Coculture and transplant of purified CD34⁺Lin⁻ and CD34⁻Lin⁻ cells reveals functional interaction between repopulating hematopoietic stem cells

Abstract

The human hematopoietic stem cell compartment is comprised of repopulating CD34⁺ and CD34⁻ cells. The interaction between these subsets with respect to their reconstitution capacity in vivo remains to be characterized. Here, lineage-depleted (Lin⁻) human CD34⁺ and CD34⁻ hematopoietic cells were isolated from human male and female umbilical cord blood (CB) and transplanted into immune-deficient NOD/SCID EMV^null mice, thereby allowing the use of human and Y-chromosome-specific DNA sequences to discriminate human reconstitution contributed by CD34⁺ vs CD34⁻ repopulating stem cells. Although cultured human CB CD34⁻Lin⁻ cells transplanted alone possessed only minimal repopulating capacity, with 15% of mice achieving low levels of engraftment, transplantation of cocultured male CD34⁻Lin⁻ cells with female CD34⁺Lin⁻ cells demonstrated human repopulation with a contribution from CD34⁻Lin⁻-derived progeny in 80% of the recipients. After coculture and transplantation, male CD34⁻Lin⁻ cells gave rise to primitive CD34⁺CD38⁻ cells isolated in vivo, which demonstrated clonogenic progenitor function into multiple lineages. Taken together, our study indicates that the presence of CD34⁺Lin⁻ cells in coculture enhanced the low repopulating function of human CD34⁻Lin⁻ cells in vivo. We propose that CD34⁺Lin and CD34⁻Lin cells represent phenotypically distinct, but related cell types that exhibit unique and previously unappreciated functional interaction.