An Improved Lentiviral Fluorescent Genetic Barcoding Approach Distinguishes Hematopoietic Stem Cell Properties in Multiplexed In Vivo Experiments

Hematopoietic stem cells (HSCs) represent a rare cell population of particular interest for biomedical research and regenerative medicine. Various marker combinations enable the isolation of HSCs, but fail to reach purity in transplantation assays. To reduce animal consumption, we developed a multiplexing system based on lentiviral fluorescent genetic barcoding (FGB) to enable the parallel characterization of multiple HSC samples within single animals. While previous FGB-mediated HSC multiplexing experiments achieved high in vitro gene marking rates, in vivo persistence of transduced cells remained suboptimal. Thus, we aimed to optimize vector design and gene transfer protocols to demonstrate the applicability of FGB for functional characterization of two highly similar HSC populations in a reduced number of mice. We developed a set of six new lentiviral FGB vectors, utilizing individual and combinatorial expression of Azami Green, mCherry, and YFP derivatives. Gene transfer rates were optimized by overnight transduction of prestimulated HSCs with titrated vector doses. Populations for competitive transplantation experiments were identified by immunophenotyping murine HSCs. This identified an LSK-SLAM(-) (Lin(-)Sca-1(+)cKit(+)CD48(-)CD150(+)EPCR(-)) cell subpopulation that lacks EPCR expression and exhibits prospectively reduced self-renewal potential compared with prototypical ESLAM (CD45(+)EPCR(+)CD48(-)CD150(+)) HSCs. We monitored 30 data points per HSC-subpopulation in two independent experiments (each n = 5) after cotransplantation of three uniquely color-coded ESLAM and LSK-SLAM(-) samples per recipient. While the first experiment was hampered by data fluctuations, increasing cell numbers and exchange of the internal promoter in the second experiment led to 74.4% chimerism, with 87.1% of fluorescent cells derived from ESLAM HSCs. Furthermore, ESLAM-derived cells produced 88.1% of myeloid cells, which is indicative of their origin from long-term repopulating HSCs. This work verifies the importance of EPCR for long-term repopulating HSCs and demonstrates the applicability of our optimized FGB-driven multiplexing approach for the efficient characterization of blood cell populations in biomedical research.

Automated summary

This study developed a multiplexing system for parallel characterization of multiple HSC samples and optimized vector design and gene transfer protocols to demonstrate its applicability in functional characterization of two highly similar HSC populations in a reduced number of mice. The results showed the importance of EPCR for long-term repopulating HSCs and the efficiency of the optimized FGB-driven multiplexing approach for blood cell population characterization in biomedical research.