Abstract
[Background] Recently, We have presented that sensitivity to anti-CD20 antibody-mediated CDC was different during cell growth dependent on expression of CD55 (ASH 2003, San Diego). In some cases with malignant lymphoma after the treatment of anti-CD20 antibody, lymphoma cells get resistance to the treatment of anti-CD20 antibody. Moreover, bulky disease of malignant lymphoma like 7.0 cm of tumor gets resistance to rituximab. One of some regulators in complement system, CD55, is a major regulator of the alternative and classical pathways of complement activation and is expressed on all serum-exposed cells. Here, we have found the relationship among extirpated lymph nodes, sensitivity to CDC, and CD55 expression, and small interference of RNA (siRNA) for CD55 is a useful tool for blockade of CD55 in monoclonal antibody therapy.
[Methods] Human B cell line, Daudi and Rajii cells were used as sensitive and insensitive controls in complement-mediated cytotoxycity (CDC) with anti-CD20 antibody. Lymphoma cells were collected from extirpated lymph nodes of the patients with lymphoma. CDC assay with anti-CD20 antibody was performed with FACscan or under confocal laser scanning microscopy system. Three parts of siRNAs for CD55 (CD55-N, -M, and -C) were designed, and transfected to the cells using lipofectin
[Results] The relationship between sensitivity to CDC and size of extirpated tumor showed negative correlation. The formula’s intercept was 7.775 cm, suggesting that lymphoma with more than 7 cm of size is not effective in rituximab therapy as Coiffier’s report. The level of CD55 expression on lymphoma cells was correlated with size of its lymph node, and in some patient with lymphoma, level of CD55 expression on Lymphoma cells and susceptibility to CDC were different among before, after relapse and after partial remission, indicating that susceptibility to CDC depends on CD55 expression. This suggests that increased cell numbers contribute to higher or enhanced CD55 expression and resistance to CDC with rituximab. Lymphoma cells from all five cases with recurrent lymphomas strongly expressed CD55 molecules under laser scanning confocal microscopy. Percentages of dead cells showed no significant differences among transfection with and without CD55-N, CD55-M and CD55-C before CDC assay. Percentage of PI-positive cells in transfection with CD55-N significantly increased from 7.1% to 67.9%. These indicate that the siRNA against CD55 (1–380 nucleotides), CD55-N could efficiently knock down the expression of CD55 on freshly isolated lymphoma cells from recurrent lymphomas, and that it could induce cell death in freshly isolated lymphoma cells from recurrent lymphomas by CDC.
[Conclusion] This siRNA for CD55 could be a good tool for blockade of CD55 in resistance and bulkiness related with highly expressed CD55 with monoclonal antibody therapy.
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