LoVIS-Seq reveals clonal dynamics of human-HSPC in humanized mice and vector integration bias

Clonal repopulation of human hemopoietic stem and progenitor cells (HSPC) in humanized mouse models remains only partially understood due to the lack of a quantitative clonal tracking technique for low sample volumes. Here, we present a low-volume vector integration site sequencing (LoVIS-Seq) assay that requires a mere 25μl mouse blood for quantitative clonal tracking of HSPC. Using LoVIS-Seq, we longitudinally tracked 897 VIS clones − providing a first-ever demonstration of clonal dynamics of both therapeutic and control vector-modified human cell populations simultaneously repopulating in humanized mice. Polyclonal repopulation of human cells became stable at 19 weeks post-transplant indicating faster clonal repopulation than observed in humans. Multi-omics data of human fetal liver HSPC provides a definitive evidence of vector integration preference for H3K36me3-enriched regions. Despite this bias the repopulation remains normal, underscoring the safety of gene therapy vectors. LoVIS-Seq provides an efficient tool for exploring gene therapy and stem cell biology in small-animal models.