High-fidelity human chromosome transfer and elimination.

The synthesis of human genomes and other gigabase-scale genomes will require new strategies. Here, we realized key steps in our pipeline for building synthetic human chromosomes. We established: (i) the facile transfer of human chromosomes from human cells to mouse embryonic stem cells (assembly cells), where they are haploid, are nonessential, and may be operated on; (ii) the transfer of these human chromosomes from monochromosomal hybrids back into human cells to generate defined, synthetic aneuploidies; and (iii) the elimination of the corresponding endogenous human chromosomes to regenerate diploid cells containing a transferred chromosome. All steps were performed in nontransformed cells without chromothripsis and generated minimal structural variants, insertions, deletions, or single-nucleotide variants. Editor's summary: Building human genomes from scratch has the potential to transform biology and medicine but will require innovative approaches. Petris et al. demonstrate key steps toward this goal by developing a method to transfer a human chromosome into specialized "assembly" cells and safely manipulate it. The engineered chromosome is then used to replace the corresponding chromosome in target human cells with minimal genetic damage. By enabling accurate chromosome transplantation and replacement, this study lays the groundwork for constructing synthetic human genomes and opens new possibilities for determining chromosome function, modeling disease, and engineering cells. —Di Jiang [ABSTRACT FROM AUTHOR]