Digital PCR as a novel way to assess chimerism of humanized immune system mice

Humanized immune system (HIS) mice contain human and murine immune cells.  Analysis of chimerism in HIS mice is typically accomplished via flow cytometry, but this requires collecting a 75 µl blood sample and access to a flow cytometer.  Repeated bleeding can negatively affect the health of HIS mice, limiting serial analysis.  Digital PCR offers a novel method for chimerism analysis, which uses much smaller blood volumes and can be performed on clotted or frozen samples, sample types unsuitable for flow cytometry.  A digital PCR assay directly comparing the presence of three human genes and one murine gene was developed. This assay was validated in the huNOG-EXL HIS mouse engrafted with CD34+ hematopoetic stem cells from 3 unique donors via blind comparison with chimerism data from flow cytometry.  At 10 weeks post engraftment, the digital PCR assay showed excellent correlation for all three human genes against chimerism as measured by flow cytometry of the peripheral blood.  This assay represents a new, user-friendly, rapid tool for the analysis of HIS mice and may permit serial chimerism measurement using 10 μL whole blood.  This assay may be useful to investigate other mouse-human chimera models, including mice harboring functional human hepatocytes, tumors, and other cells.