Learnings about Aß from human brain recommend the use of a live-neuron bioassay for the discovery of next generation Alzheimer's disease immunotherapeutics.

Despite ongoing debate, the amyloid ß-protein (Aß) remains the prime therapeutic target for the treatment of Alzheimer's disease (AD). However, rational drug design has been hampered by a lack of knowledge about neuroactive Aß. To help address this deficit, we developed live-cell imaging of iPSC-derived human neurons (iNs) to study the effects of the most disease relevant form of Aß-oligomeric assemblies (oAß) extracted from AD brain. Of ten brains studied, extracts from nine caused neuritotoxicity, and in eight cases this was abrogated by Aß immunodepletion. Here we show that activity in this bioassay agrees relatively well with disruption of hippocampal long-term potentiation, a correlate of learning and memory, and that measurement of neurotoxic oAß can be obscured by more abundant non-toxic forms of Aß. These findings indicate that the development of novel Aß targeting therapeutics may benefit from unbiased activity-based discovery. To test this principle, we directly compared 5 clinical antibodies (aducanumab, bapineuzumab,  BAN2401, gantenerumab, and SAR228810) together with an in-house aggregate-preferring antibody (1C22) and established relative EC50s in protecting human neurons from human Aß. The results yielded objective numerical data on the potency of each antibody in neutralizing human oAß neuritotoxicity. Their relative efficacies in this morphological assay were paralleled by their functional ability to rescue oAß-induced inhibition of hippocampal synaptic plasticity. This novel paradigm provides an unbiased, all-human system for selecting candidate antibodies for advancement to human immunotherapy.

SAR228810: an antibody for protofibrillar amyloid ß peptide designed to reduce the risk of amyloid-related imaging abnormalities (ARIA).

BACKGROUND: Anti-amyloid ß (Aß) immunotherapy represents a major area of drug development for Alzheimer's disease (AD). However, Aß peptide adopts multiple conformations and the pathological forms to be specifically targeted have not been identified. Aß immunotherapy-related vasogenic edema has also been severely dose limiting for antibodies with effector functions binding vascular amyloid such as bapineuzumab. These two factors might have contributed to the limited efficacy demonstrated so far in clinical studies. METHODS: To address these limitations, we have engineered SAR228810, a humanized monoclonal antibody (mAb) with limited Fc effector functions that binds specifically to soluble protofibrillar and fibrillar forms of Aß peptide and we tested it together with its murine precursor SAR255952 in vitro and in vivo. RESULTS: Unlike gantenerumab and BAN2401, SAR228810 and SAR255952 do not bind to Aß monomers, low molecular weight Aß oligomers or, in human brain sections, to Aß diffuse deposits which are not specific of AD pathology. Both antibodies prevent Aß42 oligomer neurotoxicity in primary neuronal cultures. In vivo, SAR255952, a mouse aglycosylated IgG1, dose-dependently prevented brain amyloid plaque formation and plaque-related inflammation with a minimal active dose of 3 mg/kg/week by the intraperitoneal route. No increase in plasma Aß levels was observed with SAR255952 treatment, in line with its lack of affinity for monomeric Aß. The effects of SAR255952 translated into synaptic functional improvement in ex-vivo hippocampal slices. Brain penetration and decoration of cerebral amyloid plaques was documented in live animals and postmortem. SAR255952 (up to 50 mg/kg/week intravenously) did not increase brain microhemorrhages and/or microscopic changes in meningeal and cerebral arteries in old APPSL mice while 3D6, the murine version of bapineuzumab, did. In immunotolerized mice, the clinical candidate SAR228810 demonstrated the same level of efficacy as the murine SAR255952. CONCLUSION: Based on the improved efficacy/safety profile in non-clinical models of SAR228810, a first-in-man single and multiple dose administration clinical study has been initiated in AD patients.

Polyclonal rabbit antithymocyte globulin exhibits consistent immunosuppressive capabilities beyond cell depletion.

BACKGROUND: Polyclonal antithymocyte globulins (ATGs) are used clinically to prevent and treat acute allograft rejection and are believed to modulate the immune response primarily by depleting T cells. However, nondepleting mechanisms may also be important mediators of graft survival. In the present study, 14 lots of thymoglobulin (rabbit ATG) were analyzed and compared for nondepletive immunomodulatory activities in vitro. METHODS: Coincubation of human peripheral blood mononuclear cells with thymoglobulin induces CD4+CD25(high)Foxp3+ regulatory T cells, which were evaluated for consistent ability to suppress T-cell activation in mixed lymphocyte reactions. The consistency of CD2, CD3, CD11a, and CD45 antigen specificities in thymoglobulin was determined using flow cytometry to measure inhibition of fluorescent monoclonal antibody binding to Jurkat T cells. A transwell chemotaxis assay was established and used to evaluate ATG-mediated inhibition of stromal cell-derived factor (SDF)-1alpha-driven Jurkat T-cell migration. RESULTS: Physiologic levels of thymoglobulin produced nondepletive immunomodulatory activities, which were consistent from batch to batch. All lots of thymoglobulin induced functionally immunosuppressive regulatory T cells and inhibited monoclonal antibody binding to key T-cell surface antigens. In addition, these studies provide the first demonstration that thymoglobulin effectively inhibits CXCR4/SDF-1alpha-driven T-cell chemotaxis. CONCLUSIONS: This novel, systematic in vitro analysis of 14 different manufactured lots of thymoglobulin demonstrates the overall consistency of this product and provides further insights into nondepletive mechanisms by which thymoglobulin may generate durable immunoregulation and allograft survival.