All recipients had good early-stage renal function recovery. No patient had delayed graft function (DGF). Acute rejection, diagnosed on the basis of clinical assessment and pathological biopsy results, occurred in 1 patient on day 7 and in 1 patient on day 13 post-surgery. According to the Banff 07 classification of renal allograft pathology, one of the patients was Ia and the other was IIa; the C4d staining was negative in both patients. Successful reversion of rejection was achieved following treatment with methylprednisolone (500 mg) plus cyclophosphamide (CTX) 200 mg for 3 days in one patient and ATG 50 mg for 3 days in the other patient (Table 2).
No infections of the wound, urinary tract, or respiratory passage were observed during the perioperative period. During the 7–12 month follow-up, one patient experienced pulmonary aspergillosis infection at 4 months after surgery, which was cured with amphotericin B treatment.
The sensitization refers to the pre-existence of anti-HLA antibodies in the renal transplant recipients. Based on the HLA antibody levels, recipients of renal transplant can be classified to 4 groups: non-sensitized (PRA 0–10%), slightly sensitized (PRA 11%-50%), moderately sensitized (51%-80%), and highly sensitized (PRA >80%).8 In this study, a highly sensitized patient was defined as PRA >30%. The PRA level is a good indication of the degree of sensitization. The HLA antibodies are often produced following exposure of the patients to the allogeneic antigens, which may occur, for example, in patients who may have had a history of pregnancy, blood transfusions, or a previous transplantation.9
In this study, 4 patients were twice transplant recipients. All female recipients had history of multiple pregnancies and all recipients had history of blood transfusions.
Pretransplant sensitization is believed to be related to antibody-mediated rejection of the renal graft. Therefore, the key to a successful renal transplantation in sensitized patients is the reduction or removal of the preexisting HLA antibodies in these patients before transplantation. Cai and Terasaki10 suggested that interventions in the following three areas can help to achieve successful renal transplantation in sensitized patients: (1) inhibition and reduction of antibody-producing cells, (2) removal or blockage of preexisting or newly developed antibodies, and (3) intervention of antibody-mediated tissue injury. A number of recently developed desensitization regimen, such as IVIg, plasmapheresis (PP), low-dose IVIg combined with PP, as well as anti-CD20, anti-CD52, and anti-CD5 antibody induction therapy, and proteinase inhibitors, are based on those three mechanisms.
CD20 is an internal membrane protein, which is often expressed on the surface of B cells and pre-B cells,11 but CD20 antigen is not expressed on hematopoietic stem cells, progenitor B cells, and normal plasma cells. RTX is a chimeric mouse/human monoclonal antibody raised against the CD20 antigen. RTX can specifically bind to normal or malignant pre-B cells and CD20 antigen on the surface of mature B cells. RTX was approved by the US FDA in 1997 for the treatment of recurrent, poorly differentiated refractory or follicular CD20+ B-cell non-Hodgkin's lymphoma. RTX has been studied in clinical trials for the treatment of many autoantibody-mediated diseases, such as immune thrombocytopenic purpura, systemic lupus erythematosus, myasthenia gravis, and rheumatoid arthritis.12
There are three major mechanisms by which RTX depletes B cells: (1) antibody-dependent cell-mediated cytotoxicity, (2) complement-dependent cytotoxicity, and (3) ability to induce apoptosis.13,14 It is also believed that RTX itself can reduce PRA levels. For example, Pescovitz et al15 found that PRA levels and antibody specificity were reduced in most sensitized patients following treatment with RTX. However, some scientists have different opinions; they believe that for patients with PRA >20%, RTX has played a limited role in reducing PRA antibody levels.16 At present, a single-dose preoperative RTX infusion has been adopted at most clinical centers worldwide. Genberg et al17 found that following treatment of patients (n=49) with a single-dose of preoperative RTX (375 mg/m2), peripheral blood B lymphocyte counts started to reduce 24 hours after surgery. B lymphocytes were nearly fully depleted at weeks 3–6, a phenomenon which was maintained for 14–16 months, indicating that RTX has a fast onset of action and long-lasting effects.
The use of anti-CD20 antibody in sensitized recipients is controversial. Some scientists argue that anti-CD20 antibody does not have any effect on plasma cells, even though plasma cells are the major source of rapid antibody production. In addition, given the fact that RTX does not affect existing antibodies in the circulating system, RTX monotherapy would be problematic. RTX might be more effective for sensitized patients if it is used in combination with other antibody-removing strategies. Vo et al18 reported using combination therapy with RTX and IVIg to treat sensitized patients. Successful renal transplantation was achieved in 16 of 20 patients. Mean PRA levels dropped from 77% to 40%. Time on waiting list for transplantation was reduced from 12 years to 5 months. Although the postoperative rejection rate was as high as 50%, of which 30% were antibody-mediated rejection, most rejections occurred at an early postoperative stage and were controlled. The patient and graft survival rates were 100% and 94% up to 1 year, respectively. In our report, lymphocyte cytotoxicity in donors and recipients were low. Based on our transplantation experience in sensitized patients,19 although patients’ PRA levels were higher than normal, we believe that preexisting antibodies are not the major cause of antibody-mediated rejection. Rather, we think that blockage of new antibody production is the key to successful renal transplantation. We therefore used solely anti-CD20 antibody induction therapy in patients and obtained good clinical efficacy. Our results are similar to reports conducted overseas.20
The use of RTX and antithymocyte globulin therapies is likely to increase the risk for infection and malignant tumors in transplant recipients.21 In our study, no infections occurred during the perioperative period in all patients, which may be related to our effective postoperative measures to prevent infection. However, this risk needs to be further verified.
Although desensitization treatment enables successful renal transplantation in some sensitized patients, rejection has been reported to occur in nearly 90% of patients with PRA >80% within the first 3 months after surgery.22 Acute antibody-mediated rejection (AMR) is an important cause of graft failure. RTX is also effective for the treatment of AMR. Becker et al23 reported the use of a single dose of RTX (375 mg/m2) for the treatment of refractory acute rejection in 27 sensitized patients (PRA (35.7±10.2)%) who had failed to respond to high-dose steroid hormone treatment and combined treatment with PP and ATG, with a marked clinical efficacy. However, very few similar studies have been conducted in China.
In summary, this short-term postoperative results of renal transplantation indicate that renal transplantation was successful in highly sensitized patients who underwent RTX treatment. RTX therapy is a safe and effective approach to reduce humoral rejection. However, it is still unclear whether multiple doses of RTX would be more effective in reducing or removing antibodies than a single dose. Therefore, further explorations on the optimal dosage, treatment duration, as well as the long-term prognosis of RTX induction therapy are warranted in future studies.
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