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The purpose of this communication is to describe a case that illustrates the interference of in vivo anti-CD20 treatment on B cell crossmatch (B-XM) results. A first kidney transplant candidate, female, white, 31 years-old, with systemic lupus erythematosus, without previous pregnancies, with one blood transfusion more than 15 years ago, came to the laboratory (day 1) with the brother (D1) and the mother (D2) as potential donors (D). No HLA I or II antibodies were detected by Luminex-Single Antigen assay (One Lambda). XM results with DTT-treated serum: negative T-CDC-AHG-XM with D1 and D2; positive B-CDC-XM with D1 and D2; negative auto-B-CDC-XM; positive CDC-XM against B cells from eight healthy individuals (B-CDC-PRA). Day 42: XMs with D2 and auto-XM: same results. Day 68: the patient was listed for transplant with kidney from deceased donor and four serum samples were sent to the laboratory afterwards. Day 203: all six available sera were simultaneously tested in auto-T and -B-XM, by CDC and by flow cytometry (FC) with cells from day 203: all sera were negative in auto-T-XM; the sera from days 1 and 42, which had been negative in the auto-B-CDC-XM with cells from days 1 and 42, respectively, were positive with B cells from day 203 and also positive against 100% of the B cells from the panel. The serum from day 75 was positive in the auto-B-CDC-XM, auto-B-FC-XM and B-CDC-PRA, whereas the serum from day 88 was positive only in the auto-B-FC-XM. In contrast, sera from days 174 and 203 were negative in the auto-B-XM by CDC and FC, and in B-CDC-PRA. After all these tests, we found out that the patient had been treated with anti-CD20 antibodies (Rituximab) 83 days before the first tests and we concluded: all positive B-XMs could be explained by the presence of anti-CD20 in the serum; the negative auto-B-XM with the sera and cells from days 1 and 42 could be explained by a low, or lack of, CD20 expression in the cells of the patient caused by in vivo modulation by anti-CD20 antibodies. Down-regulation of CD20 expression in B-cell lymphoma after treatment with Rituximab is a well-documented phenomenon but, to the best of our knowledge, this is the first description of CD20 modulation in normal B cells. |
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