C1qRp defines a new human stem cell population with hematopoietic and hepatic potential

Abstract

The characterization of two distinct classes of hematopoietic stem cells based on CD34 expression and the ability of human bone marrow (BM) cells to differentiate into nonhematopoietic cells introduced new levels of complexity within the stem cell compartment. Here we report the identification and purification of a rare human stem cell population with hematopoietic and hepatic potential based on the expression of a receptor for the complement molecule C1q (C1qR(p)). We show that C1qR(p) is a positive marker of all BM-repopulating stem cells because it is expressed on both CD34(-) and CD34(+) stem cells from umbilical cord blood and adult BM. In addition, we show that highly purified lineage-negative CD45(+)CD38(-)CD34(+or-)C1qR(p)(+) cells not only have BM-repopulating capacity but also can differentiate into human hepatocytes in vivo. The identification of human hepatocytes in mouse livers indicates that the NOD/SCID (nonobese diabetic/severe combined immunodeficient) mouse model can be a valuable tool to study the differentiation potential of adult human stem cells. These findings may have important scientific and clinical implications in the field of human stem cell biology and transplantation.

Fig 1.

Identification of a novel stem cell population: Lin⁻CD38⁻CD34⁻C1qR. (a) Mononuclear cells from umbilical CB were lineage-depleted (Lin⁻) and the expression of CD34 and CD38 was evaluate (Left). Cells lacking CD38 expression (Lin⁻CD38⁻) were further analyzed and subdivided into CD34⁻C1qR and CD34⁺C1qR populations (Center, regions a and b). The percentage of each subpopulation relative to total CB MNC is shown next to each sort gate. The forward and side scatter of Lin⁻CD38⁻CD34⁻C1qR (blue) and Lin⁻CD38⁻CD34⁺C1qR (red) are shown on the Right. (b) Phenotypic analysis of Lin⁻CD38⁻CD34⁻C1qR cells. Each panel is a representative flow cytometry histogram representing fluorescence intensity (x axis) as a function of cell number (y axis) for various markers associated with stem cells.

Fig 2.

Human cell engraftment of NOD/SCID mice transplanted with various doses of Lin⁻CD38⁻CD34⁻C1qR cells. Purified Lin⁻CD38⁻CD34⁻C1qR (−/−/−/−) or Lin⁻CD38⁻CD34⁻C1qR (−/−/−/+) cells isolated from CB (circle) or BM (triangle) were transplanted into NOD/SCID mice at the indicated dose ranges. The percentage of human CD45⁺ cells present in the murine BM 8–10 weeks posttransplant was determined by flow cytometry and confirmed by Southern blot analysis. For each cell phenotype and dose range, the frequency of engraftment represents the number of mice with detectable levels of human cells in the BM over the total number of mice transplanted. The multilineage potential of the transplanted cells was evidenced by the presence of human myeloid (M, CD33⁺) and lymphoid (L, CD19⁺) cells in the murine BM (Inset).

Fig 3.

Identification of human hepatocytes in livers from NOD/SCID mice transplanted with Lin⁻CD38⁻CD34⁺C1qR or Lin⁻CD38⁻CD34⁻C1qR cells (ranging from 500 to 1,500 and 8,000 to 70,000 cells, respectively). (a) Photomicrographs of NOD/SCID mouse liver sections from mice transplanted with purified human Lin⁻CD38⁻CD34^−or+C1qR cells isolated from umbilical CB. Livers from transplanted mice were recovered 8–10 weeks posttransplant, paraffin-embedded, and processed for immunocytochemistry. Serial sections were immunostained for human HSA (a–d) and c-met (g–j). Human liver sections were used as a positive control (a and g) and liver sections from noninjected NOD/SCID mice were used as a negative control for each monoclonal antibody (b and h). No HSA⁺ or c-met⁺ cells were found in liver sections from noninjected mice (b and h). Human hepatocytes were identified as single cells (c and d) or small clusters of two to eight cells (i and j) of HSA⁺ or c-met⁺ cells in mice transplanted with Lin⁻CD38⁻CD34^−or+C1qR. [Scale bars = 100 μm (a), 200 μm (b), 10 μm (c–j).] (b) Expression of human albumin in livers from NOD/SCID mice transplanted with Lin⁻CD38⁻CD34⁻C1qR (−/−/−/+) or Lin⁻CD38⁻CD34⁺C1qR (−/−/+/+) cells. RNA extracted from noninjected mice was used as a negative control and from human hepatocytes as a positive control.