Complement Inhibitors Block Complement C3 Opsonization and Improve Targeting Selectivity of Nanoparticles in Blood

Complement
is one of the critical branches of innate immunity that
determines the recognition of engineered nanoparticles by immune cells.
Antibody-targeted iron oxide nanoparticles are a popular platform
for magnetic separations, in vitro diagnostics, and molecular imaging.
We used 60 nm cross-linked iron oxide nanoworms (CLIO NWs) modified
with antibodies against Her2/neu and EpCAM, which are common markers
of blood-borne cancer cells, to understand the role of complement
in the selectivity of targeting of tumor cells in whole blood. CLIO
NWs showed highly efficient targeting and magnetic isolation of tumor
cells spiked in lepirudin-anticoagulated blood, but specificity was
low due to high uptake by neutrophils, monocytes, and lymphocytes.
Complement C3 opsonization in plasma was predominantly via the alternative
pathway regardless of the presence of antibody, PEG, or fluorescent
tag, but was higher for antibody-conjugated CLIO NWs. Addition of
various soluble inhibitors of complement convertase (compstatin, soluble
CD35, and soluble CD55) to whole human blood blocked up to 99% of
the uptake of targeted CLIO NWs by leukocytes, which resulted in a
more selective magnetic isolation of tumor cells. Using well-characterized
nanomaterials, we demonstrate here that complement therapeutics can
be used to improve targeting selectivity.