Specific binding of intravenous immunoglobulin products to tau peptide fragments

Autoantibodies targeting neuronal proteins as biomarkers for neurodegenerative diseases

Neurodegenerative diseases (NDDs) are associated with the accumulation of a range of misfolded proteins across the central nervous system and related autoimmune responses, including the generation of antibodies and the activation of immune cells. Both innate and adaptive immunity become mobilized, leading to cellular and humoral effects. The role of humoral immunity in disease onset and progression remains to be elucidated with rising evidence suggestive of positive (protection, repair) and negative (injury, toxicity) outcomes. In this study, we review advances in research of neuron-targeting autoantibodies in the most prevalent NDDs. We discuss their biological origin, molecular diversity and changes in the course of diseases, consider their relevance to the initiation and progression of pathology as well as diagnostic and prognostic significance. It is suggested that the emerging autoimmune aspects of NDDs not only could facilitate the early detection but also might help to elucidate previously unknown facets of pathobiology with relevance to the development of precision medicine.

Catalytic antibody (catabody) platform for age-associated amyloid disease: From Heisenberg's uncertainty principle to the verge of medical interventions

Quantum mechanics-based design of useful catalytic antibodies (catabodies) failed because of the uncertain structure of the dynamic catalyst-substrate complex. The Catabody Platform emerged from discovery of beneficial germline gene catabodies that hydrolyzed self-proteins by transient covalent pairing of the strong catabody nucleophile with a weak target protein electrophile. Catabodies have evolved by Darwinian natural selection for protection against misfolded self-proteins that threatened survival by causing amyloid disease. Ancient antibody scaffolds upregulate the catalytic activity of the antibody variable (V) domains. Healthy humans universally produce beneficial catabodies specific for at least 3 misfolded self-proteins, transthyretin, amyloid β peptide and tau protein. Catabody are superior to ordinary antibodies because of catalyst reuse for thousands of target destruction cycles with little or no risk of causing inflammation, a must for non-toxic removal of abundant targets such as amyloids. Library mining with electrophilic target analogs (ETAs) isolates therapy-grade catabodies (fast, specific). Ex vivo- and in vivo-verified catabodies specific for the misfolded protein are available to dissolve brain, cardiac and vertebral amyloids. Immunization with ETAs overcomes important ordinary vaccine limitations (no catabody induction, poor immunogenicity of key target epitopes). We conceive electrophilic longevity vaccines that can induce catabody synthesis for long-lasting protection against amyloid disease.

Tau-Reactive Endogenous Antibodies: Origin, Functionality, and Implications for the Pathophysiology of Alzheimer's Disease

In Alzheimer's disease (AD), tau pathology manifested by the accumulation of intraneuronal tangles and soluble toxic oligomers emerges as a promising therapeutic target. Multiple anti-tau antibodies inhibiting the formation and propagation of cytotoxic tau or promoting its clearance and degradation have been tested in clinical trials, albeit with the inconclusive outcome. Antibodies against tau protein have been documented both in the brain circulatory system and at the periphery, but their origin and role under normal conditions and in AD remain unclear. While it is tempting to assign them a protective role in regulating tau level and removal of toxic variants, the supportive evidence remains sporadic, requiring systematic analysis and critical evaluation. Herein, we review recent data showing the occurrence of tau-reactive antibodies in the brain and peripheral circulation and discuss their origin and significance in tau clearance. Based on the emerging evidence, we cautiously propose that impairments of tau clearance at the periphery by humoral immunity might aggravate the tau pathology in the central nervous system, with implication for the neurodegenerative process of AD.

Purification of Natural Antibodies Against Tau Protein by Affinity Chromatography

Natural antibodies are now widely studied for their therapeutical potential. Therefore, their isolation and subsequent characterization is desired. Here, we describe an isolation method for natural anti-tau antibodies from human plasma by utilization of affinity chromatography with epoxy-activated copolymer resin. The evalution of isolation efficiency and avidity of isolated antibodies is decribed by modified indirect ELISA assay.

Immunological memory to hyperphosphorylated tau in asymptomatic individuals

Several reports have described the presence of antibodies against Alzheimer’s disease-associated hyperphosphorylated forms of tau in serum of healthy individuals. To characterize the specificities that can be found, we interrogated peripheral IgG⁺ memory B cells from asymptomatic blood donors for reactivity to a panel of phosphorylated tau peptides using a single-cell screening assay. Antibody sequences were recovered, cloned, and expressed as full-length IgGs. In total, 52 somatically mutated tau-binding antibodies were identified, corresponding to 35 unique clonal families. Forty-one of these antibodies recognize epitopes in the proline-rich and C-terminal domains, and binding of 26 of these antibodies is strictly phosphorylation dependent. Thirteen antibodies showed inhibitory activity in a P301S lysate seeded in vitro tau aggregation assay. Two such antibodies, CBTAU-7.1 and CBTAU-22.1, which bind to the proline-rich and C-terminal regions of tau, respectively, were characterized in more detail. CBTAU-7.1 recognizes an epitope that is similar to that of murine anti-PHF antibody AT8, but has different phospho requirements. Both CBTAU-7.1 and CBTAU-22.1 detect pathological tau deposits in post-mortem brain tissue. CBTAU-7.1 reveals a similar IHC distribution pattern as AT8, immunostaining (pre)tangles, threads, and neuritic plaques. CBTAU-22.1 shows selective detection of neurofibrillary changes by IHC. Taken together, these results suggest the presence of an ongoing antigen-driven immune response against tau in healthy individuals. The wide range of specificities to tau suggests that the human immune repertoire may contain antibodies that can serve as biomarkers or be exploited for therapy.

Identification and characterization of natural antibodies against tau protein in an intravenous immunoglobulin product

The latest therapeutic approaches to Alzheimer disease are using intravenous immunoglobulin (IVIG) products. Therefore, the detailed characterization of target-specific antibodies naturally occurring in IVIG products is beneficial. We have focused on characterization of antibodies isolated against tau protein, a biomarker of Alzheimer's disease, from Flebogamma IVIG product. The analysis of IgG subclass distribution indicated skewing toward IgG3 in anti-tau-enriched IgG fraction. The evaluation of their reactivity and avidity with several recombinant tau forms was performed by ELISA and blotting techniques. Truncated non-phosphorylated tau protein (amino acids 155-421) demonstrated the highest reactivity and avidity index. We provide the first detailed insight into the reactivity of isolated natural antibodies against tau protein.

ELISA measurement of specific antibodies to phosphorylated tau in intravenous immunoglobulin products

The therapeutic effects of intravenous immunoglobulin (IVIG) products were recently studied in Alzheimer's disease (AD) patients. Pilot studies produced encouraging results but phase II and III trials gave disappointing results; a further study is in progress. IVIG products contain antibodies to tau protein, the main component of neurofibrillary tangles (NFTs). The tau used to detect IVIG's anti-tau antibodies in previous studies was non-phosphorylated recombinant human tau-441, but NFT-associated tau is extensively phosphorylated. The objective of this study was to determine if various IVIG products contain specific antibodies to phosphorylated tau (anti-pTau antibodies). ELISAs were used to evaluate binding of six IVIG products to a 12 amino acid peptide, tau 196-207, which was phosphorylated ("pTau peptide") or non-phosphorylated ("non-pTau peptide") at Serine-199 and Serine-202. Both amino acid residues are phosphorylated in AD NFTs. Each IVIG's "anti-pTau antibody ratio" was calculated by dividing its binding to the pTau peptide by its binding to the non-pTau peptide. Seven experiments were performed and data were pooled, with each experiment contributing one data point from each IVIG product. Mean anti-pTau antibody ratios greater than 1.0, suggesting specific antibodies to phosphorylated tau, were found for three IVIG products. Because administration of antibodies to phosphorylated tau has been found to reduce tau-associated pathology in transgenic mouse models of tauopathy, increasing the levels of anti-pTau antibodies, together with other selected antibodies such as anti-Aβ, in IVIG might increase its ability to slow AD's progression.

Effects of tau domain-specific antibodies and intravenous immunoglobulin on tau aggregation and aggregate degradation

Tau pathology, including neurofibrillary tangles, develops in Alzheimer's disease (AD). The aggregation and hyperphosphorylation of tau are potential therapeutic targets for AD. Administration of anti-tau antibodies reduces tau pathology in transgenic "tauopathy" mice; however, the optimal tau epitopes and conformations to target are unclear. Also unknown is whether intravenous immunoglobulin (IVIG) products, currently being evaluated in AD trials, exert effects on pathological tau. This study examined the effects of anti-tau antibodies targeting different tau epitopes and the IVIG Gammagard on tau aggregation and preformed tau aggregates. Tau aggregation was assessed by transmission electron microscopy and fluorescence spectroscopy, and the binding affinity of the anti-tau antibodies for tau was evaluated by enzyme-linked immunosorbent assays. Antibodies used were anti-tau 1-150 ("D-8"), anti-tau 259-266 ("Paired-262"), anti-tau 341-360 ("A-10"), and anti-tau 404-441 ("Tau-46"), which bind to tau's N-terminus, microtubule binding domain (MBD) repeat sequences R1 and R4, and the C-terminus, respectively. The antibodies Paired-262 and A-10, but not D-8 and Tau-46, reduced tau fibrillization and degraded preformed tau aggregates, whereas the IVIG reduced tau aggregation but did not alter preformed aggregates. The binding affinities of the antibodies for the epitope for which they were specific did not appear to be related to their effects on tau aggregation. These results confirm that antibody binding to tau's MBD repeat sequences may inhibit tau aggregation and indicate that such antibodies may also degrade preformed tau aggregates. In the presence of anti-tau antibodies, the resulting tau morphologies were antigen-dependent. The results also suggested the possibility of different pathways regulating antibody-mediated inhibition of tau aggregation and antibody-mediated degradation of preformed tau aggregates.

Should development of Alzheimer's disease-specific intravenous immunoglobulin be considered?

Recent phase II and III studies with intravenous immunoglobulin (IVIG) in patients with Alzheimer's disease (AD) did not find evidence for the slowing of AD progression compared to placebo-treated patients, in contrast to encouraging results in pilot studies. An additional phase III trial is ongoing. If negative results are found, then further AD studies with IVIG are unlikely unless a manufacturer opts for a trial with high-dose IVIG, which would increase its anti-inflammatory effects but also the risk for adverse events. An alternative approach could be an AD-specific IVIG, supplementing IVIG with higher concentrations of selected antibodies purified from it or produced via recombinant polyclonal antibody technology. These antibodies could include those to amyloid-beta (Aβ, tau protein, inflammatory cytokines, complement activation proteins, and the receptor for advanced glycation end products. IgG fragment crystallizable (Fc) fragments containing terminal sialic acid could be added to increase anti-inflammatory effects. While this product might be more effective in slowing AD clinical progression than current IVIG, there are difficulties with this approach. Preclinical studies would be required to determine which of the antibodies of interest for supplementing current IVIG (for example, antibodies to phosphorylated or oligomeric tau) are actually present (and, therefore, available for purification) in IVIG, and the effects of the product in mouse models of AD. An Investigational New Drug application for an AD-specific IVIG would require United States Food and Drug Administration approval. If the drug would be found to benefit AD patients, meeting the increased demand for IVIG would be challenging.