Reducing the amyloid burden through immunotherapy: a major therapeutic advance.

Pepys and coworkers report in a recent paper (Bodin et al., Nature 2010; 468:93–97 [1]), the rapid resorption of visceral amyloid using antibodies to a common constituent of all amyloid deposits, the serum amyloid P component (SAP), in a human SAP transgenic mice model of reactive amyloidosis (AA amyloidosis) [1]. SAP binds avidly to all types of amyloid fibrils and protects them from proteolytic degradation and resorption. In order to promote the resorption of amyloid deposits, Pepys and coworkers had previously designed the palindromic molecule (R)-1-[6-[(R)-2-carboxy-pyrrolidin-1-yl]-6-oxo-hexanoyl]pyrrolidine-2-carboxylic acid (CPHPC) that bound with high affinity human SAP and triggered its rapid clearance by the liver, thus depleting circulating SAP [2]. However, some SAP is left bound to amyloid even after months of CPHPC treatment [3]. Now they report that targeting this residual SAP with anti-SAP antibodies after treatment with CPHPC triggered the complementdependent phagocytic clearance mechanisms that rapidly removed visceral AA amyloid deposits in mice. The authors cautioned that systemic amyloidosis patients have widespread amyloid deposits in sensitive tissues, including the heart, blood vessel walls and nerves, which are not involved in the mouse AA model. Also, the trace amount of human SAP in normal glomerular basement membrane and elastic fiber microfibrils is a potential undesirable target for anti-SAP antibodies. However, no adverse events were noted and no change in plasma biochemistry or any histological abnormality was observed. This important paper highlights the feasibility and efficacy of immunotherapy in amyloid diseases.