Developmental Toxicity and Fertility Assessment in Rabbits with Tabalumab: A Human IgG4 Monoclonal Antibody

Anti-B-Cell-Activating Factor (BAFF) Therapy: A Novel Addition to Autoimmune Disease Management and Potential for Immunomodulatory Therapy in Warm Autoimmune Hemolytic Anemia

Although rituximab is not specifically approved for the treatment of warm autoimmune hemolytic anemia (WAIHA), the First International Consensus Group recommends considering its use as part of the initial therapy for patients with severe disease and as a second-line therapy for primary WAIHA. Some patients do not respond to rituximab, and relapses are common. These relapses are associated with elevated B-cell-activating factor (BAFF) levels and the presence of quiescent long-lived plasma cells (LLPCs) in the spleen. A new group of immunomodulatory drugs, B-cell-activating factor inhibitors (BAFF-i), demonstrated efficacy in multiple autoimmune diseases and have the potential to improve WAIHA treatment outcomes by targeting B-cells and LLPCs. This article reviews the role of BAFF in autoimmune disorders and the currently available literature on the use of BAFF-directed therapies in various immunologic disorders, including WAIHA. Collectively, the clinical data thus far shows robust potential for targeting BAFF in WAIHA therapy.

Development of tibulizumab, a tetravalent bispecific antibody targeting BAFF and IL-17A for the treatment of autoimmune disease

We describe a bispecific dual-antagonist antibody against human B cell activating factor (BAFF) and interleukin 17A (IL-17). An anti-IL-17 single-chain variable fragment (scFv) derived from ixekizumab (Taltz®) was fused via a glycine-rich linker to anti-BAFF tabalumab. The IgG-scFv bound both BAFF and IL-17 simultaneously with identical stoichiometry as the parental mAbs. Stability studies of the initial IgG-scFv revealed chemical degradation and aggregation not observed in either parental antibody. The anti-IL-17 scFv showed a high melting temperature (Tm) by differential scanning calorimetry (73.1°C), but also concentration-dependent, initially reversible, protein self-association. To engineer scFv stability, three parallel approaches were taken: labile complementary-determining region (CDR) residues were replaced by stable, affinity-neutral amino acids, CDR charge distribution was balanced, and a H44-L100 interface disulfide bond was introduced. The Tm of the disulfide-stabilized scFv was largely unperturbed, yet it remained monodispersed at high protein concentration. Fluorescent dye binding titrations indicated reduced solvent exposure of hydrophobic residues and decreased proteolytic susceptibility was observed, both indicative of enhanced conformational stability. Superimposition of the H44-L100 scFv (PDB id: 6NOU) and ixekizumab antigen-binding fragment (PDB id: 6NOV) crystal structures revealed nearly identical orientation of the frameworks and CDR loops. The stabilized bispecific molecule LY3090106 (tibulizumab) potently antagonized both BAFF and IL-17 in cell-based and in vivo mouse models. In cynomolgus monkey, it suppressed B cell development and survival and remained functionally intact in circulation, with a prolonged half-life. In summary, we engineered a potent bispecific antibody targeting two key cytokines involved in human autoimmunity amenable to clinical development.

An Enhanced Pre- and Postnatal Development Study in Cynomolgus Monkeys with Tabalumab: A Human IgG4 Monoclonal Antibody

Tabalumab, a human IgG4 monoclonal antibody (mAb) with neutralizing activity against both soluble and membrane B-cell activating factor (BAFF), has been under development for the treatment of autoimmune diseases. The purpose of this study was to determine the potential adverse effects of maternal tabalumab exposure on pregnancy, parturition, and lactation of the mothers and on the growth, viability, and development of the offspring through postnatal day (PND) 204. Tabalumab was administered by subcutaneous injection to presumed pregnant cynomolgus monkeys (16-19 per group) every 2 weeks from gestation day (GD) 20 to 22 until parturition at doses of 0, 0.3, or 30 mg/kg. Evaluations in mothers and infants included clinical signs, body weight, toxicokinetics, blood lymphocyte phenotyping, T-cell-dependent antibody response (infants only), antitherapeutic antibody (ATA), organ weights (infants only), and gross and microscopic histopathology. Infants were also examined for external and visceral morphologic and neurobehavioral development. There were no adverse tabalumab-related effects on maternal or infant endpoints. An expected pharmacological decrease in peripheral blood B-lymphocytes occurred in adults and infants; however, B-cell recovery was evident by PND154 in adults and infants at 0.3 mg/kg and by PND204 in infants at 30 mg/kg. At 30 mg/kg, a reduced IgM antibody response to T-cell-dependent antigen keyhole limpet hemocyanin (KLH) was observed following primary immunization. Following secondary KLH immunization, all infants in both dose groups mounted anti-KLH IgM and IgG antibody responses similar to control. Placental and mammary transfer of tabalumab was demonstrated. In conclusion, the no-observed-adverse-effect level for maternal and developmental toxicity was 30 mg/kg, the highest dose tested. Exposures at 30 mg/kg provide a margin of safety of 16× the anticipated clinical exposure.