**3.2 Anti-BlyS monoclonal antibodies**

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

#### **3.2.1 Belimumab**

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

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).

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

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

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

Epratuzumab (Immunomedics, Inc.) is a humanized monoclonal IgG antibody that specifically targets the CD22 antigen on B cells (Leonard & Goldenberg 2007). This

trials in rituximab-refractory patients or through head-to-head comparison.

**3. Other B cell targeting monoclonal antibodies** 

**3.1 Anti-CD22 antibody epratuzumab** 

**2.2.4 GA-101** 

**2.2.5 TRU-015** 

Identifier: NCT00479622).

in whole blood assays (Bologna, Gotti et al. 2011).

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 serum IgA titers in mice.

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

The Emerging Role of Monoclonal Antibodies in the Treatment of Systemic Lupus Erythematosus 263

Orencia) is a recombinant fully humanized fusion protein, composed of the extracellular domain of human CTLA-4 and a modified Fc part of IgG-1that was engineered to prevent complement fixation (St Clair 2009). It targets T cell activation by interfering with one of the costimulatory mechanisms that are essential for cell activation. CTLA4-Ig binds to B7-1 and B7-2 on antigen presenting cells and downregulates T cell activation by disrupting CD28-B7 costimulatory interaction. Abatacept blocks the interaction between CD28 expressed on the surface of T cells and CD80/CD86 on the surface of antigen-presenting cells. The drug was approved for RA by the FDA US (Food and Drug Administration) in 2005. Abatacept was compared to placebo in a randomized, placebo controlled, phase II trial of patients with active SLE characterized by arthritis, serositis, or rash (Merrill, Burgos-Vargas et al. 2010). SLE patients were randomized at a ratio of 2:1 to receive abatacept (10 mg/kg of body weight) or placebo. Prednisone (30 mg/day or equivalent) was given for 1 month, and then the dosage was tapered. There was no difference in the percentage of patients who experienced the primary endpoint of SLE flare, as defined by BILAG, over the course of 52 weeks. However, the investigators discerned a difference in flare rates between the abatacept group (64%) and placebo group (83%). This difference was especially pronounced in the subgroup of patients with arthritis. The frequency of adverse events was comparable in the abatacept and placebo groups (90.9% versus 91.5%), but serious adverse events were higher in the abatacept group (19.8 versus 6.8%). Most serious adverse events were single, disease-related events occurring during the first 6 months. Improvements in certain exploratory measures suggest that abatacept has some efficacy in patients with non-life-threatening manifestations of SLE.

In the course of SLE, a wide variety of cytokines is dysregulated, many of which are likely to influence autoimmunity and lupus tissue inflammation (La Cava. 2010; Robak, Kulczycka et al. 2007). They are not only involved in the immune dysregulation of SLE, but also in the local inflammatory response which ultimately leads to tissue injury. Proinflammatory cytokines such as tumor necrosis factor (TNF), iterleukin-6 (IL-6), IL-1 and interferon- (IFN-) may play an important role in propagating the inflammatory process responsible for tissue damage. IL-12, IL-15 and IL-18 are probably also involved in pathogenesis of SLE. The possibility of blocking the proinflammatory cascade by selective inactivation of cytokines

Data from several studies suggests that IL-6 plays an important role in the B-cell hyperactivity and immunopathology of SLE (Klashman, Martin et al. 1991). One of the most important effects of IL-6 is to induce the maturation of B lymphocytes into plasma cells and augment the imunoglobulin secretion. IL-6 binds to the IL-6 receptors which belong to the type 1 cytokine receptor superfamily that consists of two subunits, namely the IL-6 R and the gp 130. This cytokine may have a direct influence in mediating tissue damage. Elevated levels of IL-6 were detected in the serum, urine and renal glomerulli of patients with active

Tocilizumab (ACTEMRA, MRA, Roche Pharmaceuticals) is a humanized anti-human IL-6R mAb considered as a therapeutic option for patients with SLE. It is an antibody which inhibits the interleukin-6 receptor. It binds to both soluble IL-6R and transmembrane IL-6R

**5. Anticytokine monoclonal antibodies** 

can be a successful therapy for patients with SLE.

SLE and in murine models of SLE (Grondal, Gunnarsson et al. 2000).

**5.1 Anti-IL-6 monoclonal antibodies** 

days apart. The incidence of adverse events and laboratory abnormalities was similar among the belimumab and placebo groups. A significant reduction in the median percentage of CD20+ B-cells was noted with a one and two doses of belimumab versus placebo. However, SLE activity did not change after treatment with this mAb.

Wallace et al. assessed the safety, tolerability, biological activity, and efficacy of belimumab in combination with standard of care therapy in patients with active SLE (Wallace, Stohl et al. 2009). In this phase II, randomized trial 449 patients with SELENA-SLEDAI score ≥ 4 were randomly assigned to belimumab (1, 4, 10 mg/kg) or placebo in a 52-week study. In this study, belimumab treatment did not result in significant improvement compared with placebo. Percentage change in the SELENA-SLEDAI score at week 24, the primary endpoint of the study, was similar in both arms (19.5% in the belimumab group versus 17.2% in the placebo group). There was no significant difference in time to first SFI-defined flare over 52 weeks between the belimumab and placebo groups (67 versus 83 days, respectively). However, the median time to first SLE flare during weeks 24–52 was significantly longer with belimumab treatment (154 versus 108 days; P=0.0361). During the 52-week study and 8-week follow-up period, the incidence of AEs were similar in all treatment groups, including placebo. Only urticaria was statistically more frequent in belimumab-treated patients (4% versus 0%).

The efficacy and safety of belimumab in patients with active SLE was also assessed in a large, randomized, multicenter study recently reported by Navarra et al 2011 (Navarra, Guzmán et al. 2011). In this trial, 865 patients with scores of at least 6 on the Safety of Estrogens in Lupus Erythematosus National Assessment-Systemic Lupus Erythematosus Disease Activity Index (SELENA-SLEDAI) were randomly assigned to belimumab 1 mg/kg or 10 mg/kg, or placebo by intravenous infusion in 1 h on days 0, 14, and 28, and then every 28 days until 48 weeks, with standard of care. Significantly higher Systemic Lupus Erythematosus Responder Index (SRI) rates were noted with belimumab 1 mg/kg (51%, P=0.0129) and 10 mg/kg (58%, p=0.006) than with placebo (44%) at week 52. In addition, more patients had SELENA-SLEDAI score reduced by at least 4 points during 52 weeks with belimumab 1 mg/kg (53%, P=0.0189) and 10 mg/kg (58%, P=0.0024) than with placebo (46%). Moreover, more patients receiving belimumab 1 mg/kg (78%, P=0.1064) and 10 mg/kg (81%, P=0.0181) had no new BILAG A or no more than 1 new B flare than did those receiving placebo (73%). There was no difference in rates of adverse events in patients given belimumab 1 mg/kg and 10 mg/kg, and placebo. Serious infection was noted in 8%, 4%, and 6% patients, respectively. Severe or serious hypersensitivity reactions on an infusion day were reported in four patients.

#### **3.2.2 LY2127399**

Anti-BAFF monoclonal antibody LY2127399 (Eli Lilly & Company Limited) is a fully human IgG4 antibody with neutralizing activity against both membrane-bound and soluble BAFF. This may reduce the activity, proliferation and survival of B-cells. The ongoing study evaluates the efficacy, safety and tolerability of two different doses of LY2127399 administered in addition to standard of care therapy in patients with active SLE (ClinicalTrials.gov Identifier: NCT01205438).

#### **4. Monoclonal antibodies inhibiting T cell costimulation**

Cytotoxic lymphocyte-associated antigen-4 (CTLA-4) is a potent inhibitor of the costimulation pathway necessary to activate T cells. Abatacept (CTLA-4 immunoglobulin; CTLA4-Ig, Orencia) is a recombinant fully humanized fusion protein, composed of the extracellular domain of human CTLA-4 and a modified Fc part of IgG-1that was engineered to prevent complement fixation (St Clair 2009). It targets T cell activation by interfering with one of the costimulatory mechanisms that are essential for cell activation. CTLA4-Ig binds to B7-1 and B7-2 on antigen presenting cells and downregulates T cell activation by disrupting CD28-B7 costimulatory interaction. Abatacept blocks the interaction between CD28 expressed on the surface of T cells and CD80/CD86 on the surface of antigen-presenting cells. The drug was approved for RA by the FDA US (Food and Drug Administration) in 2005. Abatacept was compared to placebo in a randomized, placebo controlled, phase II trial of patients with active SLE characterized by arthritis, serositis, or rash (Merrill, Burgos-Vargas et al. 2010). SLE patients were randomized at a ratio of 2:1 to receive abatacept (10 mg/kg of body weight) or placebo. Prednisone (30 mg/day or equivalent) was given for 1 month, and then the dosage was tapered. There was no difference in the percentage of patients who experienced the primary endpoint of SLE flare, as defined by BILAG, over the course of 52 weeks. However, the investigators discerned a difference in flare rates between the abatacept group (64%) and placebo group (83%). This difference was especially pronounced in the subgroup of patients with arthritis. The frequency of adverse events was comparable in the abatacept and placebo groups (90.9% versus 91.5%), but serious adverse events were higher in the abatacept group (19.8 versus 6.8%). Most serious adverse events were single, disease-related events occurring during the first 6 months. Improvements in certain exploratory measures suggest that abatacept has some efficacy in patients with non-life-threatening manifestations of SLE.
