Clonal tracking of aged hematopoiesis by genetic barcoding in nonhuman primates. HSPCs from aged and young rhesus macaques are transduced with a GFP-expressing LV library containing unique molecular identifier (UMI) or barcode. Each LV-marked HSPC harbors a distinctive UMI stably integrated in its genome that will be inherited by its progeny after transplantation. Polymerase chain reaction (PCR) amplification and sequencing of the UMIs contained in the genomic DNA of peripheral blood–derived myeloid and lymphoid cells allows us to track and quantify clonal abundance of individual clones across time and cell lineages. The graphs on the right are a schematic example of the changes in clonal abundance and complexity over time in the blood of young and aged macaques; clones with an abundance >1% (cl1, cl2, and cl5) are color coded. Aged macaques display a reduction in clonal diversity and a pronounced expansion of both myeloid and B-cell lineage restricted clones at later time points compared with young macaques. The figure has been adapted from Figure 1 in the article by Yu et al that begins on page 1195.