|
|||||||||
|
|
|
|
|
|
|
|
|
|
|
CLINICAL OBSERVATIONS, INTERVENTIONS, AND THERAPEUTIC TRIALS
From the Division of Medical Oncology, Department of
Internal Medicine, Stanford University School of Medicine, CA.
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.
(Blood. 2001;98:1352-1357) 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 stage1
and on more than 90% of B-cell non-Hodgkin lymphoma
(NHL).2 Although the structure of CD20 suggests a function
as a membrane transporter or an ion channel,3 the function
of CD20 in B cells is still not clearly understood. CD20 has been the
target for monoclonal antibody (mAb) immunotherapy of B-cell
NHL.4 A recently developed chimeric anti-CD20 mAb,
rituximab, is an effective treatment for low-grade or follicular B-cell
NHL; its response rate is approximately 50%. In phase 1 studies,
rituximab induced a rapid depletion of CD20+ normal and
lymphoma cells.5,6 Phase 2 trials with low-grade or
follicular lymphoma showed a 50% response rate,7 whereas intermediate- to high-grade lymphomas showed a lower response rate.8 The reason for the heterogeneity of the response of different histologies and different patients is unclear.
The exact mechanism of CD20 mAb-induced antitumor or anti-B-cell
effect remains unknown. It is generally accepted that immune-effector mechanisms, which include antibody-dependent cellular cytotoxicity (ADCC) and complement-mediated cytotoxicity, are
involved.9,10 This notion has been supported by several
observations. First, though rituximab (IgG1) effectively depleted
CD20+ B cells, an equivalent IgG4 We analyzed the expression of complement inhibitors CD46, CD55, and
CD59, and performed in vitro complement-mediated cytotoxicity assay on
pretreatment tumor cells from 29 rituximab-treated patients, whose
outcome of therapy was known, to determine whether the relative levels
of complement inhibitors or their susceptibility to in vitro
complement-mediated cytotoxicity correlated with clinical outcome. 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.
Tumor cells
For analysis, tumor cells were thawed, washed twice with culture medium
(RPMI 1640 supplemented with 2% fetal calf serum, L-glutamine,
penicillin, and streptomycin), and subjected to Ficoll-Paque Plus (Amersham Pharmacia Biotech, Piscataway, NJ) density gradient centrifugation to remove dead cells. Viability of tumor cells as
determined by trypan blue dye exclusion at the time of analysis exceeded 90% in all cases. Percentages of tumor cells in all samples were estimated using the light-chain restriction expressed in tumor
cells. Coexisting normal B cells included cells expressing the other
light chain and some of the cells expressing the same light chain as
tumor cells. The number of normal B cells expressing the same light
chain can be calculated by doubling the number of the other light chain
(in Antibodies and flow cytometry Reagents and methods used to analyze expression of cell surface antigens by flow cytometry have been previously described.14 Monoclonal antibodies specific to CD3, CD20, CD46, and CD55 were labeled with fluorescein isothiocyanate (FITC), and mAbs specific to CD59 and CD20 were labeled with phycoerythrin (PE). All were purchased from BD Pharmingen (San Diego, CA). Antibodies specific to and  light chains were labeled with FITC or PE and
were purchased from Biosource (Camarillo, CA). All analyses were
conducted using 2-color staining with FITC- and PE-labeled mAb.
Briefly, 5 × 105 cells were stained with FITC-labeled
anti-CD20, anti-CD46, anti-CD55, or PE-labeled anti-CD59 and
subsequently stained with a second fluorescence-labeled anti- or
anti- light chain. In an analysis of T-cell percentages in the
tumor samples, cells were stained with FITC-labeled anti-CD3 and
PE-labeled anti-CD20. Cells were then fixed in 1% paraformaldehyde and
analyzed on a FACScan (Becton Dickinson, San Jose, CA). Negative
controls consisted of cells stained with equal concentrations of
isotype-matched FITC- or PE-labeled myeloma proteins. Expression of
CD20, CD46, CD55, and CD59 level was determined on right light
chain-positive cells based on the light-chain restriction of each
patient sample. Mean channel fluorescence (MCF) of CD20, CD46, CD55,
and CD59 staining was determined after subtracting the signal obtained
from the isotype-matched antibody from the specific mAb staining.
All 29 samples were stained and were analyzed by flow cytometry on the same day.
Complement-mediated cytotoxicity assay Lymphoma cells (5 × 105) were washed with phosphate-buffered saline (PBS) once and resuspended in 500 µL PBS. Cells were incubated with 5 µg/mL rituximab or control human IgG1 for 30 minutes at 4°C. Twenty percent of human serum from healthy donors was added, and incubation was carried out for 1 hour at 37°C. Human serum was not heat-inactivated to preserve the complement activities. The extent of complement-mediated lysis was measured by flow cytometric analysis of propidium iodide (PI)-stained cells on a FACScan (Becton Dickinson, San Jose, CA). All experiments were performed in triplicate. Specific complement-mediated cytotoxicity was determined by subtracting the percentage of PI-positive cells in IgG1-treated samples from that in the rituximab-treated sample, then dividing by the percentage of CD20+ cells in individual patient samples. The formula used was:
Statistical analysis Differences in the means of continuous measurement (MCF signal, T-cell percentage, and complement-mediated lysis) were tested by single-factor analysis of variance (ANOVA) and checked by Kruskal-Wallis (nonparametric) test. Multivariate ANOVA was used to test the difference in combinations of 2 or all complement inhibitor levels. All statistical analyses were performed using SPSS 6.1.1 for Macintosh (SPSS, Chicago, IL).
Patient characteristics Tumor samples from 29 patients treated with rituximab at Stanford Medical Center between October 1993 and December 2000 were analyzed in this study. These patients were selected because of the availability of their pretreatment tumor cells and their known responses to rituximab. Pathology review of biopsy specimens was performed at Stanford Medical Center for all patients 15 with follicular small-cleaved lymphoma, 11 with follicular mixed lymphoma, and 3 with follicular large-cell
lymphoma. All except 2 patients received 2 to 3 courses of chemotherapy
before rituximab. However, none underwent chemotherapy within 2 months
before rituximab infusion. Twenty patients underwent chemotherapy
between the time of biopsy and rituximab infusion. Twenty-seven
patients were treated with 4 weeks of weekly rituximab infusion at 375 mg/m2, one patient with 8 weeks of 375 mg/m2
infusion, and one with 4 weeks of 250 mg/m2 infusion.
Clinical responses were evaluated by physical examination and computed
tomography studies. Eight patients achieved complete response (CR), 11 patients achieved partial response (PR), and 10 patients showed no or
minimal response (NR) after rituximab therapy. There were no
significant differences in average age at the time of treatment, in
time between diagnosis and treatment, or in average number of prior
chemotherapy course among the 3 groups (Table 1). Five patients had
prior autologous bone marrow transplantation before rituximab
treatment. Overall response rate (CR+PR = 65%) was slightly higher
but similar to that in the pivotal trial (CR+PR = 60%, follicular
lymphoma group).7 Forty percent of the patients had bulky
disease (5 cm or greater) at the time of rituximab treatment. Overall
response rate was slightly higher in patients with nonbulky disease
(CR+PR = 71%) than in patients with bulky disease
(CR+PR = 58%).
CD20 expression in pretreatment follicular lymphoma cells Using 2-color flow cytometry, we determined CD20 surface expression in the pretreatment tumor cells from these 3 groups of patients. Cell suspensions from biopsy specimens were stained with FITC-labeled anti-CD20 mAb, followed by PE-labeled anti-light chain antibody corresponding to individual patients based on light-chain restriction. An example of this 2-color flow cytometric analysis is shown in Figure 1A. Using this approach, the FITC signal (representing surface CD20 expression) from specific light-chain-positive cells (gated cells shown in Figure 1A) was evaluated. MCF levels from the CD20 staining of the tumor cells from the 29 patients varied between 66 and 418. Cell surface CD20 levels expressed by the patients' tumor cells according to their clinical outcomes are shown in Figure 2A. Values were MCF = 245.8 for tumors from patients showing no responses, MCF = 229.0 for tumors from partial responders, and MCF = 171.2 for complete responders (Table 2). However, statistical analysis reveals no significant differences among the 3 groups.
The number of T cells in the biopsy specimens also varied from patient to patient (range, 2.7%-47.1%). However, again, there was no statistically significant difference between the percentage of T cells in the biopsy specimens in the 3 different groups (P = .476, ANOVA). Means of T-cell percentages were 20.3%, 20.2%, and 26.6% for nonresponder, partial responder, and complete responder, respectively (Figure 2B). Expression of complement inhibitors CD46, CD55, and CD59 in pretreatment follicular lymphoma cells To determine the possible role of complement inhibitors in the antitumor effect of rituximab, we then analyzed the surface expression of CD46, CD55, and CD59. Two-color flow cytometric staining using corresponding anti-light chain antibody and mAbs against CD46, CD55, and CD59 was performed on all tumors. CD46, CD55, and CD59 levels were determined only on corresponding light-chain-positive cells (shown as gated cells in Figure 1B). MCF was determined by subtracting the signal of isotype-matched antibody staining from the specific mAb staining. Although CD46 and CD55 expression varied from patient to patient (MCF ranges, 12.5-58.2 for CD46, 4.9-34.4 for CD55; Figure 3A-B), there were no statistically significant differences between the levels of CD46 and CD55 expression in the 3 response groups. As shown in Table 2, the means of MCF were 26.4 (NR), 21.9 (PR), and 29.9 (CR) for CD46, and they were 16.4 (NR), 14.9 (PR), and 23.2 (CR) for CD55, respectively. CD59 expression was slightly lower in patients who achieved CR (MCF = 30.6) than in patients who achieved PR or NR (MCF = 40.6 and 41.6, respectively; Figure 3C, Table 2). However, there was no statistically significant difference among the 3 groups regarding surface CD59 level. In addition, there was no statistically significant difference in the percentage of cells expressing individual complement inhibitor among the 3 groups (Table 3).
To test the possibility that the combined biologic effect of complement
inhibitors might determine rituximab's antitumor effect, scatterplots
were generated using the expression level of 2 complement inhibitors at
a time. As shown in Figure 4, each point
represents one patient plotted according to the MCF of either CD46/CD55
(Figure 4A), CD55/CD59 (Figure 4B), or CD46/CD59 (Figure 4C). There was no identifiable pattern or segregation of the 3 response groups in each
case. In addition, there were no differences in the sums of levels
among the 3 response groups, as follows: CD46 + CD55 (NR = 42.8 ± 13.9; PR = 36.9 ± 9.8; CR = 53.0 ± 16.0);
CD55 + CD59 (NR = 58.1 ± 22.8; PR = 55.5 ± 31.6;
CR = 53.8 ± 21.9); CD46 + CD59 (NR = 68.0 ± 20.1;
PR = 62.5 ± 32.1; CR = 60.5 ± 25.0); CD46 + CD55 + CD59 (NR = 84.5 ± 18.8; PR = 77.4 ± 32.6;
CR = 83.7 ± 24.3). Because CD46, CD55, and CD59 potentially
inhibit complement-mediated cytotoxicity at different steps of the
complement activation cascade in a sequential way, it is possible that
their inhibitory effects are synergistic instead of additive. If this
were the case, analysis of the sum of individual complement inhibitors
may not be able to reveal its significance. To test this possibility,
we then performed multivariate ANOVA on levels of 2 complement
inhibitors and on all 3 at a time. Again, we did not find any
relationship between expression status of any combination of 2 inhibitors or all 3 inhibitors and clinical outcome.
Susceptibility of pretreatment follicular lymphoma cells to in vitro complement-mediated cytotoxicity In vitro complement-mediated cytotoxicity assay was then performed to determine whether the susceptibility of complement-mediated killing correlated with clinical outcome. The range of rituximab-induced complement-mediated killing varied widely in all 3 response groups (NR: range, 10.7%-94.3%; PR: range, 15.5%-57.1%; CR: range, 16.4%-50.3%) (Figure 5). However, there was no statistically significant difference of rituximab-induced complement-mediated killing in the 3 response groups (means: NR, 44.8% ± 28%; PR, 35.8% ± 14%; CR, 39.6% ± 19%) (Table 4). Further statistical analysis did not show clear correlation between the expression of CD20 or individual complement inhibitors and complement-mediated killing (data not shown).
Rituximab, a chimeric mAb that targets the B-cell-specific antigen CD20, is the first therapeutic mAb available for the treatment of non-Hodgkin lymphoma (NHL). The advantages of targeting CD20 are 2-fold: (1) CD20 is a B-cell-specific antigen and is highly expressed on more than 90% of B-cell NHL; (2) on binding to mAb, CD20 does not down-modulate significantly from the cell surface, which makes it a continuous target for treatment. Although rituximab has been integrated into clinical practice in the treatment of B-cell lymphoma, the response is not uniform among different histologies or among patients with the same histologic diagnosis. The lower level of CD20 on the cell surface may explain the lower response rate in patients with chronic lymphocytic leukemia15 but not in patients with follicular lymphoma because CD20 is highly expressed in most patients. Consistent with this notion, we showed no difference in CD20 level on tumors from patients with follicular lymphoma who did or did not respond after rituximab treatment (Table 2, Figure 2A). Interestingly, the average level of CD20 in complete responders was slightly lower than in partial responders and in nonresponders. This cannot be explained by the down-modulation of surface CD20 or by a selective process after antibody treatment because all analyses were performed on pretreatment tumor cells. It is possible that there is a threshold of CD20 expression for cells to become susceptible to rituximab treatment. Given that the second lowest CD20 expression was found in one of the complete responders, we can potentially assume all but one tumor in this study exceeded that threshold. One novel idea in the design of rituximab was to replace the constant region of the original mouse antibody with the human IgG1 constant region. This chimeric human constant region is probably very important for rituximab's antitumor effect through immune-mediated cytotoxicity.16,17 One potential model of rituximab's antitumor mechanism is complement-mediated cytotoxicity. In this model, rituximab binds to cell surface CD20 and then initiates activation of complement cascade, which eventually lyses the cell.18,19 Several membrane-bound complement inhibitors were recently identified to play regulatory roles in the above-described complement-mediated cytotoxicity.20 Among these complement inhibitors, CD46, CD55, and CD59 are readily expressed in human B cells. These 3 complement inhibitors interfere with the different steps of complement activation.21-23 This is an attractive model because the heterogeneity of rituximab response in different patients may be explained by the difference in the expression status of complement inhibitors on their tumor cells. In this study, we examined the expression of complement inhibitors CD46, CD55, and CD59 on tumor cells from patients treated with rituximab. The hypothesis tested is that tumors from patients responding to treatment express less membrane-bound complement inhibitors than the ones from nonresponders. Using flow cytometry, we did not detect a significant difference in the level of any of the 3 complement inhibitors in patients with or without clinical response (Table 2). Additional analysis revealed no significant difference in the combined expression level of 2 or all 3 complement inhibitors in the 3 response groups ("Results" and Figure 4). In contrast to our expectation, tumors from patients who achieved CR expressed slightly higher levels of CD46 and CD55 than did those in the other 2 response groups. On the other hand, the complete responders had slightly lower levels of surface CD59 and fewer cells expressing CD59 (Tables 2, 3). Additional study using in vitro complement-mediated cytotoxicity assay showed a wide range of complement-mediated killing in the presence of rituximab in all 3 response groups (Table 4). However, it failed to show a relationship between susceptibility to complement-mediated killing and clinical outcome. In summary, there was no correlation between the expression of complement inhibitors on pretreatment tumors or their susceptibility to in vitro complement-mediated cytotoxicity and their clinical response to rituximab treatment. In contrast to previous studies that suggested a regulatory role of complement inhibitors in rituximab-induced cytotoxicity,11,17 our data do not show a relationship between the expression of complement inhibitors CD46, CD55, or CD59 and complement-mediated killing in follicular lymphoma cells. It is possible that other unidentified complement inhibitors or additional regulatory factors expressed by lymphoma cells are involved in this complement-mediated cytotoxicity. In addition, the expression status of these 3 complement inhibitors does not predict the clinical outcome after rituximab treatment in patients with follicular lymphoma. However, this study does not address the possibility that complement inhibitors may play a role in the development of resistance to rituximab after treatment. A recent study13 in chronic lymphocytic leukemia showed that residual tumor cells have higher levels of surface CD55 and CD59 after rituximab treatment. Further study of tumor cells after rituximab treatment should be conducted to see whether the follicular lymphoma cells resistant to treatment express higher levels of complement inhibitors or whether they are less sensitive to complement-mediated killing. Twenty patients in our study underwent chemotherapy between the time of lymph node biopsy and rituximab treatment. Although one study reports a decrease in CD59 level on adenocarcinoma cell lines after in vitro treatment with levamisole, the effect of various types of chemotherapy on expression of complement inhibitors on lymphoma cells in vivo is unknown.24 Although the susceptibility to complement-mediated cytotoxicity does
not predict clinical outcome in this study, our data do not exclude the
potential involvement of complement-mediated cytotoxicity in
rituximab's antitumor effect or a regulatory role of complement
inhibitors in the treatment of other B-cell malignancies or in
rituximab-induced normal B-cell depletion. It is conceivable that
rituximab's anti-normal B-cell effect uses a different mechanism from
its antitumor effect in patients with follicular lymphoma Another potential mechanism proposed to play a role in rituximab's antitumor effect is ADCC. In vitro studies11 support the involvement of ADCC by showing rituximab-induced lymphoma cell lines lysis in the presence of peripheral blood mononuclear effector cells. More supporting evidence is from the study12 in Fc receptor-deficient mice, in which rituximab shows significantly decreased antitumor effect. One possible explanation is that rituximab failed to recruit effector cells through Fc receptor to complete ADCC in these animals. In addition to immune-mediated mechanisms by ADCC and complement-mediated cytotoxicity, a recent study25 shows that rituximab can induce apoptosis of some lymphoma cell lines through the caspase pathway. It suggests a possible role of CD20-mediated signal transduction in rituximab's antitumor effect. Additional experiments to explore these potential mechanisms, including ADCC, apoptosis, and CD20-mediated signal transduction, should be conducted to determine their roles in rituximab's antitumor effect. This information may facilitate the development of new immunotherapy reagents.
We thank Debra Czerwinski for her technical assistance with flow cytometry analysis. We also thank Dr Robert Tibshirani for his assistance with statistical analysis.
Submitted January 24, 2001; accepted May 1, 2001.
Supported by grant CA34233 from the US Public Health Service-National Institutes of Health. W.K.W. is the recipient of a postdoctoral fellowship from the National Institutes of Health (training grant CA09287). R.L. is an American Cancer Society Clinical Research Professor.
The publication costs of this article were defrayed in part by page charge payment. Therefore, and solely to indicate this fact, this article is hereby marked "advertisement" in accordance with 18 U.S.C. section 1734.
Reprints: Ronald Levy, Division of Oncology, CCSR 1126, Stanford University School of Medicine, Stanford, CA 94305-5306; e-mail: levy{at}leland.stanford.edu.
1. Nadler LM, Korsmeyer SJ, Anderson KC, et al. B cell origin of non-T cell acute lymphoblastic leukemia. J Clin Invest. 1984;74:332-340.
2.
Anderson KC, Bates MP, Slaughenhoupt BL, et al.
Expression of human B cell-associated antigens on leukemias and lymphomas: a model of human B cell differentiation.
Blood.
1984;63:1424-1433 3. Einfeld DA, Brown JP, Valentine MA, Clark EA, Ledbetter JA. Molecular cloning of the human B cell CD20 receptor predicts a hydrophobic protein with multiple transmembrane domains. EMBO J. 1988;7:711-717[Medline] [Order article via Infotrieve]. 4. Multani PS, Grossbard ML. Monoclonal antibody-based therapies for hematologic malignancies. J Clin Oncol. 1998;16:3691-3710[Abstract].
5.
Maloney DG, Liles TM, Czerwinski DK, et al.
Phase I clinical trial using escalating single-dose infusion of chimeric anti-CD20 monoclonal antibody (IDEC-C2B8) in patients with recurrent B-cell lymphoma.
Blood.
1994;84:2457-2466 6. Maloney DG, Grillo-Lopez AJ, Bodkin DJ, et al. IDEC-C2B8: results of a phase I multiple-dose trial in patients with relapsed non-Hodgkin's lymphoma. J Clin Oncol. 1997;15:3266-3274[Abstract]. 7. McLaughlin P, Grillo-Lopez AJ, Link BK, et al. Rituximab chimeric anti-CD20 monoclonal antibody therapy for relapsed indolent lymphoma: half of patients respond to a four-dose treatment program. J Clin Oncol. 1998;16:2825-2833[Abstract].
8.
Coiffier B, Haioun C, Kerrerer N, et al.
Rituximab (anti-CD20 monoclonal antibody) for the treatment of patients with relapsed or refractor aggressive lymphoma: a multicenter phase II study.
Blood.
1998;92:1927-1932 9. Anderson DR, Grillo-Lopez A, Varns C, Chambers KS, Hanna N. Targeted anti-cancer therapy using rituximab, a chimeric anti-CD20 antibody (IDEC-C2B8) in the treatment of non-Hodgkin's B-cell lymphoma. Biochem Soc Trans. 1997;25:705-708[Medline] [Order article via Infotrieve].
10.
Golay J, Zaffaroni L, Vaccari T, et al.
Biologic response of B lymphoma cells to anti-CD20 monoclonal antibody rituximab in vitro: CD55 and CD59 regulate complement-mediated cell lysis.
Blood.
2000;95:3900-3908
11.
Reff ME, Carner K, Chambers KS, et al.
Depletion of B cells in vivo by a chimeric mouse human monoclonal antibody to CD20.
Blood.
1994;83:435-445 12. Clynes RA, Towers TL, Presta LG, Ravetch JF. Inhibitory Fc receptor modulate in vivo cytotoxicity against tumor targets. Nat Med. 2000;6:443-446[CrossRef][Medline] [Order article via Infotrieve]. 13. Bannerji R, Pearson M, Flinn IW, et al. Cell surface complement inhibitors CD55 and CD59 may mediate chronic lymphocytic leukemia (CLL) resistance to rituximab therapy [abstract]. Blood. 2000;96:164.
14.
Vuist WMJ, Levy R, Maloney DG.
Lymphoma regression induced by monoclonal anti-idiotypic antibodies correlates with their ability to induce Ig signal transduction and is not prevented by tumor expression of high levels of Bcl-2 protein.
Blood.
1994;83:899-906 15. Almasri NM, Duque RE, Iturraspe J, Everett E, Braylan RC. Reduced expression of CD20 antigen as a characteristic marker for chronic lymphocytic leukemia. Am J Hematol. 1992;40:259-263[Medline] [Order article via Infotrieve]. 16. Liu AY, Robinson RR, Murray ED Jr, Ledbetter JA, Hellstrom I, Hellstrom KE. Production of a mouse-human chimeric monoclonal antibody to CD20 with potent Fc-dependent biologic activity. J Immunol. 1987;139:3521-3526[Abstract]. 17. Harjunpaa A, Junnikkala S, Meri S. Rituximab (anti-CD20) therapy of B-cell lymphoma: direct complement killing is superior to cellular effector mechanisms. Scand J Immunol. 2000;51:634-641[CrossRef][Medline] [Order article via Infotrieve].
18.
Idusogie EE, Presta LG, Gazzano-Santoro H, et al.
Mapping of the C1q binding site on Rituxan, a chimeric antibody with a human IgG1 Fc.
J Immunol.
2000;164:4178-4184 19. Liszewski M, Farries TC, Lublin DM, Rooney IA, Atkinson JP. Control of the complement system. Adv Immunol. 1996;61:201-283[Medline] [Order article via Infotrieve]. 20. Morgan BP, Meri S. Membrane proteins that protect against complement lysis. Springer Semin Immunopathol. 1994;15:369-396[CrossRef][Medline] [Order article via Infotrieve].
21.
Seya T, Turner J, Atkinson JP.
Purification and characterization of a membrane protein (gp45-70) which is a cofactor for cleavage of C3b and C4b.
J Exp Med.
1986;163:837-855
22.
Medof ME, Walter EI, Rutgers JL, Knowles DM, Nussenzweig V.
Identification of the complement decay-accelerating factor (DAF) on epithelium and glandular cells and in body fluids.
J Exp Med.
1984;165:848-864
23.
Davies A, Simmons DL, Hale G, et al.
CD59, an Ly-6 like protein expressed in human lymphoid cells, regulates the action of the complement membrane attack complex on homologous cells.
J Exp Med.
1989;170:637-654 24. Bjorge L, Matre R. Down-regulation of CD59 (protectin) expression on human colorectal adenocarcinoma cell lines by levamisole. Scand J Immunol. 1995;42:512-516[CrossRef][Medline] [Order article via Infotrieve]. 25. Shan D, Ledbetter JA, Press OW. Signaling events involved in anti-CD20-induced apoptosis of malignant human B cells. Cancer Immunol Immunother. 2000;48:673-683[CrossRef][Medline] [Order article via Infotrieve].
© 2001 by The American Society of Hematology.
| ||||||||||
 |
|
 |
|
  V. Minard-Colin, Y. Xiu, J. C. Poe, M. Horikawa, C. M. Magro, Y. Hamaguchi, K. M. Haas, and T. F. Tedder Lymphoma depletion during CD20 immunotherapy in mice is mediated by macrophage Fc{gamma}RI, Fc{gamma}RIII, and Fc{gamma}RIV Blood, August 15, 2008; 112(4): 1205 - 1213. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 C. Meyer zum Buschenfelde, Y. Feuerstacke, K. S. Gotze, K. Scholze, and C. Peschel GM1 Expression of Non-Hodgkin's Lymphoma Determines Susceptibility to Rituximab Treatment Cancer Res., July 1, 2008; 68(13): 5414 - 5422. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
S.-Y. Wang, E. Racila, R. P. Taylor, and G. J. Weiner NK-cell activation and antibody-dependent cellular cytotoxicity induced by rituximab-coated target cells is inhibited by the C3b component of complement Blood, February 1, 2008; 111(3): 1456 - 1463. [Abstract] [Full Text] [PDF]
|
|
|
|
|
|
D. Daniel, B. Yang, D. A. Lawrence, K. Totpal, I. Balter, W. P. Lee, A. Gogineni, M. J. Cole, S. F. Yee, S. Ross, et al. Cooperation of the proapoptotic receptor agonist rhApo2L/TRAIL with the CD20 antibody rituximab against non-Hodgkin lymphoma xenografts Blood, December 1, 2007; 110(12): 4037 - 4046. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 S. E. Strome, E. A. Sausville, and D. Mann A Mechanistic Perspective of Monoclonal Antibodies in Cancer Therapy Beyond Target-Related Effects Oncologist, September 1, 2007; 12(9): 1084 - 1095. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 R. M. Sharkey and D. M. Goldenberg Targeted Therapy of Cancer: New Prospects for Antibodies and Immunoconjugates CA Cancer J Clin, July 1, 2006; 56(4): 226 - 243. [Abstract] |
Top
Abstract
Introduction
version of rituximab
was unable to deplete B cells in vivo in primates.
![(% PI<SUP>+</SUP> cells in rituximab Tx − % PI<SUP>+</SUP> cells in IgG1 Tx)/% CD20<SUP>+</SUP> cells]](/content/vol98/issue5/fulltext/1352/img002.gif)
indicates NR; 
, PR; 
, CR.
