IF a fibril-conformation-selective single-domain antibody (nanobody) engineered as a VHH-Fc fusion — raised by phage display against synthetic medin fibril aggregates derived from the MFG-E8/lactadherin C-terminal fragment (~50–70 aa), with an effector-competent IgG1 Fc tail to recruit Fcγ receptor III (CD16)-expressing perivascular macrophages — is administered intravenously (10 mg/kg, biweekly) to aged (22–24 month) male and female C57BL/6 mice for 16 weeks,

THEN a measurable reduction (≥30%) in medin amyloid burden in the thoracic aortic media (quantified by Congo red birefringence, thioflavin-S fluorescence, and medin-specific immunohistochemistry), accompanied by decreased aortic pulse wave velocity (PWV) and reduced medial smooth muscle cell disarray, will be observed compared to isotype-matched VHH-Fc vehicle controls,

BECAUSE the following causal chain links intervention to outcome:

1. Medin — derived from proteolytic cleavage of MFG-E8/lactadherin into 50–100 kDa fragments — is confirmed as the most prevalent human amyloid, present in the aortic media of >97% of individuals over age 50, with established links to thoracic aortic aneurysm (TAA) and vascular stiffening. (Medin is the most prevalent human amyloid with established TAA link)[Research Context — Edison confirmation]. Currently zero therapeutic candidates exist targeting this deposit category. (Zero therapeutic candidates confirmed)[Research Context — Edison confirmation].

2. Medin fibrils, like Aβ and ATTR fibrils, present fibril-specific conformational epitopes (cross-β sheet surfaces, hydrophobic core exposures) that are structurally absent in the soluble, natively folded MFG-E8 precursor. Phage-display selection against preformed synthetic medin fibrils, counter-selected against monomeric recombinant MFG-E8, can isolate nanobodies that are strictly fibril-conformation-selective — analogous to the strategy used to isolate lecanemab's parent antibody (BAN2401) against Aβ protofibrils and the fibril-selective VHH antibodies developed against tau aggregates. [SPECULATIVE — by mechanistic analogy; no medin-specific fibril epitope mapping data currently available in evidence set].

3. Nanobodies (VHH single-domain antibodies, ~15 kDa) demonstrate superior penetration into dense extracellular matrix environments compared to full-length IgG (~150 kDa), owing to their compact globular structure, lack of Fc-mediated steric bulk at the paratope, and demonstrated tissue penetration in solid tumors and brain parenchyma. The aortic media — a mechanically dense, elastin/collagen-rich, relatively avascular zone — represents precisely the tissue architecture where full-size IgG biodistribution is expected to be limiting. [SPECULATIVE — direct medin-tissue penetration data absent; VHH ECM penetration advantage inferred from oncology precedent].

4. Fusion of the fibril-selective VHH to an IgG1 Fc tail (forming a bivalent homodimeric VHH-Fc, ~80 kDa total) reinstates effector function: Fc-m...

SENS category: GlycoSENS