P1735USING PRONASE PRE-TREATMENT CDC-CROSSMATCH TO STUDY THE RITUXIMAB KINETICS IN KIDNEY TRANSPLANT CANDIDATES AND RECIPIENTS

Abstract

Abstract Background and Aims Rituximab (RTX) is a monoclonal antibody that targets CD20 on B cells. It is often used in the desensitization before ABO- and HLA-incompatible kidney transplant (KT) and in the treatment of antibody-mediated rejection (ABMR), glomerulonephritis and post-transplant lymphoproliferative disorders (PTLDs) in KT recipients, however in most of these conditions the kinetics of the drug has not been widely investigated. Because of its intrinsic B cytotoxic property, its use can interfere with immunogenetic techniques such as B-cell complement mediated cytotoxic crossmatch (CDCXM). Low dose pronase pretreatment has been proposed to reverse this interference, cleaving the CD20 rituximab target from these cells. We wanted therefore to test the kinetics of rituximab in the serum of kidney transplant candidates or recipients using CDCXM with or without pronase pretreatment. Method We conducted a retrospective monocentric study on all KT candidates and recipients that underwent RTX therapy at the Parma Kidney Transplant Nephrology Unit (Parma, Italy) with serial biobanked frozen sera stored at the Immunogenetic Unit of Parma (Parma, Italy). B-cell CDCXM was performed in the presence or absence of low-dose (0.5 mg/mL) B-cells pretreatment. The difference between 2 intervals was analysed by Mann-Whitney test, groups analysis was analysed by Kruskal-Wallis test. The difference in the presence of absence of pronase pretreatment was analyzed by Wilcoxon test for paired data. Results We included 31 patients, 58% were male, the average age was 46+/- 13. The majority (74%) of the patients received a living donor KT and the most common indication for RTX was the desensitization for ABO- (58%) or HLA-(13%) incompatible living donor KT. Other indications were the treatment of glomerulonephritis (13%), ABMR (10%) or PTLD (6%). One patient received 2 doses of 1 g, the rest of the patients received 375 mg/m2 once (84%) or twice (16%). In 48% of the patients RTX therapy was followed by isolated plasmapheresis (PEX) or in combination with immunoadsorption (IA)(32%). In most of the patients B-cell CXCXM turned negative at 6 months after RTX treatment (p<0.001)(Figure 1), however this cytotoxicity was more persistent (up to 12 months) in patients who did not underwent PEX+/-IA after RTX (Figure 2). The B-cell pretreatment with pronase was able to turn negative this reaction (p=0.002) in these patients. Conclusions The data of our study seem to suggest a persistence of RTX in the sera of KT patients among the 4 months of onlabel treatments, especially in the absence of PEX or IA treatment following RTX. Moreover the use of B-cell CDCXM in the the presence or absence of pronase could be used to monitor circulating levels of RTX in different diseases.