**2.2.1 Ofatumumab**

258 Autoimmune Disorders – Current Concepts and Advances from Bedside to Mechanistic Insights

Rituximab is also an active treatment agent in patients with lupus nephritis and central nervous system (CNS) involvement. Sfikakis et al. reported clinical response in 80% and sustained complete response in 40% of patients with class III and IV nephritis treated with rituximab and moderate doses of corticosteroids (Sfikakis, Boletis et al. 2005). In the study of Ng et al. 21 patients with renal involvement were treated with rituximab and cyclophosphamide (Ng, Cambridge et al. 2007). They had a decrease in median urinary protein creatinine ratio (PCR) from 446 to 190 mg/mmol 6 months. More recently, Pepper et al. treated 18 patients with class III/IV/V lupus nephritis with rituximab. All patients were on steroids prior to the development of lupus nephritis (Pepper, Griffith et al. 2009). The patients received mycophenolate mofetil maintenance therapy. Fourteen of 18 patients achieved complete or partial remission with a sustained response of 67% at 1 year. In addition, serum albumin increased from a mean of 29 g/L at presentation to 34 g/L at 1 year (P = 0.001). Importantly, following treatment with rituximab, 6 patients stopped prednisolone, 6 patients reduced their maintenance dose and 6 patients remained on the

The study performed by Tokunaga et al. showed marked improvement following rituximab therapy in patients with neuropsychiatric SLE (Tokunaga, Saito et al. 2007). A monoclonal antibody was administered at doses of 375 mg/m2 once weekly for four weeks or 1000 mg once weekly for two weeks in 10 patients with refractory neuropsychiatric SLE. Treatment resulted in rapid improvement of CNS–related manifestations, particularly acute confusional state. Rituximab also improved cognitive dysfunction psychosis and seizure and reduced the SLEDAI on day 28 in all 10 patients. These effects lasted for more than a year in 5 patients. In another study, Smith et al. (Smith, Jones et al. 2006) evaluated prospectively the effects of rituximab treatment for refractory SLE and vasculitis. Patients received four weekly infusions of rituximab at a dose of 375 mg/m2. Intravenous cyclophosphamide (500 mg) was administered along with the first infusion in an effort to achieve early disease control. Remission followeing rapid B cell depletion was achieved in all 11 patients including 6 complete responses and 5 partial responses. Moreover, a renal response occurred in all 6 patients with lupus nephritis. Clinical improvement was accompanied by a significant reduction in the daily dose of prednisone. Seven of 11 patients experienced a relapse, a median of 12 months after treatment. After relapse, six patients with SLE were retreated with rituximab and all achieved remission and did so more quickly than after the

Rituximab is generally well tolerated. Even fewer adverse events have been observed in patients treated for SLE than in the lymphoma patients (Tokunaga, Saito et al. 2007). The most common adverse events during or following rituximab therapy are infusion related symptoms, typically fever, chills, rigors and hypotension. In patients who receive premedication consisting of antipyretic and antihistaminic drugs together with corticosteroids, infusion-related side effects are usually only mild or moderate and do not require discontinuation of rituximab administration. Occasionally, serious infections were also reported. However, these may have been related to the underlying disease and/or concomitant therapy with other immunosuppressive agents. In 2006, an FDA alert was reported after two SLE patients treated with rituximab had died from progressive multifocal leukoencephalopathy (PML) (Ermann and Bermas 2007). However, both patients had received additional treatment with cyclophosphamide. At present, it is difficult to estimate the risk of this complication in SLE patients treated with rituximab. In recent analysis, among the rheumatic diseases, 43 cases of PML (0.44%) were associated with SLE, 24 (0.25%)

same dose (maximum 10 mg). No severe infections were observed.

primary treatment.

Ofatumumab (HuMax-CD20; Arzerra™, GlaxoSmithKline plc/Genmab A/S) is a secondgeneration, fully human, anti-CD20, IgG1 mAb in phase I, II and III trials for hematological malignancies and autoimmune diseases such as rheumatoid arthritis (RA) and multiple sclerosis. Ofatumumab specifically recognizes an epitope encompassing both the small and large extracellular loops of CD20 molecule, and is more effective than rituximab at CDC induction and killing target cells. In April 2010, the European Medicines Agency granted a conditional marketing authorization for ofatumumab, for the treatment of fludarabinerefractory CLL patients. It has been reported recently that ofatumumab, administered as 2 i.v. infusions at doses 300 mg, 700 mg, or 1,000 mg is clinically effective in patients with active RA (Østergaard , Baslund et al. 2010). Rapid and sustained peripheral B cell depletion was noted in all dose groups. Overall, 70% of patients receiving ofatumumab had a moderate or good response according to the European League Against Rheumatism (EULAR) criteria at week 24.

#### **2.2.2 Veltuzumab**

Veltuzumab (IMMU-106, hA20; Immunomedics Inc., Morris Plains, NJ) is a secondgeneration, type 1, humanized, anti-CD20, IgG1 mAb with complementarity-determining regions (CDRs) similar to rituximab (Goldenberg, Rossi et al. 2009). This mAb is generated using the same human immunoglobulin as epratuzumab and has a >90% humanized framework. It is also very similar to rituximab in terms of antigen binding, specificity binding, and dissociation constant. Veltuzumab differs from rituximab by one amino acid (Asp101 instead of Asn101) in the CDR 3 of the variable heavy chain. Smaller murine regions may reduce infusion reactions, infusion times, and immunogenicity. This antibody has enhanced binding avidities and a stronger effect on CDC compared with rituximab in selected cell lines. Veltuzumab is safe and active agent in NHL. B cells were depleted after the first infusion of all tested doses, including dose levels less than those typically used with rituximab (Morschhauser, Leonard et al. 2009).

#### **2.2.3 Ocrelizumab**

Ocrelizumab (Genentech Inc/Biogen Idec Inc/Chugai Pharmaceutical Co Ltd/Roche Holding Ag) is a second-generation, type 1, humanized, anti-CD20, IgG1 mAb with modifications of the Fc region that lead to enhanced ADCC and reduced CDC activities compared with rituximab (Kausar, Mustafa et al. 2009).This agent has the potential for enhanced efficacy compared with rituximab due to increased binding affinity for the low-

The Emerging Role of Monoclonal Antibodies in the Treatment of Systemic Lupus Erythematosus 261

monoclonal antibody is 90% to 95% of human origin thus greatly reducing the potential for immunogenicity. Unconjugated anti-CD22 antibodies only partially deplete B cells, but might deliver a negative signal by binding CD22 to the cell surface (Daridon, Blassfeld et al. 2010). Treatment of SLE patients with epratuzumab leads to a reduction of circulating CD27 negative B-cells, although epratuzumab is weakly cytotoxic to B-cells *in vitro*. Epratuzumab binding was higher on B-cells relative to T-cells. In addition, weak non-specific binding of epratuzumab on monocytes was noted. On B-cells, binding of epratuzumab was enhanced on CD27negative B-cells compared to CD27 positive B-cells, primarily related to a higher expression of CD22 on CD27negative B-cells. Epratuzumab also enhanced the migration of

Recently, Dorner et al. reported the results of an open-label, single-center study of 14 patients with moderately active SLE (Dörner, Kaufmann et al. 2006). Patients received 360 mg/m2 of epratuzumab intravenously every 2 weeks for 4 doses with analgesic antihistamine premedication prior to each dose. Total BILAG scores decreased by 50% in all 14 patients at some point during the study with 92% having decrease in various amounts

Epratuzumab toxicity consisted primarily of mild to moderate transient infusion–related events during the first infusion. These results support conducting multicenter controlled studies to examine the effects of epratuzumab in broader patient populations. A U.S. patent has been issued to Immunomedics, Inc. for epratuzumab as a potential new treatment for

The B-lymphocyte Stimulator (BLyS) and A Proliferatiave Inducing Ligand (APRIL) are ligands for receptors BAFF-R (B Cell Activation Factor), BCMA (B Cell Maturation Associate) and TACI (Transmembrane Activator and Calcium Reproducing Initiator). BLyS also known as BAFF, THANK, TALL-1 or zTNF4, is a member of TNF super-family, which stimulates immunoglobulin (Ig) production by binding to specific receptors (King and Hahn 2007). In patients with SLE, the serum levels of BLyS are elevated and its neutralization has suggested that higher levels of BLyS contribute to the generation of autoantibodies and is important in SLE pathogenesis (Toubi, Kessel et al. 2006). In consequence, neutralization of

Belimumab (Human Genome Sciences, (Rockville, MD, USA)/Glaxo Smith Kline, (Uxbridge, UK)) is a fully human IgG1 mAb that specifically binds and inhibits the biological activity of BLyS (Wiglesworth, Ennis et al. 2010). The antibody exerts its biological activity by preventing the binding of BLyS to its receptors, resulting in autoreactive B cell apoptosis (Baker, Edwards et al. 2003). It also inhibits soluble BLyS activity at subnanomolar concentrations in a murine model. Belimumab inhibits also BLyS- induced proliferation of B-cells *in vitro* and prevents human BLyS-induced increases in splenic B-cell numbers and

The safety, tolerability, immunogenicity, and pharmacology of belimumab were investigated in a phase I, randomized, placebo controlled, double-blind study in patients with SLE (Furie, Stohl et al. 2008). Seventy patients with mild to moderate disease were enrolled in this trial. Fifty-seven patients were treated with mAb and 13 with placebo. The drug was administered at 4 different doses (1.0, 4.0, 10 and 20 mg/kg) as single infusions, 21

CD27negative B-cells towards the chemokine CXCL12.

continuing to at least 18 weeks.

**3.2 Anti-BlyS monoclonal antibodies** 

BLyS may play a role in the therapy of this disease.

lupus.

**3.2.1 Belimumab** 

serum IgA titers in mice.

affinity variants of the FcγRIIIa receptor on immune effector cells (Genovese, Kaine et al. 2008). Ocrelizumab binds to a different, but overlapping, epitope of the extracellular domain of CD20 as compared with rituximab. Ocrelizumab is a humanized mAb with the potential for enhanced efficacy in lymphoid malignancies compared with rituximab due to increased binding affinity for the low-affinity variants of the FcγRIIIa receptor (Faria & Isenberg 2010).

#### **2.2.4 GA-101**

GA-101 (RO5072759) is a fully humanized, type II, IgG1 mAb derived from humanization of the parental B-Ly1 mouse antibody and subsequent glycoengineering using GlycoMab® technology. GA-101 was designed for enhanced ADCC and superior direct cell-killing properties, in comparison with currently available type I antibodies (Robak 2009). In contrast to rituximab GA101, mediated significant NK cell degranulation in whole blood samples. Thus, CDC and ADCC are believed to be the major effector mechanisms of GA101 in whole blood assays (Bologna, Gotti et al. 2011).

#### **2.2.5 TRU-015**

TRU-015 (CytoxB20G, Trubion Pharmaceuticals Inc and Pfizer Inc) is a small modular immunopharmaceutical (SMIP) derived from key domains of an anti-CD20 antibody. TRU-015 represents a novel biological compound that retains Fc-mediated effector functions and is smaller than mAbs (Rubbert-Roth 2010). SMIPs belong to a novel proprietary biologic compound class that retain Fc-mediated effector functions and are smaller than mAbs (Robak, Robak et al. 2009). A SMIP molecule is a single-chain polypeptide consisting of one binding domain, one hinge domain, and one effector domain. The TRU-015 SMIP molecule is the homogeneous single-chain immunotherapeutic derived from key domains of an anti-CD20 antibody, for the potential intravenous infusion treatment of RA, SLE and B-cell lymphoid malignancies (Hayden-Ledbetter, Cerveny et al. 2009). This molecule is a compact dimer of 104 kDa that co-migrates with albumin in size exclusion chromatography and retains a long half-life *in vivo*. It is effective in mediating target cell killing in the mechanism of ADCC but has reduced CDC activity compared with rituximab. TRU-015 could represent a novel therapy for the treatment of SLE, although the efficacy, safety profile, and advantages of this compound compared with existing therapeutic options would need to be established in clinical trials (Burge, Bookbinder et al. 2008). TRU-015 has shown clinical efficacy and tolerability in phase IIa and IIb studies in patients with rheumatoid arthritis, and clinical development efforts for the treatment of lymphoma and inflammatory disease are ongoing. In the ongoing trial pharmacokinetics of TRU-015 after a single administration in subjects with membranous nephropathy secondary SLE is investigated (ClinicalTrials.gov Identifier: NCT00479622).

All new anti-CD20 mAbs are potentially useful in the treatment of SLE. However, the advantage of these new drugs over rituximab should be proven by well-designed clinical trials in rituximab-refractory patients or through head-to-head comparison.
