Synthetic rewriting of the IGH locus.

V(D)J recombination, which joins V, D, and J genes across immunoglobulin loci, is essential for antibody diversity. To unlock the inherent constraints of V(D)J recombination, we systematically designed, assembled, and shuffled a synthetic human immunoglobulin heavy chain locus (SynIgh). SynIgh was designed de novo, incorporating 60 VH, 31 D, and 13 JH from global populations, along with 63 synthetic rearrangement sites, endowing it with modularity, extensibility, and dynamicity. We then synthesized the repetitive SynIgh sequence with a stabilizer. Using this construct, we generated a SynIgh mouse model capable of undergoing V(D)J recombination. Moreover, we demonstrated that a dual-rearrangement strategy, combining synthetic rearrangement with natural V(D)J recombination, enables shuffling of the SynIgh locus in mice. This strategy expands the diversity of V(D)J recombination outcomes, thereby reconfiguring the process of antibody diversity generation. SynIgh establishes a generalizable framework for the design, building, testing, and learning of mammalian genome architecture and function.