ABO 不相容腎移植病人接受Rituximab後導致B細胞交叉配對試驗呈現偽陽性的鑑別診斷與處理方式

李采霓、王碩盟、闕士傑

國立台灣大學附設醫院 泌尿部

False positive B-cell crossmatch after Rituximab administration in an ABO incompatible renal transplant recipient – Differential diagnosis and management

Tsae-Ni, Lee、Shuo-Meng Wang、Jeff S. Chueh

Department of Urology, National Taiwan University Hospital 

Abstract

Introduction:

       Rituximab, a murine/human chimeric monoclonal antibody directed against human CD20, has been used in renal transplantation for B cell depletion. However, despite the absence of preformed HLA antibodies, Rituximab exposure may cause B-cell crossmatches to appear positive. We present a case of ABO incompatible renal transplant who had positive B-cell crossmatch after Rituximab administration, and discuss about the solution for better interpretation results. 

Case presentation:

A 56-year-old woman with A positive blood type suffering from hypertensive nephropathy related impending end-stage renal disease presented for evaluation of kidney transplantation. Due to a B positive blood type living kidney donor, her sister, ABO incompatible high risk kidney transplantation was considered. Other pre-transplantation evaluations, including screening of occult infection, cardiac function, malignancy, showed no contraindication, and HLA typing revealed two mismatches at HLA-A, HLA-B, HLA-DR each. Cross matching showed negative results, and flow panel reactive antibody(PRA) for anti-HLA antibodies showed only equivocal results (about 500 at both class I and class II MFI). Anti-B antibody was checked as a titer of eight, seven days before transplantation, and double filtration plasmapheresis (DFPP) was administered for 3 cycles, as well as 200mg of rituximab 3 days before transplantation. Her anti-B antibody titer dropped to zero two days before transplantation, while crossmatching one day before transplantation showed a positive 1:8 reaction of B cell. Considering recent use of rituximab, false positive result was considered, while the effect of incidental packRBC transfusion, at the same day of crossmatching, was still suspected. After self-crossmatching, with recipient serum and recipient lymphocyte, showing the same positive B cell reaction, masking effect of rituximab was favored, the kidney transplantation proceeded as scheduled, using Lich-Gregoir's method as ureteroneocystostomy. To be mentioned, duplicated donor renal arteries and veins were noted, and reconstructed into single trunks for better anastomosis to external iliac vessels. Her anti-B antibody titer fluctuated from 4 to 1 postoperatively, and remained around 2 under immunosuppressants as mycophenolic acid and tacrolimus, while her serum creatinine level remained around 1.0 mg/dl during follow-up. 

Discussion:

Techniques for ABO desensitization include plasmapheresis, immune-adsorption, B cell depletion via Rituximab. Due to an ABO incompatible high risk kidney transplantation status in our patient, both Rituximab and DFPP were administered before renal transplantation. However, positive B-cell crossmatch reactions were still noted, leading to doubt of the authenticity of the examination result and the feasibility of transplantation. The need to distinguish whether the result is true or false is crucial in determining the feasibility of renal transplantation.

Rituximab can remain in the serum for several months after application, and prior exposure in both the donor and recipient may interfere with crossmatch results. Rituximab has a cytolytic effect on B-cells, causing a positive result in a complement-dependent cytotoxicity B-cell crossmatch (CDC) despite absence of preformed HLA antibodies. As a humanized antibody, it may also interfere with commonly used flow cytometric crossmatches, leading to a false positive result.

Pronase, a nonspecific proteolytic enzyme that cleaves Fc receptors, removes CD20 from B cells. Studies have reported improved sensitivity and specificity of B-cell crossmatches in pronase-pretreated lymphocytes. Despite having previous exposure to rituximab, when CD20 was cleaved from the B cells with pronase, B cells displayed a negative crossmatch. Rituximab could then be used without worrying about interfering with the crossmatch results.

Conclusion:

We present a case of ABO incompatible high risk kidney transplantation who had positive B cell crossmatch result after Rituximab administration, leading to worry of the feasibility of renal transplantation. Via pronase treatment, false positive results due to rituximab interference could be avoided, and rituximab could be used without worrying about interfering with transplant immunologic monitoring.