Management of the highly HLA- sensitized patient. A novel role for intravenous gammaglobulin

Ibrutinib suppresses alloantibody responses in a mouse model of allosensitization

BACKGROUND

Ibrutinib is a Bruton's tyrosine Kinase (BTK) antagonist that inhibits B cell receptor (BCR) signaling. Complete BTK deficiency is associated with absence of B-cells. Ibrutinb is currently approved by FDA for treatment of B-cell malignancies, including Waldenström macroglobulinaemia. We recently carried out studies to determine if ibrutinib could modify alloantibody responses.

MATERIALS AND METHODS

A mouse model of allogenic sensitization using a C57BL/6 mouse as the recipient of a skin allograft from an HLA-A2 transgenic mouse was utilized to examine the effects of ibrutinib on alloantibody responses and B cell effector functions. Donor-specific antibody (DSA) levels were measured in a flow-cytometric antibody binding assay. Splenic T and B cell subsets and plasma cells were analyzed in flow cytometry.

RESULTS

Control mice developed peak levels of DSA IgM at day 14 PTx while the ibrutinib treated mice had significantly lower levels of DSA IgM (p=0.0047). Control mice developed HLA.A2-specific IgG antibodies at day 14 (230±60 MFI) and reached peak levels at day 21 (426±61 MFI). In contrast, mice in the treatment group had low levels of HLA.A2-specific IgG at day 14 (109±59 MFI, p=0.004) and day 21 (241±86 MFI, p=0.003). FACS analysis found a reduction of B220⁺ or CD19⁺ B cell population (p<0.05). In addition, ibrutinib attenuated recall DSA IgG responses to re-sensitization (p<0.05) and reduced CD38⁺CD138⁺ plasma cells (p<0.05) in the spleens.

CONCLUSIONS

Ibrutinib is effective in suppressing alloantibody responses through blocking BTK-mediated BCR signaling, leading to reduction of B cells and short-lived plasma cells in the spleens. Use of ibrutinib may provide benefits to HLA-sensitized transplant patients for alloantibody suppression.

Immunological characterization of de novo and recall alloantibody suppression by CTLA4Ig in a mouse model of allosensitization

It is well known that CTLA4Ig inhibits allogenic T-cell activation in transplantation. The immunological features and mechanisms associated with alloantibody suppression by CTLA4Ig, however, are poorly understood. Here, we used a mouse model of allosensitization to evaluate the efficacy of CTLA4Ig (abatacept) in suppression of donor-specific antibody (DSA) during de novo and recall alloantibody responses. We found that abatacept inhibited de novo DSA IgM and IgG responses to HLA-A2 expressing skin grafts. Abatacept administered during primary T cell priming also reduced recall IgG responses induced by re-immunization. Suppression of de novo DSA responses by abatacept is associated with a reduction in splenic expression of the germinal center activation marker GL7 and a reduction of CD4(+)PD1(+)CXCR5(+) follicular T helper (Tfh) subset in splenic lymphocytes detected by flow cytometry. The efficacy of abatacept on recall DSA suppression is moderate. In vitro experiments demonstrated that abatacept inhibited DSA IgG secretion by CD138(+) plasma cells isolated from allograft recipients. Additional experiments using an IgG1 secreting mouse hybridoma cell line showed that abatacept binds to CD80 expressed on these cells with subsequent inhibition of cell proliferation and reduction in IgG ELISpot formation. In conclusion, CTLA4Ig is a potent suppressor of de novo DSA responses and also affects recall responses. The data suggests modification of recall DSA responses is due to a direct suppressive effect on plasma cells.

Preexisting donor-specific HLA antibodies predict outcome in kidney transplantation

The clinical importance of preexisting HLA antibodies at the time of transplantation, identified by contemporary techniques, is not well understood. We conducted an observational study analyzing the association between preexisting donor-specific HLA antibodies (HLA-DSA) and incidence of acute antibody-mediated rejection (AMR) and survival of patients and grafts among 402 consecutive deceased-donor kidney transplant recipients. We detected HLA-DSA using Luminex single-antigen assays on the peak reactive and current sera. All patients had a negative lymphocytotoxic cross-match test on the day of transplantation. We found that 8-year graft survival was significantly worse (61%) among patients with preexisting HLA-DSA compared with both sensitized patients without HLA-DSA (93%) and nonsensitized patients (84%). Peak HLA-DSA Luminex mean fluorescence intensity (MFI) predicted AMR better than current HLA-DSA MFI (P = 0.028). As MFI of the highest ranked HLA-DSA detected on peak serum increased, graft survival decreased and the relative risk for AMR increased: Patients with MFI >6000 had >100-fold higher risk for AMR than patients with MFI <465 (relative risk 113; 95% confidence interval 31 to 414). The presence of HLA-DSA did not associate with patient survival. In conclusion, the risk for both AMR and graft loss directly correlates with peak HLA-DSA strength. Quantification of HLA antibodies allows stratification of immunologic risk, which should help guide selection of acceptable grafts for sensitized patients.

[An experience of ABO-incompatible kidney transplantation using plasmapheresis and anti-CD20 monoclonal antibody]

Due to an extreme shortage of cadaveric kidneys, many centers in Japan successfully performed ABO-incompatible kidney transplantations using plasmapheresis, splenectomy and immunosuppression. Recently, a protocol including anti-CD20 monoclonal antibody (rituximab) and antigen-selective immunoadsorption has been used for ABO-incompatible transplantation in Europe. In Korea, ABO-incompatible kidney transplantation has been rarely performed. We report an experience of successful ABO-incompatible kidney transplantation using plasmapheresis and rituximab. The patient was a 32-yr-old female suffering from chronic renal failure, and her blood type was O, Rh+. The donor was her husband, and his blood type was B, Rh+. A combination therapy including 5 times of plasmapheresis starting from 10 days before transplantation with 2-day interval, intravenous gammaglobulin, rituximab at 2 weeks before transplantation and potent immunosuppression successfully decreased the titers of anti-A and anti-B antibodies to 1:2 and 1:1, respectively. The kidney transplantation was successful without any sign of hyperacute or acute rejection.

Proteasome inhibition causes apoptosis of normal human plasma cells preventing alloantibody production

Antibody production by normal plasma cells (PCs) against human leukocyte antigens (HLA) can be a major barrier to successful transplantation. We tested four reagents with possible activity against PCs (rituximab, polyclonal rabbit antithymocyte globulin (rATG), intravenous immunoglobulin (IVIG) and the proteasome inhibitor, bortezomib) to determine their ability to cause apoptosis of human bone marrow-derived PCs and subsequently block IgG secretion in vitro. IVIG, rituximab and rATG all failed to cause apoptosis of PCs and neither rituximab nor rATG blocked antibody production. In contrast, bortezomib treatment led to PC apoptosis and thereby blocked anti-HLA and antitetanus IgG secretion in vitro. Two patients treated with bortezomib for humoral rejection after allogeneic kidney transplantation demonstrated a transient decrease in bone marrow PCs in vivo and persistent alterations in alloantibody specificities. Total IgG levels were unchanged. We conclude that proteasome activity is important for PC longevity and its inhibition may lead to new techniques of controlling antibody production in vivo.

Clinical relevance of preformed HLA donor-specific antibodies in kidney transplantation

This study analyzes the influence of preformed DSA, identified by HLA-specific ELISA assays, on graft survival and evaluates the incidence of antibody-mediated rejection (AMR) in patients with and without pregraft desensitization. Kidney graft survival at 8 years was significantly worse in patients with DSA (n = 43) than in those without DSA (n = 194)(p = 0.03). The incidence of AMR in patients with DSA is 9-fold higher than in patients without DSA (p < 0.001) and their graft survival is significantly worse than in DSA patients without AMR and in non-DSA patients (p = 0.005). The prevalence for AMR in patients with DSA detected on historic serum is 32.3% in nondesensitized patients and 41.7% in desensitized patients. The risk for AMR is significantly more elevated in patients with strongly positive DSA (score 6-8) compared to those with DSA score 4 (p < 0.001), and in patients with historic DSA+/CXM+ compared to those with DSA+/CXM- (p = 0.01). The presence of preformed DSA is strongly associated with graft loss in kidney transplants, related to an increased risk of AMR. Our findings demonstrate the importance of detection and characterization of DSA before transplantation. Stratification of this risk could be used to determine kidney allocation and to devise specific strategies for these patients.

Two novel assays of alloantibody-secreting cells demonstrating resistance to desensitization with IVIG and rATG

Donor-specific alloantibody presents a major barrier to the successful transplantation of kidneys and hearts. However, the study of alloantibody production has been hampered by both an inadequate source of antibody-secreting cells (ASCs) and a paucity of assays to determine their function. We describe two new assays that allow for the determination of the frequency and specificities of allo-ASCs in humans using purified HLA as targets. These assays demonstrated allo-ASCs in the CD138(+) fraction of the bone marrow, but not in peripheral blood. Alloantibody specificities in these assays correlated well with those detected in the serum suggesting that bone marrow-derived ASCs are indeed a major source of alloantibody in vivo. However, ASCs for a specific HLA antigen were rare with an estimated frequency of only 1/2 x 10(6) marrow cells. Pretransplant treatment in vivo with multiple plasmaphereses and low-dose IVIG alone or in combination with rATG had no effect on ASC number or alloantibody production. These techniques allow for the study of allospecific ASCs and provide a method to test the potential efficacy of agents on alloantibody production in vivo.

Determinants of poor graft outcome in patients with antibody-mediated acute rejection

This study analyzes the incidence and course of antibody-mediated rejection (AMR) in a cohort of 237 renal transplant patients followed for 30 +/- 20 months. Among these, 32 patients were considered to be at risk for AMR and received intravenous immunoglobulin (IVIg), either as preconditioning (Group A, n = 18) or at the time of transplant (Group B, n = 14). The prevalence of AMR was 27.8% in Group A, 57.1% in Group B and 3.9% in the remainder of the population. Although graft loss remains greater among AMR than for acute cellular rejection (ACR) or the overall transplant population, we have identified a good outcome group (GFR > 15 mL/min/1.73 m(2)) (n = 13), whose renal function at the end of follow-up was comparable to that of the general transplant population. The factors associated with bad outcome are: (1) immunologic: presence and/or persistence of donor-specific anti-HLA antibodies post-transplantation and (2) histologic: neutrophilic glomerulitis, peritubular capillary dilatation with neutrophil infiltrates and interstitial edema at the time of first biopsy; and at the time of late biopsy (3-6 months): lesions of vascular rejection, and monocyte/macrophage infiltrates in glomeruli and dilated peritubular capillaries. Persistence of C4d does not predict outcome. This study outlines for the first time the immunologic and histologic profiles of AMR patients with poor prognosis.

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.

Pretransplant immunomodulation of highly sensitized small bowel transplant candidates with intravenous immune globulin

Presence of preformed lymphocytotoxic antibodies may represent a barrier to isolated intestinal transplantation (IITx). We developed an intravenous immunoglobulins (IVIg) based desensitization protocol for candidates with high panel-reactive antibodies (PRA). Six patients with a mean PRA of 72+/-22% were included in a four-level (L) protocol with escalating doses of IVIg (L1, L2), addition of mycophenolate mofetil (MMF) or plasmapheresis (L3); and anti-CD20 (Rituximab) (L4). Four of six candidates improved their PRAs (from a mean of 66.2% to 25.5%; P=0.01) and were successfully transplanted. At a mean follow-up of 8 months, number and severity of rejection episodes of protocol patients did not differ from patients with low PRA transplanted during the same period. These data support the use of IVIg to desensitize patients waiting for IITx. It increases the applicability of IITx, and reduces the waiting time and mortality on the waiting list with outcomes comparable to nonsensitized recipients.

ABO-incompatible kidney transplantation with anti-CD20 monoclonal antibodies, intravenous immunoglobulin and plasmapheresis without splenectomy: a case report

A 24-yr-old man was admitted to our hospital for ABO-incompatible kidney transplantation. His blood type was O, and the donor's (his father's) blood type was B. The recipient had pancytopenia, splenomegaly, splenorenal shunts and esophageal varices due to congenital hepatic fibrosis. Therefore, if splenorectomy was performed, the blood pressure of the portal vein and the growth of esophageal varices were predicted. Eventually, in return for splenectomy, anti-CD20 monoclonal antibodies (rituximab), intravenous immunoglobulin and plasmapheresis was performed for additional immunosuppression. Because of progression of pancytopenia, we had to decrease the dose of mycophenolate mofetil and gave up on using deoxyspagalin. Nevertheless the serum creatinine level decreased and remained in the 1.6 to 1.8 mg/dl range.

Extending options for highly sensitized patients to receive a suitable kidney graft

Highly sensitized patients (anti-HLA) on the kidney waiting list wait longer for a suitable crossmatch negative organ. At the moment there are two strategies to enhance transplantation of these patients. One approach is the determination of acceptable HLA mismatches and application of this knowledge for the selection of crossmatch negative donors, and the second is the desensitization of patients with intravenous immunoglobulin-based protocols to enable transplantation of an organ from a donor towards which antibodies were originally present. Both approaches have advantages and disadvantages and are only successful in a proportion of the patients. The optimal solution is an integrated strategy whereby desensitization is used for those patients for whom the acceptable mismatch approach is not successful.

Antidonor Antibodies and Transplantation: How to Deal with Them Before and After Transplantation

The presence of antibodies directed against the donor has usually been considered as an absolute contraindication to transplantation. However, recent advances both in the ABO and human leukocyte antigen settings, detailed in this paper, have led to successful transplantations in the presence of antidonor antibodies, with preliminary evidence of accommodation.

ABO incompatible kidney transplantations without splenectomy, using antigen-specific immunoadsorption and rituximab

ABO incompatible kidney transplantations have previously only been performed after several preoperative sessions of plasmapheresis and splenectomy, with the conventional triple-drug immunosuppressive protocol being reinforced with antilymphocyte globulin and B-cell-specific drugs, such as cyclophosphamide or deoxyspergualine. We have designed a protocol without splenectomy, based on antigen-specific immunoadsorption, rituximab and a conventional triple-drug immunosuppressive protocol. The protocol calls for a 10-day pretransplantation conditioning period, starting with one dosage of rituximab and followed by full dose tacrolimus, mycophenolate mofetil and prednisolone. Antigen-specific immunoadsorption was performed on pretransplantation days -6, -5, -2 and -1. After the last session, 0.5 g/kg of intravenous immunoglobulin (IVIG) was administered. Postoperatively, three more apheresis sessions were given every third day. Furthermore, if there was a significant increase in the antibody titers, extra sessions were considered. Eleven patients have received transplants with this protocol. The ABO antibodies were readily removed by the antigen-specific immunoadsorption and were kept at a low level post-transplantation by further adsorptions. There were no side effects and all patients have normal renal transplant function. We conclude that after an infusion each of rituximab and IVIG, and antigen-specific immunoadsorption; blood group-incompatible renal transplantations can be performed with excellent results using standard immunosuppression and no splenectomy.

Acute renal transplant injury and interaction between antithymocyte globulin and pooled human immunoglobulin

The increasing number of highly sensitized patients awaiting renal transplantation has prompted the use of induction immunosuppression regimens including pooled human intravenous immunoglobulin (IVIG) combined with polyclonal anti-lymphocyte sera. We report a case of a patient who received a live donor transplant after abrogation of donor-specific positive cytotoxic crossmatch by IVIG. She developed early acute tubular injury associated with IVIG, mannitol, and hypertonic saline infusion. Furthermore, a possible interaction between IVIG and rabbit antithymocyte globulin (ATG) occurred, suggested by an increased number of peripheral CD3(+) lymphocytes after initial rapid lymphodepletion. We suggest that IVIG-associated nephrotoxicity should be considered in the differential diagnosis of early allograft dysfunction, and furthermore, that IVIG may interact with polyclonal antilymphocyte serum to affect the amount of lymphodepletion achieved.

Rituximab as treatment for refractory kidney transplant rejection

Recent studies have shown that a high density of CD 20+ cells are seen in patients who have steroid-resistant rejection episodes. Rituximab is a high-affinity CD-20 specific antibody that inhibits B-cell proliferation while inducing cellular apoptosis. Thus, it is a rational choice for therapy in transplantation to abrogate B-cell-mediated events. Twenty-seven patients were diagnosed with biopsy-confirmed rejection manifested by thrombotic microangiopathy and/or endothelialitis between 2/99 and 2/02 at our institution. These individuals were treated with a single dose of rituximab, in addition to other therapies, in an effort to reverse their rejection episodes. Twenty-four received additional steroids while 22 of the 27 patients were also treated with plasmapheresis and antithymocyte globulin (ATG). Only three patients experienced graft loss not associated with patient death during the follow-up period (605 +/- 335.3 days). In the 24 successfully treated patients, the serum creatinine at the time of initiating rituximab therapy was 5.6 +/- 1.0 mg/dL and decreased to 0.95 +/- 0.7 mg/dL at discharge. The addition of rituximab may improve outcomes in severe, steroid-resistant or antibody-mediated rejection episodes after kidney transplantation.

Individuality: the barrier to optimal immunosuppression

Immunosuppressive therapy aims to protect transplanted organs from host responses. Individuals have unique repertoires of responses to foreign antigens and toxic reactions to immunosuppressants; the former determining the type or intensity of rejection reactions and the latter influencing the severity of iatrogenic effects. Because existing agents target molecules that are widely distributed in tissues, new strategies must selectively block lymphoid cells only, disrupt alloresponses but not innate immune responses, interact synergistically with other agents, facilitate the homeostatic process that naturally leads to graft acceptance and ideally only interrupt donor-specific responses. Approaches presently under investigation aim to alter cell trafficking, or selectively deviate the maturation of antigen-presenting cells or inhibit lymphocyte-activation cascades - events that are crucial to rejection responses.

Impact of the delayed graft function in hypersensitized kidney transplant patients

AIM

The aim was to study the incidence, impact, and association of pretransplantation anti-HLA antibodies and delayed graft function (DGF) on the outcome of cadaver kidney transplants independent of the immunosuppressive therapy.

METHODS

Data from 1325 cadaver donor kidneys (February 1975 to December 2002) included the variables of current and peak anti-HLA antibodies, presence of DGF, acute rejection (AR) episodes, patient survival, and graft half-life.

RESULTS

DGF (need for dialysis in the first week posttransplantation) ranged between 15% and 40% with a mean of 30% in last 5 years. Eighty-five percent of the candidates on the waiting list for kidney transplants displayed <25% panel reactive antibody (PRA) at transplantation with 4.6% between 26% and 50%, 7.7% between 51% and 75%, and 1.5% >75%. Among the patients who developed DGF, 47% displayed AR compared an incidence of 30% among patients without DGF (P=.0026). The patients displaying >50% PRA (either current or maximum) showed a worse graft survival compared with patients with <50% PRA (log rank, P=.0000). DGF reduced graft survival (P=.04), the difference appearing in the early phase after transplantation. The best outcome was observed in the no DGF-no AR group (half-life, 11.6 years) and the worst results were in the hypersensitized patient groups: peak and current PRA >50% (half-lives of 2.4 and 2.2 years). A multivariate analysis showed that the presence of peak or current PRA >50% is the most important risk factor for graft loss.

CONCLUSION

Sensitization is the key factor in graft outcome. Presensitization increases the risk of DGF and DGF increases the incidence of AR and both together produce the worst graft survivals.

Humoral theory of transplantation

According to the humoral theory of transplantation, antibodies cause allograft rejection. Publications are cited showing that antibodies: (1). cause hyperacute kidney rejection, (2). lead to C4d deposits associated with early kidney graft failures, (3). are a good indicator of presensitization leading to early acute rejections, (4). were present in 96% of 826 patients who rejected a kidney graft, (5). are associated with chronic rejection in 33 studies of kidney, heart, lung and liver grafts, and (6). in three studies, appeared in the circulation BEFORE evidence of bronchiolitis obliterans in lung transplants, and BEFORE kidney rejection. In addition, a prospective cooperative study of 1629 patients in 24 centers demonstrated that antibodies foretold subsequent failures after a follow-up period of 6 months (p = 0.05). The specificity of antibodies detected in the serum of rejecting patients were often not donor specific, presumably because they were absorbed by the rejecting organ. If the humoral theory is accepted, even provisionally, transplanted patients who have antibodies could be treated with immunosuppression until the antibodies disappear to determine whether chronic rejection can be blocked. If successful, in patients who do not have antibodies, immunosuppression could be reduced until antibodies appear.

The current state of, and future prospects for, cardiac transplantation in children

During the last two decades, several advances have resulted in marked improvement in medium-term survival, with excellent quality of life, in children undergoing cardiac transplantation. Improved outcomes reflect better selection of donors and recipients, increased surgical experience in transplantation for complex congenital heart disease, development of effective surveillance for rejection, and wider choice of immunosuppressive medications. Despite all of these advances, recipients continue to suffer from the adverse effects of non-specific immunosupression, including infections, induction of lymphoproliferative disorders and other malignancies, renal dysfunction, and other important end-organ toxicities. Furthermore, newer immunosuppressive regimes, thus far, appear to have had relatively little impact on the incidence of chronic rejection. Progress in our understanding of the immunologic mechanisms of rejection and graft acceptance should lead to more targeted immunosuppressive therapy and avoidance of non-specific immunosupression. The ultimate goal is to induce a state of tolerance, wherein the recipient will accept the allograft indefinitely, without the need for long-term immunusupression, and yet remain immuno-competent to all non-donor antigens. This quest is currently being realized in many animal models of solid organ transplantation, and offers great hope for the future.