This application proposes studies of the mechanisms of immunoglobulin heavy chain (IgH) class switch recombination (CSR) and Somatic Hypermutation (SHM). We have shown that Activation Induced Cytidine Deaminase (AID), the initiator of CSR, is a single strand DNA (ssDNA) specific cytidine deaminase and we employed a series of novel biochemical and genetic approaches to elucidate mechanisms by which AID gains access to transcribed double strand (ds)DNA sequences in the context transcription-generated ssDNA structures and/or certain AID modifications or co-factors. We also showed that CSR may employ general processes for synapsis of AID-initiated DNA double strand breaks (DSBs), that general DNA repair factors function in CSR, and that two distinct end-joining pathways fuse S region breaks to complete CSR. Our current proposal builds on these observations in the context of three specific Aims.
Our first aim proposes use of biochemical and genetic approaches to elucidate basic mechanisms of AID function and regulation. In this regard, we developed methods to purify AID from normal B cells, in vitro assays for transcription-dependent AID deamination of dsDNA DNA, and genetic approaches to evaluate in vivo AID functions elucidated biochemically.
Our second aim addresses mechanisms by which DNA sequences influence AID activity and its outcome. For these studies, we developed targeted mutation assays to replace endogenous IgH class switch (S) regions and exons encoding IgH variable regions with test sequences that will allow us to determine how substrate sequences influence activities of AID and other relevant factors in CSR and SHM. Together, the complementary biochemical and genetic assays of Aims 1 and 2 offer a powerful approach for elucidating factors and mechanisms involved in initiation and regulation of IgH CSR and SHM. A third proposed aim is to elucidate processes involved in the repair of AID induced DSBs to complete CSR. For these studies, we again have developed a large array of reagents and novel approaches, including cytogenetic methods to follow CSR related breaks in chromosomes, novel genetic approaches to study factors involved in long range synapsis of DSBs, and genetic models to elucidate DSB repair pathways that complete IgH CSR. Our proposed studies should provide novel insights into the mechanism of antibody production via IgH CSR and, therefore, be relevant to understanding immunodeficiencies, vaccine immunology, and autoimmune diseases. As CSR is required for IgE production, the work will also be relevant to understanding pathogenesis of allergic diseases and asthma. Finally, the work is relevant to B cell malignancies as they often involve chromosomal translocations that link translocated oncogenes to IgH S regions via aberrant CSR.

Public Health Relevance

Our proposed studies will continue to provide novel insights into the mechanism by which different types of antibodies are produced through the gene rearrangement process termed immunoglobulin heavy chain class switch recombination (CSR). Elucidation of the CSR mechanism has great relevance for understanding immunodeficiency and autoimmune diseases. Elucidation of the CSR mechanism also has importance for fully understanding allergic diseases and asthma, as increased production of a particular class of antibodies is an important component of the pathogenesis of these diseases. Finally, the work will help elucidate factors that underlie certain cancers of the immune system, such as lymphomas, which activate cancer causing genes through aberrant CSR.

National Institute of Health (NIH)
National Institute of Allergy and Infectious Diseases (NIAID)
Research Project (R01)
Project #
Application #
Study Section
Cellular and Molecular Immunology - B Study Section (CMIB)
Program Officer
Nasseri, M Faraz
Project Start
Project End
Budget Start
Budget End
Support Year
Fiscal Year
Total Cost
Indirect Cost
Children's Hospital Boston
United States
Zip Code
Nicolas, Laura; Cols, Montserrat; Choi, Jee Eun et al. (2018) Generating and repairing genetically programmed DNA breaks during immunoglobulin class switch recombination. F1000Res 7:458
Panchakshari, Rohit A; Zhang, Xuefei; Kumar, Vipul et al. (2018) DNA double-strand break response factors influence end-joining features of IgH class switch and general translocation junctions. Proc Natl Acad Sci U S A 115:762-767
Crowe, Jennifer L; Shao, Zhengping; Wang, Xiaobin S et al. (2018) Kinase-dependent structural role of DNA-PKcs during immunoglobulin class switch recombination. Proc Natl Acad Sci U S A 115:8615-8620
Qiao, Qi; Wang, Li; Meng, Fei-Long et al. (2017) AID Recognizes Structured DNA for Class Switch Recombination. Mol Cell 67:361-373.e4
Nguyen, Hai Vu; Dong, Junchao; Panchakshari, Rohit A et al. (2017) Histone methyltransferase MMSET promotes AID-mediated DNA breaks at the donor switch region during class switch recombination. Proc Natl Acad Sci U S A 114:E10560-E10567
Compagno, Mara; Wang, Qi; Pighi, Chiara et al. (2017) Phosphatidylinositol 3-kinase ? blockade increases genomic instability in B cells. Nature 542:489-493
Verkoczy, Laurent; Alt, Frederick W; Tian, Ming (2017) Human Ig knockin mice to study the development and regulation of HIV-1 broadly neutralizing antibodies. Immunol Rev 275:89-107
Hwang, Joyce K; Wang, Chong; Du, Zhou et al. (2017) Sequence intrinsic somatic mutation mechanisms contribute to affinity maturation of VRC01-class HIV-1 broadly neutralizing antibodies. Proc Natl Acad Sci U S A 114:8614-8619
Hu, Jiazhi; Meyers, Robin M; Dong, Junchao et al. (2016) Detecting DNA double-stranded breaks in mammalian genomes by linear amplification-mediated high-throughput genome-wide translocation sequencing. Nat Protoc 11:853-71
Kumar, Vipul; Alt, Frederick W; Frock, Richard L (2016) PAXX and XLF DNA repair factors are functionally redundant in joining DNA breaks in a G1-arrested progenitor B-cell line. Proc Natl Acad Sci U S A 113:10619-24

Showing the most recent 10 out of 30 publications