Renal transplantation following immunoadsorption in highly sensitized recipients

Therapeutic Potential of HLA-I Polyreactive mAbs Mimicking the HLA-I Polyreactivity and Immunoregulatory Functions of IVIg

HLA class-I (HLA-I) polyreactive monoclonal antibodies (mAbs) reacting to all HLA-I alleles were developed by immunizing mice with HLA-E monomeric, α-heavy chain (αHC) open conformers (OCs). Two mAbs (TFL-006 and TFL-007) were bound to the αHC’s coated on a solid matrix. The binding was inhibited by the peptide ¹¹⁷AYDGKDY¹²³, present in all alleles of the six HLA-I isoforms but masked by β2-microglobulin (β2-m) in intact HLA-I trimers (closed conformers, CCs). IVIg preparations administered to lower anti-HLA Abs in pre-and post-transplant patients have also shown HLA-I polyreactivity. We hypothesized that the mAbs that mimic IVIg HLA-I polyreactivity might also possess the immunomodulatory capabilities of IVIg. We tested the relative binding affinities of the mAbs and IVIg for both OCs and CCs and compared their effects on (a) the phytohemagglutinin (PHA)-activation T-cells; (b) the production of anti-HLA-II antibody (Ab) by B-memory cells and anti-HLA-I Ab by immortalized B-cells; and (c) the upregulation of CD4+, CD25+, and Fox P³+ T-regs. The mAbs bound only to OC, whereas IVIg bound to both CC and OC. The mAbs suppressed blastogenesis and proliferation of PHA-activated T-cells and anti-HLA Ab production by B-cells and expanded T-regs better than IVIg. We conclude that a humanized version of the TFL-mAbs could be an ideal, therapeutic IVIg-mimetic.

B cells in transplant tolerance and rejection: friends or foes?

Our understanding of the role of B cells in organ transplantation remains incomplete and continues to grow. The majority of research has focused on the detrimental role of antibodies that drive the development of pathogenesis of the transplanted organ. However, it has been shown that not all donor-specific antibodies are harmful and in some circumstances can even promote tolerance through the mechanism of accommodation. Furthermore, B cells can have effects on transplanted organs through their interaction with T cells, namely antigen presentation, cytokine production, and costimulation. More recently, the role and importance of Bregs was introduced to the field of transplantation. Due to this functional and ontogenetic heterogeneity, targeting B cells in transplantation may bring undesired immunologic side effects including increased rejection. Therefore, the selective control of B cells that contribute to the humoral response against donor antigens will continue to be an important and challenging area of research and potentially lead to improved long-term transplant outcomes.

Molecular events contributing to successful pediatric cardiac transplantation in HLA sensitized recipients

Antibodies to HLA resulting in positive cytotoxicity crossmatch are generally considered a contraindication for cardiac transplantation. However, cardiac transplantations have been performed in children by reducing the Abs and modifying immunosuppression. To identify mechanisms leading to allograft acceptance in the presence of Abs to donor HLA, we analyzed priming events in endothelial cells (EC) by incubating with sera containing low levels of anti-HLA followed by saturating concentration of anti-HLA. Pre-transplant sera were obtained from children with low levels of Abs to HLA who underwent transplantation. EC were selected for donor HLA and exposed to sera for 72 h (priming), followed by saturating concentrations of anti-HLA (challenge). Priming of EC with sera induced the phosphatidylinositol 3-kinase/Akt mediated by the BMP4/WNT pathway and subsequent challenge with panel reactive antibody sera increased survival genes Bcl2 and Heme oxygenase-1, decreased adhesion molecules, induced complement inhibitory proteins and reduced pro-inflammatory cytokines. In contrast, EC which did not express donor HLA showed decreased anti-apoptotic genes. Primed EC, upon challenge with anti-HLA, results in increased survival genes, decreased adhesion molecules, induction of complement inhibitory proteins, and downregulation of pro-inflammatory cytokines which may result in accommodation of pediatric cardiac allografts despite HLA sensitization.

Cardiac antibody-mediated rejection

Many factors limit short- and long-term survival after pediatric heart transplantation. Historically, attention had been directed toward T-cell responses and acute cellular rejection. Presence of pretransplant antibodies against HLA is associated with increased donor wait times and poor post-transplant outcomes. Therapies aimed to mitigate circulating antibodies include plasmapheresis, protein A immunoadsorption columns, intravenous immune globulin, rituximab, and bortezomib. The negative effects of B cells, HLA antibodies, and AMR and potential interventions are the focus of this review article.

Mechanism of accommodation in a sensitized human leukocyte antigen transgenic murine cardiac transplant model

BACKGROUND

Presence of donor-specific antibodies (Abs) is detrimental to posttransplant allograft function. Some sensitized recipients have successfully undergone transplantation after pretransplant conditioning regimen using plasmapheresis and/or intravenous immunoglobulin therapy, but underlying mechanisms that confer such allograft protection are undefined.

METHODS

We developed a single human leukocyte antigen (HLA)-mismatched heterotopic murine heart transplant model (HLA-A2 into HLA-A2-sensitized-C57BL/6) to determine whether pretreatment of donors with low concentration of HLA class I (W6/32) or control Ab (C1.18.4) will confer protection. Expression levels of survival genes, Bcl-2 and heme oxygenase-1, were analyzed by gene array analysis and quantitative real-time polymerase chain reaction. Expression levels of cytokine panel were analyzed by Luminex. Role of Bcl-2 in the induction of allograft protection was analyzed by silencing the Bcl-2 expression in the donor hearts using a small hairpin (shRNA) specific for Bcl-2.

RESULTS

Control Ab-pretreated hearts were rejected in less than 5 days demonstrating hemorrhage, Ab, and C4 deposition. In contrast, W6/32-pretreated hearts were rejected at 15 days (P<0.05) that was prolonged to 25 days with antilymphocyte serum treatment. W6/32-pretreated hearts on day 5 exhibited increased expression of Bcl-2 (5.5-folds), Bcl-xl (5.5-folds), and heme oxygenase-1 (4.4-folds); decreased expression of ICAM-1, VCAM-1 (3.2-fold), along with reduced levels of cytokines interleukin (IL)-1β (4.4-folds), tumor necrosis factor α (3.7-folds), IL-6 (7.5-folds), IL-12 (2.3-folds) and chemokines monocyte chemotactic protein 1 (4.5-folds), MIG (4.4-folds), MIP-1α (3.4-folds), and IL-8 (3.1-folds). Silencing of Bcl-2 in accommodated hearts before transplant resulted in loss of protection with rejection (9±3 vs. 15±2days, P<0.05).

CONCLUSION

Pretreatment of hearts with low levels of anti-HLA Abs increases expression of antiapoptotic genes that inhibits caspases, leading to decreased inflammatory cytokines and chemokines, which promote allograft survival.

Living donor kidney transplantation across positive crossmatch: the University of Illinois at Chicago experience

BACKGROUND

To increase living donation for kidney transplantation, we investigated desensitization of recipients with positive crossmatch against a potential living donor.

METHODS

Between June 2001 and March 2007, 57 consecutive sensitized candidates for kidney transplantation, with crossmatch positive potential living donors, were treated with various desensitization protocols. All patients received plasmapheresis every other day with intravenous immune globulin 100 mg/kg starting 1 week before the scheduled transplant. Postoperatively, the recipients continued to receive every other day plasmapheresis with intravenous immune globulin for the initial week. Immunosuppression therapy consisted of induction with thymoglobulin and a combination of tacrolimus, mycophenolate, and corticosteroids.

RESULTS

Six patients failed to convert with pretransplant immunomodulation and were not transplanted; 51 underwent live donor kidney transplant. Mean follow-up was 23 months and 36 patients have more than 1-year follow-up. One-year patient and graft survivals were 95% and 93%, respectively. There were 25 episodes of biopsy-proven or clinically presumed rejection in 22 patients in the first year. Of the 17 biopsy-proven episodes, 12 were antibody-mediated rejection and five were acute cellular rejection. Of the patients with antibody-mediated rejection (biopsy proven or empiric), two patients (12%) lost their graft by 1 year. The median modification of diet in renal disease at 6 and 12 months was 55 mL/min (range 9-104 mL/min) and 48 mL/min (range 8-99), respectively.

CONCLUSIONS

Despite increased rejection rates, graft and patient survivals indicate that desensitization of positive crossmatch patients is a reasonable alternative for a sensitized patient who could potentially wait 10 or more years for a suitable cadaveric kidney.

C4d deposition without rejection correlates with reduced early scarring in ABO-incompatible renal allografts

C4d deposition in peritubular capillaries is a specific marker for the presence of antidonor antibodies in renal transplant recipients and is usually associated with antibody-mediated rejection (AMR) in conventional allografts. In ABO-incompatible grafts, however, peritubular capillary C4d is often present on protocol biopsies lacking histologic features of AMR; the significance of C4d in this setting remains unclear. For addressing this, data from 33 patients who received ABO-incompatible renal allografts (after desensitization) were retrospectively reviewed. Protocol biopsies were performed at 1 and/or 3 and 6 mo after transplantation in each recipient and at 12 mo in 28 recipients. Twenty-one patients (group A) had strong, diffuse peritubular capillary C4d staining without histologic evidence of AMR or cellular rejection on their initial protocol biopsies. The remaining 12 patients (group B) had negative or weak, focal peritubular capillary C4d staining. Three grafts (two in group B) were lost but not as a result of AMR. Excluding these three patients, serum creatinine levels were similar in the two groups at 6 and 12 mo after transplantation and at last follow-up; however, recipients in group A developed significantly fewer overall chronic changes, as scored by the sum of Banff chronic indices, than group B during the first year after transplantation. These results suggest that diffuse peritubular capillary C4d deposition without rejection is associated with a lower risk for scarring in ABO-incompatible renal allografts; the generalizability of these results to conventional allografts remains unknown.

C5 blockade with conventional immunosuppression induces long-term graft survival in presensitized recipients

We explored whether a functionally blocking anti-C5 monoclonal antibody (mAb) combined with T- and B-cell immunosuppression can successfully prevent antibody-mediated (AMR) and cell-mediated rejection (CMR) in presensitized murine recipients of life-supporting kidney allografts. To mimic the urgent clinical features of AMR experienced by presensitized patients, we designed a murine model in which BALB/c recipients were presensitized with fully MHC-mismatched C3H donor skin grafts one week prior to C3H kidney transplantation. Presensitized recipients demonstrated high levels of circulating and intragraft antidonor antibodies and terminal complement activity, rejecting grafts within 8.5 +/- 1.3 days. Graft rejection was predominantly by AMR, characterized by interstitial hemorrhage, edema and glomerular/tubular necrosis, but also demonstrated moderate cellular infiltration, suggesting CMR involvement. Subtherapeutic treatment with cyclosporine (CsA) and LF15-0195 (LF) did not significantly delay rejection. Significantly, however, the addition of anti-C5 mAb to this CsA/LF regimen prevented terminal complement activity and inhibited both AMR and CMR, enabling indefinite (>100 days) kidney graft survival despite the persistence of antidonor antibodies. Long-term surviving kidney grafts expressed the protective proteins Bcl-x(S/L) and A-20 and demonstrated normal histology, suggestive of graft accommodation or tolerance. Thus, C5 blockade combined with routine immunosuppression offers a promising approach to prevent graft loss in presensitized patients.

Results of positive cross-match transplantation in African American renal transplant recipients

Positive cross-match (PXM) renal transplantation has been utilized to address the issue of the increasing demand for transplantation with the shortage of suitable organs. Our primary objective was to analyze the outcomes of African American (AA) PXM renal transplant recipients utilizing AA negative cross-match (NXM) renal transplant recipients as a comparator group. This was a retrospective study consisting of all PXM patients who underwent a desensitization protocol and all AA NXM transplant recipients at the University of Illinois at Chicago from July 2001 to March 2007. We found that AA PXM recipients had significantly lower estimated glomerular filtration rate (eGFR) at 1 year than AA NXM (46.2 vs. 60.6, p = 0.007). AA PXM who experienced acute rejection within the first year were more likely to have an eGFR less than 30 mL/min/1.73 m(2) at 1 year compared to their NXM counterparts (45.5% vs. 12.5%, p = 0.034). Positive cross-match renal transplantation in AA seems to be associated with a high degree of AR and severe renal compromise at 1 year. Larger studies are needed to determine if protocols that are associated with good short-term outcomes in non-AA need to be modified for the AA population.

Expression of complement regulatory proteins in accommodated xenografts induced by anti-alpha-Gal IgG1 in a rat-to-mouse model

Anti-graft antibodies are often associated with graft rejection. Under special conditions, grafts continue to function normally even in the presence of anti-graft antibodies and complement. This condition is termed accommodation. We developed a xenograft accommodation model in which baby Lewis rat hearts are transplanted into Rag/GT-deficient mice, and accommodation is induced by repeated i.v. injections of low-dose anti-alpha-Gal IgG(1). The accommodated grafts survived a bolus dose of anti-alpha-Gal IgG(1), while freshly transplanted second grafts were rejected. To study the mechanism of anti-alpha-Gal IgG(1)-mediated accommodation, both real-time PCR and immunohistochemical staining revealed elevated expression of DAF, Crry and CD59 in the accommodated grafts. In vitro exposure of rat endothelial cells to anti-alpha-Gal IgG(1) also induced the up-regulation of DAF, Crry and CD59, as revealed by Western blot analyses, and was associated with an acquired resistance to antibody and complement-mediated lysis in vitro. Collectively, these studies suggest that the up-regulation of complement regulatory proteins may abrogate complement-mediated rejection and permit the development of xenograft accommodation.

Inhibition of Terminal Complement Components in Presensitized Transplant Recipients Prevents Antibody-Mediated Rejection Leading to Long-Term Graft Survival and Accommodation

Ab-mediated rejection (AMR) remains the primary obstacle in presensitized patients following organ transplantation, as it is refractory to anti-T cell therapy and can lead to early graft loss. Complement plays an important role in the process of AMR. In the present study, a murine model was designed to mimic AMR in presensitized patients. This model was used to evaluate the effect of blocking the fifth complement component (C5) with an anti-C5 mAb on prevention of graft rejection. BALB/c recipients were presensitized with C3H donor skin grafts 7 days before heart transplantation from the same donor strain. Heart grafts, transplanted when circulating anti-donor IgG Abs were at peak levels, were rejected in 3 days. Graft rejection was characterized by microvascular thrombosis and extensive deposition of Ab and complement in the grafts, consistent with AMR. Anti-C5 administration completely blocked terminal complement activity and local C5 deposition, and in combination with cyclosporine and short-term cyclophosphamide treatment, it effectively prevented heart graft rejection. These recipients achieved permanent graft survival for >100 days with normal histology despite the presence of systemic and intragraft anti-donor Abs and complement, suggesting ongoing accommodation. Furthermore, double-transplant experiments demonstrated that immunological alterations in both the graft and the recipient were required for successful graft accommodation to occur. These data suggest that terminal complement blockade with a functionally blocking Ab represents a promising therapeutic approach to prevent AMR in presensitized recipients.

Subclinical acute antibody-mediated rejection in positive crossmatch renal allografts

Subclinical antibody-mediated rejection (AMR) has been described in renal allograft recipients with stable serum creatinine (SCr), however whether this leads to development of chronic allograft nephropathy (CAN) remains unknown. We retrospectively reviewed data from 83 patients who received HLA-incompatible renal allografts following desensitization to remove donor-specific antibodies (DSA). Ten patients had an allograft biopsy showing subclinical AMR [stable SCr, neutrophil margination in peritubular capillaries (PTC), diffuse PTC C4d, positive DSA] during the first year post-transplantation; 3 patients were treated with plasmapheresis and intravenous immunoglobulin. Three patients had a subsequent rise in SCr and an associated biopsy with AMR; 5 others showed diagnostic or possible subclinical AMR on a later protocol biopsy. One graft was lost, while remaining patients have normal or mildly elevated SCr 8-45 months post-transplantation. However, the mean increase in CAN score (cg + ci + ct + cv) from those biopsies showing subclinical AMR to follow-up biopsies 335 +/- 248 (SD) days later was significantly greater (3.5 +/- 2.5 versus 1.0 +/- 2.0, p = 0.01) than that in 24 recipients of HLA-incompatible grafts with no AMR over a similar interval (360 +/- 117 days), suggesting that subclinical AMR may contribute to development of CAN.

Humoral immunity is the dominant barrier for allogeneic bone marrow engraftment in sensitized recipients

We evaluated the relative contribution of the humoral and cellular arms of the immune response to bone marrow cells transplanted into sensitized recipients. We report here for the first time that humoral immunity contributes predominantly to allosensitization. Although the major role for nonmyeloablative conditioning is to control alloreactive host T cells in nonsensitized recipients, strikingly, none of the strategies directed primarily at T-cell alloreactivity enhanced engraftment in sensitized mice. In evaluating the mechanism behind this barrier, we found that humoral immunity plays a critical role in the rejection of allogeneic marrow in sensitized recipients. Adoptive transfer of as little as 25 microL serum from sensitized mice abrogated engraftment in secondary naive recipients. With the use of microMT mice as recipients, we found that T-cell-mediated immunity plays a secondary but still significant role in allorejection. Targeting of T cells in sensitized B-cell-deficient microMT mice enhanced alloengraftment. Moreover, both T- and B-cell tolerance were achieved in sensitized recipients when allochimerism was established, as evidenced by the acceptance of second donor skin grafts and loss of circulating donor-specific Abs. These findings have important implications for the management of sensitized transplant recipients and for xenotransplantation in which B-cell reactivity is a predominant barrier.

Preformed antibody, not primed T cells, is the initial and major barrier to bone marrow engraftment in allosensitized recipients

Multiply-transfused individuals are at higher risk for BM rejection. We show that whereas allosensitization resulted in the priming of both cellular and humoral immunity, preformed antibody was the major barrier to engraftment. The generation of cross-reactive alloantibody led to rejection of BM of a different MHC-disparate strain. Imaging studies indicated that antibody-mediated rejection was very rapid (<3 hours) in primed recipients, while T-cell-mediated rejection in nonprimed mice took more than 6 days. Antibody-mediated BM rejection was not due to a defect in BM homing as rejection occurred despite direct intra-BM infusion of donor BM. Rejection was dependent upon host FcR+ cells. BM cells incubated with serum from primed mice were eliminated in nonprimed recipients, indicating that persistent exposure to high-titer antibody was not essential for rejection. High donor engraftment was achieved in a proportion of primed mice by mega-BM cell dose, in vivo T-cell depletion, and high-dose immunoglobulin infusion. The addition of splenectomy to this protocol only modestly added to the efficacy of this combination strategy. These data demonstrate both rapid alloantibody-mediated elimination of BM by host FcR+ cells and priming of host antidonor T cells and suggest a practical strategy to overcome engraftment barriers in primed individuals.

C4d and C3d staining in biopsies of ABO- and HLA-incompatible renal allografts: correlation with histologic findings

Biopsies of ABO-incompatible and positive crossmatch (HLA-incompatible) renal allografts were retrospectively examined to compare results of C4d and C3d staining, and the correlation between such staining and histologic findings suggestive of antibody-mediated rejection (AMR). A total of 75 biopsies (55 protocol, 17 for graft dysfunction, 3 for other indications) of 24 ABO-incompatible grafts and 244 biopsies (103 protocol, 129 for graft dysfunction, 12 for other indications) of 66 HLA-incompatible grafts were examined; all were stained for C4d and approximately 40% for C3d. In ABO-incompatible grafts, 80% of protocol biopsies and 59% performed for graft dysfunction showed C4d staining in peritubular capillaries (PTC); this staining was not correlated with neutrophil margination in PTC. In HLA-incompatible grafts, PTC C4d was present in 26% of protocol biopsies and 60% of biopsies for graft dysfunction; 92% of biopsies with >1+ (0-4+ scale), diffuse PTC C4d had > or =1+ margination and/or thrombotic microangiopathy (TMA), compared with 12% of C4d-negative biopsies. C3d was somewhat more predictive of margination than C4d in ABO-incompatible, but not HLA-incompatible, grafts. In summary, while PTC C4d deposition indicates probable AMR in biopsies of HLA-incompatible grafts, including protocol biopsies, there is no histologic evidence that C4d deposition is correlated with injury in most ABO-incompatible grafts.

Antibody-mediated rejection in renal allografts: lessons from pathology

The past 15 years have seen major advances in the understanding of the effects of anti-donor antibodies on renal allografts at various stages after transplantation. These advances have been due in large part to pathologic examination of both early and late renal allograft biopsies, including both routine histologic evaluation and immunohistology to detect complement split products. As pathologists have become increasingly adept at diagnosing antibody-mediated rejection (AMR) on allograft biopsies, substantial progress has been made in the treatment of AMR and in successful renal transplantation in recipients with pre-existing antibodies against donor blood group (ABO) and/or major histocompatibility (HLA) antigens. This article reviews the pathologic features of hyperacute, acute, and chronic AMR, including some newer findings impacting diagnosis and outcomes, and differences in the implications of similar pathologic findings in ABO- versus HLA-incompatible renal allografts.

Heart transplantation across the antibodies against HLA and ABO

We have intentionally performed heart transplantation in a 5-year-old child, despite the most unfavourable risk factors for patient survival; the presence of high level of antibodies against donor's human leucocyte antigen (HLA) class I/II and blood group antigens. Pretransplant treatment by mycophenolate mofetil, prednisolone, tacrolimus, intravenous immunoglobulin, rituximab, protein-A immunoadsorption (IA) and plasma exchange reduced antibody titres against the donor's lymphocytes from 128 to 16 and against the donor's blood group antigen from 256 to 0. The patient was urgently transplanted with a heart from an ABO incompatible donor (A(1) to O). A standard triple-drug immunosuppressive protocol was used. No hyperacute rejection was seen. Antibodies against the donor's HLA antigens remained at a low level despite three acute rejections. Rising anti-A(1) blood group antibodies preceded the second rejection and were reduced by two blood group-specific IAs and remained at a low level. The patient is doing well despite the persistence of donor-reactive antibodies.

Decay-Accelerating Factor Prevents Acute Humoral Rejection Induced by Low Levels of Anti-αGal Natural Antibodies

BACKGROUND

Hyperacute and delayed vascular rejection due to natural antibodies (NAb) present major obstacles in pig-to-primate xenotransplantation. Although "supraphysiologic" expression of human complement regulatory proteins (CRPs) can prevent hyperacute rejection in discordant xenogenic recipients, their physiologic role in the homologous setting is undefined. We have evaluated the effect of the absence of decay-accelerating factor (DAF) on cardiac allograft rejection in the presence of different levels of antidonor antibodies (Ab).

METHODS

DAF1-deficient (DAF KO; B6129F2 H-2) mice were used as heart graft donors to alpha1,3-galactosyltransferase deficient (GalT KO; B6, H-2) recipients. Heterotopic heart grafting was performed with or without presensitization. Graft survival, histology, and anti-alphaGal Ab levels were monitored.

RESULTS

DAF knockout (KO) but not wild-type (WT) grafts showed hyperacute or acute humoral rejection in nonsensitized GalT KO mice with low levels of anti-alphaGal IgM NAb. However, humoral rejection of both DAF KO and DAF WT donor grafts occurred in presensitized GalT KO recipients.

CONCLUSIONS

The expression of DAF prevents hyperacute rejection in mice with low titers of anti-alphaGal antibody. These studies demonstrate the physiologic role of DAF in preventing humoral rejection in the presence of low levels of NAb and have implications for transplantation of discordant vascularized xenografts.

HLA class I antibody mediated accommodation of endothelial cells via the activation of PI3K/cAMP dependent PKA pathway

Allografts transplanted across ABO incompatibility or human leucocyte antigen (HLA)-sensitization undergoes antibody (Ab) mediated hyperacute rejection. Depleting anti-graft Ab from the recipient by plasmapheresis prior to transplantation can prevent this Ab-mediated rejection. Under these conditions, allografts have been shown to function even when the Ab rebound in the recipients. We have developed an in vitro model using human aortic endothelial cells (EC) and elucidated the ability of W6/32 HLA class I monoclonal Ab to provide signals following binding to MHC class I molecules. Using this model, we show that ECs undergo caspase 3-dependent cell death by apoptosis upon exposure to saturating concentrations of W6/32 and complement. In contrast, exposure of ECs to sub-saturating concentrations of W6/32 conferred resistance towards Ab/complement-mediated lysis that has been termed accommodation. Accommodated ECs exhibited a significant increase in the expression of anti-apoptotic genes Bcl-xL, Bcl-2 and Heme Oxygenase-1 and the induction of Phosphatidylinositol 3 kinase (PI3K) and cyclic adenosine monophosphate (cAMP) dependent protein kinase A activities that facilitate the phosphorylation of Bad at positions Ser(136) and Ser(112). In conclusion, exposure of sub-saturating concentrations of HLA class I Ab results in the induction of signals downstream that confers resistance to endothelial cells against Ab-complement mediated cell death. Together, the observations made in this study will provide the basis for delineating the molecular mechanisms involved in mediating accommodation and developing strategies to induce accommodation in grafts prior to transplantation in highly sensitized patients.

Efficacy and limitations of cyclophosphamide-induced tolerance against alphaGal antigen

In the present study, we have elucidated the efficacy of two cyclophosphamide (CP)-induced tolerance protocols for the induction of B-cell tolerance against Galalpha1-3Galbeta1-4GlcNAc (alphaGal) antigens. alpha1,3-galactosyltransferase-deficient (GalT-/-; H-2(b/d)) mice received with 1 x 10(8) AKR (alphaGal+/+ H-2k) spleen cells (SC) followed by 200 mg/kg CP, or alternatively followed by 200 mg/kg CP, 30 mg/kg Busulfan (BU) and 1 x 10(8) T-cell-depleted AKR bone marrow cells (BMC). The generation of both anti-alphaGal and anti-donor antibodies were completely suppressed, but normal antibody production against third party antigens was observed after BALB/c skin grafting in both groups of GalT-/- mice. In GalT-/- mice, treated with SC and CP, mixed chimerism was not observed. Cellular rejection was observed in grafted donor AKR hearts with an absence of humoral rejection, whereas humoral rejection was observed in untreated GalT-/- mice. On the other hand, long-term mixed chimerism and permanent acceptance of donor AKR skin graft and heart graft were achieved in GalT-/- mice treated with SC, CP, BU and BMC. These results demonstrate the efficacy of classical drug-induced tolerance in the induction of B-cell tolerance against alphaGal antigens. However, induction of stable mixed chimerism was required for the suppression of cellular rejection.

Humoral Theory of Transplantation: Mechanism, Prevention, and Treatment

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

Anti-HLA class I antibody-mediated activation of the PI3K/Akt signaling pathway and induction of Bcl-2 and Bcl-xL expression in endothelial cells

Anti-human leukocyte antigen (HLA) antibodies (Ab) have long been implicated in the process of acute and chronic allograft rejection, yet their mechanism(s) of action is not well understood. The aim of this study was to determine whether ligation of HLA class I molecules by anti-HLA Ab on the surface of human endothelial cells (EC) activates the PI3 Kinase (PI3K)/Akt signaling pathway and downstream target proteins of the cell death apparatus. We report that Ab ligation of major histocompatibility complex (MHC) class I molecules on the surface of EC triggers phosphorylation of Akt, PI3K, and recruitment of PI3K and Akt into a signaling unit with focal adhesion kinase. Signaling through class I also stimulated phosphorylation of Bad and upregulated expression of Bcl-2 and Bcl-xL. Pretreatment of EC with the PI3K inhibitor wortmannin blocked class I-mediated expression of Bcl-2, but not Bcl-xL, suggesting a role for the PI3K/Akt signaling pathway in regulation of class I-induced Bcl-2 expression. The intracellular events initiated by class I ligation were influenced by the concentration of the anti-HLA Ab with the lowest tested concentrations of Ab stimulating the highest level of Akt phosphorylation, Bcl-xL and Bcl-2 expression. Consistent with the in vitro experiments, analysis of biopsy samples from heart transplant recipients with evidence of Ab-mediated rejection exhibited increased Bcl-2 expression on the vascular endothelium. These results suggest that exposure of the graft endothelium to low concentrations of anti-HLA Ab may promote cell survival by transducing signals resulting in upregulation of cell survival genes.

Isometric Tubular Epithelial Vacuolization in Renal Allograft Biopsy Specimens of Patients Receiving Low-Dose Intravenous Immunoglobulin for a Positive Crossmatch

BACKGROUND

Perioperative treatment with plasmapheresis and intravenous immunoglobulin (IVIG), combined with a tacrolimus-based immunosuppressive regimen, has been used successfully to allow renal transplantations in cross-match-positive recipients. A common finding in biopsy specimens of these allografts is isometric vacuolization of proximal tubular epithelium. This finding presents a diagnostic dilemma because it may occur secondary to IVIG treatment or tacrolimus nephrotoxicity.

METHODS

We compared the frequency and severity of isometric tubular vacuolization in renal allograft biopsy specimens obtained during the first 10 days after transplantation in 24 patients who received one or more postoperative treatments with IVIG (100 mg/kg; as part of a desensitization protocol also involving plasmapheresis) with specimens obtained in 91 patients who did not receive IVIG. All patients received tacrolimus. Isometric vacuolization was graded on a 0 to 4 scale based on the fraction of proximal tubules involved: 0, none; 1, less than 10%; 2, 10% to 25%; 3, 26% to 50%; 4, more than 50%.

RESULTS

There was a higher frequency of isometric tubular vacuolization (71 % vs. 31%) and more widespread involvement in patients who received IVIG and tacrolimus versus tacrolimus alone, although mean tacrolimus levels were not significantly different between these groups. In control, but not IVIG, biopsy specimens, there was a significant association between vacuolization score and blood tacrolimus level on the day of biopsy.

CONCLUSIONS

Isometric tubular vacuolization is a common finding in renal transplant biopsy specimens of patients who receive low-dose IVIG and in many cases is likely to be related, at least in part, to IVIG. In these patients, this finding should not necessarily be interpreted as indicative of tacrolimus (or cyclosporine) nephrotoxicity.

Therapeutic apheresis therapy for ABO-incompatible renal transplantations

The most important transplantation antigen system for organ transplantation is the ABO blood group system. Crossing the blood barrier is usually not done except in emergency cases such as liver transplantations for fulminant hepatitis. Early experiences of allograft transplantations across the blood barriers were discouraging. In the 1970s, clinical trials were started transplanting kidneys of subgroup A2 into blood group O recipients because the tissues of the A2 subgroup express a lower amount of A antigens compared with subgroup A1. The recipients required no special treatment and received the standard immunosuppressive regimen as used in blood group identical cases. Many early graft loses immediately after transplantations were experienced, but these trials resulted in an excellent graft survival rate. A few centers have adapted the concept of A2 kidneys to non-A recipient transplantations with successful results by reducing anti-A blood type titers prior to transplantations. In the early 1980s, the possibility of bridging the ABO barrier was tested by several groups. A1 and B kidneys from living donors were also successfully transplanted across the blood barrier using quadruple immunosuppressive drugs and splenectomy. Since 1989, the largest number of ABO-incompatible renal transplantations have been performed in Japan because of the limited numbers of cadaveric donors. Approximately 400 cases have been successfully transplanted across the blood barrier at many centers in Japan. Owing to novel immunosuppressive drugs, the ABO-incompatible allografts exhibited a level of function comparable with that of ABO-matched allografts even though anti-A or anti-B antibodies had returned to the circulation of the recipients. In this article, we describe the historical background, the current therapeutic strategies including apheresis therapy for the ABO-incompatible transplantations, and the experiences at our institution.

The use of apheresis in immune renal disorders

Rapidly progressive glomerulonephritis (RPGN) is often associated with the presence of autoantibodies. Included in this group are the glomerulonephritides associated with anti-GBM antibody (Goodpasture's syndrome). IgA mesangial deposition (the renal component of Henoch-Schönlein purpura), lupus erythematosus, cryoglobulinemia and the antineutrophil cytoplasmic antibody (ANCA)-associated pauci-immune group. In each of these cases, apheresis may provide a therapeutically useful option. Apheresis has also been found useful in certain types of antibody-mediated transplant rejection and in lowering the levels of preformed cytotoxic antibodies which may preclude transplantation. Finally, there are renal diseases in which the immune component is less clearly involved with pathogenesis but for which apheresis may offer a clear benefit, such as in the renal failure associated with 'cast nephropathy' (multiple myeloma) or the recurrence of FSGS (focal segmental glomerulosclerosis) in transplanted kidneys. It is the purpose of this paper to review the evidence supporting the use of apheresis in immune-related diseases.

Transplant accommodation in highly sensitized patients: a potential role for Bcl-xL and alloantibody

Transplantation of renal allografts into recipients with circulating anti-HLA antibodies results in hyperacute rejection. In some cases, however, antibodies return without causing harm; this phenomenon has been termed 'accommodation'. We have investigated this process in human allotransplantation. We removed anti-HLA antibodies by immunoadsorption in seven highly sensitized dialysis patients who subsequently underwent renal transplantation. Immunohistochemistry of renal biopsies for IgG and antiapoptotic proteins was performed. We also developed a model of 'accommodation' using anti-HLA antibodies eluted from sensitized patients and incubated with human umbilical vein endothelial cells (HUVECs) at different concentrations. Their effect on HUVEC phenotype was then analysed. Anti-donor antibody returned in 4/7 patients, without evidence of hyperacute rejection. Three out of four of these 'accommodated' grafts showed specific endothelial up-regulation of Bcl-xL and 2/2 tested positive for endothelial IgG deposition. HUVECs incubated with subsaturating concentrations of anti-HLA antibody showed increased expression of Bcl-xL, were rendered refractory to endothelial cell activation and became resistant to complement-mediated lysis. In contrast, HUVECs incubated with saturating concentrations underwent activation and expressed low levels of Bcl-xL. In conclusion, endothelial Bcl-xL expression defines the accommodation process in human allografts and this phenotype may be initiated by exposure of endothelium to low concentrations of anti-donor HLA antibodies.

Apheresis for Renal Disease

Many primary renal diseases are associated with either antibody deposition within the glomerulus or an antibody associated autoimmunity, as may be seen with certain vasculitidies. Examples of these diseases include Goodpasture's syndrome, cryoglobulinemia, antineutrophil cytoplasmic antibody positive syndromes, and other forms of rapidly progressive glomerulonephritis. Immunoglobulins also may be nephrotoxic to the tubules such as is the case with myeloma related light chains. Given the rapid removal of immunoglobulins by therapeutic plasma exchange, this modality has been considered an appealing management option in the treatment of these renal diseases. Although not classically considered as autoimmune diseases, thrombotic thrombocytopenic purpura and hemolytic uremic syndrome are related syndromes which often involve the kidneys. Although previously unexplained, it has been long appreciated that therapeutic plasma exchange (PE) can be a useful treatment for these microangiopathic hemolytic anemias, but the most recent insights into their pathogenesis suggest that PE may be beneficial by replacing a missing enzyme or removing pathogenic autoantibodies.

Nitric oxide-mediated expression of Bcl-2 and Bcl-xl and protection from tumor necrosis factor-alpha-mediated apoptosis in porcine endothelial cells after exposure to low concentrations of xenoreactive natural antibody

BACKGROUND

Cardiac and renal allo- and xenografts can acquire a natural resistance to vascular rejection. This "accommodation" involves endothelial cell (EC) expression of "survival genes" such as Bcl family members and hemoxygenase 1. Understanding what initiates this protective process would have profound implications; our hypothesis is that low concentrations of antigraft antibodies may mediate these changes.

METHODS

In vitro cultured primary and immortalized porcine EC were incubated with polyclonal human IgG for 6 days and then examined for phenotype changes.

RESULTS

The cells acquired resistance to tumor necrosis factor-alpha-mediated apoptosis (50-100% reduction at 6 hr) and up-regulated expression of Bcl-2 and Bcl-xl; sustained expression was accompanied by inducible nitric oxide (NO) synthase expression and by enhanced production of NO by EC. Two observations suggested that NO was actively involved in the process of Bcl-2 and Bcl-xl induction. First, (z)-1-2-[2-aminoethyl)-N- (2-ammonioethyl)amino]diazen-1-ium-1,2-diolate, an NO donor, was able to induce similar changes in porcine EC to those induced by anti-pig antibodies. Second, an NO synthase inhibitor NG-monomethyl-L-arginine.monoacetate was able to specifically inhibit the anti-pig antibody-mediated expression of Bcl-2 or Bcl-xl.

CONCLUSIONS

These data strongly support the hypothesis that Bcl-2 and Bcl-xl expression and protection from apoptosis in EC may result from antibody-mediated NO production through the neoexpression of inducible NO synthase.

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.

The abrogation of allosensitization following the induction of mixed allogeneic chimerism

The association of preformed anti-donor Abs with the hyperacute rejection of bone marrow and solid organ allografts and the persistence of the anti-donor immune response secondary to immunologic memory make allosensitization an absolute contraindication to transplantation. Mixed allogeneic (A + B-->A) bone marrow chimerism has been demonstrated to confer donor-specific tolerance in nonsensitized recipients, but has not been evaluated in the setting of allosensitization. The current study documents that despite significant anti-donor sensitization, mixed allogeneic engraftment is possible and provides a marked advantage over fully allogeneic (B-->A) models. Moreover, the acceptance of donor skin grafts and loss of circulating anti-donor Abs suggest that allosensitization can be abrogated with the induction of stable mixed allogeneic chimerism.

Inhibition of tissue factor-dependent and -independent coagulation by cell surface expression of novel anticoagulant fusion proteins

BACKGROUND

Thrombotic vascular occlusion occurs in disorders of diverse etiology, including atherosclerosis, vasculitis, and disseminated intravascular coagulation. The same process results in hyperacute rejection of renal allografts transplanted into sensitized patients and remains a major problem in experimental xenotransplantation.

METHODS

We have previously described the design and expression of several genetic constructs encoding novel fusion proteins with anticoagulant properties. They are based on two naturally occurring soluble anticoagulant proteins, human tissue factor pathway inhibitor (hTFPI) and the leech protein hirudin, which act early and late in the clotting cascade, respectively. We report the expression of human hTFPI-CD4 on the surface of immortalized porcine endothelial cells (IPEC), and show that it functions across the species divide as evidenced by the binding of membrane-expressed porcine tissue factor (pTF)-human factor VIIa complexes.

RESULTS

Using a human plasma recalcification clotting assay, we distinguished between pTF-dependent and pTF-independent fibrin generation, and we have demonstrated that expression of hTFPI-CD4 on IPEC effectively prevented pTF-dependent clotting. Moreover, we show that when hTFPI-CD4 was co-expressed with the hirudin construct, the procoagulant properties of in vitro cultured, activated IPEC were almost completely abolished.

CONCLUSIONS

These results suggest that these novel anticoagulant molecules may prove useful therapeutic agents for gene therapy or for transgenic expression in animals whose organs may be used for cliniCal xenotransplantation.

Therapeutic apheresis for renal disorders

Many primary renal diseases are associated with either antibody deposition within the glomerulus or an antibody associated autoimmunity, as may be seen with certain vasculitidies. Other immunoglobulins may be nephrotoxic or glomerulopathic; such may be the case with myeloma related light chains or cryoglobulins. Given the rapid removal of immunoglobulins by therapeutic plasma exchange, this modality has been considered an appealing management option in the treatment of these autoimmune related renal diseases. Although not classically considered as autoimmune diseases, thrombotic thrombocytopenic purpura and hemolytic uremic syndrome are related syndromes which often involve the kidneys. In many cases therapeutic plasma exchange has been found to be a useful treatment modality for these microangiopathic hemolytic anemias. This paper will provide a concise review of the renal indications for therapeutic plasma exchange.

Protein A immunoadsorption (i.a.) in renal transplantation patients with vascular rejection

Vascular rejection after renal transplantation is connected with a higher frequency of allograft dysfunction or graft loss. Plasmapheresis as an adjunctive therapy in the treatment of humoral mediated acute graft rejection was compared with protein A immunoadsorption. Eleven patients with acute graft rejection and high titers of cytotoxic HLA-Ab and/or signs of vascular rejection at graft biopsy (performed in 9 patients) have been treated. Six of them have a stable graft function, the longest graft survival until now is 41 months, four are back on haemodialysis and one patient died from CMV-pneumonia with a stable graft function 9 months after transplantation. We conclude that IA is a useful adjunctive therapy in the treatment of vascular rejection after renal transplantation. Further investigations are necessary to optimize criteria for inclusion.

Immunology of xenotransplantation

The transplantation of tissues and organs between individuals of different species, that is, xenotransplantation, engenders a variety of immune responses. Xenogeneic immune responses mediated by naturally-occurring antibodies and complement lead to hyperacute and acute vascular rejection of vascularized organ grafts and may also cause vascular rejection of cell and tissue grafts. Under some circumstances, however, a vascularized organ graft may evade humoral rejection despite the presence of anti-donor antibodies in the circulation of the recipient; this condition is called accommodation. Xenogeneic immune responses mediated by T lymphocytes and natural killer cells may cause acute cellular rejection. The extent to which cellular rejection of xenografts resembles cellular rejection of allografts remains to be determined. New insights into the molecular mechanisms underlying the immune responses to xenotransplantation has shed light on the pathogenesis of immunological disease and has allowed the development of specific immunomodulatory strategies that may facilitate clinical application of xenotransplantation.

In vitro accommodation of porcine endothelial cells by low dose human anti-pig antibody: reduced binding of human lymphocytes by accommodated cells associated with increased nitric oxide production

Transplanted xenografts, protected from rejection by depletion of xenoreactive natural antibodies (XNA) and complement, can sometimes survive when complement levels and titres of anti-graft antibodies return to baseline; this phenomenon is called accommodation. We have previously reported that low concentrations of human IgG induce a change in the phenotype of immortalised porcine endothelial cells (IPEC) consistent with the development of accommodation. The cells acquired a resistance to lysis by human complement and showed a reduced expression of VCAM. In this study, we extend these findings by showing that VCAM expression falls on several IPEC clones and on primary porcine endothelial cells. Moreover, we show that these accommodated cells bind fewer human lymphocytes compared to controls, implying that leukocyte traffic through accommodated endothelium may be altered compared to that through normal endothelium. Finally we show that during the induction of accommodation, porcine endothelial cells produce greater amounts of nitric oxide than controls, due to the expression of inducible nitric oxide synthase (iNOS). We speculate that nitric oxide may be an important mediator in accommodation.

Recent advances in the immunology of xenotransplantation

The transplantation of tissue and organs between individuals of different species, that is xenotransplantation, engenders a variety of severe immune responses. Xenogeneic immune responses mediated by naturally occurring antibodies and complement lead to hyperacute and acute vascular rejection of vascularized organ grafts and may also cause vascular rejection of cell and tissue grafts. Under some circumstances, however, a vascularized organ graft may evade humoral rejection despite the presence of antidonor antibodies in the circulation of the recipient; this condition is called accommodation. Xenogeneic immune responses mediated by T-lymphocytes and natural killer cells may cause acute cellular rejection. The extent to which cellular rejection of xenografts resembles cellular rejection of allografts remains to be determined. New insights into the molecular mechanisms underlying the immune responses to xenotransplantation have shed new light on the pathogenesis of immunological disease and have allowed the development of specific immunomodulatory strategies that may facilitate clinical application of xenotransplantation.

Prevention of hyperacute rejection by removal of antibodies to HLA immediately before renal transplantation

BACKGROUND

Many patients with circulating antibodies to human leucocyte antigens (anti-HLA) are highly sensitised against renal transplantation and are liable to immediate graft loss through hyperacute rejection. Our aim was to find out whether removal of anti-HLA immediately before renal transplantation prevented hyperacute graft rejection.

METHODS

13 highly sensitised patients underwent cadaveric renal transplants immediately after immunoadsorption (IA) treatment to remove anti-HLA. Before IA, 12 patients had a positive crossmatch against donor cells either by cytotoxic or flow-cytometric assay; results for one patient were equivocal.

FINDINGS

Renal biopsy samples were obtained 20 min after removal of the vascular clamps in nine patients. There was no evidence of hyperacute rejection in six of the nine patients; the other three patients showed glomerular thrombosis but no other evidence of hyperacute rejection. Two of these three grafts were functioning at 31 months of follow-up. Six episodes of acute rejection occurred in five patients during the first month after transplantation and overall there were 13 rejection episodes in nine patients. At latest follow-up (median 26 months, range 9-42), 12 of 13 patients were alive and seven of 13 grafts were surviving with a median plasma creatinine concentration of 185 mumol/L (range 106-296) in the functioning grafts. No graft was lost as a result of classic hyperacute rejection.

INTERPRETATION

Immediate pretransplant IA can prevent hyperacute rejection and provide an opportunity for successful transplantation in highly sensitised patients.

In vitro accommodation of immortalized porcine endothelial cells: resistance to complement mediated lysis and down-regulation of VCAM expression induced by low concentrations of polyclonal human IgG antipig antibodies

The capacity of vascularized xenografts to survive in the face of normal levels of circulating antigraft antibodies and complement has been ascribed to a phenomenon referred to as "endothelial cell accommodation." The mechanisms whereby accommodation might occur have remained obscure. We have investigated this phenomenon in an in vitro system. A preparation of polyclonal immunoglobulin, human normal globulin (HNG), induced a change in the phenotype of immortalized porcine endothelial cells (IPEC) suggestive of accommodation; the cells became resistant to complement mediated lysis and displayed a reduced expression of surface VCAM and MHC class I. The accommodated phenotype only manifested after 72 hr incubation with HNG and was optimal after 120 hr. In an analysis of all the experiments performed, the development of resistance to complement mediated lysis appeared independent of the inducing dose of HNG. However, down-regulation of VCAM was only manifest when subsaturating doses were used. Our results suggest that IgG xenoreactive antibodies can mediate changes in porcine endothelial cell phenotype consistent with accommodation. The dependence on both time and dose of antibody applied might explain why accommodation has been difficult to achieve consistently in in vivo models of discordant xenotransplantation. By demonstrating a functional interaction between human VLA-4 and porcine VCAM, we speculate that the down-regulation in expression of VCAM on accommodated endothelium may have an important regulatory effect on traffic of inflammatory cells into xenografts. Our results have important implications for the development of strategies to promote accommodation of xenografts.

Clinical Applications of Therapeutic Hemapheresis

Therapeutic hemapheresis may be a life-saving treatment for patients with some diseases, such as thrombotic thrombocytopenic purpura (TTF), Goodpasture's syndrome, and leukemia-induced leukocytosis, among others. Although plasma exchange has been applied for treatment of many conditions, during the last decade a consensus has been reached about the specific but limited number of diseases for which it is of definitive benefit. Some patients are severely ill during the course of the disease, and they require prompt treatment in the intensive care unit. Therapy of these patients is discussed in this review in detail, in addition to technical aspects, indications, contraindications, and complications of therapeutic hemapheresis.

Antibody removal and subsequent transplantation of a highly sensitised paediatric renal patient

We report a successful renal transplant in a highly sensitised paediatric recipient following removal of HLA-specific antibodies by extracorporeal immunoadsorption. The immediate pretransplant cytotoxic titre against the donor was greater than 1:512; this was reduced to negativity by two immunoadsorption sessions prior to transplant surgery. We also describe the presence of unexpected non-HLA-specific antibody activities in this immunoadsorbed patient.