Artificial Anti-Tumor Opsonizing Proteins with Fibronectin Scaffolds Engineered for Specificity to Each of the Murine Fc?R Types.

ABSTRACT: We have engineered a panel of novel Fn3 scaffold-based proteins that bind with high specificity and affinity to each of the individual mouse Fc? receptors (mFc?R). These binders were expressed as fusions to anti-tumor antigen single-chain antibodies and mouse serum albumin, creating opsonizing agents that invoke only a single mFc?R response rather than the broader activity of natural Fc isotypes, as well as all previously reported Fc mutants. This panel isolated the capability of each of the four mFc?Rs to contribute to macrophage phagocytosis of opsonized tumor cells and in vivo tumor growth control with these monospecific opsonizing fusion proteins. All activating receptors (mFc?RI, mFc?RIII, and mFc?RIV) were capable of driving specific tumor cell phagocytosis to an equivalent extent, while mFc?RII, the inhibitory receptor, did not drive phagocytosis. Monospecific opsonizing fusion proteins that bound mFc?RI alone controlled tumor growth to an extent similar to the most active IgG2a murine isotype. As expected, binding to the inhibitory mFc?RII did not delay tumor growth, but unexpectedly, mFc?RIII also failed to control tumor growth. mFc?RIV exhibited detectable but lesser tumor-growth control leading to less overall survival compared to mFc?RI. Interestingly, in vivo macrophage depletion demonstrates their importance in tumor control with mFc?RIV engagement, but not with mFc?RI. This panel of monospecific mFc?R-binding proteins provides a toolkit for isolating the functional effects of each mFc?R in the context of an intact immune system.

SUBMITTER: Chen TF 

PROVIDER: S-EPMC5984174 | biostudies-literature | 2018 Jun

REPOSITORIES: biostudies-literature