Abstract: Fusion polypeptides including at least one Fc binding domain linked to at least one integrin binding domain are provided. In some embodiments, the at least one Fc binding domain is one or more Fc binding domains from Protein A, Protein G, or Protein Z and the at least one integrin binding domain comprises one or more fibronectin type III domains (for example repeats 12-14 of fibronectin type III domains and optionally the connecting segment of fibronectin). Protein complexes including the polypeptide and one or more antibodies are also provided. Methods of using the polypeptide and/or polypeptide:antibody complex are provided, including treating a subject with a tumor, inducing an immune response to a tumor, and/or targeting an antibody to a tumor cell.