antibodies correlated with the number of HLA-A and -B mismatches, and there was no additional impact of Bw4/6 mismatching. IgG, HLA-specific antibodies were found to be significantly increased among patients homozygous for Bw4 or Bw6, whether or not there was a Bw4/6 mismatch.

CONCLUSIONS

Mismatching for Bw4 or Bw6 does not confer any independent, increased risk for humoral sensitization or renal allograft failure.

Rejection of peritubular capillaries in renal allo- and xeno-graft

The microvasculature plays an important role in the pathogenesis of humoral- and cell-mediated renal allo- and xeno-graft rejection. Peritubular capillary (PTC) endothelium expresses the major histocompatibility complex (MHC) class I and II antigens in the resting phase, as does the glomerular capillary endothelium, suggesting that these cells may be major immune targets. However, the role of PTCs in renal allo- and xeno-graft rejection is unclear. In this review, we discuss injury and subsequent remodeling of PTCs in both humoral- and cell-mediated rejection in allo- and xeno-grafts. Recent evidence suggests that PTC injury and endothelial cell death occur during both cell- and humoral-mediated rejection. Severe PTC rejection contributes to deterioration of graft function and acute graft loss. The mild but recurrent form of PTC rejection is associated with progressive interstitial fibrosis and chronic rejection. Following endothelial injury, the remaining PTC endothelium activates with up-regulation of allo-antigens and adhesion molecules, and down-regulation of anti-coagulant proteins. Subsequent to this, more severe rejection and graft dysfunction occur. Therefore, a careful analysis of cellular- and antibody-mediated rejection in PTCs is important in the diagnosis of rejection, prediction of graft prognosis, and in further development of new anti-rejection therapies.

Passive transfer of alloantibodies restores acute cardiac rejection in IgKO mice

BACKGROUND

Alloantibody is an intrinsic component of the immune response to organ transplants. Although alloantibodies have been correlated with decreased graft survival, the mechanisms of alloantibody-mediated injury remain largely undefined in vivo. In the present study, we have established a model of alloantibody-mediated graft injury using B10.A (H-2a) hearts transplanted to wild type (WT) or immunoglobulin knock out (IgKO) C57BL-Igh-6 (H-2b) mice.

METHODS

Alloantibodies were measured in the circulation and graft by flow cytometry and in immunofluorescence staining, respectively. Intragraft cytokine mRNA expression was evaluated using a competitive template reverse transcriptase polymerase chain reaction (RT-PCR) technique. P-selectin and von Willebrand factor expression were localized by immunoperoxidase staining. The capacity of alloantibodies to restore acute cardiac allograft rejection was tested by passive transfer of monoclonal antibodies (mAbs) against donor major histocompatibility complex (MHC) class I antigens to IgKO recipients.

RESULTS

B10.A cardiac allografts are rejected acutely by WT C57BL/6 recipients, but over 50% of the cardiac allografts survived more than 50 days after transplantation in IgKO mice. Competitive template RT-PCR on the cardiac transplants demonstrated similar levels of IL-1-alpha, IL-12 (p40), TNF-alpha, IL-2, IFN-gamma, IL-4, and IL-10 mRNA in WT and IgKO recipients 8-10 days after transplantation, indicating that macrophage- and T-cell-dependent immune responses were intact in IgKO recipients. The rejection of B10.A hearts in WT recipients was characterized by interstitial and perivascular cellular infiltration; IgG, IgM, and complement (C3) deposition; vascular cell injury and intravascular platelet aggregation; and release of von Willebrand factor and P-selectin. In IgKO recipients the lower degree of vascular injury in the absence of alloantibody responses was reflected by the lack of release of von Willebrand factor and P-selectin, which remained confined to cytoplasmic storage granules of endothelial cells and platelets. Acute rejection of cardiac allografts was restored to IgKO recipients by passive transfer of proinflammatory IgG2b mAbs against donor MHC; recipients injected with isotype-matched control mAbs did not reject. In contrast, passive transfer of IgG1 mAbs against donor MHC failed to restore acute rejection of cardiac allografts to IgKO recipients. Passive transfer of IgG2b, but not IgG1 mAbs was associated with endothelial cell activation and plate. let aggregation together with the release of preformed von Willebrand factor and P-selectin from storage granules.

CONCLUSIONS

Acute rejection of cardiac allografts can be reconstituted in IgKO recipients by passive transfer of IgG2b, but not IgG1 antibody. This model allows the mechanism of alloantibody-mediate graft injury to be dissected in vivo.

Acute humoral rejection in renal allograft recipients: I. Incidence, serology and clinical characteristics

BACKGROUND

Acute rejection (AR) associated with de novo production of donor-specific antibodies (DSA) is a clinicopathological entity that carries a poor prognosis (acute humoral rejection, AHR). The aim of this study was to determine the incidence and clinical characteristics of AHR in renal allograft recipients, and to further analyze the antibodies involved.

METHODS

During a 4-year period, 232 renal transplants (Tx) were performed at our institution. Assays for DSA included T and B cell cytotoxic and/or flow cytometric cross-matches and cytotoxic antibody screens (PRA). C4d complement staining was performed on frozen biopsy tissue.

RESULTS

A total of 81 patients (35%) suffered at least one episode of AR within the first 3 months: 51 had steroid-insensitive AR whereas the remaining 30 had steroid-sensitive AR. No DSA were found in patients with steroid-sensitive AR. In contrast, circulating DSA were found in 19/51 patients (37%) with steroid-insensitive AR, and widespread C4d deposits in peritubular capillaries were present in 18 of these 19 (95%). In at least three cases, antibodies were against donor HLA class II antigens. DSA were not found in the remaining 32 patients but C4d staining was positive in 2 of 32. The DSA/C4d positive (n=18) and DSA/C4d negative (n=30) groups differed in pre-Tx PRA levels, percentage of re-Tx patients, refractoriness to antilymphocyte therapy, and outcome. Plasmapheresis and tacrolimus-mycophenolate mofetil rescue reversed rejection in 9 of 10 recipients with refractory AHR.

CONCLUSION

More than one-third of the patients with steroid-insensitive AR had evidence of AHR, often resistant to antilymphocyte therapy. Most cases (95%) with DSA at the time of rejection had widespread C4d deposits in peritubular capillaries, suggesting a pathogenic role of the circulating alloantibody. Combined DSA testing and C4d staining provides a useful approach for the early diagnosis of AHR, a condition that often necessitates a more intensive therapeutic rescue regimen.

Induction of antigraft and antirecipient antibody responses after fully allogeneic and semiallogeneic rat small bowel transplantation

BACKGROUND

Given the potential influence of alloantibodies on organ graft outcome, this study investigated the induction of antigraft and antirecipient antibodies after allogeneic and semiallogeneic rat small bowel transplantation.

METHODS

Fully allogeneic, unidirectional rejection and unidirectional graft-versus-host disease (GvHD) heterotopic small bowel transplantation was performed using DA, PVG, and (PVGxDA)F1 donor-recipient combinations. Serum was obtained before and at time points after transplantation and incubated with blood from untransplanted DA and PVG rats. Antibody binding to T cells was detected by whole blood flow cytometry using FITC-conjugated anti-rat IgM murine monoclonal antibody. Antibody levels were determined by reference to a standard curve of fluorescent intensity generated using a serum sample with known anti-target cell IgM activity. Data are presented as arbitrary units/ml (AU/ml).

RESULTS

In the PVG-->DA combination, five of six DA recipients had detectable anti-graft (PVG) antibodies by day 4 after transplantation (mean 72 AU/ml) and all animals were positive by day 6 (976 AU/ml). Antirecipient (DA) antibodies were also induced, however, they were only apparent after 6 days in five of eight animals (90 AU/ml). Antigraft (DA) antibody responses were also induced in the DA-->PVG combination (day 6-218 AU/ml), however no antirecipient (PVG) response was apparent. Transplantation induced antirecipient (DA) antibodies in the unidirectional GvHD model (day 6-90 AU/ml) and an anti-graft (PVG) response in the unidirectional rejection model (day 6-60 AU/ml). However, the latter was quantitatively lower than that generated in the PVG-->DA combination (day 6-976 AU/ml).

CONCLUSIONS

Antigraft and antirecipient antibody responses are simultaneously induced after fully allogeneic small bowel transplantation, despite rejection being the predominant clinical feature. Further studies are required to elucidate their influence on graft outcome.

Human leukocyte antigen matching in renal transplantation: an update

Cadaveric kidney allocation, in most countries, is based on human leukocyte antigen matching of the donor kidney with the recipient. Traditional human leukocyte antigen matching is based on defining human leukocyte antigen specificities by antibodies. Newer techniques have emerged from the tissue typing laboratory, which challenge the accuracy of serological typing and crossmatching. Improvements in renal allograft survival, predominantly as a result of newer immunosuppressive drugs, have led to longer survival times even in poorly matched human leukocyte antigen renal allografts. The scarcity of donor organs has focused attention on organ allocation policies, and the exact role of human leukocyte antigen matching in renal transplantation is under scrutiny. In this review, we examine developments in human leukocyte antigen matching as well as attempts to utilize this information to allocate cadaveric kidneys optimally.

Treatment of antibody-mediated accelerated rejection using plasmapheresis

Accelerated antibody-mediated rejection is believed to be due to an anamnestic response of an allograft recipient to donor antigens. Few reports have demonstrated successful reversal of this type of rejection, and no consensus exists for either diagnosis or treatment. Accelerated antibody-mediated rejection was suspected on the basis of clinical findings and confirmed by cytotoxic and flow crossmatches, and leukocyte antibody screens. Serial crossmatches and antibody screens were performed through post-transplant day 112. Plasmapheresis was performed on post-transplant days 1, 2, 4, 6, 12, 14, 20, and 28. The duration of treatment was determined by the cytotoxic crossmatch results. We present a case of successfully treated accelerated antibody-mediated rejection using plasmapheresis and aggressive immunosuppression. Serial crossmatch and leukocyte antibody screen results are presented that confirm the production of anti-donor antibody and demonstrate the effectiveness of the treatment protocol in eliminating detectable levels of the anti-donor antibody. At 6 months post-transplant, the patient has a serum creatinine of 1.1 and has not had any additional rejection episodes or infectious complications. The protocol suggested in this paper allows for rapid diagnosis, institution of treatment, and monitoring the efficacy of treatment, providing the basis for follow-up clinical trials.

Plasmapheresis and intravenous immune globulin provides effective rescue therapy for refractory humoral rejection and allows kidneys to be successfully transplanted into cross-match-positive recipients

BACKGROUND

Hyperacute rejection (HAR) and acute humoral rejection (AHR) remain recalcitrant conditions without effective treatments, and usually result in graft loss. Plasmapheresis (PP) has been shown to remove HLA- specific antibody (Ab) in many different clinical settings. Intravenous gamma globulin (IVIG) has been used to suppress alloantibody and modulate immune responses. Our hypothesis was that a combination of PP and IVIG could effectively and durably remove donor-specific, anti-HLA antibody (Ab), rescuing patients with established AHR and preemptively desensitizing recipients who had positive crossmatches with a potential live donor.

METHODS

The study patients consisted of seven live donor kidney transplant recipients who experienced AHR and had donor-specific Ab (DSA) for one or more mismatched donor HLA antigens. The patients segregated into two groups: three patients were treated for established AHR (rescue group) and four cross-match-positive patients received therapy before transplantation (preemptive group).

RESULTS

Using PP/IVIG we have successfully reversed established AHR in three patients. Four patients who were cross-match-positive (3 by flow cytometry and 1 by cytotoxic assay) and had DSA before treatment underwent successful renal transplantation utilizing their live donor. The overall mean creatinine for both treatment groups is 1.4+/-0.8 with a mean follow up of 58+/-40 weeks (range 17-116 weeks).

CONCLUSIONS

In this study, we present seven patients for whom the combined therapies of PP/IVIG were successful in reversing AHR mediated by Ab specific for donor HLA antigens. Furthermore, this protocol shows promise for eliminating DSA preemptively among patients with low-titer positive antihuman globulin-enhanced, complement-dependent cytotoxicity (AHG-CDC) cross-matches, allowing the successful transplantation of these patients using a live donor without any cases of HAR.

Role of humoral immune reactions as target for antirejection therapy in recipients of a spousal-donor kidney graft

Excellent graft outcome has been reported for spousal-donor kidney transplantation. In husband-to-wife transplantation, however, a tendency toward inferior graft survival has been described for recipients who were previously pregnant. In our series of spousal-kidney transplantations (nine transplantations; three female recipients), actual graft survival is 100% (median observation time, 339 days). Five patients experienced early allograft rejection. In four transplant recipients, rejection was easily reversible by conventional antirejection therapy. In a multiparous recipient, however, mild interstitial allograft rejection associated with early graft dysfunction was resistant to anticellular treatment (antilymphocyte antibody, tacrolimus rescue therapy). The particular finding of polymorphonuclear neutrophils in peritubular capillaries and the finding of diffuse capillary deposits of the complement split product, C4d, in a posttransplantation biopsy specimen suggested a role of antibody-mediated graft injury. Retrospective flow cytometry cross-matching showed the presence of preformed immunoglobulin G (IgG) antibodies to HLA class I antigens that were not detectable by pretransplantation lymphocytotoxic cross-match testing or screening for panel reactive antibodies. After transplantation, however, complement-fixing antibodies, also presumably triggered by reexposure to spousal-donor HLA antigens, could be detected in the patient's serum. These findings suggested antibody-mediated allograft rejection and led to the initiation of immunoadsorption therapy (14 sessions) with staphylococcal protein A. Selective removal of recipient IgG resulted in complete reversal of graft dysfunction. Our findings suggest that in husband-to-wife transplantation, donor-specific antibodies, presumably triggered by previous pregnancies, might occasionally induce sustained allograft dysfunction. Thus, in this particular setting, a detailed immunologic and histopathologic work-up regarding antibody-mediated allograft dysfunction is warranted because immunoadsorption may be a highly effective treatment modality.

Specific B cell tolerance is induced by cyclosporin A plus donor-specific blood transfusion pretreatment: prolonged survival of MHC class I disparate cardiac allografts

Donor-specific blood transfusion (DST), designed to prolong allograft survival, sensitized recipients of the high-responder PVG-RT1u strain, resulting in accelerated rejection of MHC-class I mismatched (PVG-R8) allografts. Rejection was found to be mediated by anti-MHC class I (Aa) alloantibody. By pretreating recipients 4 wk before grafting with cyclosporin A (CsA) daily (x7), combined with once weekly (x4) DST, rejection was prevented. The investigation explores the mechanism for this induced unresponsiveness. CD4 T cells purified from the thoracic duct of CsA/DST-pretreated RT1u rats induced rejection when transferred to R8 heart-grafted RT1u athymic nude recipients, indicating that CD4 T cells were not tolerized by the pretreatment. To determine whether B cells were affected, nude recipients were pretreated, in the absence of T cells, with CsA/DST (or CsA/third party blood) 4 wk before grafting. The subsequent transfer of normal CD4 T cells induced acute rejection of R8 cardiac allografts in third party- but not DST-pretreated recipients; prolonged allograft survival was reversed by the cotransfer of B cells with the CD4 T cells. Graft survival correlated with reduced production of anti-MHC class I (Aa) cytotoxic alloantibody. The results indicated that the combined pretransplant treatment of CsA and DST induced tolerance in allospecific B cells independently of T cells. The resulting suppression of allospecific cytotoxic Ab correlated with the survival of MHC class I mismatched allografts. The induction of B cell tolerance by CsA has important implications for clinical transplantation.

Plasmapheresis, intravenous cytomegalovirus-specific immunoglobulin and reversal of antibody-mediated rejection in a pediatric renal transplant recipient: a case report

This is a pediatric case report illustrating the development of antibody (Ab)-mediated rejection in a patient with low levels of pretransplant anti-human leucocyte antigen (HLA) panel reactive antibodies (PRA). The clinical course of this patient suggests that aggressive use of a combination of plasmapheresis, monoclonal anti-T-lymphocyte antibody therapy, and intravenous immunoglobulin (IVIG) therapy can reverse Ab-mediated rejection in previously allosensitized pediatric transplant recipients.

Prevention and restoration of second-set liver allograft rejection in presensitized mice: the role of "passenger" leukocytes, donor major histocompatibility complex antigens, and host cytotoxic effector mechanisms

BACKGROUND

The aim was to determine whether sublethal donor total body irradiation (TBI) might be as effective as lethal TBI in preventing mouse second-set liver allograft rejection, and to evaluate the role of passenger leukocytes, donor major histocompatibility complex (MHC) antigens, and host effector mechanisms in the response to livers from sublethally irradiated donors.

METHODS

B10 (H2b) donors received various doses of TBI at different times before their livers were transplanted orthotopically into normal or donor skin-presensitized C3H (H2k) recipients. The influence of irradiation on graft non-parenchymal cells (NPC) was determined by monoclonal antibody staining, and flow cytometric analysis. Hematopoietic cells within the grafts were reconstituted by intravenous infusion of syngeneic or third-party bone marrow cells. Allograft survival was determined in recipients that received no treatment, or that were given spleen cells from either normal B10 donors, or MHC class I - or class II-deficient mice syngeneic with the donors. Cytotoxic activity of graft-infiltrating cells and host spleen cells, and complement-dependent cytotoxic alloantibody titers were determined by isotype release assays.

RESULTS

The protective effect of donor TBI was observed both at lethal (9.5 Gy) and sublethal doses (5 and 3 Gy; graft median survival time: >100 days). Extended delay in liver transplantation, allowing hematopoietic recovery and graft reconstitution eliminated the effect. Liver NPC were reduced about 80% within 24 hr of 3 Gy TBI, with a selective reduction in the incidence of B cells. The NPC-depleted livers underwent accelerated rejection when donor (but not third-party) spleen cells (5 x 10(7) were administered systemically to the recipient immediately after graft revascularization. Spleen cells from MHC class I-deficient (but not MHC class II-deficient) mice failed to fully restore accelerated rejection of TBI liver grafts. Freshly isolated graft NPC, or spleen cells from TBI liver recipients, harvested 4 days after transplantation, exhibited lower, donor-specific cytotoxic activity than cells from mice given normal livers. Recipients of TBI livers also showed much lower serum complement-dependent cytotoxic alloantibody titers.

CONCLUSIONS

By substantially depleting "passenger leukocytes," sublethal donor TBI undermines anti-donor cell-mediated and humoral immune reactivity and inhibits second-set liver allograft rejection in presensitized recipients. The interval between irradiation and transplantation is important in conferring resistance to rejection. Expression of MHC class I on donor leukocyte infusions is important for overcoming resistance to second-set rejection induced by donor irradiation.

Plasma exchange and tacrolimus-mycophenolate rescue for acute humoral rejection in kidney transplantation

BACKGROUND

Acute renal allograft rejection associated with the development of donor-specific alloantibody (acute humoral rejection, AHR) typically carries a poor prognosis. The best treatment of this condition remains undefined.

METHODS

During a 14-month period, 73 renal transplants were performed. During the first postoperative month, five recipients (6.8%) with AHR were identified. The diagnosis was based on: (1) evidence of severe rejection, resistant to steroid and antilymphocyte therapy; (2) typical pathologic features; and (3) demonstration of donor-specific alloantibody (DSA) in recipient's serum at the time of rejection. Pretransplant donor-specific T- and B-cell cross-matches were negative.

RESULTS

Plasma exchange (PE, four to seven treatments per patient) significantly decreased circulating DSA to almost pretransplant levels in four of five patients, and improvement in renal function occurred in all patients. One patient had recurrent renal dysfunction in the setting of an increase in circulating DSA. A second series of five PE treatments decreased DSA and reversed the rejection episode. Rescue therapy with tacrolimus (initial mean dose: 0.14+/-0.32 mg/kg/day) and mycophenolate mofetil (2 g/day) was used in five of five and four of five patients, respectively. With a mean follow-up of 19.6+/-5.6 months, patient and allograft survival are 100%. Renal function remains excellent with a mean current serum creatinine of 1.2+/-0.3 mg/dl. (range: 0.9-1.8 mg/dl).

CONCLUSIONS

Our findings suggest that a therapeutic approach combining PE and tacrolimus-mycophenolate mofetil rescue has the potential to improve the outcome of AHR.

Analysis of the relationship between chimerism and the allgeneic humoral response

BACKGROUND

Persistence of antigens has been suggested to play a role in two opposing immunological phenomena: tolerance and memory. Therefore, we studied the impact of chimerism on alloreactive antibody (allo-Ab) production in kidney transplant patients.

METHODS

Thirty-five female renal transplant recipients of male donor organs were classified into the following groups: group 1, 13 sensitized uremic patients on dialysis; group 2, 5 nonsensitized uremic patients on dialysis; group 3, six sensitized patients experiencing graft rejection (3 acute vascular, 1 acute cellular, and 2 chronic); and group 4, 11 nonsensitized with functioning allografts (9 with good function, 1 with acute cellular rejection, and 1 with chronic rejection). Mean duration of dialysis after graft failure was similar in groups 1 (56+/-29.7 months) and 2 (41.8+/-42.4 months), as was dialysis efficiency. Chimerism was measured indirectly in the peripheral blood lymphocytes by polymerase chain reaction amplification of a specific Y chromosome DNA gene sequence with a detection sensitivity limit of 1 male cell per 1 million female cells. Allo-Ab production was measured by the PRA-STAT enzyme-linked immunosorbent assay (Sangstat) method.

RESULTS

Chimerism was observed in 60% of groups 1 and 2, 83% of group 3, and 82% of group 4. Among all groups, graft existence, irrespective of its function, positively predicted chimerism in 92% with a sensitivity of 88% and a specificity of 78%. In group 3, all three patients with acute vascular rejection had chimerism and donor-specific allo-Abs. In group 4, eight of the nine patients with no rejection had chimerism.

CONCLUSION

Chimerism relates to persistence of allogeneic stimulus irrespective of its function. Chimerism did not confer protection against allo-Ab production or vascular rejection, and its existence was not crucial for sustenance of allo-Ab production.

Contrasting outcomes of donor-specific blood transfusion: effectiveness against cell-mediated but not antibody-mediated rejection

BACKGROUND

Giving recipients a prior donor-specific blood transfusion (DST) is effective in prolonging organ allograft survival in some inbred strains but not in others. The present investigation analyzed two such contrasting strains of rats in an attempt to define the basis for this variation.

METHODS AND RESULTS

The survival of fully mismatched Dark Agouti (RT1a) cardiac allografts was significantly prolonged (from 7 to 44 days, median survival times) in PVG (RT1c) rats given a prior (-14 day) DST, whereas it shortened survival in the high-responder PVG-RT1u strain. Injecting PVG recipients with blood from strains bearing defined differences indicated that each disparity contributed to the increased survival time in an incremental way: blood and heart matched at the MHC class I (A) and/or class II (B/D) loci had a major influence on survival; class I-like (C) and non-MHC antigens made only minor contributions. MHC disparities had contrasting effects in RT1u rats. Blood transfusions from Dark Agouti or PVG-R8 (AaB/DuCu) rats induced accelerated rejection and anti-Aa alloantibody formation; transfusing PVG-R23 (AuB/DaCa) blood, a class II and class I-like difference, induced indefinite R23 heart allograft survival. Although produced in high titer, anti-class II antibody was not able to induce rejection in RT1u rats. Specific anti-Aa alloantibody was able, after passive transfer, to destroy class I-disparate allografts in both RT1u nude and PVG nude recipients. However, under normal circumstances, acute rejection in the PVG strain occurred in the absence of anti-Aa antibodies, presumably by a cell-mediated mechanism.

CONCLUSION

Anti-class I alloantibody, when produced, seemed to override the unresponsiveness induced by DST. The results indicated that DST was effective only when rejection was induced by a cell-mediated response. The two contrasting response patterns in animals may reflect the experience of transplant patients who either benefit from DST or become sensitized instead.

Patterns of allosensitization in allograft recipients: long-term cardiac allograft acceptance is associated with active alloantibody production in conjunction with active inhibition of alloreactive delayed-type hypersensitivity

BACKGROUND

The immunologic characteristics of experimental allograft acceptance remain ill-defined. This study evaluates humoral and cell-mediated immunity in transiently immunosuppressed mice that have accepted cardiac allografts.

METHODS

DBA/2-->C57BL/6 heterotopic cardiac allograft recipients were immunosuppressed with either GK1.5 monoclonal antibody or gallium nitrate and monitored for donor-reactive delayed-type hypersensitivity (DTH) assessed by ear challenge and for alloantibody production detected by flow cytometry.

RESULTS

Cardiac allograft function continued for >90 days in approximately 50% of GK1.5-treated and 97% of gallium nitrate-treated transplant recipients. All nonsuppressed recipients lost graft function within 7 to 10 days. Among mice that accepted allografts, donor-reactive IgG was produced by about 50% of GK1.5 monoclonal antibody-treated mice and 80% of gallium nitrate-treated mice. None of the these mice exhibited donor-reactive DTH responses, and all could down-regulate third-party DTH responses in a donor alloantigen-dependent manner. This down-regulation is not found in nonsuppressed allograft recipients or in naive mice. Importantly, transfer into SCID mice of splenocytes from mice that accepted allografts, but not naive splenocytes, provided them with a similar ability to accept cardiac allografts, even if the grafts co-expressed third-party alloantigens.

CONCLUSIONS

IgG alloantibody production by murine cardiac allograft recipients is not a precise indicator of allosensitization leading to either cardiac allograft rejection or acceptance. However, expression of alloreactive DTH is a reliable indicator of allosensitization leading to acute rejection, and the absence of DTH in association with active DTH down-regulatory mechanisms is a reliable indicator of allograft acceptance in this experimental model. Thus, DTH analysis may hold more promise than alloantibody detection for clinical assessment of posttransplant immune status.

Role of electron microscopy in transplant renal pathology

The crucial role that electron microscopy plays in diagnostic renal pathology is undisputed. By allowing recognition of findings not identifiable by light microscopic evaluation, electron microscopy has contributed significantly to the understanding of renal diseases and has proven to be of unquestionable value in many diagnostic situations. However, the percentage of cases in which electron microscopic examination adds important information that is either key for establishing or confirming a diagnosis or provides valuable data that influence patient's management remains controversial. This figure depends on the renal biopsy service that is surveyed, but it is reported that on the average ultrastructural evaluation is of value in approximately 30 to 45% of the cases. Correct interpretation of a renal biopsy depends on the ability to correlate light, immunofluorescence, and ultrastructural findings. In contrast, the role of electron microscopy in the examination of renal transplant specimens remains controversial. Many centers do not use routine electron microscopy to examine these specimens and insist that there are only a few specific indications that require ultrastructural evaluation. There is general agreement among renal pathologists that electron microscopy is of importance in the evaluation of renal specimens from patients with proteinuria to distinguish between transplant glomerulopathy, recurrent or de novo glomerulonephritis in order to correctly manage these patients and predict survival of the graft. The other possible indications are much more controversial. This paper summarizes and critically reviews the literature available on this subject and defines recommendations based on the information available at the current time.

Expression of the membrane attack complex of complement and its inhibitors during human liver allograft transplantation

BACKGROUND/AIMS

In order to test the possible role of activated complement in human liver allograft rejection, we evaluated the expression of the membrane attack complex of complement, its soluble inhibitors clusterin and vitronectin and its membrane inhibitor protectin during the evolution of liver transplants.

METHODS

An indirect immunoperoxidase technique was applied to biopsy specimens obtained from liver allografts in 16 patients without complications, nine with acute rejection, four with chronic rejection and five with biliary complications.

RESULTS

Two types of membrane attack complex deposition were observed: (a) extracellular deposits in portal tracts and perisinusoidal matrix, associated with clusterin and vitronectin, similar to those found in the normal liver; and (b) intra-portal vascular deposits, devoid of clusterin and vitronectin. Vascular membrane attack complex deposition was detected in four clinically stable patients, three patients with chronic rejection and two patients with biliary complications. In clinically stable patients, vascular membrane attack complex deposition was restricted to large portal vessels and was detected in a minority of portal tracts. In patients with chronic rejection or biliary complications, vascular membrane attack complex deposition was detected along both large and small portal vessels and was present in the majority of portal tracts. Protectin induction on hepatocytes was detected in 33 cases.

CONCLUSIONS

Our results suggest that membrane attack complex deposition is unlikely to play a major role in the pathogenesis of acute liver allograft rejection but may contribute to the vascular and biliary lesions observed in chronic rejection.

Influence of complement on the allospecific antibody response to a primary vascularized organ graft

The induction of antibody responses against T cell-dependent antigens has been reported to be influenced by complement. We therefore asked if the primary induction of alloantibodies against transplantation antigens, an important determinant of transplant outcome, is complement sensitive and whether this has functional implications. We transplanted rat kidney allografts into fully major histocompatibility complex-mismatched recipients, in which complement activation was inhibited by daily injection of soluble recombinant human complement receptor type 1 (sCR1). Control allograft recipients were injected with saline. Animals in the control group showed a marked antibody response against donor-specific antigens and an increase in the proportion of activated B and T splenocytes by day 5 after transplantation. Complement-inhibited rats showed a reduced level of antibody binding on target cells sharing the same histocompatibility antigens as the donor strain (p < 0.001), and a reduced level of activated splenic B (p < 0.01) and T (p < 0.01) cells. In a functional assay, the plasma of complement-inhibited rats showed reduced cytotoxic activity against donor-specific cells, and their grafts contained less bound antibody than controls. Analysis beyond 6 days was obscured due to the development of antibodies against sCR1. We conclude that complement activation facilitates the induction of the alloantibody response. Sparing of vascular injury and prolongation of graft survival, previously reported in complement-inhibited rats (Pratt J. R. et al., Am. J. Path. 1996, 149: 2055), could therefore be due to down-regulation of the B cell response as well as reduced complement-dependent cytotoxicity. Inhibition of complement may provide an ancillary approach to the prevention of allospecific antibody formation and the prolongation of allograft survival in primary kidney grafting.

Antibody-mediated rejection of human renal allografts: an electron microscopic study of peritubular capillaries

The role of humoral rejection in acute and chronic rejection of human renal allografts other than in hyperacute rejection has not been well established, and its importance may be underestimated. Recently, a specific histological pattern of antibody-mediated rejection of renal allografts has been recognized. The antigens targeted by this mode of rejection are not well defined but are likely located on the endothelium of small vessels (arterioles and glomerular and peritubular capillaries). In both cellular and humoral rejection, the microvasculature of transplanted organs appears to be a main target of injury. This study describes the ultrastructural changes of peritubular capillaries, over a period of up to 8 months, in 14 biopsy specimens obtained from 5 renal allograft recipients diagnosed with "pure" antibody-mediated rejection. In peritubular capillaries, there is progression of injury from necrosis of endothelial cells with lifting and denudation of basement membrane to complete disappearance of capillaries. Acutely, acute tubular necrosis is a constant finding. At 2 to 3 months post-transplantation, the remaining capillaries are dilated, misshapen, and distorted, and are surrounded by a reduplicated and thickened basement membrane. These changes are associated with increased interstitial fibrosis and tubular atrophy, comparable to a sort of renal "asphyxial" death. The author concludes that in "pure" antibody-mediated rejection, the endothelium of peritubular capillaries is a main target of injury. The potential role of antibody-mediated rejection in acute and chronic rejection of renal allografts needs to be explored further.

Pathologic features of acute renal allograft rejection associated with donor-specific antibody, Analysis using the Banff grading schema

Alloantibody frequently appears during the immune response to alloantigens in renal transplant recipients. We studied whether the presence of antibody against donor class I antigens correlated with the clinical and pathologic features of acute rejection episodes. We identified patients who had (1) clinical evidence of acute rejection, (2) a renal biopsy showing pathologic features of acute rejection, defined by the Banff criteria, and (3) pre- and posttransplant sera screened against donor T cells. We divided these patients into those with or without donor-specific alloantibody reactive with donor T cells. Of 44 patients with biopsy-proven rejection, 20 were antibody negative (Ab-R) and 24 were antibody positive (Ab+R). The biopsies from Ab+R patients had a higher incidence of severe vasculitis (P=0.0009) and glomerulitis (P=0.01). Fibrin thrombi in the glomeruli and/or vessels, fibrinoid necrosis, and dilatation of peritubular capillaries were also more frequent in the Ab+R group. Infarction was present in biopsy specimens from 9/24 Ab+R patients versus none in the Ab-R group (P=0.002). The Ab+R biopsy specimens more often had polymorphonuclear leukocytes in the peritubular capillaries (P=0.003). In contrast, specimens of Ab-R patients showed tubulitis more often than the specimens of Ab+R patients: moderate and severe tubulitis was present in 19/20 (95%) Ab-R patients versus 12/24 (50%) Ab+R patients (P=0.002). Graft loss was increased in Ab+R patients, particularly in the first 3 months (12/24 compared with 3/20, P=0.025). Thus, during biopsy-proven acute rejection episodes, anti-class I antibody correlates with severe vascular lesions, glomerulitis, and infarction, whereas more severe tubulitis predominates in rejection episodes without antibody.

The humoral response to vascular and nonvascular allografts of bone

The cytotoxic donor specific antibody response after vascularized and nonvascularized bone allograft implantation was assessed in rats and dogs. Nonvascularized segmental femoral grafts were studied in rats; nonvascularized fresh and cryopreserved massive osteochondral allografts were studied in dogs; and vascularized and nonvascularized fibular allografts were studied in dogs. The major histocompatibility complex antigens of all animals were defined. All grafts were stabilized by internal fixation and the antibody response was measured in a 51chromium release microcytotoxicity assay using donor lymphocytes as target cells. In all cases, donor specific antibody responses were elicited by major histocompatibility complex mismatched grafts. The response was directed primarily at Class I specificities although there was likely and antiClass II response as well. Among fully mismatched grafts, antidonor antibody was detectable earlier in animals receiving vascularized grafts (1 week after surgery) than in animals receiving nonvascularized grafts (3 weeks after surgery). Massive grafts elicited a sustained response whereas relatively smaller grafts, such as the fibula did not. The antidonor antigen antibody response was transient and less frequent in animals receiving frozen grafts. The clinical implications of these data are unclear. Although some improvement of clinical outcome has been observed with grafts matched for major histocompatibility complex antigens, the potential benefits of tissue antigen matching or modulation of the host immune response remain unresolved.

International standardization of criteria for the histologic diagnosis of renal allograft rejection: the Banff working classification of kidney transplant pathology

A group of renal pathologists, nephrologists, and transplant surgeons met in Banff, Canada on August 2-4, 1991 to develop a schema for international standardization of nomenclature and criteria for the histologic diagnosis of renal allograft rejection. Development continued after the meeting and the schema was validated by the circulation of sets of slides for scoring by participant pathologists. In this schema intimal arteritis and tubulitis are the principal lesions indicative of acute rejection. Glomerular, interstitial, tubular, and vascular lesions of acute rejection and "chronic rejection" are defined and scored 0 to 3+, to produce an acute and/or chronic numerical coding for each biopsy. Arteriolar hyalinosis (an indication of cyclosporine toxicity) is also scored. Principal diagnostic categories, which can be used with or without the quantitative coding, are: (1) normal, (2) hyperacute rejection, (3) borderline changes, (4) acute rejection (grade I to III), (5) chronic allograft nephropathy ("chronic rejection") (grade I to III), and (6) other. The goal is to devise a schema in which a given biopsy grading would imply a prognosis for a therapeutic response or long-term function. While the clinical implications must be proven through further studies, the development of a standardized schema is a critical first step. This standardized classification should promote international uniformity in reporting of renal allograft pathology, facilitate the performance of multicenter trials of new therapies in renal transplantation, and ultimately lead to improvement in the management and care of renal transplant recipients.