Summary Statement of Research Interests Dr. Xiaojiang Chen's combined expertise in biochemistry, molecular and structural biology (X-ray) enables him to study important questions in Cancer Biology and Immunology at molecular/cellular levels. He has done landmark work on tumor viruses (HPV, SV40, EBV) and oncogenes, as well as important DNA modifying enzymes (the ring-shaped helicases and APOBEC mutases), which are critical to genomic stability, cancer, and immunity. His current studies focus on the following areas: [1] Cancer biology, with emphasis on cell growth regulation through oncogenes, tumor suppressors, and DNA/RNA modifying enzymes (deaminases, helicases, polymerases); [2] Immune regulation (B, T cells) and host innate/acquired humoral responses (APOBEC3s, AID, CR2/C3d) against viral infection by HIV, HPV and HCV. [3] Structure-based drug design using the atomic structures of cancer-promoting protein targets, in order to develop molecular probes for studying cancer biology, as well as for potential lead candidates for cancer therapy.