EXPERIMENTAL AND CLINICAL TRANSPLANTATION

Objectives: Antibody-mediated rejection after kidney transplant is less responsive to conventional antirejection therapies. The proteasome inhibitor bortezomib has activity against mature plasma cells that produce damaging donor-specific antibodies. We present our experience of using a bortezomib-based regimen in patients with severe antibody-mediated rejection.

Materials and Methods: A retrospective chart review was performed on patients with biopsy-proven antibody-mediated rejection after kidney transplant at our institution over 12 months. Diagnosis of antibody-mediated rejection was made on the basis of positive peritubular capillary C4d staining along with either histologic evidence of acute rejection or positive donor-specific antibody titers. Treatment for antibody-mediated rejection included plasmapheresis, intravenous immunoglobulin, steroids, single-dose rituximab (375 mg/m²) along with bortezomib (1.3 mg/m²) on days 1, 4, 8, and 11. Antibody-mediated rejection was diagnosed in 6 patients. Patients received induction with either alemtuzumab (n=4) or rabbit-antithymocyte globulin (n=2) and were maintained on a tacrolimus/mycophenolate mofetil/early steroid withdrawal protocol.

Results: Four of 6 patients responded to treatment. Patients had stable kidney function during follow-up (median 14 months) after bortezomib therapy.

Conclusions: In this series, we demonstrated the effectiveness of a bortezomib-based treatment regimen in achieving reduction of donor-specific antibody titers and stable renal function in patients experiencing severe antibody-mediated rejection.

Key words : Bortezomib, Donor-specific antibodies, Humoral rejection, Kidney transplant, Plasma cells

Antibody-mediated rejection (AMR) has gained importance because of the high risk of early graft loss that ranges from 27% to 40% in first year after an event.¹ Antibody-mediated rejection occurs in up to 20% to 30% of all acute rejection episodes, and 60% of the cases coexist with acute cellular rejection (ACR).² The increased recognition of AMR as a cause of early graft loss stimulated interest to find new therapeutic interventions. The mechanism of injury involves production of high levels of donor-specific antibodies (DSA) by plasma cells, and this knowledge has provided insights in developing therapeutic strategies. We present our experience with the use of bortezomib, a proteasome inhibitor with activity against mature plasma cells for the successful treatment of AMR in kidney transplant recipients along with a review of the literature.

A retrospective chart review was performed on patients with biopsy-proven AMR after kidney transplant at our institution over 12 months (February 2010 to February 2011). Six patients were diagnosed with AMR based on positive peritubular capillary C4d staining along with either histologic evidence of acute rejection or positive DSA titers. Renal biopsies were analyzed by a single pathologist and graded using Banff updated 2005 criteria.³ Donor-specific antibodies titers were measured using Luminexx platform (LABScreen, One Lambda, Inc, Canoga Park, CA, USA), were expressed as mean fluorescent intensity. Owing to the extreme sensitivity of this test and the uncertain clinical significance of lower values, a DSA level of 4000 mean fluorescent intensity was used as an arbitrary lower cutoff value for positivity. Mean age of the recipients was 43 ± 13 years, with panel reactive antibody range 0% to 80%, and 4 ± 1 human leukocyte antigen (HLA) mismatches. Of 6 patients, 5 were females, 5 had their first kidney transplant, 2 had live donors, 4 received alemtuzumab (30 mg IV intraoperatively) and 2 received rabbit-antithymocyte globulin (r-ATG) (6 mg/kg IV in 4 divided doses of 1.5 mg/kg/d). All patients were maintained on tacrolimus (trough level, 8-10 ng/mL), mycophenolate mofetil (500-1000 mg twice daily), and an early steroid withdrawal protocol (methylprednisolone 500 mg IV intraoperatively, 250 mg IV postoperative day [POD] No. 1, and 125 mg IV POD No. 2, prednisone 60 mg POD No. 3, and 30 mg POD No. 4). Patient demographics are shown in Table 1.

Two of 6 patients (patients A and B) were initially treated with conventional therapy for AMR including plasmapheresis, intravenous immunoglobulin (IVIg), and steroids. Owing to the continued rise in serum creatinine and DSA titers, therapy with single-dose rituximab and 4 doses of bortezomib was initiated. In the other 4 patients, bortezomib was started on day 1 of diagnosis of AMR along with a single dose of rituximab (375 mg/m²) and the rest of the conventional therapy for AMR. Peak serum creatinine and DSA titers at the time of diagnosis of AMR and end of treatment are shown in Table 2. Individual treatments of AMR in each patient are detailed in Tables 3, 4, 5, 6, 7, 8.

Patients A and B remained to have excellent graft function 27 months after transplant. Patient C had 2 more episodes of biopsy-proven ACR after 4 and 5 months after AMR secondary to noncompliance that were treated with steroid boluses. Her last biopsy 6 months after AMR was negative for rejection. Patient D developed biopsy-proven ACR 7 months after AMR that was treated with steroid boluses. She had multiple episodes of acute kidney injury secondary to recurrent urinary tract infections and pyelonephritis. Her last transplant kidney biopsy was done 8 months after AMR, and it did not show any rejection. Patient E had refractory AMR and became dialysis-dependent. Patient F had chronic AMR. Her DSA titers did not improve with treatment. In summary, 2 of 6 patients did not respond to treatment but responders had stable kidney function during median follow-up of 14 months (range, 3-27 mo) after bortezomib therapy.

We present our experience with the successful use of bortezomib in 4 out of 6 patients who presented with AMR after kidney transplant. The repeat kidney biopsies after completion of treatment were consistent with resolution of AMR although the clinical outcomes varied over the long-term follow-up.

Use of currently available therapies for AMR (plasmapheresis, IVIg, rATG, rituximab) have shown inconsistent and suboptimal results. This could be due to their inability to suppress mature plasma cell activity, which is the major source of antibody production in AMR. The beneficial effects of bortezomib (Millennium: The Takeda Oncology Company, Cambridge, MA, USA), an anti-plasma cell agent used to treat AMR, was first reported by Everly and associates in 2008 in patients with refractory AMR and ACR.⁴ Bortezomib was originally synthesized in 1995 and approved by the US Food and Drug Administration in 2003 for treating multiple myeloma.

Our approach to AMR followed the protocol described by Everly and associates.⁴ The first step is plasmapheresis, which helps not only in removing previously secreted antibodies but also, in increasing the metabolic demands on memory B cells and plasma cells and thereby, enhancing their susceptibility to proteasome inhibition.^5,6 The usual prescription includes 1.0 to 1.5 volume exchange using albumin solution daily or on alternate days, continued until serum creatinine falls within 30% of previous baseline values. This modality does not suppress antibody production and in fact, can cause a rebound in DSA levels after plasmapheresis. Pulse corticosteroids, hypothesized to treat AMR by potentially down-regulating B-cell activity, were given concomitantly.

The second step is the administration of IVIg products derived from pooled human plasma. The exact mechanism of action of IVIg is unclear, however, it is hypothesized that they suppress immunoglobulin synthesis, has anti-idiotypic activity against DSA, blocks Fc receptor, inhibits complement activation, and possesses anticytokine activity. When given with plasmapheresis, IVIg helps replenish lost gammaglobulin and decreases the risk of infection. The recommended dose is 100 mg/kg after each session and 300 to 400 mg/kg for 1 to 2 days after the last session of plasmapheresis with a cumulative dose of 1000 mg/kg.⁷ The third step is to give rituximab, a chimeric anti-CD20 antibody that directly inhibits B-cell proliferation by antibody-, cell-, and complement-mediated cytotoxicity and induces cellular apoptosis. It has been demonstrated that the high density of CD20+ B cells is found in the biopsies of patients with steroid-resistant rejection episodes. The main limitation of rituximab is the inability to remove CD20-negative plasma cells that continue to produce HLA antibodies.⁸ The final step in treatment is to administer bortezomib, a boronic acid dipeptide that specifically inhibits 26S proteasome preventing activation of the transcriptional activator nuclear factor kappa B. This leads to disruption of normal cell homeostasis and plasma cell apoptosis.⁹ Targeting the plasma cells directly destroys the source of damaging DSA. The recommended dose is 1.3 mg/m²/dose × 4 doses.

Experience with the use of bortezomib in treating AMR thus far is limited to case reports and series. Perry and associates report successful use of bortezomib in 2 patients after transplant AMR with reduction in the number of bone marrow plasma cells and normal renal function at 1 year after transplant.¹⁰ Walsh and associates showed undetectable DSA levels within 14 days of bortezomib-based therapy in 2 living-donor transplant recipients who developed AMR within first 2 weeks of renal transplant.⁴ Everly and associates reported 2 different case series of patients with AMR and coexisting ACR with prompt reversal of rejection with use of bortezomib.^4,11 They did not observe any opportunistic infections or serious adverse events except transient gastrointestinal adverse effects and thrombocytopenia with bortezomib therapy. Sberro and associates did not show any significant reduction in DSA titers in 4 renal transplant recipients with subacute AMR at 5 months after transplant with the use of 4 doses of bortezomib alone.¹² These findings are consistent with 1 of our patients (Patient F), who had chronic AMR with elevated DSA titers that did not improve with bortezomib therapy. Trivedi and associates demonstrated reduction in DSA titers with bortezomib therapy in 9 out of 11 patients with stable graft function at 4 months after transplant.¹³ Our study had a longer follow-up after AMR therapy. We have followed these patients closely with monthly serum creatinine, DSA titers, and periodic renal allograft biopsies.

In conclusion, our experience in treating AMR after kidney transplant demonstrates the effectiveness of a bortezomib-based treatment regimen in achieving reduction of DSA titers and stable renal function over a relatively longer follow-up. Patients tolerated treatment without significant adverse effects, but larger studies with longer follow-ups are required for a more-definitive evaluation of this approach.

Volume: 10 Issue: 6 December 2012

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