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MAbs. 2010 Jan-Feb; 2(1): 14–19.
PMCID: PMC2828574

Evolution of anti-CD20 monoclonal antibody therapeutics in oncology

Abstract

Approval of an anti-CD20 chimeric monoclonal antibody, rituximab, has revolutionized cancer treatment and also validated CD20 targeting for providing benefit and improvement of overall response rate in B cell malignancies. Although many patients have benefited from the treatment of rituximab, there are still significant numbers of patients who are refractory or develop resistance to the treatment. Here we discuss pre-clinically well-defined potential mechanisms of action for rituximab and review the ways next generation anti-CD20 monoclonal antibodies can potentially exploit them to further enhance the treatment of B cell malignancies. Although the relative importance of each of these mechanism remains to be established in the clinic, well-designed clinical trials will help to define the efficacy and understanding of which effector activity of modified next generation anti-CD20 mAb will be important in the treatment of B-cell malignancies.

Key words: CD20, NHL, CLL, monoclonal antibody, next generation anti-CD20 antibodies, ADCC, CDC, ADCP, PCD, rituximab

Introduction

The treatment of B cell malignancies has undergone substantial change since initial marketing approval in 1997 of the chimeric anti-CD20 antibody rituximab for the treatment of both aggressive and indolent subtypes of Non-Hodgkin lymphoma (NHL).1 Rituximab is approved for use as monotherapy and in combination with chemotherapeutics. Treatment with rituximab has resulted in significant improvement in overall response rates and survival of patients with NHL.29 Despite these improvements, there are significant numbers of relapsed/refractory lymphoma patients1,10 and infusion related adverse events in the clinical setting.11

Several studies have suggested that rituximab activity is dependent on CD20 expression12 for both direct killing activity via CD20 signaling e.g., programmed cell death (PCD), sensitization of cells to chemotherapy13 and engagement of effector pathways,13 i.e., complement dependent cytotoxicity (CDC), antibody dependent cellular cytotoxicity (ADCC) and antibody dependent cellular phagocytosis (ADCP) (Fig. 1).13 Furthermore, passive immunization has been hypothesized as another potential mechanism for improving efficacy of rituximab, which supported the idea of using rituximab in a maintenance setting.14 In this study, it was shown that rituximab induced apoptosis of lymphoma cells promotes phagocytosis by dendritic cells and cross-priming of CD8 positive cytotoxic T lymphocytes. At this stage, whether this immunization effect is specific to rituximab or to chemotherapeutic regimens is still unclear in the clinical setting.

Figure 1
Mechanism of action of rituximab. rituximab can induce cell death via several mechanisms. Antigen-antibody (Ag-Ab) complexes formation and Fc-Fc gamma receptor (FcγR) complexes binding to CD20 can induce programmed cell death (PCD) by triggering ...

Programmed Cell Death Activity

Rituximab can induce PCD as a result of CD20 signaling and this activity can be augmented when rituximab is hypercrosslinked via a secondary antibody or binding via Fc gamma receptors in vitro.15 Although how this crosslinking activity is achieved in vivo still remains to be proven, primary tumors derived from rituximab treated chronic lymphocytic leukemia (CLL) patients were shown to express activated caspase-3 and caspase-9 indicating the presence of PCD activity in vivo.16 A xenograft model has also shown that increased expression of anti-apoptotic Bcl-2 family proteins can result in rituximab insensitivity.17 Whether, a similar phenomenon applies to primary tumors remains to be determined. Recently, Lim et al.13 have summarized studies where they compared the ability of rituximab to deplete human CD20 transgenic mouse B cells in vivo in the presence or absence of a second transgene encoding high levels of Bcl-2, which blocks the intrinsic apoptosis pathway.13 They report ed that B cells expressing the Bcl-2 transgene were relatively resistant to apoptotic stimuli in vitro whereas in vivo they were just as susceptible to rituximab activity as B-cells lacking the transgene.13 The conclusion from these studies was that in a fully syngeneic system, induction of the intrinsic apoptosis pathway is not important for subsequent B cell depletion.13 While all these studies suggest that rituximab is involved in promoting cell death, whether this mechanism is critical for the depletion of CD20 positive target cells in vivo remains to be determined.

Fc-Fc Gamma Receptor Interaction Dependent Activity

Fc binding to Fc gamma receptors expressed on monocytes, macrophages, natural killer (NK) cells and neutrophils can lead not only to ADCC and ADCP activities but also direct killing via CD20 signaling due to hypercrosslinking.1518 The early preclinical evidence for the involvement Fc-Fc gamma receptor interaction came from an in vivo study with the xenograft model, showing that rituximab activity is dependent on the gamma chain associated activating Fc receptors.19 Additional supporting evidence comes from a clinical study showing a better response with rituximab in NHL patients with higher affinity allelic variants of Fc gamma IIIa receptor.2023 However, this correlation has not been observed in CLL patients,24 and it is hypothesized that this might be due in part to lower level of CD20 expression and the presence of higher levels of soluble CD20 in plasma.12 It also has been noted that in mice monocytes/macrophages are the main effector cells that contributes to the activity of rituximab compared to the NK cells and neutrophils in humans.2527 Moreover, maximal monoclonal antibody (mAb) response activity has been shown to be dependent on intact compartments of the reticulo-endothelial system, as shown in experiments that surgical limitation of the hepatic blood supply correlated with lower B cell depletion.2527 It has also been demonstrated that mouse Fc gamma receptor IV, a homolog of human Fc gamma receptor IIIa, is strongly involved in the effects of human IgG1.28 It is expressed on murine monocytes and macrophages, but not on murine NK cells, whereas human Fc gamma receptor IIIa is expressed on human NK cells, neutrophils and monocyte/macrophages.28 Due to differences of Fc gamma receptor expression profiles in human and mouse NK cells, the impact of NK cell activity in vivo preclinical models might not be relevant in, and translate to, clinical settings. Although human NK cells are shown to be mediating ADCC activity in vitro,29 questions remain as to whether NK cells are the key cells in mediating rituximab activity or whether, ADCC is the dominant mechanism in tissues.

Complement Dependent Cytotoxicity Activity

Although Fc-Fc gamma receptor interaction is widely accepted to be critical for the activity of rituximab in vivo, CDC activities are still being debated.18,28 Supporting evidence for the role of CDC comes from studies where rituximab was shown to be capable of C1q binding and inducing CDC against malignant B cells in vitro.3032 Moreover, when rituximab activity was tested in complement deficient or cobra venom inactivated complement studies rituximab was shown to exhibit reduced activity in vivo.33,34 Additional evidence comes from studies in patients showing that soon after rituximab infusion, complements were being consumed in vivo, and that addition of complement ex vivo was capable of restoring the activity of rituximab in CDC assays.35,36 Although earlier studies show the critical role of CDC activity of rituximab, it should be noted that this preclinical activity of rituximab was not sufficient to deplete B cells in vivo nor it did correlate with the expression of complement inhibitory receptors.25,37,38 Yet it has also been shown that deposition of C3b not only facilitated the removal of rituximab:CD20 complexes from the B lymphoma cells by Fc gamma receptor expressing macrophages through the process of trogocytosis, but it also blocked the interaction between the Fc domain of rituximab and Fc gamma receptor IIIA on NK cells thereby decreasing ADCC activity.35,3941 Human genetic polymorphism correlation provides an additional line of evidence suggesting the involvement of complement in the mechanism of action of rituximab. A study investigating the impact of C1qA polymorphisms on the efficacy of rituximab demonstrated that follicular lymphoma patients with a low C1q expressing A allele correlated with enhanced rituximab responses compared to those patients with the high C1q expressing G allele.42 All these studies indicate that CDC plays a role in rituximab activity, but whether this activity is critical and has a positive or negative impact remains unresolved.

Next Generation Anti-CD20 Monoclonal Antibodies

While successes, limitations and elucidation of the mechanism of action of rituximab have increased our understanding and helped advance the engineering of next generation anti-CD20 mAbs with the goal of improving the efficacy and decreasing associated adverse events, one still needs to better understand the potential interplay between the multiple proposed mechanisms of action-binding kinetics to different epitopes, PCD, CDC, ADCC and ADCP (Table 1). Depending on the proposed modification, next generation antibodies may be grouped in one of two categories: second or third generation anti-CD20 mAb.

Table 1
Development status and mechanism of action of monoclonal antibodies targeting CD20 that are approved or in clinical development

Second generation antibodies can be tailored to be humanized or fully human with unmodified Fc domain, with the aim of reducing immunogenicity. Likewise, third generation antibodies can be modified to include engineered Fc domains with the aim of improving the therapeutic activity in all patients, particularly in genetically defined subpopulations that express a low affinity version of the Fc receptor on their immune effector cells. Second generation antibodies include ofatumumab, ocrelizumab and veltuzumab. Compared to the other CD20 mAbs, fully human IgG1 ofatumumab is at the most advanced stage: it is approved in the US and undergoing regulatory review in the EU for the treatment of CLL.4345 Ofatumumab binds a different CD20 epitope compared to rituximab and has a slower off rate such that over 3 hours the disassociation for ofatumumab is only 20–30%, but 70–80% for rituximab.46,47 Moreover, ofatumumab exhibits not only ~10 fold higher CDC activity in rituximab sensitive tumor cell lines but also exhibits CDC activity in rituximab resistant cell lines.43,48 ADCC activities of ofatumumab have been shown to be similar to rituximab although it is a weaker PCD inducer than rituximab.43,48 Ocrelizumab is currently being developed for non-oncology indications, and has been shown to bind to the same CD20 epitope as rituximab,47,49 but the molecule has relatively higher ADCC and low CDC activities compared to rituximab.50,51 Veltuzumab is a humanized IgG1 and has similar mechanisms as rituximab, with the exception of a 2.5 fold slower off rate and higher CDC activity (mean EC50 of <100 ng/ml) compared to rituximab (EC50 of ~150 ng/ml).52,53 Phase 1/2 studies with recurrent B cell lymphomas have shown a 53% overall response rate, including 6 patients with complete response at a median follow up of 12 weeks.54 Phase 2 clinical trials using the new subcutaneous formulation of veltuzumab for NHL, CLL and ITP patients are on going.55 Clinical trials testing veltuzumab and ofatumumab may provide further insights into the importance of different epitope on PCD activity in the clinical context.

Third generation anti-CD20 mAbs in early phases of clinical development include AME133v, Pro13192 (v114), GA101 and R603/EMAB-6. TRU-015, is another third generation anti-CD20 molecule that is a small modular immunopharmaceutical drug composed of human IgG1 Fc and CH2 and CH3 hinge regions linked directly to an anti-CD20 scFv.5658 It is slightly smaller than an IgG and has high ADCC and low complement activating ability. It is currently in Phase 2 clinical development for RA.5962 AME-133v, an Fc protein engineered antibody, is currently being evaluated in a Phase 1/2 dose escalation study using weekly intravenous doses for four consecutive weeks in patients with relapsed/refractory follicular B cell NHL. In vitro models have shown that the Fc domain of AME-133v binds to the low-affinity variant of Fc gamma RIIIa (FF or FV) with a higher affinity (mean EC50 <10 ng/ml) thereby improving killing of B cells ~10 fold over rituximab.63,64 The improvement in efficacy of AME-133v that has been seen in preclinical settings has yet to be demonstrated in a clinical setting. Although the current clinical trial with AME-133v started in July of 2006 and had an estimated primary completion date of December 2008, clinical data remain unavailable as of October 2009.

Pro131921 (v114), is another Fc protein engineered antibody and displays 30-fold greater binding to the low-affinity variant of Fc gamma RIIIa (FF or FV) than rituximab.65 In vitro, this binding affinity exhibits improved ADCC activity up to 10 fold more than rituximab. Preclinical studies in non-human primates showed that treatment with Pro13192 (v114) resulted in a dose-dependent reversible neutropenia and thrombocytopenia.65 Phase 1/2 clinical studies to assess safety of escalating doses of Pro13192 (v114) in patients with NHL and CLL were recently terminated.

GA101 is a third-generation anti-CD20 mAb with a glyco-engineered Fc portion which exhibits improved binding affinity to FcgammaRIII by 50-fold, that results in a 10- to 100-fold increase in ADCC against CD20 positive NHL cell lines.6670 On the other hand, CDC activity of GA101 is much lower than rituximab in vitro.6670 Moreover, GA101 depleted normal B cells as well as B cell lymphoma, significantly more than other CD20 directed antibodies, including rituximab Fc variants with improved ADCC activity.69,70 In vivo xenograft experiments in which cobra venom factor was used to inhibit complement activity demonstrated that GA101 may be efficacious in that setting.71 Structurally, GA101 contains a modified Fc domain hinge region that results in stronger induction of apoptosis of several NHL cell lines and primary malignant B cells.66 These modifications may provide GA101 with an increased therapeutic efficacy, leading to complete responses and long-term survival in xenograft models of diffuse large B cell lymphoma and mantle cell lymphoma (MCL).7174 In cynomolgus monkeys, GA101 compared to rituximab induced complete, rapid and long-lasting B cell depletion not only in peripheral blood but also in spleen and lymph nodes.74,75 It is still unknown whether this superior activity comes from PCD or decreased CDC activity compared to rituximab.

LFB-R603/EMAB-6 is a chimeric third generation IgG1 and is produced in rat cell line YB2/0 using EMABLING technology thus resulting in naturally low fucose content in its Fc region.76 Compared to rituximab, LFB-R603/EMAB-6 has similar CDC and PCD activities whereas FcγRIIIA binding and FcγRIIIA-dependent effector functions are higher and results in producing an ADCC plateau around 35% at 50 ng/ml, while rituximab induced less than 5% ADCC at the same concentration.76 Furthermore, LFB-R603/EMAB-6 induces higher ADCC activity against CLL cells than rituximab even when target cells express fewer CD20 molecules.76 Although the improvement in efficacy of LFB-R603/EMAB-6 that has been seen in preclinical settings, the clinical activity is yet to be demonstrated in the future.

Perspective

In the face of the excitement and perhaps uncertainty generated by the next generation of anti-CD20 mAbs, their potential success in the treatment of B cell malignancies will depend on their clinically demonstrated safety and efficacy profiles. There is the potential to achieve far better therapeutic efficacy than rituximab, and, significantly, demonstrate efficacy in rituximab-resistant populations. Additionally, all third generation antibodies appear to be Fc engineered (protein or glyco-engineering) with the hopes of improving the affinity of Fc-Fc gamma receptor interaction, thereby improving the ADCC activity. Although improvement of these interactions has increased ADCC activity in vitro, the significance of this mechanism is yet to be determined in the clinic. Furthermore, one should note that modulating Fc interactions can also affect other mechanisms of cell cytotoxicity such as ADCP activity and CD20 mediated apoptosis due to hypercrosslinking via Fc gamma receptor.

Although the mechanisms of action of each CD20 mAb are well-studied in preclinical settings, the variability seen in clinical response to rituximab may also depend on level of CD20 expression, levels of circulating soluble CD20, presence and abundance of effector cells, CD20 binding epitope and kinetics, tissue distribution and tumor burden. The predictive value of preclinical models in terms of quantification of the dose-concentration-effect relationship of rituximab using pharmacokinetic-pharmacodynamic analysis, identification of the individual factors influencing the response, relative importance of each of these mechanisms of action and resistance remains to be better understood and proven in the clinic. Well-designed clinical trials will help define and refine efficacy and provide increased understanding of which activity of modified next generation anti-CD20 mAb will prevail. It is interesting to note that rituximab in combination with methotrexate is also approved for treatment of adult RA patients who have had inadequate response to TNF antagonist therapies, and the product is also currently being studied in additional indications. Evaluations of modified next generation anti-CD20 mAb as treatments for non-oncology indications can potentially add to our understanding of the critical activities required for efficacy.

Acknowledgements

We would like to thank Michele Mccolgan and Greg Roland for their help with the figure and the table, respectively.

Footnotes

References

1. McLaughlin P, Grillo-Lopez AJ, Link BK, Levy R, Czuczman MS, Williams ME, 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. [PubMed]
2. Forstpointner R, Unterhalt M, Dreyling M, Bock HP, Repp R, Wandt H, et al. Maintenance therapy with rituximab leads to a significant prolongation of response duration after salvage therapy with a combination of rituximab, fludarabine, cyclophosphamide and mitoxantrone (R-FCM) in patients with recurring and refractory follicular and mantle cell lymphomas: results of a prospective randomized study of the German Low Grade Lymphoma Study Group (GLSG) Blood. 2006;108:4003–4008. [PubMed]
3. Ghielmini M, Schmitz SFH, Cogliatti SB, Pichert G, Hummerjohann J, Waltzer U, et al. Prolonged treatment with rituximab in patients with follicular lymphoma significantly increases event-free survival and response duration compared with the standard weekly X 4 schedule. Blood. 2004;103:4416–4423. [PubMed]
4. Gordan LN, Grow WB, Pusateri A, Douglas V, Mendenhall NP, Lynch JW. Phase II trial of individualized rituximab dosing for patients with CD20-positive lymphoproliferative disorders. J Clin Oncol. 2005;23:1096–1102. [PubMed]
5. Habermann TM, Weller EA, Morrison VA, Gascoyne RD, Cassileth PA, Cohn JB, et al. Rituximab-CHOP versus CHOP alone or with maintenance rituximab in older patients with diffuse large B-cell lymphoma. J Clin Oncol. 2006;24:3121–3127. [PubMed]
6. Hagenbeek A, Van Glabbeke M, Teodorovic I. The role of rituximab maintenance treatment in relapsed folicular NHL an interim analysis of the EORTC randomized intergroup trial. Ann Oncol. 2005;16:61.
7. Hainsworth JD, Litchy S, Burris HA, Scullin DC, Corso SW, Yardley DA, et al. Rituximab as first-line and maintenance therapy for patients with indolent non-Hodgkin’s lymphoma. J Clin Oncol. 2002;20:4261–4267. [PubMed]
8. Hochster HS, Weller EA, Gascoyne RD, Ryan TS, Habermann TM, Gordon LI, et al. Rituximab after CVP results in superior clinical outcome in advanced folicular lymphoma (FL): results of the E1496 Phase III Trial from the eastern Cooperative Oncology Group and Cancer Leukemia Group B. Blood. 2005;106:349.
9. van Oers MHJ, Klasa R, Marcus RE, Wolf M, Kimby E, Gascoyne RD, et al. Rituximab maintenance improves clinical outcome of relapsed/resistant follicular non-Hodgkin lymphoma in patients both with and without rituximab during induction: results of a prospective randomized phase 3 intergroup trial. Blood. 2006;108:3295–3301. [PubMed]
10. Davis TA, Grillo-Lopez AJ, White CA, McLaughlin P, Czuczman MS, Link BK, et al. Rituximab anti-CD20 monoclonal antibody therapy in non-Hodgkin’s lymphoma: Safety and efficacy of re-treatment. J Clin Oncol. 2000;18:3135–3143. [PubMed]
11. Genentech Inc., and Biogen Idec. Rituxan, authors. Prescribing information. 2008.
12. Manshouri T, Do KA, Wang XM, Giles FJ, O’Brien SM, Saffer H, et al. Circulating CD20 is detectable in the plasma of patients with chronic lymphocytic leukemia and is of prognostic significance. Blood. 2003;101:2507–2513. [PubMed]
13. Lim SH, Beers SA, French RR, Johnson PW, Glennie MJ, Cragg MS. Anti-CD20 monoclonal antibodies-historical and future perspectives. Haematologica. 2009 [PubMed]
14. Selenko N, Majdic O, Draxler S, Berer A, Jager U, Knapp W, et al. CD20 antibody (C2B8)-induced apoptosis of lymphoma cells promotes phagocytosis by dendritic cells and cross-priming of CD8(+) cytotoxic T cells. Leukemia. 2001;15:1619–1626. [PubMed]
15. Shan D, Ledbetter JA, Press OW. Apoptosis of malignant human B cells by ligation of CD20 with monoclonal antibodies. Blood. 1998;91:1644–1652. [PubMed]
16. Byrd JC, Kitada S, Flinn IW, Aron JL, Pearson M, Lucas N, et al. The mechanism of tumor cell clearance by rituximab in vivo in patients with B-cell chronic lymphocytic leukemia: evidence of caspase activation and apoptosis induction. Blood. 2002;99:1038–1043. [PubMed]
17. Stolz C, Hess G, Hahnel PS, Grabellus F, Hoffarth S, Schmid KW, et al. Targeting Bcl-2 family proteins modulates the sensitivity of B-cell lymphoma to rituximab-induced apoptosis. Blood. 2008;112:3312–3321. [PubMed]
18. Glennie MJ, French RR, Cragg MS, Taylor RP. Mechanisms of killing by anti-CD20 monoclonal antibodies. Mol Immunol. 2007;44:3823–3837. [PubMed]
19. Clynes RA, Towers TL, Presta LG, Ravetch JV. Inhibitory Fc receptors modulate in vivo cytoxicity against tumor targets. Nat Med. 2000;6:443–446. [PubMed]
20. Cartron G, Dacheux L, Salles G, Solal-Celigny P, Bardos P, Colombat P, et al. Therapeutic activity of humanized anti-CD20 monoclonal antibody and polymorphism in IgG Fc receptor Fc gamma RIIIa gene. Blood. 2002;99:754–758. [PubMed]
21. Treon SP, Fox EA, Hansen M, Verselis S, Branagan A, Touroutoglou N, et al. Polymorphisms in Fc gamma RIIIa (CD16) receptor expression are associated with clinical response to rituximab in Waldenstrom’s macro-globulinemia. Blood. 2002;100:573.
22. Weng WK, Levy R. Two immunoglobulin G fragment C receptor polymorphisms independently predict response to rituximab in patients with follicular lymphoma. J Clinl Oncol. 2003;21:3940–3947. [PubMed]
23. Lejeune J, Thibault G, Ternant D, Cartron G, Watier H, Ohresser M. Evidence for Linkage Disequilibrium Between Fc gamma RIIIa-V158F and Fc gamma RIIa-H131R Polymorphisms in White Patients, and for an Fc gamma RIIIa-Restricted Influence on the Response to Therapeutic Antibodies. J Clin Oncol. 2008;26:5489–5491. [PubMed]
24. Farag SS, Flinn IW, Modali R, Lehman TA, Young D, Byrd JC. Fc gamma RIIIa and Fc-gamma RIIa polymorphisms do not predict response to rituximab in B-cell chronic lymphocytic leukemia. Blood. 2004;103:1472–1474. [PubMed]
25. Gong Q, Ou QL, Ye SM, Lee WP, Cornelius J, Diehl L, et al. Importance of cellular microenvironment and circulatory dynamics in B cell immunotherapy. J Immunol. 2005;174:817–826. [PubMed]
26. Uchida JJ, Hamaguchi Y, Oliver JA, Ravetch JV, Poe JC, Haas KM, et al. The innate mononuclear phagocyte network depletes B lymphocytes through Fc receptor-dependent mechanisms during anti-CD20 antibody immunotherapy. J Exp Med. 2004;199:1659–1669. [PMC free article] [PubMed]
27. Minard-Colin V, Xiu Y, Poe JC, Horikawa M, Magro CM, Hamaguchi Y, et al. Lymphoma depletion during CD20 immunotherapy in mice is mediated by macrophage Fc gamma RI, Fc gamma RIII and Fc gamma RIV. Blood. 2008;112:1205–1213. [PubMed]
28. Nimmerjahn F, Ravetch JV. Antibodies, Fc receptors and cancer. Curr Opin in Immunol. 2007;19:239–245. [PubMed]
29. Flieger D, Renoth S, Beier I, Sauerbruch T, Schmidt-Wolf I. Mechanism of cytotoxicity induced by chimeric mouse human monoclonal antibody IDEC-C2B8 in CD20-expressing lymphoma cell lines. Cell Immunol. 2000;204:55–63. [PubMed]
30. Cragg MS, Morgan SM, Chan HTC, Morgan BP, Filatov AV, Johnson PWM, et al. Complement-mediated lysis by anti-CD20 mAb correlates with segregation into lipid rafts. Blood. 2003;101:1045–1052. [PubMed]
31. Golay J, Zaffaroni L, Vaccari T, Borleri GM, Tedesco F, Dastoli G, et al. Biological response of B lymphoma cell lines to anti-CD20 monoclonal antibody rituximab in vitro: CD55 and CD59 regulate complement mediated lysis. Blood. 1999;94:92. [PubMed]
32. Reff ME, Carner K, Chambers KS, Chinn PC, Leonard JE, Raab R, et al. Depletion of B-Cells In-Vivo by A Chimeric Mouse-Human Monoclonal-Antibody to CD20. Blood. 1994;83:435–445. [PubMed]
33. Cragg MS, Glennie MJ. Antibody specificity controls in vivo effector mechanisms of anti-CD20 reagents. Blood. 2004;103:2738–2743. [PubMed]
34. Golay J, Cittera E, Di Gaetano N, Manganini M, Mosca M, Nebuloni M, et al. The role of complement in the therapeutic activity of rituximab in a murine B lymphoma model homing in lymph nodes. Haematol-the Hematol J. 2006;91:176–183. [PubMed]
35. Kennedy AD, Beum PV, Solga MD, DiLillo DJ, Lindorfer MA, Hess CE, et al. Rituximab infusion promotes rapid complement depletion and acute CD20 loss in chronic lymphocytic leukemia. J Immunol. 2004;172:3280–3288. [PubMed]
36. Klepfish A, Schattner A, Ghoti H, Rachmilewitz EA. Addition of fresh frozen plasma as a source of complement to rituximab in advanced chronic lymphocytic leukaemia. Lancet Oncol. 2007;8:361–362. [PubMed]
37. Beers SA, Chan CHT, James S, French RR, Attfield KE, Brennan CM, et al. Type II (tositumomab) anti-CD20 monoclonal antibody out performs type I (rituximab-like) reagents in B-cell depletion regardless of complement activation. Blood. 2008;112:4170–4177. [PubMed]
38. Weng WK, Levy R. Expression of complement inhibitors CD46, CD55 and CD59 on tumor cells does not predict clinical outcome after rituximab treatment in follicular non-Hodgkin lymphoma. Blood. 2001;98:1352–1357. [PubMed]
39. Beum PV, Kennedy AD, Williams ME, Lindorfer MA, Taylor RP. The shaving reaction: Rituximab/CD20 complexes are removed from mantle cell lymphoma and chronic lymphocytic leukemia cells by THP-1 monocytes. J Immunol. 2006;176:2600–2609. [PubMed]
40. Li YL, Williams ME, Cousar JB, Pawluczkowycz AW, Lindorfer MA, Taylor RP. Rituximab-CD20 complexes are shaved from Z138 mantle cell lymphoma cells in intravenous and subcutaneous SCID mouse models. J Immunol. 2007;179:4263–4271. [PubMed]
41. Williams ME, Densmore JJ, Pawluczkowycz AW, Beum PV, Kennedy AD, Lindorfer MA, et al. Thrice-weekly low-dose rituximab decreases CD20 loss via shaving and promotes enhanced targeting in chronic lymphocytic leukemia. J Immunol. 2006;177:7435–7443. [PubMed]
42. Racila E, Link BK, Weng WK, Witzig TE, Ansell S, Maurer MJ, et al. A Polymorphism in the Complement Component C1qA Correlates with Prolonged Response Following Rituximab Therapy of Follicular Lymphoma. Clin Can Res. 2008;14:6697–6703. [PMC free article] [PubMed]
43. Teeling JL, French RR, Cragg MS, van den Brakel J, Pluyter M, Huang H, et al. Characterization of new human CD20 monoclonal antibodies with potent cytolytic activity against non-Hodgkin lymphomas. Blood. 2004;104:1793–1800. [PubMed]
44. Hagenbeek A, Plesner T, Johnson P, Pedersen L, Walewski J, Hellmann A, et al. HuMax-CD20, a novel fully human anti-CD20 monoclonal antibody: Results of a phase I/II trial in relapsed or refractory follicular non-Hodgkins’s lymphoma. Blood. 2005;106:270.
45. Coiffier B, Tilly H, Pederson LM, Plesner T, Frederiksen H, van Oears MHJ, et al. HuMax-CD20, a novel human monoclonal antibody in chronic lymphocytic leukemia:early results from an ongoingPhase I/II clinical trial. Blood. 2005;106:448.
46. Du JM, Yang H, Guo YJ, Ding JP. Structure of the Fab fragment of therapeutic antibody Ofatumumab provides insights into the recognition mechanism with CD20. Mol Immunol. 2009;46:2419–2423. [PubMed]
47. Du JM, Wang H, Zhong C, Peng BZ, Zhang ML, Li BH, et al. Structural basis for recognition of CD20 by therapeutic antibody rituximab. J Biol Chem. 2007;282:15073–15080. [PubMed]
48. Taylor RP, Pawhiczkowycz AW, Lindorfer MA, de Winkel JGJV, Beurskens FJ, Parren PWHI. Binding of Submaximal C1q to B Cells Opsonized with Anti-CD20 Mabs Ofatumumab (OFA) or Rituximab (RTX) Promotes Complement Dependent Cytotoxicity (CDC), and Considerably Higher Levels of CDC Are Induced by OFA Than by RTX. Blood. 2008;112:560. [PubMed]
49. Du JM, Wang H, Zhong C, Peng BZ, Zhang ML, Li BH, et al. Crystal structure of chimeric antibody C2H7 Fab in complex with a CD20 peptide. Mol Immunol. 2008;45:2861–2868. [PubMed]
50. Genovese MC, Kaine JL, Lowenstein MB, Del Giudice J, Baldassare A, Schechtman J, et al. Ocrelizumab, a humanized anti-CD20 monoclonal antibody, in the treatment of patients with rheumatoid arthritis-A phase I/II randomized, blinded, placebo-controlled, dose-ranging study. Arthritis Rheum. 2008;58:2652–2661. [PubMed]
51. Hutas G. Ocrelizumab, a humanized monoclonal antibody against CD20 for inflammatory disorders and B-cell malignancies. Curr Opin Investig Dr. 2008;9:1206–1215. [PubMed]
52. Goldenberg DM, Chang C, Rossi EA, Cardillo TM, Wegener WA, Teoh N, et al. Activity of veltuzumab, a second-generation humanized anti-CD20 mAb, in laboratory and clinical studies. Ann Oncol. 2008;19:130.
53. Goldenberg DM, Rossi EA, Stein R, Cardillo TM, Czuczman MS, Hernandez-Ilizaliturri FJ, et al. Properties and structure-function relationships of veltuzumab (hA20), a humanized anti-CD20 monoclonal antibody. Blood. 2009;113:1062–1070. [PubMed]
54. Morschhauser F, Leonard JP, Fayad L, Coiffier B, Petillon MO, Coleman M, et al. Humanized Anti-CD20 Antibody, Veltuzumab, in Refractory/Recurrent Non-Hodgkin’s Lymphoma: Phase I/II Results. J Clin Oncol. 2009;27:3346–3353. [PubMed]
55. Milani C, Castillo J. Veltuzumab, an anti-CD20 mAb for the treatment of non-Hodgkin’s lymphoma, chronic lymphocytic leukemia and immune thrombocytopenic purpura. Curr Opin Mol Ther. 2009;11:200–207. [PubMed]
56. Barone D, Burge DJ, Baum P, Ledbetter J, Hayden-Ledbetter M, Mohler K. Prolonged depletion of circulating B cells in cynomolgus monkeys after a single dose of TRU-015, a novel CD20 directed therapeutic. Ann Rheum Dis. 2005;64:159–160. [PubMed]
57. Barone D, Nilsson C, Ledbetter J, Hayden-Ledbetter M, Mohler K. TRU-015, a novel CD20-directed biologic therapy, demonstrates significant anti-tumor activity in human tumor xenograft models. J Clin Oncol. 2005;23:178.
58. Hayden-Ledbetter MS, Cerveny CG, Espling E, Brady WA, Grosmaire LS, Tan P, et al. CD20-Directed Small Modular Immunopharmaceutical, TRU-015, Depletes Normal and Malignant B Cells. Clin Can Res. 2009;15:2739–2746. [PubMed]
59. Burge DJ, Bookbinder SA, Kivitz AJ, Fleischmann RM, Shu C, Bannink J, et al. Phase 1 study of TRU-015, a CD20-directed small modular immunopharmaceutical (SMIP (TM)) protein therapeutic, in subjects with rheumatoid arthritis. Arthritis Res Ther. 2007;9 [PubMed]
60. Burge DJ, Shu C, Martin RW, Littlejohn TW, Wallace DJ, Taborn J, et al. TRU-015, a small modular immunopharmaceutical (SMIP (TM)) drug candidate directed against CD20, demonstrates clinical improvement in subjects with rheumatoid arthritis. Arthritis Res Ther. 2007;9
61. Burge D, Chopiak V, Dvoretskiy L, Koshukova G, Nasonov E, Povoroznyuk V, et al. TRU-015 improves rheumatoid arthritis disease activity in a randomized, double-blind, placebo-controlled, multi-center phase 2 dose ranging trial. Arthritis Rheum. 2007;56:4234–4235.
62. Burge DJ, Bookbinder SA, Kivitz AJ, Fleischmann RM, Shu C, Bannink J, et al. Phase 1 study of TRU-015, a CD20 directed small modular immunopharmaceutical (SMIP TM) protein therapeutic, in subjects with rheumatoid arthritis. Ann Rheum Dis. 2006;65:180.
63. Bowles JA, Wang SY, Link BK, Allan B, Beuerlein G, Campbell MA, et al. Anti-CD20 monoclonal antibody with enhanced affinity for CD16 activates NK cells at lower concentrations and more effectively than rituximab. Blood. 2006;108:2648–2654. [PubMed]
64. Weiner GJ, Bowles JA, Link BK, Allan B, Beuerlein G, Campbell MA, et al. An anti-CD20 monoclonal antribody (mAb) with enhanced affinity for CD16 activates NK cells at a lower concentrations and more effectively than rituximab. Blood. 2005;106:348. [PubMed]
65. Bello C, Sotomayor EM. Monoclonal antibodies for B-cell lymphomas: rituximab and beyond. Hematology Am Soc Hematol Educ Program. 2007;233-242 [PubMed]
66. Umana P, Moessner E, Bruenker P, Unsin G, Purntener U, Suter T, et al. Novel 3rd generation humanized type II CD20 antibody with glycoengineered Fc and modified elbow hinge for enhanced ADCC and superior apoptosis induction. Blood. 2006;108:229.
67. Umana P, Moessner E, Bruenker P, Unsin G, Puentener U, Grau R, et al. GA101: A humanized third generation type II CD20 antibody with superior cell death induction and glycoengineered Fc region for enhanced ADCC. American Association of Cancer Research Meeting. 2007;48:4186.
68. Umana P, Moessner E, Bruenker P, Unsin G, Suter T, Grau R, et al. Novel third generation humanized type II CD20 antibody with superior direct cell death induction and glycoengineered Fc region for enhanced ADCC induction. AACR-NCI-EORTC International Congress. 2007;19:56.
69. Umana P, Ekkehard M, Peter B, Gabriele K, Puentener U, Suter T, et al. GA101, a novel humanized type II CD20 antibody with glycoengineered Fc and enhanced cell death induction, exhibits superior anti-tumor efficacy and superior tissue B cell depletion in vivo. Blood. 2007;110:2348.
70. Robak T. GA-101, a third-generation, humanized and glyco-engineered anti-CD20 mAb for the treatment of B-cell lymphoid malignancies. Curr Opin Investig Drugs. 2009;10:588–596. [PubMed]
71. Dalle S, Reslan L, Manquat SB, Herting F, Klein C, Umana P, et al. Compared antitumor activity of GA101 and rituximab against human RL folicular lymphoma xenografts in SCID beige mice. Blood. 2008;112:1585.
72. Friess T, Herting F, Bauer S, Nopora A, van Puijenbroek E, Gerdes C, et al. GA101, a novel therapeutic type II CD20 antibody with outstanding efficacy and clear superiority in subcutaneous non Hodgkin lymphoma xenograft models. American Association of Cancer Research Meeting. 2008;99:3982.
73. Nopora A, Preiss S, Nicolini V, Rommele M, van Puijenbroek E, Freyetg O, et al. Contribution of enhanced ADCC to superior in vivo efficacy of a novel type II humanized, third generation CD20 antibody (GA101) in NHL xenograft models. American Association of Cancer Research Meeting. 2008;99:3991.
74. Klein C, Herting F, Friess T, Gerdes C, Nopora A, Bauer S, et al. GA101, a therapeutic glycoengineered CD20 antibody recognizing a type II epitope mediates outstanding anti-tumor efficacy in non-Hodgkin’s lymphoma xenograft models and superior B cell depletion. P EJS SUPPL. 2008;6:504.
75. Umana P, Moessner E, Grau R, Gerdes C, Nopora A, Schmidt C, et al. GA101, a novel human therapeutic type II CD20 antibody with outstanding anti tumor efficacy in non Hodgkins lymphoma xenograft models and superior B cell depletion. Ann Oncol. 2008:19.
76. de Romeuf C, Dutertre CA, Graff-Tavernier M, Fournier N, Gaucher C, Glacet A, et al. Chronic lymphocytic leukaemia cells are efficiently killed by an anti-CD20 monoclonal antibody selected for improved engagement of Fc gamma RIIIA/CD16. Br J Haematol. 2008;140:635–643. [PubMed]

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