During the humoral immune response, somatic hypermutation (SHM) introduces point mutations in rearranged immunoglobulin (Ig) genes of activated germinal center (GC) B cells. SHM is essential for the fine-tuning of antibody affinity, the generation of B cells expressing high-affinity antibody, and the efficacy of many vaccines. Mistargeted SHM activities can lead to mutations and chromosomal translocations that contribute to the development of B cell lymphoma. Recent studies suggest that the three-dimensional (3D) organization of the genome regulates SHM targeting and mistargeting. However, it is largely unknown how the genome is spatially organized across multiple length scales in GC B cell development and lymphoma, and how 3D genome architecture mechanistically affects the targeting and mistargeting of SHM. Conventional approaches cannot address these questions in the primary GC tissue environment due to technical limitations. Here, we propose to apply a new method recently developed by our team, termed Multiplexed Imaging of Nucleome Architectures (MINA), to primary human tonsil tissue samples and malignant GC-derived human B cell lymphomas. We will investigate and test the association between SHM susceptibility and a variety of 3D nucleome architectures, including topologically associating domain (TAD) architecture, phase separation, and nuclear positioning of genomic regions relative to nuclear lamina, nucleoli, and nuclear pores. Through targeted genomic perturbations in human B cell lymphomas, we will test specific hypotheses linking SHM targeting elements to elevated chromatin looping interactions, TAD phase separation, nuclear pore proximity, and mutation vulnerability. Our study will significantly advance our understanding of the role of 3D genome architecture and nuclear organization in GC B cells undergoing SHM in both the developmental and tumorigenesis contexts. We expect this study to establish a new research paradigm and transform 3D nucleome investigations in immunobiology.
Human B cells actively recombine and mutate their DNA in a controlled fashion to generate a diverse pool of antibodies to defend our bodies from the numerous harmful pathogens we encounter, while the same mutation mechanism can cause lymphoma cancer when it goes awry. Previous evidence suggests that DNA folding and nuclear organization may regulate the mutation mechanism, but how the DNA organization varies between different B cell states in human tissue and between normal and cancer cells are largely unknown. Here we use our new imaging technology to address these important questions of B cell development and lymphoma.