Abstract
Rituximab is a chimeric monoclonal antibody that targets B-cell-specific antigen CD20 and an effective treatment for B-cell non-Hodgkin lymphoma. Although it is readily used in clinical practice, the exact mechanism of its antitumor effect is unclear. One potential mechanism involves complement-mediated cytotoxicity. It has been shown that rituximab induces complement-mediated cytotoxicity in follicular lymphoma cells in vitro, and complement inhibitors CD55 and CD59 may regulate this process. To determine whether complement inhibitors play a role in regulating the antitumor effect of rituximab, the expression of complement inhibitors CD46, CD55, and CD59 was analyzed in pretreatment tumor cells from 29 rituximab-treated follicular lymphoma patients. Among them, 8 patients achieved complete responses, 11 patients achieved partial responses, and 10 patients showed no or minimal responses to rituximab treatment. Expression of surface CD20, CD46, CD55, and CD59 was determined by 2-color flow cytometry. Although the CD59 level was slightly lower in the complete response group, there was no statistically significant difference in the expression of individual complement inhibitor CD46 (mean channel fluorescence [MCF]: NR, 26.4; PR, 21.9; CR, 29.9), CD55 (MCF: NR, 16.4; PR, 14.9; CR, 23.2), or CD59 (MCF: NR, 41.6; PR, 40.6; CR, 30.6), the combination of any 2 inhibitors, or all 3 on tumor cells from 3 response groups. In addition, there was no difference in the rituximab-induced complement-mediated cytotoxicity in an in vitro assay using tumor cells from 3 response groups. Thus, CD46, CD55, and CD59 expression on pretreatment tumor cells, or their susceptibility to in vitro complement-mediated killing, does not predict clinical outcome after rituximab treatment.
Highlights
The B-cell–specific antigen CD20 is first expressed on the surfaces of B-cell precursors shortly after the appearance of CD19 and throughout the mature B-cell stage[1] and on more than 90% of B-cell non-Hodgkin lymphoma (NHL).[2]
This work was aimed at testing whether complement inhibitor expression pattern or in vitro complement-mediated cytotoxicity can predict the clinical outcome in rituximab-treated patients
There were no differences in the sums of levels among the 3 response groups, as follows: CD46 ϩ CD55 (NR ϭ 42.8 Ϯ 13.9; partial response (PR) ϭ 36.9 Ϯ 9.8; complete response (CR) ϭ 53.0 Ϯ 16.0); CD55 ϩ CD59 (NR ϭ 58.1 Ϯ 22.8; PR ϭ 55.5 Ϯ 31.6; CR ϭ 53.8 Ϯ 21.9); CD46 ϩ CD59 (NR ϭ 68.0 Ϯ 20.1; PR ϭ 62.5 Ϯ 32.1; CR ϭ 60.5 Ϯ 25.0); CD46 ϩ CD55 ϩ CD59 (NR ϭ 84.5 Ϯ 18.8; PR ϭ 77.4 Ϯ 32.6; CR ϭ 83.7 Ϯ 24.3)
Summary
The B-cell–specific antigen CD20 is first expressed on the surfaces of B-cell precursors shortly after the appearance of CD19 and throughout the mature B-cell stage[1] and on more than 90% of B-cell non-Hodgkin lymphoma (NHL).[2]. The reason for the heterogeneity of the response of different histologies and different patients is unclear
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