Opportunities for Conformation-Selective Antibodies in Amyloid-Related Diseases

Structure and function of therapeutic antibodies approved by the US FDA in 2023

In calendar year 2023, the United States Food and Drug Administration (US FDA) approved a total of 55 new molecular entities, of which 12 were in the class of therapeutic antibodies. Besides antibody protein drugs, the US FDA also approved another five non-antibody protein drugs, making the broader class of protein drugs about 31% of the total approved drugs. Among the 12 therapeutic antibodies approved by the US FDA, 8 were relatively standard IgG formats, 3 were bivalent, bispecific antibodies and 1 was a trivalent, bispecific antibody. In 2023, no new antibody-drug conjugates, immunocytokines or chimeric antigen receptor-T cells were approved. Of the approved antibodies, two targeted programmed cell death receptor-1 (PD-1) for orphan indications, two targeted CD20 for diffuse large B cell lymphoma, two targeted different receptors (B-cell maturation antigen [BCMA] and G-coupled protein receptor class C, group 5, member D [GPRC5D]) for treatment of multiple myeloma, and one each that targeted amyloid-β protofibrils for Alzheimer's disease, neonatal Fc receptor alpha-chain for myasthenia gravis, complement factor C5 for CD55 deficiency with hyper-activation of complement, angiopathic thrombosis and severe protein-losing enteropathy disease, interleukin (IL)-23p19 for severely active ulcerative colitis, IL-17A-F for plaque psoriasis and respiratory syncytial virus (RSV)-F protein for season-long RSV prophylaxis in infants.

Are fibrinaloid microclots a cause of autoimmunity in Long Covid and other post-infection diseases?

It is now well established that the blood-clotting protein fibrinogen can polymerise into an anomalous form of fibrin that is amyloid in character; the resultant clots and microclots entrap many other molecules, stain with fluorogenic amyloid stains, are rather resistant to fibrinolysis, can block up microcapillaries, are implicated in a variety of diseases including Long COVID, and have been referred to as fibrinaloids. A necessary corollary of this anomalous polymerisation is the generation of novel epitopes in proteins that would normally be seen as 'self', and otherwise immunologically silent. The precise conformation of the resulting fibrinaloid clots (that, as with prions and classical amyloid proteins, can adopt multiple, stable conformations) must depend on the existing small molecules and metal ions that the fibrinogen may (and is some cases is known to) have bound before polymerisation. Any such novel epitopes, however, are likely to lead to the generation of autoantibodies. A convergent phenomenology, including distinct conformations and seeding of the anomalous form for initiation and propagation, is emerging to link knowledge in prions, prionoids, amyloids and now fibrinaloids. We here summarise the evidence for the above reasoning, which has substantial implications for our understanding of the genesis of autoimmunity (and the possible prevention thereof) based on the primary process of fibrinaloid formation.

Passive immunotherapies targeting Aβ and tau in Alzheimer's disease

Amyloid-β (Aβ) and tau proteins currently represent the two most promising targets to treat Alzheimer's disease. The most extensively developed method to treat the pathologic forms of these proteins is through the administration of exogenous antibodies, or passive immunotherapy. In this review, we discuss the molecular-level strategies that researchers are using to design an effective therapeutic antibody, given the challenges in treating this disease. These challenges include selectively targeting a protein that has misfolded or is pathological rather than the more abundant, healthy protein, designing strategic constructs for immunizing an animal to raise an antibody that has the appropriate conformational selectivity to achieve this end, and clearing the pathological protein species before prion-like cell-to-cell spread of misfolded protein has irreparably damaged neurons, without invoking damaging inflammatory responses in the brain that naturally arise when the innate immune system is clearing foreign agents. The various solutions to these problems in current clinical trials will be discussed.

New tool to tackle Alzheimer's disease: amyloid-β protofibril-selective antibody AbSL: An Editorial Highlight for 'The conformational epitope for a new Aβ42 protofibril-selective antibody partially overlaps with the peptide N-terminal region' on page 736

This Editorial highlights a study by Colvin et al. (2017) in the current issue of Journal of Neurochemistry, in which the authors describe the development and characterisation of a new rabbit antibody (termed antibody St. Louis; AbSL) that preferentially recognises amyloid-β (Aβ) protein 42 (Aβ42) protofibrils over other Aβ species.

Immunoaffinity extraction using conformation-dependent antibodies coupled to SE-HPLC for the development of stability and potency-indicating assay for quadrivalent human papillomavirus vaccine

Quadrivalent human papillomavirus (HPV) vaccine is formulated of four types of non-infectious recombinant virus like particles (VLPs) that are structurally and immunologically similar to the corresponding infectious HPV virus types 6, 11, 16 and 18. With almost identical physical, chemical and structural properties of the four types of VLPs, ELISA remains the only approved in vitro potency testing assay. In this study, an alternative industry-friendly, stability- and potency-indicating assay protocol was developed and validated for the determination of HPV vaccine. Vacuum-driven immunoaffinity extraction (IAE) was employed using type-specific, conformation-dependent antibodies against each type of HPV VLPs. ELISA assay was employed to evaluate the ability of IAE columns to specifically separate each of the four types of VLPs from their quadrivalent mixture. Mean percentage recoveries of 76.76±2.69, 69.12±5.79, 84.86±5.25 and 71.14±4.50% were obtained for VLPs types 6, 11, 16 and 18, respectively with no significant interference in each case. Antigen content was then determined using SE-HPLC over a concentration range of 5.00-20.00μg/mL (r>0.998) for VLPs type 6, 11, 16 and 18, respectively. The SE-HPLC assay was found accurate and precise (RSD<10.00%) with LOD ranging from 1.23-3.85μg/mL. The assay protocol was found superior to conventional ELISA assay with respect to simplicity, total analysis time and cost. Good correlation between the results of analysis obtained using IAE-SE-HPLC and ELISA demonstrated the suitability of the suggested assay protocol for stability and potency assessment with a good potential for implementation for batch release. This approach should be applicable for quality assessment of other vaccine preparations based on VLPs.