Protein interactions are important for understanding of biological function, and for prevention, diagnosis and treatment of diseases. Our research focuses on antibody-antigen and ligand-receptor interactions. We identify novel human monoclonal antibodies, characterize and improve their properties, elucidate their mechanisms of interactions with viruses and cancer-related antigens, investigate antibody-mediated modulation of ligand-receptor interactions, and apply the knowledge gained to solve biomedical problems. Our major long-term goal is to develop antibody-based therapeutics including small engineered antibody fragments (nanoantibodies) and antibody-guided nanoparticles against cancer and viruses. Currently, we identify, engineer and characterize antibodies against components of the insulin-like growth factor (IGF) system and other cancer-related antigens, HIV, and emerging and biodefense-related viruses including Nipah and Hendra viruses. We also study mechanisms of escape from antibody-mediated neutralization of viruses and cancer cells with applications to the development of vaccines and therapeutics against HIV and cancer.